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The scope of the present paper is to understand the effects of crystalline admixture on the self-healing capacity of the cementitious composites. Previous studies were examined and a conclusion was drawn to the effect that different additives to crystalline admixture tend to improve self-healing of concrete for larger cracks. It is recommended that initial treatment with chemical admixture can stimulate and heal further cracks and it has the better repeatability trend in mixing with the concretes and mechanical recovery is possible even under repetitive preloading. Effective self- healing with chemical admixtures even under open-air exposure, leads to study the importance of a service ability design parameter including the maximum allowable crack width by repeatability analysis as a function of the exposure with the concept of sealable crack width.

The civil research community has been attracted to concrete with self-healing properties since they are an intelligent solution for sustainable infrastructures with long duration. The present study is analyzing the self- healing capability of early age and structural cracks in concrete by using crystalline admixture as self-healing agent under four different exposure conditions by assessing the regained mechanical properties of concrete. Physical (morphological) and chemical composition of the hardened pastes, were studied using Fourier transform infrared spectroscopy (FTIR) and energy-dispersive spectroscopy (EDS). The analysis showed that for all exposure conditions the compressive strength and split tensile strength of the tested concrete with crystalline admixture (CCA) samples regains after early age and structural cracks. This is due to substantial increase in the calcite content which is evident from SEM-EDS and FTIR analysis. Keywords: Self-healing concrete, Early age cracks, Structural cracks, Crystalline admixture

The present study is the investigation of durability constraints of geopolymer concrete made up of binary blending of industrial waste exhaust materials viz., Class F fly ash, GGBS under alkali activation. Two grades of concrete M30 and M70 were developed for OPC and GPC concretes. The developed concretes were tested for durability under sulphate, chloride attacks and also tested for sorptivity and water absorption tendencies. The two grades of GPC and OPC concrete were exposed to 1, 3 and 5% concentrated solutions of H2SO4, HCl and NaCl for 28, 56 & 90 days. The alkaline liquid to binder ratio adopted in this study was 2.5. The molarity concentration of NaOH adopted for this study was 12. The properties like density, surface deterioration, compressive strength were tested. SEM image characteristics and XRD analysis were also performed on samples to study microstructural properties. From the test results, it was inferred that water absorption is less for higher grades compared to normal grade in both the two types of concretes. The resistance of GPC concrete against sulphate and chloride attack shows better performance than OPC concrete irrespective of the grade. Regression analysis was performed between the concentration of solutions and compressive strength for two types of concretes. The test results indicated that binary blended GPC concrete in both the grades for specified time period achieved superior strength properties than OPC concrete under aggressive media.

This paper is aimed at adapting Artificial Neural Networks (ANN) to predict the strength properties of SIFCON containing different minerals admixture. The investigations were done on 84 SIFCON mixes, and specimens were cast and tested after 28 days curing. The obtained experimental data are trained using ANN which consists of 4 input parameters like Percentage of fiber (PF), Aspect Ratio (AR), Type of admixture (TA) and Percentage of admixture (PA). The corresponding output parameters are compressive strength, tensile strength and flexural strength. The predicted values obtained using ANN show a good correlation between the experimental data. The performance of the 4-14-3 architecture was better than other architectures. It is concluded that ANN is a highly powerful tool suitable for assessing the strength characteristics of SIFCON.

An experimental investigation is conducted on the blended GGBS with fly ash-based geopolymer concrete. In this investigation, it is aimed to know the mechanical properties of the geopolymer concrete as well as the crushing strength of the short columns under monotonically increasing uniaxial compressive loading. The short columns are casted with the incorporation of steel and polypropylene fibers by hybridization of fibers in the ratios of 0.5, 1, 1.5, 2% along with longitudinal reinforcement. Conventional reinforced columns of the same geometry and same strength are also casted and tested to make a comparison between GPC and conventional RCC to know the behavior under uniaxial loading. The possible effects of volume fraction of fibers are studied. The experimental results are validated with analytical equation proposed for conventional reinforced cement concrete short columns. A good agreement is achieved between experimental and analytical results.

