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This study investigates the effects of film thickness and substrate bias on the microstructure and stress state of tungsten (W) films prepared by arc ion plating (AIP) on substrates including 304 stainless steel (SS), tungsten (W), and Si (100). The microstructure of the films was characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Residual stress was analyzed using substrate curvature techniques combined with Stoney's formula and Huseh's formula. The results indicate that the W films are single-phase, predominantly comprising the pure α-phase. The film surfaces are dense and smooth, with the absence of large particles. The films consist of closely packed columnar grains, and no microcracks, voids, or delamination were observed at the film-substrate interface, indicating strong adhesion. As the film thickness increased, the curvature of the W/SS system and the compressive stress in the film both increased, which closely matched the fitted curves. As the substrate bias increased, the curvature of the W/SS system decreased, and the compressive stress in the W film increased. At higher substrate biases, deposition temperatures are higher, and growth stress remains nearly constant across a range of continuous bias variations, with the increase in residual stress primarily due to thermal stress. [ABSTRACT FROM AUTHOR]

With an increasing temperature gradient, the internal stress in composites can cause many problems, such as the plastic yield of the matrix, fracture of the reinforcements, growth of pores in the matrix, and debonding of the interface. The reinforcement particularly affects the internal stress, considerably changing the various properties of the composites. ZrMgMo3O12particle (p)/2024Al composites were fabricated using 5−30 vol. % of a near-zero expansion material, ZrMgMo3O12, as a reinforcement. This was achieved via high-energy milling followed by vacuum hot pressing. The influence of the ZrMgMo3O12 content on the thermal expansion and dimensional stability of the composites was investigated. The results indicated that the large thermal mismatch stress between ZrMgMo3O12 and 2024Al limited the addition of ZrMgMo3O12 to the composites. The composites with 30 vol. % ZrMgMo3O12 failed after solid solution treatment during water quenching. With increasing ZrMgMo3O12 content from 5 to 20%, the coefficients of thermal expansion (CTEs) first decreased and then increased, whereas the dimensional stability of the composites first increased and then decreased. The composites with 10% ZrMgMo3O12 had the lowest CTE of 11.3 × 10–6 °C−1 from − 100 °C to 400 °C, and exhibited dimensional stability from room temperature (RT) to 400 °C. [ABSTRACT FROM AUTHOR]

A colorimetric sensing platform based on carboxymethyl cellulose-silver nanoparticles (CMC-AgNPs) metallogel was proposed to monitor the temperature history and quality of perishable products stored at low temperature. The carboxymethyl cellulose (CMC) metallogel, fabricated in the presence of Ag+, incorporates ionic crosslinking of biopolymers, complexation between reactants, and subsequent in situ synthesis of AgNPs, which are designed to lead the color transition of metallogel from colorless to dark brown depending on temperature and time. The mechanical and structural properties of metallogels and AgNPs were characterized by rheology, XRD, and FT-IR. Color changes associated with temperature, time, and metal ion precursors were examined by UV–visible spectroscopy and colorimetry. The longer the exposure time to thermal stress condition such as room temperature (25 °C) or high temperature (60 °C), the deeper the color of metallogel. The CMC-AgNPs metallogel-based sensor provides an efficient, safe way to track temperature history and assess perishable products' quality, crucial for the safe distribution of food, vaccines, and medicines. This cost-effective and reliable visual sensor minimizes spoilage and health risks by enabling accurate temperature monitoring without the need for complicated equipment. [ABSTRACT FROM AUTHOR]

Y2O3 materials have been widely applicated in high temperature industry owing to its high temperature stability. However, the poor sintering behavior and thermal shock resistance limited its application. The existing studies were focused on its sintering properties, yet the increase in densification of Y2O3 materials could weaken its thermal shock resistance. Y2O3 materials with smaller closed pores were fabricated by the decomposition of Al(OH)3 and the effect of Al(OH)3 on the microstructure, mechanical properties and thermal properties of Y2O3 materials were investigated in this paper. We concluded that the migration of grain boundaries was accelerated due to the ionic radii difference and the diffusion coefficient between Y3+ and Al3+, and the diffusion coefficient of Y3+ was relatively weak while the diffusion of Al3+ was mainly dominated. The Al2O3 produced by decomposition of Al(OH)3 was active, which promoted the sintering of Y2O3 materials. Meanwhile, the porosity and pore structure of Y2O3 materials were affected by the decomposition of Al(OH)3, and the appropriate pores improved the thermal shock resistance by absorbing thermal stresses. Furthermore, it indicated that adding Al(OH)3 into Y2O3 materials had a powerful influence in balancing its sintering properties and thermal shock resistance. The sample with 3 wt% Al(OH)3 exhibited the better performance in this study, with the relative density of 93.2% and the thermal shock stability factor parameter Rst of 1.74 W m1/2. [ABSTRACT FROM AUTHOR]

The wear behavior of two plasma-sprayed zirconia–yttria coatings was studied at high temperatures. Agglomerated and sintered, as well as fused and crushed zirconia–yttria feedstock powders were used to manufacture bimodal and monomodal coatings by atmospheric plasma spraying onto an INCONEL 718 substrate previously coated with a NiCrAlY bond coat. The structure of the coatings was analyzed by SEM on their cross section and surface. The samples were subjected to wear conditions by sliding contact through a ball-on-disk test up to 1000 °C, using an alumina ball 6 mm in diameter as the counterbody, on which a load of 5 N was applied. The samples were rotated during 20000 cycles, reaching a speed of 0.10 m·s−1 at the contact area with the counterbody. The porosity, phase, and mechanical properties were determined before and after wear tests. The results indicate that at 25 °C, both coatings have enough mechanical resistance to withstand the tribological conditions they were exposed to. Therefore, low wear rates were produced by ductile deformation. The tribological conditions became more aggressive as the thermal stresses increased with the test temperature, producing cracking, and detaching particles in the coatings tested at 500 and 750 °C. Consequently, high wear rates related to brittle deformation were obtained. However, the transformation of the amorphous phase to the t′-zirconia phase, produced at 1000 °C, increased the hardness of both coatings and, consequently, their wear resistance; thus, the predominant mechanism of damage was ductile deformation, with wear rates similar to those obtained when the coatings were tested at 25 °C. [ABSTRACT FROM AUTHOR]

