Enhanced failure prediction of compression after impact strength of composites at elevated temperature using discrete damage modelling

In this work, a coupled experimental and numerical investigation into compression after impact of composites at elevated temperature is presented. Quasi-isotropic composite specimens were subjected to low velocity impact (with approximately 8 J impact energy) to generate barely visible impact damage. Impact damage was characterised non-destructively using ultrasonic inspection and X-ray micro computed tomography to create a post-impact damage map. The impacted specimens were loaded in compression until failure, with specimens tested at room temperature and an elevated temperature of 70°C. The numerical analysis utilised BSAM™ for high fidelity computational analysis at ply level incorporating all critical damage and structural mechanisms. The post-impact damage map was incorporated into the model, which included capturing the matrix cracking, delamination, fibre fracture and indentation. The residual strength analysis captured progression and interaction of damage mechanisms, as well as sub-laminate buckling and contact across the delaminated interfaces. The effect of temperature on material properties was incorporated based on material data from standardised tests. The numerical results were correlated to the experimental results, which demonstrated the effectiveness and capabilities of the modelling approach, and also allowed for novel insights into the effect of elevated temperature on compression after impact strength. The outcomes of the work contribute towards improved sustainment of aircraft, by supporting a physics-based composite strength assessment, which increases reliability and accuracy in predictive tools. This leads towards less conservative assessments and less reliance on experimental testing, which in turn can translate to an increase in the service life for aircraft and reduction in the cost of operation.