2009 Vol. 26, No. 5
2009, 26(5): 1-7.
Abstract:
GMA was used exploringly as a coupling agent to improve the mechanical properties and durability of Wood Polymer Composites (WPC). The reaction mechanism and complex effect of interface between polymers and wood cell walls were analyzed before and after adding GMA into Styrene (St) with SEM and FTIR. The analysis results with SEM and FTIR indicate that GMA reacts with the hydroxyl groups of wood cell walls by it s epoxy group，and reacts with styrene as a free radical copolymerization form by its double bond，which makes the polymers graftfully on wood sell walls；and the polymers fill mainly in wood cell lumina as a solid form，which contact tightly with the wood cell walls. The testing results of comprehensive performance show that the modulus of rupture (MOR)，modulus of elasticity (MOE)，compression strength and hardness of WPC modified by GMA increase 45%，52%，71% and 141% compared with the unmodified WPC，respectively；the dimensional stability of modified WPC improves 3 times；and the decay resistance of the modified WPC increases by 8.56 times that of the unmodified WPC.
GMA was used exploringly as a coupling agent to improve the mechanical properties and durability of Wood Polymer Composites (WPC). The reaction mechanism and complex effect of interface between polymers and wood cell walls were analyzed before and after adding GMA into Styrene (St) with SEM and FTIR. The analysis results with SEM and FTIR indicate that GMA reacts with the hydroxyl groups of wood cell walls by it s epoxy group，and reacts with styrene as a free radical copolymerization form by its double bond，which makes the polymers graftfully on wood sell walls；and the polymers fill mainly in wood cell lumina as a solid form，which contact tightly with the wood cell walls. The testing results of comprehensive performance show that the modulus of rupture (MOR)，modulus of elasticity (MOE)，compression strength and hardness of WPC modified by GMA increase 45%，52%，71% and 141% compared with the unmodified WPC，respectively；the dimensional stability of modified WPC improves 3 times；and the decay resistance of the modified WPC increases by 8.56 times that of the unmodified WPC.
2009, 26(5): 8-13.
Abstract:
A kind of glass fiber textile/epoxy prepreg and two kinds of carbon fiber textile/epoxy prepregs were studied by means of the solid torsional method，which provides a feasible measurement for the gel point and gelation process. The effects of the sample dimension and the type of fabric on the gel properties of the prepreg were investigated. The results show that the influence of the sample width on the gelation is negligible，while the increase of the sample thickness results in the decrease of the dynamic modulus，making the gel point less distinguishable. Textile fabric affects the gel point of prepreg significantly，so it demonst rates that the rheological property of prepreg is an integrated behavior of resin rheological property and the deformability of fiber bed.
A kind of glass fiber textile/epoxy prepreg and two kinds of carbon fiber textile/epoxy prepregs were studied by means of the solid torsional method，which provides a feasible measurement for the gel point and gelation process. The effects of the sample dimension and the type of fabric on the gel properties of the prepreg were investigated. The results show that the influence of the sample width on the gelation is negligible，while the increase of the sample thickness results in the decrease of the dynamic modulus，making the gel point less distinguishable. Textile fabric affects the gel point of prepreg significantly，so it demonst rates that the rheological property of prepreg is an integrated behavior of resin rheological property and the deformability of fiber bed.
2009, 26(5): 14-19.
Abstract:
Variable thickness laminates under different conditions were prepared with autoclave process for two types of carbon fiber fabric/epoxy prepregs. The consolidating process and the influencing factors of fiber distribution for the variable thickness laminates were investigated by measuring the structure of fabric in cured laminate，laminate thickness，fiber content，bleeding quantity and permeability of fabrics. The results showed that the fiber content in thick area was higher than that in thin area for cured laminates due to the two dimensional resin flow. The ratio of in-plane permeability to the permeability along thickness direction of G0827 unidirectional fabric was larger than that of G0803 satin fabric，resulting in that the fiber distribution in G0827 variable thickness laminate was more uneven. Fiber distribution without bleeder was uniform and it indicates that the two dimensional resin flow in the bleeder influences the fiber distribution remarkably.
Variable thickness laminates under different conditions were prepared with autoclave process for two types of carbon fiber fabric/epoxy prepregs. The consolidating process and the influencing factors of fiber distribution for the variable thickness laminates were investigated by measuring the structure of fabric in cured laminate，laminate thickness，fiber content，bleeding quantity and permeability of fabrics. The results showed that the fiber content in thick area was higher than that in thin area for cured laminates due to the two dimensional resin flow. The ratio of in-plane permeability to the permeability along thickness direction of G0827 unidirectional fabric was larger than that of G0803 satin fabric，resulting in that the fiber distribution in G0827 variable thickness laminate was more uneven. Fiber distribution without bleeder was uniform and it indicates that the two dimensional resin flow in the bleeder influences the fiber distribution remarkably.
2009, 26(5): 20-26.
Abstract:
To analyze and study the process parameters of bismaleimide resin with pultrusion process，the curing reaction kinetics of the bismaleimide resin BMI-QC130 was studied with DSC analysis. The curing degree prediction model was established，and the predicted values are well coincident with the test values. The viscosity prediction model was established by the dual-Arrhenius equation to predict the resin rheological behavior of the BMI resin system，which has a good prediction precision when the temperature is lower than 120℃. Based on the analysis results of the curing degree model and the viscosity model，the pultrusion process parameters of the bismaleimide resin BMI-QC130 are determined：the resin is melted at 95℃ in the resin bath，precured at 200℃ in pultrusion mould and postcured at 280℃ in hot tunnel. The carbon fiber reinforced BMI-QC130 composite samples are successfully manufactured with the pultrusion process under such process conditions.
To analyze and study the process parameters of bismaleimide resin with pultrusion process，the curing reaction kinetics of the bismaleimide resin BMI-QC130 was studied with DSC analysis. The curing degree prediction model was established，and the predicted values are well coincident with the test values. The viscosity prediction model was established by the dual-Arrhenius equation to predict the resin rheological behavior of the BMI resin system，which has a good prediction precision when the temperature is lower than 120℃. Based on the analysis results of the curing degree model and the viscosity model，the pultrusion process parameters of the bismaleimide resin BMI-QC130 are determined：the resin is melted at 95℃ in the resin bath，precured at 200℃ in pultrusion mould and postcured at 280℃ in hot tunnel. The carbon fiber reinforced BMI-QC130 composite samples are successfully manufactured with the pultrusion process under such process conditions.
2009, 26(5): 27-32.
