A low-cost residual stress measuring instrument

The hole-drilling method is the approach most used for residual stress measurement and most of the commercially available instruments are based on this working principle. The idea is quite simple: drill a small hole on the surface of the components and measure the strain/displacement components resulting on the surface. The stress components can be estimated from these data with a reverse calibration process. The measurement of the displacement/strain field is usually performed using either strain gauges or interferometric optical methods, thus the cost of the instruments is significant. Recently, it has been proposed to replace the interferometric method with an integrated Digital Image Correlation (i-DIC) approach: by using problem-specific displacement functions, all difficulties related to the low sensitivity of DIC are avoided and the measurement procedure simply requires acquisition of an image after each drilling step. This paper describes the development of a low-cost instrument based on this working principle: the imaging subsystem is based on a Raspberry-Pi camera module whereas step motors are controlled by an Arduino board. Finally, the frame is built using a 3d-printer.