Mechanical System Failure

This chapter shall talk about the basic ideas—Newton’s or quantum mechanics, transport theories, etc.—of mechanical unsuccessfulness such as fracture and fatigue, which consist of roughly 80–90% of all constructional failures and are caused by a little crack or a preexisting defect in a product’s part. Based on a variety of principles of mechanical engineering, engineers can design new functions in mechanical products. The fundamental building blocks of structural materials, which have imperfections such as point defects that can be transported, are atoms, and the bonds play a part in deciding the structure. As there are design faults in mechanical products which can cause lack of strength (or stiffness) when the products are subjected to repeated loads, the product material shall generate voids and transport them. After repeated stresses, a crack occurs and propagates to the end. Finally, they will fail in their lifetime. Fatigue catastrophically happens at stress raisers such as notches, holes, or fillets in the structure. However, the modern reliability methodology does not judge whether the product endures the stress for its lifetime. To robustly design the product structure, including the mechanism, engineers should understand fatigue. To do so, we can discover the problematic designs of parts by parametric accelerated life testing (ALT) and modify them.