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Background In vitro studies has demonstrated that non-vitamin K antagonist oral anticoagulants (NOACs) down-regulated the expression of proteins responsible for valve calcification and inflammation in valve interstitial cells (VICs) cultures. Aims Our goal was to evaluate whether long-term anticoagulation with NOACs, including dabigatran (thrombin inhibitor), rivaroxaban and apixaban (FXa inhibitors) can impair the valvular calcification and inflammation in patients with severe AS. Methods We enrolled 38 patients with severe AS aged 70±5.9 years (mean gradient - PGmean: 50mmHg, max gradient - PGmax: 80mmHg), including 18 individuals with AS and concomitant atrial fibrillation taking NOACs for at least 3 years (51±10 months) (AS-NOACs group). Stenotic aortic valves were obtained during valve replacement surgery. Valvular calcification was estimated ex vivo using micro-computed tomography (micro-CT). Total volume of each calcification (bone volume - BV), the distribution of clods sizes of calcification parts (trabecular thickness -Tbth) and the volume of the hardest / most calcified part (hard CT) of each valve were assessed. Valvular expression of bone morphogenetic protein 2 (BMP-2) and NFκB was evaluated by immunostaining. The fluorescence intensity (FI) was computed as the ratio (%) of positively and negatively stained areas. Results AS patients did not differ from AS-NOACs participants with regard to demographic or risk factors. Micro-CT analysis showed 65.5% lower BV in AS-NOACs valves compared to patients not taking NOACs (87±47 mm3 vs. 252±146 mm3, p=0.0017). Of note, in AS-NOACs patients Tbth showed strong association with transvalvular pressure gradients (PGmean: r=0.76, p=0.033; PGmax: r=0.77, p=0.01), as clinical measures of the AS severity. The duration of anticoagulation was associated with the lower Tbth (from 0.35 mm for 60 months to 0.51 mm for 36 months, p Conclusions NOACs can inhibit the increase of valvular calcium volume and its ossification via suppressed NFkB expression. Our study may suggest that long-term anticoagulation with NOACs could slow down the rate of AS progression, at least in patients with an indication for anticoagulant therapy. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Polish National Science Centre

Optical microscopy has been a basic and standard technique in cell biology research for decades. Microscopy techniques function well for thin, optically transparent cultures and allow for the imaging of thicker biological specimens. There is no better method of in vitro cell observation and analysis, hence microscopic techniques are extensively used and constitute an optimal tool for cell culture studies. This paper proposes an original methodology of optical microscopy data processing based on the phase contrast technique during cell culture monitoring. By exploiting images recorded during cell proliferation, a surface reconstruction was performed based on assumption, it can be considered that the local brightness of the image depends on the cells' thickness and thus the obtained results can be interpreted in the form of a surface that represents a three-dimensional structure, which allowed for a quantitative description of the cell evolution. The 3D data obtained enabled the investigation of parameters describing the morphology of the cells and the topology of their proliferation. These parameters included cell sizes in plane but also in the direction perpendicular to it, cell volume changes, their spatial distribution, as well as anisotropy and directivity. The method presented provides data carrying information similar to that obtained using a holographic microscope, e.g. A HoloMonitor (Phase Holographic Imaging PHI Inc.), or from confocal scanning microscopy with the "z-stack" mode. The techniques of bright field or phase contrast cell observation are, however, much cheaper, and widely available when compared to holographic microscopy, for instance. Besides, these also enable monitoring of cell activity over time, i.e. the study and quantitative description of dynamic changes in the cells. The proposed approach uses generally available free tools such as ImageJ software with BoneJ and Particle Analyzer plugins. The methodology is suitable for even a basic microscope, it can be easily implemented as a script, and thus data processing can be significantly shortened, the methodology can be automated, and also applied for data processing in real time.

