Fracture
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Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially, it is called a shear crack, slip band, or dislocation.
Ductile failure of a metallic specimen strained axially
Brittle fracture in glass
Fracture of an aluminum crank arm of a bicycle, where the bright areas display a brittle fracture, and the dark areas show fatigue fracture
Brittle cleavage fracture surface from a scanning electron microscope
Stress (mechanics)
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In continuum mechanics, stress is a physical quantity that describes forces present during deformation. For example, an object being pulled apart, such as a stretched elastic band, is subject to tensile stress and may undergo elongation. An object being pushed together, such as a crumpled sponge, is subject to compressive stress and may undergo shortening. The greater the force and the smaller the cross-sectional area of the body on which it acts, the greater the stress. Stress has dimension of force per area, with SI units of newtons per square meter (N/m2) or pascal (Pa).
Residual stresses inside a plastic protractor are revealed by the polarized light.
Roman-era bridge in Switzerland. The stone arches in the bridge are subject to compressive stresses.
Inca bridge on the Apurimac River. The rope in the bridge is subject to tensile stresses.
Glass vase with the craquelé effect. The cracks are the result of brief but intense stress created when the semi-molten piece is briefly dipped in water.