2019 Vol. 36, No. 8
2019, 36(8): 1787-1795.
doi: 10.13801/j.cnki.fhclxb.20181023.003
Abstract:
Polyphenylthiourea (ArPTU) is a new type of high breakdown, low loss material. In order to improve its energy storage density, ArPTU can be blended with poly(vinylidene fluoride)(PVDF). The problem that how to improve its solubility and reduce the interface during blending with PVDF has become one of the research hotspots. Modification with dopamine (DA) can effectively improve its interface with PVDF. DA modified ArPTU-PVDF(DA/ArPTU-PVDF) composite films with different blending ratios were prepared by solution casting hot pressing method and characterized by X-ray diffractometry, scanning electron microscopy, nuclear magnetic resonance, gel permeation chromatography and impedance analyzer. The results show that when the mass fraction of DA/ArPTU is 10wt%-15wt%, the relative content of β crystal form of PVDF increases remarkably, which is one of the main reasons for the increase of dielectric properties. At 100 Hz, the dielectric constant can be the largest. It reaches 10.3 (10wt% DA/ArPTU), while the dielectric loss decreases, and the minimum reaches 0.008 (25wt% DA/ArPTU). The energy storage density of the composite material also increases significantly, up to 3.0 J/cm3 (10wt% DA/ArPTU), which is 63.3% higher than that of the pure PVDF. In addition, the breakdown characteristics of the composites are greatly improved compared to the pure PVDF, up to 556.4 MV/m (15wt% DA/ArPTU). Moreover, the mechanical properties of the modified composites have also been greatly improved. The maximum elongation at break can reach 196.7% (5wt% DA/ArPTU), showing the potential of flexible high breakdown energy storage materials.
Polyphenylthiourea (ArPTU) is a new type of high breakdown, low loss material. In order to improve its energy storage density, ArPTU can be blended with poly(vinylidene fluoride)(PVDF). The problem that how to improve its solubility and reduce the interface during blending with PVDF has become one of the research hotspots. Modification with dopamine (DA) can effectively improve its interface with PVDF. DA modified ArPTU-PVDF(DA/ArPTU-PVDF) composite films with different blending ratios were prepared by solution casting hot pressing method and characterized by X-ray diffractometry, scanning electron microscopy, nuclear magnetic resonance, gel permeation chromatography and impedance analyzer. The results show that when the mass fraction of DA/ArPTU is 10wt%-15wt%, the relative content of β crystal form of PVDF increases remarkably, which is one of the main reasons for the increase of dielectric properties. At 100 Hz, the dielectric constant can be the largest. It reaches 10.3 (10wt% DA/ArPTU), while the dielectric loss decreases, and the minimum reaches 0.008 (25wt% DA/ArPTU). The energy storage density of the composite material also increases significantly, up to 3.0 J/cm3 (10wt% DA/ArPTU), which is 63.3% higher than that of the pure PVDF. In addition, the breakdown characteristics of the composites are greatly improved compared to the pure PVDF, up to 556.4 MV/m (15wt% DA/ArPTU). Moreover, the mechanical properties of the modified composites have also been greatly improved. The maximum elongation at break can reach 196.7% (5wt% DA/ArPTU), showing the potential of flexible high breakdown energy storage materials.
2019, 36(8): 1796-1803.
doi: 10.13801/j.cnki.fhclxb.20181030.001
Abstract:
Hindered phenol AO-60/nitrile butadiene rubber-epoxidized natural rubber-natural rubber composites were prepared by using hindered phenol AO-60/nitrile butadiene rubber (NBR) (mass ratio 40:100) as damping phase and epoxidized natural rubber (ENR) as compatibilizer. It is found that the microstructure of the composites is "sea-island structure" and the co-continuous morphology appears when the mass ratio of NR/NBR is 60:40 and 50:50. The composite exhibit two glass transition temperatures, which occur near -60℃ and around -10℃. With the increase of mass ratio of AO-60/NBR, the effective damping of the composite in the temperature range of -20-40℃ is widened from 0℃ to 35.9℃, and the loss factor increases slightly with increasing strain. The composites exhibit low stress at low strain and exhibits high flexibility. At the same time, it has a stress crack point at higher strain, showing high tensile strength and elongation at break.
Hindered phenol AO-60/nitrile butadiene rubber-epoxidized natural rubber-natural rubber composites were prepared by using hindered phenol AO-60/nitrile butadiene rubber (NBR) (mass ratio 40:100) as damping phase and epoxidized natural rubber (ENR) as compatibilizer. It is found that the microstructure of the composites is "sea-island structure" and the co-continuous morphology appears when the mass ratio of NR/NBR is 60:40 and 50:50. The composite exhibit two glass transition temperatures, which occur near -60℃ and around -10℃. With the increase of mass ratio of AO-60/NBR, the effective damping of the composite in the temperature range of -20-40℃ is widened from 0℃ to 35.9℃, and the loss factor increases slightly with increasing strain. The composites exhibit low stress at low strain and exhibits high flexibility. At the same time, it has a stress crack point at higher strain, showing high tensile strength and elongation at break.
2019, 36(8): 1804-1812.
doi: 10.13801/j.cnki.fhclxb.20180925.002
Abstract:
Based on the phenomenological kinetic model, DiBenedetto equation, gelation model, the isothermal and non-isothermal curing kinetic of homemade rapid curing epoxy resin was studied, and the time-temperature-transfer (TTT) diagram was established. The resin system shows both longer open time and shorter cure time, as shown in TTT diagram, which serves as a guidance for rapid resin transfer molding(RTM) process design. The flow and impregnation of resin system into carbon fiber fabric was monitored, and the interfacial mechanical properties and microstructure of rapid prototyping carbon fiber/epoxy resin composites were also evaluated. The wettability of resin system at the injection temperature is good, and the mechanical properties and internal quality of carbon fiber/epoxy resin composites from rapid RTM process are acceptable.
Based on the phenomenological kinetic model, DiBenedetto equation, gelation model, the isothermal and non-isothermal curing kinetic of homemade rapid curing epoxy resin was studied, and the time-temperature-transfer (TTT) diagram was established. The resin system shows both longer open time and shorter cure time, as shown in TTT diagram, which serves as a guidance for rapid resin transfer molding(RTM) process design. The flow and impregnation of resin system into carbon fiber fabric was monitored, and the interfacial mechanical properties and microstructure of rapid prototyping carbon fiber/epoxy resin composites were also evaluated. The wettability of resin system at the injection temperature is good, and the mechanical properties and internal quality of carbon fiber/epoxy resin composites from rapid RTM process are acceptable.