The injection and balance of charge carriers in organic light-emitting diodes (OLEDs), as well as the contact at the organic/metal interface, are essential to OLED under thermal stress. We employed electron transporting layers (ETLs) with different glass transition temperature (Tg) to investigate the effect of thermal stress on the organic/metal interface and proposed a strategy of realizing highly thermally stable OLEDs of using 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine:8-quinolin-olato lithium (B3PYMPM:Liq) bulk heterojunction as ETL. We found that the thermal stability of the organic/metal interface was strengthened with the increase of the Tg of the organic material. OLEDs with low-Tg ETL were destroyed after being heated at 100 °C, while the performance of the OLED with high-Tg ETL could be maintained. By combining the advantages of the good electron transport ability of Liq and high Tg of B3PYMPM, the OLED with B3PYMPM:20% Liq bulk heterojunction ETL obtained the best thermal stability, with an optimal current efficiency (CE) of 59.22 cd/A under 85 ℃ heating. The CE of the optimized OLED after heating at 100 ℃ was still 1.49% higher than its original performance. The strategy of employing the heterojunction ETL consisting of materials with good electron transporting properties and thermal stability is an effective way to improve the thermal stability of OLED. [ABSTRACT FROM AUTHOR]

The present study aims to evaluate and compare the effect of 5 vol.% TiC or WC addition on densification, phase stability, microstructure, mechanical properties, thermal residual stress and reciprocating wear behaviour of spark plasma-sintered ZrB2-20 vol.% SiC composite. ZrB2–20SiC–5TiC (vol.%) composite attains 99.6% mean sintered density even at 1700 °C, while WC containing composites (ZrB2–20SiC–2.5TiC–2.5WC and ZrB2–20SiC–5WC, vol.%) necessitates a sintering temperature of 1800 °C for > 98% densification. Phase and microstructure analyses confirm that respective incorporation of TiC and WC leads to in situ formation of (Zr,Ti)B2 and (Zr,W)B2 solid solution in the sintered composite. Elastic modulus and thermal expansion coefficients of the composites have been estimated utilizing well-established analytical models. The thermal residual stress of the sintered composites is determined analytically utilizing Taya's model and Hsueh's model and compared with residual stress of SiC reinforcement determined by Raman spectroscopy. Nano-indentation analysis confirms that the minimum resistance to deformation and maximum plasticity index are observed in ZrB2–20SiC–2.5TiC–2.5WC composite due to its relatively low elastic modulus. The maximum Vickers hardness is observed in ZrB2–20SiC–2.5TiC–2.5WC composite, whereas an excellent combination of indentation toughness and indentation modulus is found in ZrB2–20SiC–5WC. Owing to relatively high fracture toughness exponent and low brittleness index, ZrB2–20SiC–5WC composite records the minimum wear volume and wear rate in linear reciprocating wear test. [ABSTRACT FROM AUTHOR]

Additive manufacturing provides alternative solutions for complex geometry and design freedom for the customization of aluminum alloys, while the unique microstructure as well as the complex solidification behavior is of great concern due to the severe thermal stress in the layer-by-layer accumulated process. In this work, the effects of laser power, laser scanning speed, and hatch spacing on the microstructure and mechanical properties of a laser powder bed fusion (LPBF) fabricated thermal conductive aluminum alloy 6063 (AA6063) were studied. The relationship between processing parameters and metallurgical defects was investigated. The element distribution and misorientation between grains around the crack were characterized. The results revealed that the majority of cracks were parallel to the building direction. The crack density was suppressed by increasing the scanning speed. The orientated cracks lead to the anisotropy of mechanical properties. The strength and ductility of the vertical samples are both higher than those of the horizontal samples. After aging treatment, an ultimate tensile strength of 241 MPa, yield strength of 215 MPa, and elongation of 4.9% were obtained in the vertical specimen of the LPBF processed AA6063. It was demonstrated that cracks tend to stretch along the high-angle grain boundaries because of the concentration of local thermal stress at the final stage of solidification. This work provides guidance for defects suppression and mechanical properties optimization in additively manufactured AA6063 and other aluminum alloys. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF), categorized as additive manufacturing technique, has a capability to fabricate NiTi (Nitinol) shape memory alloys with tailorable functional properties and complex geometries. An important processing parameter, hatch distance (h), is often related to macroscale structural defects; however, its role on controlling the microstructure and functional properties is usually underestimated in L-PBF of NiTi. In this work, equiatomic NiTi (50.0 at% Ni) parts were fabricated with various hatch distances to tailor the microstructure and their shape memory characteristics. Contrary to what is observed in Ni-rich NiTi alloys, in this work, we demonstrate that phase transformation temperatures of L-PBF equiatomic NiTi do not decrease proportionally with hatch distance but rather relate to a critical hatch distance value. This critical value (120 μm) is derived from the synergistic effect of thermal stress and in situ reheating. Below this value, epitaxial grain growth and in situ recrystallization are enhanced, while above, irregular grains are formed and dislocations induced by thermal stresses decrease. However, the critical value found herein is characterized by high dislocation density and fine grain size, resulting in a superior thermal cyclic stability. The proposed finite element model is proven to be an effective tool to understand and predict the effect of hatch distance on grain morphology and dislocation density evolutions in L-PBF NiTi SMAs. In the present study, we provide a comprehensive understanding for in situ controlling L-PBF NiTi microstructure and functional characteristics, which contributes to designing 4-dimensional shape memory alloys. [ABSTRACT FROM AUTHOR]

