Interlaminar Failure Behavior And Mechanisms Of GLARE Laminates

GLARE laminate(glass fiber reinforced aluminum laminate)has applied in aircraft structure like skin,due to excellent mechanical properties and weight saving.GLARE was manufactured by alternating layers of thin aluminum alloy sheets and glass/epoxy composites.Thus,GLARE has a complex multi-interface system including the interfaces of aluminum alloy sheet-matrix,fiber-matrix and fiber-aluminum alloy sheet,etc.Obviously,characterizing the interlaminar shear failure resistance of GLARE with the reliable method is essential.However,experimentally sound failure observation to corroborate the selection of appropriate L/h ratio for GLARE has not been proposed.In our work,interlaminar failure behavior and mechanisms of GARE laminates were investigated with short-beam shear test method,to obtain reliable L/h for evaluating interlaminar property of GARE laminates.Meanwhile,applicability of double short-beam shear test method was studied for estimating interlaminar property of GLARE laminates.In this paper,interlaminar failure behavior and failure mechanisms of GLARE laminates under short-beam three-point load were investigated.Four typical lay-up laminates were prepared: GLARE 2A,GLARE 3,GLARE 4A,GLARE 6.Actually,these laminates represented different GLARE variants.In addition,4/3,5/4,6/5 laminate structure were manufactured for structure evolution of interlaminar property,and considered adaptability of reliable L/h for different structure.Failure modes and load curve were studied to obtain appropriate L/h for evaluating GLARE laminates.L/h varying from 5 to 12 was selected in our study.The results showed that a shear dominant failure mode was obtained at the L/h ratio of 8 for four lay-up laminates.The mode means a delamination occurring close to neutral layer,and yielding reliable apparent interlaminar shear strength to evaluating interlaminar property of GLARE laminates.However,these four specimens behaved in the localized compression-deformation failure mode at the L/h ratio of 5.It was found that specimen deformation is severe between the nose and the support and the apparent ILSS value was inadvisable to evaluate the interfacial bonding strength for GLARE laminates.Furthermore,at the larger L/h ratios,specimens bore greater bending stress with the deflection increasing so that the local flexural failure occurred,also resulting in the reduction of the apparent interlaminar shear strength value.Meanwhile,applicability of double short-beam shear test method for GLARE laminates was studied by investigating failure behavior and failure mechanisms.The apparatus of double short-beam method was designed and manufactured in our work,and was stable during test processing.In this part,failure behavior and failure mechanisms were investigated with varying L/h ratio.The results showed that failure mode was only shear failure due to pure shear point in the beam.Actually,delamination between central aluminum alloy layer and composite layer was obvious for GLARE 2A and GLARE 6.There were cracks in 90° layer and delamination between central aluminum alloy sheet and composite layer for GLARE 3.GLARE 4A debonded at interface of central aluminum alloy layer and 0° composite layer.In addition,the average apparent ILSS generated was greater than SBS value,but the two method did not show exclusiveness.In addition,the results showed that the L/h of 8 was reliable for GLARE 2A-4/3,5/4 and 6/5 under short-beam test load.L/h of 7 was appropriate for GLARE 3-5/4,6/5 and GLARE 6-5/4,6/5.Double short-beam shear test with L/h of 5 was able to evaluate interlaminar shear strength of GLARE-4/3,5/4 and 6/5.Evolution of interlaminar shear strength value is similar to each other for the two methods.