18.6: Hooke's Law
Hooke's law, a pivotal principle in material science, establishes that the strain a material undergoes is directly proportional to the applied stress, defined by a factor called the modulus of elasticity or Young's modulus.
The implementation of Hooke's law holds true until the material reaches its proportional limit. Beyond this point, the stress-strain relationship becomes nonlinear. This limit often coincides with the yield point for materials that are ductile in nature. However, identifying this limit for other types of materials can be challenging due to the non-linearity of the stress-strain relationship.
Materials are categorized into two main types based on mechanical characteristics, such as isotropic and anisotropic. Isotropic materials, such as metals, exhibit consistent properties regardless of the direction of the load. As such, their stress-strain relationship, including the modulus of elasticity, remains constant irrespective of the direction of the applied stress. On the other hand, anisotropic materials like fiber-reinforced composites display mechanical properties that depend on the load's direction. These materials consist of fibers of a robust material embedded within a softer matrix. The moduli of elasticity along directions parallel and perpendicular to the fibers differ significantly, resulting in varying resistances to load. The maximum strength of these materials can be achieved when the fibers align in the same direction as the load.
