基于单射流冲击试验的复合材料高速雨滴撞击损伤研究

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.