The Performance Study On Interlaminar Tension And Shear In Laminate

In various different composites applied in aviation,composite laminate structure is widely used in the airplane structure.Interlaminar performance of composite laminate mainly depends on the matrix performance.Interlaminar material performance is only several tenths of fiber direction,thus interlaminar hierarchical failure s one of leading forms in composite laminate failure.Generally speaking,such failure is caused by normal stress and shear stress of composite laminate and it happens in the adjacent layer of composite laminate.In this thesis,based on interlaminar tension and interlaminar shear's quasi-static test of laminate,after improving the test fixture,fatigue test platform meeting the loading requirements was constructed.The interlaminar tensile-tensile fatigue test and interlaminar shear fatigue test were conducted on the laminate.In the end,by combining with ABAQUS finite element software,interlaminar quasi-static test of laminate was conducted the finite element modeling simulation.Firstly,a set of four-point bend loading test fixture was improved.IM7/M91 laminate with the layer sequence as [-45°/0°/+45°/0°]n was conducted the interlaminar quasi-static tensile test.The improved four-point fixture was implemented quasi-static test and pre-loaded centring performance test of fatigue load working conditions.By analyzing the centring performance test,it could be found that fixture centring performance under two working conditions could meet the test requirements.According to quasi-static test results of interlaminar tensile quasi-static test,three stress load values were selected for interlaminar tensile-tensile fatigue test of laminate.Based on stress-lifetime curve,tensile-tensile fatigue test lifetime prediction formula of IM7/M91 laminate was fitted.Moreover,four-point bending interlaminar tensile-tensile fatigue test effect was evaluated based on the test results.Furthermore,a set of double-V gap shear test fixture was improved.IM7/M91 laminate with the layer sequence as [-45°/0°/+45°/0°]n was conducted the interlaminar shear quasi-static test.As preparing for double-V gap test articles(including G13 shear test articles and G31 shear test articles),the machining mode of polishing open-V groove and cutting the piece as a whole was used.The processed test articles were conducted nondestructive testing,finding that they could meet the test criteria and form a set of machining process that could greatly improve the efficiency of producing double-V gap test articles.Since G13 shear could bear load after failure,G13 shear quasi-static test machine's displacement drop result was analyzed and studied.G13 fatigue shear test's fatigue fracture criteria based on testing machine displacement drop was proposed.On the basis of the quasi-static shear strength and fatigue criteria,interlaminar G13 shear of laminate was conducted the fatigue shear test.Stress-lifetime curve was used to fit for interlaminar G13 fatigue shear test lifetime prediction formula of IM7/M91 laminate.At last,two strain collection methods were used: electrical measuring method and spraying DIC speckle full-field strain method were applied to study influences of different strain collection methods on interlaminar G31 shear modulus results of laminate.The findings showed that two collection methods had the smaller error.The mutual comparison of each other indicated that electrical measuring method and DIC method could accurately collect shear strain.Based on the single-layer board failure variable and constitutive equation,3D Hashin failure criterion and index failure evolvement model were adopted to construct G31 quasi-static shear finite element model in ABAQUS.Through the simulation results,G31 shear failure evolution process could be obtained.Simulation stress strain was highly consistent with the test results.Also,failure mode and position could be greatly suitable.Simulation strength and errors of modulus results and test results could be kept in the acceptable range,indicating that this simulation model could show the higher reference significance on judging G31 shear failure.