Thermal expansion of hydroxyapatite between − 100 °C and 50 °C

Hydroxy apatite (HAp) ceramic was synthesized using traditional sintering. Dilatometric and lattice thermal expansion properties of a HAp ceramic were evaluated at temperatures of ? 100–50 °C. In that temperature range, the dilatometric thermal expansion coefficient and the lattice thermal expansion coefficient of the HAp ceramic were, respectively, 10.6 × 10^? 6/°C and 9.9 × 10^? 6/°C. Furthermore, thermal expansion properties of a human tooth were measured. The thermal expansion coefficient of the horizontal direction perpendicular to the growing direction of a tooth was 15.5 × 10^? 6/°C; that of the vertical direction along with the direction of tooth growth was 18.9 × 10^? 6/°C at the temperature range described above.     

Aging of a polymer core composite conductor: Mechanical properties and residual stresses

Polymer core composite conductor specimens were aged in atmospheric conditions at 140 and 180 °C and then tested under four point bending. When aged up to a year at a temperature of 140 °C no detrimental effect on flexural performance of the composite was observed, as opposed to aging at 180 °C, which had a very negative effect on the properties. A finite element model was developed to characterize the residual stress in the composite on a micro scale using representative volume elements (RVE). The residual stresses developed after aging at 140 °C for a year were minimal. However, at temperatures higher than 160 °C significant increases in the stresses were observed. The effect of chemical aging on the failure process of the rods was not considered but could result in the rapid reduction in the loads at failure for the rods tested at 180 °C for up to a year.     

Research on heat treatment of TiBw/Ti6Al4V composites tubes

Heat treatment with different parameters were performed on the hot-hydrostatically extruded and swaged 3.5 vol.% TiBw/Ti6Al4V composites tubes. The results indicate that the primary α phase volume fraction decreases and transformed β phase correspondingly increases with increasing solution temperatures. The α + β phases will grow into coarse α phases when the aging temperature is higher than 600 °C. The hardness and ultimate tensile strength of the as-swaged TiBw/Ti6Al4V composite tubes increase with increasing quenching temperatures from 900 to 990 °C, while they decrease with increasing aging temperatures from 550 to 650 °C. A superior combination of ultimate tensile strength (1388 MPa) and elongation (6.1%) has been obtained by quenching at 960 °C and aging at 550 °C for 6 h. High temperature tensile tests at 400–600 °C show that the dominant failure modes at high temperatures also differ from those at room temperature.     

Effect of heat treatment on the tribological properties of Al–Cu–Mg/nanoSiC composites

In this study, the effect of heat treatment on the tribological properties of Al–Cu–Mg alloy reinforced with 4 wt.% SiC particles with 650 nm average particle size has been investigated. The age hardening process consists of solution treatment at 540 °C for 6 h, followed by water quenching and ageing at different temperatures of 175, 200 and 225 °C with soaking times of 3, 6 and 9 h. Hardness measurements were applied to monitor the precipitation effect and the aged samples were then subjected to wear tests under dry sliding conditions against steel and alumina counterfaces. The results showed that the reinforced material exhibits an enhanced ageing response compared to the unreinforced material in the same heat treatment conditions. The rate of ageing increases with increasing temperature; however, ageing at 200 and 225 °C for more than 6 h resulted in over-ageing. The best combinations for the enhanced tribological properties for the composite material were selected as 6 h ageing at 225 °C. The precipitation effect for this alloy can be enhanced by the small addition of SiC nanoparticles. Having a small amount of nanoSiC particles with fine precipitates inside the matrix further increases the hardness and wear properties.     

Synthesis of nanoporous silicon carbide via the preceramic polymer route

Nanoporous silicon carbide materials were prepared by the pyrolysis of the preceramic polymer, polycarbosilane (PCS), with and without the addition of an inert filler (nano- and micron-sized silicon carbide powders). Hydrosilylation crosslinking of PCS with divinylbenzene prior to pyrolysis appeared to have little influence on the development of micro- and mesoporosity. Maximum micropore volumes were 0.28 cm³ g^?1 for non-crosslinked PCS and 0.25, 0.33 and 0.32 cm³ g^?1 for PCS crosslinked with 2, 6 and 10 wt.% DVB respectively. Micropore volumes decreased under hydrothermal conditions to 0.03 cm³ g^?1 for non-crosslinked and 0 cm³ g^?1 for crosslinked PCS. Porosity was also lost at temperatures above 700 °C. The addition of nano-sized SiC powders to PCS prior to pyrolysis maintained mesoporosity to temperatures of 1200 °C, however, micron-sized SiC powders did not maintain porosity above 800 °C. The modal pore size in pellets formed by compressing micron-sized powders with the preceramic polymer was 5 μm compared to 30 nm when nano-sized powders were used.     

