Deep hole drilling measurement technique

[1] DHD is a semi-destructive mechanical strain relaxation (MSR) technique, which seeks to measure the distribution of stresses along the axis of a drilled reference hole.

The process is unique in its ability to measure residual stresses at a microscopic level with a penetration of over 750 millimetres (30 in), without total destruction of the original component.

[3] For engineering metals, the trepanning process is typically performed using electrical discharge machining (EDM) to minimise the introduction of further stresses during the cutting.

Firstly, reference bushes are attached to the front and back surfaces of the component at the measurement location, to minimise "bell-mouthing" and assist with aligning the data sets during analysis.

The DHD technique uses an elastic analysis to convert the measured distortions of the reference hole into a residual stress profile.

[6] A lower elastic modulus will result in larger distortions for a given stress release, meaning a higher measurement resolution and thus a greater achievable accuracy.