Two different types of shear-deformation behaviour in Au–Cu multilayers

Localised shear deformation of a material is usually identified as a particular feature of deformation inhomogeneity. Here, we show two different types of shear deformation-behaviour that occurred in Au–Cu multilayers subjected to microindentation load, namely, a cooperative-layer-buckling-induced shear banding in a nanoscale multilayer and a direct localised shearing across a layer interface along a shear plane in a submicron-scale multilayer. Theoretical analysis indicates that the formation of the two different types of shear deformation in the multilayers depends on a competition between the dislocation-pile-up-induced stress concentration at the layer interface and the barrier strength of the layer interface for glissile dislocation transmission.     

Inverse deformation-fracture responses between dendrite and matrix in Ti-based nanostructure–dendrite composite

The room-temperature deformation and fracture mechanisms of Ti-based nanostructured alloys are investigated. The monolithic nanostructured alloy goes through a shear banding???kinetic softening vicious cycle and exhibits very limited plasticity. The nanostructure–dendrite composite exhibits large plasticity while retaining a very high strength. Three fracture modes, namely shear fracture of the nanostructured matrix phase, normal ductile fracture of the dendritic phase and the peeling off of the dendrites from the matrix, are clearly observed. With increasing deformation, the nanostructured matrix is kinetically softened while the dendrite phase is work hardened. The inverse deformation responses and the interaction between the nanostructured matrix and the dendrites can effectively retard the inhomogeneous shear deformation of the nanostructured phase and lead to a large plasticity.     

Scaling of stacking fault energy and deformation temperature on strain hardening of FCC metals and alloys

The strain-hardening behaviour of metals and alloys are significantly affected by the dynamic recovery process, the rate of which can be increased by increases in deformation temperature and/or stacking fault energy (SFE). In the present work, the decay slope of the strain-hardening rate with flow stress as a function of both temperature and stacking fault energy is quantitatively evaluated for several face-centered cubic metals and alloys. A universal and quantitative approach to the scaling of the effects of temperature and stacking fault energy on strain-hardening behaviour is developed, which could be useful for predicting deformation behaviour or for material design.     

Dorsomedial prefrontal cortex 5-HT6 receptors regulate anxiety-like behavior

The dorsomedial prefrontal cortex (dmPFC) plays a very important role in decision-related and anxiety-related information processing. It has enriched 5-HT6 receptors; however, the precise role of dmPFC 5-HT6 receptors in anxiety remains to be fully investigated. In this study, we injected dmPFC with the 5-HT6 receptor agonist EMD 386088 and antagonist SB 271046 using stereotactic technology. 5-HT6 receptor activation in mice increased time spent in the center area on the open-field test, increased exploration of the open arms on the elevated plus maze test, and increased ratio on the social interaction test. 5-HT6 receptor inactivation induced the opposite effects. In brain slices, EMD 386088 decreased both spontaneous inhibitory postsynaptic currents (sIPSC) and spontaneous excitatory postsynaptic currents (sEPSC), while SB 271046 only increased sEPSC. These effects of EMD 386088 and SB 271046 could be reversed by the GABA_A receptor antagonist bicuculline (BMI) and positive allosteric modulator clonazepam (CLZ), respectively. Our results suggest that neurotransmission in the dmPFC by 5-HT6 receptor activation and inhibition may play an important role in anxiety-like behavior, and may provide new insight into the pathological mechanism and potential target of anxiety disorders.     

Enhanced plastic deformation in a metallic glass induced by notches

It is shown that the compressive plasticity of a metallic glass, namely Zr_52.5Ni_14.6Al₁₀Cu_17.9Ti₅, can be improved by the introduction of two symmetrical notches. The enhanced plasticity may be ascribed to a blocking effect of the propagation of shear bands caused by large stress gradients around the notches. In contrast to ceramic specimens with similar notches, the plasticity enhancement of metallic glass induced by notches can provide a new approach to understanding its unique mechanism of deformation.     

Large apparent compressive strain of metallic glasses

Very high plastic strains exceeding 20% in uniaxial compression tests, which show an inflection in the stress–strain curves of Zr-based bulk metallic glasses, are shown to be a spurious effect due to mechanical interlocking of cracks with shear bands. This type of stress–strain behaviour is misinterpreted as an actual deformation in the literature. The effect of mechanical interlocking is explained by fractographic analysis.     

Investigating the potential of EDA data from biometric wearables to inform inclusive design of the built environment

This paper presents a pilot of a method which measures quantitative biometric data to understand the emotional response of people to their physical environment. The aim of the audit method is to address the problem of lack of accessibility of public buildings for those with hidden disabilities. People with invisible disabilities such as Autistic Spectrum Disorders (ASD, Autism) sometimes feeling forced to withdraw from public spaces and communities and unfamiliar or busy environments such as art galleries can be particularly problematic (Amaze, 2018). As part of the Audit, data is collected using a wearable biometric device that is mapped against internal location. In this study the EDA (Electrodermal Activity) Audit was trialed with participants with ASD at a public art gallery in UK. The results reveal that participants with ASD experienced a greater increase in stress level compared to the neurotypical control participants. Areas where noticeable ‘peaks’ of stress were recorded usually had a restricted view or required human interaction. Comparison of GSR (Galvanic Skin Response) data with questionnaire information gathered before and after visiting the gallery also implies that the participants with ASD were less able to articulate their emotional response to spaces. We discuss the development of an EDA Audit method that could provide knowledge to help designers envision spaces that are more inclusive.     

