In situ uniaxial pressure cell for x-ray and neutron scattering experiments.

We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes.

Autonomy and competence satisfaction as resources for facing chronic pain disability in adolescence: a self-determination perspective.

This study aimed to test empirically the developmental goal pursuit model of paediatric chronic pain, which draws upon Self-Determination Theory for understanding risks and resources for living with chronic pain. This study examined the relationship between basic psychological need satisfaction (i.e. the satisfaction of the needs for autonomy, relatedness and competence) and the fear-avoidance model of pain in adolescents suffering from chronic pain. Hundred and twenty adolescents (mean age = 14.52, 71.6% female), receiving treatment through paediatric pain centres for chronic pain, were enrolled. Adolescents completed measures of basic psychological need satisfaction, fear and avoidance of pain, and pain-related functional impairment. Path analyses model indicated that higher levels of autonomy and competence satisfaction were associated with lower levels of functional disability, through the mediation of fear and avoidance of pain. Relatedness satisfaction was not significatively related to fear of pain, avoidance, and functional disability. The integration of Self-Determination Theory in the paediatric pain literature may further our understanding of potential resources for decreasing functional disability in children living with chronic pain.

Stresses and Strains in Cruciform Samples Deformed in Tension.

The stress and strain relationship in the gauge region of six cruciform geometries is studied: the ISO standard geometry with slits in arms, two geometries with thinned gauge areas, two geometries with thinned gauge areas and slits in arms, and one modified ISO standard geometry with slits in arms and a thinned gauge area. For all the geometries, finite element simulations are performed under uniaxial loading to compare the plastic strain, the von Mises stress distribution and the in-plane stress evolution. Results show that less plastic strain can be achieved in the gauge of the two ISO standard geometries. For the remaining cruciform geometries, a strong non-linear coupling between applied forces in arms and gauge stresses is generated. The evolution of this non-linear coupling depends on the geometry type, applied biaxial load ratio and the elastic-plastic properties of the material. Geometry selection criteria are proposed to reduce this non-linear coupling.

Intergranular Strain Evolution During Biaxial Loading: A Multiscale FE-FFT Approach.

Predicting the macroscopic and microscopic mechanical response of metals and alloys subjected to complex loading conditions necessarily requires a synergistic combination of multiscale material models and characterization techniques. This article focuses on the use of a multiscale approach to study the difference between intergranular lattice strain evolution for various grain families measured during in situ neutron diffraction on dog bone and cruciform 316L samples. At the macroscale, finite element simulations capture the complex coupling between applied forces and gauge stresses in cruciform geometries. The predicted gauge stresses are used as macroscopic boundary conditions to drive a mesoscale full-field elasto-viscoplastic fast Fourier transform crystal plasticity model. The results highlight the role of grain neighborhood on the intergranular strain evolution under uniaxial and equibiaxial loading.

Origin of anomalous slip in tungsten.

Low-temperature deformation of body-centered cubic metals shows a significant amount of plastic slip on planes with low shear stresses, a phenomenon called anomalous slip. Despite progress in atomistic modeling of the consequences of complex stress states on dislocation mobility, the phenomenon of anomalous slip remained elusive. Using in situ Laue microdiffraction and discrete dislocation dynamics in micrometer sized tungsten single crystals, we demonstrate the occurrence of significant anomalous slip. It occurs as a consequence of cross kinks, topological configurations generated by prior dislocation interactions. This clearly identifies anomalous slip as a multidislocation process and not a property of isolated dislocations. The cross-kink mechanism also explains the ambiguous reporting of anomalous slip traces in the past and directs us to ways of including anomalous slip in continuum crystal plasticity formulations.