2019, 36(8): 1813-1821.
doi: 10.13801/j.cnki.fhclxb.20180925.003
Abstract:
Based on the study of the basic properties of vinyl-containing polysilazane (PSN1) resin, a polysilazane-based high-temperature wave-penetrating composite quartz fiber/PSN1(QF/PSN1) was fabricated by laminated pressing method using quartz fiber cloth as the reinforcing material. The mechanical properties and dielectric properties of the QF/PSN1 composites at room and high temperature were investigated. The results show that PSN1 resin has excellent processing ability with viscosity lower than 1 Pas between 60℃ and 151℃, and low curing temperature less than 200℃. The cured PSN1 resin exhibits high thermal stability T5% (the temperature at which the mass of the resin lost 5%) above 480℃ and WR (the mass residual fraction) above 76% at 800℃ in both N2 and air atmosphere. The flexural strength and interlaminate shear strength (ILSS) of QF/PSN1 composites show a trend of decreasing first and then increasing with the rising of temperature. And the flexural strength is more than 120 MPa after holding for 10 min at 450℃, which demonstrates that the QF/PSN1 composites possess excellent mechanical properties. QF/PSN1 composites show superior dielectric properties with dielectric constant (ε) lower than 3.2 and dielectric loss (tanδ) all less than 0.01 from room temperature to 450℃ in the frequency range of 1~12 GHz. The above studies indicate that PSN1 resin has high potentials as a new type of resin matrix for the high-temperature wave-penetrating composites.
Based on the study of the basic properties of vinyl-containing polysilazane (PSN1) resin, a polysilazane-based high-temperature wave-penetrating composite quartz fiber/PSN1(QF/PSN1) was fabricated by laminated pressing method using quartz fiber cloth as the reinforcing material. The mechanical properties and dielectric properties of the QF/PSN1 composites at room and high temperature were investigated. The results show that PSN1 resin has excellent processing ability with viscosity lower than 1 Pas between 60℃ and 151℃, and low curing temperature less than 200℃. The cured PSN1 resin exhibits high thermal stability T5% (the temperature at which the mass of the resin lost 5%) above 480℃ and WR (the mass residual fraction) above 76% at 800℃ in both N2 and air atmosphere. The flexural strength and interlaminate shear strength (ILSS) of QF/PSN1 composites show a trend of decreasing first and then increasing with the rising of temperature. And the flexural strength is more than 120 MPa after holding for 10 min at 450℃, which demonstrates that the QF/PSN1 composites possess excellent mechanical properties. QF/PSN1 composites show superior dielectric properties with dielectric constant (ε) lower than 3.2 and dielectric loss (tanδ) all less than 0.01 from room temperature to 450℃ in the frequency range of 1~12 GHz. The above studies indicate that PSN1 resin has high potentials as a new type of resin matrix for the high-temperature wave-penetrating composites.
2019, 36(8): 1822-1829.
doi: 10.13801/j.cnki.fhclxb.20180925.001
Abstract:
The hydrophobic fumed SiO2 particles were dispersed in solvent-free epoxy resin (EP) by sand milling, hydrophobic fumed SiO2/EP composites with different hydrophobic fumed SiO2 mass fractions were prepared by heating and curing. The results of XRD detection and SEM observation confirm that the hydrophobic fumed SiO2 nanoparticles are uniformly dispersed in EP in amorphous form. The results of the physical and chemical properties of the hydrophobic fumed SiO2/EP composites show that the thermal stability, dielectric constant, dielectric loss and electrical conductivity of the hydrophobic fumed SiO2/EP composites increase with the increase of the doping amount of SiO2 nanoparticles. The breakdown field strength reaches the maximum value of 24.66 kV/mm with 2wt% nanoparticle addition, which is 21.35% higher than the pure EP. When the doping amount of SiO2 nano particles is 8wt%, the corona life of the hydrophobic fumed SiO2/EP can reach 42.7 h, which is 18.9 times that of the pure EP.
The hydrophobic fumed SiO2 particles were dispersed in solvent-free epoxy resin (EP) by sand milling, hydrophobic fumed SiO2/EP composites with different hydrophobic fumed SiO2 mass fractions were prepared by heating and curing. The results of XRD detection and SEM observation confirm that the hydrophobic fumed SiO2 nanoparticles are uniformly dispersed in EP in amorphous form. The results of the physical and chemical properties of the hydrophobic fumed SiO2/EP composites show that the thermal stability, dielectric constant, dielectric loss and electrical conductivity of the hydrophobic fumed SiO2/EP composites increase with the increase of the doping amount of SiO2 nanoparticles. The breakdown field strength reaches the maximum value of 24.66 kV/mm with 2wt% nanoparticle addition, which is 21.35% higher than the pure EP. When the doping amount of SiO2 nano particles is 8wt%, the corona life of the hydrophobic fumed SiO2/EP can reach 42.7 h, which is 18.9 times that of the pure EP.
2019, 36(8): 1830-1837.
doi: 10.13801/j.cnki.fhclxb.20181119.002
Abstract:
The carbon fiber reinforced bismaleimide prepreg CCM40J/HT-280 was placed in different storage environments(vacuum, N2, O2, air)for room temperature aging experiments, and the relationship among the prepreg tack and storage environment and aging time was studied. The samples before and after the tack failure in different environments were analyzed by DSC, rheological and infrared spectroscopy. The CCM40J/HT-280 composites were prepared by autoclave molding process with the prepreg in different tack levels, and both the internal molding quality and mechanical properties of the composites were studied. The results show that the tack failure period of the CCM40J/HT-280 prepreg under the vacuum and N2 storage environment is about 40% longer than that of the sample in O2 and air.DSC and rheological test results show that the degree of crosslinking of the resin after aging is greater than that of virgin resin with the minimum viscosity significantly promoted, which is more obvious in the O2 environment. The analysis of the characteristic peaks by infrared spectrum shows that the degree of crosslinking reaction of the resin in the O2 environment storage is higher than that in the vacuum environment, indicating that O2 promotes the aging of the bismaleimide resin at room temperature. The CCM40J/HT-280 composites prepared by the tack failure prepreg have dense pores inside or between layers, and the flexural strength of the composites decreases by about 13.0%, the flexural modulus decreases by about 6.5%, and the interlaminar shear strength decreases by about 10.7%.