Syntactic foams with high strength and light weight are essential for aerospace and deep sea explorations. In this study, high-performance carbon fiber/hollow glass microspheres/epoxy syntactic foams were prepared, and the reinforcing mechanism of carbon fiber is discussed. The syntactic foam with 3 wt% short carbon fiber achieves a uniaxial compressive strength of 141.7 MPa, which is among the highest values reported in the literature. The thermal conductivity of syntactic foam increased by 66.7% with the addition of 3 wt% short carbon fibers, which helped to control the cracking issue caused by the inner temperature surge during the curing process. Further stress characterizations using fiber Bragg gratings (FBGs) confirmed that carbon fiber can relieve the evolution of thermal stress and reduce the residual thermal stress. [ABSTRACT FROM AUTHOR]

One of the big challenges for realizing future nuclear fusion reactors is the development of materials able to withstand the high thermal loads and particle fluxes typical of these reactors. This work investigated the residual stresses in a W coating deposited through plasma spraying on a substrate of CuCrZr alloy used in the active cooling system of ITER (International Thermonuclear Experimental Reactor). To this purpose, a graded interlayer consisting of a mixture of W and Cu whose composition gradually changes was deposited between coating and substrate. The W coating-interlayer-CuCrZr substrate system showed good adhesion and no cracks were observed. Residual stresses were investigated by X-ray diffraction (XRD) and nanoindentation tests. Residual stresses in the interlayer have different sign in W (compressive) and in Cu (tensile) and reach their maximum value in the inner part of the interlayer where the relative amounts of the two deposited metals are similar. The main contribution to residual stresses comes from thermal stresses arising when deposited metal and substrate cool together from deposition temperature to ambient temperature owing to the different coefficients of thermal expansion (CTE). The residual stresses measured in W are always below the critical value for crack formation (275 ± 50 MPa) but not negligible. Based on present results, the optimization of deposition temperature seems to be the key for reducing residual stresses in the interlayer. [ABSTRACT FROM AUTHOR]

Chemical effect of rare earth element erbium (Er) doped in yttria-stabilized zirconia (YSZ) is studied via experimental and theoretical methods in calcium-magnesium-alumino-silicate (CMAS) melt. It is found that the penetration depth of YSZ doped by Er element is only 10.75 ± 1.13 μm, which is smaller than that of undoped YSZ (21.97 ± 1.52 μm). Theoretical results show that a decrease in the thermal expansion coefficient of YSZ(Er) and in the Griffith rupture work of CMAS/YSZ(Er) and CMAS/ZrSiO4 weakens their thermal stress and adhesive strength. And doped Er element in YSZ can setback the diffusion of Y elements and enhance the diffusion of Si ↔ Zr elements in the YSZ(Er) TBC, which can slow down the phase transition from t-ZrO2 to c-ZrO2 and promote the formation of the ZrSiO4 corrosion products to block the interface pores within a YSZ(Er) structure. Thus, our findings open another way to probe the advantage of rare earth element doped in thermal barrier coating. [ABSTRACT FROM AUTHOR]

The present study focuses on the preparation and characterization of a poly(ether ether ketone)/poly(ether imide) [PEEK/PEI] blend for application in additive manufacturing using fused filament fabrication (FFF). Polymer miscibility was evaluated using differential scanning calorimetry analysis and Fourier transform infrared analysis. The results confirmed the full miscibility of PEEK and PEI at all compositions. Seen as the best compromise between mechanical properties and glass transition temperature, a 70/30 wt/wt% PEEK/PEI blend was extruded into filaments for use by FFF. Nozzle temperature, layer orientation, and layer thickness were selected as printing parameters to evaluate their effect on the tensile properties and degree of crystallinity ( X c) . Optimum printing parameters were achieved at 380 °C nozzle temperature, a [0/15/−15°] layer orientation, and a 0.15 mm layer thickness. The printed PEEK/PEI samples were annealed at various temperatures to erase residual thermal stress generated during printing. Samples annealed for two hours at 200 °C have improved elastic modulus by 21.6%, while X c increased by 24.3%. Adding 30 wt% of PEI to the semicrystalline PEEK yielded three advantages, namely improving the operating and service temperatures by 20 °C, decreasing the processing temperature by 20 °C while maintaining most of the high tensile properties of PEEK. [ABSTRACT FROM AUTHOR]

Crack is one of the common problems in preparation of NiCrBSi alloy coatings by laser cladding, especially for high hardness coatings. In this study, the crack behavior and prevention of Ni60A coating by coaxial laser cladding are investigated. The results indicate that the nonuniform hard Cr-rich precipitates and large residual tensile stress are the main reason for cracking of Ni60A coating. According to the difference of thermophysical properties and temperature between the coating and the substrate, the thermal stress models are established, in which the stress perpendicular to the scanning direction σ y is smaller than the stress along the scanning direction σ x . Due to the change in the relative relationship among σ x , σ y and fracture strength σ f , the crack distribution changes from network to parallel, until to no crack with the increasing line energy and the decreasing powder feed rate. And the angle θ 0 between the direction of resultant stress of σ x and σ y and Y-axis is 52.85°, which fits with the direction of long and short cracks in network crack distribution. In addition, the substrate preheating can effectively reduce cracking rate of Ni60A coating and completely prevent crack when preheated up to 500 °C. Also, the crack-free coating can be obtained by the combination of preheating to 300 °C and placing insulated plank under the substrate, which can reduce thermal damage of the substrate and obtain higher microhardness. [ABSTRACT FROM AUTHOR]

