Internal Thermal Stresses Research Articles

A Deeper Learning approach in exploring the eventualities of solvent-free microwave-based extraction of lemongrass essential oil: Understanding milky emulsion, biomass temperature, first drop appearance, oil quality and biorefinery

The current research work is a deep learning initiative to explore the various eventualities of solvent-free microwave-based extraction (SFME) of lemongrass essential oil and strategize recovery of more than two distinct classes of fractions (volatile and non-volatile) in a single-step extraction. The model does not make use of any solvent and extraction is based on rupturing of oil glands due to internal thermal stress followed by draining of the oil under gravity. From the various microwave power level attempted (170 W–510 W), 255 W was found to be optimal, producing the highest Citral content of 68.32% in 56 min with a total yield of EO of 1.6%. Results were comparable to the Citral content of EO obtained from 4 h of SD (67.81%) with a total yield of 1.56%. Comparable antioxidant activity zones (SFME-22323 & SD-21782) were obtained as well. A zone of milky emulsion was reported when the temperature of biomass exceeded 90 °C during SFME which can adversely affect the oil quality. The advantage of steam distillation was in terms of saving time and making the biomass available for re-extraction of phenolic principles thus making the biomass available for the simultaneous extraction of volatile oil and non-volatile principles.

Simulation and analysis of sintering warping and thermal stress for a cermet half-cell of solid oxide fuel cells

Warping deformation often appears due to internal thermal stress generated during sintering process of solid oxide fuel cell (SOFC) functional layers composed of metal and ceramic composite materials. In this study, a model is developed for a half-cell of an anode-supported design SOFC to simulate warping displacement and thermal stress generated at the highest sintering temperature of 1673 K. A sensitivity analysis is further conducted, and the orthogonal experimental method is applied for parameter optimization. The predicted results reveal that the warping displacement is reduced by 64.3%, while the maximum thermal stress decreases by 55.8% as combined parameters are optimized. In addition, the effects of thickness and fillet treatment on the thermal stress and deformation are also investigated. It is found that the anode support layer is a dominant factor, and its thickness should not be less than 550 μm; the thickness of the electrolyte layer should be maintained at 20 μm; while the treatment of 10 mm fillets on the 10 × 10 cm2 scaled half-cells is favorite.

Thermomechanical performance of continuous carbon fibre composite materials produced by a modified 3D printer

First of all, this article aimed to evidence the role of a modified printer developed for continuous carbon fibre reinforced PolyAmide (cCF/PA6-I) together with the use of a fully open slicing step on the printing quality and the longitudinal/transverse tensile and in-plane shear properties. A comprehensive assessment of the microstructure and properties with a similar material (cCF/PA6-I), but produced with a commercial printer (i.e., Markforged® MarkTwo) has been achieved. Our customised printer and the open slicer used have made possible to better control the print conditions (i.e., layer height and distance between filaments), to reduce the porosity from more than 10% to about 2% and improve the mechanical properties.Moreover, the understanding of the behaviour of these 3D printed composites with wide-ranging external temperatures is mandatory for future use in a severe environment and/or development of new thermally active 4D printed composites.The 3D printed cCF/PA6-I composites have been then thermomechanically characterised along different printing directions (0, 90 and ± 45°) from −55 to +100 °C. Unlike the longitudinal properties that hardly change with temperature, the transverse and in-plane shear stiffness and strength of these 3D printed composites were particularly sensitive to temperature variations, with decreases of 25–30% and 30–55%, respectively. This was due to the high sensitivity of the polymer matrix, the fibre/matrix and interfilament interfaces when the composites were loaded along those directions, because damages induced by internal thermal stresses. Fractography has also been carried out to reveal damage mechanisms.

