Experimental Study And Model Of Statics Property Of Fiber Metal Laminates

Glass-reinforced aluminum laminates are composed of glass fiber reinforced composite material and high strength aluminum alloy sheet,having both the advantages of the two types of materials.GLARE laminates have lighter and more excellent fatigue performances compared to aluminum alloy sheet,and easier machining,cutting,and better impact resistance in contrast with a single plate of glass fiber composites.So far,the static performance of aluminum alloy and composite have been investigated extensively,and many corresponding prediction models have been developed.The statics performance and prediction method of Fiber Metal Laminates(FMLs)are very rate.The damage mechanism under tensile loading is more complicated owing to the intercoupling between the aluminum alloy and composite.Through the systematic researches on the static tensile properties,damage mechanism and a prediction method for representative FML named GLARE,the present thesis aims at providing a theoretical basis and analytical method for the structural optimization design and static strength prediction.In this paper,the static tensile properties and damage mechanism of unnotched GLARE2-2/1,GLARE2-3/2,GLARE3-2/1,GLARE3-3/2,GLARE6-2/1 and GLARE6-3/2 laminates with an open hole and a big gap under tensile loading were systematically investigated.The changes of static performance were analyzed.The performance changes of constituent materials of different GLARE laminate were discussed.Besides,the stress and strain response and residual strength prediction methods for FMLs under tensile loading were also proposed(1)The on-line measurement method-Digital Image Correlation(DIC)on the injury initiation and evolution in prepreg layers during loading are studied.The research shows that by comparing the strain cloud map at different loading stages and the change of strain difference at different positions,the damage mechanism and final fracture conditions can be determined.Through the research,the on-line measurement of injury initiation and evolution of GLARE laminates with a big gap under tensile loading by the DIC method is realized for the first time(2)Static tensile test were carried out on GLARE2-2/1,GLARE2-3/2,GlARE3-2/1,GLARE3-3/2,GLARE6-2/1 and GLARE6-3/2 laminates.The results show that the stress-strain curve of GLARE laminates under tensile loading has a sharp transition process due to the yielding of aluminum alloy,while the strain range is not the same.The Poisson ratio is not a constant value in the range of 0.24%axial strain.The deformation and bearing capacity of GLARE laminates are major affected by prepreg layer after the aluminum alloy yield.The elastic modulus of GLARE laminate is decreased when increasing the number of layers,while the tensile strength is not proportional to the number of layers.(3)The static tensile test was carried out on GLARE2-2/1,GLARE2-3/2,GlARE3-2/1,GLARE3-3/2,GLARE6-2/1 and GLARE6-3/2 laminates with a central hole.The results show that the notch strength of GLARE2,GlARE3,and GlARE6 laminates were respectively about 62%,59%and 70%tensile strength of the smooth specimens.The change of notch strength of GLARE laminates with a centre hole is not consistent with that of the smooth sample when increasing the ply numbers but have the same trend to the results predicted by volume fraction method for a smooth sample.Damage began to occur at the side of the hole of the GLARE2 and GlARE3 specimens at approximately 78%and 86%notch strength and no damage was observed at the hole side of the GLARE6 specimen before 91%notch strength.(4)The static tensile test was carried out on GLARE2-2/1 and GLARE2-3/2 laminates with a big central gap.The results showed that the notch strength of the large opening specimen was about 55%of the smooth specimen,and the net cross section strength was about 65%of the smooth specimen.When increasing the ply numbers,the notch strength of GLARE2-3/2 laminates with a big gap increase about 15%,the notch strength of GLARE2-3/2 laminates with a central hole increase about 11%,the tensile strength of GLARE2-3/2 laminates increase about 6%(5)In order to simulate the nonlinear deformation behavior of fiber metal laminates under static tensile load,a general continuous damage model is proposed,and the classical laminates theory is revised.The axial tension,transverse tension and the interfacial shear stress-strain relation of composite and 2024-T3 aluminum alloy were predicted accurately.The yielding strength and hardening modulus of the 2024-T3 aluminum alloy in different laminates were not the same,and the performance of the composite laminates are not exactly the same as if they were used alone.(6)A finite element analysis model based on ANSYS software was established,and the gradual failure analysis method was applied.The finite element analysis was performed on the GLARE laminates as the test conditions.The numerical simulation results were compared with the experimental results.The characteristic length of the GLARE laminate with a centre hole was calculated using the WN model.It was found that the performance degradation of the notched GLARE2 and GLARE3 laminates under tensile loading can be well simulated by adopting the gradual degradation method,and a uniform degradation factor of the hardening modulus of the aluminum alloy and the elastic constant of the composite layer was proposed.Assume that the ±45° prepreg layer is an anisotropic elasto-plastic material can well describe the damage process of the GLARE6 laminate with a central hole.The feature-length of the GLARE lamination with a central hole calculated according to the formula are not the same obtained by the finite element method,which cannot be simply converted to each other.The feature-length of the GLARE2 laminate with a large gap is greater than that of a circular hole as the laminate increases.