Ronald Rogge

On the influence of crystal elastic moduli on computed lattice strains in AA-5182 following plastic straining

Crystal lattice plane spacing is modified by the application of stress. The changes in spacing can be measured with neutron diffraction and used to determine the elastic strains in loaded crystals. Using finite element methods, elastic strains can be computed under loading that mimics the experiment. The quality of comparisons between the measured and computed strains depends strongly on accurate knowledge of parameters that quantify the single crystal elastic and plastic responses. For one aluminum alloy in particular, we have found that we can improve the match of lattice strains through careful choice of the single crystal elastic moduli. The parameters are selected on the basis of comparisons between the experimental results and a series of simulations in which the single crystal moduli were varied systematically. Good correspondence is obtained for a set of moduli with higher single crystal anisotropy than those of pure aluminum.

Neutron diffraction residual stress mapping in same gauge and differential gauge tailor-welded blanks

Abstract Neutron diffraction has been used to determine the residual stresses in the weld region of laser-welded tailor-welded blank (TWB) samples. Residual stresses in same gauge and differential gauge TWB samples are examined in the as-welded condition as well as after uniaxial loading to 0.5, 3.0 and 7.0% strain. Results indicate that stress distributions can be quite complex, particularly following deformation. Overall, however, two major conclusions were drawn: first, residual stresses around laser welds in these TWBs tend to be small compared with stresses reported for conventional welding processes. Secondly, in most cases the peak residual stresses tend to remain the same or diminish with subsequent deformation.

Residual stress characterization in structural materials by destructive and nondestructive techniques

Transmutation of nuclear waste is currently being considered to transform long-lived isotopes to species with relatively short half-lives and reduced radioactivity through capture and decay of minor actinides and fission products. This process is intended for geologic disposal of spent nuclear fuels for shorter durations in the proposed Yucca Mountain repository. The molten lead-bismuth-eutectic will be used as a target and coolant during transmutation, which will be contained in a subsystem vessel made from materials such as austenitic (304L) and martensitic (EP-823 and HT-9) stainless steels. The structural materials used in this vessel will be subjected to welding operations and plastic deformation during fabrication. The resultant residual stresses cannot be totally eliminated even by stress-relief operations. Destructive and nondestructive techniques have been used to evaluate residual stresses in the welded and cold-worked specimens. Results indicate that tensile residual stresses were generated at the fusion line of the welded specimens made from either austenitic or martensitic stainless steel, with reduced stresses away from this region. The magnitude of residual stress in the cold-worked specimens was enhanced at intermediate cold-reduction levels, showing tensile residual stresses in the austenitic material while exhibiting compressive stresses in the martensitic alloys. Comparative analyses of the resultant data obtained by different techniques revealed consistent stress patterns.

Intergranular strain correlation with magnetic behavior in steel

The correlation between the magnetic behavior and intergranular residual strain was investigated on several mild steel samples which were plastically deformed in the range 0.5%–20% engineering strain followed by unloading. At low deformation levels (0.5%–∼2%) the samples exhibited Luders banding, but after 2% strain the samples appeared uniformly deformed. Magnetic Barkhausen noise (MBN) measurements were used to characterize magnetic behavior and neutron diffraction measurements were used to determine the inter-granular strain. MBN results indicated a high MBN value in the direction transverse to the applied stress. This corresponded to a high strain in the (100) crystallographic direction (the easy magnetization direction), as observed using neutron diffraction. Little correlation was obtained between the MBN result and the (112) strain, which is generally assumed to reflect the macroscopic residual stress. Angular MBN and neutron diffraction results further confirmed the strong correlation between the ...

Distributions of residual stresses in stiffened plates with one and two stiffeners

This study was undertaken for a better understanding of the residual stress distributions associated with welds typically found in ship hulls. Specimens that represent small sections of an actual ship hull were built and tested using the neutron diffraction method at the Canadian Neutron Beam Centre in the Chalk River Laboratories. The specimens comprised 9.5 mm thick steel plates stiffened by L127 × 76 × 9.5 steel angles. This paper presents one- and three-dimensional distributions of all three components of residual stress created from the production of the steel plate and from the welding of one and two stiffeners onto the parent steel plate. Subsequently, the longitudinal stress in the transverse direction of the stiffened plate specimens was compared with the Faulkner model. It was found that the Faulkner model is able to predict the general distributions of this stress; however, it was unable to predict the stress values correctly.