The carbon fiber reinforced bismaleimide prepreg CCM40J/HT-280 was placed in different storage environments(vacuum, N2, O2, air)for room temperature aging experiments, and the relationship among the prepreg tack and storage environment and aging time was studied. The samples before and after the tack failure in different environments were analyzed by DSC, rheological and infrared spectroscopy. The CCM40J/HT-280 composites were prepared by autoclave molding process with the prepreg in different tack levels, and both the internal molding quality and mechanical properties of the composites were studied. The results show that the tack failure period of the CCM40J/HT-280 prepreg under the vacuum and N2 storage environment is about 40% longer than that of the sample in O2 and air.DSC and rheological test results show that the degree of crosslinking of the resin after aging is greater than that of virgin resin with the minimum viscosity significantly promoted, which is more obvious in the O2 environment. The analysis of the characteristic peaks by infrared spectrum shows that the degree of crosslinking reaction of the resin in the O2 environment storage is higher than that in the vacuum environment, indicating that O2 promotes the aging of the bismaleimide resin at room temperature. The CCM40J/HT-280 composites prepared by the tack failure prepreg have dense pores inside or between layers, and the flexural strength of the composites decreases by about 13.0%, the flexural modulus decreases by about 6.5%, and the interlaminar shear strength decreases by about 10.7%.
2019, 36(8): 1838-1846.
doi: 10.13801/j.cnki.fhclxb.20181009.005
Abstract:
In order to quantitatively evaluate the worn degree of carbon fiber tows and investigate the mechanism of friction and wear between carbon fiber tows, a frictional simulation device was designed to study the effects of frictional cycle times, loading force and frictional angle on the abrasion of carbon fiber tows. The worn degree was characterized by comparing tensile strength at break, surface morphology and the amount of hairiness of the carbon fiber tows before and after friction. The results show that the wear of carbon fiber tows gradually increases with the increase of frictional cycle times and loading force. As the frictional angle changes from 90° to 30°, the tensile strength at break of the carbon fiber tows decreases slightly as the angle decreases. However, when the frictional angle is 0°, the tensile strength at break of the carbon fiber tows has a significant decrease. The wear mechanism of carbon fiber tows was explained by combining with fiber tow contact theory and viscous film indentation method. The results reveal that the contact area is the main factor causing the worn degree of fiber tows. The real contact area between fiber tows increases with the the loading force increasing and decreases with the frictional angle increasing.
In order to quantitatively evaluate the worn degree of carbon fiber tows and investigate the mechanism of friction and wear between carbon fiber tows, a frictional simulation device was designed to study the effects of frictional cycle times, loading force and frictional angle on the abrasion of carbon fiber tows. The worn degree was characterized by comparing tensile strength at break, surface morphology and the amount of hairiness of the carbon fiber tows before and after friction. The results show that the wear of carbon fiber tows gradually increases with the increase of frictional cycle times and loading force. As the frictional angle changes from 90° to 30°, the tensile strength at break of the carbon fiber tows decreases slightly as the angle decreases. However, when the frictional angle is 0°, the tensile strength at break of the carbon fiber tows has a significant decrease. The wear mechanism of carbon fiber tows was explained by combining with fiber tow contact theory and viscous film indentation method. The results reveal that the contact area is the main factor causing the worn degree of fiber tows. The real contact area between fiber tows increases with the the loading force increasing and decreases with the frictional angle increasing.
2019, 36(8): 1847-1853.
doi: 10.13801/j.cnki.fhclxb.20180928.002
Abstract:
Aramid nanofibers (NAF) with a diameter of 40-50 nm and a length of 2-5 μm were successfully prepared by dissolving macroscopic aramid fiber (AF) in dimethyl sulfoxide(DMSO)-KOH system, and the microstructure, chemical and crystal structure of NAF and AF were analyzed by SEM, TEM, FTIR, Raman and XRD. The results show that NAF and AF have similar chemical structures, while NAF retains most of the crystalline structure of AF, only a certain difference in fiber size. NAF composite film with layered dense structure was prepared by vacuum-assisted layer-by-layer self-assembled method. The film exhibits good transparency, flexibility, temperature resistance and mechanical properties. The film also has certain lyophilic properties (contact angle is 81.5°) and excellent resistance to liquid penetration and liquid absorption.
Aramid nanofibers (NAF) with a diameter of 40-50 nm and a length of 2-5 μm were successfully prepared by dissolving macroscopic aramid fiber (AF) in dimethyl sulfoxide(DMSO)-KOH system, and the microstructure, chemical and crystal structure of NAF and AF were analyzed by SEM, TEM, FTIR, Raman and XRD. The results show that NAF and AF have similar chemical structures, while NAF retains most of the crystalline structure of AF, only a certain difference in fiber size. NAF composite film with layered dense structure was prepared by vacuum-assisted layer-by-layer self-assembled method. The film exhibits good transparency, flexibility, temperature resistance and mechanical properties. The film also has certain lyophilic properties (contact angle is 81.5°) and excellent resistance to liquid penetration and liquid absorption.
2019, 36(8): 1854-1863.
doi: 10.13801/j.cnki.fhclxb.20181009.001
Abstract:
The acoustic emission(AE) technique was used to study the failure behavior of carbon fiber reinforced polymer(CFRP) bolted joints with different geometric sizes under static load, and the relationship between the damage behavior of the joint and the AE signal under different geometric was compared. The AE technology was used to collect and convert the AE in the process of structural damage, and the relationship between the amplitude, entropy curve, Andrews curve and the failure behavior was analyzed by combining the load-displacement curve of CFRP bolted and the macro/meso damage morphology. The results show that the load-displacement curves of bearing and shear failure specimens show obvious plastic characteristics. When the specimen is failure in bearing and shear, the AE is the medium amplitude signal, and a small number of high amplitude signals are accompanied. The medium amplitude signal occurs when the tensile damage happens. According to the characteristics of entropy curve, the failure process of CFRP joint is divided into four stages, and the failure modes such as fiber fracture and delamination occur at the stage of damage evolution, and the failure is dominated by delamination failure in the stage of structural failure. Based on the Andrews curve analysis, a variety of damage types are found in the failure evolution stage of the bearing and tensile failure modes, and many types of damage will appear in the failure stage of the shear failure mode.
The acoustic emission(AE) technique was used to study the failure behavior of carbon fiber reinforced polymer(CFRP) bolted joints with different geometric sizes under static load, and the relationship between the damage behavior of the joint and the AE signal under different geometric was compared. The AE technology was used to collect and convert the AE in the process of structural damage, and the relationship between the amplitude, entropy curve, Andrews curve and the failure behavior was analyzed by combining the load-displacement curve of CFRP bolted and the macro/meso damage morphology. The results show that the load-displacement curves of bearing and shear failure specimens show obvious plastic characteristics. When the specimen is failure in bearing and shear, the AE is the medium amplitude signal, and a small number of high amplitude signals are accompanied. The medium amplitude signal occurs when the tensile damage happens. According to the characteristics of entropy curve, the failure process of CFRP joint is divided into four stages, and the failure modes such as fiber fracture and delamination occur at the stage of damage evolution, and the failure is dominated by delamination failure in the stage of structural failure. Based on the Andrews curve analysis, a variety of damage types are found in the failure evolution stage of the bearing and tensile failure modes, and many types of damage will appear in the failure stage of the shear failure mode.
