ACOUSTIC EMISSION FOR IDENTIFICATION OF THE DOMINANT STRESS COMPONENT IN POLYMER COMPOSITES AT EARLY LOADS,

Carbon Fiber Reinforced Polymer (CFRP) composites are broadly used in engineering applications. Their inherent anisotropy due to different fiber orientations can be considered an advantage since the strength of the component can be designated in preferential loading directions. However, this anisotropy leads to multiaxial stress conditions, complicating their damage sequence and mechanical response. Identification of these multiaxial conditions at early loading stages is of paramount importance to predict the upcoming structural response of the material. Acoustic Emission (AE) is applied in this study to CFRP laminates with different stacking sequences, in which different multiaxial conditions are generated. Laminates consisting of 30o plies are characterized by dominant shear stresses, whereas in laminates with 60o layers transverse normal stresses govern the stress state. Through quasi-static and incremental loading, it is shown that certain AE features can be used to identify the dominant stress component rather than just the occurring damage mode even at early loads, before severe fracture influences the mechanical capacity. This is of great importance in cases that detrimental shear stresses are generated, leading to delaminations and mechanical deterioration. AE can be used in this direction to predict the upcoming damage and to take necessary measures to avoid final failure.