Over the last decades, the medical device industry has grown significantly. Complex and highly functionalized medical devices and implants are being developed to improve patient treatment and to enhance their health-related quality of life. However, medical devices from this new generation often cannot be sterilized by standard methods such as autoclaving or sterilizing gases, as they are temperature sensitive, containing electronic components like sensors and microchips, or consist of polymers. Gamma irradiation for sterilization of such products is also problematic due to long processing times under highly reactive conditions resulting in material degradation or loss of functionality. Low-energy electron-beam treatment could enable irradiation sterilization of medical surfaces within seconds. This method is very fast in comparison to gamma irradiation because of its high dose rate and therefore degradation processes of polymers can be reduced or even prevented. Additionally, electron penetration depth can be precisely controlled to prevent damage of sensitive components like electronics and semiconductors. The presented study focuses on two key aspects: 1.) Can new and highly functionalized medical products in future be sterilized using low-energy electron-beam irradiation; and 2.) Is the low-energy electron-beam technology suitable to be set up on-site to speed up sterilization processing or make it available “just-in-time”. To address these questions, different test specimens were chosen with complex geometry or electronic functional parts to gather information about the limitations and chances for this new approach. The test specimens were inoculated with clinical relevant test organisms (Pseudomonas aeruginosa) as well as with approved radiation resistant organisms (Deinococcus radiodurans and Bacillus pumilus) to prove the suitability of low-energy electron-beam treatment for the above-mentioned medical products. The calculation of the D10 value for B. pumilus revealed equal efficacy when compared to standard high-energy irradiation sterilization. All of the above-mentioned germs were successfully inactivated by low-energy electron-beam treatment when test specimens were inoculated with a germ load > 10^6 CFU and treated with doses ≥ 10 kGy (for B. pumilus and P. aeruginosa) and > 300 kGy (for D. radiodurans) respectively. As an example, for specialized electronic components to be sterilized, an impedance sensor for cell culture applications was sterilized and unimpaired functionality was demonstrated even after five repeated sterilization cycles to a total dose of 50 kGy. To address the second aspect of on-site suitability of this technology, the product handling for low-energy electron-beam treatment had to be adapted to minimize the size of the electron-beam facility. Therefore, a mini electron-beam source was used and a specialized sample holder and 3D-handling regime were developed to allow reproducible surface treatment for complex product geometries. Inactivation of B. pumilus inoculated medical screws (> 10^6 CFU) was successful using the developed handling procedure. In addition, a packaging material (PET12/PE50) for medical products was investigated for its suitability for low-energy irradiation sterilization. Biocompatibility assessment revealed the material to be eligible for this application as even overdoses did not impair the biocompatibility of the material. With these results, the principal suitability of low-energy electron-beam treatment for sterilization of medical products containing electronics like sensors is demonstrated. The low-energy technology and the specialized 3D-handling regime allow the on-site setup of the technology in hospitals, medical practices or any other point of care.

Boana icamiaba is an Amazonian anuran species reported for sites in the mid-lower Madeira-Rio Tapajós River and lower Tapajós-Rio, and Xingu River interfluves – municipalities of Juruti, Altamira, Santarém, and Itaituba, state of Pará, northern Brazil. We provided the first records of Boana icamiaba for the states of Mato Grosso and Rondônia, central and northern Brazil, which enlarges the knowledge on its distribution in approximately 470 km southmost and circa 886 km southwestmost from the nearest previously recorded locality.

Boana icamiaba is an Amazonian anuran species reported for sites in the mid-lower Madeira-Rio Tapajós River and lower Tapajós-Rio, and Xingu River interfluves – municipalities of Juruti, Altamira, Santarém, and Itaituba, state of Pará, northern Brazil. We provided the first records of Boana icamiaba for the states of Mato Grosso and Rondônia, central and northern Brazil, which enlarges the knowledge on its distribution in approximately 470 km southmost and circa 886 km southwestmost from the nearest previously recorded locality.

