Damage assessment of carbon fiber reinforced composites under accelerated aging and validation via stochastic model-based analysis

Abstract

Composite materials used in technically advanced structures are subjected to constant aging from exposure to changing environmental conditions. Studying the effects on such materials due to exposure to varying temperature, humidity, ultraviolet radiation, etc. reveals the impact on their mechanical behavior. This study assesses alterations in static, dynamic, and viscoelastic response of polymer matrix woven carbon fiber lamina composites upon exposure to varying environmental conditions recreated in a climatic chamber. Therein, specimens suffered temperature changes from –35 to +40℃ and humidity variations from <10% to 95% RH (noncondensing) over a period of up to 30 days. Alternating cycles simulating conditions of actual 3–4 h flights were specified. Additionally, specimens of the same material were subjected to thermal shock under similar (to the aging scenario) temperature extremes. All specimens were comparatively assessed via experimental procedures involving three-point bending tests performed in both static and dynamic mechanical analysis for a range of temperatures and frequencies, frequency and thermal scans, and finally impact tests. Results indicate that aged materials exhibit increased dynamic stiffness (expressed by the storage moduli) and decreased material damping ability (expressed by the tan  δ parameter). Macroscopic assessment of impact test data was performed via stochastic model-based damage detection methodologies. Results indicate that differences in the impact behavior between pristine and aged specimens are statistically detectable and quantifiable, without input from mechanical testing analysis. More importantly, this assessment of aging-induced effects on the specimens corroborates the findings on storage moduli and tan  δ from mechanical testing analysis, thus validating the latter.