The elastic modulus, also known as Young's modulus, is one of the most important and characteristic mechanical properties of elastic materials. It characterizes the ease with which an object undergoes elastic deformation and is denoted by. It is defined as the ratio of stress to strain when an ideal material undergoes small deformation. It is expressed as the force per unit area, with units of . The properties of the modulus depend on the nature of the deformation. The modulus under shear deformation is called the shear modulus, denoted by ; the modulus under compressive deformation is called the compressive modulus, denoted by . The reciprocal of the modulus is called the compliance modulus, denoted by .
The yield strength and ultimate tensile strength obtained in tensile tests reflect the material's ability to withstand forces, while elongation or reduction of section reflects the material's ability to undergo plastic deformation. To represent the ease with which a material resists deformation within its elastic range, in practical engineering structures, the elastic modulus E is usually expressed in terms of the stiffness of the component. This is because once a component is designed according to stress, its stiffness is judged by the amount of deformation caused by the load it experiences during service within its elastic deformation range.
As can be seen from the above formula, to improve the stiffness of a component, that is, to reduce its elastic deformation, materials with high elastic modulus and appropriately increased cross-sectional area for load bearing can be selected. The importance of stiffness lies in its determination of the stability of the component during service, which is especially important for slender rods and thin-walled components. Therefore, elastic modulus is an important mechanical performance indicator that is frequently used in the theoretical analysis and design calculation of components.
