Intrinsic Residual Stresses in 3D Woven Composites: Measurement, Modeling, and Mitigation of Their Impact on Properties

University Of New Hampshire, Durham NH

Investigators

Abstract

Three-dimensional (3D) woven composites are a relatively new class of materials that show great promise as an alternative to the traditional metallic materials used in the aerospace, renewable energy and automotive industries. The material exhibits exciting properties including higher toughness, greatly enhanced strength, and better fatigue resistance compared to the traditional laminated composites. 3D woven composites can also be manufactured into large, complex shapes that were previously unattainable using laminates. However, the reinforcement complexity that is responsible for the improved properties presents researchers and engineers with new challenges. It has been observed that processing of some polymer matrix 3D woven composites results in development of microcracks. The damage occurs as a result of high residual stresses that develop during cooling of the composites after curing due to the mismatch in the properties between the material constituents. This award supports research to understand the fundamental scientific phenomena controlling these residual stresses, their magnitudes and distributions within the composites, and how these in turn affect material performance under cyclic loading. The research will be incorporated into teaching environments including classroom instruction, and direct involvement of undergraduate and graduate students in hands-on research opportunities. This award supports novel study of intrinsic residual stresses in 3D woven polymer matrix composites. The research calls for creation of new experimental and numerical methods including the following: 1) incremental hole-drilling method combined with electronic speckle pattern interferometry and Raman spectroscopy for microscale residual stress estimation; 2) inverse finite element analysis method to relate experimentally determined strains in the fibers and high resolution displacement field measurements resulting from material removal (holes and slits) to the spatially varying stress field in the composite; 3) evaluation of modifications to the industry-standard curing cycle to lower the residual stresses in the epoxy-matrix composites; 4) detailed mechanical testing of 3D woven composites with known magnitudes of the residual stresses to determine their effect on monotonic and cyclic mechanical properties the composites. The project will advance the fundamental understanding of the development mechanisms and strategies for mitigation of the residual stresses and related damage in 3D woven composites, which will lead to improvements in technology of manufacturing and better performance of these materials for a broad range of industrial applications.