In this work, the proposal and appraisal of a method to describe in a quantitative manner the phenomenon of thermal stresses formation in welding at different heat-affected zone (HAZ) regions and under different cooling rates, by means of physical simulation, are explained. Under the denomination of welding thermal stress diagrams (WTSD), initially the concept and experimental arrangements needed to use the idea, based on a Gleeble simulator, are revealed. An approach to determine more realistic thermal cycles (peak temperature and heating/cooling rates) is introduced and applied. The method assessment was carried out by using specimens of a HSLA quenchable steel subjected to different cooling rates (covering a wide range of typical welding heat inputs) and peak temperatures (representing regions progressively farther away from the fusion line). The different thermal stress (TS) curves proved the concept based on the justification of the results. In addition, it was physically demonstrated that TS curves are governed mainly by two complex concurrent phenomena, namely contraction under restriction of heated areas and the expansibility of phase transformation. It was concluded that due to this balance, the highest residual stress (RS) does not occur either at slowest cooling rate or at fastest cooling rate. Nevertheless, the highest RS may not occur at the coarse grain zone either. TS progressively drops along the HAZ regions away from critical regions, and even at sub-critical regions there is tensile RS. Complementarily, it was also concluded that WTSD by physical simulation allows one to determine the deformation behaviour of a material as a function of temperature. This information can be used as input or calibration in modelling for thermal stress generation in steels. [ABSTRACT FROM AUTHOR]

Fischer–Tropsch reaction is applied to produce ultra-clean fuels based on the synthesis gases. Supported cobalt catalysts are used for Fischer–Tropsch synthesis due to their high stability and good catalytic activity. These catalysts are generally prepared by wet chemical methods which involve impregnation, drying and calcination. A new approach to the analysis of degradation of catalysts under thermal stress during the various steps of catalyst preparation has been applied to the support (γ-Al2O3) and to the catalysts (10 wt% Co/Al2O3). Low particle damages occur when the catalyst is prepared by impregnation. Thus, a rate of about 1 wt% of fine particles with sizes less than 63 µm has been quantified. However, the effect of temperature during drying at 100 °C and calcination at 400 °C becomes significant: a degradation rate of 2% and 5% is noted for temperatures of 100 °C and 400 °C, respectively. These results show particle degradation through cleavage and fragmentation. These mechanisms result in the initial heterogeneous structure (fractures and cracks) of the support which reduces the mechanical resistance of the catalyst and initiates the rupture of the particles under an increase in temperature. To describe the particle breakage, a numerical approach was implemented under thermal stresses on modeled Co/Al2O3 ring particles. Calculations were performed using COMSOL Multiphysics® (Structural Mechanics Module) following a 2D geometry. The effect of temperature, crack height (radial and axial components) and porosity on the particle breakage were studied. The results obtained highlighted the solid breakage at high temperature (calcination phase), high-size cracks and low porosity. [ABSTRACT FROM AUTHOR]

Enhancing the strength and thermal conductivity of A319 aluminium alloy powertrain components can reduce instances of premature failure, by resisting or alleviating thermal stresses that develop during engine operation. These properties can be manipulated theoretically through microstructural control, for example via variation of the alloy solidification rate. Although increasing solidification rate has been observed to achieve improved mechanical properties, its influence on thermal conductivity is yet unclear. In this study, A319 alloy was cast with a succession of solidification rates by using a permanent mould preheated to a range of temperatures. The as-cast samples were comprehensively characterized in terms of their dendritic structures, secondary phase morphologies and area fractions, porosity, ultimate tensile strengths and Rockwell hardness values, and thermal conductivities, the latter of which was measured via the transient plane source method. The results demonstrated that refinement and other changes in microstructure with increasing solidification rate promoted no noticeable variation in thermal conductivity, despite improvements to strength and hardness. Thus, solidification rate can be controlled effectively to design the mechanical properties of A319 components without detriment to its thermal properties. [ABSTRACT FROM AUTHOR]

This study investigated the evolution of solidification microstructure and dynamic recrystallisation (DRX) during the laser solid forming of the Ni-based Inconel 625 superalloy. The as-deposited microstructure mainly showed epitaxially grown columnar grains with fine equiaxed grains between them. These fine equiaxed grains were formed by the discontinuous DRX (DDRX) and continuous DRX (CDRX) processes, which were induced by the cyclic thermal stress resulting from the repeated laser deposition. The bulging of pre-existing grains and sub-grain rotation were the main mechanisms of the DDRX and CDRX phenomena, respectively. Additionally, after the occurrence of DRX, the dislocations were released and there was no distortion in the recrystallised grains. Coarse equiaxed grains were present in the top zone of the deposit; these grains were formed by the columnar-to-equiaxed transition during the solidification of the molten pool after the end of the laser re-melting and deposition process. [ABSTRACT FROM AUTHOR]

In this study, a temperature-dependent longitudinal tensile strength model for short-fiber-reinforced polymer composites (SFRPCs) is established based on the sensitivities of thermal-physical properties of polymer materials to temperature and our previous work. The effects of temperature, fiber orientation distribution, fiber length distribution and residual thermal stress are considered in this model. The theoretical model is verified by comparison with tensile strength of glass SFRPCs at different temperatures. Good agreement between the model predictions and experimental results is obtained, which indicates the reasonability of the proposed models. Furthermore, the comparisons between the present models and the classical models are discussed, and the influencing factors analysis for SFRPCs is also conducted in detail. This study can not only provide a potential convenient means for predicting the temperature-dependent tensile strength of SFRPCs, but also offer useful suggestions for the material evaluation, strengthening and design. [ABSTRACT FROM AUTHOR]

In order to clarify the interaction of electrochemistry, thermal and diffusion-induced stress, in this work, we present a coupled electrochemical-thermal-mechanical model for spiral-wound Li batteries by coupling the mass, charge, energy and mechanics conservations as well as the electrochemical kinetics. A series of temperatures and Li concentration parameters on the reaction rate and Li+ transport are employed in this model. The results show that this model is validated for both the electrochemical performances and thermal behaviors at a constant discharge current by finite element simulation. Furthermore, the heat generation of three thermal sources and stress analysis are also discussed. This work is helpful to the battery structural design and battery thermal management. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Finite element modeling of effective thermomechanical properties of Al-B4C metal matrix composites" published in the Journal of Materials Science. The correction states that Figures 1, 2a (8vol%), 2a (12vol%), 2b, and 2c in the article were re-used from the authors' previous work without appropriate acknowledgement. The article aims to investigate the influences of thermal residual stresses and material properties on the thermomechanical deformation behavior of Al-B4C composites reinforced with aluminum matrix composites. The correction notice also includes a statement from the publisher, Springer Nature, regarding jurisdictional claims and institutional affiliations. [Extracted from the article]