Aluminium alloy sheets were asymmetrically rolled and annealed. Asymmetric rolling was applied by imposing different velocity ratios between the top and bottom rolls, from 1 to 1.5. After cold rolling, the microstructures of various samples were analysed by electron back scatter diffraction, whereas the mechanical properties were characterized by stress–strain curves and microhardness measurements. The asymmetrical rolling process was examined as an alternative method to obtain fine- or even ultrafine-grained aluminium. The main purpose of this paper is to describe, qualitatively and quantitatively, the influence of asymmetrical rolling on microstructure evolution. Grain size, misorientation, image quality factor and other parameters were characterized and analysed in some detail. In the present study, a unique approach has been used for the first time to examine the possibility of applying the asymmetric rolling process in the preparation of materials with controlled heterogeneity.

Thermo-Calc modelling was employed to predict liquid phase amounts for Fe–0·85Mo–(0·4–0·6)Si–(1·2–1·4)C in the temperature range of 1285–1300°C and such powder mixes were pressed and liquid phase sintered. In high C steels, carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat treated. To assist the break-up of these continuous carbide networks, 0·4–0·6% silicon, in the form of silicon carbide, was added. After solution of processing problems associated with the formation of CO gas in the early part of the sintering cycle, and hence large porosity, densities in excess of 7·75 g cc−1 were attained. A spheroidising treatment resulted in microstructures having the potential of producing components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains up to 16% were attained.

This paper presents some textures obtained on one Al alloy after symmetrical and asymmetrical rolling performed at two different temperatures, and followed by annealing. It is shown that there is a strong influence of rolling temperature and degree of asymmetry on the texture development and its heterogeneity through the thickness of the sheet. In particular, it is shown that the Cube component, originally present in the texture of the as-received material, disappears during warm rolling but re-appears during subsequent annealing. These data indicate that the exact schedule to suppress completely this component is not yet found but also that the recrystallization mechanisms are very sensitive to the exact rolling schedule.

Powder metallurgy (PM) parts acceptance is determined by compositional and processing parameters and their controls. Statistical procedures are used for assessment; normal distribution and 'six sigma' appear to predominate. For fatigue of metallic materials and strengths of ceramics, fibres and composites, however, Weibull probability of survival analyses are widely used. The original analysis considers a threshold stress at which the probability of failure is zero. This stress is frequently taken to be zero, simplifying the analysis to two parameters. The yield stress has been suggested for the threshold stress, probably not sufficiently conservative for less ductile PM materials. A new three-parameter Weibull analysis, in which it is taken to be the fracture strength minus six standard deviations, is presented. Powder metallurgy manganese steels are under commercial consideration and this approach is applied to 12 variants of such laboratory processed specimens. It is compared with the two-param...

Mn was introduced, with graphite, as fine ferromanganese particles to form compacts of Fe–3%Mn–0·5%C. Each was sintered in dry 25%H2 + 75%N2 for 3 min at 770, 1040, 1080, 1170 and 1220°C respectively, held for 3 min and quenched. The surface of a successively heated specimen was similarly examined. Specimens were sectioned and, especially the reacting ferromanganese particles and adjoining regions, investigated using light and scanning electron microscopy and EDX. Development of microstructure and microcompositions during sintering was related, from 740°C, to diffusion and condensation of Mn vapour on iron particle surfaces and subsequent chemical reactions. Above 1080°C microstructures included features resulting from a transient liquid phase, in accord with a ∼45 wt%Mn ternary eutectic calculated by ThermoCalc. The thicknesses of the highly Mn enriched regions were substantially higher than those resulting from bulk Mn diffusion in the Fe lattice; our interpretation invokes predominant operation...

