Formula Home Failure Criteria Introduction Yield of Ductile Materials Failure of Brittle Materials Failure of Brittle & Ductile Materials Prevention/Diagnosis Calculators Ductile Materials Yield Brittle Materials Failure Related Subjects Stress Strain Hooke's Law Resources Bibliography
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 Maximum Shear Stress Criterion The maximum shear stress criterion, also known as Tresca's or Guest's criterion, is often used to predict the yielding of ductile materials. Yield in ductile materials is usually caused by the slippage of crystal planes along the maximum shear stress surface. Therefore, a given point in the body is considered safe as long as the maximum shear stress at that point is under the yield shear stress sy obtained from a uniaxial tensile test. With respect to 2D stress, the maximum shear stress is related to the difference in the two principal stresses (see Mohr's Circle). Therefore, the criterion requires the principal stress difference, along with the principal stresses themselves, to be less than the yield shear stress, Graphically, the maximum shear stress criterion requires that the two principal stresses be within the green zone indicated below,
 Von Mises Criterion The von Mises Criterion (1913), also known as the maximum distortion energy criterion, octahedral shear stress theory, or Maxwell-Huber-Hencky-von Mises theory, is often used to estimate the yield of ductile materials. The von Mises criterion states that failure occurs when the energy of distortion reaches the same energy for yield/failure in uniaxial tension. Mathematically, this is expressed as, In the cases of plane stress, s3 = 0. The von Mises criterion reduces to, This equation represents a principal stress ellipse as illustrated in the following figure, Also shown on the figure is the maximum shear stress criterion (dashed line). This theory is more conservative than the von Mises criterion since it lies inside the von Mises ellipse. In addition to bounding the principal stresses to prevent ductile failure, the von Mises criterion also gives a reasonable estimation of fatigue failure, especially in cases of repeated tensile and tensile-shear loading.
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Injection Molding Design Guide

Guide for high quality and cost-effective plastic injection molding.

STEM Career Outlook

Wages, employment opportunities, and growth projections for STEM jobs.

Mechanical Engineers Outlook

Guide for those interested in becoming a mechanical engineer. Includes qualifications, pay, and job duties.

Selecting the Right 3D Printer

Discover how to choose the right 3D printer for your needs and the key performance attributes to consider.