Primary and shear stresses (Sx, Sy, Sz, τxy, τxz, τyz) are always oriented (at right-angles) as shown in the [calculator] image.
Combined stresses refer to the combination of more than one primary and/or shear stress into 2-D or 3-D stress vectors that eliminate shear stresses but include their effects. These combination techniques only apply to stresses (primary and combined) that obey Hooke's law. The two best known and most used combined stresses are principal and equivalent.
Principal stresses are the two or three primary stress vectors (Sx, Sy and/or Sz) re-vectored (together) by the shear stresses (τxy, τxz and/or τyz), the largest of which is normally used in fatigue calculations
(see CalQlata’s Fatigue calculator).
An equivalent stress is a single stress vector resolved mathematically from all the primary and shear stresses (Sx, Sy, Sz, τxy, τxz, τyz). An equivalent stress will be more conservative than the largest principal stress and tends to be used for extreme design loads.
The two most used equivalent stresses were devised by Hencky & Von-Mises (strain energy) and St Venant (principal strain).
Combined Stress calculates the combined; principal (including cosines) and equivalent (Hencky/Von-Mises and St Venant) stresses from your coincident primary and shear stress input data.
The combined stress calculator has one calculation option that produces all of the various combined stresses and cosines at the same time, including a self-check principal equivalent stress that uses different formulas to generate a Hencky/Von Mises equivalent stress via the principal stresses.
Combined Stress imports data from CaQlata’s Pipe Strength calculator
For help using this calculator, including its internal self-checking facility, see Technical Help
Combined Stress Calculator - Options
Combined Stress converts uni-directional stresses into their various 3-D equivalents along with their orientations.
and the combined stress calculator will provide:
The three primary stresses; sx, sy & sz
The three shear stresses; τxy, τxz & τyz
The three Principal stresses; S1, S2, S3
The equivalent stress from primary and shear stresses
The equivalent stress from Principal stresses
St Venant’s equivalent stress
The three cosine displacements per Principal stress
Combined Stress includes a data import facility from CalQlata's Pipe calculator
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