Detailed quantitative micrographic data are presented for Stages I and II of a Powder Metallurgy Fe-1.5Cr-0.2Mo-0.7C steel specimen fatigued in bending with R = -1 at 24 Hz and a stress amplitude of 312 MPa. The fatigue limit was ∼240 MPa, at which stress level no microcracks were detected in static loading. Testing was interrupted at 100 cycles and at further 29 intervals until failure after 49 900 cycles. For each arrest, surface replicas were made in the two regions where maximum stress was applied. Microcracks could nucleate below 100 cycles, when their sizes ranged from

Nucleation of microcracks, their growth and coalescence are analysed in powder metallurgy (PM). Fe–1·5Cr–0·2Mo–0·7C steel by fractography allied to surface replica microscopy – at several stress levels as the maximum tensile stress in three-point bend specimens was raised to 99·6% of the transverse rupture strength TRS of 1397 MPa. The fatigue limit in this material is ∼240 MPa, at which stress level no microcracks were detected in static loading. Numerous microcracks, ranging in size from

Certain carbonyl nickel powders manufactured by the Mond chemical vapour deposition (CVD) process are coated with a nanometric layer of graphitic carbon. Through a simple chemical process of acid leaching of the nickel metal a dry filtrate is obtained, which consists of carbon nanopowder. As imaged in a transmission electron microscope (TEM), the powder consists of hollow carbon shells, termed carbon nanoshells (CNS) that are replicas of the nickel particulates. The shell thickness may vary from a few nanometers to tens of nanometers. Each carbon shell is composed of layered nanocrystals of turbostratic graphite distinguished by of the presence of a high density of defects, such that the basal planes tend to follow the curvature of the original Ni core. EELS analysis showed that the electronic character of the CNS is closer to that of graphite than to amorphous carbon.

To compete with wrought steels for demanding applications such as gears in automotive engines, Powder Metallurgy, PM, materials must possess structural reliability. Density has been shown to be the dominant factor in determining fatigue resistance in PM structural components. PM routes which could overcome the 7.4 g/cm barrier in ferrous components include: double press-double sinter, hot isostatic pressing (HIP), sinterHIP, sinter + HIP, powder forging and (transient and supersolidus) liquid phase sintering. In order to provide high green densities, high pressure (1GPa) cold compaction, warm (~ 140C) compaction and hydrocarbon-coated powders can be employed. Surface densification can be achieved by cold or warm work and includes cold work of hypoeutectoid alloys and ausforming. These processing routes are briefly reviewed, with particular attention to coated powders, warm compaction, high temperature sintering and the novel technique of carbothermic sintering in nitrogen of ferrous powders containing the easily oxidisable chromium and manganese.

The potential of PM Mn steels has been established in laboratory experiments. This paper deals with sintering of Fe–(2–4)Mn–(0.3/0.7)C, also with 0˙85%Mo addition, in an industrial pusher furnace at 1180°C in an atmosphere of 25% hydrogen plus 75% nitrogen, obtained from a cryogenic liquid, giving an inlet dew-point of −55 °C. Tensile, bend (including fatigue) and miniature Charpy specimens were sintered in flowing gases and in semiclosed containers with a getter of ferromanganese, carbon and alumina. The quenched and tem- pered state was investigated, as was sinter hardening (cooling rate of 55 K min −1), simulated for comparison with slow cooling at 10 K min −1. As there was no forma tion of oxide networks at the combination of sintering temperature and dewpoint, in accordance with the Ellingham–Richardson diagram for Mn oxidation/reduction, the use of semiclosed containers was superfluous. The quenched and tempered specimens were brittle. Sinter hardening lead to an improvement in mechanical pr...

Tensile properties of powder metallurgy 3% manganese-0·8% carbon (content of green compact) steels were determined following laboratory sintering in (nearly) full, semiclosed containers with no getter powders in dry, 0-100% hydrogen-nitrogen atmospheres. Manganese was mixed with the NC 100·24 sponge iron powder as low carbon ferromanganese and carbon as a graphite addition. Dogbone compacts were pressed at 660 MPa, the sintering temperatures were 1120 and 1250°C and cooling rates ~65 K min- 1. In specimens sintered in nitrogen containing atmospheres at 1120°C, final carbon content was ~0·7% and for those processed at 1250°C ~0·6%. Sintering in dry hydrogen resulted in lower carbon and oxygen contents. Independent of the H2/N2 ratio in the furnace atmosphere, however, all the specimens were ductile and exhibited similar strengths. Yield strengths R 0·2 were in the range: 426-464 MPa, tensile strengths Rm were 724-780 MPa and strains to failure were 1·6-2·0% after sintering at 1250°C. The 1120°C si...