Abstract:
The mechanical characteristics of the foam filled 3-D spacer fabric composites under flatwise compressive，shear and three points flexural loads were compared with 3-D spacer fabric composites and foam sandwich composites，and the effects of pile height and foam density on the mechanical properties were investigated.The results indicate that there are synergy effects between pile and foam under flatwise compressive strength and fabric piles fractured under flatwise compression. The flatwise compressive and shear strength decrease with increasing of the pile height. The flatwise compressive strength increases as exponent with increasing of the foam density.
The mechanical characteristics of the foam filled 3-D spacer fabric composites under flatwise compressive，shear and three points flexural loads were compared with 3-D spacer fabric composites and foam sandwich composites，and the effects of pile height and foam density on the mechanical properties were investigated.The results indicate that there are synergy effects between pile and foam under flatwise compressive strength and fabric piles fractured under flatwise compression. The flatwise compressive and shear strength decrease with increasing of the pile height. The flatwise compressive strength increases as exponent with increasing of the foam density.
2009, 26(5): 33-38.
Abstract:
Nano-sized magnesium hydroxide particles (MH) were modified with vinyl silane followed by in situ polymerization of styrene. The MH/polypropylene (PP) composites were prepared by melt compounding of PP with MH and modified MH (MMH)，respectively. The morphological structure and rheological properties were characterized by scanning electron microscopy and capillary rheometer. The results show that the MH/PP composite is a shear-thinning non-Newtonian，and its apparent viscosity and non-Newtonian index (n) are bigger than those of the PP melt. With increasing the MH content，its apparent viscosity and n increase. The low MH content decreases the flow activation energy (ΔE) of the MH/PP composites melts，but ΔE values of the composites increase with MH content. However，the in situ polymerization of styrene on the surface of MH enhances the dispersion of MH in composites. The “ball bearing” effect of the modified MH particles decreases the apparent viscosity of MMH/PP composites，their n and ΔE values are lower than those of PP，and ΔE values decrease with increasing the MMH content in composites.
Nano-sized magnesium hydroxide particles (MH) were modified with vinyl silane followed by in situ polymerization of styrene. The MH/polypropylene (PP) composites were prepared by melt compounding of PP with MH and modified MH (MMH)，respectively. The morphological structure and rheological properties were characterized by scanning electron microscopy and capillary rheometer. The results show that the MH/PP composite is a shear-thinning non-Newtonian，and its apparent viscosity and non-Newtonian index (n) are bigger than those of the PP melt. With increasing the MH content，its apparent viscosity and n increase. The low MH content decreases the flow activation energy (ΔE) of the MH/PP composites melts，but ΔE values of the composites increase with MH content. However，the in situ polymerization of styrene on the surface of MH enhances the dispersion of MH in composites. The “ball bearing” effect of the modified MH particles decreases the apparent viscosity of MMH/PP composites，their n and ΔE values are lower than those of PP，and ΔE values decrease with increasing the MMH content in composites.
2009, 26(5): 39-46.
Abstract:
The influences of stirring time and surface modification of carbon black (CB) on the resistivity and electromechanical properties of CB filled epoxy matrix composites were experimentally studied. The test results indicate that the dispersion of CB in the epoxy can be improved with the increase of stirring time，which is at tributed to the fact that some conductive chains in the epoxy formed by CB are broken up when the stirring time increases and thus the resistivity of composites is improved. Consequently，the variation coefficient of resistivity and the fractional change of resistance versus strain between the specimens prepared at the same time are decreased. But the dispersion of CB in epoxy cannot be further improved when the stirring time becomes longer and the CB particles dispersed in epoxy are still in formation of big agglomerations. The dispersion of CB particles in epoxy is improved further after the surface of CB particles is modified by silane coupling agent. The CB particles modified by silane coupling agent are dispersed in epoxy in formation of little agglomerations and even single particles，so the epoxy gaps between CB agglomerations become thinner and the resistivity and the fractional change of resistance versus strain of the composites decrease accordingly.
The influences of stirring time and surface modification of carbon black (CB) on the resistivity and electromechanical properties of CB filled epoxy matrix composites were experimentally studied. The test results indicate that the dispersion of CB in the epoxy can be improved with the increase of stirring time，which is at tributed to the fact that some conductive chains in the epoxy formed by CB are broken up when the stirring time increases and thus the resistivity of composites is improved. Consequently，the variation coefficient of resistivity and the fractional change of resistance versus strain between the specimens prepared at the same time are decreased. But the dispersion of CB in epoxy cannot be further improved when the stirring time becomes longer and the CB particles dispersed in epoxy are still in formation of big agglomerations. The dispersion of CB particles in epoxy is improved further after the surface of CB particles is modified by silane coupling agent. The CB particles modified by silane coupling agent are dispersed in epoxy in formation of little agglomerations and even single particles，so the epoxy gaps between CB agglomerations become thinner and the resistivity and the fractional change of resistance versus strain of the composites decrease accordingly.
2009, 26(5): 47-53.
Abstract:
To provide a theoretical basis for developing heat-resisting material and cryogenic temperature material，the tensile properties of nylon short fiber reinforced foam rubber composite materials with the identical spongy rate but different short fiber volume fraction and with the identical short fiber volume fraction but different spongy rate were tested at 213～398 K. The results show that increasing the short fiber volume fraction and reducing spongy rate can improve tensile properties of the composite materials at ordinary temperatures. At different temperatures，the initial modulus and breaking st rength of SFRFRC decrease with temperature increasing，and the elongation at break of SFRFRC increases at first and then decreases with temperature increasing. The glass transition temperature is between 213～233 K. At the same time，although the added staple fiber does not change the glass transition temperature of SFRFRC，it makes the range of glass transition temperature wider. The initial modulus，breaking strength and elongation at break of SFRFRC reached the lowest values at 398 K，which is related to the vulcanization temperature of rubber. The vulcanization temperature of rubber is 423 K. The closer to the vulcanization temperature，the worse the tensile properties of SFRFRC.
To provide a theoretical basis for developing heat-resisting material and cryogenic temperature material，the tensile properties of nylon short fiber reinforced foam rubber composite materials with the identical spongy rate but different short fiber volume fraction and with the identical short fiber volume fraction but different spongy rate were tested at 213～398 K. The results show that increasing the short fiber volume fraction and reducing spongy rate can improve tensile properties of the composite materials at ordinary temperatures. At different temperatures，the initial modulus and breaking st rength of SFRFRC decrease with temperature increasing，and the elongation at break of SFRFRC increases at first and then decreases with temperature increasing. The glass transition temperature is between 213～233 K. At the same time，although the added staple fiber does not change the glass transition temperature of SFRFRC，it makes the range of glass transition temperature wider. The initial modulus，breaking strength and elongation at break of SFRFRC reached the lowest values at 398 K，which is related to the vulcanization temperature of rubber. The vulcanization temperature of rubber is 423 K. The closer to the vulcanization temperature，the worse the tensile properties of SFRFRC.
