In-Plane Response and Mode II Fracture Response of Z-pin Woven Laminates.

[摘要] Textile composites are proven to be an attractive choice over traditional pre-preg based composites because of reduced manufacturing costs and improved transverse mechanical properties.However, similar to traditional pre-preg composites, 2D laminates consisting of multiple layers of laminae still suffer from delamination under impact or transverse loads. Z-pin (carbon fiber of small diameter inserted in the thickness direction-z) composites are a means to provide higher through-the-thickness stiffness and strength that 2D woven composites lack. In this thesis, The influences of Z-pin density and Z-pin diameter on the response of Z-pin under in-plane loads (compression) and transverseloads (mode II fracture) are examined. Both experiments and numerical simulations were performed to address the problems. Compression tests were conducted first and failure mechanisms in each loading scenario was identified, through optical and mechanical measurements, during and after the tests.This wasfollowed by the development of different numerical models of varying degree of sophistication, which include in-plane 2D models, (used to study fiber distortion and damage due to Z-pin insertion),multi-layer 2D models, (used to provide an inexpensive multi-layer model to study the effect of phase difference due to stacking consolidation), and multi-layer-multi-cell models (used to provide afull 3D multi-layer and multi-representative unit cell description). The second part of this thesis investigates the mode II fracture response under static and dynamic loading. Discrete Cohesive Zone Model (DCZM) was adopted to obtain the fracture toughness inconjunction with experimental data. In dynamic test, a crack advance gage (CAG) was designed to capture the exact time when the crack begins to propagate. By use of these CAGs, the corresponding crack propagation speed between different CAGs can be computedaccordingly. These observations are supplemented through high speed optical images that capture the dynamic event.

[发布机构] University of Michigan

[效力级别] Textile Composite

[关键词] Z-pin;Textile Composite;In-plane Compression;Mode II Fracture;Aerospace Engineering;Mechanical Engineering;Engineering;Aerospace Engineering