Internal force lines are denser near the hole A<unk>  (also called a stress raiser or a stress riser) is a location in an object where the stress is significantly greater than the surrounding region.<unk> s occur when there are irregularities in the geometry or material of a structural component that cause an interruption to the flow of stress. This arises from such details as holes, grooves, notches and fillets.<unk> s may also occur from accidental damage such as nicks and scratches. The degree of<unk>  of a discontinuity under typically tensile loads can be expressed as a non-dimensional<unk>  factor , which is the ratio of the highest stress to the nominal far field stress. For a circular hole in an infinite plate, . The<unk>  factor should not be confused with the stress intensity factor, which is used to define the effect of a crack on the stresses in the region around a crack tip. For ductile materials, large loads can cause localised plastic deformation or yielding that will typically occur first at a<unk>  allowing a redistribution of stress and enabling the component to continue to carry load. Brittle materials will typically fail at the<unk> . However, repeated low level loading may cause a fatigue crack to initiate and slowly grow at a<unk>  leading to the failure of even ductile materials. Fatigue cracks always start at stress raisers, so removing such defects increases the fatigue strength. Description ==<unk> s occur when there are irregularities in the geometry or material of a structural component that cause an interruption to the flow of stress. Geometric discontinuities cause an object to experience a localised increase in stress. Examples of shapes that cause<unk> s are sharp internal corners, holes, and sudden changes in the cross-sectional area of the object as well as unintentional damage such as nicks, scratches and cracks. High local stresses can cause objects to fail more quickly, so engineers typically design the geometry to minimize<unk> s. Material discontinuities, such as inclusions in metals, may also concentrate the stress. Inclusions on the surface of a component may be broken from machining during manufacture leading to microcracks that grow in service from cyclic loading. Internally, the failure of the interfaces around inclusions during loading may lead to static failure by microvoid coalescence.
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