Effect of Mg content on Portevin–Le Chatelier band strain in Al–Mg sheet alloys

Experimental measurements of stress drops and band strains in type-B Portevin–Le Chatelier (PLC) bands were carried out for 5xxx series Al–Mg sheets with Mg content between 1.8 and 4.5?wt%. While the stress drops increase with global strain, the band strain values in all the samples follow a common linear relationship with global strain. The results indicate that the type-B PLC band strain is independent of solute content at given strain rate.     

Tension and compression of bulk Al-7.5 wt% Mg alloy

The mechanical behaviour of bulk ultrafine-grained Al-7.5 wt% Mg alloy consolidated from cryomilled powders has been investigated. The experimental data show that the alloy exhibits high strength, low strain hardening, serrated flow and relatively high ductility. In addition, the data indicate that the yield strength in tension is essentially equal to that in compression. The yield and flow strengths of the alloy are discussed in terms of strengthening processes that are related to grain size, the Orowan mechanism and solid-solution hardening. The serrations in the stress-strain curve are discussed in terms of dynamic strain ageing and deformation twinning.     

Strain rate response of a Ni–Ti shape memory alloy after hydrogen charging

In this work, we investigate the susceptibility of Ni–Ti superelastic wires to the strain rates during tensile testing after hydrogen charging. Cathodic hydrogen charging is performed at a current density of 10?A/m² during 2–12?h in 0.9% NaCl solution and aged for 24?h at room temperature. Specimens underwent one cycle of loading-unloading reaching a stress value of 700 MPa. During loading, strain rates from 10^?6 to 5?×?10^?2?^?s^?1 have been achieved. After 8?h of hydrogen charging, an embrittlement has been detected in the tensile strain rate range of 10^?6 to 10^?4?s^?1. In contrast, no embrittlement has been detected for strain rates of 10^?3?s^?1 and higher. However, after 12?h of hydrogen charging and 24?h of annealing at room temperature, the embrittlement occurs in the beginning of the austenite-martensite transformation for all the studied strain rate values. These results show that for a range of critical amounts of diffused hydrogen, the embrittlement of the Ni–Ti superelastic alloy strongly depends on the strain rate during the tensile test. Moreover, it has been shown that this embrittlement occurs for low values of strain rates rather than the higher ones. This behaviour is attributed to the interaction between the diffused hydrogen and growth of the martensitic domain.     

A longitudinal person-centred approach to the job demands-control model

We used a longitudinal design and a person-centred methodology to test the strain and learning hypotheses of the job demands–control model among Finnish employees (n = 926), who were followed-up at three time points covering a period of 2 years (2008–2010). First, we identified longitudinal subgroups in demands and control across three measurement points. Second, we examined how these subgroups differed in strain (job exhaustion) and motivation-related outcomes (vigour at work, work–family enrichment). Growth mixture modelling revealed four subgroups: “stable high strain”, “stable low strain”, “increasing control”, and “decreasing control”. The stable high- and low-strain subgroups also differed in the outcomes studied (exhaustion, work–family enrichment) as suggested by the demands–control model. The findings also suggest that job control is subject to changes over time and that these changes are likely to be associated with changes in employee outcomes. Malleability of job control should be kept in mind in job stress interventions, likewise the fact that some employees suffer from chronic job stress.     

Correlating the internal length in strain gradient plasticity theory with the microstructure of material

The internal length is the governing parameter in strain gradient theories which among other things have been used successfully to interpret size effects at the microscale. Physically, the internal length is supposed to be related with the microstructure of the material and evolves during the deformation. Based on Taylor hardening law, we propose a power-law relationship to describe the evolution of the variable internal length with strain. Then, the classical Fleck–Hutchinson strain gradient theory is extended with a strain-dependent internal length, and the generalized Fleck–Hutchinson theory is confirmed here, by comparing our model predictions to recent experimental data on tension and torsion of thin wires with varying diameter and grain size. Our work suggests that the internal length is a configuration-dependent parameter, closely related to dislocation characteristics and grain size, as well as sample geometry when this affects either the underlying microstructure or the ductility of the material.     

