基于单射流冲击试验的复合材料高速雨滴撞击损伤研究

飞行器高速飞越云雨区时，前表面会受到雨滴的冲击侵蚀。基于一级轻气炮搭建了一种单射流冲击试验平台用于材料雨蚀试验，可产生速度200～600 m/s、直径4～7 mm、头部呈光滑圆弧形的稳定水射流；并对一种碳纤维树脂基复合材料层合板进行了不同速度和直径的单射流冲击试验。结果表明，复合材料单次水射流冲击的典型损伤形貌为:冲击表面凹陷，中心几乎完好无损伤，周围产生一环状损伤带，环内有树脂去除、基体开裂、少量纤维断裂等损伤形式；内部损伤主要由基体开裂和层间分层组成。损伤尺寸呈现典型的各向异性，纵向尺寸大于横向尺寸；随射流速度和直径的增加，表面环状损伤和内部损伤的尺寸均向外扩展，环状损伤面积和内部分层面积也随之增加。水锤压力的压缩和卸载、侧向射流的剪切和应力波的相互作用是造成复合材料单射流冲击损伤的主要机理。

High-speed raindrop impingement damage of composites based on single waterjet impact tests

When an aircraft flies over the cloud at high speed, the front surface will be eroded by raindrops. In this paper, a single waterjet impact test platform was established based on the first-stage light gas gun in order to conduct the rain erosion tests on materials. Its principle was that the gas gun launches a metallic projectile to impact the water storage chamber sealed by the rubber piston, and then the liquid was driven from the small nozzle to form a high-speed waterjet. The apparatus could generate stable waterjets with speeds of 200?600 m/s, diameters of 4?7 mm and a smooth circular-arc head, which simulated a waterdrop with the same diameter. A series of single waterjet impact tests were carried out on a symmetrically cross-ply carbon-fiber-reinforced composite (CFRP) laminate under different waterjet velocities and diameters. The results show that the typical damage modes of CFRP laminates impacted by single waterjets are as follows. The impacted surface is depressed, and the surface damage consists of resin removal, matrix cracking, minor fiber fracture and fiber exposure around the rim of a central undamaged region. The internal damage range gradually expands from the impact surface to the bottom ply, mainly composed of intralaminar matrix cracking with a pyramid shape and interlaminar delamination with a diamond shape. Both the surface and internal damage are more extensive in the longitudinal than the transversal direction, thus presenting typical anisotropy due to the anisotropic elastic and strength properties of CFRP materials. With the increase of waterjet velocity and diameter, both the surface annular damage and internal damage expand outwards, and the damage areas also increase correspondingly. Compression and release waves of water hammer pressure, shear stress of lateral jetting and interaction of stress waves are the main mechanisms leading to damage and failure of composites impacted by waterjets. The area of the undamaged center of the surface can be predicted by multiplying the contact boundary diameter of the water hammer pressure by a dimensionless damage function.