The present work aims to investigate the influences of thermal residual stresses and material properties on the thermomechanical deformation behavior of Al-BC composites. Boron carbide-reinforced aluminum matrix composites having 4, 8, and 12 vol% boron carbide were fabricated using squeeze liquid stir casting method for experimental characterization of their microstructure, effective elastic moduli and effective CTEs at room temperature as well as elevated temperatures. Next, the thermomechanical behavior of fabricated composites was investigated using finite element modeling. The effects of thermal residual stresses on the effective material properties were examined by simulating the cooling process of MMCs from processing temperature to room temperature. The effective elastic moduli and the effective CTEs were predicted considering linear elastic as well as elastoplastic deformation of aluminum matrix, and the results obtained were compared with the experimental values. The effects of voids on effective material behavior are studied by simulating the void growth and nucleation using Gurson-Tvergaard-Needleman model. [ABSTRACT FROM AUTHOR]

As a result of manufacturing processes, thermal residual stresses often occur in fibre-reinforced polymer composites and affect the fibre/matrix interface properties, e.g. interfacial shear strength (IFSS), which is commonly evaluated by the microbond test. In thermoplastic matrices, thermal residual stresses can be relieved by annealing. In this study, to examine the effect of thermal residual stress on IFSS, microbond tests on both air-quenched (control) and annealed polyphenylene sulphide/carbon fibre samples are conducted. Comparing the pull-out results of the control to the annealed samples subjected to six different annealing temperatures between 80 and 230 °C, it is found that the thermal residual stresses in the fibre axial and radial directions are reduced progressively below and can be neglected above 120 °C. Thermal residual stresses in the fibre direction can be calculated to explain the microbond test results and construct a master curve for the IFSS. Post-debond frictional shear stresses can also be analysed in terms of the calculated fibre radial thermal residual stresses and debonded fibre morphologies. [ABSTRACT FROM AUTHOR]

Analysis of the crack growth behavior is critical for fracture and thermal shock assessment. The current work presents a simple methodology to visualize cracks in ceramic materials. The procedure is exemplified for refractory materials on the basis of images obtained during mechanical loading using a wedge splitting test. Complementary in situ crack growth observation verify that for one of the materials growth and opening displacement of the main crack is accompanied by pronounced micro-cracking, branching, and bridging processes. Apparent fracture resistance and thermal shock resistance parameters are discussed. [ABSTRACT FROM AUTHOR]

A magnetoelectric (ME) composite consisting of a single PZT rod embedded in a matrix of continuous Terfenol-D fiber and epoxy medium has been fabricated and characterized. With an optimized aspect ratio of the composite rods, a large ME effect has been observed. The magnetostrictive effect of the continuous Terfenol-D fiber/epoxy medium can be enhanced by imposing an optimal pre-loading stress on the material and this pre-loading stress can be induced by suitable heat treatment. Experimental results show that the ME effect of the single PZT rod/continuous Terfenol-D fiber/epoxy composites can be enhanced significantly by a post-curing process. A thermal stress-mediated continuous fiber composite model has been used to explain the ME enhancement of the post-cured composites. [ABSTRACT FROM AUTHOR]

The negative thermal expansivity of a type of space frame structure is investigated herein. On the basis of space frame structure consisting of tetrahedral representative volume elements, a volumetric thermal strain, and a volumetric coefficient of thermal expansion (CTE) models are developed in this article for a special category of tetrahedron that is made from two types of materials, each for the three apex and the three base rods. Based on these models, the conditions for attaining negative volumetric thermal strain and negative coefficient of volumetric thermal expansion are established. Plotted results reveal a trend in which the extent of negative expansivity is increased for lower apex-to-base rod length and CTE ratios, and higher base rod CTE. [ABSTRACT FROM AUTHOR]

In this article, pristine carbon nanotubes (CNTs) and hydroxylated CNTs (CNT-OH) were employed to enhance the thermal stability and flame retardancy of polypropylene (PP)/wood flour composites (WPC) compatibilzed by maleic anhydride-grafted polypropylene (PP- g-MA). Incorporating 10 wt% PP- g-MA only enhanced the mechanical and thermal properties to some extent, but did not improve the flame retardancy of WPC. Thermogravimetric analysis (TGA) showed that the thermal stability of WPC was further increased with the addition of CNTs or CNT-OH and the increase of their loading level. Cone calorimeter measurements suggested that CNTs and CNT-OH could effectively reduce the peak heat release rate (PHRR) of WPC, and the flame retardancy properties reached the optimum value when both of their loading was 1.0 wt%, for instance, a reduction in PHRR by 16.7% and 25% for CNTs and CNT-OH, respectively. In addition, CNT-OH conferred better flame retardancy on WPC relative to pristine CNTs due to the better interfacial adhesion with wood flour and PP matrix, which was evidenced by scanning electron microscopy (SEM) observations. [ABSTRACT FROM AUTHOR]