A methodology, involving fretting tests, to develop wear and crack resistant materials for tribological applications for automotive valve train parts (e.g. cams, tappets) has been recently reported for high speed steels. Modifications to one of these sintered steels, M3 Class 2, were effected by additions, singly and in combination, of 5 wt.% of wear resistant titanium carbide and of solid lubricant manganese sulphide. In our fretting tests alternate displacements were imposed between the test material (plane) and a chromium steel or alumina ball. Running conditions fretting and material response fretting maps were constructed for the four materials. Two types of fretting damage were detected and analysed: cracking or particle detachment and wear through the tribologicaly transformed structure (TTS). Crack initiation, associated with porosity and interfaces, was detected when the maximum tensile stress in the contact reached 1.2 GPa. Cracking analyses were also carried out using static and fatigue mechanical tests and replica scanning electron microscopy. Crack growth and propagation were influenced by details of the microstructure, e.g. TiC was observed to arrest crack growth, whereas MnS made it easier. Wear analysis included the determination after each test of the wear volume, which could be related to the coefficient of friction and the cumulative dissipation energy during the fretting test.

Disc and toroidal shaped samples of composites made from powders of Na-β-alumina and tin-stabilised tetragonal zirconia by conventional mixing and sintering processes have been used to establish data on the effect of the zirconia on the sintering efficiency, the mechanical strength, hardness and fracture toughness. These data have been compared to the results obtained when the β-alumina powder was first pre-sintered and then infiltrated with solutions of zirconium salts or suspensions of the tin-stabilised tetragonal zirconia. The results indicate that significant improvements to the mechanical properties can be made when the zirconia is introduced via an organometallic salt dissolved in an organic solvent. For the conventionally made samples the strength and toughness peak at 15 wt% zirconia addition. Sample densities in excess of 97% are achieved by pressurless sintering at temperatures up to 1600 °C.

This paper reviews progress made in understanding the factors which control the supersolidus liquid phase sintering of high speed steel powders to full density. The correlation between alloy composition and sintering behaviour is discussed for a number of alloy systems. Realising that for complete densification it is necessary for sintering to take place in the liquid +γ+M6C+MC (or MX) phase region, two approaches have been developed to extend this critical phase field. This enables a scientific development of alloys that are more robust to process variations than currently sintered high speed steels of standard (for wrought materials) compositions. The new alloy systems possess wider process or sintering windows and have lower optimum sintering temperatures. The first approach relies on computer aided alloy design: vacuum sintering windows extending to 30–40 K at temperatures of 1170–1200°C have been achieved for novel Fe–C–4Cr–14Mo(–8Co)systems. The second approach involves sintering vanadium en...

The effects of 0·5 wt-%Mo addition on the processing, microstructure, and strength of PM Fe–3·5Mn–0·7C steel are described. Water atomised and sponge irons, Astaloy 1·5Mo, milled ferromanganese, and graphite were the starting powders. During sintering in 75H2 /25N2 or pure hydrogen the dewpoint was controlled and monitored; in particular the effects of improving it from -35 to -60°C were investigated. Faster heating rates (≥20 K min-1), sufficient gas flowrates, milling the ferro alloy under nitrogen, a low dewpoint (

Mechanical properties of 2–4% manganese PM steels were determined in tension and in bending following laboratory sintering in dry, hydrogen rich atmospheres. Young's modulus determined by an extensometric technique was about 115 GPa; when measured by an ultrasonic method it was about 153 GPa, in accordance with the‘law of mixtures’. The microstructures, significantly devoid of oxide networks, were predominantly pearlitic, but frequently with variability for specimens similarly processed, resulting in appreciable variations in the stresses for macroscopic yielding and fracture. The majority of the experiments were conducted on 3 and 4Mn–0·6C alloys and for these R0·1 was in the range 275–500 MPa, tensile strength (TS) 300–600 MPa, and (apparent) transverse rupture strength (TRS) 640–1260 MPa. Statistical techniques were employed to analyse the data. When careful control of processing was maintained, the Weibull modulus was highest, at about 17, for TS of furnace cooled specimens, and lowest, about ...

