STRESS

Properties of Metals DOE-HDBK-1017/1-93 STRESS STRESS Any component, no matter how simple or complex, has to transmit or sustain a mechanical load of some sort. The load may be one of the following types: a load that is applied steadily ("dead" load); a load that fluctuates, with slow or fast changes in magnitude ("live" load); a load that is applied suddenly (shock load); or a load due to impact in some form. Stress is a form of load that may be applied to a component. Personnel need to be aware how stress may be applied and how it effects the component. EO 1.1 DEFINE the following terms: a. Stress b. Tensile stress c. Compressive stress d. Shear stress e. Compressibility EO 1.2 DISTINGUISH between the following types of stresses by the direction in which stress is applied. a. Tensile b. Compressive c. Shear When a metal is subjected to a load (force), it is distorted or deformed, no matter how strong the metal or light the load. If the load is small, the distortion will probably disappear when the load is removed. The intensity, or degree, of distortion is known as strain. If the distortion disappears and the metal returns to its original dimensions upon removal of the load, the strain is called elastic strain. If the distortion disappears and the metal remains distorted, the strain type is called plastic strain. Strain will be discussed in more detail in the next chapter. When a load is applied to metal, the atomic structure itself is strained, being compressed, warped or extended in the process. The atoms comprising a metal are arranged in a certain geometric pattern, specific for that particular metal or alloy, and are maintained in that pattern by interatomic forces. When so arranged, the atoms are in their state of minimum energy and tend to remain in that arrangement. Work must be done on the metal (that is, energy must be added) to distort the atomic pattern. (Work is equal to force times the distance the force moves.) Rev. 0 Page 1 MS-02