Residual stresses-induced damages in multilayered films grown on technical substrates present a reliability issue for the fabrication and applications of multilayered superconductor systems. Using closed-form solutions for residual stresses in multilayered systems, specific results were calculated for residual stresses induced by the lattice and the thermal mismatches in the system of YBCO/CeO2/YSZ/Y2O3 films on a Ni-5 W substrate. It was concluded that lattice mismatch-induced residual stresses must be relaxed by forming interfacial defects. Studies of residual thermal stresses showed the following. When the thickness of a film is negligible compared to the substrate, the changes of its properties modify the residual stresses in this film layer but have negligible effects on the residual stresses in other layers in the system. On the other hand, when the thickness of certain film layer is not negligible compared to the substrate, residual stresses in each layer can be controlled by adjusting the properties and thickness of this film layer. Finally, the effects of buffer layers on thermal stresses in YBa2Cu3O7–x (YBCO) were addressed by using YBCO/LaMnO3/homo-epi MgO/IBAD MgO/Y2O3/Al2O3 films on Hastelloy substrate as an example. [ABSTRACT FROM AUTHOR]

Cordierite disks were obtained by slip casting and sintering at 1,450 °C for 2 h. Sintered disks were indented at the center of one flat surface. The fracture strength of indented disks was measured in biaxial flexure. The critical temperature differential was determined by sudden cooling of the center of the indented surface at high temperature, using a high-velocity air jet at room temperature. The initial temperature was successively increased by 10 °C until crack propagation was detected with the naked eye. Temperature and stress distributions during air impinging were calculated by a finite element analysis. The heat transfer coefficient was estimated by fitting experimental temperature profiles. A radial variation of the coefficient that considers its increment beyond the stagnation region and a diminution toward the disk periphery was assumed. The calculated cordierite thermal stresses were analysed in relation to experimental data. Also, the comparison with alumina tested in similar conditions was included. [ABSTRACT FROM AUTHOR]

Carbon/carbon composites are well suited to high-friction applications due to their excellent mechanical and thermal properties. Since interfacial shear strength is critical to composite performance, characterization of fiber/matrix interface is a crucial step in tailored design of composites. This article presents a hybrid experimental/analytical study to evaluate the interfacial shear strength (IFSS) of PAN-fiber-reinforced carbon matrix composites. Microstructure was studied by light and high-resolution transmission electron microscopy (HRTEM). A series of push-out tests were conducted to examine the fiber/matrix debonding process. The residual fiber displacement was confirmed by scanning electron microcopy (SEM). The validity of the calculated IFSS value was demonstrated by a simplified analytical approach, where the components contributing to the measured displacement were analyzed considering the mechanics of the indentation. The method described in this article has been successfully used for determining the IFSS of PAN-fiber-reinforced carbon matrix composites. [ABSTRACT FROM AUTHOR]

AISI 1045 steel surface was alloyed with pre-placed ferrotitanium and graphite powders by using a 5-kW CO2 laser. In situ TiC particles reinforced Fe-based surface composite coating was fabricated. The microstructure and wear properties were investigated by means of scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, as well as dry sliding wear test. The results showed that TiC carbides with cubic or flower-like dendritic form were synthesized via in situ reaction between ferrotitanium and graphite in the molten pool during laser cladding process. The TiC carbides were distributed uniformly in the composite coating. The TiC/matrix interface was found to be free from cracks and deleterious phase. The coatings reinforced by TiC particles revealed higher wear resistance than that of the substrate. [ABSTRACT FROM AUTHOR]

The breaking force during transversal loading of fibre-cement corrugated roofing sheets was measured on several test samples from a serial production. The results were statistically analyzed assuming the 2-parameter Weibull statistics. In addition, Monte Carlo statistical simulations were made by using a computerised built-in random-number generator. While smaller sample data groups, mostly containing up to 50 samples, were studied in the literature, we extended their size up to 400 samples. We showed that some trends in the evaluation of statistical parameters which hold for smaller data groups, apply well to larger data groups. In particular, we confirmed that the statistical distribution of the Weibull parameters obtained from repeated Monte Carlo simulations is log-normal. Furthermore, we considered the influence of the measurement uncertainty on the statistical parameters. [ABSTRACT FROM AUTHOR]

An induced optical anisotropy is observed as a result of interaction of a high-power CW Ar+ laser beam, with silver-ion-exchanged glasses. We have shown that the absorption of the beam by the thin layer of Ag+ produces a temperature gradient resulting in a radial stress on the surface of the sample. The induced anisotropy makes the sample behave as a thin uniaxial optical medium with axis along the direction of the beam propagation. For the polarized light, the induced anisotropy restricts the application of micro-lenses, which are made by this method. The average refraction index of the interaction area is measured. [ABSTRACT FROM AUTHOR]

The present paper involves a metal/polymer joint in a tailcone in a kinetic energy penetrator (KEP), one of the ammunition types used by the military. It is currently made of aluminum 7075 alloy, which could be partly replaced by long fiber thermoplastic (LFT) composite. Two different types of aluminum insert geometries were considered, viz., beaded and threaded. Thermal stresses set in during cooling of the tailcone from the processing temperature mainly because of the difference in the values of coefficients of thermal expansion and differential cooling between the aluminum and the LFT composite. Finite element (FE) modeling was done to predict the temperature profile during the cooling of the tailcone from the processing temperature. FE results showed that the LFT composite part of the tailcone cooled faster than the aluminum insert. Experimental verification of this temperature profile was obtained by infrared (IR) thermography. Based on the temperature profile, thermal stresses at the metal/LFT composite interface were estimated using an FE model. Different magnitudes of thermal stresses were present at the aluminum/LFT composite interface owing to the nature of distribution of fibers around the insert. Magnitude of thermal stresses in the case of a beaded insert was approximately 2.5 MPa whereas in the case of a threaded insert, it was approximately 12 MPa. [ABSTRACT FROM AUTHOR]

Thermal cycling of an epoxy coating on silicon through the glass transition temperature ( T g) revealed a large stress hysteresis on the first thermal cycle through T g and a change in the stress–temperature slope at T g resulting from the change in the epoxy elastic properties due to the glass transition. This stress hysteresis was not observed on subsequent thermal cycles through T g. However, after the coating was annealed (aged) below T g (for hours or longer)—during which the stress relaxed exponentially with time—the stress hysteresis returned. The magnitude of stress hysteresis, on cycling through T g, was found to correlate to the magnitude of long-time relaxation that occurred during annealing at temperatures below T g. [ABSTRACT FROM AUTHOR]