Deformation of nanograined Ni–60Co alloy with low stacking fault energy

The evolution of deformation texture in a Ni–60Co alloy with low stacking fault energy and a grain size in the nanometre range has been investigated. The analyses of texture and microstructure suggest different mechanisms of deformation in nanocrystalline as compared to microcrystalline Ni–60Co alloy. In nanocrystalline material, the mechanism responsible for texture formation has been identified as partial slip, whereas in microcrystalline material, a characteristic texture forms due to twinning and shear banding.     

Homogeneous nucleation of dislocation loops under stress in perfect crystals

We present an analysis and results on the homogeneous nucleation of a dislocation loop under stress in a perfect crystal. By using a variational boundary integral method in the Peierls-Nabarro framework, we have determined the saddle-point configurations of embryonic dislocation loops and their associated activation energies under stress levels up to the ideal shear strength. The high-energy barriers under the usual levels of applied shear stresses, differing markedly from the ideal shear strength, confirm the widely held view that thermal motion should play no role in such nucleation. The result provides means for more definitive solutions of fundamental problems involving homogeneous nucleation of dislocation loops and has significant implications for models based on the mechanism of nucleation of dislocations from a perfect crystal.     

Shear band evolution during large plastic deformation of brittle and ductile metallic glasses

Four monolithic metallic glasses (MMGs) with different plasticities varying from brittle to ductile behavior under unconstrained loading were subjected to small punch testing. All specimens undergo large plastic deformation with multiple cobweb-like shear bands under these conditions. The process of shear band evolution was carefully controlled and investigated. Plasticity of MMGs is characterized by equivalent plastic strain ε* (product of shear band density and critical shear offset). Thus, this article provides an experimental basis for a better understanding of the shear band evolution during plastic deformation of MMGs.     

The Young-Laplace equation associated with transverse shear stress within the surface layer of a solid

ABSTRACT

The Young-Laplace equation was firstly established based on a liquid film without shearing resistance. It is not valid for a solid. By taking into account the in-plane shearing and transverse shearing within a surface layer, we reconstruct the Young-Laplace equation for a solid. This new version shows that the equilibrium of a solid surface is determined by the bulk stress, the surface membrane stress and the transverse shear stress acting together. The transverse shear stress depends on the gradient of the Gaussian curvature of the surface and the strain. The intrinsic membrane stress and transverse shear stress cause residual stresses to appear in the interior of the solid. The intrinsic transverse shear stress occurs only in a non-spherical shaped body.     

Strain localization in nickel single crystals cyclically deformed at 77 K

Nickel monocrystals oriented for single slip have been cyclically deformed at 77 K at plastic strain amplitude between 5 x 10^-4 and 1 x 10^-2 up to saturation of the stress amplitude. After unloading from maximum compression, the slip markings on the surface of the specimens were removed and the deformation continued for one half cycle in tension. As previously observed for room-temperature deformation, the plastic strain was found to be localized in narrow slip bands (SBs). Using atomic force microscopy at a given imposed strain amplitude, a wide spectrum of local plastic strains was found. The averaged resolved shear strain of the SBs was found to be independent of the imposed plastic strain amplitude and turned out to be a factor of three larger than the upper plateau strain limit of the cyclic stress-strain curve.     

Cumulative parenting stress across the preschool period: relations to maternal parenting and child behaviour at age 5

Despite increasing interest in the effects of parenting stress on children and families, many questions remain regarding the nature of parenting stress and the mechanism through which stress exerts its influence across time. In this study, cumulative parenting stress was assessed across the preschool period in a sample of 125 typically developing children and their mothers. Indices of parenting stress included both major life events stress‐assessed annually from age 3 to 5, and parenting daily hassles assessed every 6 months across the same period. Naturalistic home observations were conducted when children were age 5, during which measures of parent and child interactive behaviour as well as dyadic pleasure and dyadic conflict were obtained. Mothers also completed the CBCL to assess children's behaviour problems. Results indicated that parenting daily hassles and major life stress are relatively stable across the preschool period. Both cumulative stress indices also proved to be important predictors of parent and child behaviour and dyadic interaction, although the predictions were somewhat differential. Despite meaningful relations between the stress factors and child well being, no evidence was found to support the premise that parent behaviour mediates the association between parenting stress and child outcomes. Results are discussed within a developmental framework to understand the stability and complexity of cumulative stress associations to early parent–child relationships. Copyright © 2005 John Wiley & Sons, Ltd.     