2019, 36(8): 1864-1872.
doi: 10.13801/j.cnki.fhclxb.20181217.001
Abstract:
The structual strength of blades is a significant factor of the safety of wind turbines and the levelised cost of energy. A three-dimentional finite element model was built to investigate the strength of blade segment, which inherited the geometrical and laminate cross-sectional characteristics of American SNL 100 m glass fiber reinforced polymer composites(GFRP) blade at critical span location. The coupling behaviors of nonlinear buckling, adhesive debonding and composite failure were jointly studied. The results indicate that composite of blade segment fails firstly, then the adhesive debonds, and the adhesive breaks finally under the flap-wise load. Nonlinear buckling initiates firstly, then the composite fails and adhesive debonds, and the adhesive breaks finally under the edge-wise load, which implies that the adhesive debonding at trailing edge is triggered by the buckling deformation.
The structual strength of blades is a significant factor of the safety of wind turbines and the levelised cost of energy. A three-dimentional finite element model was built to investigate the strength of blade segment, which inherited the geometrical and laminate cross-sectional characteristics of American SNL 100 m glass fiber reinforced polymer composites(GFRP) blade at critical span location. The coupling behaviors of nonlinear buckling, adhesive debonding and composite failure were jointly studied. The results indicate that composite of blade segment fails firstly, then the adhesive debonds, and the adhesive breaks finally under the flap-wise load. Nonlinear buckling initiates firstly, then the composite fails and adhesive debonds, and the adhesive breaks finally under the edge-wise load, which implies that the adhesive debonding at trailing edge is triggered by the buckling deformation.
2019, 36(8): 1873-1878.
doi: 10.13801/j.cnki.fhclxb.20181025.003
Abstract:
In order to prepare an ideal interphase of continuous fiber reinforced ceramic composite, three types of (BN-SiC)n composite coatings were deposited on the surface of SiC fibers by chemical vapor deposition (CVD). The microstructure of the (BN-SiC)n coatings was characterized. The monofilament tensile properties of SiC fibers with various (BN-SiC)n coatings were investigated. The results show that the (BN-SiC)n coatings deposited on the SiC fibers are dense and uniform. The tensile strength of SiC fibers monofilament decreases with the increasing coating layers. The SiC fibers with single BN coating have the high monofilament strength retention of about 70% and the maximum elongation of about 2.3%. Compared to the original SiC fiber, the monofilament tensile properties of SiC fibers with (BN-SiC)1 and (BN-SiC)2 composite coatings decrease obviously, and the tensile strength retention rates are 42.1% and 32.3%, respectively.
In order to prepare an ideal interphase of continuous fiber reinforced ceramic composite, three types of (BN-SiC)n composite coatings were deposited on the surface of SiC fibers by chemical vapor deposition (CVD). The microstructure of the (BN-SiC)n coatings was characterized. The monofilament tensile properties of SiC fibers with various (BN-SiC)n coatings were investigated. The results show that the (BN-SiC)n coatings deposited on the SiC fibers are dense and uniform. The tensile strength of SiC fibers monofilament decreases with the increasing coating layers. The SiC fibers with single BN coating have the high monofilament strength retention of about 70% and the maximum elongation of about 2.3%. Compared to the original SiC fiber, the monofilament tensile properties of SiC fibers with (BN-SiC)1 and (BN-SiC)2 composite coatings decrease obviously, and the tensile strength retention rates are 42.1% and 32.3%, respectively.
2019, 36(8): 1879-1885.
doi: 10.13801/j.cnki.fhclxb.20181018.001
Abstract:
In order to study the failure mechanism of the 3D braided SiC/SiC composites, the uniaxial tension and three-point bending tests at room temperature were carried out. Before the experiment, the morphology of the braided structure of the 3D braided SiC/SiC specimen was clarified by means of scanning computed tomography (CT). Microscopic analysis of tensile and three-point bending specimens shows that during the tensile process, the local stress concentrations are developed in the material as a result of the primary pores and microcracks. As the tensile load increasing, the cracks in the transverse direction of the matrix as well as the longitudinal interlaminar cracks between the fiber bundles gradually develop into internal fiber cracks form, ultimately resulting in a brittle fracture of the material. Under the three-point bending load, a combination of shear and tension failure mode is found. The failure firstly happens in the bottom side of the specimen with tensile stress. Then, shear occurrs at the neutral surface. After that, the cracking develops towards both of the top and bottom sides, and finally the 3D braided SiC/SiC specimen fails totally. The fracture surface is strong correlative to the direction of the fiber bundle. The crack propagates substantially along the interface between the fiber bundles, which makes the real failure location different from the theoretical prediction position.
In order to study the failure mechanism of the 3D braided SiC/SiC composites, the uniaxial tension and three-point bending tests at room temperature were carried out. Before the experiment, the morphology of the braided structure of the 3D braided SiC/SiC specimen was clarified by means of scanning computed tomography (CT). Microscopic analysis of tensile and three-point bending specimens shows that during the tensile process, the local stress concentrations are developed in the material as a result of the primary pores and microcracks. As the tensile load increasing, the cracks in the transverse direction of the matrix as well as the longitudinal interlaminar cracks between the fiber bundles gradually develop into internal fiber cracks form, ultimately resulting in a brittle fracture of the material. Under the three-point bending load, a combination of shear and tension failure mode is found. The failure firstly happens in the bottom side of the specimen with tensile stress. Then, shear occurrs at the neutral surface. After that, the cracking develops towards both of the top and bottom sides, and finally the 3D braided SiC/SiC specimen fails totally. The fracture surface is strong correlative to the direction of the fiber bundle. The crack propagates substantially along the interface between the fiber bundles, which makes the real failure location different from the theoretical prediction position.
2019, 36(8): 1886-1892.
doi: 10.13801/j.cnki.fhclxb.20181108.001
Abstract:
A surrogate based technique to address natural frequency optimization problems of a power-law functionally graded plate was proposed. The natural element method was employed to conduct the direct free vibration analysis based on the first order shear deformation plate theory, which is a kind of meshless method based on the natural neighbor interpolation. Initially, some sample data were selected to construct the gradient index-frequency surrogate model. Later, a nonlinear optimization problem of the fundamental frequency was formulated, and the optimum solution was obtained by using Nelder-Mead simplex method. Several numerical examples were given to validate the efficiency and feasibility of the proposed method. It is observed that the piecewise cubic Hermite interpolating polynomial produces the best surrogate model with few sample data. The surrogate-based method improves the numerical efficiency by eliminating repeated frequency calculations.
