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von Mises yield criterion
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<h2 id="mathematical-formulation">Mathematical formulation</h2> <p>Mathematically the von Mises <a href="/facts/Yield_(engineering)/mrSg02gW">yield</a> criterion is expressed as: </p> J 2 = k 2 {\displaystyle J_{2}=k^{2}\,\!} <p>Here k {\displaystyle k} is <a href="/facts/Yield_(engineering)/mrSg02gW">yield</a> stress of the material in pure shear. As shown later in this article, at the onset of yielding, the magnitude of the shear yield stress in pure shear is √3 times lower than the tensile yield stress in the case of simple tension. Thus, we have: </p> k = σ y 3 {\displaystyle k={\frac {\sigma _{y}}{\sqrt {3}}}} <p>where σ y {\displaystyle \sigma _{y}} is tensile yield strength of the material. If we set the von Mises stress equal to the yield strength and combine the above equations, the von Mises yield criterion is written as: </p> σ v = σ y = 3 J 2 {\displaystyle \sigma _{v}=\sigma _{y}={\sqrt {3J_{2}}}} <p>or </p> σ v 2 = 3 J 2 = 3 k 2 {\displaystyle \sigma _{v}^{2}=3J_{2}=3k^{2}} <p>Substituting J 2 {\displaystyle J_{2}} with the <a href="/facts/Cauchy_stress_tensor/5MsXPQVH">Cauchy stress tensor</a> components, we get </p> σ v 2 = 1 2 [ ( σ 11 − σ 22 ) 2 + ( σ 22 − σ 33 ) 2 + ( σ 33 − σ 11 ) 2 + 6 ( σ 23 2 + σ 31 2 + σ 12 2 ) ] = 3 2 s i j s i j {\displaystyle \sigma _{\text{v}}^{2}={\frac {1}{2}}\left[(\sigma _{11}-\sigma _{22})^{2}+(\sigma _{22}-\sigma _{33})^{2}+(\sigma _{33}-\sigma _{11})^{2}+6\left(\sigma _{23}^{2}+\sigma _{31}^{2}+\sigma _{12}^{2}\right)\right]={\frac {3}{2}}s_{ij}s_{ij}} , <p>where s {\displaystyle s} is called deviatoric stress. This equation defines the <a href="/facts/Yield_surface/nM09XVJe">yield surface</a> as a circular cylinder (See Figure) whose yield curve, or intersection with the deviatoric plane, is a circle with radius 2 k {\displaystyle {\sqrt {2}}k} , or 2 3 σ y {\textstyle {\sqrt {\frac {2}{3}}}\sigma _{y}} . This implies that the yield condition is independent of hydrostatic stresses. </p> <h2 id="reduced-von-mises-equation-for-different-stress-conditions">Reduced von Mises equation for different stress conditions</h2> <h3>Uniaxial (1D) stress</h3> <p>In the case of uniaxial stress or simple tension, σ 1 ≠ 0 , σ 3 = σ 2 = 0 {\displaystyle \sigma _{1}\neq 0,\sigma _{3}=\sigma _{2}=0} , the von Mises criterion simply reduces to </p> σ 1 = σ y {\displaystyle \sigma _{1}=\sigma _{\text{y}}\,\!} , <p>which means the material starts to yield when σ 1 {\displaystyle \sigma _{1}} reaches the <i>yield strength</i> of the material σ y {\displaystyle \sigma _{\text{y}}} , in agreement with the definition of tensile (or compressive) yield strength. </p> <h3>Multi-axial (2D or 3D) stress</h3> <p>An equivalent tensile stress or equivalent von-Mises stress, σ v {\displaystyle \sigma _{\text{v}}} is used to predict yielding of materials under multiaxial loading conditions using results from simple uniaxial tensile tests. Thus, we define </p> σ v = 3 J 2 = ( σ 11 − σ 22 ) 2 + ( σ 22 − σ 33 ) 2 + ( σ 33 − σ 11 ) 2 + 6 ( σ 12 2 + σ 23 2 + σ 31 2 ) 2 = ( σ 1 − σ 2 ) 2 + ( σ 2 − σ 3 ) 2 + ( σ 3 − σ 1 ) 2 2 = 3 2 s i j s i j {\displaystyle {\begin{aligned}\sigma _{\text{v}}&={\sqrt {3J_{2}}}\\&={\sqrt {\frac {(\sigma _{11}-\sigma _{22})^{2}+(\sigma _{22}-\sigma _{33})^{2}+\left(\sigma _{33}-\sigma _{11})^{2}+6(\sigma _{12}^{2}+\sigma _{23}^{2}+\sigma _{31}^{2}\right)}{2}}}\\&={\sqrt {\frac {(\sigma _{1}-\sigma _{2})^{2}+(\sigma _{2}-\sigma _{3})^{2}+(\sigma _{3}-\sigma _{1})^{2}}{2}}}\\&={\sqrt {{\frac {3}{2}}s_{ij}s_{ij}}}\end{aligned}}\,\!