Stress concentration

In <a href="/facts/Solid_mechanics/e1Yq50IS">solid mechanics</a>, a stress concentration (also called a stress raiser or a stress riser or notch sensitivity) is a location in an object where the <a href="/facts/Stress_(mechanics)/ErAXDbbd">stress</a> is significantly greater than the surrounding region. Stress concentrations 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 <a href="/facts/Holes/zkt0gnbV">holes</a>, <a href="/facts/Groove_(engineering)/3UXJSVdf">grooves</a>, <a href="/facts/Notch_(engineering)/UIYWJNaj">notches</a> and <a href="/facts/Fillet_(mechanics)/CJ0HPCVC">fillets</a>. Stress concentrations may also occur from accidental damage such as nicks and scratches.
The degree of concentration of a discontinuity under typically <a href="/facts/Tension_(physics)/waNGYp3a">tensile</a> loads can be expressed as a non-dimensional stress concentration factor 
 
 
 
 
 K
 
 t
 
 
 
 
 {\displaystyle K_{t}}
 
, which is the ratio of the highest stress to the nominal far field stress. For a circular hole in an infinite plate, 
 
 
 
 
 K
 
 t
 
 
 =
 3
 
 
 {\displaystyle K_{t}=3}
 
. The stress concentration factor should not be confused with the <a href="/facts/Stress_intensity_factor/pLrUo683">stress intensity factor</a>, which is used to define the effect of a <a href="/facts/Fracture/nxDNAj0d">crack</a> on the stresses in the region around a crack tip.
For <a href="/facts/Ductile/SBJsahEk">ductile</a> materials, large loads can cause localised <a href="/facts/Plastic_deformation/z1LEmkQX">plastic deformation</a> or <a href="/facts/Yield_(engineering)/mrSg02gW">yielding</a> that will typically occur first at a stress concentration allowing a redistribution of stress and enabling the component to continue to carry load. <a href="/facts/Brittle/cn27H2vg">Brittle</a> materials will typically fail at the stress concentration. However, repeated low level loading may cause a <a href="/facts/Fatigue_(material)/zmJY8hMt">fatigue</a> crack to initiate and slowly grow at a stress concentration leading to the failure of even ductile materials. Fatigue cracks always start at stress raisers, so removing such defects increases the <a href="/facts/Fatigue_strength/vXjgmJSn">fatigue strength</a>.

Stress concentration open-in-new

Stress concentration