Effect of Chlorine Salts on TiC Coating Morphology and Bonding Strength of Diamond Surface in Molten Salt Reaction

To obtain a high-quality TiC coating on the diamond (D) surface and improve the interfacial properties of metal matrix composites, the optimized molten salt method is used to prepare TiC coatings on the D surface. The effects of NaCl, KCl, and NaCl–KCl molten salts on the uniformity, surface morphology, composition, and bonding ability of TiC coatings are investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction, and cold–hot cycling experiments. The results show that the boiling and pickling processes after the molten salt reaction can effectively remove the residual chloride salts and Ti powders to obtain clean TiC-coated D. The TiC particles of the coating surfaces prepared by NaCl and KCl molten salts are finer and more uniform, which is due to their higher melting points and shorter real reaction time compared with NaCl–KCl mixed salts. The TiC coating prepared by KCl has the best bonding ability and can withstand 50 times as many cold–hot cycles due to its uniform fine deposition particles and appropriate thickness. And, during cold–hot cycles, it can be found that the TiC coating cracking and shedding occur primarily at the edges and corners of the D with internal thermal stress concentration.

Numerical Simulation and Experimental Study of the Stress Formation Mechanism of FDM with Different Printing Paths

Environmental contamination has been caused by petroleum-based polymeric materials in the melt deposition process. Nowadays biodegradable materials have been widely used in the fused deposition modeling (FDM) industry, such as polylactic acid (PLA). However, internal complex thermal stress and deformations in part caused by an uneven distribution of PLA filament deposition temperatures during FDM, which will seriously affect the geometric accuracy of the printed part. In order to reduce material waste and environmental pollution during the printing process, the accuracy of PLA part can be improved. Herein, numerical simulation was carried out to investigate the temperature field and stress field during the building and cooling process of cuboid specimens. The effects of printing path on the thermal stress and temperature field during the building process were mainly studied. The results show that the printing path has a significant effect on the stress distribution. The most uniform stress distribution and the smallest deformation were obtained using the Zig Zag printing path. Finally, the residual stress during the cooling process was collected using strain gauges embedded at the mid-plane of the FDM built cuboid specimens. The simulation results are consistent with the experimental results.

THEORETICAL MODELING OF THE NUCLEATION OF INTERNAL LATENT THERMAL DEFECTS IN A BITUMINOUS MEDIUM WITH RUBBER INCLUSIONS

The current state and progress of the technology and science associated with the reuse and recycling of the tyre rubber worldwide in the road industry compels to study more thoroughly high and low temperature performance of the road bitumen modified with rubber crumbs, permitting to understand influence of the temperature, rubber grain size and mixture bitumen-rubber modification on the composite strength and sustainability. Below, these issues are studied taking into account the peculiarities of the thermomechanical properties of rubber associated with its low rigidity when changing shape, practical incompressibility when changing volume, and low (zero or even negative) coefficient of linear thermal expansion. The purpose of the study is to determine the reasons leading to a violation of the strength of asphalt concrete materials with admixtures of rubber crumb. For this purpose, the influence of the incompatibility of thermomechanical characteristics (moduli of elasticity, Poisson's ratios and coefficients of thermal expansion) of bitumen and rubber on the concentration of additional internal thermal stresses in the system caused by seasonal and daily temperature changes is analyzed. Using the relations of the theory of thermoelasticity, a mathematical model of thermal deformation of crumb rubber in a bitumen medium has been constructed. With the possibility of complete and surface modification of rubber with bitumen, solutions for three-phase media are constructed, which make it possible to trace the influence of the parameters of each phase on the thermal stress fields in the system. It has been established that additional thermal stresses in bitumen, due to the thermomechanical incompatibility of the physical parameters of the phases, are concentrated in the zone of its contact with the surface of the rubber crumb and can cause defects and chippings in it. The influence of the effect of modifying rubber crumb with bitumen and of the depth of its penetration into crumb of different sizes on reducing thermal stresses in the system and increasing its sustainability is considered.