Equivalent and effective strains during severe plastic deformation (SPD)

ABSTRACT

This paper considers the characteristics of severe plastic deformation (SPD) to estimate its efficacy and to compare different processing techniques. In contrast to effective strains by von Mises and Hencky, the rotation component of the strain rate is included in the analysis as a mode of deformation, which ranges from simple shear to pure shear. Distortions of material elements during a uniform plane plastic flow are calculated using a kinematic approach. For the fixed deformation mode, the current state is defined by the accumulated shears that are identical to the von Mises effective shear strains. In specific cases of pure shear and simple shear, the accumulated shears match the specific distortions of round or square elements prescribed by Hencky or von Mises approach, respectively. The mode of deformation is important to the structural effects of SPD. In general, two separated characteristics, accumulated shear and the coefficient of deformation mode, are necessary to describe strains during SPD.     

Deformation mechanism transitions in nanoscale fcc metals

We consider possible mechanisms that lead to transitions in the mechanisms of deformation in fcc metals and alloys. In particular, we propose that, when grain sizes are below a critical size (i.e. below 100?nm), deformation can occur via the emission of stacking faults from grain boundaries into the intragranular space. A model is developed that accounts for observed experimental data and which, in turn, shows how stacking-fault energy together with shear modulus determines achievable strength. A mechanism is proposed based on this model for transitions at both high and quasistatic strain rates, including grain-boundary sliding.     

Ductility enhancement in nanoglass: role of interaction stress between flow defects

Using a thermodynamically consistent non-local plasticity model, the mechanistic origin of enhancement in ductility and suppression of dominant shear banding in nanoglasses (NGs) is analysed. It is revealed that the interaction stress between flow defects plays a central role in promoting global plasticity of NGs. Specifically, we find that the intrinsic length associated with this stress provides a scaling for the shear band width and its coupling with grain size governs the level of enhancement in the deformation behaviour of NGs. The present work may provide useful insights in developing highly ductile NGs for practical engineering applications.     

The relationship between dynamic strain aging and serrated flow behaviour in magnesium alloy

The relationship between dynamic strain ageing (DSA) and serrated flow has been investigated via alternately switching strain rates at various temperatures in a Mg–3Nd–1Zn alloy. The results reveal that serrated flow is enhanced with decreasing strain rate and increasing temperature and tends to vanish, while the DSA continually intensifies as revealed by a higher flow stress even after the serration flow disappears. A mechanism is proposed, which could explain some abnormal deformation behaviour, such as a negative strain rate sensitivity and thermal hardening.     

DIMENSIONS OF DESIRE

This study provides an example of how feminist psychology can bridge qualitative and quantitative methods while keeping lived experience at the center of an inquiry. The goal of the study was to begin to understand adolescent girls' experiences of sexual desire. We describe three separate and synergistically related analyses of interviews with 30 adolescent girls. We begin with a qualitative analysis of their voiced experiences of sexual desire; follow with a quantitative analysis of the differences in how urban and suburban girls describe these experiences, assessing the role of reported sexual violation; and conclude with a second qualitative analysis exploring the interaction between social location and reported sexual violation. These three analyses enabled us to understand qualitatively and to quantify interrelated dimensions of desire as described by adolescent girls.     

心理解脱与幼儿教师生活满意度的关系：家庭压力的调节作用

下班后从工作状态中解脱出来有利于减少工作应激对劳动者健康的损害。家庭作为劳动者下班后生活的主要场所。家庭中的压力因素可能影响劳动者的解脱结果。本研究以 215 名幼儿教师为被试,考察家庭压力影响心理解脱结果的机制。结果发现,高家庭压力会削弱心理解脱对生活满意度的正向预测。该结果支持资源保持理论和付出-恢复模型,提示在工作应激相关的职业健康保护中应注意家庭因素的作用。     

Relation between coping and posttrauma cognitions on PTSD in a combat-trauma population

Individual differences in cognitive processes and coping behaviors play a role in the development and maintenance of posttraumatic stress disorder (PTSD). Given the large numbers of combat-exposed service members returning from the Operation Enduring Freedom (OEF), Operation Iraqi Freedom (OIF), and Operation New Dawn (OND) conflicts, exploring individual differences in cognitive-affective processes is important for informing our understanding of PTSD etiology and early intervention in military samples. The present study examined the unique main and interactive effects of negative posttrauma cognitions (i.e., negative beliefs about self [NS], the world [NW], and self-blame [SB]) and coping strategies (i.e., positive behavioral, positive cognitive, avoidant coping, and social and emotional coping) on PTSD diagnosis within 155 (M_age = 30.7, SD = 4.48) OEF/OIF/OND combat trauma-exposed Veterans recruited from an ongoing study examining the effects of combat trauma and stress reactivity. In the final, stepwise logistic regression analysis, avoidant coping, but no other coping strategy, was significantly positively related to PTSD diagnosis in the initial step. Higher levels of NS, but not NW, were significantly associated with having a PTSD diagnosis, whereas SB was associated with decreased likelihood of PTSD, above and beyond coping strategies. A significant interaction effect was found between NS and positive cognitive coping, such that greater positive cognitive coping weakened the relationship between NS and PTSD. Examining and addressing coping behaviors and negative thoughts of self jointly may benefit assessment and intervention approaches in a combat-trauma population.