Pore evolution and mechanical properties of carbon fiber laminates subjected to low-velocity impacts

Abstract In order to study the effect of impact loading on the porosity within carbon fiber laminates and the effect of porosity on performance under external loading, six different energy gradients (0 J, 6 J, 10 J, 15 J, 20 J, 25 J) were applied to impact the carbon fiber laminates, followed by tensile and compression experiments on the impacted laminates. Various characterization methods, including industrial CT, ultrasonic C-scan, metallographic microscopy, scanning electron microscopy, and mercury intrusion porosimetry, were used to investigate the changes in porosity and their effects on mechanical properties. The study found that impact loading leads to the formation of new porosity between layers, and these pores connect through cracks and coalesce to form larger pores, ultimately resulting in delamination. Under tensile loading, cracks form near the interlaminar and intralaminar porosity, and propagate along the thickness direction and interlaminar direction, respectively, leading to a decrease in the mechanical properties of the laminate. Using ultrasonic A-scan technology, sound attenuation and sound impedance data for the impacted regions of the laminates were obtained, and mathematical models for sound attenuation, sound impedance, and porosity were established. The average errors of the models were 6.6 % and 5.5 %, respectively. Additionally, finite element simulations of the laminate’s impact and tensile experiments were conducted, and tensile strength values for the 0 J, 10 J, and 20 J samples were output. The simulation results showed an accuracy rate of 95.4 %, 97.2 %, and 95.2 %, respectively.