Remarks on residual stress measurement by hole-drilling and electronic speckle pattern interferometry

Influence of the Plastic Deformation Process on the Residual Stresses and Hardness of an Al-5Mg Alloy

The service behavior of ductile metallic materials, when they have previously undergone technological plastic deformation, depends on the deformation conditions. These are represented, among others, by the deformation rate, the process temperature, the applied pressures, and the introduced stresses, as well as other process variables. The investigation of the mechanical properties obtained after plastic deformation is an important means that contains two characteristics: on the one hand, to determine to what extent the parameters of the technological manufacturing process influence the main characteristics of the final component; and, on the other hand, on the basis of these characteristics, to analyze whether the component subjected to plastic deformation will be able to function reliably and safely. In the present work, an experimental study was made of the residual stresses developed and hardnesses obtained both in the immediate vicinity of a highly plastically deformed area and in an area previously obtained by rolling, without additional plastic deformation. For the determination of the residual stresses, the tensiometric rosette drilling method was used. By determining the same quantities in a non-plastically deformed area, significant changes in the values of the two quantities in the plastically deformed area were found. An increase in the maximum principal normal stresses by approx. 60 MPa and an increase in the Rockwel hardness by approx. 10 HRC was found. A sample was taken from the area under a plastic deformed circular shape, and was analyzed microscopically.

A Novel Low-Cost DIC-Based Residual Stress Measurement Device

Residual stress often has a significant impact on part performance and lifetime. Existing measurement techniques using strain gauges or non-destructive methods are often expensive and time-consuming. This paper presents a low-cost, novel measurement device that uses digital image correlation with the hole-drilling method to quantify the magnitude and preferred orientation of these locked-in forces. A two-axis measurement device that rapidly drills and images the surface around the hole was developed to measure residual stresses as a function of depth with sub-millimetre resolution. Validation of the device and DIC methodology was performed using a four-point bending specimen and comparison with conventional strain gauge methods. The results showed strong correlations between the two measurement techniques, as well as the theoretical estimates. The total cost of production was estimated to be approximately £380, which is significantly cheaper than competitors. The device also substantially reduced the cost per measurement point (less than £1 vs. £50+) and shortened the experiment duration from 2 h per point to 45 min per measurement. A functional, rapid, economical device has been designed and produced, which is currently being used for residual stress analysis of industrial samples. The presented design is completely open-source, and the relevant links are provided.

Frequency-Shifted Optical Feedback Measurement Technologies Using a Solid-State Microchip Laser

Since its first application toward displacement measurements in the early-1960s, laser feedback interferometry has become a fast-developing precision measurement modality with many kinds of lasers. By employing the frequency-shifted optical feedback, microchip laser feedback interferometry has been widely researched due to its advantages of high sensitivity, simple structure, and easy alignment. More recently, the laser confocal feedback tomography has been proposed, which combines the high sensitivity of laser frequency-shifted feedback effect and the axial positioning ability of confocal microscopy. In this paper, the principles of a laser frequency-shifted optical feedback interferometer and laser confocal feedback tomography are briefly introduced. Then we describe their applications in various kinds of metrology regarding displacement measurement, vibration measurement, physical quantities measurement, imaging, profilometry, microstructure measurement, and so on. Finally, the existing challenges and promising future directions are discussed.