As an integral part the railway network infrastructure, insulated rail joints (IRJs) electrically isolate track segments providing critical feedback to both track signaling and train position detection systems. Because of the discontinuous nature of IRJs, accumulated damage at the railhead is high. Failure modes include plastic flow of metal across joints, bolt and fishplate failures, delamination of insulated material and, as a result of rolling contact fatigue, end post and endpost surface damage. In the current investigation, microstructural changes in the vicinity of endposts of IRJs made from both surface coated and uncoated rail are investigated using techniques of optical and scanning electron microscopy. Damaged IRJs made from pearlitic head hardened rail steel are compared with head hardened rail steel laser coated with martensitic stainless steel, the latter having an increased service life. Problems associated with the surface coating are identified and approaches to further improving IRJ resistance to rolling contact fatigue suggested. Keywords: Insulated rail joints, rail, head hardened, surface coated rail

The aim of this study is to analyse the self-healing capability of high-strength fibre-reinforced concrete (M70) with fly ash and crystalline admixture (CA) in four types of environmental exposures i.e. Water Immersion (WI), Wet-Dry Cycles (WD), Water contact (WC) and Air Exposure (AE). Specimens for four mixes are cast, one mix containing 1.1% of CA and three mixes with 10%, 20% and 30% partial replacement of cement with fly ash and additions of 1.1% CA. The specimens were pre-cracked at 28 days, in the range of 0.10-0.40 mm and the time set for healing was 42 days. The result shows that all the mixes have considerable amount of closing ability and strength-regaining capability for all exposure conditions. The concrete with 20% fly ash and 1.1% CA has complete crack closing ability and 100% strength-regaining capability for WI and WD cycle conditions. From SEM analysis, it is confirmed that self-healing products are CaCO3 and C-S-H gel.

The densification behavior of WC composites based on iron aluminide binder was investigated using laser scanning confocal mi¬croscopy (LSCM). Doped Fe60Al40 alloys with boron levels ranging from 0 to 0.1 wt% were used as the aluminide binders. The aluminide binders were prepared using controlled atmosphere ring grinding and then blended with WC powder. The composite powder compacted in an alumina crucible and held in a platinum holder in the confocal microscope. The temperature increased from ambient temperature up to 1500 °C under high purity argon. The presence of boron was found to facilitate compaction of the composites and improve the wetting between WC and FeAl binder during liquid phase sintering. Increasing the amount of boron in the binder resulted in the melting of binder at lower temperature and increasing of the compacting of the intermetallic tungsten carbide composites.

The effect of boron on the WC morphology and on the grain size of binders in sub micron WC composites containing Fe60Al40 and Ni3Al binders was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composites were prepared under uniaxial hot pressing of milled powder samples at 1500 °C in inert argon atmosphere. Doped aluminides with boron levels ranging from 0 to 0.1 wt% were used as the binders. It was found that the microstructural characteristics of boron doped aluminide WC composites were similar to those of hot pressed WC-Co and commercial grade WC-10wt%Co (H10F) hardmetals. The contiguity of WC particles (WC/WC contact) and the grain sizes of aluminides decreased and the extent of faceting of tungsten carbide increased in the aluminide tungsten carbide composites in presence of boron.

This research is part of a larger project to investigate the wear and friction of the centre bearing of a rail freight truck. Existing centre bearing surfaces include flame hardened AISI 1030 steel and AISI 1053 cast steel top centres mating against un-greased and/or greased Hadfield steel centre bowl liners, and polyethylene centre bowl liners. The wear life of the unlubricated steels against Hadfield steel is short, greasing the bearings is costly, and industry reports some failures of polyethylene centre bowl liners due to excessive plastic flow and cracking of the rim wall.