A surrogate based technique to address natural frequency optimization problems of a power-law functionally graded plate was proposed. The natural element method was employed to conduct the direct free vibration analysis based on the first order shear deformation plate theory, which is a kind of meshless method based on the natural neighbor interpolation. Initially, some sample data were selected to construct the gradient index-frequency surrogate model. Later, a nonlinear optimization problem of the fundamental frequency was formulated, and the optimum solution was obtained by using Nelder-Mead simplex method. Several numerical examples were given to validate the efficiency and feasibility of the proposed method. It is observed that the piecewise cubic Hermite interpolating polynomial produces the best surrogate model with few sample data. The surrogate-based method improves the numerical efficiency by eliminating repeated frequency calculations.
2019, 36(8): 1893-1900.
doi: 10.13801/j.cnki.fhclxb.20180908.001
Abstract:
A novel honeycomb was proposed by adding double arrowhead cells into star-shaped honeycomb (SSH), and named as star-arrowhead honeycomb (SAH). The dynamic crushing behaviors and energy absorption capacities of the evolved structure SAH were systematically studied by finite element method with the commercial software package ANSYS/LS-DYNA explicit code. Adding double arrowhead cells into SSH improves the localized necking deformation of SSH under the low-velocity impact, enhances plateau stress, and makes a rhombus-shape band forming near the impact end. The results of finite element simulations show that SAH can absorb much more energy per unit mass than SSH under different impact velocities. Furthermore, the effects of the relative density and the impact velocity on the plateau stresses of SAH were discussed, and the empirical formula of plateau stress of SAH is given.
A novel honeycomb was proposed by adding double arrowhead cells into star-shaped honeycomb (SSH), and named as star-arrowhead honeycomb (SAH). The dynamic crushing behaviors and energy absorption capacities of the evolved structure SAH were systematically studied by finite element method with the commercial software package ANSYS/LS-DYNA explicit code. Adding double arrowhead cells into SSH improves the localized necking deformation of SSH under the low-velocity impact, enhances plateau stress, and makes a rhombus-shape band forming near the impact end. The results of finite element simulations show that SAH can absorb much more energy per unit mass than SSH under different impact velocities. Furthermore, the effects of the relative density and the impact velocity on the plateau stresses of SAH were discussed, and the empirical formula of plateau stress of SAH is given.
2019, 36(8): 1901-1910.
doi: 10.13801/j.cnki.fhclxb.20181114.003
Abstract:
Functionally graded shape memory alloy (FGSMA) is widely used in micro-electromechanical systems, aerospace and other practical engineering regions due to its excellent properties of both functionally graded material and shape memory alloy(SMA) material. In order to investigate the bending behavior of FGSMA composite, the nonlinear constitutive model of SMA was simplified, and the mechanical model of FGSMA composite beam was established according to the composite laminated plate theory in this paper. The effects of the laying angle of SMA fiber in FGSMA cantilever beam with linear variation of SMA volume fraction along the thickness direction on the cross-section strain, the axial displacement of the middle plane, the height of the neutral plane and the height of the phase change layer were studied by using the established model. And the variation of mid-plane strain, curvature, critical layer height of SMA martensitic transformation and the height of neutral plane in cantilever beam with different bending moment loads were also discussed. The results indicate that the neutral plane does not coincide with the mid-plane of the cantilever beam, and the positions of the upper and lower martensitic transformation critical layers of SMA are asymmetrical. In the cross section, the absolute value of axial strain increases, but the absolute value of longitudinal strain increases first and then decreases with the increase of laying angle, as well as the axial displacement of the middle plane. With the increase of the laying angle, the height of phase transformation finish layer decreases first and then increases under tensile condition, but the trend is opposite under compression state. With the increasing of the absolute value of the moment load, the height of neutral plane position shows a tendency of first stabilizing, then decreasing and finally increasing, and the phase transformation critical layers moves gradually closer to the position of the neutral plane. The positive strain and flexural rate of the middle plane change with the increasing of the absolute value of the moment load, and the change rate increases first and then slows down.
Functionally graded shape memory alloy (FGSMA) is widely used in micro-electromechanical systems, aerospace and other practical engineering regions due to its excellent properties of both functionally graded material and shape memory alloy(SMA) material. In order to investigate the bending behavior of FGSMA composite, the nonlinear constitutive model of SMA was simplified, and the mechanical model of FGSMA composite beam was established according to the composite laminated plate theory in this paper. The effects of the laying angle of SMA fiber in FGSMA cantilever beam with linear variation of SMA volume fraction along the thickness direction on the cross-section strain, the axial displacement of the middle plane, the height of the neutral plane and the height of the phase change layer were studied by using the established model. And the variation of mid-plane strain, curvature, critical layer height of SMA martensitic transformation and the height of neutral plane in cantilever beam with different bending moment loads were also discussed. The results indicate that the neutral plane does not coincide with the mid-plane of the cantilever beam, and the positions of the upper and lower martensitic transformation critical layers of SMA are asymmetrical. In the cross section, the absolute value of axial strain increases, but the absolute value of longitudinal strain increases first and then decreases with the increase of laying angle, as well as the axial displacement of the middle plane. With the increase of the laying angle, the height of phase transformation finish layer decreases first and then increases under tensile condition, but the trend is opposite under compression state. With the increasing of the absolute value of the moment load, the height of neutral plane position shows a tendency of first stabilizing, then decreasing and finally increasing, and the phase transformation critical layers moves gradually closer to the position of the neutral plane. The positive strain and flexural rate of the middle plane change with the increasing of the absolute value of the moment load, and the change rate increases first and then slows down.
