Interlaminar shear fatigue of carbon/epoxy laminates
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Otavio ZIMMERMANN DE ALMEIDA (FRANCE), Yann MARCO , Nicolas CARRERE , Matthieu LE SAUX (FRANCE), Sylvie CASTAGNET , Gurvan MOREAUAbstract :
Carbon fiber reinforced polymer composite laminates are used as structural materials in many applications. In some of them, the material is subjected to cyclic loadings. Numerous studies have been conducted to characterize the fatigue behavior of this class of material under in-plane cyclic loadings [1]. However, in some cases, structural pieces can experience out-of-plane cyclic loadings due to drastic changes in ply orientation in the composite, to a complex geometry or to a complex loading case, all being situations which can lead to delamination. Furthermore, the value of approaches based on self-heating measurements for accelerating fatigue life characterization has been demonstrated for a wide range of materials, but very few studies have yet been carried out on laminates, particularly for out-of-plane loadings.
In this context, this work deals with the fatigue of laminates under interlaminar shear stresses. In particular, it aims to establish an approach for characterizing the fatigue life of the material, identifying the failure mechanisms and establishing a relevant fatigue criterion for such out-of-plane loading conditions. In addition, it investigates the ability of the self-heating method to characterize the fatigue life of laminates subjected to interlaminar shear.
The study is conducted on unidirectional carbon/epoxy laminates. From the available tests to evaluate interlaminar shear strength of laminates [2], the short beam shear test [3] is used. This test is generally used to characterize static strength, having rarely been used to characterize fatigue. Quasi-static monotonic and cyclic tests were carried out until failure. High-speed optical camera was used to observe the onset of delamination on the specimen surface. Digital optical microscope observations were carried out after the tests to precise the location of failure. Temperature measurements were made during the tests using an infra-red camera with suitable spatial resolution, to determine intrinsic dissipation and thermo-elastic coupling fields. Finite element simulations were carried out to refine test analysis.
The results show different locations of failure initiation between static and fatigue loading. Under static loading, a sudden and catastrophic failure occurs close to the mid-plane of the specimen, whereas in fatigue loading failure occurs closer to the loading roller. Tests results agree with previous studies [4], were the same effect is observed for a similar material. In order to unify the interpretation of the two cases, a coupled stress and energy criterion [5] is studied. The ability of the self-heating method to characterize fatigue life is discussed.
In this context, this work deals with the fatigue of laminates under interlaminar shear stresses. In particular, it aims to establish an approach for characterizing the fatigue life of the material, identifying the failure mechanisms and establishing a relevant fatigue criterion for such out-of-plane loading conditions. In addition, it investigates the ability of the self-heating method to characterize the fatigue life of laminates subjected to interlaminar shear.
The study is conducted on unidirectional carbon/epoxy laminates. From the available tests to evaluate interlaminar shear strength of laminates [2], the short beam shear test [3] is used. This test is generally used to characterize static strength, having rarely been used to characterize fatigue. Quasi-static monotonic and cyclic tests were carried out until failure. High-speed optical camera was used to observe the onset of delamination on the specimen surface. Digital optical microscope observations were carried out after the tests to precise the location of failure. Temperature measurements were made during the tests using an infra-red camera with suitable spatial resolution, to determine intrinsic dissipation and thermo-elastic coupling fields. Finite element simulations were carried out to refine test analysis.
The results show different locations of failure initiation between static and fatigue loading. Under static loading, a sudden and catastrophic failure occurs close to the mid-plane of the specimen, whereas in fatigue loading failure occurs closer to the loading roller. Tests results agree with previous studies [4], were the same effect is observed for a similar material. In order to unify the interpretation of the two cases, a coupled stress and energy criterion [5] is studied. The ability of the self-heating method to characterize fatigue life is discussed.