The objective of this work is to investigate the effects of environmental conditions on the axial fatigue behavior of a carbon/epoxy plain-weave laminate with an embedded flaw subjected to a partially reversed cyclic load (stress ratio R = −0.1) in tension–compression. This specific material is more commonly used in aerospace engineering for the manufacturing of aircraft structural parts, which are directly exposed to various environmental conditions during service. Specific environmental and loading conditions that are appropriate to simulate real-life conditions are considered to observe and collect information about the material's behavior. For the investigation, dry and wet coupons were submitted to room temperature, 82 and 121 ℃ under loading frequencies of 7 and 15 Hz. A maximum allowable strain increase criterion is used to monitor the flaw growth threshold or delamination onset, during fatigue testing. The ultrasonic imaging (C-scan) technique is used to verify and confirm the delamination onset. Results show that the delamination onset strain increase criterion, along with fatigue life, generally decreased as the operating temperature and humidity were increased and that frequency had little effect on the delamination onset fatigue life. The S–N curves obtained from the tension–compression fatigue data were then compared to those of a previous work carried out in tension–tension fatigue loading. Results show a clear degradation in the delamination onset fatigue life of the coupons tested under tension–tension cyclic loading when the minimum tensile component of the cyclic load was replaced with a compressive load of the same magnitude.

中文翻译：

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环境条件对含裂纹碳/环氧树脂平纹层压板轴向拉压疲劳行为的影响

这项工作的目的是研究环境条件对带有嵌入缺陷的碳/环氧树脂平纹层压板在拉伸 - 压缩中承受部分反向循环载荷（应力比 R = -0.1）的轴向疲劳行为的影响. 这种特殊材料更常用于航空航天工程，用于制造在服役期间直接暴露于各种环境条件的飞机结构部件。考虑适合模拟现实生活条件的特定环境和负载条件，以观察和收集有关材料行为的信息。为了进行研究，干和湿试样在 7 和 15 Hz 的加载频率下经受室温、82 和 121 ℃。在疲劳测试期间，最大允许应变增加标准用于监测缺陷增长阈值或分层开始。超声成像（C 扫描）技术用于验证和确认分层开始。结果表明，随着工作温度和湿度的增加，分层起始应变增加标准随着疲劳寿命的增加而普遍降低，并且频率对分层起始疲劳寿命的影响很小。然后将从拉伸-压缩疲劳数据中获得的 S-N 曲线与之前在拉伸-拉伸疲劳载荷中进行的工作的曲线进行比较。