Development of a Novel In-plane Tension-Tension Biaxial Cruciform Specimen

Abstract

This study presents a combined experimental and numerical investigation of an inplane tension-tension (IPTT) biaxial test geometry. The IPTT specimen was based on an existing design which was previously optimized to minimize stress concentrations in the corners of the cruciform geometry. To facilitate ex situ 3D Xray computed tomography (CT) imaging of the gage region, the overall dimensions of the specimen were scaled down. In parallel with the experimental effort, a numerical simulation using AFRL’s BSAM code was performed to assess the feasibility of using high-fidelity progressive damage tools for design and optimization of biaxial test geometries. The single experiment performed in this study revealed that the IPTT test is highly sensitive to local geometric imperfections, which had an unexpected effect on initiation and evolution of transverse cracking and delamination in the gage region. This was concluded from post-mortem X-ray CT and optical imaging of the specimen, which revealed an intricate network of intralaminar cracks and delaminations that emanated from a machining flaw on the surface of the circular gage region. The numerical simulation of the idealized IPTT test geometry showed good promise in predicting the overall pattern of inter- and intralaminar damage. Overall, this study provided a wealth of experimental and numerical data that will be used as a starting point for further development of the IPTT test geometry.