Study on failure mechanisms of tufted composite laminates under tensile loading

Abstract

Layered fiber reinforced polymer (FRP) composite materials are known for their excellent inplane stiffness and strength, but they have a weakness in delamination, particularly when exposed to transverse loading. To address this issue, through-thickness reinforcement (TTR) techniques can be utilized to enhance the delamination resistance of layered composites. Tufting techniques have gained popularity among engineers due to their ability to improve outof- plane properties at a lower cost compared to other through-thickness reinforcement (TTR) techniques. The initial focus of this study is on the production of tufted laminates, considering different tufting geometries and laminate sequences with a full release film placed in the midlayer of laminates. To analyze the impact of tufting loops on the behavior of laminates under transvers loading, two types of laminates are manufactured: loop-less and with-loop laminates that contain a single tuft. The loop-less laminates are created by milling down the surface of laminates. Additionally, this study employs two laminate sequences (quasi-isotropic and orthotropic) to investigate how preform layering affects the failure mechanisms of tufted laminates exposed to transverse loading. To gain a deeper understanding of the failure modes present within tufted laminates of varying tufting geometries and laminate sequences, the CTscan technique is utilized incrementally during pure tensile transvers loading. This technique highlights detailed observation and analysis of the internal damage and failure modes of laminates at different tensile displacements. Upon analyzing the force-separation curves and fracture surfaces, it is found that for either laminate sequence, the loop-less tufting geometry fails due to tuft pull-out and possesses higher fracture energy in comparison to the standard tuft (with-loop) geometry. Nonetheless, withloop tuft laminates demonstrate a higher ultimate load than loop-less ones. According to the force-separation curves, the tuft exhibits a more brittle behavior in the quasi-isotropic laminate than in the orthotropic one. For both tufting geometries, switching the laminate sequences from orthotropic to quasi-isotropic leads to a 60% rise in the ultimate load and a 62% reduction in fracture energy. CT-scan analysis indicates that the primary failure modes during the linear regime are inter-fiber and interface debonding. However, during the plastic regime, interface failure, tuft rupturing, and pullout are observed. The quantity of resin surrounding a tuft can greatly impact its properties under tensile loading. Since there is a limited quantity of resin surrounding the tuft and the tuft is in contact with laminate, then tuft failure at the mid-plane is likely to occur. Conversely, a larger amount of resin surrounding the tuft tends to promote fiber pull-out instead. Lastly, a reliable 3D damage micro modelling tool has been developed in Abaqus for predicting the failure modes of orthotropic with-loop tufted laminates. The Hashin damage criteria for the tuft and elastoplastic respond for the tuft interface are incorporated into the model using Abacus plasticity tool and the user-defined field (USDFLD) method. Despite a convergence issue preventing the model to reach full failure, it has been observed that the selected material properties and tools have demonstrated high effectiveness in accurately simulating the behavior of a tufted laminate during the initial stage of a tensile test.

Date	31 Aug 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Simon Joncas (Supervisor)