Raman microscopic analysis of internal stress in boron-doped diamond

Analysis of the induced stress on undoped and boron-doped diamond (BDD) thin films by confocal Raman microscopy is performed in this study to investigate its correlation with sample chemical composition and the substrate used during fabrication. Knowledge of this nature is very important to the issue of long-term stability of BDD coated neurosurgical electrodes that will be used in fast-scan cyclic voltammetry, as potential occurrence of film delaminations and dislocations during their surgical implantation can have unwanted consequences for the reliability of BDD-based biosensing electrodes. To achieve a more uniform deposition of the films on cylindrically-shaped tungsten rods, substrate rotation was employed in a custom-built chemical vapor deposition reactor. In addition to visibly preferential boron incorporation into the diamond lattice and columnar growth, the results also reveal a direct correlation between regions of pure diamond and enhanced stress. Definite stress release throughout entire film thicknesses was found in the OPEN ACCESS current Raman mapping images for higher amounts of boron addition. There is also a possible contribution to the high values of compressive stress from sp2 type carbon impurities, besides that of the expected lattice mismatch between film and substrate.

Rapidly cured epoxy/anhydride composites: effect of residual stress on laminate shear strength

The drive towards rapid cure thermosetting composites requires a better understanding of the residual stresses that develop during curing. This study investigates the impact of residual stresses on the interlaminar shear strength of resin-infused epoxy/anhydride carbon-fibre laminates. The magnitude of the residual stress was varied by changing the initial injection cure temperature between 75 °C and 145 °C. The corresponding cycle times and the final glass transition temperature of the resin were also measured. The experimentally measured chemical shrinkage and thermal expansion properties of the resin after vitrification were used as inputs to a finite element analysis to calculate the peak residual stresses in the composite. An increase in the initial cure temperature from 85 to 135 °C resulted in an increase of 25% in the residual stress, which led to an experimentally measured reduction in the composite's short beam shear strength of approximately 16% (8 MPa), in good agreement with model prediction.

Identification of expressed HSP`s in blacklip abalone (Haliotis rubra Leach) during heat and salinity stresses

Both prokaryotes and eukaryotes express a set of highly conserved proteins in response to external and internal stress. The stressors include tissue trauma,anoxia, heavy metal toxicity, infection, changed salinity, and the mmost characterized, heat shock. The result is an expression of stress proteins or heat shock proteins (HSP's) which lead to protection of protein integrity, and also to tolerance under continued heat stress conditions. The Australian backflip abalone (Haliotis rubra) is found principally in southern coastal water and also in estuarine/bay environments. Esturaine/bay environments have greater fluctuations in environmental conditions, especially those of salinity and water temperature, than they are found along oceanic coasts. Abalone from esturaine/bay and oceanic coastal environments were subjected to either increased temperature (2° C/day for a total of 10°C) or hyposalinity (80% seawater). Esturaine/bay abolone were less affectes than the oceanic animals by temperature increase and also demonstrated the ability to volume regualte 3 h after the initial salinity shock. SDS-PAGE and Western blotting techniques, together with dot blots of total protein, using HSP70 specific antibodies, were used to detect HSP70s in the foot muscle of the animals and indicated an expression of HSP70 in response to heat shock in abalone, but not following hyposalinity shock. RT-PCR yeilded a partial cDNA clone of HSP70 from the foot muscle.

Effect of grain size on corrosion of high purity aluminium

A complete understanding of how grain refinement, grain size, and processing affect the corrosion resistance of different alloys has not yet been fully developed. Determining a definitive 'grain size-corrosion resistance' relationship, if one exists, is inherently complex as the processing needed to achieve grain refinement also imparts other changes to the microstructure (such as texture, internal stress, and impurity segregation). This work evaluates how variation in grain size and processing impact the corrosion resistance of high purity aluminium. Aluminium samples with a range of grain sizes, from ∼100 μm to ∼2000 μm, were produced using different processing routes, including cold rolling, cryo rolling, equal channel angular pressing, and surface mechanical attrition treatment. Evaluation of all the samples studied revealed a tendency for corrosion rate to decrease as grain size decreases. This suggests that a Hall-Petch type relationship may exist for corrosion rate and grain size. This phenomenon, discussed in the context of grain refinement and processing, reveals several interesting and fundamental relationships.

Yielding behaviour of martensite in steel

Although martensite is recognised as a very strong phase in carbon steels, its initial yielding commences at low stresses and the tensile stress-strain curve shows a smooth, rounded form. Evidence is presented from x-ray diffraction to show that this behaviour is due to the presence of intra-granular stresses that are residues after the shear transformation from austenite to martensite. These internal stresses are reduced in magnitude by plastic deformation and also by tempering. Reduction of internal stress due to plasticity is shown by a decrease in XRD line broadening after deformation. A simple model is presented in which the stress-strain behaviour is controlled by relaxation of the internal stresses almost up to the point of the ultimate tensile strength. It demonstrates that only a very small fraction of the material remaining in a purely elastic state provides a large stabilising effect resisting necking. A corollary of this is that the uniform elongation of martensitic steel actually increases with increase in the strength level. Effects of heat treatment are also reproduced in the model, including the increase in conventional yield stress (Rp0.2) that occurs after low temperature tempering.