The paper deals with elastic thermal stresses in an isotropic multi-particle-matrix system consisted of periodically distributed spherical particles in an infinite matrix, imaginarily divided into cubic cells containing a central spherical particle. Originating during a cooling process as a consequence of the difference in thermal expansion coefficients between the matrix and the particle, and investigated within the cubic cell, the thermal stresses, as functions of the particle volume fraction v, being transformed for v = 0 to those of an isotropic one-particle-matrix system, are maximal at the critical particle volume fraction, representing a considerable value related to maximal resistance of the thermal-stress strengthened multi-particle-matrix system against mechanical loading. The thermal stresses are derived for such temperature range within which the multi-particle-matrix system exhibits elastic deformations, considering the yield stress and the particle-matrix boundary adhesion strength. With regard to a curve integral of the thermal-stress induced elastic energy density, critical particle radii related to crack initiation in ideal-brittle particle and matrix, functions describing crack shapes in a plane perpendicular to the direction of crack formation in the particle and in the matrix, and consequently dimensions of a crack in the particle and in the matrix are derived along with the condition concerning the direction of the crack formation. Additionally, derived by two equivalent mathematical techniques, the elastic energy gradient within the cubic cell, representing a surface integral of the thermal-stress induced elastic energy density, is presented to derive the thermal-stress induced strengthening in the spherical particle and in the cubic cell matrix. The former parameters for v = 0 are derived using the model of a spherical cell with the radius $${R_c\rightarrow\infty}$$ . Derived formulae are applied to the SiC–Si3N4 multi-particle-matrix system, and calculated values of investigated parameters are in a good agreement with those from published experimental results. [ABSTRACT FROM AUTHOR]

In this paper, an accurate formula for calculating the thermal residual stress field in a particle-reinforced composite are presented. Numerical examples are given to show r-variations of the thermal residual stresses. The increase in fracture toughness of matrix predicted by the thermal residual stress field is compared well with the experimentally measured increase. [ABSTRACT FROM AUTHOR]

An investigation was conducted to determine the cause of weld cracking in laser Be/Al weldments. In agreement with earlier studies, features consistent with hot shortness cracking on the fracture surfaces were observed. Closer examinations of the fusion zone crack regions reveal that the cracking was a result of thermal stress, shape of weld roots and impurities segregation. The defects are related to the weld parameters. The cracks easily nucleate at conduction mode weld and blowholes easily appear at keyhole mode weld. [ABSTRACT FROM AUTHOR]

Fluorescence microprobe spectroscopy was used to characterize the stress fields that develop within an interpenetrating Al–Al2O3 composite resulting from both the thermal expansion mismatch during sample processing, and from an external applied load. The 30 vol% Al–70 vol% Al2O3 composite that was investigated had an aluminum and alumina phase feature size of 50–100 μm. The residual thermal compressive stress measured in the alumina was ∼40–340 MPa. The effect of varying the metal ligament size on the residual stress distribution is discussed. Additionally, the application of an external load caused a non-uniform stress distribution to develop within the alumina regions around the crack-tip, which was attributed to microstructure inhomogeneities. The crack was further extended and the influence of the stress distribution within the alumina regions on the crack extension direction is briefly discussed. [ABSTRACT FROM AUTHOR]

Thermomechanical analysis of a refractory, woven fabric composite was conducted using a multi-scale analysis technique. The composite was made of carbons and ceramic materials. The fibers were made of carbons and the outer coating was made of a ceramic material. In order to reduce the thermal stress in the carbon fibers and the ceramic material caused by mismatch of coefficients of thermal expansion between the two materials, a graphitized carbon layer was introduced between the fiber and the ceramic coating. For the multi-scale analysis, a new analysis model was developed and used to bridge the micro-scale characteristics, i.e. the constituent material level such as carbon and ceramic materials, to the macro-scale behavior, i.e. the woven fabric composite level. Furthermore, finite element analyses were undertaken with discrete modeling of the representative fibers, coating, and the graphitized middle layers. Then, both multi-scale analytical and numerical results were compared. In this study, thermal stresses at the micro-level, i.e. in the fibers and coating materials, as well as effective thermomechanical properties of the refractory composites were computed using the multi-scale technique. [ABSTRACT FROM AUTHOR]

Quantitative estimation of failure of a LiTaO3 single crystal due to thermal stress was investigated. Cylindrical test slabs were heated in a silicone oil bath, then subjected to large thermal stress by pouring silicone oil with room temperature. Cracking occurred during cooling. A transient heat conduction analysis was performed to obtain a temperature distribution in a test slab at the time of cracking, using the surface temperatures measured in the test. Then thermal stress was calculated using a temperature profile of the test slab obtained from the heat conduction analysis. It is found from the results of thermal stress analyses and the observation of the cracking in the test slabs that the cracking induced by thermal stress occurs mainly in the cleavage planes due to the stress component normal to the plane. As for a size effect of failure stress, large-sized cylindrical test slabs show lower failure stress than small-sized ones. Four-point bending tests were also performed to examine the relationship between the critical stress for cracking induced by thermal stress and the four-point bending strength. A useful relation was derived for predicting the critical stress for cracking induced by thermal stress from the four-point bending strength. [ABSTRACT FROM AUTHOR]

The article cites a study on self-propagating high-temperature synthesis (SHS) of rotator mixed and mechanically alloyed nickel aluminides. The concepts of the theory of plasticity of porous bodies are used to evaluate the influence of mechanical alloying (MA). A table is presented depicting the summary of compact theoretical yield stress and combustion temperature. The reduced porosity findings may have important implications for processes including the mechanically activated SHS (MASHS).

