Progressive Damage and Failure Analysis of 3D Textile Composites Subjected to Flexural Loading.

Abstract

3D textile composites (3DTCs) are becoming increasingly attractive as light-weight materials for a variety of structural load bearing applications, including those in the aerospace, marine, automotive, and energy generation sectors. The focus of this research is to investigate the deformation response of 3DTCs through flexural tests. The experimental results are subsequently used as a basis for the development of a multiscale mechanics based model for the deformation, damage and failure response of 3DTCs, predominantly under flexural loading.

Quasi-static flexural tests were performed either on a screw-driven loading device or on a hydraulically activated loading machine. To achieve higher loading rates, tests were carried out using a drop tower facility, which can provide different impact velocities by varying the height of the weight that is dropped onto the specimen. Fiber tow kinking, which developed on the compressive side of the specimen was found to be a strength limiting mechanism for this class of materials. Distributed matrix cracking was observed in regions of predominant tension.

A mechanics based multiscale computational model was developed for 3DTCs based upon a global-local modeling strategy, in which the influence of textile architecture is incorporated in a mesoscale finite element model, while the composite is homogenized at the macroscale. The fiber tow pre-peak nonlinear response is computed using a novel, two-scale model, in which the subscale micromechanical analysis is carried out in closed form based upon on a unit cell of a fiber-matrix concentric cylinder. Therefore, the influence of matrix microdamage at the microscale manifests as the progressive degradation of the fiber tow stiffness at the mesoscale. The post-peak strain softening responses of the fiber tows and matrix are modeled through the smeared crack approach, which is designed to be mesh objective.

The load-deflection response, along with the progressive damage and failure events, including matrix cracking, tow kinking, and tow tensile breakage, are successfully predicted through the proposed multiscale model. Since all the inputs are from the constituent level, the model is useful in understanding how the 3DTC macroscopic response is influenced by the geometry of textile architecture and the constitutive response of the constituents.