Numerical and Experimental Design of a Cruciform Specimen for a Novel Cryobiaxial Experiment

Abstract

This study presents a combined numerical and experimental attempt to develop a new cruciform geometry for cryobiaxial loading. Two candidate cruciform specimens with crossply stacking sequences are evaluated at room temperature based on their ability to initiate and evolve intralaminar damage in the gage region. The first design, developed by the Utah Composites Lab (UCL), was meant to ensure damage would occur at the center of the specimen. The second design utilizes sharp corner transitions to arrest unwanted damage from evolving outside of the gage region of the specimen. Numerical simulations were done using AFRL’s BSAM code to optimize each geometry and determine load intervals for progressive damage tests. Three specimens were then tested for each geometry using a custom table-top biaxial load frame. Experimental results revealed that the UCL design successfully initiated damage at the desired location, but extensive damage accumulation occurred in the chamfer region. Ultimately, a through-thickness crack network was not formed before unstable delamination growth extended across the gage region of the entire specimen. The Hallett specimen initiated damage in the corners during the first load interval, but at increased load steps numerous intralaminar cracks evolved in each of the loading arms. Once again a through-thickness crack network was not formed. Despite observing several issues with the two designs proposed in this study, a wealth of numerical and experimental data was collected that will be used to improve each cruciform design. Numerical results indicated that BSAM is an effective tool for designing and optimizing tape-laminate cruciform specimens. It is expected that an improved cruciform design for the investigation of intralaminar failure under cryobiaxial load will be achieved as a result of this work.