Abstract
Damage to the body or critical components caused by stone strikes to automotive coatings affects the safety of the car. More and more attention are being paid to the study of the anti-stone-damage mechanism of coatings. Firstly, a computational fluid dynamics (CFD) model was established based on a single-impact anti-stone tester, and the simulation results show the following: (a) At 90° incidence, the air pressure of the stone impact suddenly and rapidly increases when the semicircular surface projectile velocity is greater than 30 m/s. The air pressure of the conical projectile stone at the distance of 0.3 and 0.15 mm suddenly increases at the projectile velocity of 10 and 20 m/s, respectively. (b) When the projectile velocity exceeds 15 m/s, the pressure of the semicircular surface projectile suddenly increases. (c) When the speed is less than 20 m/s, the shedding area decreases with the increase in the speed, while the stone impact pressure increases with the increase in the speed. Then, the simulation results of the incident velocity of 40 m/s show that the working pressure is 195.48 kPa, and the impact force is 8142.56 N. Finally, the relationship between the impact force and the driving air flow pressure was obtained according to the DIN 55996-1 standard stone impact resistance test and compared with the simulation results, showing that trend of the impact force increasing with the increase in driving air flow pressure is consistent, the simulation results are about 1.40 times the experimental results, and the simulation results are large and can be considered by increasing the test correction coefficient adjustment. Based on the CFD method, research on the mechanism of anti-stone-damage automotive coating can greatly reduce the number of stone strike instrument experiments, shorten the cycle, and reduce the research and development costs.
Highlights
When the car is driving, the body coating is often impacted by heavy objects such as sand particles and road gravel, leading to the composite coating being peeled off in single or multiple layers or even completely
According to reports, when a 10 g piece of gravel collides with a body with a relative speed of 80 km/h, its impact force is 100 times its own weight, which is enough to break through the paint coating of 30 μm; if the paint coating is damaged, the local sheet metal is directly exposed to the atmosphere, which can very cause corrosion problems
Pressure waves are reflected in the form of tension on the free surface of the impactor and target, and when the tension wave reaches the impact interface, the impactor separates from the target, creating further stress wave jets
Summary
When the car is driving, the body coating is often impacted by heavy objects such as sand particles and road gravel, leading to the composite coating being peeled off in single or multiple layers or even completely. According to reports, when a 10 g piece of gravel collides with a body with a relative speed of 80 km/h, its impact force is 100 times its own weight, which is enough to break through the paint coating of 30 μm; if the paint coating is damaged, the local sheet metal is directly exposed to the atmosphere, which can very cause corrosion problems. As pressure waves propagate through the coating, local stresses may far exceed the strength limits of the layer and the bonding surface, causing structural damage, coating delamination, and fragmentation [3]. Coatings with good adhesion properties fail due to mechanical failure mechanisms such as scraping and two other cuts [4]
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