} <p>where s i j {\displaystyle s_{ij}} are components of <a href="/facts/Cauchy_stress_tensor/5MsXPQVH">stress deviator tensor</a> σ dev {\displaystyle {\boldsymbol {\sigma }}^{\text{dev}}} : </p> σ dev = σ − tr ( σ ) 3 I {\displaystyle {\boldsymbol {\sigma }}^{\text{dev}}={\boldsymbol {\sigma }}-{\frac {\operatorname {tr} \left({\boldsymbol {\sigma }}\right)}{3}}\mathbf {I} \,\!} . <p>In this case, yielding occurs when the equivalent stress, σ v {\displaystyle \sigma _{\text{v}}} , reaches the yield strength of the material in simple tension, σ y {\displaystyle \sigma _{\text{y}}} . As an example, the stress state of a steel beam in compression differs from the stress state of a steel axle under torsion, even if both specimens are of the same material. In view of the stress tensor, which fully describes the stress state, this difference manifests in six <a href="/facts/Degrees_of_freedom_(mechanics)/2BqcdnLA">degrees of freedom</a>, because the stress tensor has six independent components. Therefore, it is difficult to tell which of the two specimens is closer to the yield point or has even reached it. However, by means of the von Mises yield criterion, which depends solely on the value of the scalar von Mises stress, i.e., one degree of freedom, this comparison is straightforward: A larger von Mises value implies that the material is closer to the yield point. </p><p>In the case of pure <a href="/facts/Shear_stress/aWWnzIhE">shear stress</a>, σ 12 = σ 21 ≠ 0 {\displaystyle \sigma _{12}=\sigma _{21}\neq 0} , while all other σ i j = 0 {\displaystyle \sigma _{ij}=0} , von Mises criterion becomes: </p> σ 12 = k = σ y 3 {\displaystyle \sigma _{12}=k={\frac {\sigma _{y}}{\sqrt {3}}}\,\!} . <p>This means that, at the onset of yielding, the magnitude of the shear stress in pure shear is 3 {\displaystyle {\sqrt {3}}} times lower than the yield stress in the case of simple tension. The von Mises yield criterion for pure shear stress, expressed in principal stresses, is </p> ( σ 1 − σ 2 ) 2 + ( σ 2 − σ 3 ) 2 + ( σ 1 − σ 3 ) 2 = 2 σ y 2 {\displaystyle (\sigma _{1}-\sigma _{2})^{2}+(\sigma _{2}-\sigma _{3})^{2}+(\sigma _{1}-\sigma _{3})^{2}=2\sigma _{y}^{2}\,\!} <p>In the case of principal plane stress, σ 3 = 0 {\displaystyle \sigma _{3}=0} and σ 12 = σ 23 = σ 31 = 0 {\displaystyle \sigma _{12}=\sigma _{23}=\sigma _{31}=0} , the von Mises criterion becomes: </p> σ 1 2 − σ 1 σ 2 + σ 2 2 = 3 k 2 = σ y 2 {\displaystyle \sigma _{1}^{2}-\sigma _{1}\sigma _{2}+\sigma _{2}^{2}=3k^{2}=\sigma _{y}^{2}\,\!} <p>This equation represents an ellipse in the plane σ 1 − σ 2 {\displaystyle \sigma _{1}-\sigma _{2}} . </p> <h3>Summary</h3> <table><tbody><tr><th>State of stress</th><th>Boundary conditions</th><th>von Mises equations</th></tr><tr><td>General</td><td>No restrictions</td><td> σ v = 1 2 [ ( σ 11 − σ 22 ) 2 + ( σ 22 − σ 33 ) 2 + ( σ 33 − σ 11 ) 2 ] + 3 ( σ 12 2 + σ 23 2 + σ 31 2 ) {\displaystyle \sigma _{\text{v}}={\sqrt {{\frac {1}{2}}\left[(\sigma _{11}-\sigma _{22})^{2}+(\sigma _{22}-\sigma _{33})^{2}+(\sigma _{33}-\sigma _{11})^{2}\right]+3\left(\sigma _{12}^{2}+\sigma _{23}^{2}+\sigma _{31}^{2}\right)}}} </td></tr><tr><td>Principal stresses</td><td> σ 12 = σ 31 = σ 23 = 0 {\displaystyle \sigma _{12}=\sigma _{31}=\sigma _{23}=0\!} </td><td> σ v = 1 2 [ ( σ 1 − σ 2 ) 2 + ( σ 2 − σ 3 ) 2 + ( σ 3 − σ 1 ) 2 ] {\displaystyle \sigma _{\text{v}}={\sqrt {{\frac {1}{2}}\left[(\sigma _{1}-\sigma _{2})^{2}+(\sigma _{2}-\sigma _{3})^{2}+(\sigma _{3}-\sigma _{1})^{2}\right]}}} </td></tr><tr><td>General plane stress</td><td> σ 3 = 0 σ 31 = σ 23 = 0 {\displaystyle {\begin{aligned}\sigma _{3}&=0\!\\\sigma _{31}&=\sigma _{23}=0\!\end{aligned}}} </td><td> σ v = σ 11 2 − σ 11 σ 22 + σ 22 2 + 3 σ 12 2 {\displaystyle \sigma _{\text{v}}={\sqrt {\sigma _{11}^{2}-\sigma _{11}\sigma _{22}+\sigma _{22}^{2}+3\sigma _{12}^{2}}}\!