Preparation of rodlike t-ZrO2 nanoparticles by two-step calcination of 1,12-diaminododecane–zirconia mesostructured composites

Rodlike t-ZrO₂ nanoparticles with aspect ratio of 1.3–8.0 and large surface area (152 m²/g) have been produced by two-step calcination of 1,12-diaminododecane–hydrous zirconia mesostructured composites. The two-step calcination consists of first calcination at 300 °C for 24 h and then at 400 °C for another 24 h. The resulting t-ZrO₂ nanoparticles can be stored under ambient conditions for at least 2 months without discernible transformation to the monoclinic phase. Compared to one-step calcination at 400 °C, the two-step calcination increases the amount of hydrocarbon fragments (3.6 wt% versus 2.9 wt%) adsorbed onto the resulting t-ZrO₂ nanoparticles. This increase may account for the improved phase stability of the rodlike t-ZrO₂ nanoparticles.     

Effects of hot-working parameters on microstructural evolution of high nitrogen austenitic stainless steel

The microstructural evolution of high nitrogen austenitic stainless steel under various deformation conditions was characterized by isothermal compression test. Special attention was paid to the variation of microhardness and its relationship with grain size was also derived. Results indicated that two kinds of strengthening mechanism acted during the whole temperature range. When the temperature is between 950 °C and 1150 °C, grain refinement plays a dominant role. But at temperatures lower than 900 °C, no recrystallization occurs and substructure (dislocations and twins) contributes massively to the strength. Furthermore, it was found that the peak precipitation of grain boundary carbides which are seriously detrimental to toughness appeared at 850 °C. Therefore, an optimizing processing route could be recommended to achieve a good combination of high strength and good toughness. Firstly, the hot-rolling at 950–1100 °C should have large stain to gain refined grains, and accelerated cooling is applied from 950 to 750 °C in order to avoid carbide precipitation along grain boundary. Lastly, at temperatures lower than 750 °C warm-rolling with medium stain can get substructure strengthening effects.     

Mechanical and physical properties of medium density fiberboard panels laminated with thermally compressed veneer

The objective of study was to evaluate some of the physical and mechanical properties of medium density fiberboard (MDF) panels laminated with veneer sheets compressed at different levels of pressure and temperature. Rotary peeled veneer samples of European beech (Fagus orientalis Lipsky) were compressed at temperatures of 150 °C, 180 °C, and 200 °C using 4 MPa and 6 MPa pressure for 8 min. Commercially produced MDF samples also were laminated with such compressed veneer sheets. Both modulus of elasticity (MOE) and modulus of rupture (MOR) of the specimens increased with increasing pressure and press temperature. Bending characteristics of the samples tested parallel to the grain orientation resulted in significantly higher values than that perpendicular to the grain orientation for each manufacturing parameter. Thickness swelling of the samples also was influenced by increased pressure but variation in press temperature did not result in any influence on dimensional stability. The findings of this work provide potential to produce sandwich type panels with improved properties. Initial results found in this study could be used to manufacture laminated panels with a fixed rate of adhesive while controlling press parameters as a function of the magnitude of pressure and temperature.     

Coral-like hydroxy sodalite particles from rice husk ash as silica source

Coral-like hydroxy sodalite (HS) particles were prepared from rice husk ash as silica source in the presence of other aqueous-based precursor materials following a simple process under hydrothermal condition at 90 °C for 15 h. The particles obtained at 90 °C for different times (6, 10 and 15 h) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). The HS crystals along with a small amount of zeolite A particles were observed at 90 °C/6 h while phase pure HS particles were obtained at 90 °C for 10 and 15 h. The characteristic vibration bands of the HS particles were confirmed by FTIR spectroscopy. FESEM images showed that the HS particles obtained at 90 °C/15 h were coral-like morphology which were formed through the self-assembly of the smaller particles generated at the initial stage of reaction (6 and 10 h) under the same experimental conditions. A proposed mechanism for the formation of coral-like HS particles was also illustrated.     