2009, 26(5): 54-59.
Abstract:
UHMWPE-g-AA graft copolymer was synthesized by mutual radiation grafting. UHMWPE/PA1010 alloys were prepared by blending UHMWPE，UHMWPE-g-AA and PA1010. UHMWPE-g-AA graft copolymer serves as compatibilizer in the alloys. Due to the strong interaction between PA1010 and UHMWPE-g-AA，the impact strength and elongation at break of UHMWPE/PA1010 alloys were improved，which indicates the increase of toughness of the alloys. The compatibilization effect limits the crystallization process of PA1010，which leads to the decrease of the normal crystals and the shift of the crystallization temperature to the higher temperature. SEM result shows that the compatibilization reaction decreases the interfacial tension and increases the interfacial strength，which makes UHMWPE disperse in the PA1010 matrix uniformly and in small particle size. The tension phenomenon can be clearly observed. Compared to the pure PA1010，the friction coefficients of the blends decrease. UHMWPE forms an intact protection film on PA1010 surface，which decreases the abrasion loss and the friction coefficients.
UHMWPE-g-AA graft copolymer was synthesized by mutual radiation grafting. UHMWPE/PA1010 alloys were prepared by blending UHMWPE，UHMWPE-g-AA and PA1010. UHMWPE-g-AA graft copolymer serves as compatibilizer in the alloys. Due to the strong interaction between PA1010 and UHMWPE-g-AA，the impact strength and elongation at break of UHMWPE/PA1010 alloys were improved，which indicates the increase of toughness of the alloys. The compatibilization effect limits the crystallization process of PA1010，which leads to the decrease of the normal crystals and the shift of the crystallization temperature to the higher temperature. SEM result shows that the compatibilization reaction decreases the interfacial tension and increases the interfacial strength，which makes UHMWPE disperse in the PA1010 matrix uniformly and in small particle size. The tension phenomenon can be clearly observed. Compared to the pure PA1010，the friction coefficients of the blends decrease. UHMWPE forms an intact protection film on PA1010 surface，which decreases the abrasion loss and the friction coefficients.
2009, 26(5): 60-67.
Abstract:
Nano-hydroxyapatite(n-HA)/poly((1，2-propanediol-sebacate)-citrate) (1，2-PPSC) composites were synthesized by condensation of 1，2-propanediol，sebacic acid，citric acid and n-HA. The structure was characterized by FTIR and 13C NMR；the micromorphology of n-HA and the dispersion property of n-HA in n-HA/1，2-PPSC composites were characterized by SEM and TEM. The results show that the chemical reactions between n-HA and sebacic acid never occur，n-HA and 1，2-PPSC matrix do not generate obviously chemical bond，and n-HA disperses uniformly in 1，2-PPSC matrix. DMA shows that there is a good nterfacial bonding between n-HA and 1，2-PPSC matrix. DSC and DMA show that n-HA decreases the chemical cross-link density of the composites，so the Tg of the composites decreases with increasing of mass fractions of n-HA. N-HA improves the hydrophilicity，decreases water absorption and reduces the degradation rates of n-HA/1，2-PPSC composites. Compared to the matrix，the mechanical properties of the composites are improved obviously；when the mass fraction of n-HA is 20%，the modulus of n-HA/1，2-PPSC composites increases 11.4 times，the tensile strength of n-HA/1，2-PPSC composites increases 8.2 times，while the elongation at break of n-HA/1，2-PPSC composites is basically unchanged.
Nano-hydroxyapatite(n-HA)/poly((1，2-propanediol-sebacate)-citrate) (1，2-PPSC) composites were synthesized by condensation of 1，2-propanediol，sebacic acid，citric acid and n-HA. The structure was characterized by FTIR and 13C NMR；the micromorphology of n-HA and the dispersion property of n-HA in n-HA/1，2-PPSC composites were characterized by SEM and TEM. The results show that the chemical reactions between n-HA and sebacic acid never occur，n-HA and 1，2-PPSC matrix do not generate obviously chemical bond，and n-HA disperses uniformly in 1，2-PPSC matrix. DMA shows that there is a good nterfacial bonding between n-HA and 1，2-PPSC matrix. DSC and DMA show that n-HA decreases the chemical cross-link density of the composites，so the Tg of the composites decreases with increasing of mass fractions of n-HA. N-HA improves the hydrophilicity，decreases water absorption and reduces the degradation rates of n-HA/1，2-PPSC composites. Compared to the matrix，the mechanical properties of the composites are improved obviously；when the mass fraction of n-HA is 20%，the modulus of n-HA/1，2-PPSC composites increases 11.4 times，the tensile strength of n-HA/1，2-PPSC composites increases 8.2 times，while the elongation at break of n-HA/1，2-PPSC composites is basically unchanged.
2009, 26(5): 68-73.
Abstract:
Short carbon fiber (Cf) reinforced nano-hydroxyapatite (HA)-poly (methyl methacrylate) (PMMA) hybrid bio-composites were prepared by an in-situ processing and solution co-mixing process. The influences of surface modification of carbon fibers and nano-HA on the microstructures and mechanical properties of the Cf/HA-PMMA composites were investigated. The structures and fracture surface morphologies of nano-HA，carbon fiber and the composites were characterized by XRD，FTIR，XPS and SEM analyses. The flexural and compressive properties of the Cf/HA-PMMA composites were tested by a universal testing machine. The results show that the interfacial combination between the surface modified-HA particles by lecithin or pre-oxidized carbon fibers by nitric acid and PMMA matrix is evidently improved. Flexural properties of as-prepared Cf/HA-PMMA composites with the surface modification of HA particles and carbon fiber are obviously increased. Compared with the Cf/HA-PMMA composites using unmodified-HA particles and untreated-carbon fiber，the flexural strength，compressive strength and elastic modulus of modified composites increase 1.6 times，2 times and 4.3 times，respectively.
Short carbon fiber (Cf) reinforced nano-hydroxyapatite (HA)-poly (methyl methacrylate) (PMMA) hybrid bio-composites were prepared by an in-situ processing and solution co-mixing process. The influences of surface modification of carbon fibers and nano-HA on the microstructures and mechanical properties of the Cf/HA-PMMA composites were investigated. The structures and fracture surface morphologies of nano-HA，carbon fiber and the composites were characterized by XRD，FTIR，XPS and SEM analyses. The flexural and compressive properties of the Cf/HA-PMMA composites were tested by a universal testing machine. The results show that the interfacial combination between the surface modified-HA particles by lecithin or pre-oxidized carbon fibers by nitric acid and PMMA matrix is evidently improved. Flexural properties of as-prepared Cf/HA-PMMA composites with the surface modification of HA particles and carbon fiber are obviously increased. Compared with the Cf/HA-PMMA composites using unmodified-HA particles and untreated-carbon fiber，the flexural strength，compressive strength and elastic modulus of modified composites increase 1.6 times，2 times and 4.3 times，respectively.