Calculated multicomponent phase diagrams were used to identify high speed steel (HSS) type alloys having the potential to exhibit enhanced sinter ability. The requirement was for an extensive austenite + carbide + liquid phase field. Of the six tungsten and molybdenum based systems studied, Fe–14Mo–C + 4Cr–8Co systems were potentially the most promising. Appropriate compositions were water atomised and additional alloys prepared by blending annealed powders with graphite powders. Powders were compacted to green densities of about 70% theoretical and then vacuum sintered. Sinterability was assessed in terms of sintered densities and microstructures. Alloys containing Fe–13Mo–1·3C, Fe–14Mo–4Cr–1·3C, and Fe–14Mo– 8Co–4Cr–1·4C were sintered to full density at temperatures as low as 1170°C, 70–150 K lower than for existing HSSs. Sintering windows were 20– 30 K, a significant improvement on existing HSSs. As sintered microstructures consisted of angular M6 C carbides dispersed in martensitic matrixes, w...

The increased market for high speed steels (HSSs) is increasingly associated with their use as wear resistant materials. The tribological properties can be enhanced by incorporating into the HSS further ceramic particles to increase wear resistance and solid lubricants to minimise friction, either at the surface, or by powder metallurgy into the steel matrix, already containing some 15% of 'natural', predominately MC and M6C, carbides. The difficulty of relating engineering performance of a component in reciprocating motion to a simple tribological test, such as pin on disc, is well recognised. The present paper will present a methodology of fretting testing, where the eventual failure is comparable to service damage of autoengine valve train parts, for which modified HSSs are prospective materials. Wear induced by fretting and microcracking of the surface and bulk material were studied in M3 class 2 and T42 HSSs in a newly developed fretting machine. The HSS plane specimens underwent reciprocati...

To prevent the formation of continuous brittle phosphides when steel is brazed with Cu–P–Sn alloy, barrier layers were deposited on the steel: nickel on stainless steel and copper for mild steel. Their effectiveness is demonstrated by the increase in the lap shear strength from

The design and use of a novel temperature–time–gap width (TETIG) test specimen to characterise brazing alloys is described. The assembly was constructed from longitudinally sectioned bar(s) of the parent material(s), with outer segments of the two halves providing datum surfaces for the selfgapping system, conveniently bound in place with wire. Gap filling took place from alloy reservoirs in two machined grooves and flow could be chosen to take place from one or both, in a horizontal or vertical plane. Brazing alloys in the form of wire, sheet, paste, or powder can be used. The design overcomes a problem associated with conventional TETIG specimen design in which the effects of the flow distance of the molten filler metal are indistinguishable from the effects owing to the gap width of the joint. To investigate the reproducibility of the design, a Cu–Sn–Ni–Si–Ag alloy in both powder and solid forms was investigated in identical steel assemblies. Results which led to the use of the specimen design ...

The stresses for macroscopic plastic flow and critical stages of fracture, fracture toughness and hardness of sintered plus forged T1 high speed steel were determined. The results are compared to similar data for sintered, sintered to closed porosity plus hot isostatically pressed and electroflux refined (EFR) alloys of comparable composition. EFR meltstock, with addition of 0.6 wt% Mo, was water-atomized in a 200 kg unit which incorporated ceramic filters and an argon shroud to ensure maximum cleanliness. The powder was sieved