Thermo-mechanical analysis of fire effects on the structural performance of shield tunnels

Investigating fire effects is a continuing endeavour in the research and practice communities concerned with the design and safety of shield tunnels. This paper aims to provide a comprehensive model for the assessment of structural safety of a shield tunnel segmental ring exposed to fire. A thermo-mechanical model for assembled shield tunnel structure in fire is developed to provide a basis for a holistic analysis by incorporating tunnel lining segments and longitudinal joints, as well as improved predictions for the temperature, stress and deformation distributions in the tunnel structure. Validation of the numerical results against experimental data shows satisfactory agreement. Parametric studies are subsequently conducted to investigate the effects of spalling, buried depth and cooling-off phases on the fire behaviour of the shield tunnel. The results show that the damage and failure of a tunnel lining structure under high temperature are mainly due to the combined action of internal thermal expansion force and thermal stress. Spalling leads to the loss of a key “insulation” layer of a tunnel lining structure. On the other hand, the constraint of strata on the tunnel structure under high temperature not only restrains the deformation of key parts of the structure, but also helps offset the adverse effect of load on the structure through elastic resistance.

Experimental and theoretical study on residual ultimate strength after impact of CF/PEEK-titanium hybrid laminates with nano-interfacial enhancement

Fiber metal laminates (FMLs) provide a reliable approach for achieving lightweight in high-speed aerospace vehicles. However, the weak interfacial properties between metals and composites could significantly affect the deformation and failure modes of FMLs. In this paper, the low-velocity impact responses and damage mechanisms of CF/PEEK-Ti hybrid laminates with nano-interfacial enhancement by multi-walled carbon nanotubes (CNTs) were characterized and analyzed. The post-impact residual tensile strengths (RTS) were investigated experimentally using quasi-static uniaxial tests combined with digital image correlation, and were evaluated theoretically by developing an analytical prediction model that considers the internal thermal stress and dent geometry. Results show that the initial delamination thresholds of force and displacement during impact can be effectively increased via interfacial enhancement of CNT network. By using a 5% decrease in RTS retention rate as a criterion for damage tolerance, a significant strength decrease starts to appear at 3 J for the sandblasted-only laminates, which is improved to 10 J for the laminates with nano-interfacial enhancement. The proposed unified constitutive model can yield an acceptable prediction for RTS and failure strain of the hybrid laminate after impact, providing a guidance for the structural design and engineering applications of FMLs.

An elliptical inhomogeneity under nonuniform heat flux

We use complex variable techniques to study the decoupled two-dimensional steady-state heat conduction and thermoelastic problems associated with an elliptical elastic inhomogeneity perfectly bonded to an infinite matrix subjected to a nonuniform heat flux at infinity. Specifically, the nonuniform remote heat flux takes the form of a linear distribution. It is found that the internal temperature and thermal stresses inside the elliptical inhomogeneity are quadratic functions of the two in-plane coordinates. Explicit closed-form expressions of the analytic functions characterizing the temperature and thermoelastic field in the matrix are derived.

Stability and Failure Analysis of a W-Based Microhotplate

In this paper, we present the stability and failure of a tungsten-based microhotplate (W-MHP) fabricated with 0.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> standard CMOS technology. Resistance measurements and three-dimensional optical profilometer results combined with scanning electron microscopy observations were used to analyze the failure mechanisms of the W-MHP at operation temperatures up to 1000 °C. The electro-stress migration of the W film, recrystallization of the polycrystal W thin film, and breakage of the dielectric membrane were the dominant stability-failure mechanisms observed. The W-MHP had recoverable deformation and no evident resistance drift when the working temperature was below 450 °C. Correspondingly, at the operating temperature range of 500 °C– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$850~^{\circ }\text{C}$ </tex-math></inline-formula> , the W-MHP showed unrecoverable deformation and regular resistance drift caused by the electro-stress migration of the W heater and the interdiffusion of atoms between the W, Ti/TiN and SiO2. At temperatures higher than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1000~^{\circ }\text{C}$ </tex-math></inline-formula> , the recrystallization of the polycrystalline W film caused a sharp drop in resistance. In addition, sudden and large heat pulses were more likely to cause the suspended membrane to rupture, which resulted from the rapid accumulation of internal thermal stress and lack of time to release, indicating that the operating temperature of the MHP should slowly increase or decrease. One million cycles of thermal pulse between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~^{\circ }\text{C}$ </tex-math></inline-formula> and 300 °C did not cause performance degradation of the device. Self-heating high-temperature rapid thermal annealing significantly improved the high-temperature stability of the MHP. [2022-0135]

