工程材料在使用过程中,总要受到各种外力的作用,这种外力通常称为载荷,载荷使材料产生变形。变形一般由弹性变形开始,然后发展成塑性变形,最后破坏(见图1)。因为材料本身具有抵抗变形和破坏的能力,可以利用它担负一定的工作。这种性能就叫材料的强度。人们对材料和结构不仅要求在长期工作中不会产生塑性变形和破坏,而且,弹性变形也必须控制在很小的范围内。例如,制造飞机的材料,如果在飞行中产生过大的弹性变形,飞行状态将会恶化甚至完全失去稳定,汽车超载 Engineering materials in the use of the process, always subject to a variety of external forces, this force is usually called the load, the load deformation of the material. Deformation generally begins with elastic deformation, and then develops into plastic deformation, the final destruction (see Figure 1). Because the material itself has the ability to resist deformation and destruction, it can be used to take on some work. This performance is called the strength of the material. People’s material and structure not only require no plastic deformation and damage during long-term work, but also elastic deformation must be controlled within a very small area. For example, the materials used to make an airplane will deteriorate or even lose stability if the aircraft undergoes excessive elastic deformation in flight, and the vehicle is overloaded