Measurement of a Stress Gradient through the Bulk of an Aluminum Alloy Using Neutrons

Neutron diffraction has been employed to measure an applied stress gradient through the bulk of a 25.4 mm thick aluminum alloy bar. The experiment was designed to test the feasibility of combining the penetrating power of neutrons with the residual stress measurement methodology developed for near-surface regions using X-rays. The load was applied on a curved beam sample so that the tangential stress (σ θ) ranged from +302.4 MPa (+43851 psi) to −413.7 MPa (−60000 psi). A small radial stress component (σ r) was also present. Three methods of measurement were employed which enabled gradients ofσ θ –σ r/v,σ θ, andσ θ –σ r to be measured(v is Poisson’s ratio) through the sample. Two diffraction peaks, 311 and 333/511, were used. The depth of gradient sampled at each point ranged nominally from 2 to 7 mm; however, the effective depth sampled ranged from 1 to 3 mm. Experiment and theory are in reasonable agreement, suggesting that the method has potential.