Hygrothermal Conditioning Effects and Statistical Analysis of Interfacial Shear Strength and the Performance of Carbon Nanotube Polymer Composites

Conditioning treatments are essential to understanding composite material properties, especially the composite interfacial shear strength (IFSS). The IFSS denotes the strength of the matrix/reinforcement phase bond. A strong adhesion between the matrix and the fibers under varying environmental conditions is crucial, as the mechanical properties of the composite material rely on the integrity of the load transfer. To this end, this paper presents a systematic analysis to study the effects of mechanical loading on the IFSS of carbon nanotube (CNT) yarn/polymer matrix composites by conducting randomized experiments under controlled environmental conditions. The experimental data are analyzed using a response surface model to statistically quantify the nonlinear effects of temperature, immersion time, strain rate, and embedded length on the interfacial performance. CNT yarns are tested under various environmental temperatures and time constraints, in addition to fiber embedded length and strain rate. When immersed in water for 7 days, at room temperature compared to 70°C, the IFSS increased by an average of 16.15%. Conditioning the composite for 3 days with an embedded length of 4 mm increased the IFSS by an average of 30.21% compared to an embedded length of 3 mm. Axial point testing demonstrated nonlinear effects, characterized by an initial rise in IFSS with prolonged immersion times and reduced strain rates, succeeded by a decrease at elevated temperature extremes. Response surface modeling validated substantial second‐order interactions. This study provides valuable insights into how environmental factors influence composite material performance, emphasizing bonding to ensure mechanical reliability.