Residual stress determination

A 3-element target strain gauge rosette is bonded to the component surface and connected to a strain indicator. 

A drill holder is aligned with the gauge.  A hole is drilled through the gauge and into the component using an inverted cone cutter.  

Relaxation of residual stresses at the hole boundary results in changes in strain gauge output.

The hole diameter is, typically, 2 mm.  Drilling usually proceeds in 11 increments to a maximum depth of 1,4 mm with the strains measured at each increment.

A 1/2 size gauge is also available.
Residual stresses are calculated from relaxed strains using software based on the `integral method' (after G. S. Schajer).  This method is capable of detecting high stress gradients and is not limited to use with uniform stress distributions.

The Stresscraft strain-to-stress program smooths the input strains and calculates the distributions of stresses to a depth of 1,27 mm over a number of pre-set calculation increments.

A single results data sheet is produced for  each gauge.  This sheet includes : 

  • a table of strains and stresses,

  • distributions of stresses vs. depth,

  • the gauge layout and directions of principal stresses.

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