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Considering the inherent characteristics of strength degradation, a residual strength model is improved reasonably through the incorporation of the two‐parameter Weibull distribution. Building upon this foundation, an enhanced nonlinear fatigue damage accumulation model that is closer to the actual situation is proposed in view of the randomness of fatigue damage. The model takes into account the effect of load action on fatigue damage. To ascertain the feasibility of the proposed model, the time‐varying reliability of the model is evaluated by applying the probability density evolution method. The model's precision in predicting residual life is corroborated through five experimental data sets under bilevel and multilevel loading conditions. The results demonstrate that the proposed model exhibits excellent applicability and remarkable precision, thereby confirming its potential value in practical applications. Highlights: Using strength degradation characteristics, new residual strength model is crafted.Combined with the Weibull distribution, a new fatigue damage model is established.The PDEM is applied to obtain the time‐varying fatigue reliability curve. [ABSTRACT FROM AUTHOR]

The coupling effects of high and low temperature-humidity-applied load on the longitudinal tensile mechanical properties and the durability performance of epoxy resin-based carbon fiber reinforced composites (EP-CFRP) are studied in this paper. It considers two high and low alternating temperature ranges [−40°C∼40°C]/[−40°C∼25°C], two humidity conditions (soaking in water and anhydrous), and three load levels of unstressed state or 30% and 60% of the ultimate load. The results indicate that all these three factors have a significant impact on the durability of EP-CFRP. The tensile strength varies with the high and low temperature alternating cycle, showing a trend of first decreasing, then increasing, and then decreasing; however, the peak and valley values appear in the quite different alternating cycle. The coupling effects of these factors have less influence on the tensile modulus. The microcracks generated at the interface between the resin matrix and the fiber have been proved to be the main reason for the strength reduction at the later stage. The coupling effect of humidity and load promotes the expansion of cracks and exacerbates the damage to EP-CFRP. Based on the cumulative damage theory, the residual strength damage model of EP-CFRP under the three-factor coupling action of "high and low temperature cycling-humidity-load" is calibrated by nonlinear fitting method. [ABSTRACT FROM AUTHOR]

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This paper studies the durability of epoxy resin-based-carbon fiber reinforced polymer (EP-CFRP) under the combined action of aggressive environmental conditions and load. Environmental conditions such as high and low temperature cycles of −40-40 ℃ / −40-25 ℃ and humidity (water immersion and no water) are investigated in an unstressed state or loaded in about 30% or 60% of the initial ultimate load. The results indicate that both of the dual-factor coupling of “high and low temperature cycle-humidity” and the three-factor coupling of “high and low temperature cycle-humidity-load” have a greater impact on the durability of EP-CFRP. The tensile strength varies with the cycle of high and low temperature. The overall increase shows a simulated trend of first decreasing, then increasing, and then decreasing; however, the appearance of the peak and valley values are quite different. Humidity and load level have little effect on the tensile modulus of EP-CFRP The microcracks generated at the interface between the resin matrix and the fiber have been proved to be the main reason for the strength reduction at later stage. The coupling effect of humidity and load promotes the expansion of cracks and exacerbates the damage to EP-CFRP. According to the damage analysis, a non-linear fitting method is used to give the residual strength damage model of EP-CFRP after the coupling action of the three factors “high and low temperature cycle-humidity-load”.

The coupling effects of high and low temperature-humidity-applied load on the longitudinal tensile mechanical properties and the durability performance of epoxy resin-based carbon fiber reinforced composites (EP-CFRP) are studied in this paper. It considers two high and low alternating temperature ranges [-40°C~40°C]/[-40°C~25°C], two humidity conditions (soaking in water and anhydrous), and three load levels of unstressed state or 30% and 60% of the ultimate load. The results indicate that all these three factors have a significant impact on the durability of EP-CFRP. The tensile strength varies with the high and low temperature alternating cycle, showing a trend of first decreasing, then increasing, and then decreasing; however, the peak and valley values appear in the quite different alternating cycle. The coupling effects of these factors have less influence on the tensile modulus. The microcracks generated at the interface between the resin matrix and the fiber have been proved to be the main reason for the strength reduction at the later stage. The coupling effect of humidity and load promotes the expansion of cracks and exacerbates the damage to EP-CFRP. Based on the cumulative damage theory, the residual strength damage model of EP-CFRP under the three-factor coupling action of "high and low temperature cycling-humidity-load" is calibrated by nonlinear fitting method. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Aeronautical Materials is the property of Editorial Board of Journal of Aeronautical Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The use of composite materials in the most varied industrial sectors has increased considerably in recent years, especially those made of carbon fiber/epoxy resin. For this reason, the use of these materials need a better understanding of their mechanical behavior, especially when submitted to cyclical load requests, especially about compression, which is the object of study of this work. Residual strength degradation in CFRP is evaluated by numerical models and experimental tests relating the residual strength to the applied fatigue cycles and the maximum stress. The present work proposes to characterize the static and fatigue mechanical properties in compression of a carbon fiber/epoxy resin composite, used in the aeronautical industry, to present a mathematical model to determine the residual strength. The experimental methodology for strain limit evaluation has involved the residual strength after the fatigue test limited to 120,000 or 240,000 cycles, considering frequency of 12 Hz and stress ratio R=10 in different strain levels. This study establishes that the strain limit corresponds to deformation in which the residual strength becomes equal to the design stress (stress reduced statically to the B − basis value). Lastly, the adjusted mathematical model for determining the residual strength and the finite element simulations showed consistent results when compared with experimental tests. This study shows the relevance of the allowable levels determined from static strength to the onset of abrupt failure as a function of increasing maximum fatigue stress level that is a significant finding for the fatigue design community. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)