Ceramic monolithic and multilayered composites were produced by stacking water based green ceramic cast tapes. Two different mixtures of composites within the Al2O3/YTZP, system were investigated. The difference in the coefficient of thermal expansion (CTE) between the composites fabricated, resulted in the development of residual stresses when the same compositions were combined in a multilayered structure. The magnitude and the distribution of these residual stresses were assessed by the piezo-spectroscopic technique. The stress within the layers varied with a parabolic trend, with the highest values at the interfaces and a reduction toward the centre of the layers. The influence of symmetry of the multilayered laminate on the magnitude and distribution of the residual stresses within the structure are discussed. [ABSTRACT FROM AUTHOR]

The modulus and fracture toughness of an ATH-filled PMMA composite are determined as a function of temperature. The modulus can be modelled as a series addition of the two phases, giving a decreasing modulus with temperature tending to zero at 110°C. The K 1C value remains constant. Fatigue crack growth data in the form of da/dN versus K were obtained as a function of temperature and modelled using the Paris Law. The power index remained constant at 7.5, but the coefficient had a maximum at 50°C. It is suggested that this arises from microcracks generated by interparticle thermal stresses which are shown to have a maximum at the same temperature (50°C). A two-stage zone fatigue crack growth model was also applied to the data and gave a damage stress which correlated with the thermal stress and suggested a criterion based on achieving a constant energy per unit area. [ABSTRACT FROM AUTHOR]

A detailed investigation of residual thermal stress and misfit strain in GaN epitaxial layers grown on technologically important substrates is performed. The thermal stress is low when GaN is grown on AlN, SiC and Si, and relatively higher when Al2O3 substrate is used. The stress is compressive for AlN and Al2O3 and tensile for Si and SiC substrates. Residual thermal stress analysis was also performed for three layer heterostructures of GaN/AlN/6H-SiC and GaN/AlN/Al2O3. The stress remains the same when a sapphire substrate is used with or without an AlN buffer layer but reduces by an order of magnitude when a 6H-SiC substrate is used with an AlN buffer layer. [ABSTRACT FROM AUTHOR]

Ti-35V-15Cr, Ti-25V-15Cr and Ti-25V-15Cr-0.4Si alloys were exposed to different temperatures in air (450-600°C) for aging times between 0 and 200 h and subsequently tensile tested at room temperature with the surface oxide retained or removed. The influence of an applied tensile stress (50-200 MPa) during thermal exposure was also investigated. The results showed that post-exposure tensile properties deteriorated with the increase in exposure temperature and time. The decrease in tensile properties resulted from the combination of surface oxidation and microstructural changes. The main change of the microstructure during thermal exposure is the heterogeneous precipitation of α phase on beta grain boundaries. Both increased vanadium content in the alloy and the addition of silicon have shown an adverse effect on alloys' thermal stability. [ABSTRACT FROM AUTHOR]

The aim of the paper is to present a model of thermal stresses in a layered plane system, and consequently to verify the model validity by comparing calculated thermal stresses with measured thermal stresses. The paper deals thus with thermal stresses in the Fe-3%Si sheet for magnetic applications, having a surface coating of the 2MgO·TiO2, ZrO2, TiO2, Al2O3, 2MgO·SiO2, MgO·Al2O3 oxides. The thermal stresses, originating during a cooling process as a consequence of the difference in thermal expansion coefficients between the Fe-3%Si sheet and the surface coating, degrade hysteresis losses of the Fe-3%Si sheet. Magnetic properties of the presented coating–Fe-3%Si systems, as the magnetic induction and the hysteresis losses before and after coating formation, are presented. The theoretical background, including the model of the thermal stresses in anisotropic and isotropic two-layered plane systems, consequently transformated to the three-layered plane system, is presented. Calculated thermal stresses are compared with those of a tension measurement of the presented coating—Fe-3%Si systems, numerical equality of the calculated and measured thermal stresses is observed. [ABSTRACT FROM AUTHOR]

Treating fibrous composites with multilayered interfaces as a cylindrical assemblage consisting of multiple coaxial circular cylinders, a model has been developed with which the thermal stresses in such composites reinforced with axisymmetrically orthotropic fibers, can be analytically calculated. The developed model is employed to examine the influences of the volume fractions of the constituents as well as mechanical and physical properties of the interfacial layers on the thermal stresses in the composites. For the composites reinforced with different types of axisymmetrically orthotropic fibers, the effects of the volume fractions of the constituents on the stresses in the composites are different. The variety of mechanical and physical properties of the interfacial layers can greatly change the stress distributions in the composites. Therefore, reasonable design of the volume fractions of the constituents as well as mechanical and physical properties of the interfacial layers can help reduce the thermal stresses in the composites and improve the thermal mismatch of the composites under the thermal loading. [ABSTRACT FROM AUTHOR]

Thermal stresses have been measured in single carbon fibre polypropylene matrix composites using micro Raman spectroscopy. The study focuses on the influence of a transcrystalline interlayer on the thermal residual stress distribution in composites. A series of three experiments were made in order to systematically study the influence of thermal history, transcrystalline interlayer thickness and matrix supermolecular structure. From the experiments it was shown that the transcrystalline interlayer results in higher thermal residual shear stress. This was explained by anisotropy in the transcrystalline interlayer resulting in higher radial thermal expansion and thus higher radial stress. [ABSTRACT FROM AUTHOR]

Specimens of high purity α-Fe were deformed in the GLEEBLE-1500 at temperatures of 550°C, 700°C, 800°C and 900°C at strain rates ranging from 0.001 to 10 s−1. The microstructural changes, which occur during the hot compression, have been investigated by optical microscopy and related to the true stress-true strain curves. The experimental results show that the dynamic recrystallization is accelerated with increase of deformation temperature and decrease of strain rate. The relation between the dynamic recrystallization and Z-parameter has been investigated. Dynamic recrystallization takes place approximately in a certain range of Z parameter, i.e., 25 < ln Z < 37. [ABSTRACT FROM AUTHOR]