Discrete dislocation simulations and size dependent hardening in single slip

Plastic deformation in two-dimensional monophase and composite materials is studied using a discrete dislocation dynamics method. In this method, dislocations are represented by line defects in a linear elastic medium, and their interactions with boundaries or second-phase elastic particles are incorporated through a complementary finite element solution. The formulation includes a set of simple constitutive rules to model the lattice resistance to dislocation glide, as well as the generation, annihilation and pinning of dislocations at point obstacles. The focus is on the predicted strain hardening of these materials when only a single slip system is active. When the particle morphology is such as to require geometrically necessary dislocations, hardening in the composite materials exhibits a distinct size effect. This size effect is weaker than that predicted by simple analytical estimates based on geometrically necessary dislocations.

Plasticity size effects in tension and compression of single crystals

The effect of size and loading conditions on the tension and compression stress–strain response of micron-sized planar crystals is investigated using discrete dislocation plasticity. The crystals are taken to have a single active slip system and both small-strain and finite-strain analyses are carried out. When rotation of the tensile axis is constrained, the build-up of geometrically necessary dislocations results in a weak size dependence but a strong Bauschinger effect. On the other hand, when rotation of the tensile axis is unconstrained, there is a strong size dependence, with the flow strength increasing with decreasing specimen size, and a negligible Bauschinger effect. Below a certain specimen size, the flow strength of the crystals is set by the nucleation strength of the initially present Frank–Read sources. The main features of the size dependence are the same for the small-strain and finite-strain analyses. However, the predicted hardening rates differ and the finite-strain analyses give rise to some tension–compression asymmetry.

Scaling of discrete dislocation predictions for near-threshold fatigue crack growth

Analyses of the growth of a plane strain crack subject to remote mode I cyclic loading under small scale yielding are carried out using discrete dislocation dynamics. Plastic deformation is modelled through the motion of edge dislocations in an elastic solid with the lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation being incorporated through a set of constitutive rules. An irreversible relation is specified between the opening traction and the displacement jump across a cohesive surface ahead of the initial crack tip in order to simulate cyclic loading in an oxidizing environment. Calculations are carried out with different material parameters so that values of yield strength, cohesive strength and elastic moduli varying by factors of three to four are considered. The fatigue crack growth predictions are found to be insensitive to the yield strength of the material despite the number of dislocations and the plastic zone size varying by approximately an order of magnitude. The fatigue threshold scales with the fracture toughness of the purely elastic solid, with the experimentally observed linear scaling with Young's modulus an outcome when the cohesive strength scales with Young's modulus. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

“You can’t be a person and a doctor”. The work-life balance of doctors in training: a qualitative study

Objectives Investigate the work–life balance of doctors in training in the UK from the perspectives of trainers and trainees. Design Qualitative semistructured focus groups and interviews with trainees and trainers. Setting Postgraduate medical training in London, Yorkshire and Humber, Kent, Surrey and Sussex, and Wales during the junior doctor contract dispute at the end of 2015. Part of a larger General Medical Council study about the fairness of postgraduate medical training. Participants 96 trainees and 41 trainers. Trainees comprised UK graduates and International Medical Graduates, across all stages of training in 6 specialties (General Practice, Medicine, Obstetrics and Gynaecology, Psychiatry, Radiology, Surgery) and Foundation. Results Postgraduate training was characterised by work–life imbalance. Long hours at work were typically supplemented with revision and completion of the e-portfolio. Trainees regularly moved workplaces which could disrupt their personal lives and sometimes led to separation from friends and family. This made it challenging to cope with personal pressures, the stresses of which could then impinge on learning and training, while also leaving trainees with a lack of social support outside work to buffer against the considerable stresses of training. Low morale and harm to well-being resulted in some trainees feeling dehumanised. Work–life imbalance was particularly severe for those with children and especially women who faced a lack of less-than-full-time positions and discriminatory attitudes. Female trainees frequently talked about having to choose a specialty they felt was more conducive to a work–life balance such as General Practice. The proposed junior doctor contract was felt to exacerbate existing problems. Conclusions A lack of work–life balance in postgraduate medical training negatively impacted on trainees' learning and well-being. Women with children were particularly affected, suggesting this group would benefit the greatest from changes to improve the work–life balance of trainees