ストレス

Stress is the magnitude of applied force per unit area acting on an object. It quantifies the intensity of internal forces generated when an external force causes deformation. The SI unit of stress is the pascal, defined as one newton of force exerted over one square meter of surface area. Stress is a tensor quantity that describes how forces are distributed across a body's surface.

Stress is categorized into four types based on the direction of applied forces and resulting deformation. Tensile stress occurs when forces pull an object, increasing its length. Compressive stress occurs when forces squeeze an object, decreasing its length. Volumetric stress results from forces acting on all dimensions, changing the object's volume. Shear stress occurs when forces act parallel to the cross-sectional area, changing the object's shape.

Tensile stress results from forces pulling an object apart, causing an increase in length. Compressive stress results from forces squeezing or pressing an object, causing a decrease in length. Both are categorized by how the deforming force affects the object's length dimension. The magnitude of stress is calculated the same way for both types: force per unit area.

When an external force is applied to a body, it undergoes deformation. Simultaneously, an internal restoring force develops within the body to counteract the applied force. This restoring force is equal in magnitude to the applied force but acts in the opposite direction. The restoring force per unit area is what we measure as stress.

Volumetric stress, also called volume stress, occurs when applied forces act on all sides or dimensions of a body simultaneously, resulting in a change in the body's overall volume. Unlike tensile or compressive stress, which primarily affect length, volumetric stress affects the three-dimensional size of an object. This type of stress is common in applications involving pressure on all surfaces.

Shear stress occurs when the direction of the applied force is parallel to the cross-sectional area of an object, resulting in a change in the object's shape rather than its size. The deforming force causes layers within the material to slide past one another. Understanding shear stress is essential for solving stress and strain problems in engineering applications.

Stress quantifies how forces affect materials and structures, enabling engineers to predict deformation and failure. By calculating stress as force per unit area, professionals can compare material behavior under different loading conditions. Stress analysis is fundamental to designing safe structures and understanding material properties like elasticity and plasticity.