} </td></tr><tr><td>Principal plane stress</td><td> σ 3 = 0 σ 12 = σ 31 = σ 23 = 0 {\displaystyle {\begin{aligned}\sigma _{3}&=0\!\\\sigma _{12}&=\sigma _{31}=\sigma _{23}=0\!\end{aligned}}} </td><td> σ v = σ 1 2 + σ 2 2 − σ 1 σ 2 {\displaystyle \sigma _{\text{v}}={\sqrt {\sigma _{1}^{2}+\sigma _{2}^{2}-\sigma _{1}\sigma _{2}}}\!} </td></tr><tr><td>Pure shear</td><td> σ 1 = σ 2 = σ 3 = 0 σ 31 = σ 23 = 0 {\displaystyle {\begin{aligned}\sigma _{1}&=\sigma _{2}=\sigma _{3}=0\!\\\sigma _{31}&=\sigma _{23}=0\!\end{aligned}}} </td><td> σ v = 3 | σ 12 | {\displaystyle \sigma _{\text{v}}={\sqrt {3}}|\sigma _{12}|\!} </td></tr><tr><td>Uniaxial</td><td> σ 2 = σ 3 = 0 σ 12 = σ 31 = σ 23 = 0 {\displaystyle {\begin{aligned}\sigma _{2}&=\sigma _{3}=0\!\\\sigma _{12}&=\sigma _{31}=\sigma _{23}=0\!\end{aligned}}} </td><td> σ v = σ 1 {\displaystyle \sigma _{\text{v}}=\sigma _{1}\!} </td></tr></tbody></table> <h2 id="physical-interpretation-of-the-von-mises-yield-criterion">Physical interpretation of the von Mises yield criterion</h2> <p><a href="/facts/Heinrich_Hencky/II2oh7WG">Hencky</a> (1924) offered a physical interpretation of von Mises criterion suggesting that yielding begins when the elastic energy of distortion reaches a critical value.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> For this reason, the von Mises criterion is also known as the maximum distortion strain energy criterion. This comes from the relation between J 2 {\displaystyle J_{2}} and the elastic strain energy of distortion W D {\displaystyle W_{\text{D}}} : </p> W D = J 2 2 G {\displaystyle W_{\text{D}}={\frac {J_{2}}{2G}}\,\!} with the elastic shear modulus G = E 2 ( 1 + ν ) {\displaystyle G={\frac {E}{2(1+\nu )}}\,\!} . <p>In 1937 <a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> Arpad L. Nadai suggested that yielding begins when the <a href="/facts/Cauchy_stress_tensor/5MsXPQVH">octahedral shear stress</a> reaches a critical value, i.e. the octahedral shear stress of the material at yield in simple tension. In this case, the von Mises yield criterion is also known as the maximum octahedral shear stress criterion in view of the direct proportionality that exists between J 2 {\displaystyle J_{2}} and the octahedral shear stress, τ oct {\displaystyle \tau _{\text{oct}}} , which by definition is </p> τ oct = 2 3 J 2 {\displaystyle \tau _{\text{oct}}={\sqrt {{\frac {2}{3}}J_{2}}}\,\!} <p>thus we have </p> τ oct = 2 3 σ y {\displaystyle \tau _{\text{oct}}={\frac {\sqrt {2}}{3}}\sigma _{\text{y}}\,\!} Strain energy density consists of two components - volumetric or dialational and distortional. Volumetric component is responsible for change in volume without any change in shape. Distortional component is responsible for shear deformation or change in shape. <h2 id="practical-engineering-usage-of-the-von-mises-yield-criterion">Practical engineering usage of the von Mises yield criterion</h2> <p>As shown in the equations above, the use of the von Mises criterion as a yield criterion is only exactly applicable when the following material properties are isotropic, and the ratio of the shear yield strength to the tensile yield strength has the following value:<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> F s y F t y = 1 3 ≈ 0.577 {\displaystyle {\frac {F_{sy}}{F_{ty}}}={\frac {1}{\sqrt {3}}}\approx 0.577\!