A novel damage evaluation of CFRPs under mode-I loading by using multi-instrument structural health monitoring methods

Mode-I fracture toughness test provides valuable information in the thickness direction of fiber reinforced polymer matrix composites. However, damage propagation under mode-I loading is dependent on the configuration of reinforcing material of the laminate. Understanding the damage types and their growth rate in mode-I fracture toughness test is a vital factor to obtain material allowable for safe design. In this study, mode-I tests are conducted on unidirectional, and twill woven carbon fiber reinforced polymer composite laminates. A new approach is proposed to interpret passive infrared thermography results based on correlating acoustic emission and thermography results in time whereby thermal activities can be classified into two main groups corresponding to matrix and fiber dominant failure types. It is demonstrated that matrix and fiber dominant failures lead to thermal activities with line-wise and point-wise form, respectively. Results show that four different damage types can be seen for mode-I fracture of both laminates. The temporal observations during thermoelastic cooling of the materials show that twill woven laminate releases relatively higher energies due to matrix dominant damage developments which means this configuration type is more prone for delamination failures.