1991 Vol. 8, No. 1
1991, 8(1): 1-6.
Abstract:
The paper presents an investigation on the switching effect exhibited by the condutive composite made from carbon black and graphite filled high density polyethylene under alternating electric field.Its specific nonohmic voltage-current characteristic has been discussed and a possible mechanism of such behaviour is suggested.
The paper presents an investigation on the switching effect exhibited by the condutive composite made from carbon black and graphite filled high density polyethylene under alternating electric field.Its specific nonohmic voltage-current characteristic has been discussed and a possible mechanism of such behaviour is suggested.
1991, 8(1): 7-12.
Abstract:
It ia difficult to coparate carboxyl-randomized butadiene acrylonitrile copolymer(CBN) from phenolic epoxy resin(F-51)in au anhydride curing system because of the food compatibility of CBN/F-51.With the increasing of the amount of CBN in the resin,the glass transition peak of the blend is widened greatly for the semi-compatible microstructure of the dual phase continuity.It is found that the phase separation of CBN from the resin is promoted evidently by adding small amount of butadiene acrylonitrile copolymer (BN-26) into the CBN/F-51 blend system.
It ia difficult to coparate carboxyl-randomized butadiene acrylonitrile copolymer(CBN) from phenolic epoxy resin(F-51)in au anhydride curing system because of the food compatibility of CBN/F-51.With the increasing of the amount of CBN in the resin,the glass transition peak of the blend is widened greatly for the semi-compatible microstructure of the dual phase continuity.It is found that the phase separation of CBN from the resin is promoted evidently by adding small amount of butadiene acrylonitrile copolymer (BN-26) into the CBN/F-51 blend system.
1991, 8(1): 13-20.
Abstract:
Based on the curing temperature,three types of behavior of various surface characterized PPTA fiber/epoxy systems were observed,(Ⅰ) below Tgg(the glass transition tem perature of the reaction systems at the gel point) only vitrification come about;(Ⅱ) between Tgg and Tg∞(the glass transition temperature of the ultim ately cured polymers)both gelatinization and vitrification come about,and(Ⅲ)above Tg∞,only gelatinination takes place.Overall activation energies and apparent overall rate constant of the curing reactions for various surface characterized PPTA fiber/epoxy systems based on third-order overall kinetics were determined before gelation,after gelation but before vitrification and after vitrification,from the gelation time,relative rigidity and glass transion temperature Tg(t) of the polymers as the kinetic terms.The influence of the curing temperature and surface property of the fibers on the kinetic parameters is discussed.Based on various relative rigidity and damping curves vs.time under isothermal conditions,we obtained Time-Temperature-Transition(T.T.T.) state diagrams of various surface characterized PPTA.fiber/apoxy systems.These state digrams (T.T.T.)can be used in formulating the curing technology for various kinds of fiber reinforced epoxy composites.
Based on the curing temperature,three types of behavior of various surface characterized PPTA fiber/epoxy systems were observed,(Ⅰ) below Tgg(the glass transition tem perature of the reaction systems at the gel point) only vitrification come about;(Ⅱ) between Tgg and Tg∞(the glass transition temperature of the ultim ately cured polymers)both gelatinization and vitrification come about,and(Ⅲ)above Tg∞,only gelatinination takes place.Overall activation energies and apparent overall rate constant of the curing reactions for various surface characterized PPTA fiber/epoxy systems based on third-order overall kinetics were determined before gelation,after gelation but before vitrification and after vitrification,from the gelation time,relative rigidity and glass transion temperature Tg(t) of the polymers as the kinetic terms.The influence of the curing temperature and surface property of the fibers on the kinetic parameters is discussed.Based on various relative rigidity and damping curves vs.time under isothermal conditions,we obtained Time-Temperature-Transition(T.T.T.) state diagrams of various surface characterized PPTA.fiber/apoxy systems.These state digrams (T.T.T.)can be used in formulating the curing technology for various kinds of fiber reinforced epoxy composites.
1991, 8(1): 21-25.
Abstract:
This paper deals with high-tensile-stength C/AI composites with σb> 760MPa fabricated by casting.PAN I carbon fibers coated with coatings are arranged in investment casting moulds in tows,and the moulds are infiltrated with molten AI-Si-Mg alloy under the condition of vacuum 4000 Pa and air prcssure of 0.75 MPa.The tensile strength of specimens containing fibers of 0.35 volume fraction reaches up to 764 MPa.The effects of fiber arrangement in tows on infiltration of molten metal and on toughness of composites are also discusseda.
This paper deals with high-tensile-stength C/AI composites with σb> 760MPa fabricated by casting.PAN I carbon fibers coated with coatings are arranged in investment casting moulds in tows,and the moulds are infiltrated with molten AI-Si-Mg alloy under the condition of vacuum 4000 Pa and air prcssure of 0.75 MPa.The tensile strength of specimens containing fibers of 0.35 volume fraction reaches up to 764 MPa.The effects of fiber arrangement in tows on infiltration of molten metal and on toughness of composites are also discusseda.
1991, 8(1): 27-33.
Abstract:
On the basis of principle of stable non-geodesic filament winding,the formula for calculating the sliding and stable positions of ellipsoidal(cylin-drical) curvatures is derived,and the obtained formula is useful and simple.
On the basis of principle of stable non-geodesic filament winding,the formula for calculating the sliding and stable positions of ellipsoidal(cylin-drical) curvatures is derived,and the obtained formula is useful and simple.
1991, 8(1): 45-52.