} <p>Since no material will have this ratio precisely, in practice it is necessary to use engineering judgement to decide what failure theory is appropriate for a given material. Alternately, for use of the Tresca theory, the same ratio is defined as 1/2. </p><p>The yield margin of safety is written as </p> M S yld = F y σ v − 1 {\displaystyle MS_{\text{yld}}={\frac {F_{y}}{\sigma _{\text{v}}}}-1} <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Yield_surface/nM09XVJe">Yield surface</a></li> <li><a href="/facts/Huber%2527s_equation/IGomTqvI">Huber's equation</a></li> <li><a href="/facts/Henri_Tresca/RFGy7FTe">Henri Tresca</a></li> <li><a href="/facts/Stephen_Timoshenko/A8x2HG97">Stephen Timoshenko</a></li> <li><a href="/facts/Mohr%25E2%2580%2593Coulomb_theory/UK40uyWc">Mohr–Coulomb theory</a></li> <li><a href="/facts/Hoek%25E2%2580%2593Brown_failure_criterion/AlySgSwB">Hoek–Brown failure criterion</a></li> <li><a href="/facts/Yield_(engineering)/mrSg02gW">Yield (engineering)</a></li> <li><a href="/facts/Stress_(physics)/ErAXDbbd">Stress</a></li> <li><a href="/facts/Strain_(materials_science)/xK7R59oI">Strain</a></li> <li><a href="/facts/3-D_elasticity/rQ7PFtH5">3-D elasticity</a></li> <li><a href="/facts/Bigoni%25E2%2580%2593Piccolroaz_yield_criterion/YfX9QK3o">Bigoni–Piccolroaz yield criterion</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Von Mises Criterion (Maximum Distortion Energy Criterion)". Engineer's edge. Retrieved 8 February 2018. <a href="https://www.engineersedge.com/material_science/von_mises.htm" target="_blank">https://www.engineersedge.com/material_science/von_mises.htm</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>von Mises, R. (1913). "Mechanik der festen Körper im plastisch-deformablen Zustand". Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-Physikalische Klasse. 1913 (1): 582–592. <a href="http://www.digizeitschriften.de/dms/resolveppn/?PID=GDZPPN002503697" target="_blank">http://www.digizeitschriften.de/dms/resolveppn/?PID=GDZPPN002503697</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Jones, Robert Millard (2009). Deformation Theory of Plasticity, p. 151, Section 4.5.6. Bull Ridge Corporation. ISBN 9780978722319. Retrieved 2017-06-11. <a href="9780978722319" target="_blank">9780978722319</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>von Mises, R. (1913). "Mechanik der festen Körper im plastisch-deformablen Zustand". Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-Physikalische Klasse. 1913 (1): 582–592. <a href="http://www.digizeitschriften.de/dms/resolveppn/?PID=GDZPPN002503697" target="_blank">http://www.digizeitschriften.de/dms/resolveppn/?PID=GDZPPN002503697</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Ford (1963). Advanced Mechanics of Materials. London: Longmans. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Huber, M. T. (1904). "Właściwa praca odkształcenia jako miara wytezenia materiału". Czasopismo Techniczne. 22. Lwów. Translated as "Specific Work of Strain as a Measure of Material Effort". Archives of Mechanics. 56: 173–190. 2004. <a href="http://am.ippt.pan.pl/am/article/viewFile/v56p173/pdf" target="_blank">http://am.ippt.pan.pl/am/article/viewFile/v56p173/pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Hill, R. (1950). The Mathematical Theory of Plasticity. Oxford: Clarendon Press. <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Timoshenko, S. (1953). History of strength of materials. New York: McGraw-Hill. <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Hencky, H. (1924). "Zur Theorie plastischer Deformationen und der hierdurch im Material hervorgerufenen Nachspannngen". Z. Angew. Math. Mech. 4 (4): 323–334. Bibcode:1924ZaMM....4..323H. doi:10.1002/zamm.19240040405. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Hill, R. (1950). The Mathematical Theory of Plasticity. Oxford: Clarendon Press. <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>S. M. A. Kazimi. (1982). Solid Mechanics. Tata McGraw-Hill. ISBN 0-07-451715-5 <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Nadai, A. (1950). Theory of Flow and Fracture of Solids. New York: McGraw-Hill. <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> </ol>