Influence of boundary conditions on the failure behavior of T joint shape overmolded composite structure
Topic(s) : Special Sessions
Co-authors :
Xiaofei SONG (FRANCE), Federica DAGHIA (FRANCE), Christophe CLUZEL , Yannick ELIEAbstract :
Overmolding is a widely adopted manufacturing technique in multiple industries in which a material, typically a thermoplastic, is molded over a pre-existing substrate. An essential point of attention in the design of the parts is the behavior of the interface between the substrate and the overmolding, where delamination is more likely to occur. The study of the adhesion between the composite laminate and the overmolding material has consistently been a focal point, spanning various material scenarios, for example thermoplastic overmolding on thermoplastic substrate [1][2], or thermoplastic overmolding on metal substrate [3].
For the structure that is considered (Fig. 1), both the laminate and the overmold are made of Carbon-Polyetherketoneketone (C-PEKK). More specifically, the laminate substrate consists of long-fiber woven plies while the overmolding part contains short fibers only. This work is a continuation of previous studies, which involved numerical simulations by means of a cohesive zone model and delamination characterization tests, with the aim of parametric identification and approach validation.
Tensile tests on T joints are commonly performed to evaluate the mechanical behavior of these structures. However, during a tensile test, the lower part (laminate) can be subjected to an uncontrolled state of bending largely depending on the accuracy of the imposed boundary conditions. Moreover, misalignment in loading conditions can lead to unforeseen fractures. First simulations show that extra bending needs to be added to be consistent with tensile test results conducted previously, which proves that boundary conditions can easily be inadequately controlled. Additionally, numerical results demonstrate a significant decrease in failure load when the loading axis is misaligned. As a consequence, an isostatic setup is pertinent regarding the need for correct evaluation of the mechanical performance of the T joint shape structure.
In this work, characterization tests are carried out by using novel isostatic setups to investigate the influence of the boundary conditions, bending in particular, and the geometry on the behavior of this kind of structure. Two types of junctions are studied: a simple T joint and a T joint with added chamfer. In terms of boundary conditions, the distance between the bending supports are set to 5 - 14 mm to allow more or less bending in the laminate. Furthermore, the impact of the distance from the injection point is studied by performing the test on samples initially located at different positions. Compared to classical tensile test configurations, two rolling-element bearings are employed to form two ball joints instead of the rigid connections to the rest of the machine. Therefore, the setups become isostatic and the loading axes can be controlled without unintentionally adding extra moment.
Acknowledgements
This work was motivated and supported by CETIM within CompInnov OpenLab.
For the structure that is considered (Fig. 1), both the laminate and the overmold are made of Carbon-Polyetherketoneketone (C-PEKK). More specifically, the laminate substrate consists of long-fiber woven plies while the overmolding part contains short fibers only. This work is a continuation of previous studies, which involved numerical simulations by means of a cohesive zone model and delamination characterization tests, with the aim of parametric identification and approach validation.
Tensile tests on T joints are commonly performed to evaluate the mechanical behavior of these structures. However, during a tensile test, the lower part (laminate) can be subjected to an uncontrolled state of bending largely depending on the accuracy of the imposed boundary conditions. Moreover, misalignment in loading conditions can lead to unforeseen fractures. First simulations show that extra bending needs to be added to be consistent with tensile test results conducted previously, which proves that boundary conditions can easily be inadequately controlled. Additionally, numerical results demonstrate a significant decrease in failure load when the loading axis is misaligned. As a consequence, an isostatic setup is pertinent regarding the need for correct evaluation of the mechanical performance of the T joint shape structure.
In this work, characterization tests are carried out by using novel isostatic setups to investigate the influence of the boundary conditions, bending in particular, and the geometry on the behavior of this kind of structure. Two types of junctions are studied: a simple T joint and a T joint with added chamfer. In terms of boundary conditions, the distance between the bending supports are set to 5 - 14 mm to allow more or less bending in the laminate. Furthermore, the impact of the distance from the injection point is studied by performing the test on samples initially located at different positions. Compared to classical tensile test configurations, two rolling-element bearings are employed to form two ball joints instead of the rigid connections to the rest of the machine. Therefore, the setups become isostatic and the loading axes can be controlled without unintentionally adding extra moment.
Acknowledgements
This work was motivated and supported by CETIM within CompInnov OpenLab.