Fatigue is an irreversible thermodynamic process accompanied by multi-component energy dissipation and entropy accumulation. This study analyzes the energy composition of total mechanical input hysteresis energy during the fatigue process of composites. By excluding thermal dissipation and viscoelastic internal friction dissipation energy, which do not directly contribute to fatigue damage, the irrecoverable damage energy is extracted. This portion of energy is closely related to the final failure of the specimen and the accumulation of damage entropy. The differences in energy dissipation mechanisms between low-cycle and high-cycle fatigue are evaluated, and a fatigue life prediction model for composites is established based on different damage entropy thresholds. Fatigue tests were conducted on glass fiber-reinforced polymer (GFRP) composite laminates, and the fatigue properties were investigated using infrared thermography (IRT) and digital image correlation (DIC). The proposed damage entropy model for fatigue life prediction was validated at various loading frequencies (2–5 Hz) and across a wide range of cycles (102-106 cycles), showing good agreement with the experimental results.

中文翻译：

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基于能量守恒和损伤熵累积的复合材料层合板疲劳寿命预测

疲劳是一个不可逆的热力学过程，伴随着多组分能量耗散和熵积累。本研究分析了复合材料疲劳过程中总机械输入磁滞能的能量组成。通过排除不直接导致疲劳损伤的热耗散和粘弹性内部摩擦耗散能量，提取出不可恢复的损伤能量。这部分能量与试件的最终破坏和损伤熵的积累密切相关。评估了低周和高周疲劳耗能机理的差异，并基于不同的损伤熵阈值建立了复合材料疲劳寿命预测模型。对玻璃纤维增强聚合物 （GFRP） 复合材料层压板进行了疲劳测试，并使用红外热成像 （IRT） 和数字图像相关 （DIC） 研究了疲劳性能。所提出的用于疲劳寿命预测的损伤熵模型在各种加载频率 （2-5 Hz） 和较宽的循环范围 （102-106 次循环） 下进行了验证，与实验结果具有良好的一致性。