2019, 36(8): 1911-1917.
doi: 10.13801/j.cnki.fhclxb.20180907.003
Abstract:
A self-supported electrode of MnOOH-graphene-foam Ni(NF) was synthesized by the method of vapor deposition and subsequent electrode position. Its physical properties including the phase, morphology and valence state were measured by the characterizations such as XRD, SEM and XPS, while the electrochemical performance was studied by constant current charge-discharge, cyclic voltammetry and the AC impedance technique. The results show that this method can be successfully used to prepare the self-supported MnOOH-graphene-NF electrode. The thin graphene layer is uniformly covered on the surface of NF, while the MnOOH microspheres are covered on the surface of graphene. The self-supported composite structure can be directly used as a supercapacitor electrode which shows great pseudocapacitance storage capacity in the electrolyte of 5 mol/L KOH. It can exhibit a large specific capacitance of 934 F/g at the current density of 0.5 A/g. When the current density increases to 5 A/g, the capacitance still remain at a high value of 771 F/g. The capacitance retention keeps at 98% after 5000 cycles at 2 A/g, and maintains a high coulombic efficiency close to 100%, indicating good supercapacitive performance. A new method was provided to synthesize the self-supported electrode of MnOOH-graphene-NF and it is expected to become a newly potential supercapacitor electrode material.
A self-supported electrode of MnOOH-graphene-foam Ni(NF) was synthesized by the method of vapor deposition and subsequent electrode position. Its physical properties including the phase, morphology and valence state were measured by the characterizations such as XRD, SEM and XPS, while the electrochemical performance was studied by constant current charge-discharge, cyclic voltammetry and the AC impedance technique. The results show that this method can be successfully used to prepare the self-supported MnOOH-graphene-NF electrode. The thin graphene layer is uniformly covered on the surface of NF, while the MnOOH microspheres are covered on the surface of graphene. The self-supported composite structure can be directly used as a supercapacitor electrode which shows great pseudocapacitance storage capacity in the electrolyte of 5 mol/L KOH. It can exhibit a large specific capacitance of 934 F/g at the current density of 0.5 A/g. When the current density increases to 5 A/g, the capacitance still remain at a high value of 771 F/g. The capacitance retention keeps at 98% after 5000 cycles at 2 A/g, and maintains a high coulombic efficiency close to 100%, indicating good supercapacitive performance. A new method was provided to synthesize the self-supported electrode of MnOOH-graphene-NF and it is expected to become a newly potential supercapacitor electrode material.
2019, 36(8): 1918-1925.
doi: 10.13801/j.cnki.fhclxb.20181108.008
Abstract:
Polyvinyl alcohol(PVA) fiber reinforced cementitious composites containing steel slag powder were prepared by replacing cement by steel slag powder. Both of the basic mechanical and microscopic properties were tested. Two series of PVA fiber reinforced cementitious composites containing steel slag powder with water to binder ratio of 0.25 and 0.35 were investigated, and the mass fraction of steel slag powder were 0, 30wt%, 60wt% and 80wt%. The basic mechanical properties and crack control capacity were investigated through cubic compressive test and four-point bending test. The morphology of PVA fiber reinforced cementitious composites containing steel slag powder was observed via SEM technique. The test results indicate that water to binder ratio and steel slag content can both influence the basic mechanical properties distinctly. The specimens with water to binder mass ratio of 0.25 performs good toughness and crack control capacity, meeting the basic requirements of engineering when the content of steel slag powder up to 80wt%. The steel slag content should not exceed 60wt% when the water to binder mass ratio is 0.35 for good performance. Meanwhile, considering energy saving and emission reduction, it is feasible to use high volume steel slag in producing PVA fiber reinforced cementitious composites containing steel slag powder.
Polyvinyl alcohol(PVA) fiber reinforced cementitious composites containing steel slag powder were prepared by replacing cement by steel slag powder. Both of the basic mechanical and microscopic properties were tested. Two series of PVA fiber reinforced cementitious composites containing steel slag powder with water to binder ratio of 0.25 and 0.35 were investigated, and the mass fraction of steel slag powder were 0, 30wt%, 60wt% and 80wt%. The basic mechanical properties and crack control capacity were investigated through cubic compressive test and four-point bending test. The morphology of PVA fiber reinforced cementitious composites containing steel slag powder was observed via SEM technique. The test results indicate that water to binder ratio and steel slag content can both influence the basic mechanical properties distinctly. The specimens with water to binder mass ratio of 0.25 performs good toughness and crack control capacity, meeting the basic requirements of engineering when the content of steel slag powder up to 80wt%. The steel slag content should not exceed 60wt% when the water to binder mass ratio is 0.35 for good performance. Meanwhile, considering energy saving and emission reduction, it is feasible to use high volume steel slag in producing PVA fiber reinforced cementitious composites containing steel slag powder.
2019, 36(8): 1926-1934.
doi: 10.13801/j.cnki.fhclxb.20180929.001
Abstract:
The effect of basalt fiber (BF) on the mechanical properties and toughness of basalt fiber reinforced spray concrete (BF/SC) was studied through the experiment. The microstructure of BF/SC was studied by SEM and nuclear magnetic resonance (NMR).The results show that the compressive strength, splitting tensile strength and flexural strength of BF/SC are significantly increased by adding BF. Compared to the plain SC, the flexural strength of BF/SC with 3 kg/m3 and 7.5 kg/m3 are better, and are energy absorption capacity are 2.42 times and 2.69 times as high as the plain SC, respectively. BF has a good dispersion rate in the SC, and displays reasonable bonding within the SC substrate. A proper amount of BF effectively inhibits the formation of large volume pores, in which the proportion of the large pore size of 3 kg/m3 BF/SC is only 0.25%, and the addition of excessive BF leads to an increase of fiber agglomeration and porosity. At the same time, the optimum content of fiber is found to be 3 kg/m3.
The effect of basalt fiber (BF) on the mechanical properties and toughness of basalt fiber reinforced spray concrete (BF/SC) was studied through the experiment. The microstructure of BF/SC was studied by SEM and nuclear magnetic resonance (NMR).The results show that the compressive strength, splitting tensile strength and flexural strength of BF/SC are significantly increased by adding BF. Compared to the plain SC, the flexural strength of BF/SC with 3 kg/m3 and 7.5 kg/m3 are better, and are energy absorption capacity are 2.42 times and 2.69 times as high as the plain SC, respectively. BF has a good dispersion rate in the SC, and displays reasonable bonding within the SC substrate. A proper amount of BF effectively inhibits the formation of large volume pores, in which the proportion of the large pore size of 3 kg/m3 BF/SC is only 0.25%, and the addition of excessive BF leads to an increase of fiber agglomeration and porosity. At the same time, the optimum content of fiber is found to be 3 kg/m3.
