ENGIN-X

Abstract: Residual stress refers to stress that remains in a structure when all applied stresses have been removed. It is important because the combination with applied stress can cause failure at the level below at which the failure could occur. A study has been carried out using the non-destructive neutron diffraction (ND) technique of ENGIN-X to quantify the redistribution of residual stresses in a pipe. A three-dimensional residual stress-measurements test is fully performed on a 89 mm (3.5 in) diameter pipe in AA6063 grade aluminium (5 mm wall thickness) containing a girth friction stir weld. The results have shown an opposite residual stress effect due to tool rotational speed increment especially on the retreating side of the weld. This weld residual stress analysis is an important factor for Fitness-For-Purpose Assessments. This residual stress measurement data provides a basis for structural integrity assessment and inspection planning.

Abstract: Polycrystalline geological materials are not normally single phase materials and commonly contain second phases which are known to influence the grain size and mechanical properties of bulk material. Despite the well documented significance of second phases, there are relatively few detailed systematic experimental studies of the effect of second phases on isostatic high temperature grain growth in geological materials. Grain growth is a process that is fundamental to our understanding of how rocks behave in the lower crust / upper mantle where grain size is considered to play an important role in the localization of deformation in addition to determining the strength of materials at these pressure and temperature conditions. Furthermore, the effect that the spatial distribution and grain size of the second phases have on the mechanical properties of rocks is generally acknowledged, but it is not well constrained. Spatial variation is particularly significant in geological systems where a strength contrast exists between phases. With these two things in mind, a two-part study is presented in which the influence of a pore second phase on the microstructural evolution of halite during grain growth (Part I), and the influence of a calcite second phase on the mechanical behaviour of two phase calcite + halite aggregates (Part II), is investigated.In Part I, high temperature (330 �-600 �C), high confining pressure (200 MPa) isostatic grain growth experiments were carried out on 38-125 ?m reagent grade halite (99.5%+ NaCl) powder over durations of 10 secs up to 108 days. After hot-pressing, the halite displays a foam texture. Some porosity remained along the grain boundaries, the size and distribution of which appears to impact significantly on the resulting grain size, growth mechanism and kinetics of halite grain growth.Halite grain growth was found to be well described by the normal grain growth equation: d^(1/n)-d0^(1/n)=k0(t-t0)exp(-H/RT) where t is the duration of the growth period, t0 is the time at which normal growth begins, d is the grain size, d0 is the grain size at t0, k0 is a constant, H is the activation enthalpy for the growth controlling process, R is the universal gas constant,T is temperature and n is a growth constant. At 330 �-511 �C, the data is best described by n = 0.25 indicating growth controlled by surface diffusion around pores that lie on the grain boundaries. An activation enthalpy of 122�34 kJ/mol was obtained using the grain size data from these data sets. At 600 �C the data is best described by n = 0.5, suggesting that a transition to interface controlled growth takes place between 511 �C and 600 �C. To investigate the impact of porosity, the Zener parameter (Z = pore size/pore volume fraction) was determined for individual grains in 10 samples. A general trend of increasing with increasing halite grain size is observed, indicating pore elimination keeps pace with pore accumulation in the growing grains. In some samples, the largest grains display a decrease in the Zener parameter corresponding with an increase in pore volume fraction. These grains are interpreted as having experienced a short-lived, abnormal growth phase shortly after t0 during which pore accumulation outpaced pore elimination. A model of pore controlled grain growth is proposed with a view to explaining these observations.In Part II, calcite + halite aggregates of constant volume fraction (0.60 calcite : 0.40 halite) and varying calcite clast size (6 ?m 361 ?m) were axially deformed to <1% bulk strain at room temperature in a neutron diffraction beamline. Elastic strain and stress in each phase was determined as a function of load from the neutron diffraction data. The strain (and stress) behaviour correlates well with the microstructural parameters: 1) halite mean free path and 2) calcite contiguity.Both phases behaved elastically up to aggregate axial stresses of 20-37 MPa, above these stresses the halite yielded plastically while the calcite remained elastic. Once yielding began, the rate of enhanced load transfer from halite to calcite with increasing applied load decreased with halite mean free path and increased calcite with contiguity. A Hall-Petch relationship between halite mean free path and aggregate yield stress was observed.

Abstract: In this study we present a direct comparison between residual strain measurements carried out on the same inertia friction weld using ENGIN-X at ISIS, UK and the new strain scanner SALSA at ILL, France. ENGIN-X is a time of flight (TOF) instrument, which receives neutrons from a neutron spallation source, while the SALSA Strain-Imager, a high resolution diffractometer, is based at a research reactor source with a continuous neutron flux and is operated with a constant wavelength. The purpose of this study was to demonstrate a confidence in cross-comparing future strain measurements to be performed at ENGIN-X and SALSA. Measurements were carried out on medium size inertia friction welded nickel superalloy test-piece, which show no significant crystallographic texture across the weld line. The results demonstrate that, even though residual stresses determined on SALSA only rely on a single peak analysis (in this case the (111) reflection), the results show excellent agreement with the measurements carried out on ENGIN-X, where strain is determined from multi-peak Rietveld analysis.

Abstract: Pulsed neutron beams available at the ISIS spallation source offer diverse possibilities for materials characterization. ENGIN-X [1] is the dedicated materials engineering neutron beamline at ISIS. The Engin-X diffractometer operates in time-of-flight (TOF) diffraction mode, using neutron pulses with a range of energies which travel a distance of 50 meters towards the sample before being elastically scattered, so that the TOF of a given neutron is proportional to its wavelength. The primary function of the beamline is the determination of residual stresses within the interior of bulk engineering components and test samples, in particular for the development of modern engineering processes (e.g. welding, peening) and variety of structural integrity investigations. A second important function of the beamline is for studies of fundamental material behaviour, such as composite and rock mechanics, the basic deformation mechanisms of metals, and phase transformations in shape memory alloys and ferroelectrics. In-situ straining neutron diffraction experiments can provide a way to verify assumptions regarding the relative activity of the different deformation systems which can provide valuable information for various polycrystalline deformation models. These models require inputs of the relative activity of the different damage mechanisms operating during deformation. To address this need, a range of sample environment equipment such as hydraulic dynamic mechanical testing rigs, cryogenic [2] and radiant furnaces [3] are available for these investigations on Engin-X as it shown in Table 1.