2009, 26(5): 74-79.
Abstract:
By the use of sessile drop and Wilhelmy plate，regularities of the total surface energy of two typical epoxy resin systems during curing were characterized；besides，polar and dispersive components of the total surface energy by sessile drop were well studied. The results indicate that the total surface energy in each resin system declines with the extension of time by the two test methods，and the surface energies obtained from sessile drop method is bigger in comparison with those from Wilhelmy plate method. The polar component of the total surface energy in the two resin systems declines with time elapse from the results of sessile drop. FTIR result shows that the change of polar component of the total surface energy in the epoxy 618-imidazole resin system is caused by the drop of content of hydroxyl and epoxy groups.
By the use of sessile drop and Wilhelmy plate，regularities of the total surface energy of two typical epoxy resin systems during curing were characterized；besides，polar and dispersive components of the total surface energy by sessile drop were well studied. The results indicate that the total surface energy in each resin system declines with the extension of time by the two test methods，and the surface energies obtained from sessile drop method is bigger in comparison with those from Wilhelmy plate method. The polar component of the total surface energy in the two resin systems declines with time elapse from the results of sessile drop. FTIR result shows that the change of polar component of the total surface energy in the epoxy 618-imidazole resin system is caused by the drop of content of hydroxyl and epoxy groups.
2009, 26(5): 80-85.
Abstract:
Hygrothermal behavior of unidirectional carbon fiber reinforced BMI matrix composite laminates was investigated，which were subjected to three-point flexural load in the distilled water at 70℃ for different times. Compared with the unstressed specimens，there are no significant differences in apparent moisture absorption，as the glass transition temperature and residual flexural properties were observed for flexural-stressed specimens. However，the flexural-stressed specimens show a greater decrease in glass transition temperature before saturation. The tensile-stressed section absorbs water faster than the compressive-stressed section for the flexural -stressed specimens. The SEM of the flexural fracture surface shows that the adhesion property of the fiber and matrix in the tensile-fracture section of the stressed specimens suffers more severe deterioration than that of the unstressed specimens. It indicates that the stress has significant influence on the hygrothermal property of the composite，which depends on the direction of the stress.
Hygrothermal behavior of unidirectional carbon fiber reinforced BMI matrix composite laminates was investigated，which were subjected to three-point flexural load in the distilled water at 70℃ for different times. Compared with the unstressed specimens，there are no significant differences in apparent moisture absorption，as the glass transition temperature and residual flexural properties were observed for flexural-stressed specimens. However，the flexural-stressed specimens show a greater decrease in glass transition temperature before saturation. The tensile-stressed section absorbs water faster than the compressive-stressed section for the flexural -stressed specimens. The SEM of the flexural fracture surface shows that the adhesion property of the fiber and matrix in the tensile-fracture section of the stressed specimens suffers more severe deterioration than that of the unstressed specimens. It indicates that the stress has significant influence on the hygrothermal property of the composite，which depends on the direction of the stress.
2009, 26(5): 86-92.
Abstract:
A serial montmorillonite (MMT)/polypyrrole (PPy) composites (MMT/PPy) were prepared by vapor-liquor phase polymerization of pyrrole vapor with Fe3+ impregnated MMT suspension. It was found that the polymerization of pyrrole took place within the silicate layers of MMT. XRD of MMT/PPy composites showed that the basal spacing of MMT layers increased with increasing the PPy content. FTIR of MMT/PPy exhibited both characteristic adsorption peaks of MMT and PPy，while some peaks appeared blue shift. The obtained MMT/PPy displayed flake like morphology. Even after etching of MMT from MMT/PPy by HF，the resultant PPy still displayed a flake-like morphology，which was very different from the inherent globular PPy obtained by the same method. The conductivity of MMT/PPy became higher with increment of the PPy content. When the PPy content reached 40.9 wt%，the composite possessed almost the same conductivity as PPy. Furthermore，the composite containing 54.3 wt% PPy even showed a higher conductivity than PPy. This phenomenon might be attributed to the special morphology of the PPy in composite，which was caused by in situ polymerization within a confined space of MMT layers.
A serial montmorillonite (MMT)/polypyrrole (PPy) composites (MMT/PPy) were prepared by vapor-liquor phase polymerization of pyrrole vapor with Fe3+ impregnated MMT suspension. It was found that the polymerization of pyrrole took place within the silicate layers of MMT. XRD of MMT/PPy composites showed that the basal spacing of MMT layers increased with increasing the PPy content. FTIR of MMT/PPy exhibited both characteristic adsorption peaks of MMT and PPy，while some peaks appeared blue shift. The obtained MMT/PPy displayed flake like morphology. Even after etching of MMT from MMT/PPy by HF，the resultant PPy still displayed a flake-like morphology，which was very different from the inherent globular PPy obtained by the same method. The conductivity of MMT/PPy became higher with increment of the PPy content. When the PPy content reached 40.9 wt%，the composite possessed almost the same conductivity as PPy. Furthermore，the composite containing 54.3 wt% PPy even showed a higher conductivity than PPy. This phenomenon might be attributed to the special morphology of the PPy in composite，which was caused by in situ polymerization within a confined space of MMT layers.
2009, 26(5): 93-99.
Abstract:
In order to improve the layer structure of montmorillonite，cetylt rimethyl ammonium bromide (CTAB) and octedacy trimethyl ammonium chloride (OTAC) were used as organic intercalating cations to modify sodium montmorillonite. The effects of modification by the type and amount of organic cation added，reaction temperature，and pH were investigated，and the samples were systemically characterized with XRD，FTIR，TGA，SEM and TEM. The results showed that OTAC had a better intercalating effect than CTAB. It was found that a reaction temperature of 80℃ and low pH favored intercalation，and the best intercalating effect was observed when the amount of organic cation added was twice the cation exchange capacity (CEC). Under the above reaction conditions，ordered and high layer spacing organic nano-montmorillonite was successfully obtained，with a basal spacing of 4.12 nm and even exfoliated parts of silicate layer .