Insulated rail joint assemblies provide electrical insulation between two sections of rail for signalling purposes. In this work, rail steel was successfully bonded to PSZ ceramic using an active brazing technique. In order to increase the wettability of the PSZ ceramics, titanium coating was deposited on the ceramic surface using a filtered arc deposition system. A filler metal called BVAg-18 (60%Ag-30%Cu-10%Sn) was used and the joining was performed at a temperature of 750 °C. Bonding between partially stabilised zirconia and rail steel with BVAg-18 filler metal was not achieved using a standard brazing method. Bonding did occur with the BVAg-18 filler metal using the advanced brazing technique of active metal brazing, with best results obtained using a brazing temperature of 750oC and a dwell time of 10 minutes. The microstructure of the coating and joint interface were characterised by XRD, SEM and EDS.

The hardness and indentation fracture toughness of sub micron WC composites based on aluminide and cobalt binders were investigated. Doped Fe60Al40 and Ni3Al alloys with boron levels ranging from 0 to 0.1 wt%, were used as the aluminide binders. The composite materials were processed by uniaxial hot pressing of milled powder samples at 1500 °C under argon atmosphere. The hardness of WC-40vol%(FeAl-B) was found to be higher than that of WC-40vol%(Ni3Al-B), and it approached to the hardness level of the commercial grade of WC-10wt%Co (H10F). The fracture toughness of both WC-40vol%(FeAl-B) and WC-40vol%(Ni3Al-B) cermets was higher than that of WC-40vol%Co and the toughness increased with increasing boron content. It is believed that boron addition to the aluminide binders leads to improvement in the fracture toughness of the intermetallic matrix composites as a result of increase in the ductility and toughness of the aluminides and also due to increase in WC solubility in the aluminide binders in presence of boron.

The abrasion resistance of WC–40vol%(FeAl–B), WC–40vol%(Ni 3 Al–B), and WC–40vol%Co, prepared from ultra fine precursor powders and processed by uniaxial hot pressing, has been investigated using a pin-on-drum tester. Intermetallic binders, with different amount of boron including 0, 250, 500, 750, and 1000 ppm B, were prepared in ultrafine form under controlled atmosphere using ring grinding, blended with submicron (0.8 μm) WC powder and then uniaxially hot pressed at 1500 °C under a pressure of 20 MPa for 4 min in 10 −2 MPa argon atmosphere. In an additional investigation, wear results were compared with that of commercial H10F (WC–10wt%Co, WC particle size of 0.7 μm). It was found that the wear resistance of WC–FeAl–B and WC–Ni 3 Al–B increased with the increasing amount of boron. WC–40vol%FeAl–B showed the highest abrasion resistance, close to that for WC–10wt%Co (H10F) composite, followed by WC–40vol%Ni 3 Al–B and WC–40vol%Co.

Mechanical deformation and subsequent thermal treatment have been widely used in BSCCO superconductor processing. The purposes of this treatment include introducing texture microstructure, obtaining desired phases and healing the microcracks. It has been shown that most supercurrent flows through the thin layer of superconductor next to the silver sheath. It was proposed that this was related to the good grain alignment in this area. However, the effects of mechanical deformation on the formation and distribution of the texture microstructure in BSCCO superconductors have not been fully understood. The present paper reports a detailed study of the relationships between the mechanical deformation and texture distribution in the BSCCO tapes. Results indicate that the texture distribution behaviours in Bi2223 and Bi2212 are different. Mechanical deformation produces a stronger texture and deeper texture distribution in Bi2223 than in Bi2212. Based on the experimental results, the formation mechanisms of the texture microstructure during mechanical deformation are discussed.

