Gary S. Schajer

Bio: Gary S. Schajer is an academic researcher from University of British Columbia. The author has contributed to research in topics: Residual stress & Hole drilling method. The author has an hindex of 25, co-authored 89 publications receiving 2985 citations. Previous affiliations of Gary S. Schajer include University of California, Berkeley.

Measurement of Non-Uniform Residual Stresses Using the Hole-Drilling Method. Part I—Stress Calculation Procedures

Abstract: The Incremental Strain, Average Stress, Power Series, and Integral methods are examined as procedures for determining non-uniform residual stress fields using strain relaxation data from the hole drilling method. Some theoretical shortcomings in the Incremental Strain and Average Stress methods are described. It is shown that these two traditional methods are in fact approximations of the Integral Method. Theoretical estimates of the errors involved are presented for various stress fields. Also, some simple transformations of stress and strain variables are introduced so as to decouple the stress/strain equations and simplify the numerical solution.

Practical residual stress measurement methods

Abstract: Residual stresses play major roles in engineering structures, with highly beneficial effects when designed well, and catastrophic effects when ignored. With ever-increasing concern for product performance and reliability, there is an urgent need for a renewed assessment of traditional and modern measurement techniques. Success critically depends on being able to make the most practical and effective choice of measurement method for a given application.

Use of Inverse Solutions for Residual Stress Measurements

Abstract: For most of the destructive methods used for measuring residual stresses, the relationship between the measured deformations and the residual stresses are in the form of an integral equation, typically a Volterra equation of the first kind. Such equations require an inverse method to evaluate the residual stress solution. This paper demonstrates the mathematical commonality of physically different measurement types, and proposes a generic residual stress solution approach. The unit pulse solution method that is presented is conceptually straightforward and has direct physical interpretations. It uses the same basis functions as the hole-drilling integral method, and also permits enforcement of equilibrium constraints. In addition, Tikhonov regularization is shown to be an effective way to reduce the influences of measurement noise. The method is successfully demonstrated using data from slitting (crack compliance) measurements, and excellent correspondence with independently determined residual stresses is achieved.

Residual stress. Part 1 – Measurement techniques

Abstract: Residual stress is that which remains in a body that is stationary and at equilibrium with its surroundings. It can be very detrimental to the performance of a material or the life of a component. Alternatively, beneficial residual stresses can be introduced deliberately. Residual stresses are more difficult to predict than the in-service stresses on which they superimpose. For this reason, it is important to have reliable methods for the measurement of these stresses and to understand the level of information they can provide. In this paper, which is the first part of a two part overview, the effect of residual stresses on fatigue lifetimes and structural integrity are first summarised, followed by the definition and measurement of residual stresses. Different types of stress are characterised according to the characteristic length scale over which they self-equilibrate. By comparing this length to the gauge volume of each technique, the capability of a range of techniques is assessed. In the sec...

Residual stress and its role in failure

Abstract: Our safety, comfort and peace of mind are heavily dependent upon our capability to prevent, predict or postpone the failure of components and structures on the basis of sound physical principles While the external loadings acting on a material or component are clearly important, There are other contributory factors including unfavourable materials microstructure, pre-existing defects and residual stresses Residual stresses can add to, or subtract from, the applied stresses and so when unexpected failure occurs it is often because residual stresses have combined critically with the applied stresses, or because together with the presence of undetected defects they have dangerously lowered the applied stress at which failure will occur Consequently it is important that the origins of residual stress are understood, opportunities for removing harmful or introducing beneficial residual stresses recognized, their evolution in-service predicted, their influence on failure processes understood and safe structural integrity assessments made, so as to either remove the part prior to failure, or to take corrective action to extend life This paper reviews the progress in these aspects in the light of the basic failure mechanisms

Cross-sectional mapping of residual stresses by measuring the surface contour after a cut

Abstract: A powerful new method for residual stress measurement is presented. A part is cut in two, and the contour, or profile, of the resulting new surface is measured to determine the displacements caused by release of the residual stresses. Analytically, for example using a finite element model, the opposite of the measured contour is applied to the surface as a displacement boundary condition. By Bueckner's superposition principle, this calculation gives the original residual stresses normal to the plane of the cut. This contour method is more powerful than other relaxation methods because it can determine an arbitrary cross-sectional area map of residual stress, yet more simple because the stresses can be determined directly from the data without a tedious inversion technique. The new method is verified with a numerical simulation, then experimentally validated on a steel beam with a known residual stress profile.