Recent advances in neutron detector technology and the ability of neutrons to penetrate through many millimeters of most engineering materials have made it feasible to investigate the effects of sub-surface stress-concentration in the vicinity of notches. Neutron-diffraction strain measurements are non-destructive and capable of tracking the development of the elastic strain field as a function of applied load in a single specimen. This paper presents two demonstrations of neutron-diffraction strain-scanning with high spatial resolution. First, the development of the strain field near a notch in an HY-100 steel bar is scanned as a three-point bending load is increased to the point of metal-tearing. Second, the stress-concentration effects of a blunt notch in a tensile test specimen are presented. The measurements are performed while the specimen is held at a temperature of 250°C and while load is applied to maintain constant total strain. The neutron diffraction measurements reveal a gradual redistribution of the stress concentration over time. In both examples, the gradients of the strain distribution are substantial, but neutron diffraction has a sufficient spatial resolution (of the order 0.5 mm to 1.0 mm) to characterize the details of a stress concentration field.

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