R-curve behaviour in the microstructurally short crack regime has been reported mainly in ceramics, composites and polymers; this paper describes it for a metallic material: brittle cast and wrought T42 high speed steel. Continuum mechanics has demonstrated the general admissibility of sub-critical growth of cracks with a cohesive zone. Results now reported show that, in a metallic material, growth of microstructurally short cracks under monotonic loading, as in fatigue, is governed by microstructure (texture). Natural cracks, i.e. produced by the hot forging operation, or induced by the application of stress in the range 0.5 to 1.1 GPa in four-point bending experiments, of depths extending to 25µm were always associated with MC carbides. At comparable stress levels cracks were nucleated in compression -- surprisingly some transverse to the compressive axis. Observations of crack nucleation and subsequent studies of subcritical growth of these microcracks were made by surface replica microscopy. Crack extension was easy within the carbide stringers (a characteristic feature of hot-worked high speed steels), but, at higher stresses, took place between these bands to reach up to ∼ 100 µm (surface) length. Dormant cracks were shallow, no more than 6 µm deep; whereas those responsible for failure, at stresses ranging from 0.6 to 1.9 GPa, had a semicircular geomerty -- identified by scanning electron fractography. Step-wise monotonic subcritical crack growth is modelled asR -curves and it is shown that the maximum estimated (microscopic) applied stress intensity factor K a can vary from 0.5 to 1.0 K1C, the macroscopic fracture toughness independently determined using sharp artificial long cracks.

The adhesive fracture energy, G1c, of a model adhesive/adherend system, consisting of poly(methyl-methacrylate) plates bonded with a cyanoacrylate adhesive, has been evaluated using the Tapered Double Cantilever Beam and Blister test geometries. A refined Blister testing technique is described which, using relatively large diameter test plates [200mm], is capable of arresting the initial propagation of the-invariably less than naturally sharp-starter crack. This allows us to three subsequent Gc determinations for the same specimen from starter cracks of natural sharpness. Adhesive fracture energy values determined for the model system using TDCB test pieces, 0.110±0.017 kJm−2, were in good agreement with those obtained for Blister specimens in which arrested cracks had been repropagated, 0.119±0.013 kJm−2. As is generally observed, values calculated from the initial propagation of starter cracks were somewhat higher for the TDCB specimens, 0.140±0.045 kJm−2. Corresponding values for the Blister t...

The axial compressive strengths of three 0·52 V f glass-fibre/polyester pultrusions were determined under superposed hydrostatic pressures extending to 300 MPa. Atmospheric strengths were in the range 380–790 MPa, and all materials showed a strong, about 3, pressure-dependence. Kinking of fibre bundles or sub-bundles preceded fracture in all materials at all pressures, but failure to detect non-propagating transverse cracks, which allow such groups of fibres to act in unison, indicates that bundle-debonding controlled the critical mechanism of failure. The effects of shape, size, and eccentricity of the bundles on buckling and debonding are considered. It is tentatively concluded that the critical parameter is the transverse tensile strain of the resin, ϵ 1 , causing bundles (rather than individual fibres) to debond. The pressure-dependence of the compressive strength is well predicted by the ϵ 1 criterion. To obtain fair correlations with the measured values, the bundle-bundle decohesion strengths would have to be to the order of 223 MPa, rather than approximately 50–100 MPa estimated for the fibre-fibre debond strengths.

The tensile and compressive strengths of three polyester resins were measured under superposed hydrostatic pressure extending to 300 MPa, in an attempt to establish yield criteria. The polyesters were brittle in uniaxial tension at all pressures, and accordingly, a third testing geometry, diametral compression of a disc, was employed to complete the two or three necessary parameters to establish the yield surface in stress space. From the biaxial (disc) and axial compressive test data, the atmospheric tensile yield strength (higher than the fracture strength) was computed to be ∼67 MPa in comparison with the compressive strength of ∼120 MPa, their ratio 0.56 being significantly less than the more common 0.75 found for thermoplastics and epoxides. The data for compressive yield strength under superposed pressure were compared with the predictions of the two-parameter pyramidal, conical and paraboloidal criteria and the fit, though reasonable for the latter, could be significantly improved if a further independent material parameter was employed to give a three-parameter pyramidal criterion (the principal stresses σ1, σ2 and σ3 being measured in MPa) of the form 0.0150σ1−0.0039σ2−0.0083σ3=1

