Research in Non-Destructive Strain Measurement

Background

Residual stress or strain in engineering components is one of the most important factors influencing their fatigue life in high stress applications. Inaccurate prediction of residual stress fields resulting from either the service loading e.g. mechanical and thermal loading or due to manufacturing processes e.g. grinding, surface treatment etc. than therefore significantly influence the components life with catastrophic consequences e.g. for aerospace industry. It is therefore critical to evaluate these residual stress fields non-destructively such that the components performance can be predicted.

Current Research

The aim of the existing research is to investigate the influence of residual stress profiles on the failure modes of engineering materials. Influence of manufacturing process on conventional steel components, as well as the influence of surface treatment such as sprayed (thermally sprayed) or vapour deposited (Physical Vapour Deposition). Typical example of the factors influencing the residual strain in thermal spray coatings can be appreciated from the schematic shown in Figure 1 below.

Residuals strain measurements have been performed using conventional x-rays, high energy x-rays, and neutrons. Use of facilities such as the Daresbury and Rutherford Laboratories, UK are therefore critical for such investigations. All of these techniques have inherent advantages e.g. conventional x-rays are generally a cheaper way of measuring one-dimensional strain in conventional steels and ceramics, where as for three dimensional strain measurements and for high-density materials such as WC-Co coatings, penetration depth of x-rays is generally very low. Hence, state of the art facilities such as Engin-X at Rutherford labs thus provide a solution for such materials.

Experimental results obtained from such experimental analysis are thus incorporated in numerical (or mathematical) models to predict components life or failure modes. Some typical experimental results can be appreciated from the list of publications and also from the enclosed ISIS report.