In order to improve the layer structure of montmorillonite，cetylt rimethyl ammonium bromide (CTAB) and octedacy trimethyl ammonium chloride (OTAC) were used as organic intercalating cations to modify sodium montmorillonite. The effects of modification by the type and amount of organic cation added，reaction temperature，and pH were investigated，and the samples were systemically characterized with XRD，FTIR，TGA，SEM and TEM. The results showed that OTAC had a better intercalating effect than CTAB. It was found that a reaction temperature of 80℃ and low pH favored intercalation，and the best intercalating effect was observed when the amount of organic cation added was twice the cation exchange capacity (CEC). Under the above reaction conditions，ordered and high layer spacing organic nano-montmorillonite was successfully obtained，with a basal spacing of 4.12 nm and even exfoliated parts of silicate layer .
2009, 26(5): 100-104.
Abstract:
For the better utilization of vapor grown carbon fiber (VGCF) as the reinforcing material in polymer matrix composites，the VGCF surface was modified by three methods，the two-step treatment with hydrogen peroxide and concentrated nitric acid，treatment with the silane coupling agent，and the treatment with hydrogen peroxide and concentrated nitric acid combined with the silane coupling agent，respectively. The effects of surface modification on the microstructure of VGCF were studied and comparatively analyzed by AFM，FTIR，TG and XRD. The results show that the three modification methods have no significant effect on the crystal lattice of VGCF. Oxygen-containing groups such as carboxyl groups can be grafted onto the surface of VGCF through the two-step treatment with hydrogen peroxide and concentrated nitric acid. And siloxane oligomer can be grafted on the surface of VGCF through the modification with silane coupling agent. More siloxane oligomers can be grafted onto the surface of VGCF by the treatment with hydrogen peroxide and concentrated nitric acid combined with the silane coupling agent，which may be of great benefit to the improvement of the compatibility between VGCF and polymer matrix materials.
For the better utilization of vapor grown carbon fiber (VGCF) as the reinforcing material in polymer matrix composites，the VGCF surface was modified by three methods，the two-step treatment with hydrogen peroxide and concentrated nitric acid，treatment with the silane coupling agent，and the treatment with hydrogen peroxide and concentrated nitric acid combined with the silane coupling agent，respectively. The effects of surface modification on the microstructure of VGCF were studied and comparatively analyzed by AFM，FTIR，TG and XRD. The results show that the three modification methods have no significant effect on the crystal lattice of VGCF. Oxygen-containing groups such as carboxyl groups can be grafted onto the surface of VGCF through the two-step treatment with hydrogen peroxide and concentrated nitric acid. And siloxane oligomer can be grafted on the surface of VGCF through the modification with silane coupling agent. More siloxane oligomers can be grafted onto the surface of VGCF by the treatment with hydrogen peroxide and concentrated nitric acid combined with the silane coupling agent，which may be of great benefit to the improvement of the compatibility between VGCF and polymer matrix materials.
2009, 26(5): 105-111.
Abstract:
C/C composites were prepared by resin infiltration and pyrolysis with 3D needle-punched carbon fiber preforms. The reactive melt infiltration process was used subsequently to prepare C/SiC composites，and the liquid Si or Si-Mo alloy was used as the reactive melt. The microstructure evolution during the preparation process of C/C composites was investigated. The results indicate that resin mainly exists in the small pores of the fiber bundles. Pores become more and bigger but there are dense C/C segments within the fiber bundles after pyrolysis. High temperature treatment leads to a higher graphitization degree and makes the closed pores open，which acts as the channel for silicon infiltration. Some fibers inside the fiber bundles of C/SiC composite infiltrated by Si are damaged and much residual Si exists in big pores. When C/SiC composites are fabricated by Si-Mo infiltration，the remaining Si content is reduced，the damage of fibers inside the fiber bundles is much slighter and the C/C segments remain intact.
C/C composites were prepared by resin infiltration and pyrolysis with 3D needle-punched carbon fiber preforms. The reactive melt infiltration process was used subsequently to prepare C/SiC composites，and the liquid Si or Si-Mo alloy was used as the reactive melt. The microstructure evolution during the preparation process of C/C composites was investigated. The results indicate that resin mainly exists in the small pores of the fiber bundles. Pores become more and bigger but there are dense C/C segments within the fiber bundles after pyrolysis. High temperature treatment leads to a higher graphitization degree and makes the closed pores open，which acts as the channel for silicon infiltration. Some fibers inside the fiber bundles of C/SiC composite infiltrated by Si are damaged and much residual Si exists in big pores. When C/SiC composites are fabricated by Si-Mo infiltration，the remaining Si content is reduced，the damage of fibers inside the fiber bundles is much slighter and the C/C segments remain intact.
2009, 26(5): 112-119.
Abstract:
C/SiC composites drilled with the blind holes of various diameters and various depths were prepared in order to simulate defects of air voids or delaminations under the surface of the material. Thermographic technique，due to its high sensitivity to thermal radiation ability of different materials，was utilized to detect sizes and locations of the defects in specimens. The detection resolution，advantages and disadvantages of thermographic technique were compared with those of X-ray radiography and X-ray CT. The results indicate that thermographic technique is able to detect the geomet ries，dimensions and depths of the defects in C/SiC composite. For the blind holes with the same depth，the measurement error of diameter and depth increases as the diameters decrease；for the blind holes with the same diameter，the measurement error of diameter increases as the depths decrease，but the measurement error of depths reduces. The thermographic quantitative measurement of blind holes in C/SiC composites has a lower limit.
C/SiC composites drilled with the blind holes of various diameters and various depths were prepared in order to simulate defects of air voids or delaminations under the surface of the material. Thermographic technique，due to its high sensitivity to thermal radiation ability of different materials，was utilized to detect sizes and locations of the defects in specimens. The detection resolution，advantages and disadvantages of thermographic technique were compared with those of X-ray radiography and X-ray CT. The results indicate that thermographic technique is able to detect the geomet ries，dimensions and depths of the defects in C/SiC composite. For the blind holes with the same depth，the measurement error of diameter and depth increases as the diameters decrease；for the blind holes with the same diameter，the measurement error of diameter increases as the depths decrease，but the measurement error of depths reduces. The thermographic quantitative measurement of blind holes in C/SiC composites has a lower limit.
2009, 26(5): 120-126.
Abstract:
The damage evolution in 3D SiCf/SiC composites in the fatigue-oxidation environment was investigated，and the failure mechanism of SiCf/SiC in such environments was also discussed. The results indicate that the main damages in SiCf/SiC composites in fatigue-oxidation environments include：cracking of SiC matrix；debonding，oxidation and ordering of pyrolytic carbon (PyC) interphase；fracture，oxidation and change in microstructure of the fiber. The composite interior is oxidized by the oxidizing atmosphere infiltrating the composites through the cracking matrix. The fibers are pulled out more easily due to the debonding and ordering of PyC interphase. The strength of the fibers is decreased because of the oxidation of the fibers，the increase of the amorphous carbon and the growth of the SiC grain in the SiC fiber.
