In the present work, the feasibility of axial ultrasonic tests for exploring the fully reversed fatigue response of composite materials even in the Very High Cycle Fatigue (VHCF) regime is proved. VHCF tests are run on hourglass specimens made of twill 2x2 carbon woven fabric impregnated with epoxy resin with stacking sequences [0]8 and [0/90/+45/-45]s and designed through Finite Element (FE) modal analysis. The stress distribution within the specimen and the absence of buckling are first determined through an extensive strain gage campaign, which has validated the FE model. As the temperature is a main concern in ultrasonic tests, the temperature increment within the composite specimen is investigated by means of an embedded fiber optic sensor and controlled during the tests with an infrared sensor. With the proposed experimental setup, fully reversed ultrasonic tests have been carried out up to 109 cycles and the failure of the two investigated specimen types has been analyzed by comparing the failure origin location in relation to the stress distributions.

中文翻译：

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用于探索复合材料极高周疲劳的超声全反向轴向试验


在本工作中，证明了轴向超声检测在探索复合材料即使在甚高周疲劳 （VHCF） 状态下也能完全反向疲劳响应的可行性。VHCF 测试是在由浸渍有环氧树脂的斜纹 2x2 碳织织物制成的沙漏试样上进行的，堆叠顺序为 [0]8 和 [0/90/+45/-45]s，并通过有限元 （FE） 模态分析设计。试样内的应力分布和无屈曲首先通过广泛的应变计活动来确定，该活动已经验证了 FE 模型。由于温度是超声检测中的主要关注点，因此通过嵌入式光纤传感器研究复合材料试样内的温度增量，并在检测过程中使用红外传感器进行控制。使用建议的实验装置，已经进行了长达 109 个循环的完全反向超声测试，并且通过比较与应力分布相关的失效原点位置来分析两种研究的试样类型的失效。