Temperature effect on elastic and fracture behaviour of lead-free piezoceramic BaTiO3

Ferroelectric ceramics, especially piezoceramics, are widely used in the field of sensors, micromanipulators, and capacitors. Barium titanate and its derivates are the first choices between lead-free materials. The main aim of the paper is to clarify fundamental processes taking place in the vicinity of Curie temperature with a focus on the fracture behaviour of pure polycrystalline barium titanate. The explanation of observed changes in the mechanical behaviour of this material is based on the experimental approach supported by numerical simulations utilising features of the real microstructure on the grain level. Several model materials with various grain microstructures were manufactured from the submicron barium titanate powder sintered at various temperatures. Two resulting materials with a suitable distribution of grains were selected for further investigation. The grain size influenced not only the exact position of the temperature of the Curie point but also the kinetics of the lattice transformation, elastic, and fracture properties. The significant drop observed in the fracture resistance was attributed to the development of localised internal thermal stresses, which was supported by the results of the performed numerical simulations. The coincidence of the volume change of neighbouring grains due to lattice transformation together with a significant variation in elastic properties can lead up to a 20% decrease in the measured fracture toughness. Understanding this behaviour is essential for the processing and correct application of lead-free barium titanate materials.

A Digital Control Structure for Lissajous Frequency-Modulated Mode MEMS Gyroscope

This article proposes a digital control structure for a doubly decoupled gyroscope working in the Lissajous frequency-modulated (LFM) mode based on digital phase-locked loops (PLLs), which demodulates the angular rate signal directly from the readable digital gyroscope resonance frequency, eliminating the need for specific frequency readout circuits. The resonance frequencies of the LFM gyroscope working modes contain a mode mismatch frequency modulated by input angular rate, respectively, which are tracked by two digital PLLs followed by subsequent digital demodulation and filtering. A linearized model of the digital PLL is built to analyze noise and control characteristics for different PI parameters. The impact of different amplitude–phase extraction architectures on the extracted phase signal is also addressed in this article. Contrast experiments are carried out using the same gyroscope with large internal thermal stress due to the silicon-glass bonding process and no stress relief structure around the sensing element, working in the traditional amplitude-modulated (AM) mode and the LFM mode. Overall, the LFM working mode maintains its low-temperature sensitivity and high stability in spite of the large internal thermal stress in the gyroscope compared to AM working modes. The maximum scale factor variation over the temperature range from 10 °C to 50 °C is 1000 ppm for the LFM mode compared to 51 900 ppm for the AM closed mode. The maximum zero rate output drift over the same temperature range is 0.1248 °/s for the LFM mode and 10.7139 °/s for the AM closed mode. The scale factor nonlinearity is 329 ppm with an angular rate input range of ±50 °/s for the LFM mode compared to 1902 ppm for the AM closed mode. The LFM mode zero-bias fluctuation for ten days is less than 0.12 °/s. The angle random walk (ARW) and the bias instability (BI) of the LFM gyroscope are 0.316 °/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd \text{h}$ </tex-math></inline-formula> and 2 °/h, respectively.