The damage evolution in 3D SiCf/SiC composites in the fatigue-oxidation environment was investigated，and the failure mechanism of SiCf/SiC in such environments was also discussed. The results indicate that the main damages in SiCf/SiC composites in fatigue-oxidation environments include：cracking of SiC matrix；debonding，oxidation and ordering of pyrolytic carbon (PyC) interphase；fracture，oxidation and change in microstructure of the fiber. The composite interior is oxidized by the oxidizing atmosphere infiltrating the composites through the cracking matrix. The fibers are pulled out more easily due to the debonding and ordering of PyC interphase. The strength of the fibers is decreased because of the oxidation of the fibers，the increase of the amorphous carbon and the growth of the SiC grain in the SiC fiber.
2009, 26(5): 127-131.
Abstract:
SiC1. 12O0. 12 ceramic powders were obtained by pyrolyzing the high-branched polycarbosilane (HBPCS). The oxidation behavior of the powders in the dried air was investigated by the thermal gravimetric method. The mean particle size of the HBPCS derived SiCO ceramic powders was about 7μm. The samples were oxidized at temperatures of 900℃，950℃，1000℃ and 1050℃ for 4 h. The results show that the mass change during the oxidation process exhibits two distinguished stages. At the first stage (from 80 min at 900℃ to 20 min at 1050℃)，the mass is rapidly increased with the oxidation time. However，the mass of the powders changes little at the second stage due to the pore sealing. The molecular oxygen diffusion is the controlling process for oxidation at this stage. The activation energy of this material oxidized at 1173～1373 K is about 121 kJ/mol. The relationship between parabolic rate constants obtained by the thermal gravimetric method and oxide thickness change is deduced.
SiC1. 12O0. 12 ceramic powders were obtained by pyrolyzing the high-branched polycarbosilane (HBPCS). The oxidation behavior of the powders in the dried air was investigated by the thermal gravimetric method. The mean particle size of the HBPCS derived SiCO ceramic powders was about 7μm. The samples were oxidized at temperatures of 900℃，950℃，1000℃ and 1050℃ for 4 h. The results show that the mass change during the oxidation process exhibits two distinguished stages. At the first stage (from 80 min at 900℃ to 20 min at 1050℃)，the mass is rapidly increased with the oxidation time. However，the mass of the powders changes little at the second stage due to the pore sealing. The molecular oxygen diffusion is the controlling process for oxidation at this stage. The activation energy of this material oxidized at 1173～1373 K is about 121 kJ/mol. The relationship between parabolic rate constants obtained by the thermal gravimetric method and oxide thickness change is deduced.
2009, 26(5): 132-136.
Abstract:
The finite element method was employed to simulate the crack growth behavior of ceramics matrix composites. The model used the combined elements for simulating the separation between matrix and fiber and the contact elements for simulating the friction between matrix and fiber，considering interfacial bond strength on the basis of the fracture model of fiber reinforced composites. It predicted that the interfacial bond strength between matrix and fiber affects the fracturing process through FEM calculation and studied the impacts on the composites with different elastic moduli of matrix for further discussion. Compared with other results，this result showed that the moderate interfacial bond strength was suitable for the composites，whether its elastic modulus of matrix was “strong”or“weak”，to improve the toughness and tensile strength.
The finite element method was employed to simulate the crack growth behavior of ceramics matrix composites. The model used the combined elements for simulating the separation between matrix and fiber and the contact elements for simulating the friction between matrix and fiber，considering interfacial bond strength on the basis of the fracture model of fiber reinforced composites. It predicted that the interfacial bond strength between matrix and fiber affects the fracturing process through FEM calculation and studied the impacts on the composites with different elastic moduli of matrix for further discussion. Compared with other results，this result showed that the moderate interfacial bond strength was suitable for the composites，whether its elastic modulus of matrix was “strong”or“weak”，to improve the toughness and tensile strength.
2009, 26(5): 137-142.
Abstract:
Alumina silicate fibres/TCP biological functionally gradient material (FGM) was fabricated by hot pressing technique. X-ray diffraction analysis，SEM，EDAX linear scanning analysis，density and hardness test were adopted to carry out the research of the FGM. The results show that fibre contents distribution changes symmetrically in the FGM. No flaws and breakages appear in the FGM. FGM presents indistinct gradient distribution in macrostructure and continuous component changes in microstructure. TCP matrix combines with silicate fibres tightly in the FGM. Decomposition of hydroxyapatite leads to phase transformation from HA to TCP and no chemical reaction happens among TCP and fibre and the hot pressing die. With the increase of fibre contents，the fracture way changes from brittle fracture to toughness fracture and the toughness degree increases. The hardness and relative density are enhanced with the increase of fibre contents. 60 vol% fibres gradient layer behaves the highest value with hardness and relative density equal to 92.7 MPa and 86.5%，respectively.
Alumina silicate fibres/TCP biological functionally gradient material (FGM) was fabricated by hot pressing technique. X-ray diffraction analysis，SEM，EDAX linear scanning analysis，density and hardness test were adopted to carry out the research of the FGM. The results show that fibre contents distribution changes symmetrically in the FGM. No flaws and breakages appear in the FGM. FGM presents indistinct gradient distribution in macrostructure and continuous component changes in microstructure. TCP matrix combines with silicate fibres tightly in the FGM. Decomposition of hydroxyapatite leads to phase transformation from HA to TCP and no chemical reaction happens among TCP and fibre and the hot pressing die. With the increase of fibre contents，the fracture way changes from brittle fracture to toughness fracture and the toughness degree increases. The hardness and relative density are enhanced with the increase of fibre contents. 60 vol% fibres gradient layer behaves the highest value with hardness and relative density equal to 92.7 MPa and 86.5%，respectively.
2009, 26(5): 143-147.
Abstract:
The attapulgite clay with pore-network structures has favorable adsorption performance toward organic materials. According to its adsorption properties，the attapulgite clay was compounded with paraffin wax to produce phase change composites for energy storage (PCCES). As the paraffin was adsorbed into the pores and changed phase in a fixed space，the problems like leakage or flowage were avoided. The experimental results show that the optimal adsorption effect emerges when the mass ratio of at tapulgite containing 80% palygorskite to paraffin wax is 2∶1. The DSC tests indicated that the quantity of composites latent heat is related with the proportion of at tapulgite and paraffin. The quantity of palygorskite in the composites is the main factor to affect the ability of adsorption. It can be learned from the temperature circle tests that the PCCES can absorb certain amount of heat when the environmental temperature rises，and release it during the cooling process. These properties may be developed and find applications in the energy saving field.
