Co-authors​ :

 Thomas MARTINONI (ITALY), Valentin OTT , Valter CARVELLI (ITALY), Giovanni Pietro TERRASI (SWITZERLAND) 

The lack of ductility of unidirectional long fibre reinforced polymers under tensile loading can be overcome by interlayer hybridization where low elongation (LE) material is sandwiched between high elongation (HE) material. This results in complex failure mechanisms, including multiple interacting damage modes, such as ply fragmentation and delamination [1]. Thick ply unidirectional all-carbon hybrid laminates with different layup sequences were manufactured to study their pseudo-ductile behaviour and damage evolution. High elongation Toho® Tenax® IMS60 and low elongation DIALEAD® K13916 carbon fibres were used. An available analytical model was exploited to design the laminates and predict the damage scenario by damage mode maps [2]. Quasi-static tensile tests were carried out using different measurement and observation techniques including digital image correlation (DIC), embedded distributed fibre optic sensors (dFOS) and helicoidal X-ray computed tomography (CT). A two-dimensional finite element model, inspired by [3], was also developed to predict the damage mechanisms. The model simulates the main damage modes observed experimentally, namely fragmentation and delamination. Fragmentation in the LE layer was predicted using translaminar embedded cohesive elements governed by a unimodal Weibull strength distribution. Delamination at the LE and HE layers interface was simulated using interlaminar cohesive elements. Validated by experimental results, the numerical model was found to accurately predict the quasi-static tensile damage modes and their evolution in the considered thick ply unidirectional all-carbon hybrid laminates and to accurately predict the pseudo-ductile tensile stress - strain behaviour.

References
1. Swolfs, Gorbatikh, Verpoest, 2014, doi:10.1016/j.compositesa.2014.08.027
2. Jalalvand, Czel, Wisnom, 2015, doi:10.1016/j.compositesa.2014.11.006
3. Jalalvand, Czel, Wisnom, 2014, doi:10.1016/j.compscitech.2014.01.013