Analysis of tensile properties allowable value for composite materials under wet and thermal conditions based on performance surface equation

The mechanical properties of composite materials exhibit considerable variability due to the influence of manufacturing processes and operational environments, which restricts their widespread application. At present, allowable values are employed to ensure the reliability of composites in service; however, prevailing determination criteria frequently neglect the effects of environmental conditions, resulting in limited generalizability. To address this limitation, this study develops a modeling framework to characterize the evolution of mechanical properties of composites under hygrothermal conditions. A methodology is introduced for determining the allowable tensile strength based on a performance surface equation. Coupled hygrothermal testing is conducted to quantify the effects of temperature and humidity on tensile properties using Arrhenius and power -law models. These individual influence models are integrated to construct a temperature-humidity tensile performance surface equation. By incorporating the variability in mechanical properties, the method enables the calculation of allowable tensile strength. In comparison with conventional single-point and combination methods, the proposed approach offers substantially improved accuracy in allowable value estimation, thereby providing refined guidance for the structural design of composite materials.