A study of the practicality and performance of CFRP applications using post-curing at moderately elevated temperatures

The application of post-curing influences the final structure of the adhesive by extending the curing reaction of the epoxy to help it reach its full physical characteristics, such as ultimate cross-link density and T_g. This study explores the practical means of post-curing CFRP/concrete systems at moderately elevated temperatures, namely at 60 °C, using bonding adhesive under specific operating conditions. Adhesive samples and CFRP/concrete specimens were subjected to a post-curing regime at 60 °C after different periods of ambient temperature curing (3 h, 6 h and 72 h). The outcomes from this work will provide guidelines for post-curing applications for outdoor structures in an attempt to find practical methods to improve the bonding capacity of CFRP/concrete systems under more extreme environmental conditions.     

Investigation of impact toughness of a Ni-based superalloy at elevated temperature

The impact toughness of M951 alloy is investigated in temperature range between 20 °C and 800 °C. The results show that the impact toughness of samples impacted at 600 °C shows highest impact toughness value, the impact toughness value drops sharply when the samples impacted at 760 °C. In addition samples impacted at 800 °C show the higher impact toughness than that of samples impact at 760 °C. The scanning electron microscope observations show that cracks initiate at carbides particles due to high stress concentration, which leads to low impact toughness value at 20 °C. The dimples which can absorb more energy are formed during the impact at 600 °C. The samples impacted at 760 °C show lowest impact toughness. Additionally, the dimples nucleation, growth and coalescence are the major fracture mechanism at elevated temperature.     

The effects of superchilled storage at −2 °C on the microbiological and organoleptic properties of cold-smoked salmon before retail display

The aim of this study was to investigate the impact of superchilling (?2 °C) on the evolution of Listeria monocytogenes and organoleptic characteristics of cold-smoked salmon samples. An Hadamard matrix experimental design was carried out on artificially inoculated samples stored at +4 °C for 10 d and at +8 °C for 18 d to know the influence of four factors: salt content, strain, cold stiffening and superchilling time, on the level of L.monocytogenes in cold-smoked salmon. The growth of L. monocytogenes in naturally contaminated cold-smoked salmon and the organoleptic properties were investigated under superchilling conditions.Superchilling (?2 °C for 28 d) had a limited impact on some of the organoleptic properties but the level of L. monocytogenes at the end of the shelf-life (4 °C for 10 d and 8 °C for 18 d) could exceed the microbiological criterion set by the European legislation.     

Partially pyrolyzed composites with basalt fibres – Mechanical properties at laboratory and elevated temperatures

Mechanical properties of partially pyrolyzed at 650 °C or 750 °C unidirectional basalt fibre composites with polysiloxane matrix were studied at laboratory and elevated temperatures. Ten pyrolysis processes differing mutually in heating courses and ultimate temperatures were compared. The material treated at 650 °C revealed at laboratory temperature flexural strength around 850 MPa. Fracture toughness of this material exceeded that of the cured only (at 250 °C) and treated at 750 °C composites. However, the composite pyrolyzed at 750 °C is more suitable for applications at elevated temperatures because of its slower degradation in hot air.     

Behavior and failure of uniformly hydrided Zircaloy-4 fuel claddings between 25 °C and 480 °C under various stress states,including RIA loading conditions

The anisotropic plastic behavior and the fracture of as-received and hydrided Cold-Worked Stress Relieved Zircaloy-4 cladding tubes are investigated under thermal–mechanical loading conditions representative of Pellet–Clad Mechanical Interaction during Reactivity Initiated Accidents in Pressurized Water Reactors. In order to study the combined effects of temperature, hydrogen content, loading direction and stress state, Axial Tensile, Hoop Tensile, Expansion Due to Compression and hoop Plane Strain Tensile tests are performed at room temperature, 350 °C and 480 °C on the material containing various hydrogen contents up to 1200 wt. ppm (hydrides are circumferential and homogeneously distributed). These tests are combined with digital image correlation and metallographic and fractographic observations at different scales. The flow stress of the material decreases with increasing temperature. The material is either strengthened or softened by hydrogen depending on temperature and hydrogen content. Plastic anisotropy depends on temperature but not on hydrogen content. The ductility of the material decreases with increasing hydrogen content at room temperature due to damage nucleation by hydride cracking. The plastic strain that leads to hydride fracture at room temperature decreases with increasing hydrogen content. The influence of stress triaxiality on hydride cracking is negligible in the studied range. The influence of hydrogen on material ductility is negligible at 350 °C and 480 °C since hydrides do not crack at these temperatures. The ductility of the material increases with increasing temperature. The evolution of material ductility is associated with a change in both the macroscopic fracture mode of the specimens and the microscopic failure mechanisms.     