ОСОБЛИВОСТІ ТЕРМОНАПРУЖЕНОГО СТАНУ АСФАЛЬТОБЕТОННОГО ДОРОЖНЬОГО ПОКРИТТЯ З ГУМОВИМИ ВКЛЮЧЕННЯМИ

Introduction. According to international estimates [18], 1.5 billion worn tires go to waste every year in the world. A significant part of them is stored in landfills, buried in the ground or burned, thus polluting the air, wastewater and soil with harmful and poisonous gases, as well as liquid and solid fractions. At the same time, rubber has a number of useful and valuable substances for the industry, the recycling of which will allow to significantly reduce environmental pollution and obtain material benefits. In addition, worn tire material has a number of unique thermomechanical properties attractive for industrial applications, including low density, good thermal and electrical insulating properties, mechanical elasticity and strength, etc. One of the promising directions of recycling worn tires is their use as admixtures in asphalt concrete materials for road surfaces. However, as field tests have shown, the mechanical properties of such materials largely depend on impurities in the material and modification of their properties by the bitumen fraction. Since these issues have not been sufficiently analyzed in the scientific environment, the problem of their study is urgent. Problems. The problem of recycling the material of worn car tires in road construction is largely limited by the instability of the thermomechanical properties of asphalt concrete mixtures with rubber crumb admixtures depending on its grain size, the percentage of its volume inclusions and the level of bitumen modification. Establishing rational parameters that characterize these factors can be implemented by mathematically solving the problem of the thermally deformed state of the road surface using methods of the theory of thermoelasticity. Purpose. The purpose of the article is to determine the reasons leading to a violation of the strength of asphalt concrete materials with admixtures of rubber crumb. For this purpose, the influence of the incompatibility of thermomechanical characteristics (moduli of elasticity, Poisson’s ratios and coefficients of thermal expansion) of bitumen and rubber on the concentration of additional internal thermal stresses in the system caused by seasonal and daily temperature changes is analyzed. Materials and methods. Mathematical modeling methods are used to conduct research using the main provisions of the theory of thermoelasticity. It is believed that bitumen is an elastic medium, which includes a rubber crumb modeled by an elastic ball. Equations of thermoelastic equilibrium of the system when its temperature changes are formulated, boundary equations and conditions of elastic interaction of the bituminous medium and rubber inclusion on their contact surface are formulated. Using the methods of analytical transformations, the solutions of these equations were built in a closed form, which allow determining the thermal stress in both fractions of the system and their dependence on the values ​​of the parameters of thermoelasticity. The principle of correspondence of the solutions of problems of the theory of elasticity and viscoelasticity is formulated, which allows to use the obtained solutions for the analysis of the thermal strength of real asphalt concrete road surfaces. The results. In the work, the reasons for the low thermal strength of bituminous materials with inclusions in the form of rubber crumbs were revealed using mathematical modeling methods. It is shown that it is related to the thermoelastic incompatibility of bitumen and rubber, which is due to the practical volumetric incompressibility of rubber and the difference in the values ​​of the thermal linear expansion coefficients of these materials. The positive role of modifying rubber with bitumen is noted, which allows to reduce the thermoelastic incompressibility of these materials and the resulting concentration of thermal stresses on the contact surface of bitumen and rubber grain. Conclusions. With the help of a theoretical analysis of the thermoelastic state of bituminous material with rubber inclusions, the reason for the concentration of thermal stresses on the contact surface of these fractions, which is caused by the incompatibility of their thermoelasticity parameters, has been established. The obtained results allow establishing ways of rational modification of rubber with bitumen, which make it possible to increase the thermal strength of road surfaces in conditions of seasonal and daily temperature changes and thereby increase their durability.

Internal Thermal Stress-Driven Phase Transformation in Van der Waals Layered Materials.

High pressure or strain is an effective strategy for generating phase transformations in van der Waals (vdW) layered materials without introducing defects, but this approach remains difficult to perform consistently. We present a scalable and facile method for achieving phase transformation in vdW materials, wherein solid vdW materials are subject to internal thermal stress within a molten metal mantle as it undergoes cooling. This internal thermal stress is principally the product of differential thermal expansion between mantle and core and can be tuned by the mantle material and temperature conditions. We validated this approach by achieving phase transformation of red phosphorus to black phosphorus, and metallic 1T'- to semiconducting 2H-MoTe2 crystals. We further demonstrate quantum electronic phase transformation of suppressed charge density wave in TiSe2 by means of electron-phonon coupling using the same system.

