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Accuracy improvements for interior residual stress measurements

University of British Columbia

The accuracy of interior residual stress measurements using the layer-removal, hole-drilling and ring-core methods was enhanced in two ways. In the first way, the mathematical method for calculating residual stresses from the measured strains was made more robust by applying an inverse solution method based on Linear Inverse Theory. This approach eliminates the two main weaknesses of the existing method, stress solution sensitivity to strain measurement errors and not obeying equilibrium. Optimal smoothing is introduced as an effective method for reducing sensitivity to strain data errors. With the proposed method, stress equilibrium can be easily enforced. Both experimental and theoretical results show that the inverse solution method stabilizes the calculation procedure and it is an effective and reliable method for determining residual stresses in a material. The second way of enhancing residual stress measurement is to develop a new residual stress measurement technique. The new technique, called ring-hole drilling, overcomes the limitations of strain sensitivity to subsurface stresses of the hole-drilling and ring-core methods. By moving the strain gauges from the material surface to the interior, the overall strain sensitivity of the ring-hole drilling method is increased to double that of the ring-core method, and about four times that of the hole-drilling method. The experimental measurements made with ring-hole method correspond very closely with theoretical expectations determined using finite element method. The results show that ring-hole drilling is a practical method for evaluating residual stresses in a material.

Thesis/Dissertation

application/pdf

2009-06-11

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http://hdl.handle.net/2429/9001

Mechanical Engineering

University of British Columbia

UBCV

DSpace