A comparative study to map the residual strain/stress states through the walls of autofrettaged thick-walled steel cylinders has been conducted with neutron diffraction, Sachs boring and the compliance methods. Test samples with different wall thickness ratios were prepared to have significant amounts of reverse yielding due to the Bauschinger effect. All three methods indicate that the autofrettage action primarily influenced the hoop stresses, which varied rapidly close to the bores from compressive to tensile within the first half of the wall thickness. Quantitatively, results from the neutron diffraction and Sachs boring techniques compare favourably across large regions of the cylinder walls, while the compliance results showed different features. The existence of reverse yielding close to the cylinder bores has been sensed to different magnitudes and distances from the bores. Plastically yielded material regions identified from the neutron diffraction results correlated well with theoretical modelling.

Recently, reliable and hermetic joining of stainless steel to niobium pipes has been achieved with the explosive bonding technique. Joining of these two materials are essential to ensure production of a bimetallic transition element of pipe-type for its further use as a part of charged beam acceleration systems of the new generation. A non-destructive neutron diffraction investigation of the tri-axial strains along a radial cross-sectional line through the joint section has been performed. Residual stress results indicate inherently different natures in the residual stress values within the respective pipe sections. In the external stainless steel pipe the residual stresses are tensile, showing a sudden increase to 600 MPa as the interface is approached, whilst being compressive in the internal niobium pipe, not exceeding 650 MPa. A characteristic abrupt stress discontinuity exits at the interface region.

Dimensional tolerances for high-speed-machined aluminum products continue to tighten due to the demand for automated assembly of complex monolithic parts in aerospace and other industries. Understanding the contribution of inherent residual stress in wrought Al 7050-T7451 plate, common in aircraft manufacture, to distortion of high-aspect-ratio machined parts is critical but remains problematic due to the alloy's low residual stress magnitude over large geometries. Prior investigations into residual stress effects on machined part distortion suffer inadequate characterizations of the wrought material stress field, either because of low fidelity due to “slitting” methods, confounding effects in machined-layer removal methods, or small sample size when using neutron diffraction (ND). In this work, inherent residual stress is measured via ND at 860 locations in a 90.5 mm thick Al 7050-T7451 plate having dimensions 399 mm in the rolling direction and 335 mm in the transverse direction. Unlike prior studies, the ND residual stress is reconstructed using an iterative algorithm to ensure fully compatible, equilibrated 3D field prior to examining its effect on distortion. The findings from simulations and experiments show that inherent residual stress alone could distort a high-aspect-ratio part beyond aerospace industry requirements, that slitting measurements may not sufficiently characterize residual stress for predicted distortion, and that parts machined from different plate thickness locations could exhibit reversed distortion patterns. Thus, research into distortion prediction that considers machining should carefully characterize and reconstruct inherent residual stress so that the coupled machining effects are accurately modeled.

Ideal isotropic or kinematic hardening is often utilized in order to simplify the modeling of the loading and reverse loading behavior of materials when using finite element analysis. Unfortunately, this simplification can result in significant error if the material exhibits the Bauschinger effect (BE), which is the loss of strength of the material upon reverse loading. The error associated with this simplification is further compounded in heavily autofrettaged, Cr-Mo-V, thick walled cylinders due to the fact that the Bauschinger effect and the reverse loading strain hardening exponent are a strong function of the initial applied plastic strains, which can vary significantly throughout the wall of the cylinder.