Abstract It is widely known that damage induced by low-velocity impact events will significantly affect the damage tolerance and integrity of composite structures. This study investigates the damage evolution and failure mechanism of impacted laminates under fatigue loadings using the infrared thermography and ultrasonic methods. Low-velocity impact damage was introduced by a drop weight with a hemispherical impactor, and compression-after-impact (CAI) tests were conducted to determine the residual compressive strength. Four stress levels were selected to conduct compression-compression fatigue tests with a stress ratio R = 10 based on the static CAI strength. During fatigue tests, the surface temperature variations were monitored online by an infrared camera, and the delamination damage evolution was observed using ultrasonic C-scan methods. The thermal images, delamination contours and stiffness degradation were analyzed. The maximum temperature increase and the stiffness degradation show the characteristic with three stages “rapid-slow-rapid”. For evolution of damage area, two stages were observed. The damage area extends from the impact indentation to two outer free edges in the perpendicular direction until the final collapse of the specimen.

中文翻译：

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用红外热像法和超声波方法评估疲劳载荷下冲击复合材料层压板的损伤演变

摘要 众所周知，低速撞击事件引起的损伤会显着影响复合材料结构的损伤容限和完整性。本研究使用红外热成像和超声波方法研究了疲劳载荷下冲击层压板的损伤演变和失效机制。低速冲击损伤是由带有半球形冲击器的落锤引入的，并进行了冲击后压缩 (CAI) 测试以确定残余抗压强度。基于静态 CAI 强度，选择四个应力水平进行压缩-压缩疲劳试验，应力比 R = 10。在疲劳试验过程中，通过红外摄像机在线监测表面温度变化，并使用超声波 C 扫描方法观察分层损伤演变。分析了热图像、分层轮廓和刚度退化。最大温升和刚度下降表现出“快-慢-快”三个阶段的特征。对于损伤区域的演变，观察到两个阶段。损伤区域从冲击压痕沿垂直方向延伸到两个外部自由边缘，直到试样最终坍塌。