Wenhong Xu

Date of Graduation

1998

Document Type

Dissertation/Thesis

Abstract

In this research, a combined hole-drilling/phase shift moire interferometry method was applied to determine the residual stress state. This new method overcomes the drawbacks of the conventional hole-drilling/strain-gage method in that it has the advantage of high sensitivity full field measurement. For a cracked structure, the integrity of the structure depends not only on the external applied loads but also on residual stress state at the crack tip. Hence, determination of the residual stress intensity at the crack tip is essential to ensure the safety of the structure. In this research a hole-drilling/phase-shift moire interferometry method was developed to measure the residual stress intensity of the cracked structure. The experimental approach involves drilling a small hole at the crack tip, which will locally relax the residual stress at the crack tip. The released crack-tip displacement fields are measured by using phase shift moire interferometry. The original residual stress intensity factor at the crack tip can then be determined. The proposed method has the advantage that it is a nondestructive method and can even prevent further crack growth. In this research, both mode-I and mixed-mode crack cases were studied and the related theoretical analyses were carried out. The measured experimental results agree well with the theoretical predictions as well as the FEM results. Furthermore, the residual stress state of a structure is also related to the material properties (e.g. Young's modulus, Poisson's ratio) and for an “aging” structure, the mechanical properties may suffer degradation during years of service. At present, appropriate method for determining aging material properties without substantially damage the structure has not yet been developed. In this research, based on the hole-drilling/phase-shift moire interferometry method, a procedure was also developed to determine Young's modules of an “aging” structure. This procedure has the advantage that the “aging” structure does not need to be taken out when measuring its Young's modulus.

Download

Share

COinS