From the inside to the outside. Architecture Venice Biennales 2014 and 2016

The comparison between the Position Statements of the latest two Venice Biennale of Architecture, Fundamentals, directed by Rem Koolhaas in 2014 and Reporting from the front that Alejandro Aravena prepares for 2016, is an evident sign of the internal stress that architectural practice has been suffering during the last decade. Koolhaas intensively focused on the immediate past whilst Aravena presents a Biennalle strongly decided to explore possible alternatives for the future of Architecture. The first one tried to define the core, theessence, the most elemental particles that utterly compose Architecture. The second looks at the boundaries, the periphery, the outskirts, the limits of the discipline. Fundamentals was theoretical, personal, abstract, compact and aesthetic. Reporting from the front will be practical, collective, concrete, permeable and ethical. This fertile antagonism or counterpoint between both approaches is too frequently understood as incompatible. However, as a matter of fact the coexistence of these two different perspectives within architectural practice is the mostdistinctive feature of the complex contemporary architectural landscape. The insertion of the analysis of both position statements within the historical evolution of the Venice Bienale since 1980, allows a reinterpretation of the antagonism between the two exhibitions and evidences some lines of thought and action in the architectural world. Following the war industry terminology that Report from the front has chosen, Aravena identifies with precision the theatre of operations; the space and time that is requesting an urgent response from architecture.Previously Koolhaas had defined the armament that Architecture has available to undertake this crucial mission: to define the role and relevance of Architecture in the immediate future. Until now, battles in the front have been a guerrilla warfare. More reactive than proactive. Battles for survival more than for experience. Necessary but, at the same time, insufficient. Valuable actions in radical contexts; heroic acts in extreme situations; occasional infiltrations that find their final reason for being in their own audacity. Time has come for these counterattackarchitectures to evolve from protests to proposals.

Analysis of work hardening and recrystallization during the hot working of steel using a statistically based internal variable model

A mathematical model has been developed which describes the hot deformation and recrystallization behavior of austenite using a single internal variable: dislocation density. The dislocation density is incorporated into equations describing the rate of recovery and recrystallization. In each case no distinction is made between static and dynamic events, and the model is able to simulate multideformation processes. The model is statistically based and tracks individual populations of the dislocation density during the work-hardening and softening phases. After tuning using available data the model gave an accurate prediction of the stress–strain behavior and the static recrystallization kinetics for C–Mn steels. The model correctly predicted the sensitivity of the post deformation recrystallization behavior to process variables such as strain, strain rate and temperature, even though data for this were not explicitly incorporated in the tuning data set. In particular, the post dynamic recrystallization (generally termed metadynamic recrystallization) was shown to be largely independent of strain and temperature, but a strong function of strain rate, as observed in published experimental work.

Sources of stress in South African soccer coaches

It has been noted that coaches face a number of challenges, frustrations, conflicts and tensions, most of which translate into perceived stress. With the re-entry of South Africa into the international sporting arena, little is known about South African coaches and what specific stresses they experience. Thus, the present study used a mixed-method approach in exploring the perceptions of stress among South African soccer coaches. More specifically, 12 South African coaches were interviewed (using semi-structured interview guides) on their perceptions of sources of stress. Furthermore, 112 soccer coaches (at the provincial level and higher) were approached to complete a 32-item questionnaire on the sources of stress related to their job as coaches. Content analysis was used to evaluate the qualitative data while the descriptive data analysis was completed using the Statistical Package for Social Sciences (SPSS – version 16). The reliability was tested for the sources of stress (a= .817) for the 32 items. The sources of stress experienced by the coaches were evaluated. The results revealed the three main themes related to sources of stress were Resource Issues, External Pressure and Internal Capacity. Complementing these results, the top three sources of stress found through the descriptive statistics were lack of resources, fixture backlog and games where the outcome is critical, while the lowest three sources of stress were political interference, physical assaults from players and substituting a player. Specific academic and practical implications of the study the results were discussed.

Thermomechanical properties of Ni-Ti shape memory wires containing nanoscale precipitates induced by stress-assisted ageing.

This paper systematically examines the thermomechanical properties and phase transformation behaviour of slightly Ni-rich Ni-Ti biomedical shape memory wires containing homogeneously distributed nanoscale precipitates induced by stress-assisted ageing. In contrast to previous studies, particular attention is paid to the role of precipitates in impeding twin boundary movement (TBM) and its underlying mechanisms. The size and volume fraction of precipitates are altered by changing the ageing time. The martensitic transformation temperatures increase with prolonged ageing time, whereas the R-phase transformation temperature remains relatively unchanged. The stress-strain behaviour in different phase regions during both cooling and heating is comprehensively examined, and the underlying mechanisms for the temperature- and thermal-history-dependent behaviour are elucidated with the help of the established stress-temperature phase diagram. The effect of precipitates on TBM is explored by mechanical testing at 133K. It is revealed that the critical stress for TBM (σcr) increases with increasing ageing time. There is a considerable increase of 104MPa in σcr in the sample aged at 773K for 120min under 70MPa compared with the solution-treated sample, owing to the presence of precipitates. The Orowan strengthening model of twinning dislocations is insufficient to account for this increase in σcr. The back stress generation is the predominant mechanism for the interactions between precipitates and twin boundaries during TBM that give rise to the increase in σcr. Such results provide new insights into the thermomechanical properties of precipitate containing Ni-Ti biomedical shape memory wires, which are instructive for developing high-performance biomedical shape memory alloys.