Numerical analysis of deformation and failure mechanism of metal truss structure of spacecraft under re-entry aerothermodynamic environment

A coupled aerodynamic-thermoelastic analysis framework is presented to simulate the deformation and failure mechanism of metal truss structure for spacecraft under re-entry aerothermodynamic environment. The three-dimensional dynamic thermo-mechanical coupling finite element algorithm is developed by computable modeling of thermoelasticity and heat conduction equations to solve the thermo-mechanical coupling response of spacecraft structure. The aerodynamic boundary conditions such as temperature, heat flux and pressure distribution are computed and provided by the gas-kinetic unified algorithm (GKUA) based on the Boltzmann model equation. The linear interpolation method is designed and employed to couple the boundary conditions between the external aerodynamic flow field and the solid structure interface. The present thermo-mechanical coupling algorithm is verified on one-dimensional and two-dimensional transient heat flow problems with analytical solutions, and good consistency is achieved. The reliability of the GKUA for solving the boundary conditions of the external flow field and the dynamic thermo-mechanical coupling algorithm for the thermal response behavior of the internal structure material is verified by the consistency calculation of the internal and external temperature distribution. Then, the aerodynamic-thermoelastic analysis framework is further applied to study the deformation behavior of structural thermo-mechanical responses and failure mechanism of a hollow sphere under re-entry aerothermodynamic environment with emphasis placed on the influence of flight speeds, rarefied effects, algorithm schemes and damping effects. The numerical results obtained by the presented algorithm including the internal temperature, thermal stress and deformation distribution law are compared and analyzed. Finally, the deformation and failure mechanism of spacecraft structure during re-entry process are solved and analyzed by the present algorithm framework. The displacement, temperature and stress distribution contours of the structure are presented to make a preliminary understanding and evaluation on the process of spacecraft deformation and failure disintegration. It is indicated that the present coupled aerodynamic-thermoelastic analysis framework can provide a reliable, applicable and efficient platform for the thermo-mechanical coupling responses and failure mechanism of re-entry spacecraft in the end of life.

ОЦЕНКА ТРЕЩИНОСТОЙКОСТИ ЗАЩИТНО-ДЕКОРАТИВНЫХ ПОКРЫТИЙ В ЗАВИСИМОСТИ ОТ ПОРИСТОСТИ ПОДЛОЖКИ

The issue of assessing the stress state of protective and decorative coatings, depending on the porosity in the contact zone "coating-substrate" is considered. Several schemes are considered: the absence of pores, the pores are filled with a paint composition, the pores are not filled with a paint composition. To assess the stress state of the coatings, the SCAD Office software module is used. It has been established that the presence of pores in the contact zone leads to the appearance of a more inhomogeneous stress state. When a pore is filled with a paint composition, the maximum stresses in the coating occur in the zone of contact between the coating and the substrate. In the absence of filling the pores with paint, the maximum stresses occur on the surface of the coating. The influence of the substrate on the change in the values of internal thermal stresses is revealed. Stresses in coatings on a claydite-concrete substrate are significantly lower compared to the use of heavy concrete as a substrate. The ratio of maximum thermal stresses and long-term cohesive strength is analyzed. It is established that cracking is possible in the polymer lime coating from the action of temperature stresses in the period from August to January

Investigation on low-temperature cracking characteristics of asphalt mixtures: A virtual thermal stress restrained specimen test approach

In order to characterize the effects of aggregate characteristics on the low-temperature cracking characteristics of asphalt mixtures, a virtual approach for the thermal stress restrained specimen test (TSRST) was established based on the discrete element method (DEM) and the simulation software particle flow code in two-dimension (PFC2D). A two-dimensional (2D) virtual specimen was established according to the random generation algorithm. The meso contact parameters between each phase in materials at different temperatures were determined through laboratory tests. The internal thermal stress curve of the specimen and the meso mechanism of crack propagation were analyzed during the virtual test, and the reliability of the virtual test was confirmed by the results of laboratory tests. Finally, the effects of aggregate properties on the low-temperature crack resistance of asphalt mixtures were analyzed. The results of the virtual test and the laboratory test are highly consistent, which proves that the virtual TSRST can be used as a reliable method to evaluate the low-temperature crack resistance of asphalt mixtures. The damage of the specimen can be divided into three stages: crack initiation, stable propagation, and unstable propagation. The asphalt mixture with less aggregate content, coarser gradation and smaller flat ratio has better low-temperature crack resistance.

