<i>In-situ</i> SEM study of slip-controlled short-crack growth in single-crystal nickel superalloy

Initiation and growth of short cracks in a nickel-based single crystal were studied by carrying out in-situ fatigue experiments within a scanning electron microscope (SEM). Specimens with two different crystallographic orientations, i.e., [001] and [111], were tested under load-controlled tension fatigue in vacuum. Slip-caused crack initiation was identified at room temperature while initiation of a mode-I crack was observed at 650°C. Slip traces continuously developed ahead of the crack tip once initiated and acted as nuclei for early-stage crack growth at both room and high temperature (650°C). These slip traces were caused by accumulated shear deformation of activated octahedral slip systems, which were specifically identified by analysing the surface slip traces and crack-propagation planes. The crack-growth rates were evaluated against stress intensity factor range, revealing the anomaly of slip-controlled short-crack growth. The effects of crystallographic orientations and temperature on fatigue crack growth were subsequently analysed and discussed, including the influence of microstructural features such as carbides and pores

Environmental Resource - Economized Processes of Recycling Mineral Raw Materials of Complex Composition

The results of the studies on the justification of technological processes providing recycling of the warehoused ferruginous quartzites of complex composition and waste non-ferrous metals allowing to receive additional commodity products are given. The example of amphibole and biotite varieties of ferruginous quartzites of CMA and tailings of copper-zinc sulphide Ural ores determines the reasons of ineffective use of traditional technology solutions for recycling. The reasons of environmental hazards concerning varieties of technogenic mineral substances to the environment are identified. The presence in ferruginous quartzites complex composition of various silicates, carbonates and iron sulphides change their technological properties. So to get the iron concentrate from them suggests a new combination of technological operations performed in specially selected operating conditions. The specifics of the presence of mineral components in solid mineral wastes of nonferrous metal ores indicates the possibility of obtaining additional marketable products. With the use of laboratory multiscale modelling and physical methods of analysis regularities of variation of fractionation, separation and mineral concentration operations efficiency by varying its composition and the various influencing factors are identified. To improve the efficiency of the individual technological operations it is recommended to use different techniques, using physical and physico-chemical effects on the polymineral systems. The flow diagrams for the considered varieties of technogenic processing of mineral substances, allowing them to obtain standared quality products (metal-containing concentrates), and the results of their testing are submitted. The suggested technological solutions can reduce the amount of environmentally hazardous mineral substance, hosted in technogenic formations

Low-cycle fatigue of single crystal nickel-based superalloy – mechanical testing and TEM characterisation

Low-cycle fatigue (LCF) is studied for a nickel-based single-crystal superalloy in this paper, with a focus on the effect of crystal orientation and temperature. Specifically, cyclic deformation of the alloy was compared for [001]- and [111]-oriented samples tested under strain-controlled conditions at room temperature and 825 °C. Either cyclic hardening or softening was observed during the LCF process, depending on the strain amplitude, crystallographic orientation and temperature. LCF life was also reduced significantly by changing loading orientation from [001] to [111] or increasing temperature to 825 °C. Employing a comprehensive study with transmission electron microscopy (TEM), a connection between microstructure and mechanical behaviour of the alloy is discussed. It was found that the processes of γ′-precipitate dissolution and dislocation recovery were responsible for cyclic softening. Alignments and pile-ups of dislocations in the γ matrix, which prohibited their movement and reduced the interaction of dislocations on different slip systems, contributed to cyclic hardening

Identification of elastic parameters of composite using experimental data on modal characteristics of samples

In order to determine the elastic parameters of polymer composites, a mixed numericalexperimental method of identification was developed in the 1990s - 2000s, based on the use of experimental data on natural frequencies and eigenmodes of oscillation of samples. Its practical application involves the choice of a shape and a size of samples, a set used to identify the natural frequencies and eigenmodes of vibration, a methods of their experimental determination, a finiteelement model for modal analysis, and an algorithm for solving the identification problem. The object of the research is laminated polymer composite materials reinforced with carbon or glass fibers. The aim of the work is to develop practical aspects of implementation and assessment of the accuracy of the mixed experimental-calculation method for identifying of the elastic parameters of such materials based on experimental data on natural frequencies and eigenmodes of vibration of standard samples. Parameter identification for the material is considered as an optimization problem with an optimization function, which is a weighted sum of squares of differences between the experimental and calculated values of natural frequencies. A procedure was developed to implementing the main steps of the suggested technique: experiments, calculations and control of results. An error analysis of main steps was carried out, and the accuracy of the determined parameters of the ply was estimated. To determine the natural frequencies and eigenmodes of oscillation of the samples, the method of three-component scanning laser vibrometry was used. The experimental technique was established and parameters of the technique were chosen to ensure the necessary accuracy in determining of the natural frequencies. The parameters of the identification procedure and the finite-element model of the sample were selected. To control the obtained values of the elastic parameters, the natural frequencies of the samples were calculated, including those not used in the identification procedure. The error assessment of the in determined elastic parameters was performed on three different series of samples of carbon-fiber-reinforced laminates with the same material of the plies and different ply numbers and stacking orders. The developed technique can be recommended to determine the parameters of material models required for strength and vibrations assessment of products manufactured with layered composites

3D DDD modelling of dislocation-precipitate interaction in a nickel-based single crystal superalloy under cyclic deformation

