Extraction of mechanical properties over a range of strain rates from indentation data

A procedure is described for indentation creep plastometry. It is based on iterative numerical simulation of the indentation process, with repeated comparison between an experimental outcome and the corresponding model prediction, systematically varying the values of parameters in a constitutive law until optimal agreement is achieved. The experimental outcome is the penetration depth as a function of time, under a constant applied load. An important feature of the procedure is the prior creation of a spherical recess in the sample, having a pre-selected depth and a curvature radius equal to that of the indenter. This allows control over the stress levels created during the indentation creep testing and can be used to ensure that no (time-independent) plastic deformation is stimulated during the test. Confirmation of the viability of the procedure is provided via comparisons between the creep characteristics of pure nickel samples at 750˚C, obtained in this way and via conventional uniaxial tensile testing. A similar procedure has been applied for the study of rate-dependent plasticity in bulk metallic materials. Ballistic impact (indentation) of hard spherical projectiles was used to study a rigidly held target, with operative strain rates of the order 105 s-1. Input for the FEM model includes data characterizing the (temperature-dependent) quasi-static plasticity, obtained by conventional uniaxial testing. The experimental outcomes are displacement-time plots for the projectile and the residual indent profile. Since the strain rate sensitivity is characterised by a single parameter value (C in the Johnson–Cook formulation), convergence on its optimum value is straightforward, although a parameter characterizing interfacial friction is also required. Using experimental data from (both work-hardened and annealed) copper samples, this procedure has been carried out and best-fit values of C (∼0.016 and ∼0.030) have been obtained. This procedure has been extended for the study of fracture characteristics (under high imposed strain rates). The strain rate sensitivity of magnesium was evaluated (C~0.026) as above. The main emphasis, however, is on study of its fracture characteristics, with tomographic imaging being used to obtain crack patterns for different projectile velocities. An approach based on fracture mechanics, and on use of FEM modelling to estimate the strain energy release rate required for crack propagation (i.e. the fracture energy of the material) is proposed and applied to these experimental results, leading to a value of the order of 2 kJ m-2. While such a procedure is unlikely to produce accurate values, partly because the crack propagation takes place under local conditions that change rapidly and are not well-defined, this figure is plausible for the case concerned. While there are several sources of complexity, it may be possible to develop this methodology, both as a technique for fracture toughness measurement (requiring only small samples of simple shape) and as an improved approach to prediction of ballistic impact outcomes

Indentation Plastometry of Welds

This investigation concerns the application of the profilometry-based indentation plastometry (PIP) methodology to obtain stress–strain relationships for material in the vicinity of fusion welds. These are produced by The Welding Institute (TWI), using submerged arc welding to join pairs of thick steel plates. The width of the welds varies from about 5 mm at the bottom to about 40–50 mm at the top. For one weld, the properties of parent and weld metal are similar, while for the other, the weld metal is significantly harder than the parent. Both weldments are shown to be approximately isotropic in terms of mechanical response, while there is a small degree of anisotropy in the parent metal (with the through-thickness direction being slightly softer than the in-plane directions). The PIP procedure has a high sensitivity for detecting such anisotropy. It is also shown that there is excellent agreement between stress–strain curves obtained using PIP and via conventional uniaxial testing (tensile and compressive). Finally, the PIP methodology is used to explore properties in the transition regime between weld and parent, with a lateral resolution of the order of 1–2 mm. This reveals variations on a scale that would be very difficult to examine using conventional testing

Indentation Plastometry of Particulate Metal Matrix Composites, Highlighting Effects of Microstructural Scale

Herein, it is concerned with the use of profilometry-based indentation plastometry (PIP) to obtain mechanical property information for particulate metal matrix composites (MMCs). This type of test, together with conventional uniaxial testing, has been applied to four different MMCs (produced with various particulate contents and processing conditions). It is shown that reliable stress–strain curves can be obtained using PIP, although the possibility of premature (prenecking) fracture should be noted. Close attention is paid to scale effects. As a consequence of variations in local spatial distributions of particulate, the “representative volume” of these materials can be relatively large. This can lead to a certain amount of scatter in PIP profiles and it is advisable to carry out a number of repeat PIP tests in order to obtain macroscopic properties. Nevertheless, it is shown that PIP testing can reliably detect the relatively minor (macroscopic) anisotropy exhibited by forged materials of this type

Public involvement in the governance of population-level biomedical research: unresolved questions and future directions.