Abstract:
In this paper,the problem of free vibration of a composite material pipe containing flo wing fluid is discussed.The pipe is made in mufti-layes and the layers are so numerous. that a designer can set A16,A26,B16,B26,D16,D26,and C45 to vanish.Consequently,the pipe may be regarded as an orthotropic cylindrical shell.
In this paper,the problem of free vibration of a composite material pipe containing flo wing fluid is discussed.The pipe is made in mufti-layes and the layers are so numerous. that a designer can set A16,A26,B16,B26,D16,D26,and C45 to vanish.Consequently,the pipe may be regarded as an orthotropic cylindrical shell.
1991, 8(1): 53-60.
Abstract:
The significance of studing fracture properties of composites under low temperature is summarized in this paper.The low temperature device and the surveying system made by us is introduced.The fracture toughness of three kinds of composite under low temperature is measured and fracture mechanism of composite under different temperature is analysed.
The significance of studing fracture properties of composites under low temperature is summarized in this paper.The low temperature device and the surveying system made by us is introduced.The fracture toughness of three kinds of composite under low temperature is measured and fracture mechanism of composite under different temperature is analysed.
1991, 8(1): 61-69.
Abstract:
In this paper the investigations on the delamination damage of fiber-reinforced composite laminated plates have been done by both experiments and three dimensional finite element analysis.The obtained results show that the delamination of these laminates always occurs on A/90 interfaces where both interlaminar shear stresses and interlaminar normal stress are much bigger. It can also be seen that the critical strain energy release rates GⅠC and GⅡC vary with the stacking angle θ for different A/90 interfaces of laminates.A delamination criterion of mixed mode strain energy release rate has been improved for its applications.The experimental results obtained show that this improvment is effective.
In this paper the investigations on the delamination damage of fiber-reinforced composite laminated plates have been done by both experiments and three dimensional finite element analysis.The obtained results show that the delamination of these laminates always occurs on A/90 interfaces where both interlaminar shear stresses and interlaminar normal stress are much bigger. It can also be seen that the critical strain energy release rates GⅠC and GⅡC vary with the stacking angle θ for different A/90 interfaces of laminates.A delamination criterion of mixed mode strain energy release rate has been improved for its applications.The experimental results obtained show that this improvment is effective.
1991, 8(1): 71-79.
Abstract:
The buckling of composite laminate with stiffeners under loads in plate (axial compression、shear and loads combined compression and shear) is investigated by means of the triangular finite difference method and energy variational principle in this paper.For the problem under study,the normal simple and clamp support boundary conditions are considered,but the lateral deflection springs and bending springs are used as well to simulate the elastic support boundary conditions.The buckling governing equation in matrix is deduced in detail,in which the eigen values are loads in plane and the eigen vectors are difference point deflections.Numerical results are given for several kinds of composite laminates with stiffeners under loads in plane and compared with experimental results.
The buckling of composite laminate with stiffeners under loads in plate (axial compression、shear and loads combined compression and shear) is investigated by means of the triangular finite difference method and energy variational principle in this paper.For the problem under study,the normal simple and clamp support boundary conditions are considered,but the lateral deflection springs and bending springs are used as well to simulate the elastic support boundary conditions.The buckling governing equation in matrix is deduced in detail,in which the eigen values are loads in plane and the eigen vectors are difference point deflections.Numerical results are given for several kinds of composite laminates with stiffeners under loads in plane and compared with experimental results.
1991, 8(1): 81-90.
Abstract:
In this paper,the delamination solution to the angularly and symmetrically stacked composite laminates is given for the anti-plane warping condition.First of all,the eigen function expansions of stress and displacement fields are derived,for which all of the basic equations,boundary conditions on crack surfaces and conditions of continuties between different plies are satisfied.
In this paper,the delamination solution to the angularly and symmetrically stacked composite laminates is given for the anti-plane warping condition.First of all,the eigen function expansions of stress and displacement fields are derived,for which all of the basic equations,boundary conditions on crack surfaces and conditions of continuties between different plies are satisfied.
1991, 8(1): 91-98.
Abstract:
The connection between fiber microbuckling and dislamination of laminated plate is one problem of interest for discussion about failure mechanism.In this paper,the bifurcation behaviour of laminated plate subjected to longitudinal compressive load is investigated by elastic-plastic finite element method with finite deformation.The laminated plate is composed of elastic layers with higher modulus (which simulate the fiber) and elastic-plastic layers with lower modulus(which simulate the matrix). When the compressive strain roaches its bifurcation value, the fiber microbuckling phenomenon takes place.After that small amplitude waves of deformation arise in interface plane,then also shear stress and transverse normal stress vary from zero to an obvious value with the compressive strain increase. Under this shear stress a dislamination can occur in the local interface of laminated plate,where the shear strength is quite low.In the numerical example of symmetric laminate fiber microbuckling,both extensional mode and shear mode exist simultaneously.
The connection between fiber microbuckling and dislamination of laminated plate is one problem of interest for discussion about failure mechanism.In this paper,the bifurcation behaviour of laminated plate subjected to longitudinal compressive load is investigated by elastic-plastic finite element method with finite deformation.The laminated plate is composed of elastic layers with higher modulus (which simulate the fiber) and elastic-plastic layers with lower modulus(which simulate the matrix). When the compressive strain roaches its bifurcation value, the fiber microbuckling phenomenon takes place.After that small amplitude waves of deformation arise in interface plane,then also shear stress and transverse normal stress vary from zero to an obvious value with the compressive strain increase. Under this shear stress a dislamination can occur in the local interface of laminated plate,where the shear strength is quite low.In the numerical example of symmetric laminate fiber microbuckling,both extensional mode and shear mode exist simultaneously.
