Study on Rain Erosion Damage Characteristics of Oriented Polymethyl Methacrylate Based on a Continuous Jet Rain Erosion Test System

To address rain erosion damage of oriented polymethyl methacrylate (PMMA) under high-speed droplet impact, three types of tests (single pulsed jet impact, continuous single pulsed jet impact and continuous twin pulsed jet coupled impact) were conducted using a self-developed continuous jet rain erosion test system. High-speed photography, optical microscopy, optical profilometer and computed tomography (CT) were used to investigate the effects of impact velocity, number of impacts, and twin pulsed jet coupling on damage evolution. Single pulsed jet impact tests show that with increasing velocity, damage evolves from slight annular crazing to a central undamaged region surrounded by extensive annular crazing. Continuous single pulsed jet impact tests indicate that higher velocity shortens the incubation period and accelerates volume loss and damage area growth. The erosion crater profile exhibits a “two valleys and one peak” morphology: a central protrusion from repeated water-hammer compression, and side depressions from lateral outflow scouring. Continuous twin pulsed jet coupled impact tests reveal distinct features: due to mutual hindrance of lateral flows, ring cracks appear only on the side away from the adjacent impact; stress wave superposition may cause stress concentration between impact points, resulting in an asymmetric “single-peak” crater cross-section. This study achieves laboratory simulation of twin pulsed jet coupled impacts, providing an experimental basis for multi-jet interaction damage mechanisms.