Population-level biomedical research offers new opportunities to improve population health, but also raises new challenges to traditional systems of research governance and ethical oversight. Partly in response to these challenges, various models of public involvement in research are being introduced. Yet, the ways in which public involvement should meet governance challenges are not well understood. We conducted a qualitative study with 36 experts and stakeholders using the World Café method to identify key governance challenges and explore how public involvement can meet these challenges. This brief report discusses four cross-cutting themes from the study: the need to move beyond individual consent; issues in benefit and data sharing; the challenge of delineating and understanding publics; and the goal of clarifying justifications for public involvement. The report aims to provide a starting point for making sense of the relationship between public involvement and the governance of population-level biomedical research, showing connections, potential solutions and issues arising at their intersection. We suggest that, in population-level biomedical research, there is a pressing need for a shift away from conventional governance frameworks focused on the individual and towards a focus on collectives, as well as to foreground ethical issues around social justice and develop ways to address cultural diversity, value pluralism and competing stakeholder interests. There are many unresolved questions around how this shift could be realised, but these unresolved questions should form the basis for developing justificatory accounts and frameworks for suitable collective models of public involvement in population-level biomedical research governance

Effects of Erythrocyte Aggregation on Blood Rheology in Regard to Future Sepsis Diagnosis Application

Sepsis is a condition resulting from the overreaction of the body to an infectious agent and results in millions of deaths worldwide each year. Sepsis has a very short infection-to-mortality time and can be hard to detect and treat before related afflictions become permanent. A device that could quickly and effectively diagnose sepsis could be incredibly beneficial to ensuring proper treatment is given to septic patients. Furthermore, providing alternative methods of testing than the currently used standard would allow for additional in-depth analysis and the possibility of increased diagnostic success. This paper works to therefore describe the design of a prototype, the included tests, and the reason for use in regard to future septic diagnosis

The relationship between age, workplace slips and the effectiveness of slip-resistant footwear among healthcare workers

Objectives. To explore any age-related trend in workplace slip rate and assess the effectiveness of appropriate slip-resistant footwear in preventing workplace slips by age. Methods. Secondary data analysis of the Stopping Slips among Healthcare Workers (SSHeW) trial, a two-arm randomised controlled trial conducted between March 2017 and May 2019. 4553 National Health Service (NHS) staff across seven sites in England were randomised 1:1 to the intervention group (provision of 5* GRIP-rated slip-resistant footwear) or the control group (usual work footwear). The primary outcome was self-reported workplace slips, ascertained primarily through weekly text messages throughout the 14-week trial follow-up and analysed using mixed effects negative binomial regression. This paper reports a control-group only analysis of the association between age and slip rate, and a full intention-to-treat analysis of the effectiveness of slip-resistant footwear by age. Results. The mean age of participants was 43 years (range 18-74). In the control-group only analysis, slip rate differed by age (p<0.001) with those aged 60+ having double the slip rate of those aged <30 years (95% CI 1.40-2.87). In the intention-to-treat analysis, the interaction between allocation and age was statistically significant (p=0.002). In addition, for all age groups except those aged <30 years, the slip rate in the intervention group was statistically significantly lower than the control group; the smallest incidence rate ratio (i.e., the biggest effect) was 0.39 (95% CI 0.25-0.65) in the 60+ age group. Conclusions. The provision of appropriate slip-resistant footwear was more effective at reducing workplace slips for older NHS staff. Keywords: Interventions; Occupational Injury; Randomised Trial; Workplace; Older Peopl

Indentation plastometry of welds

This investigation concerns the application of the profilometry-based indentation plastometry (PIP) methodology to obtain stress–strain relationships for material in the vicinity of fusion welds. These are produced by The Welding Institute (TWI), using submerged arc welding to join pairs of thick steel plates. The width of the welds varies from about 5 mm at the bottom to about 40–50 mm at the top. For one weld, the properties of parent and weld metal are similar, while for the other, the weld metal is significantly harder than the parent. Both weldments are shown to be approximately isotropic in terms of mechanical response, while there is a small degree of anisotropy in the parent metal (with the through-thickness direction being slightly softer than the in-plane directions). The PIP procedure has a high sensitivity for detecting such anisotropy. It is also shown that there is excellent agreement between stress–strain curves obtained using PIP and via conventional uniaxial testing (tensile and compressive). Finally, the PIP methodology is used to explore properties in the transition regime between weld and parent, with a lateral resolution of the order of 1–2 mm. This reveals variations on a scale that would be very difficult to examine using conventional testing

Limiter bias experiments in DIII-D

In DIII-D, H{sub {alpha}} emission was reduced by a factor of 2--3 both at the limiter and at the inner wall by negative biasing (V{sub lim}{approx} {minus}300 V). In these discharges, the line-average electron densities were approximately the same with and without limiter bias, which suggests that {tau}{sub p} was improved by negative bias. Edge Bremsstrahlung emission signals were reduced by a factor of two. Repetitive bursts were observed in H{sub {alpha}} signals and edge Bremsstrahlung signals. Impurity levels increased with limiter bias, which induced major disruptions. No improvement of {tau}{sub E} was observed. These experimental data suggest that particle confinement characteristics of limiter biased discharges are similar to those with divertor H-mode. 11 refs., 5 figs