Controlled seeding of contact cracks in test pieces for the evaluation and validation of non-destructive testing systems

Background: A major inhibitor in the development and certification of non-destructive test equipment is the lack of access to statistically appropriate numbers of test pieces which contain relevant flaws. Methods of introducing these flaws in a controllable and repeatable manner are always in demand. Methods: : This paper discusses the development and evaluation of a method for seeding contact cracks in ASTM F519-18 Type 1a.1 notched tensile coupons. Contact cracks of controlled dimensions are successfully introduced into a set of these specimens by closely monitoring the resonance frequency and peak splitting due to anisotropy. Results: : Results are confirmed using Scanning Electron Microscopy, carried out on a selection of the coupons. The least exposed coupon was shown to have a crack propagating inwards from the notch with a length of approximately 50 microns. More heavily exposed samples had longer cracks spanning nearly the entire notch with a crack width of 1.3 microns. Conclusions: : The correlation between crack growth and the frequency monitoring proves that this technique could be further developed for the controlled creation of contact cracks for NDT validation or other applications.