基于红外热成像的编织复合材料低速冲击和冲击后压缩试验研究

针对二维三轴编织复合材料（two-dimensional triaxially braided composite, 2DTBC）在低速冲击和冲击后压缩（compression after impact, CAI）载荷下的损伤失效机理，开展了2DTBC试样的不同能量低速冲击试验以及相应的CAI试验，并采用红外热像仪监测在低速冲击和CAI试验过程中的温升现象。通过C扫描表征了不同能量低速冲击后试样的分层损伤情况，讨论了试样背面温度场分布特性及其随冲击能量的演化规律；对比分析了2DTBC冲击后剩余压缩强度与冲击能量的对应关系，基于数字图像相关（digital image correlation, DIC）技术监测了CAI试验中的全局应变场，结合热成像、变形场和光学图像数据，阐明了不同能量冲击后2DTBC的压缩失效特性，讨论了基于红外热成像技术表征编织复合材料损伤失效行为的有效性。试验结果显示:编织复合材料低速冲击和CAI试验中的温度场分布图与编织几何构型有明显关联度；低速冲击试验的温升幅值随冲击能量的增加而快速上升，CAI试验的温升现象随着冲击能量的增加而减弱；分层面积随冲击能量的增大而增大，冲击后剩余压缩强度随冲击能量的增大而降低。研究结果表明:红外热成像技术能够很好地捕捉试样破坏瞬间释放断裂能所产生的温升现象，温度场图像相较于全局应变场能更好地捕捉破坏的起始位置和失效特征。

Experimental research on low-velocity impact and compression after impact of braided composites based on infrared thermal imaging

The damage and failure mechanism of two-dimensional triaxially braided composite (2DTBC) under low-velocity impact and compression after impact (CAI) was experimentally investigated through tests with various impact energies (5, 10, 20 and 30 J). The low-velocity impact specimens were prepared according to the ASTM D7136 standard and tested using the Instron drop tower 9250HV with a hemispherical punch, and CAI tests were carried out on an Aowei PLD-250 fatigue machine following the ASTM D7137 standard. An infrared thermal imaging camera was employed to monitor the temperature distribution of the specimens during the low-velocity impact and CAI tests. Delamination damage of impacted specimens was characterized by an ICS-Ⅱ ultrasonic C-scanner. The relationship between impact energy and residual compression strength of 2DTBC after impact load was compared and analyzed. The evolution of the temperature field and its sensitivity against impact energy were discussed based on the infrared image data. Regarding the CAI tests, the global strain field was measured using the digital image correlation (DIC). Combining the thermal and deformation fields, and the optical failure images, the compression failure behavior of 2DTBC after impact of different energies were systematically investigated, validating the feasibility of infrared thermal imaging technology on characterizing the damage and failure behavior of braided composites. The experimental results show that the temperature field contours in low-velocity impact and CAI tests of braided composites are significantly correlated with braided architecture. The magnitude of temperature rise during the low-velocity impact test increases rapidly with the increase of impact energy, while the magnitude of temperature rise during the CAI test decreases with the increase of impact energy. Moreover, the maximum temperature rise is about 56.2 oC in the 30 J low-velocity impact test. The delamination area is found to increase with the increase of impact energy, and the residual compression strength after impact decreases with the increase of impact energy. The residual compression strengths ratios are 90.9%, 82.2%, 73.8% and 65.8% for specimens after 5, 10, 20 and 30 J impacts, respectively. Through this study, we demonstrate that infrared thermal imaging camera can clearly capture the temperature rise phenomenon of composite specimens, which is caused by the releasing of fracture energy at the failure instant. More notably, the temperature contour can better reflect the damage location and failure characteristics than the global strain field.