9. Gây ứng suất sơ bộ

Nguyên tắc con

1. Apply in advance an opposite action that cancels a harmful one to come
2. If a stress is going to appear, load the part with the opposite stress beforehand

Ví dụ

• A prestressed concrete beam
• A plate bent slightly the opposite way before welding
• Masking tape applied before painting

Ứng dụng theo lĩnh vực

• mechanical: A thick tube under high pressure fails from the inner wall first. Pressurizing it once beyond its working level during manufacture leaves compressive stress inside, so it holds more in service.
• electronics: Switching power on sends a surge of current that stresses components. Charging first through a resistor and then bypassing it prevents the surge.
• medical: A first infection catches the body unprepared. A vaccine given beforehand, made from a weakened or inactivated pathogen or one of its antigens, builds immunity so the real infection is fought off faster.
• everyday: Ice bonded to a road after snowfall is hard to clear. Spreading de-icer before the snow keeps it from freezing to the surface.