2019, 36(8): 1935-1948.
doi: 10.13801/j.cnki.fhclxb.20180917.001
Abstract:
Fiber aspect ratio has a significant effect on the mechanical properties of concrete. Because the change in aspect ratio is essentially the change in fiber diameter and morphology, the existing researches mostly change the aspect ratio gradient by changing the diameter or the cross-sectional shape of polypropylene(PP) fiber (including coarse and fine PP fiber), resulting that the variables are not unique. An experiment was carried out on the effects of the aspect ratio of coarse PP fiber (d=700 μm) and fine PP fiber (d=80 μm) on the mechanical properties of concrete. The mechanical properties of coarse and fine PP fiber reinforced concrete were analyzed. The results show that the slump of coarse and fine PP fiber concrete decreases first and then stends to be stable with the increase of the aspect ratio. The compressive strength, flexural strength and tensile strength tend to increase first and then decrease with the increasing aspect ratio. There is an optimum aspect ratio which is 42 for the 700 μm coarse PP fiber, and 200 for the 80 μm fine PP fiber. In addition, the macromechanical fitting calculation theory was proposed to analyze the influence of the aspect ratio of coarse PP fiber on the flexural strength of fiber concrete, so as to enhance the predictability and controllability of the test results. The analysis of the frictional bonding mechanism of the coarse and fine PP fibers in concrete was carried out, and the specific factors affecting the frictional bonding force were mastered.
Fiber aspect ratio has a significant effect on the mechanical properties of concrete. Because the change in aspect ratio is essentially the change in fiber diameter and morphology, the existing researches mostly change the aspect ratio gradient by changing the diameter or the cross-sectional shape of polypropylene(PP) fiber (including coarse and fine PP fiber), resulting that the variables are not unique. An experiment was carried out on the effects of the aspect ratio of coarse PP fiber (d=700 μm) and fine PP fiber (d=80 μm) on the mechanical properties of concrete. The mechanical properties of coarse and fine PP fiber reinforced concrete were analyzed. The results show that the slump of coarse and fine PP fiber concrete decreases first and then stends to be stable with the increase of the aspect ratio. The compressive strength, flexural strength and tensile strength tend to increase first and then decrease with the increasing aspect ratio. There is an optimum aspect ratio which is 42 for the 700 μm coarse PP fiber, and 200 for the 80 μm fine PP fiber. In addition, the macromechanical fitting calculation theory was proposed to analyze the influence of the aspect ratio of coarse PP fiber on the flexural strength of fiber concrete, so as to enhance the predictability and controllability of the test results. The analysis of the frictional bonding mechanism of the coarse and fine PP fibers in concrete was carried out, and the specific factors affecting the frictional bonding force were mastered.
2019, 36(8): 1949-1956.
doi: 10.13801/j.cnki.fhclxb.20180921.001
Abstract:
Two types of recycled steel fiber from waste tires were used to prepare ultra-high-performance concrete (UHPC) containing coarse aggregate and their mechanical properties, including compressive strength, splitting tensile strength, fracture energy and static elastic modulus were determined. Plain UHPC without steel fiber and UHPC with different types of normal commercial steel fibers were also prepared for comparison. The results indicate that the recycled steel fiber without rubber particles has a slightly negative effect on the compressive strength of UHPC with a decrease of 3.91% and other types of steel fiber can improve the mechanical properties of UHPC. The recycled steel fiber with rubber particles significantly improves the fracture energy of UHPC and is approximately 4 times as high as that of the normal steel fiber. Additionally, the improvement of the recycled steel fiber on the splitting tensile strength and static elastic modulus of UHPC is superior to that of the normal steel fiber. This suggests that the recycled steel fiber especially that with rubber particles can be a toughening material used in concrete, and can substitute for the normal commercial steel fiber to be applied in UHPC engineering.
Two types of recycled steel fiber from waste tires were used to prepare ultra-high-performance concrete (UHPC) containing coarse aggregate and their mechanical properties, including compressive strength, splitting tensile strength, fracture energy and static elastic modulus were determined. Plain UHPC without steel fiber and UHPC with different types of normal commercial steel fibers were also prepared for comparison. The results indicate that the recycled steel fiber without rubber particles has a slightly negative effect on the compressive strength of UHPC with a decrease of 3.91% and other types of steel fiber can improve the mechanical properties of UHPC. The recycled steel fiber with rubber particles significantly improves the fracture energy of UHPC and is approximately 4 times as high as that of the normal steel fiber. Additionally, the improvement of the recycled steel fiber on the splitting tensile strength and static elastic modulus of UHPC is superior to that of the normal steel fiber. This suggests that the recycled steel fiber especially that with rubber particles can be a toughening material used in concrete, and can substitute for the normal commercial steel fiber to be applied in UHPC engineering.
2019, 36(8): 1957-1967.
doi: 10.13801/j.cnki.fhclxb.20181101.001
Abstract:
In order to make full use of fiber reinforced polymer (FRP) in retrofitting and overcome the poor anti-cracking property of textile reinforced mortar, a new composite was developed, where the engineering cement composite (ECC) replaces the mortar as the inorganic adhesive to bond the FRP textile, while, it still lacks of fundamental researches on the mechanism for retrofitting. Taking polyethylene type ECC as substrate, the mechanism for strengthening concrete columns by FRP grid/ECC was focused. The experimental study was conducted for standard concrete cylinder, strengthened by FRP grid/ECC where new ECC material was served as the matrix. The testing variables were plain concrete strength and different textile grid, i.e. basalt fiber reinforced polymer (BFRP) and carbon fiber reinforced polymer (CFRP) grid. The uniaxial compressive performance was studied. The test results show that the new strengthening method can improve the crushing failure mode, and enhance the compression strength and ductility. Based on the material property of FRP grid/ECC, the two-phase strengthening mechanism was proposed in this study, for the development of method to predict the compression capacity of FRP grid/ECC strengthened concrete cylinder.
In order to make full use of fiber reinforced polymer (FRP) in retrofitting and overcome the poor anti-cracking property of textile reinforced mortar, a new composite was developed, where the engineering cement composite (ECC) replaces the mortar as the inorganic adhesive to bond the FRP textile, while, it still lacks of fundamental researches on the mechanism for retrofitting. Taking polyethylene type ECC as substrate, the mechanism for strengthening concrete columns by FRP grid/ECC was focused. The experimental study was conducted for standard concrete cylinder, strengthened by FRP grid/ECC where new ECC material was served as the matrix. The testing variables were plain concrete strength and different textile grid, i.e. basalt fiber reinforced polymer (BFRP) and carbon fiber reinforced polymer (CFRP) grid. The uniaxial compressive performance was studied. The test results show that the new strengthening method can improve the crushing failure mode, and enhance the compression strength and ductility. Based on the material property of FRP grid/ECC, the two-phase strengthening mechanism was proposed in this study, for the development of method to predict the compression capacity of FRP grid/ECC strengthened concrete cylinder.
