Strain rate effect on compressive damages of thermo-oxidative aged 3D braided composites

• Strain rate and thermo-oxidative ageing effects for 3D braided composites were revealed. • Surface impact deformations were analyzed based on DIC technique. • Inner impact damage distributions were observed with micro-CT. • Ageing effect changed the near-surface crack distribution and crack propagation path. • Impact deformations and failure modes showed significant strain rate correlation. Revealing mechanical behaviors of three-dimensional five-directional (3D5d) braided composites at different strain rates is a key point to its durability design and structural optimization. Here we report compressive responses, surface deformations and failure behaviors of aged 3D5d braided composites under different strain rates with digital image correlation (DIC) technique, X-ray micro-computed (micro-CT) tomography and finite element analysis (FEA). The compressive rigidity, peak stress, maximum strain, energy absorption, surface strain and damages exhibit strain rate strengthening effects and ageing weakening behaviors. The strain concentration zone transfers from X-shaped to transverse V-shaped at the square cross-section with the increasing of strain rate. Moreover, ageing effect does not change the internal shear mode, while it changes the near-surface crack distribution along axial direction and crack propagation path under impact loading. The failure modes show strain rate correlation. The FEA results reveal the failure mechanisms of the aged 3D5d braided composites under different strain rates.