Papers by Author: Mark R. Daymond

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Authors: O. Zanellato, Michael E. Fitzpatrick, Mark R. Daymond, Lyndon Edwards, Mark Turski
Abstract: This paper reports results of an in-situ compression experiment carried out on a hot rolled Zircaloy-4 plate at ENGIN-X, ISIS. The experiment was aimed at characterizing the plastic anisotropy of the alloy, which can give rise to high intergranular stresses in the polycrystal. As expected from the crystal anisotropy, the various lattice reflections had very different behaviours. In the compression directions, the basal <0002> reflections appeared to bear much more load than the other planes. The resulting intergranular elastic strains could therefore reach up to 5000 microstrain after 10% total deformation, and were responsible for high type II residual stresses after unloading. Considering the macroscopic behaviour, the normal direction had higher mechanical properties than the other two processing directions. The strong texture measured from EBSD measurements suggest that the crystal anisotropy has been brought to a macroscopic level. The experiment also evidenced a significant change in texture for compression along the rolling direction which indicates twinning activation.
Authors: E.C. Oliver, Mark R. Daymond, Philip J. Withers
Abstract: The influence of texture and anisotropy on the generation of intergranular stresses in clock-rolled zirconium is investigated using neutron diffraction and elastoplastic self-consistent modelling. Comparison between experimental data and model calculations indicates that the operation mainly of prismatic and basal slip explains the trends in intergranular stress evolution during in-plane tensile and through-thickness compressive deformation, whilst twinning plays a significant role during in-plane compression.
Authors: S. Cai, Mark R. Daymond, R.A. Holt, E.C. Oliver
Authors: Yu. V. Taran, Jürgen Schreiber, Mark R. Daymond, E.C. Oliver
Abstract: On ECRS-6 [1], we have presented first results of the researches of fatigue degradation and martensitic transformation of austenitic stainless steel AISI 321 by neutron diffraction stress analysis. A series of samples preliminary ex-situ cyclically fatigued at the frequency of 5 and 0.5 Hz was in-situ tested on the stress rig of the ENGIN instrument. In the high cycle fatigued (HCF) samples, the applied stress-elastic strain responses of austenite and martensite phases were find out to be strongly different as compared to the low cycle fatigued (LCF) samples, in which they are close. Moreover, the martensite Poisson ratio in the HCF-samples is almost twice to that of observed 0.28-0.30 in austenite and in both phases of the LCF-samples. With the purpose to search the reason of such unusual behavior of the martensite phase, one of the HCF-samples has been anew in-situ tested on the stress rig of the ENGIN-X in: 1) a LCF-mode at the frequency of 0.1 Hz to increase the fatigue level, and 2) a quasistatic mode to measure the applied stress-elastic strain responses of both phases. Also, two of the LCF-samples have been subjected to the ex-situ secondary HCF-testing at the frequency of 5 Hz and again in-situ measured on the ENGIN-X stress rig. Results of the mechanical characterization of phases in the twice fatigued austenitic stainless steel are presented and discussed.
Authors: Bjørn Clausen, Robert C. Rogan, Ersan Üstündag, Mark R. Daymond, Volker Knoblauch
Authors: Mark R. Daymond, Carlos Tomé, Mark A.M. Bourke
Authors: Ersan Üstündag, Robert C. Rogan, Mark R. Daymond, Nobumichi Tamura, L. Margulies, Henning Friis Poulsen
Authors: E.C. Oliver, Mark R. Daymond, Philip J. Withers
Abstract: Neutron diffraction has been used to study the progress of deformation twinning and intergranular strain evolution in extruded magnesium during cyclic and monotonic loading at two temperatures. Differences in the intergranular strains generated during tensile and compressive tests are attributed to the operation of twinning in compression. Twinning activity is reduced relative to slip at higher temperature, leading to greater similarities between tension and compression. During cyclic loading, a distinct Bauschinger effect is observed after each compressive loading stage. The origin of this effect is identified as the reversal of twinning during unloading and subsequent tensile loading.
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