Ah Mahmoudi

Measurement and prediction of the residual stress field generated by side-punching

Side-punching is proposed as a method of introducing a well-defined residual stress field into a laboratory-sized test specimen. Such a specimen may subsequently be used to assess the influence of residual stresses on the fracture behavior of materials. Side-punching consists of simultaneously indenting opposite faces of a plate of material with rigid tools, using sufficient force to cause localized yielding over a finite-sized volume of material adjacent to tire punching tools. This paper presents experimental measurements, obtained using three independent measurement techniques of the residual stress field generated in an aluminium alloy plate after side-punching. Incremental center hole drilling is used to determine the near-surface residual stress field, while synchrotron x-ray diffraction and deep hole drilling are used to measure the through-thickness residual stress field along a path linking the two punch center points. Finite element (FE) predictions are also presented and compared to tire measurements. There is very good agreement between all three sets of measurements and the FE results. which all show that the through-thickness residual stresses are compressive and attain a maximum value at the center of the plate. The results confirm the potential use of side-punching in residual stress-crack interaction studies.

Residual stress measurement by deep hole drilling and trepanning – analysis with distributed dislocations

It is shown that the conventional ‘sheet by sheet’ analysis of residual stress measurement by the deep hole drilling method is inaccurate when in-plane stress gradients exist. The influence of the interfacial tractions is analysed by the distributed dislocation technique. Finite element modelling is used to provide data for an example residual stress field with radial variation.

Application of the Local Approach to Predict Load History Effects in Ferritic Steels

The effect of residual stresses on fracture behaviour of ferritic steels at low temperature has been investigated using a local approach based on the Beremin model [1]. The study aims to enhance the use of local approach in failure prediction when residual stress is present. A tensile residual stress field has been introduced in the laboratory specimens and their subsequent behaviour was investigated at low temperature. Local compression methods, including side-punching and in-plane loading, were employed to introduce residual stress fields. These methods are discussed and comprehensive range of experimental presented. The transferability of the Weibull parameters between the cracked specimens with different constraint, test temperatures and also from unstrained specimens to specimens with residual stresses are illustrated. The general scheme in failure prediction using the local approach is that the Weibull parameters in the Beremin type model calibrated to the as-received data should predict the failure following complex interaction of residual and applied stresses. The paper compares the predictions and the experimental results.Copyright

Generating Well Defined Residual Stresses in Laboratory Specimens

Residual stresses play an important role in increasing and decreasing the possibility of failure. The magnitude and direction of the residual stresses is an important factor in the integrity of engineering structures, including those containing defects. Ideally, we would like to gain insight into the integrity of a structure through testing laboratory samples. The purpose of this paper is to review methods of introducing residual stresses into laboratory specimens that are either subsequently loaded to fracture or used to assess the influence of residual stress on material damage mechanisms. Three methods, mechanical, thermal and welding, are scrutinized and illustrative examples provided. The advantages and disadvantages are explored. We conclude that new methods that do not introduce microstructural changes during the generation of residual stress should be sought if an improved understanding of the effects residual stress on fracture is required.Copyright