The fracture behaviour of a composite based on 7075 aluminium alloy was studied under uniaxial tensile loading in the temperature range 25–400 °C at a strain rate of 10 −3 s −1 . The ductility of the composite was found to be much lower than that of the monolithic alloy at all temperatures, but both materials exhibited similar strength levels above 300 °C. Particle fracture was the main damage mechanism prior to final fracture at room temperature, while interface debonding together with inter-particle voids were dominant features in fracture at high temperature. Large particles and regions of clustered particles were found to be the locations prone to damage in the composite at both room and high temperatures. At room temperature, particle fracture was observed at clusters of particles as well as in large particles, whereas at high temperature voids nucleated in the matrix closely adjacent to particles and at particle ends. This can be attributed to the high local stress in these regions and the high probability of flaws in large particles. It was also found that the internal damage associated with particle clusters was in regions below the fracture surface and that the extent of damage in the reinforced alloy increased with increasing temperature.

When deformation is carried out near the A1 temperature in low carbon steel, ferrite recrystallisation appears to be the dominant mechanism in controlling the grain size. The present investigation has shown the dominance of ferrite recrystallisation at low temperature between 665-690°C by the application of an austenite recrystallisation power law on experimentally measured grain sizes in 0.05%C steel. Comparison has also been made between predictions using this power law and the experimentally measured grain size after deformation in the two phase (α+γ) region. The results show that the ferrite grain size is influenced significantly by the relative proportions of γ and α phases within the structure just prior to deformation. In addition the good correlation found between predicted and measured grain sizes indicates that ferrite recrystallisation dominates between 850-690°C. Despite this, the possibility still exists for the occurrence of a transformation induced mechanism within this temperature region.

Hot compression of 6061Al alloy and the alloy containing 15 vol% of Al2O3 particles shows that the composite has higher strength than the monolithic alloy at all the temperatues studied. However, as the temperature increases, difference in strength between the two alloys decreases. This decrease is found to be related to microstructural development in the composite during hot compression.

Intergranular and interphase cavitation in binary alpha/beta brass has been investigated in tension at 600° C under conditions of superplastic deformation. The sites for nucleation of cavities has been studied by quantitative metallography and the cavities are observed to nucleate preferentially atα-β interfaces. The process of cavitation is associated with grain boundary sliding and cavity nucleation occurs at points of stress concentrations in the sliding interfaces. Measurements of grain and phase boundary sliding at various interfaces demonstrate that sliding occurred onα-β boundaries more readily than onα-α andβ-gb interfaces. The predominance ofα-β interface cavitation is believed to be as a result of greater sliding at theα-β boundary and of an unbalanced accommodation of sliding adjacent to this type of boundary.

Constant strain rate hot compression tests were carried out on a 0.07 % C-1.18 % Mn-0.07 % Nb steel at 815 and 930° C. The material was deformed to a strain of 0.25 and then held at temperature for times from 10 to 2.8 × 103s. The interruption strain was chosen to be well below the critical strain for dynamic recrystallization. The size distributions of the Nb(CN) precipitates were determined by the method of extraction replication. The effect of the static recrystallization which occurred during holding on the rate of coarsening of the particles was established. It was found that the fifth power of the mean particle radius, r5, increased linearly with ageing time, t, in keeping with a model for coarsening controlled by the rate of pipe diffusion. It was also observed that r5 increased about three times as fast in the presence of static recrystallization as it does in the absence of recrystallization. The particle number density decreased during recrystallization, apparently as a result of the dis...

The force required to extrude a strain rate sensitive material under conditions of homogeneous deformation is calculated by the uniform work method. The force is shown to be a strong function of the rate sensitivity of the material. A new definition of the mean strain rate during extrusion is proposed, which is particularly appropriate to rate sensitive materials. For extrusion ratios of 40 to 160 and a power law strain rate sensitivity of 0.2, the present method leads to extrusion pressures 30 to 60 pct higher than when no account is taken of the rate sensitivity of the flow stress in the die zone. In an appendix, a design for a constant true strain rate (CTSR) die is described, which permits experiments to be carried out without the necessity for rate sensitivity corrections.

