Stresses

Stresses refer to internal forces that develop within a material in response to externally applied loads or internal constraints. In physics and engineering, stress is defined as force per unit area and is typically categorized as normal stress (acting perpendicular to a plane) and shear stress (acting parallel to the plane). Normal stress can be tensile or compressive. The state of stress at a point is described by a stress tensor, and principal stresses are the eigenvalues of this tensor.

In linear elastic materials, Hooke's law relates stress and strain: sigma = E * epsilon for uniaxial loading, where E is Young's modulus. The behavior becomes more complex in anisotropic or inelastic materials, where yield strength, ultimate tensile strength, creep, and fatigue govern performance and safety.

Design and analysis use concepts such as yield criteria, safety factors, and stress concentration factors around holes or notches. Measurement methods include strain gauges, extensometers, and non-destructive techniques; numerical methods such as finite element analysis predict detailed stress distributions.

Stresses can also describe psychological or physiological states arising from perceived challenges or threats. Acute stress is short term; chronic stress persists and may contribute to health problems. The stress response involves the autonomic nervous system and the hypothalamic-pituitary-adrenal axis, releasing cortisol and adrenaline.

Assessment and management include time management, social support, relaxation techniques, and professional help when needed. Perceived measures such as the Perceived Stress Scale are used in research, while lifestyle and cognitive strategies help reduce impact on mood, sleep, and cardiovascular function.