Synthesis and dielectric properties of polyarylene ether nitriles with high thermal stability and high mechanical strength

A series of polyarylene ether nitriles were synthesized by the nucleophilic aromatic substitution polymerization of 2, 6-dichlorobenzonitrile with various bisphenol monomers. Owing to the different structural units, the derived copolymers showed different glass transition temperatures in the range of 166–260 °C. Moreover, they all showed good film-forming properties and high mechanical strength ranging from 75 MPa to 117 MPa, and also exhibited high thermal stability with the 5% weight loss temperatures ranging from 373 °C to 498 °C. Furthermore, both the dielectric constant and dielectric loss were found to be relatively stable with respect to temperature before the turning point temperature, which is very near to the glass transition temperature.     

Microstructure degradation in high temperature fatigue of TiAl alloy

Low cycle fatigue properties of lamellar TiAl with 8 at.% Nb were studied at four temperatures: room temperature, 700, 750 and 800 °C. Up to 750 °C, stable cyclic behaviour is observed while cyclic softening is characteristic for 800 °C. The strength of the alloy is still high even at 800 °C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling at RT. At 750 °C, the lamellar structure was in some places destroyed by cyclic plastic straining and pure γ-phase islands with high density of dislocation debris were formed. At 800 °C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure and possible annealing of dislocation debris is the reason for marked cyclic softening at 800 °C.     

The effect of temperatures on hybrid composite laminates under impact loading

The present experimental investigation deals with the impact responses of hybrid composites (carbon–glass fiber/epoxy) under various temperatures. A number of samples were subjected to increasing impact energy at the temperature range of ?20 to 60 °C until complete perforation of samples. With this use of increasing impact energies, it was possible to examine the impact response and failure mechanisms of hybrid composites until perforation of sample. An Energy Profiling Diagram (EPD) was used to obtain the penetration and perforation thresholds of hybrid composites. Besides, the temperature effects on impact characteristics such as load, contact time and permanent deflection were also presented in figures. Test results showed that temperature variations affect the impact characteristics of hybrid composites and they get their maximum values at ?20 °C or 60 °C.     

Effect of heat treatment on microstructure,hardness and rollability of V55Ti30Ni15 alloy membranes

The effect of heat treatment on the microstructure, hardness and rollability of V₅₅Ti₃₀Ni₁₅ alloy membranes has been investigated in this study. The microstructure resulting from different heat treatment conditions has a great influence on hardness. Fine NiTi particles precipitate from the supersaturated V-matrix solid solution at temperatures above 600 °C, increase in quantity until 800 °C, then dissolve back into the V-matrix with a further increase in temperature up to 950 °C. The resultant hardness decreases with temperature until 800 °C, and then increases from 800 to 950 °C. In the present study, a comparison has been made between the rollability of the as-cast and the heat treated state selected for deformation at different rolling temperatures. The percent reduction in thickness of the heat-treated alloy (800 °C/18 h) has been found to be up to 30% higher than that of the as-cast alloy, even at room temperature (cold rolling).     

Effect of post weld heat treatment on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel weldments

The effect of postweld heat treatment (PWHT) on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel joints with ER316LMn filler material was investigated. PWHT aging was performed for 1 h at four different temperatures of 600 °C, 760 °C, 870 °C and 920 °C, respectively. The microstructure revealed the sigma phase precipitation occurred in the weld metals heat-treated at the temperature of 870 °C and 920 °C. The PWHT temperatures have the less effect on the tensile strength, and the maximum tensile strength of the joints is about 630 MPa, reaching the 95% of the base metal, whereas the elongation is enhanced with the rise of PWHT temperatures. Meanwhile, the sigma phase precipitation in the weld metals reduces the impact toughness.     

Fatigue crack growth and damage characteristics of high-speed rail at low ambient temperature

Low temperature can be a significant problem affecting safety and maintenance of railway. In this study, the fatigue crack growth rate and rolling contact fatigue damage behaviors of high-speed rail material under different temperature conditions were investigated by a series of experiments. The results indicate that the stress and strength of rail material increase with the decrease of ambient temperature. The crack growth rate at 0 °C and − 20 °C is similar with that at 20 °C. While, when the temperature decreases to − 60 °C, the growth rate of crack increases sharply. The promotion of rail embrittlement at low temperature accompanied with the action of high stress causes the rapid failure and increase of surface crack length and subsurface crack damage. Meanwhile, three crack growth mechanism models at different temperatures can be inferred. The brittle fracture mode is increasingly apparent with the temperature decreasing.