利用超声成像分析不同复合材料层压结构冲击损伤行为

复合材料各向异性和吸能的特点，在受到外来冲击作用时容易产生损伤，呈现表里迥然不同的损伤行为和分布规律。为研究不同复合材料层压结构的冲击损伤行为，设计制备树脂传递模型工艺(Resin transfer molding, RTM)缝合和预浸料复合材料层压结构两种不同成型工艺的试样，通过冲击试验模拟复合材料在外力作用下产生的冲击损伤，采用超声反射法，通过点聚焦换能器对试样进行超声B扫描成像，揭示两种复合材料层压结构试样内部断面损伤行为及其扩展规律。试验结果表明，冲击引起的试样内部损伤比表面损伤要大得多；随着冲击能量在试样内部传递，会在不同深度铺层产生新的损伤，而且损伤分布并不仅沿层间界面扩展；冲击点附近和远离冲击点附近的内部损伤具有明显不同的分布规律；RTM缝编与预浸料复合材料结构呈现明显不同的损伤行为，其中RTM缝合复合材料结构中的纵向缝线，对冲击损伤在试样内部沿层间的扩展有显然的阻止作用。研究结果对更好地理解复合材料的损伤行为、寻找新的改进复合材料层压结构损伤行为的机制有非常重要的指导意义和帮助。

Investigation of Impact Damage Behavior of Different Composite Laminates by Using Ultrasonic Imaging

Composite laminates are very sensitive to foreign impact because of their anisotropy and good absorbing ability to impact energy. They may exhibit different impact damage behavior in body under impact loading. Two kinds of specimens-RTM-stitched and prepreg composite laminate, are manufactured to investigate their behaviors of impact damages. The specimens are subjected to a given energy impact. An ultrasonic B-scan is arranged to the specimens by using focal system in order to study behaviors of impact damages in cross-sections of the specimen bodies. Experimental results have demonstrated that interior damaged area is much larger than damage on surface; new damages occur in different inetrlaminar layers with impact energy going into specimen body deeper and deeper, and they evolve not only along interfaces of layers; the distribution and orientation of damages between near- and far-impact point are significantly different; a clear difference in damage behavior between RTM-stitched and prepreg composite laminates is demonstrated very well, and the stitching fiber thread in depth direction of RTM-stitched composite laminate has obvious help on restriction to development of damages along interlaminar interfaces. The results provide very helpful and practical understanding of the damage behavior in different composite laminate bodies. That may motivate to find new mechanism to improve damage behavior of composite laminates.