Flaw and damage assessment in torsionally loaded CFRP cylinders using experimental and numerical methods

CFRP structural elements are prone to failure initiating from defects. While defects are expected after damage has occurred, flaws and voids can already be present after manufacturing. To study the criticality of such defects, CFRP cylinders have been manufactured from a lay-up that was designed to predict damage mode and to allow for controlled damage growth under torsional load. FEA simulations of defect-free and flawed cylinder models were performed to first ply/interface failure. X-ray computed tomography revealed that cylinders manufactured with different finishing had a completely different void content and distribution. Simulations of failure, using finite element models, for the two classes of void distribution are corroborated by experimental results for the ultimate load, and damage initiation from manufacturing flaws is confirmed. Digital speckle pattern interferometry was used to identify flaws using thermal and mechanical loading, while infrared thermography and thermoelastic stress analysis were used to identify possible failure initiation sites and monitor the failure process and damage growth, whilst the specimen was loaded in torsion.