Residual stress measurement techniques

Residual stresses exist in most materials and structures. Processes like forging, rolling, extruding, quenching, additive manufacturing, machining, and welding can cause residual stresses to develop. These stresses can influence the way that materials perform (e.g., fatigue, fracture, distortion, and corrosion). There are many different residual stress measurement techniques available to quantify residual stresses. The following are some examples of common measurement techniques. Continue reading Residual stress measurement techniques

Hole drilling residual stress measurement method

This week, we have uploaded a new vlog to Hill Engineering’s YouTube channel revolving around a particularly handy residual stress measurement technique. The hole drilling measurement method is one of our most popular residual stress measurement options, and involves the incremental drilling of a small hole into the surface of a specimen. Watch the video below and read on to learn more about the hole drilling method. Continue reading Hole drilling residual stress measurement method

The Contour Method (book chapter)

Chapter 5 of Practical Residual Stress Measurement Methods.

The contour method, which is based upon solid mechanics, determines residual stress through an experiment that involves carefully cutting a specimen into two pieces and measuring the resulting deformation due to residual stress redistribution. The measured displacement data are used to compute residual stresses through an analysis that involves a finite element model of the specimen. As part of the analysis, the measured deformation is imposed as a set of displacement boundary conditions on the model. The finite element model accounts for the stiffness of the material and part geometry to provide a unique result. The output is a two-dimensional map of residual stress normal to the measurement plane. The contour method is particularly useful for complex, spatially varying residual stress fields that are difficult (or slow) to map using conventional point wise measurement techniques. For example, the complex spatial variations of residual stress typical of welds are well-characterized using the contour method. A basic measurement procedure is provided along with comments about potential alternate approaches, with references for further reading.

The Slitting Method (book chapter)

Chapter 4 of Practical Residual Stress Measurement Methods.

The slitting method is a technique for measuring through thickness residual stress normal to a plane cut through a part. It involves cutting a slit (i.e., a thin slot) in increments of depth through the thickness of the work piece and measuring the resulting deformations as a function of slit depth. Residual stress as a function of through thickness position is determined by solving an inverse problem using measured deformations. The chapter describes practical measurement procedures, provides a number of example applications, and summarizes efforts to determine the quality of the residual stress information obtained with the method.

Citation

The Impact of Forging Residual Stress on Fatigue in Aluminum

Large aluminum forgings are seeing increased application in aerospace structures, particularly as an enabler for structural unitization. These applications, however, demand an improved understanding of the forging process induced bulk residual stresses and their impact on both design mechanical properties and structural performance. In recent years, significant advances in both computational and experimental methods have led to vastly improved characterization of residual stresses.

Repeatability of residual stress measurements

Residual stresses are of interest from an engineering perspective because they can have a significant influence on material performance. For example, fatigue initiation, fatigue crack growth rate, stress corrosion cracking, and fracture are all influenced by the presence of residual stress. Current design methods for aerospace structure typically assume that the material is residual stress-free.