How deep is a deep hole?
Deep hole drilling sounds like a technique that would be used in the oil industry for extracting oil from kilometres inside the Earth. In fact, it is a means of measuring residual stress in complex engineering components, and the holes drilled are only a few centimetres ‘deep’. VEQTER Ltd is a leading-edge spin-out company employing this unique technology, as Managing Director Dr Ed Kingston explains. Residual stresses are introduced into any component that is manufactured. Take a pipe that’s made by welding two sections together. As the hot weld metal cools, it pulls on the two sections of pipe until the weld metal in the centre is under tension. The stress created is what is known as a residual stress, and it can be both detrimental to the life of a product and, perhaps rather surprisingly, beneficial. The rivet holes in an aeroplane wing, for example, are sites of high stress that could cause the wing to fail. In order to avoid this, compressive residual stresses are added to the wi