The Demand–Control model and target's reports of bullying at work: A test within Spanish and Belgian blue-collar workers

The present study explores whether Karasek's Job Demand–Control (JDC) model's strain hypothesis can be applied to target's reports of bullying at work in matched samples of Spanish and Belgian blue-collar workers. In the Spanish sample, results reveal a positive main effect of workload and a negative main effect of autonomy. The relationship between workload and bullying is particularly strong under the condition of low autonomy (i.e., interaction), in line with Karasek's strain hypothesis. In the Belgian sample, results show a positive main effect of workload and a significant workload–autonomy interaction effect in accordance with the strain hypothesis. In sum, high strain jobs associate with target's reports of bullying in both the Spanish and Belgian sample. Karasek's JDC model may accordingly be extended to target's reports of bullying as a form of social behavioural strain. These findings furthermore enhance research in the realm of bullying at work by introducing a well-established theoretical framework to account for the relationship between workload, autonomy, and target's reports of bullying.     

Ultrafine grain development in copper during multidirectional forging at 195 K

Strain-induced evolution of ultrafine grains in pure copper was studied in multidirectional forging (MDF) at 195?K. The stress–strain behaviour was characterized by rapid strain hardening during early processing and the rate of strain hardening gradually decreased with straining, leading to an apparent steady-state flow at large cumulative strains of more than 5. The structural changes were associated with the development of high-density microshear bands crossed by MDF. The new fine grains 0.16?µm in size, which was smaller than the subgrain size evolved during early deformation, were evolved primarily at microshear band intersections, and then the new fine grains filled out the whole sample as the number of microshear band intersections increased at large strains. This is essentially similar to continuous dynamic recrystallization. The size of new grains can be expressed by a power law function of flow stress with a grain size exponent of about –0.3. The kinetics of the strain-induced grain evolution is analyzed and the mechanisms are discussed.     

Are you tired? Spillover and crossover effects of emotional exhaustion on the family domain

This paper examines the spillover and crossover effects of emotional exhaustion on marital satisfaction for both employees and partners as well as on employee work–family conflict and partner family–work conflict. It investigates how the transmission of psychological strain from the workplace to the family domain mediates these relationships. In a sample of 226 employee–partner dyads from manufacturing, electronics, banking, service industries and public organizations, the results support the notion that employees' emotional exhaustion spawns negative strain in the home. More specifically, the results of spillover mediation analyses show the relationships between emotional exhaustion and employee marital satisfaction/work–family conflict in the home. In a crossover model, the results indicate that employee psychological strain mediates the relationships between emotional exhaustion and the marital satisfaction of partners/family–work conflict in partners. These findings provide supports for spillover and crossover models to investigate a direction for the effectiveness of emotional exhaustion on family issues. Theoretical and practical implications of the results are discussed, and directions for future research are offered.     

Influence of strain rate on the orientation dependence of microstructure in nickel single crystals

The deformation microstructures of nickel single crystals (99.945 wt.%) during dynamic plastic deformation and quasi-static compression to a true strain of 0.20 were comparatively investigated. The deformation microstructures are orientation dependent, forming cell structure, slip plane aligned or not slip plane aligned extended boundaries. It is found that the orientation spread decreases, remains unchanged and becomes enhanced when loading along 〈0?0?1〉, 〈0?1?1〉 and 〈1?1?1〉, respectively, as strain rate increases.     

