Bridging the Gap: Correlating Ultrasonically Quantified BVID with the Compressive Strength of CFRP Composites

Carbon fiber laminates are susceptible to impact damage due to the lack of fibers in the direction of impact. Often such damage can be difficult to find with visual assessment, prompting the need for detection via nondestructive testing techniques. This study quantifies the ultrasonically characterized impact damage diameters in 22 layered CFRP samples from 16 J, 18 J, 20 J, 22 J, and 24 J impact energies. These energies result in damage often defined as barely visible impact damage. This study utilizes x-ray computed tomography as a baseline to verify the results of the ultrasonic testing. Compression after impact test measurements are used in this study to find the ultimate compressive residual strength of the impacted carbon fiber laminates and to investigate the negative correlation between impact energy and residual mechanical properties of the damaged carbon fiber laminates. Many studies focus on the characterization of impact damage from various impact energies and setups via ultrasonic testing or, separately, the effect of the impact setups on the residual strength of the composite. This study strengthens the bridge between the barely visible impact damage quantified via ultrasonic testing and the residual compressive strength of the affected composite. Overall, this paper offers further insights into the relationship between internal damage size obtained using ultrasonic testing and correlates the characterized internal damage geometry to the resultant compressive strength reduction, providing a path for future studies in predictive modeling of the residual strength after impact.

碳纤维层合板（Carbon Fiber Laminates）因冲击方向缺乏纤维补强，极易产生冲击损伤。此类损伤往往难以通过目视检查发现，因此亟需借助无损检测技术开展检测工作。本研究针对22个碳纤维增强聚合物基复合材料（Carbon Fiber Reinforced Polymer, CFRP）层合试样，在16 J、18 J、20 J、22 J及24 J冲击能量下，量化了超声表征得到的冲击损伤直径。上述冲击能量所产生的损伤通常被定义为几乎不可见冲击损伤（Barely Visible Impact Damage, BVID）。本研究以X射线计算机断层扫描（X-ray Computed Tomography, XCT）作为基准方法，对超声检测的结果进行验证。本研究通过冲击后压缩试验（Compression After Impact, CAI）测试，获取受冲击碳纤维层合板的极限压缩剩余强度，并探究冲击能量与受损碳纤维层合板剩余力学性能之间的负相关关系。现有诸多研究多聚焦于通过超声检测表征不同冲击能量与冲击工况下的冲击损伤，或是单独探究冲击工况对复合材料剩余强度的影响。本研究进一步夯实了通过超声检测量化的几乎不可见冲击损伤与受冲击复合材料剩余压缩强度之间的关联纽带。综上，本研究进一步揭示了超声检测获取的内部损伤尺寸与表征所得内部损伤几何形态之间的内在关联，并将该几何特征与由此产生的压缩强度衰减建立对应联系，为后续开展冲击后剩余强度预测建模研究提供了可行路径。