Mechanical properties of engineering materials

TLDR: In this article, the authors discuss the mechanical properties of engineering materials and define the direct strain and direct strain measured along the line of action of the direct force on a structural member.

Abstract: This chapter discusses the mechanical properties of engineering materials. The mechanical properties of those materials that are commonly used in engineering need to be understood to determine the size and shape of each member to carry its respective load. First, it is necessary to define some of these properties. When a direct force is applied to a structural member it tends to lengthen if the force is tensile, or to shorten if the force is compressive. Strain is a measure of the deformation, and direct strain is the deformation determined along the line of action of the direct force. If a length of mild steel bar is subjected to an axial tensile load the extension of the specimen is, at first, very small and would be undetectable by direct measurement, such as with a scale. It is necessary, therefore, to make use of an instrument known as an extensometer. This instrument is clamped over a known length of the specimen, and the elongation of that length is magnified so that it can be determined easily. As the tensile load increases so the extension increases until a point is reached where the extension increases rapidly and becomes measurable by dividers and a scale.