A new image for ferrous PM emerged some 20 years ago with the economically successful sintering of HSS cutting tools to net shape and near full density with acceptable and uniform microstructures, especially for single point turning. This process relies on cheap water atomized powders. Simultaneously processing of gas atomized powders by HIPing was perfected and superior quality materials, especially with high alloying additions, improved cleanliness and finer, uniform microstructures became available. Amongst subsequent developments CVD and PVD coating of HSS with TiN, continuous sintering and copper infiltration of HSS for valve seat inserts and binder assisted powder extrusion of water atomized T15 for oil hole drills should be mentioned. Ferrous PM is no longer synonymous with ‘dirty, porous and cheap’. Andrew Wronski and his fellow researchers describe three types of application relating to machining, automotive valve train and aerogas turbine bearings.

An attempt was made to achieve, by direct vacuum sintering of water atomised T15 powder, the microstructure and optimum transverse rupture strength (TRS), ∼3200 MN m−2, characteristic of the containerlessly hipped undersintered counterpart. The processing variables were: compacting pressure 400–800 MPa, sintering temperature 1260–1290°C, and sintering time 5–60 min. Ground, ground and polished, and hipped and unhipped specimens were tested, and the failure process investigated by metallographic and fractographic techniques. The highest strengths were associated with the absence of porosity and grain boundary films, which are responsible for cracking of oversintered specimens, and uniform distribution of fine (

An attempt was made to measure indirectly the transverse tensile strengths of uniaxially aligned fibre pultrusions by the diametral compression of disc-shaped samples using concave loading anvils. Two types of composite were investigated, containing ∼60%Vf of either type AS carbon fibres (CFRP) or S glass fibres (GRP), both in an epoxy resin matrix. Testing was carried out at atmospheric and under superposed hydrostatic pressures, −H, extending to 300 M Pa. The resultant principal stresses at the disc centre were δ1 = δA +H; δ2 =H; δ3 = −3δA +H, where δA = 2P/πdt for a disc of diameter,d, and thickness,t, subjected to a loadP. Deviations from linearity in the load-deflection response were detected throughout the pressure range at a70% and a90% of the failure load for CFRP and GRP, respectively, and these were associated with resin yielding. The pressure dependence of δA, approximately −0.1H, was consistent with a two-parameter yielding criterion predicting hypothetical yield stresses in simple tension and compression of a81 and −109 MPa, respectively, for both matrix materials. Irrespective of pressureeventual fractures took place along the loading diameter, but in the CFRP specimens tested under pressure initial cracks at the disc centres were at a45 ° to the loading axis, i.e. on the plane of maximum shear stress. Fractographic observations were consistent with transverse failure taking place by fibre-matrix decohesion in GRP and by resin fracture in CFRP. Other than the atmospheric datum point for CFRP, the pressure dependence of δA for failure, δF, was also approximately −0.1H. Of the various stress, strain and strain energy criteria for failure examined, only critical tensile strain was found consistent with this pressure dependence.

Fine spherical powder with tetragonal Nd2Fe14B phase was prepared by high‐pressure gas atomization. Magnetic powder with iHc = 7.0 kOe was obtained from the Nd9Fe78B11Si2 alloy. Thus, the Nd content was lower than the one used for preparation of either sintered or melt‐spun material. Three distinctive microstructures were found in the atomized particles: dendritic, microcrystalline, and amorphous. The amorphous phase crystallizes at 601 °C. The Curie temperature Tc of the fully recrystallized powder is 311 °C. Bonded magnets were prepared from either atomized or melt‐spun annealed powders. The iHc was improved by 37% after optimal annealing of the atomized powder. The observed effects were related to the microstructure refinement. From the initial magnetization curve, it is presumed that the generation of iHc is mainly due to the random‐strength pinning mechanism of the domain walls.

Processing through powder metallurgy becomes the only feasible way for the most highly alloyed of high speed steels (HSS), with carbon contents between 0.7 wt % and 2.5 wt% containing substantial amounts of carbide formers W and/or Mo, V, Cr.