Fatigue crack nucleation in a powder metallurgy produced nickel alloy containing a non-metallic inclusion has been investigated through integrated small-scale bend testing, quantitative characterisation (HR-DIC and HR-EBSD) and computational crystal plasticity which replicated the polycrystal morphology, texture and loading. Multiple crack nucleations occurred at the nickel matrix-inclusion interface and both nucleation and growth were found to be crystallographic with highest slip system activation driving crack direction. Local slip accumulation was found to be a necessary condition for crack nucleation, and that in addition, local stress and density of geometrically necessary dislocations are involved. Fatemi-Socie and dissipated energy were also assessed against the experimental data, showing generally good, but not complete agreement. However, the local stored energy density (of a Griffith-Stroh kind) identified all the crack nucleation sites as those giving the highest magnitudes of stored energy

An integrated experimental, characterisation and computational crystal plasticity study of cyclic plastic beam loading has been carried out for nickel single crystal (CMSX4) and oligocrystal (MAR002) alloys in order to assess quantitatively the mechanistic drivers for fatigue crack nucleation. The experimentally validated modelling provides knowledge of key microstructural quantities (accumulated slip, stress and GND density) at experimentally observed fatigue crack nucleation sites and it is shown that while each of these quantities is potentially important in crack nucleation, none of them in its own right is sufficient to be predictive. However, the local (elastic) stored energy density, measured over a length scale determined by the density of SSDs and GNDs, has been shown to predict crack nucleation sites in the single and oligocrystals tests. In addition, once primary nucleated cracks develop and are represented in the crystal model using XFEM, the stored energy correctly identifies where secondary fatigue cracks are observed to nucleate in experiments. This (Griffith-Stroh type) quantity also correctly differentiates and explains intergranular and transgranular fatigue crack nucleation

who died as the result of a tragic climbing accident during the period this paper was in preparation. On the evaluation of the Bauschinger effect in an austenitic stainless steel-The role of multiscale residual stresses

In-situ neutron diffraction combined with the incremental deformation at room temperature has been used to provide a measure of the internal stress and internal resistance generated by the prior inelastic deformation at high temperature in an austenitic stainless steel. Interactions between the internal stress and internal resistance are considered explicitly by using the proposed measurement technique.The magnitude of the intergranular internal stress is found to be a function of the total inelastic strain created by high temperature prior deformation. The deviation from linearity observed in the lattice strain response is used to derive the microscopic internal resistance, but a crystal plasticity model is required to infer the absolute value.The macroscopic internal resistance is shown to be consistent with Taylor hardening.A refined internal state concept is proposed based on the Kocks-Mecking model to provide a further step to predict the inelastic deformation.

. (2015) Role of the misfit stress between grains in the Bauschinger effect for a polycrystalline material. Acta Materialia, http://dx.doi.org/10.1016/j.actamat. .11.021 DOI 10.1016/j.actamat.2014.11.021 ISSN 1359 Publisher: Elsevier Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. This document is the author's post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version may remain and you are advised to consult the published version if you wish to cite from it. AbstractThe role of misfit stress on kinematic hardening under reversed straining of a Type 316H austenitic stainless steel has been investigated by using the neutron diffraction technique combined with in-situ deformation. Initial misfit stresses, often referred to an intergranular internal stresses, were created by the tensile pre-straining at high temperature. The misfit stresses at the length-scale of grain families, measured by neutron diffraction, were shown to be a function of the magnitude of the tensile prestrain. The pre-strained specimens were further subjected to either continued (tensile) straining or reversed (compressive) straining at room temperature. In-situ neutron diffraction measurements were undertaken to monitor the change of the misfit stresses during loading. The macroscopic stress-strain behaviour was used to derive isotropic and kinematic hardening stresses developed in the pre-strained specimens. Resultsshow that the change of the transient softening stress towards a zero value is accompanied by a decrease in the change of the misfit stresses. A multi-scale selfconsistent model has been developed to assist in understanding the measured change of the misfit stresses when subjecting the material to strain reversal. An important conclusion is that the origin of the kinematic hardening of Type 316H austenitic stainless steel arises from the misfit stress between grains.