Investigation of residual stress in a bent Ti-clad Cu bus-bar by neutron diffraction and finite element modelling§

Titanium-clad copper bus-bars are used to provide corrosion resistance in high temperature electrolytic cells. When cold-formed, such components will have a complex residual stress pattern. We report the investigation of residual stress in a high conductivity Cu bus-bar clad with Grade-2 Ti by neutron diffraction and finite element modelling. Straight bars were co-extruded, air-cooled and cold-stretched. The bars were cold-bent into an inverted ‘top-hat’ shape with four 90° bends. Residual stresses were investigated at the apex of a 90° bend. Three sets of measurements were performed in each of the measurement directions (transverse, normal and axial, relative to the straight bar): one set along the centre line in Cu; one set along the edge in Cu and one set along the edge in Ti. Residual stresses were then calculated in the three directions assuming both materials are elastically isotropic. The cooling, stretching and bending processes were simulated with an explicit finite element program, while the spr...

In-Situ Neutron Diffraction Study of the Behavior of AL6XN Stainless Steel Under Biaxial Loading

In–situ neutron diffraction has been used to measure lattice strains parallel to two principal stress directions in biaxially-loaded AL6XN stainless steel. A new fixture was developed for loading thin-walled tubular specimens through combinations of internal pressure and axial loading. Under these conditions, the principal directions (σ zz and σ θθ in a cylindrical r, θ, z coordinate system) remain constant with respect to the initial crystallographic texture regardless of the level of biaxiality, a distinct advantage for diffraction experiments over the traditional tension/torsion tests for which this condition does not hold. Specimens were first pressurized to the level required to obtain a chosen value of σ θθ . The axial load was then increased to reach the yield surface at different σ θθ /σ zz ratios, ranging from uniaxial to balanced biaxial loading (0, 0.4, 0.7, 1 according to Tresca). The {200}, {220}, {222}, and {311} reflections were measured in the axial and hoop directions as a function of axial load. A sequence of axial loading/unloading episodes was applied for different levels of plastic deformation. Under uniaxial tension, the {200} reflection showed the highest axial strains, followed by the {311}, and {220}/{222} reflections. With increasing internal pressure (biaxiality), the axial lattice strains corresponding to a given axial stress tended to decrease, and the responses of the various reflections tended to merge.

Measuring the influence of magnesium on the elastic anisotropy of aluminum using in situ neutron diffraction

Comparison of lattice strains in crystals of various orientations is a primary method of validating polycrystal plasticity simulations. These strains can be measured using in situ neutron diffraction experiments while the corresponding information can be extracted from the simulation results. If the single crystal elastic moduli—particularly the anisotropy of the moduli with respect to lattice direction—are not accurately known, simulations cannot provide a favorable comparison to experiments. Previous work simulating deformation of an aluminum alloy with significant magnesium content (AA-5182) revealed that consistency with the experiments required a higher degree of anisotropy in the elastic moduli in the finite element simulations than that typically reported for pure aluminum. We undertook the current research to determine if the magnesium content causes that larger single crystal elastic anisotropy. Using in situ loading, we measured lattice strains and determined diffraction moduli of materials cove...

The Investigation of the Triaxial Residual Stress in the Friction Stir Welded Lap Joint Using Neutron Diffraction

A detailed study of the complex triaxial residual stress distribution of the double-pass friction stir welded (FSW) lap-joint between two different high strength aluminum alloy sheet materials was conducted. A non-destructive technique known as neutron diffraction was used to measure the internal residual stress distribution in the three principal direction of the lap-joint in the as-welded and hammer peened configurations to determine effects of hammer peening on redistribution of residual stresses across the weld. The residual stress variation across the weld in the transverse direction contained the highest values of tensile stress in all three principal directions. The residual stress in the hammer peened test specimen was in most cases reduced in all three principal directions.

Residual Stresses in Welded Stiffened Steel Plates—An Experimental Comparative Study

This paper examines the residual stress distributions at selected depths in three stiffened 350WT steel plates representing typical stiffened steel plates used in modern ship construction. Residual stresses can develop from the welding process, and the magnitude of these stresses can be high enough to cause an early onset of yielding. Therefore, fatigue or other failures can also occur when welding-induced residual stresses are combined with service-load-induced stresses. In this study, the welding-induced residual stresses of these stiffened steel plate specimens were quantified at the near surface using the X-Ray diffraction method and at various depths using the neutron diffraction method. Transverse and longitudinal stress components for all three specimens were collected and analyzed. The residual stress profiles determined from both methods were found to be similar. However, some disagreement was found within the heat-affected zone of the weld bead. This paper discusses the residual stress distributions found in the three specimens and compares the two methods of measurement.