دانلود رایگان مقاله تجزیه و تحلیل شکست یک فنر خودرو

1. Introduction

A motor car coil spring of a rear shock absorber has been ruptured during car operation. The surface of a spring was protected against corrosion with a thick layer of paint on polymer basis. Around the fracture surface, a protective layer was damaged and removed over a length of several centimeters. In this area, spring has long been exposed to corrosion attack and thus surface heavily corroded and winkled (Fig. 1). The fracture surface of a spring is discontinuous and in major part of it covered with fresh rust. On a minor portion of a fracture surface, a compact, dark brown rust (like on the circumference of the spring) is visible, which was formed substantially (months) before the final rupture of the spring (Fig. 2). From this part of the fracture surface, crack gradually propagated (the ‘‘arrest lines’’ are clearly visible), due to the combination of corrosion attack and cyclic loading during the car operation (Fig. 3), until the length of the crack reached its critical value, and the spring broke instantly (Fig. 4). Part of the fracture surface, covered with thick, compact and dark rust is the primary crack, which was exposed to corrosion attack for months. Part of the fracture surface (Fig. 5), where a layer of compact surface rust and indentations of rust into the material are clearly visible represents a propagating stage of a fatigue and part of a surface (Fig. 6), which is covered with thin fresh rust (formed in a few days after final rupture) the terminating stage of the fatigue.

4. Conclusion

Rupture of the spring results from the corrosion induced fatigue of steel. The main reason that this has occurred was damaged corrosion protection layer (paint) on the surface of the spring, where corrosion attack has started. Simultaneous activity of corrosion and cycling loads caused failure of the spring.