A novel synergistic multi-scale modeling framework to predict micro- and meso-scale damage behaviors of 2D triaxially braided composite

A novel synergistic multi-scale modeling framework with a coupling of micro- and meso-scale is proposed to predict damage behaviors of 2D-triaxially braided composite (2DTBC). Based on the Bridge model, the internal stress and micro damage of constituent materials are respectively coupled with the stress and damage of tow. The initial effective elastic properties of tow (IEEP) used as the predefined data are estimated by micro-mechanics models. Due to in-situ effects, stress concentration factor (SCF) is considered in the micro matrix, exhibiting progressive damage accumulation. Comparisons of IEEP and strengths between the Bridge and Chamis’ theory are conducted to validate the values of IEEP and SCF. Based on the representative volume element (RVE), the macro properties and damage modes of 2DTBC are predicted to be consistent with available experiments and meso-scale simulation. Both axial and transverse damage mechanisms of 2DTBC under tensile or compressive load are revealed. Micro fiber and matrix damage accumulations have significant effects on the meso-scale axial and transverse damage of tows due to multi-scale coupling effects. Different from existing meso-/multi-scale models, the proposed multi-scale model can capture a crucial phenomenon that the transverse damage of tow is vulnerable to micro fiber fracture. The proposed multi-scale framework provides a robust tool for future systematic studies on constituent materials level to larger-scale aeronautical materials. </jats:p

Gradient-degraded material-induced trigger to improve crashworthiness of composite tubes in a controlled manner

A type of gradient-degraded material-induced trigger has a greater potential to induce a progressive crushing mode in a controlled manner to reduce the initial crushing load and increase the specific energy absorption. Thus, different material degradation strategy-based triggers are designed to improve the crashworthiness of composite tubes. To understand the triggering mechanisms, effects of height of trigger and level of degradation are studied using single material degradation strategies. In turn, gradient material degradation strategies are novelly presented to explore different crushing behaviors of tube. Further, an improved gradient material degradation gathering all features of single material degradation and gradient material degradation is proposed. The virtual quasi-static crushing tests are conducted where the model considers intra-ply and inter-ply failure initiation and damage evolution. The crushing behaviors of all triggered tubes are compared. From the predicted results, it is found that both the height of trigger and level of degradation have significant effects on the crushing behavior. The multi-phased or progressive initial crushing process is presented by using gradient material degradation. By comparison, the tube using the improved gradient material degradation presents 8.26% lower peak load, 8.75% higher specific energy absorption, and 25% higher crushing load stability than the original tube.</jats:p