应变率显像评价尿毒症EF正常患者左心室局部功能

为探讨应变率显像(SRI)技术评价尿毒症左心室射血分数(EF)正常患者左心室局部功能的价值,对41例尿毒症EF正常患者及20例健康自愿者左心室心肌纵向SRI曲线进行分析,测量各曲线收缩峰值应变率(SRs)、舒张早期峰值应变率(SRe)、舒张晚期峰值应变率(SRa)并计算SRe/SRa。结果显示,尿毒症组左心室各节段SRs、SRe、SRe/SRa均低于对照组(P0.05)。因此,尿毒症EF正常患者已经存在局部心肌舒缩功能障碍,并且这种障碍可以被SRI技术敏感、定量地评价。     

Dislocation formation in the partially coherent interfaces of an embedded layer in a semi-infinite matrix

The formation of two misfit edge dislocations is theoretically investigated in the interfaces of a layer embedded in a semi-infinite matrix. Assuming the matrix–layer interfaces are partially coherent, the energy variation resulting from the formation of the dislocations from the lateral free surface of the structure has been determined in the shearing stress field due to the partial misfit. The mechanical stability of the structure is analysed with respect to the dislocation formation as a function of the size of the coherent region of the interface and the misfit strain.     

Tensile properties of precracked tempered martensitic steel specimens tested at ultralow strain rates in high-pressure hydrogen atmosphere

Tensile tests were performed on precracked Cr–Mo martensitic steel (C: 0.38, Si: 0.22, Mn: 0.84, P: 0.024, S: 0.021, Ni: 0.08, Cr: 1.11, Mo: 0.15, Cu: 0.12, Fe: bal. (wt%)) specimens at various strain rates (ranging from 6.5 × 10^?8 s^?1 to 1.0 × 10^?4 s^?1) in high-pressure (95 MPa) hydrogen and helium atmospheres. Irrespective of the strain rate, the tensile strength in the helium atmosphere was 1400 MPa. In the hydrogen atmosphere, the tensile strength decreased to less than 600 MPa at a strain rate of 2.0 × 10^?5 s^?1. However, the tensile strength increased to 900 MPa when the strain rate was decreased to 6.5 × 10^?8 s^?1. This recovery of the tensile strength was because of the decrease in the local stress in the vicinity of the precrack because of hydrogen.     

Dynamic properties of an ultrafine-grained Mg–Zn–Zr alloy

The effect of ultrafine-grained structure formation in Mg–Zn–Zr alloy ZK60 on its mechanical response was investigated at strain rates ranging from quasi-static to dynamic regimes. The study demonstrated that the strength characteristics of the material rise significantly with increasing strain rate, while its ductility is reduced. These effects are particularly pronounced in the dynamic loading regime, at strain rates in the (1?5)?×?10²?s^?1 range. In the ultrafine-grained alloy ZK60, the energy absorption per unit volume, W, is enhanced by grain refinement by a factor as high as eight for the highest strain rate of 5?×?10²?s^?1 investigated. The analysis is focused on the microstructure features that bring about the observed improvement of the tensile characteristics, as well as the deformation and fracture modes prevalent at different strain rates. The results obtained contribute to the exploration and understanding of dynamic behaviour of magnesium alloys.     

On elastic–viscoplastic modeling of nanotwinned metals based on coupled intra-twin and twin-boundary-mediated deformation mechanisms

An elastic–viscoplastic model has been developed for nanotwinned (nt) metals based on coupled intra-twin and twin-boundary-mediated (TBM) deformation mechanisms. The grain-size dependence of intra-twin plasticity was incorporated in the proposed model to determine the transitional twin thickness corresponding to the maximum strength. In addition, the joint distribution of grain size and twin thickness was also taken into account to simulate the microstructure of nt metals. The results obtained show that the TBM deformation mechanism dominated at low strain rate and small twin thickness, and that the grain-size and twin-thickness distributions had significant influence on the macroscopic behavior of nt metals. A linear relation between the transitional twin thickness and grain size is predicted by the proposed model, which is in good agreement with the results obtained from three-dimensional molecular dynamics simulations and experiments.     