2019, 36(8): 1968-1976.
doi: 10.13801/j.cnki.fhclxb.20181108.006
Abstract:
The shear toughness of polyvinyl alcohol fiber reinforced engineered cementitious composite (PVA/ECC) beams without stirrups was studied in this paper. Based on the testing results of shear failure from five groups of PVA/ECC beams, the shear toughness of the PVA/ECC beams with different fiber contents were analyzed and evaluated while using the shear toughness index and the diagonal crack composite index as indicators. The results show that the incorporation of PVA fibers can improve the cracking performance and the deformation capacity of the beam, enhance the bearing capacity of the oblique section, and thereby increase the shear toughness of the member. Additionally, within 0-2vol% of volume fraction of PVA fiber, the larger volume of PVA fiber, the more energy is consumed in the loading process, and the greater deflection is made before reaching to the ultimate load with the higher shear capacity of the oblique section, the better shear toughness of the beam is obtained.
The shear toughness of polyvinyl alcohol fiber reinforced engineered cementitious composite (PVA/ECC) beams without stirrups was studied in this paper. Based on the testing results of shear failure from five groups of PVA/ECC beams, the shear toughness of the PVA/ECC beams with different fiber contents were analyzed and evaluated while using the shear toughness index and the diagonal crack composite index as indicators. The results show that the incorporation of PVA fibers can improve the cracking performance and the deformation capacity of the beam, enhance the bearing capacity of the oblique section, and thereby increase the shear toughness of the member. Additionally, within 0-2vol% of volume fraction of PVA fiber, the larger volume of PVA fiber, the more energy is consumed in the loading process, and the greater deflection is made before reaching to the ultimate load with the higher shear capacity of the oblique section, the better shear toughness of the beam is obtained.
2019, 36(8): 1977-1983.
doi: 10.13801/j.cnki.fhclxb.20181015.001
Abstract:
The effects of fiber volume fraction of basalt fibers and cellulose fibers and fiber length of basalt fibers on the freezing resistance of C60 high strength concrete were studied by the quick freezing and thawing cycle test of fiber reinforced high strength concrete. The appearance damage form, relative dynamic modulus of elasticity, freezing resistance grade and freezing durability index of specimens were analyzed. The results show that, basalt fiber and cellulose fiber can improve the appearance of spalling of high strength concrete. The freezing resistance of C60 high strength concrete increases with the increase of the volume fraction of basalt fiber (18 mm length) and cellulose fiber. Within volume fraction of 0.10vol%-0.20vol%, the improvement degree of basalt fiber is much greater than that of cellulose fibers. Basalt fiber reinforced high strength concrete can be used for a longer period of time in the harsher cold environments. The fiber length of basalt fiber greatly affects the freezing resistance of C60 high strength concrete. Compared with the basalt fibers with 18 mm length, the effect of basalt fibers with 6 mm or 30 mm length on the freezing resistance of C60 high strength concrete is very limited.
The effects of fiber volume fraction of basalt fibers and cellulose fibers and fiber length of basalt fibers on the freezing resistance of C60 high strength concrete were studied by the quick freezing and thawing cycle test of fiber reinforced high strength concrete. The appearance damage form, relative dynamic modulus of elasticity, freezing resistance grade and freezing durability index of specimens were analyzed. The results show that, basalt fiber and cellulose fiber can improve the appearance of spalling of high strength concrete. The freezing resistance of C60 high strength concrete increases with the increase of the volume fraction of basalt fiber (18 mm length) and cellulose fiber. Within volume fraction of 0.10vol%-0.20vol%, the improvement degree of basalt fiber is much greater than that of cellulose fibers. Basalt fiber reinforced high strength concrete can be used for a longer period of time in the harsher cold environments. The fiber length of basalt fiber greatly affects the freezing resistance of C60 high strength concrete. Compared with the basalt fibers with 18 mm length, the effect of basalt fibers with 6 mm or 30 mm length on the freezing resistance of C60 high strength concrete is very limited.
2019, 36(8): 1984-1994.
doi: 10.13801/j.cnki.fhclxb.20181030.002
Abstract:
In order to study the mechanical properties of self-compacting lightweight aggregate concrete under combined compression-shear loading, hydraulic servo machine and material compression-shear testing machine were used to study the uniaxial compression, uniaxial splitting tension and compression-shear composite loading of self-compacting lightweight aggregate concrete. The failure modes and force-deformation curves of aggregate concrete were compared with those of ordinary concrete and lightweight aggregate concrete under combined compression-shear loading. The results show that the failure modes of self-compacting lightweight aggregate concrete under combined compression-shear loading are different from those of ordinary concrete and lightweight aggregate concrete. Similarly, with the increase of axial compression ratio, the frictional trace of shear failure section is gradually obvious, and the concrete slag is also increased. At the same time, the shear failure strength, residual load and shear failure displacement of self-compacting lightweight aggregate concrete are gradually increased, and the shear failure strength affected by axial compression ratio is higher than that of ordinary concrete and concrete. While its residual load by axial compression ratio increases more than ordinary concrete, slightly lower than lightweight aggregate concrete. Based on the principal stress space and the compression-shear test data of ordinary concrete and lightweight aggregate concrete, the unified failure criterion equation of concrete under combined compression-shear loading was proposed, and the failure criterion of self-compacting lightweight aggregate concrete was proposed based on octahedron stress space. The proposed failure criterions have good applicability.
In order to study the mechanical properties of self-compacting lightweight aggregate concrete under combined compression-shear loading, hydraulic servo machine and material compression-shear testing machine were used to study the uniaxial compression, uniaxial splitting tension and compression-shear composite loading of self-compacting lightweight aggregate concrete. The failure modes and force-deformation curves of aggregate concrete were compared with those of ordinary concrete and lightweight aggregate concrete under combined compression-shear loading. The results show that the failure modes of self-compacting lightweight aggregate concrete under combined compression-shear loading are different from those of ordinary concrete and lightweight aggregate concrete. Similarly, with the increase of axial compression ratio, the frictional trace of shear failure section is gradually obvious, and the concrete slag is also increased. At the same time, the shear failure strength, residual load and shear failure displacement of self-compacting lightweight aggregate concrete are gradually increased, and the shear failure strength affected by axial compression ratio is higher than that of ordinary concrete and concrete. While its residual load by axial compression ratio increases more than ordinary concrete, slightly lower than lightweight aggregate concrete. Based on the principal stress space and the compression-shear test data of ordinary concrete and lightweight aggregate concrete, the unified failure criterion equation of concrete under combined compression-shear loading was proposed, and the failure criterion of self-compacting lightweight aggregate concrete was proposed based on octahedron stress space. The proposed failure criterions have good applicability.