Strain-controlled cyclic deformation of a nickel-based single crystal superalloy has been modelled by using three-dimensional (3D) discrete dislocation dynamics (DDD) for both [001] and [111] orientations. The work focused on the interaction between dislocations and precipitates during cyclic plastic deformation at elevated temperature, which has not been well studied yet. A representative volume element (RVE) with cubic γ’-precipitates was chosen to represent the material, with enforced periodical boundary conditions. In particular, cutting of superdislocations into precipitates was simulated by a back-force method. The global cyclic stress-strain responses were captured well by the DDD model when compared to experimental data, particularly the effects of crystallographic orientation. Dislocation evolution showed that considerably high density of dislocations was produced for [111] orientation when compared to [001] orientation. Cutting of dislocations into the precipitates had a significant effect on the plastic deformation, leading to material softening. Contour plots of in-plane shear strain proved the development of heterogeneous strain field, resulting in the formation of shear-band embryos

Relations between parameters of fracture processes on different scale levels

© 2018, Pleiades Publishing, Ltd. Abstract: The processes of ultrasonically-assisted drilling (UAD) and the dynamic tests on split Hopkinson pressure bar (SHPB), fracture in which is implemented at various structural-scale levels, are considered. The simulation of UAD based on the Hertz contact problem and the structural−time criterion is presented. The problem of using the value of the fracture incubation time and its linear size obtained from the tests on SHPB in the simulation is considered. A principle of equal power is used for converting the strength parameters into another structural−scale level. The theoretical curve obtained in the simulation is compared with the results of experiments on conventional drilling (CD) and UAD

Ti alloy with enhanced machinability in UAT turning

Metastable β-titanium alloys such as Ti 15V 3Al 3Cr 3Sn are of great technological interest thanks to their high fatigue strength-to-density ratio. However, their high hardness and poor machinability increase machining costs. Additionally, formation of undesirable long chips increases the machining time. To address those issues, a metastable β-titanium alloy (Ti 15V 3Al 3Cr 2Zr 0.9La) with enhanced machinability was developed to produce short chips even at low cutting speeds. A hybrid ultrasonically assisted machining technique, known to reduce cutting forces, was employed in this study. Cutting force components and surface quality of the finished work-pieces were analyzed for a range of cutting speeds in comparison with those for more traditional Ti 15V 3Al 3Cr 3Sn. The novel alloy demonstrated slightly improved machining characteristics at higher cutting speeds and is now ready for industrial applications

The construction of an idealised urban masculinity among men with concurrent sexual partners in a South African township

Background : The perspectives of heterosexual males who have large sexual networks comprising concurrent sexual partners and who engage in high-risk sexual behaviours are scarcely documented. Yet these perspectives are crucial to understanding the high HIV prevalence in South Africa where domestic violence, sexual assault and rape are alarmingly high, suggesting problematic gender dynamics. Objective : To explore the construction of masculinities and men&#x0027;s perceptions of women and their sexual relationships, among men with large sexual networks and concurrent partners. Design : This qualitative study was conducted in conjunction with a larger quantitative survey among men at high risk of HIV, using respondent-driven sampling to recruit participants, where long referral chains allowed us to reach far into social networks. Twenty in-depth, open-ended interviews with South African men who had multiple and concurrent sexual partners were conducted. A latent content analysis was used to explore the characteristics and dynamics of social and sexual relationships. Results : We found dominant masculine ideals characterised by overt economic power and multiple sexual partners. Reasons for large concurrent sexual networks were the perception that women were too empowered, could not be trusted, and lack of control over women. Existing masculine norms encourage concurrent sexual networks, ignoring the high risk of HIV transmission. Biological explanations and determinism further reinforced strong and negative perceptions of women and female sexuality, which helped polarise men&#x0027;s interpretation of gender constructions. Conclusions : Our results highlight the need to address sexuality and gender dynamics among men in growing, informal urban areas where HIV prevalence is strikingly high. Traditional structures that could work as focal entry points should be explored for effective HIV prevention aimed at normative change among hard-to-reach men in high-risk urban and largely informal contexts

Childbearing and Economic Work: The Health Balance of Women in Accra, Ghana

Objectives: This study aims to investigate (1) whether the health of working women with young children differs from that of working women without young children, and (2) which social factors mediate the relationship between economic and maternal role performance and health among mothers with young children. Methods: The analyses uses panel data from 697 women present in both waves of the Women's Health Study for Accra (WHSA-I and WHSA-II); a community based study of women aged 18 years and older in the Accra Metropolitan Area of Ghana conducted in 2003 and 2008-2009. Change in physical and mental health between the survey waves is compared between women with a biological child alive at WHSA-II and born since WHSA-I and women without a living biological child at WHSA-II born in the interval. To account for attrition between the two survey waves selection models were used with unconditional change score models being used as the outcome model. Results: We found in our sample of working women that those who had a child born between WHSA-I and WHSA-II who was still alive at WHSA-II did not experience a change in mental or physical health different from other women. Among working women with young children, educational status, relationship to the household head and household demography were associated with change in mental health at the 5 % level, whilst migration status and household demography was associated with change in physical health scores. Conclusion: The results suggest there are no health penalties of combining work and childbearing among women with young children in Accra, Ghana