The attapulgite clay with pore-network structures has favorable adsorption performance toward organic materials. According to its adsorption properties，the attapulgite clay was compounded with paraffin wax to produce phase change composites for energy storage (PCCES). As the paraffin was adsorbed into the pores and changed phase in a fixed space，the problems like leakage or flowage were avoided. The experimental results show that the optimal adsorption effect emerges when the mass ratio of at tapulgite containing 80% palygorskite to paraffin wax is 2∶1. The DSC tests indicated that the quantity of composites latent heat is related with the proportion of at tapulgite and paraffin. The quantity of palygorskite in the composites is the main factor to affect the ability of adsorption. It can be learned from the temperature circle tests that the PCCES can absorb certain amount of heat when the environmental temperature rises，and release it during the cooling process. These properties may be developed and find applications in the energy saving field.
2009, 26(5): 148-152.
Abstract:
For understanding the influence of deformations of the mould on process-induced deformations of the composite component，the geometrical deformation of framed-mould in autoclave processing was studied. A finite element model was developed to simulate deformations of the mould. And then an experiment was presented to demonstrate the use of the present finite element procedure. Deformations of a plate framed-mould in autoclave processing were studied. The results of numerical simulation show that deformations of the framed-mould depended on not the magnitude of framed-mould temperature but the temperature distribution of the framed-mould. And the maximum framed-mould surface warpage was generated in the middle of the cooling period. It remained about 20 min. At that moment，the temperature in the center of framed-mould surface was the highest，and in the circumambiency the temperature was the lowest.
For understanding the influence of deformations of the mould on process-induced deformations of the composite component，the geometrical deformation of framed-mould in autoclave processing was studied. A finite element model was developed to simulate deformations of the mould. And then an experiment was presented to demonstrate the use of the present finite element procedure. Deformations of a plate framed-mould in autoclave processing were studied. The results of numerical simulation show that deformations of the framed-mould depended on not the magnitude of framed-mould temperature but the temperature distribution of the framed-mould. And the maximum framed-mould surface warpage was generated in the middle of the cooling period. It remained about 20 min. At that moment，the temperature in the center of framed-mould surface was the highest，and in the circumambiency the temperature was the lowest.
2009, 26(5): 153-158.
Abstract:
The compressive properties of composite honeycomb sandwich plates containing interface delamination defect between the facesheet and the core at the plate center were experimentally studied and theoretically analyzed.The influence of one circular delamination and two rectangular delamination defects on the compressive strength was discussed. A sub-laminate local buckling model was used to estimate the compressive strength of the sandwich plates. The results show that general buckling of the sandwich plates without any defects causes the final compression failure. But for the sandwich plates with delamination defect，there are different failure mechanisms with different delamination shapes and sizes. In general，facesheet local buckling cannot play a controlling role in the sandwich plate failure when the long side of the rectangular defect is vertical to the load direction. While the plate exhibits general buckling failure when the long side of the rectangular defect is parallel to the load direction. The sub-laminate local buckling model is effective to predict the compressive strength of the sandwich plate containing delamination defect while the facesheet local buckling acts as a controlling factor .
The compressive properties of composite honeycomb sandwich plates containing interface delamination defect between the facesheet and the core at the plate center were experimentally studied and theoretically analyzed.The influence of one circular delamination and two rectangular delamination defects on the compressive strength was discussed. A sub-laminate local buckling model was used to estimate the compressive strength of the sandwich plates. The results show that general buckling of the sandwich plates without any defects causes the final compression failure. But for the sandwich plates with delamination defect，there are different failure mechanisms with different delamination shapes and sizes. In general，facesheet local buckling cannot play a controlling role in the sandwich plate failure when the long side of the rectangular defect is vertical to the load direction. While the plate exhibits general buckling failure when the long side of the rectangular defect is parallel to the load direction. The sub-laminate local buckling model is effective to predict the compressive strength of the sandwich plate containing delamination defect while the facesheet local buckling acts as a controlling factor .
2009, 26(5): 159-166.
Abstract:
A three-dimensional (3D) nonlinear progressive damage analysis (PDA) model at the mesoscale level was presented in order to take into account the interlaminar stress and damaged material nonlinearity. The typical PDA consists of stress analysis，material failure initiation criteria and damaged material degradation rules. Adamaged material degradation rule was discussed mainly to introduce damage status invariables corresponding to different damage modes. The material stiffness matrix at each material point was degraded directly through damage status invariables. The proposed model can predict composites laminates damage initiation，progression until final failure and ultimate strength. 12 laminates with different stacking designs were analyzed with the model. The good agreement between the predicted ultimate strength and the experiments shows correctness of the model for laminates ultimate strength prediction.
A three-dimensional (3D) nonlinear progressive damage analysis (PDA) model at the mesoscale level was presented in order to take into account the interlaminar stress and damaged material nonlinearity. The typical PDA consists of stress analysis，material failure initiation criteria and damaged material degradation rules. Adamaged material degradation rule was discussed mainly to introduce damage status invariables corresponding to different damage modes. The material stiffness matrix at each material point was degraded directly through damage status invariables. The proposed model can predict composites laminates damage initiation，progression until final failure and ultimate strength. 12 laminates with different stacking designs were analyzed with the model. The good agreement between the predicted ultimate strength and the experiments shows correctness of the model for laminates ultimate strength prediction.
2009, 26(5): 167-172.
Abstract:
An axisymmetric rigid-plastic and coupled thermo-mechanical FEM model of SiCP/2024Al composite (volume fraction of SiCP12%) for plat die hot extrusion process was established based on the software MSC. Marc. The model was used to simulate the hot extrusion process of the material. The pressure-stroke curves and flow lines were analyzed and the effects of temperature of billet and extrusion velocity were discussed. The result sindicate that bars without surface defects can be obtained smoothly under the condition of the extrusion ratio 30∶1，temperature 400～450℃，extrusion rate 0.1～1.0 mm/s and extrusion pressure 4.0 ×106～5. 0 ×106N. The quality bars were got following the same process on 700 t hydraulic press to prove the feasibility of this process.
An axisymmetric rigid-plastic and coupled thermo-mechanical FEM model of SiCP/2024Al composite (volume fraction of SiCP12%) for plat die hot extrusion process was established based on the software MSC. Marc. The model was used to simulate the hot extrusion process of the material. The pressure-stroke curves and flow lines were analyzed and the effects of temperature of billet and extrusion velocity were discussed. The result sindicate that bars without surface defects can be obtained smoothly under the condition of the extrusion ratio 30∶1，temperature 400～450℃，extrusion rate 0.1～1.0 mm/s and extrusion pressure 4.0 ×106～5. 0 ×106N. The quality bars were got following the same process on 700 t hydraulic press to prove the feasibility of this process.