Flexural Toughness Test and Inversion Research on a Thermal Conductivity Formula on Steel Fiber-Reinforced Concrete Components Post-Fire.

Steel fibers are widely used because they can effectively improve the tensile, compressive and flexural properties of concrete structures. The selection of steel fiber dosage and aspect ratio at high temperature has an important impact on the flexural toughness of concrete components post-fire. In this paper, discussions are made on the simulated fire test in compliance with the ISO 834 standard to study the steel fiber-reinforced concrete (SFRC) components post-fire. The research reveals the influence of two commonly used steel fiber aspect ratios (50, 70) and steel fiber dosages (30 kg/m3, 40 kg/m3, 45 kg/m3) on the changes of the internal temperature field, the initial crack flexural strength and the flexural toughness of the SFRC components under a single-side fire. Moreover, combined with the four-point flexural test of the SFRC components post fire, the research also describes the damage of high temperatures to the flexural toughness of SFRC components, and suggests a calculation formula for SFRC thermal conductivity by way of the numerical inversion method. The results of this study have verified that the incorporation of steel fiber into concrete helps to reduce its internal thermal stress difference and improve the crack resistance and fire resistance of the concrete. Moreover, under high temperature conditions, the concrete component added with the steel fiber in an aspect ratio of 70 and a dosage of 45 kg/m3 increased their initial crack flexural strength by 56.8%, higher than that of plain concrete components, and the loss of equivalent flexural strength and flexural toughness of SFRC post fire was only 45.2% and 13.6%, respectively. The proposed calculation formula of thermal conductivity can provide a reference for a numerical simulation study of the temperature field of SFRC components in a high temperature environment.

Influence of Raster Pattern on Residual Stress and Part Distortion in FDM of Semi-Crystalline Polymers: A Simulation Study.

In fused deposition modelling (FDM) based on the selected raster pattern, the developed internal thermal residual stresses can vary considerably affecting the mechanical properties and leading to distinct part distortions. This phenomenon is more pronounced in semi-crystalline than amorphous polymers due to crystallisation. Hence, this study focuses on the simulation of the FDM process of a semi-crystalline polymer (polypropylene) with raster patterns such as line (90°/90°), line (0°/90°), zigzag (45°/45°), zigzag (45°/−45°), and concentric from Cura (slicing software). The simulation provides visualisation and prediction of the internally developed thermal residual stresses and resulting warpage with printing time and temperature. The sample with a line (90°/90°) raster pattern is considered as the reference sample in order to compare the relative levels of residual stress and warpage in the other printed/simulated samples. Among the considered raster patterns, the concentric pattern displays the lowest amount of warpage (5.5% decrease) along with a significant drop in residual stress of 21%. While the sample with a zigzag (45°/−45°) pattern showed the highest increase of 37% in warpage along with a decrease of 9.8% in residual stresses. The sample with a zigzag (45°/45°) pattern, exhibited a considerable increase of 16.2% in warpage with a significant increase of 31% in residual stresses. Finally, the sample with a line (0°/90°) raster pattern displayed an increase of 24% increase in warpage with an increase of 6.6% in residual stresses.

Fatigue behavior and damage analysis of PIP C/SiC composite

In this work, we study the fatigue behavior of a C/SiC composite produced by several cycles of polymer infiltration and pyrolysis (PIP). Fatigue tests were performed with maximum stresses corresponding to 60–90% of the tensile strength of the composite. During the fatigue tests, acoustic emission (AE) monitoring was performed and the measured AE energy was utilized to quantify the damage and distinguish possible damage mechanisms. Most of the fatigue damage in the form of matrix cracking, interface damage and fiber breakage occurs in the first cycle. As loading cycles proceeded, damage in form of matrix crack re-opening and interfacial friction constantly accumulates. Nevertheless, all samples survived the run-out of 1,000,000 cycles. After the fatigue tests, an increase of the tensile strength is observed. This phenomenon is associated with the relief of process-induced internal thermal stresses and the weakening of the fiber-matrix interface. In general, the studied material shows very high relative fatigue limit of 90% of its tensile strength.