Densification behavior of sub micron tungsten carbide composites based on boron doped Fe 60 Al 40 and Ni 3 Al binders were investigated. Soft cobalt binder phase in WC hard metals was replaced by harder and tougher Fe 60 Al 40 and Ni 3 Al intermetallics with boron level up to 0.1wt%. Intermetallic binders were prepared in ultrafine form under controlled atmosphere using ring grinding, blended with sub micron WC powder and then uniaxilly hot pressed under 20 MPa pressure in argon atmosphere for 4 minutes duration at temperatures of 1450 °C, 1500 °C and 1550 °C. It was found that the density of composites increased significantly and WC grain size increased slightly with increase in sintering temperature. The composites exhibited highest density (about 99.5 %TD) and minimal grain growth in WC at sintering temperature of 1500 °C. The presence of boron was found to facilitate densification during liquid phase sintering and boron also resulted in achieving uniform microstructure with continuous binder phase, nearly full density and high faceted features in the structure.

The grain alignment in the deformed Bi2223 superconductor tapes can be improved by mechanical deformation and thermal treatment. The present research studies the mechanisms of the texturing and grain growth processes in the deformed Bi2223 superconductor tapes during annealing. The results indicate that the texturing processes can be divided into two independent stages with different mechanisms. The first stage of the texturing process was the reconnection of the fractured crystals which resulted from mechanical deformation. The second stage was dominated by the recrystallisation and growth of the crystals. There are also two different grain growth mechanisms in the deformed Bi2223 superconductors during the recrystallisation annealing: `ledge-growth' and `screw dislocation-growth' mechanisms. The distinctive texturing and grain growth behaviours of Bi2223 oxide during recrystallisation are related to the plate-like microstructure and the brittle nature of the oxide.

International audience; The mechanical properties of nickel superalloys are related to the spatial distribution of hardening phases, their size and composition, and on the configurations of dislocations introduced by plastic and viscoplastic straining. Heterogeneous plastic flow in relation with dynamic strain aging is examined and synthesized. Dislocations are usually faced with the alternative of shearing or bypassing the y' phase occupying up to 60 vol.%. Depending on y' size, several Orowan bypassing mechanisms are observed, alternatively shearing by dislocation pairs or complex configurations involving S-ISF and S-ESF. Variables such as temperature, strain rate and Schmid factor play a decisive role in determining the dislocation configurations which either percolate through the matrix or shear the y-y' structure. Various dislocation strategies and microstructures are analyzed and illustrated; they are reviewed critically and summarized in a strain rate versus 1/T mechanism map.

The mechanisms of fatigue crack initiation due to second phase particles are studied in 2050-T8 and 7050-T74 plate material. The particles in the specimens gauge lengths are imaged using SEM at the initial state. In 7050-T74, Mg2Si particles are very often cracked before any loading, whereas Al7Cu2Fe particles are not. In 2050-T8, the fraction of (Al, Cu, Fe, Mn) particles initially cracked is larger than that of Al7Cu2Fe in 7050-alloy, but lower than that of Mg2Si particles for similar sizes. For (Al, Cu, Fe, Mn) particles, the proportion of cracked particles increases when the modified shape ratio (aspect ratio including orientation versus rolling direction) increases. This effect is present but less pronounced for Mg2Si particles in 7050-T74. Fatigue cracks initiate at cracked (Al, Cu, Fe, Mn) particles in 2050-T8 alloy, and at both Al7Cu2Fe (cracked during cycling) and Mg2Si in 7050-T74 alloy.

International audience; Cold spray is now well recognized as one of the most powerful and efficient coating process because it is cost-attractive and "green". However, this process still shows limitations to achieve coatings for highly-demanding service conditions such as those required in certain automotive and/or aircraft applications. Beyond these limitations, cold spray is expected to compete with conventional P/M routes.The present work therefore focussed on the study of damage mechanisms in cold-sprayed AISI 316L and 316L-matrix-Cu composites coatings due to high-loading conditions. Different damage mechanisms could occur depending on the content of Cu particle addition, due to changes in the response of the microstructure to the loading. These mechanisms were studied using the newly-developed "impact-sliding" test. In this test, a steel ball impacts the coating surface at a given frequency, with a fixed angle. The influence of major testing parameters was investigated.Microstructures before and after testing were studied using optical microscopy, scanning electron microscopy (SEM), and microprobe analysis in addition to 3D optical profilometry of impacted areas. Damage mechanisms were seen to be of two types, i.e. plastic deformation and wear. These resulted in decohesion of splats, formation of wear debris and formation of a layer with a tribologically-transformed structure (TTS) at the contact surface.Results showed that cold spray could be claimed to be suitable for the achievement of high-performance coatings for industrial applications provided that the coating microstructure can be controlled. This could be done using a composite approach to the coating composition.