2009, 26(5): 173-177.
Abstract:
Based on requirement of intensity and thickness for the tubular nonwoven composite material by the big pipeline rehabilitation，the structure of the tubular nonwoven composite material was designed. To add fabric to reinforce the tubular nonwoven composite material，two pieces or more of the reinforced nonwoven were designed，forming a structure of the tubular nonwoven composite material with equidistant seams in the circumferential direction. This structure of the tubular nonwoven composite material with many seams is symmetric，during inversion，the concent ration of the stress of the single seam can be avoided，so the cracking of the seam is prevented；when the reinforced nonwoven is coverd with film，the areas at its two sides for sewing were obligated，the difficulty of the sewing is decreased，the efficiency of the sewing is increased，and the thickness of the seam is decreased；the film jointing of the seam becomes much easier，the airproof of the tubular nonwoven composite material being guaranteed. At last through the test，the rationality of the structure design was tested.
Based on requirement of intensity and thickness for the tubular nonwoven composite material by the big pipeline rehabilitation，the structure of the tubular nonwoven composite material was designed. To add fabric to reinforce the tubular nonwoven composite material，two pieces or more of the reinforced nonwoven were designed，forming a structure of the tubular nonwoven composite material with equidistant seams in the circumferential direction. This structure of the tubular nonwoven composite material with many seams is symmetric，during inversion，the concent ration of the stress of the single seam can be avoided，so the cracking of the seam is prevented；when the reinforced nonwoven is coverd with film，the areas at its two sides for sewing were obligated，the difficulty of the sewing is decreased，the efficiency of the sewing is increased，and the thickness of the seam is decreased；the film jointing of the seam becomes much easier，the airproof of the tubular nonwoven composite material being guaranteed. At last through the test，the rationality of the structure design was tested.
2009, 26(5): 178-185.
Abstract:
The tubular textile composite material as the liner is inversed in the pipeline by gas or water pressure，so that the damaged pipeline can be rehabilitated. During inversion，because of the inversion pressure，the tubular textile composite material must endure the complicated stress and strain. Adopting the finite element method，the paper analyzed the stress and strain of the tubular textile composite material during inversion，and the finite element simulation data are compared respectively with theory data and test data. The results show that the stress and strain in the head of the tubular textile composite material during inversion is instable，where the stress is concent rative，so the head of tubular textile composite material is easy to break；when the geometry parameter and component material of the tubular textile composite material are determined，the scope of diameter of the pipeline，within which the tubular textile composite material can be repaired is confirmed by the finite element method.
The tubular textile composite material as the liner is inversed in the pipeline by gas or water pressure，so that the damaged pipeline can be rehabilitated. During inversion，because of the inversion pressure，the tubular textile composite material must endure the complicated stress and strain. Adopting the finite element method，the paper analyzed the stress and strain of the tubular textile composite material during inversion，and the finite element simulation data are compared respectively with theory data and test data. The results show that the stress and strain in the head of the tubular textile composite material during inversion is instable，where the stress is concent rative，so the head of tubular textile composite material is easy to break；when the geometry parameter and component material of the tubular textile composite material are determined，the scope of diameter of the pipeline，within which the tubular textile composite material can be repaired is confirmed by the finite element method.
2009, 26(5): 186-192.
Abstract:
The bridging forces provided by the fiber Z-pins were assumed to be proportional to their length embedded in the laminates. Based on the currently available Z-pin micro-model，a Z-pin element was developed and a beam element model was proposed in this paper to study the effect of Z-pins on modeⅠdelamination toughness of Z-pinned double cantilever beam (DCB) specimens. A contact element was also introduced to the proposed model to avoid the unrealistic penetration of the two substrate beams at the delamination crack tip. The numerical results show that the Z-pins can significantly improve the modeⅠdelamination toughness of the Z-pinned laminated DCB specimens. However，less enhancement on modeⅠdelamination toughness is obtained when the delamination is close to the surface of DCB.
The bridging forces provided by the fiber Z-pins were assumed to be proportional to their length embedded in the laminates. Based on the currently available Z-pin micro-model，a Z-pin element was developed and a beam element model was proposed in this paper to study the effect of Z-pins on modeⅠdelamination toughness of Z-pinned double cantilever beam (DCB) specimens. A contact element was also introduced to the proposed model to avoid the unrealistic penetration of the two substrate beams at the delamination crack tip. The numerical results show that the Z-pins can significantly improve the modeⅠdelamination toughness of the Z-pinned laminated DCB specimens. However，less enhancement on modeⅠdelamination toughness is obtained when the delamination is close to the surface of DCB.
2009, 26(5): 193-200.
Abstract:
It was assumed that the friction between the fiber Z-pins and the surrounding matrix，during its pull-out process，provides the bridging forces to enhance the delamination toughness of the laminates. Based on the currently available Z-pin micro-model，a Z-pin element was developed and a beam element model was proposed in this paper to study the effect of Z-pins on modeⅡdelamination toughness of Z-pinned end notched flexure (ENF) specimens. A contact element was also introduced on the delamination crack surface in the proposed finite element model to avoid the unrealistic penetration of the two substrate beams. The numerical results showed that the Z-pins can significantly improve the modeⅡdelamination toughness of the Z-pinned laminated ENF specimens. However，fewer enhancements on modeⅡdelamination toughness are obtained when the delamination crack is close to the surface of ENF specimens. The thickness of the thinner substrate beam is the key parameter to determine the enhanced modeⅡdelamination toughness of ENF specimens.
It was assumed that the friction between the fiber Z-pins and the surrounding matrix，during its pull-out process，provides the bridging forces to enhance the delamination toughness of the laminates. Based on the currently available Z-pin micro-model，a Z-pin element was developed and a beam element model was proposed in this paper to study the effect of Z-pins on modeⅡdelamination toughness of Z-pinned end notched flexure (ENF) specimens. A contact element was also introduced on the delamination crack surface in the proposed finite element model to avoid the unrealistic penetration of the two substrate beams. The numerical results showed that the Z-pins can significantly improve the modeⅡdelamination toughness of the Z-pinned laminated ENF specimens. However，fewer enhancements on modeⅡdelamination toughness are obtained when the delamination crack is close to the surface of ENF specimens. The thickness of the thinner substrate beam is the key parameter to determine the enhanced modeⅡdelamination toughness of ENF specimens.
