From Laser Shock Peening: Performance and Process Simulation

2.4 Measurement of Residual Stress

Residual stresses after LSP are the stresses remaining in a metal after the shock wave is dispersed. Such residual stresses play a key role in enhancing the fatigue performance of metallic materials. The measurement of residual stresses allows engineers to understand fully the residual stress profile in the treated metallic components. Thus, an accurate residual stress measurement is important in the design and quality control of mechanical or thermal treatment processes for metal components. The residual stress is often measured using a special technique such as centre-hole drilling, layer removal, X-ray diffraction or neutron diffraction and so on (Lu, 1996). The main technical characteristics of these method are described as follows.

One of the most widely used techniques for measuring residual stress is the hole-drilling strain gauge method. The general principle of the procedure involves drilling a small hole into a specimen containing residual stresses. A special residual stress strain gauge rosette, allowing back calculation of residual stress to be made, can measure the relieved surface strains. This method is semi-destructive and cannot be checked by repeat measurement.

The layer removal technique is often used for measuring the presence of residual stress in simple test piece components. The methods are generally quick and require only simple calculations to relate the curvature to the residual stresses. When layers are removed from one side of a flat plate containing residual stresses, the stresses become unbalanced, leading to bend of the plate. The curvature depends on the original...

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Deflectometers and Extensometers
Deflectometers and extensometers are used to indicate the deformation of material while it is subjected to stress.
Strain Gauges
Strain gauges are measuring elements that convert force, pressure, tension, etc., into an electrical signal.
Nondestructive Testing (NDT) Material Testers
Non-destructive testing (NDT) material testers are devices, machines and equipment that are used to determine residual stress, alloy type, hardness, microstructure, elasticity, heat treatment and other material conditions without permanently altering or destroying the material being examined.
Diffractometers are used to measure crystal structure, grain size, texture, and/or residual stress of materials and compounds through the interaction of X-ray beams, gamma rays, electron beams, or neutron beams with a sample.
Plastic Machining Services
Plastic machining services fashion or fabricate parts and components out of various plastic and thermoplastic materials.

Topics of Interest

2.5 Characteristics of Residual Stresses Induced by Laser Shock Peening 2.5.1 Physical Models of Residual Stress When the laser power density reaches a level of several GW/cm 2, high-amplitude shock...

Abrasion of a metallic surface to improve bonding during strain gage installation is generally thought to produce negligible effect on the measurement of applied or residual stresses by blind hole...

One of the advantages of ultrasonic techniques for residual stress measurement is that they are non-destructive. Using such techniques, one can measure the residual stresses in the same points many...

Accurate knowledge of the subsurface residual stress and hardness distributions is required for failure analysis, fatigue life prediction and process control of induction hardened components. X-ray...

A brief overview of the theory and practice of x-ray diffraction residual stress measurement as applied to shot peened materials is presented. The unique ability of x-ray diffraction methods to...