International audience; The plasticity of hexagonal materials is strongly anisotropic and involves different microscopic mechanisms such as mechanical twinning and dislocation glide. Twins are often considered to be responsible for a particular three-stage shape of compression curves, unusual for polycrystals with cubic structure. However, the role of twins remains a matter of debate and it is not clear if the same features appear in other testing conditions. We performed tensile tests on commercially-pure Ti samples cut along the rolling and the transverse direction, which yielded several unexpected results. In particular, the work hardening rate was found to be lower in the latter case, although the EBSD measurements revealed for them a larger volume fraction of twins. Also, the two kinds of specimens showed an opposite sign for the strain-rate effect on the proneness to the three-stage shape of the deformation curves. As a first approach, these observations are compared to the results derived from a simple Kocks-Mecking model. The possible role of twinning and dislocation glide on the anisotropy of mechanical behavior of titanium is then discussed.

International audience; This paper deals with the pressure dependence of plasticity in metallic glasses below glass transition. Recent results indicate that some metallic glasses have such a dependence and that it increases with temperature (Keryvin et al., Phil. Mag., 88, 1773, 2008). We investigate the possibility that such a situation could be a common feature for all metallic glasses by performing a literature review. Results indicate that it is not straightforward to draw decisive conclusions.

MCrAlY-typed coatings are conventional for applications to land-based turbines against hightemperature oxidation and corrosion. However, improvements are still currently expected from innovations in the coating process and/or in the selection of the starting materials. Both types of innovations were studied in the present work. The former consisted in cold spray as a substitute for plasma spray which is conventionally used as the coating process. The latter consisted in developing mechanically-alloyed powders to be suitable for the targeted application especially. In this study, coating-substrate adhesion was considered as the justice of the peace to assess improvements from these innovations. This was determined using the LAser Shock Adhesion Test, namely LASAT, which was recently developed as innovative adhesion testing of thermal spray coatings. Among the main results, mechanical alloying was shown to be satisfactory to result in an homogeneous powder from the mixing of CoNiCrAlY with Mo. This powder could be coldsprayed, all the more easily because of a fine grain size. Results were compared with those obtained from conventional commercial pre-alloyed powders. As a general result, it was shown that cold spray could lead to highly-dense and high-adhesion MCrAlY-typed coatings onto Inconel 625 even though the process is usually claimed to be convenient for high-ductility materials such as copper. Incidentally, LASAT was confirmed to be a flexible and powerful testing tool to study adhesion; which resulted in the ranking of the various types of coatings involved in the work. Results are discussed in the light of an experimental simulation of the impinging of cold-sprayed particles using so-called “laser flier impact experiments”. In this development of this simulation approach to cold spray, the flier was made of a 50μm-thick disc machined from HIP’ed CoNiCrAlY.

Three interface factors may influence thermally-sprayed coatings adhesion: interface morphology (as usual), thermal and chemical features. It was shown that these three aspects of adhesion mechanisms are shown to be dependent and very local. It is especially true for cold spray which is one of the most promising spray processes. As this spraying technique is based on rapid deformation, cold spray coating/substrate interfaces show local morphological, thermal and chemical features, in a way that none of them can be neglected. LASAT is particularly suitable for testing these coatings because it can be applied to small areas (~1 mm²). From this, it has the outstanding advantage to be sensitive to fine-scaled phenomena responsible for coating adhesion.