Lock-in thermographic measurement and model-based evaluation of effective thermal diffusivity to quantify early stage fatigue damage of CFRP

Abstract

Fatigue characteristics of carbon fiber reinforced plastics (CFRP) are an important factor in predicting the design life of structures such as wind turbine blades. Due to the anisotropic and heterogeneous structure of CFRP, design life prediction under fatigue stress is a challenging task. The authors proposed an approach to assess fatigue damage at the microscale using a laser-periodic-heating method based on lock-in thermography (LIT). It assumes that the rate of fatigue progression correlates with the number of micro-voids, micro-cracks, and fiber/resin delamination that inhibit heat transfer. The effective thermal diffusivity in the out-of-plane direction of CFRP laminates, which were tested under fatigue loading, showed a decreasing trend with the number of loading cycles.