Developed in the early 1960’s under Bernie Langer at the Bettis Atomic Power Laboratory

Basis for SDB-63, Section III of the ASME Boiler and Pressure Vessel Code, and Section VIII, Division 2 of the ASME Boiler and Pressure Vessel Code (Appendix 4)

ASME "Design by Analysis" approach is based on Tresca (shear stress) failure theory with an elastic-perfectly plastic stress-strain curve

Tresca failure theory states that "yielding will occur when the maximum shear stress equals the shear stress at yielding in an uniaxial-tension test"

Maximum Shear Stress/2 = (Maximum Principal Stress – Minimum Principal Stress)/2

Max Shear Stress = Max Principal Stress – Min Principal Stress => Stress Intensity

Tresca failure theory is less accurate than Von Mises (Distortion-Energy) failure theory, but slightly more conservative and simpler

Definitions

Normal Stress: Stress component normal to the plane reference

Shear Stress: Stress component tangent to plane of reference

Membrane Stress: Uniform normal stress

Bending Stress: Linear normal stress

General Stress: Stress away from any discontinuities

Local Stress: Stress near a discontinuity

Primary Stress: Stress developed by imposed loading that is necessary to satisfy the simple laws of equilibrium of external and internal forces and moments

Secondary Stress: Stress developed by constraint of adjacent parts or self-constraint of structure – Secondary stresses are self-limiting – They can be relieved by local yielding minor distortions

Peak Stress: Localized stress that does not cause any noticeable distortion and is objectionable only as a possible source of fatigue crack or brittle fracture

Stress Intensity: Difference between maximum and minimum principal stress

Design Stress Intensity: Allowable Stress Intensity – typically the lesser of 2/3 the Yield Stress (YS) or 1/3 the Ultimate Tensile Stress (UTS)

Five Basic Stress Categories

1. General Primary Membrane Stress Intensity (P_m)
2. Local Membrane Stress Intensity (P_L) – Primary Stress
3. Primary Membrane Plus Primary Bending Stress (P_L + P_b) – either General or Local Membrane Stress
4. Primary Plus Secondary Stress Intensity (P_L + P_b + Q)
5. Peak Stress Intensity (P_L + P_b + Q + F)