On the ultra-high-strain rate shock deformation in copper single crystals: multiscale dislocation dynamics simulations

Multiscale dislocation dynamics plasticity (MDDP) calculations are carried out to simulate the mechanical response of copper single crystals that have undergone shock loading at high strain rates ranging from 1?×?10⁶ to 1?×?10¹⁰?s^?1. Plasticity mechanisms associated with both the activation of pre-existing dislocation sources and homogeneous nucleation of glide loops are considered. Our results show that there is a threshold strain rate of 10⁸?s^?1 at which the deformation mechanism changes from source activation to homogeneous nucleation. It is also illustrated that the pressure dependence on strain rate follows a one-fourth power law up to 10⁸?s^?1 beyond which the relationship assumes a one-half power law. The MDDP computations are in good agreement with recent experimental findings and compare well with the predictions of several dislocation-based continuum models.     

Parental employment status and adolescents’ health: The role of financial situation,parent-adolescent relationship and adolescents’ resilience

The paper deals with parental employment status and its relationship to adolescents’ self-reported health. It studies the role of the financial situation, parent–adolescent relationship and adolescent resilience in the relationship between parental employment status and adolescents’ self-rated health, vitality and mental health. Multiple regression analyses were used to analyse questionnaire data obtained from 2799 adolescents (mean age 14.3) in 2006. The results show a negative association of the father’s, but not mother’s unemployment or non-employment with adolescents’ health. Regression analyses showed that neither financial strain nor a poor parent–adolescent relationship or a low score in resilience accounted for the relationship between the father’s unemployment or non-employment and poorer adolescent health. Furthermore, resilience did not work as a buffer against the negative impact of fathers’ unemployment on adolescents’ health.     

Family Strain and Adolescent Delinquency in Two Chinese Cities,Guangzhou and Hong Kong

Elucidating the conditions in which family strain takes effect in adolescent delinquency is one avenue along which to substantiate general strain theory. These conditions include family relationship and the type of delinquency. In the context of Chinese societies, the conditions also include the differences between socialist, collectivist Mainland China and capitalist, more individualist Hong Kong. We collected survey data from 1,026 secondary school students in Guangzhou in Mainland China, and from 1,116 in Hong Kong, to demonstrate these conditions. The results, which indicate the intimate relationship between parents and adolescents, verify that family strain has a very strong impact on adolescent delinquency. In this connection, family strain comprised parental support as a negative indicator. However, the effect of parental support on adolescent strain was only weakly negative in Guangzhou and even positive in the case of nonworking mothers. The differentials in parental influence between Guangzhou and Hong Kong are attributable to the different family policies and structures in the two cities. On the other hand, family strain exhibited similar effects on two types of delinquency, violence and status offense.     

Deformation kinetics in Zr-based bulk metallic glasses and its dependence on temperature and strain-rate sensitivity

Micromechanical analysis of ductile bulk metallic glasses at various temperatures and strain rates revealed accurate information on inhomogeneous flow kinetics. The disappearance of flow instabilities (i.e. serrations) at low temperatures correlates with a change from negative to positive strain-rate sensitivity and exhibits an activation energy of 0.37?eV. Based on these findings, a constitutive deformation model for thermally-activated flow in disordered systems is presented, which accounts for possible structural relaxation processes within the shear bands. Similarities in the flow behaviour of bulk metallic glasses with the Portevin–Le Châtelier effect known for crystalline metals are discussed.     

Psychological state and psychological strain in relation to infertility

The purpose of the study was to explore the relationship between psychological state and perceived strain in relation to fertility problems. Couples presenting at an infertility clinic completed, on two occasions seven months apart, a series of standardized measures to assess psychopathology. In addition, they completed a weekly diary rating their mood state or distress/strain over a period of 22 weeks, during which investigations and treatment were taking place. Little evidence of psychopathology was found in the sample; the weekly diaries also suggested a general lack of distress/strain, even in response to medical investigations and diagnosis. The results are discussed in the light of wide individual variations in ratings obtained from the diaries. Participants with high distress/strain scores tended to have significantly higher initial scores on the psychometric measures administered. Participants with high distress/strain scores were also more likely to show a further significant increase in distress/strain scores in relation to diagnostic information. It is argued that a task for future research is to determine the characteristics of those couples who are likely to experience difficulty in coping with the strain of infertility investigations so that counselling resources and support services can be most effectively targeted. © 1998 John Wiley & Sons, Ltd.