Search Results (1,161)

Frictional energy piles are a more desirable form of shallow geothermal energy utilization. A pure friction pile condition cannot be achieved in field tests. In this study, foam was placed beneath the model pile tip to weaken the end-bearing resistance. The effects of different cyclic temperature patterns (including cyclic path, external load, and variable temperature duration) on the bearing characteristics of pure friction energy piles are investigated by conducting model tests in a self-designed model box, and the variation patterns of pile stress–strain and pile-top displacement are measured. The results show the following: (1) Under no load, the displacement of the pile top changes with temperature; each round of temperature change produces a partial irrecoverable displacement, and the pile maintains a raised state at the end of both rounds with no stress accumulation. (2) Under the combined action of working load and cyclic temperature, the pile strain reaches its peak and then partially rebounds. Thermal stress accumulates progressively with increasing cycle numbers, and after the cycling ends, an irrecoverable settlement displacement (0.52% D) remains at the pile top and continues to increase. (3) The temperature cycle caused the soil volume to shrink and decreased the shear strength of the pile–soil interface, resulting in a decrease in the ultimate bearing capacity of the test pile compared to the initial state. Full article

Mg-Gd-Y-Zr alloys, with strong age-hardening and thermal stability, are ideal for lightweight load-bearing components, yet forming large complex parts is limited by high sensitivity to hot deformation parameters. This work investigates the hot deformation behavior and microstructure evolution of a Mg-9Gd-4Y-0.5Zr (wt.%) alloy via hot compression at 400 to 510 °C and strain rates of 0.001 to 10 s⁻¹. An Arrhenius constitutive equation with an activation energy Q of 158.63 kJ/mol was established, and a hot processing map was constructed. EBSD characterization revealed the dynamic recrystallization, grain size evolution, and texture transition. The results show that flow stress depends strongly on temperature and strain rate. At strain rates of 0.001~1 s⁻¹, a dynamic balance between work hardening and dynamic softening is achieved, and the post-peak flow stress gradually stabilizes. At a high strain rate of 10 s⁻¹, the flow stress continues to decrease because the competition between softening from dynamic recrystallization and work hardening is disrupted by deformation-induced heating. Low strain rates (≤0.01 s⁻¹) and high temperatures (≥470 °C) promote dynamic recrystallization and significant grain refinement. Two optimal processing windows were determined: 400 to 430 °C at 0.001 to 0.01 s⁻¹, giving fully recrystallized fine equiaxed grains, and 440 to 460 °C at 0.01 to 0.1 s⁻¹ with a power dissipation efficiency η of 0.43 to 0.51, balancing processing efficiency and microstructural uniformity. This work provides systematic theoretical and data support for optimizing hot forming parameters of large Mg-Gd-Y-Zr load-bearing components and offers guidance for applying high-strength magnesium alloys in high-end equipment. Full article

In the broader context of ecological transition, it is essential to identify solutions that ensure indoor environmental quality encompassing thermal, visual, acoustic, and indoor air quality conditions to safeguard occupant health and well-being. These solutions should also meet the demand for energy-efficient buildings. With specific regard to thermal environments, a distinction must be made between residential and non-residential settings, where comfort conditions can be achieved, and industrial environments, where thermal stress—and consequently health risks—may arise. To evaluate the quality of a thermal environment, key metrics are necessary. These include the Predicted Mean Vote (PMV) and the Predicted Percentage of Dissatisfied (PPD) for global thermal comfort, Predicted Heat Strain (PHS) and the Wet Bulb Globe Temperature (WBGT) for hot environments, and Required Insulation (IREQ) for cold environments, all governed by ISO-EN standards. The use of indices in residential and non-residential buildings outlines two critical challenges. The first relates to the fact that, in certain instances involving non-air-conditioned buildings, conditions can be borderline between comfort and thermal stress, which must be accurately identified. Secondly, the application of indices frequently neglects necessary variables, disregarding the fundamental limitations and operational boundaries inherent to both objective and personal input quantities. Moreover, the use of measurement devices inconsistent with the minimum requirements laid down by the standards in the field results in unwanted biases with unforeseeable consequences. This review explores the formulation, use, and limitations of the four indices mentioned, providing a perspective on their future development. It establishes the criteria for reliable long-term assessments of thermal and energy environments, encompassing the analysis of both heat and cold strain. Full article

High-strength steel has attracted increasing attention in civil engineering because of its high strength-to-weight ratio and potential for material-efficient design. This narrative review, supported by a structured literature search, summarizes recent advances in the material behaviour, durability and structural performance of high-strength steel. The discussion covers constitutive behaviour, fatigue and fracture, corrosion degradation, high-temperature and post-fire properties, residual stresses, structural members and connections. Existing studies show that increasing steel strength is commonly accompanied by reduced ductility and strain-hardening capacity, while local buckling, residual stress, welding-induced heterogeneity, fatigue damage, corrosion and thermal degradation remain important design concerns. The accuracy of current design provisions varies with steel grade, product form, section geometry, failure mode and exposure condition, and direct extension from conventional steels is not always appropriate. Future research should emphasize coupled degradation mechanisms, consistent material characterization, broader experimental validation and design models with clearly defined applicability limits. Full article

This article presents an experimental investigation into the mechanical properties of new laminated bamboo and bamboo–timber hybrid composite materials for construction. A total of thirty-six bamboo and bamboo–timber hybrid composite specimens were manufactured, which include a new configuration that integrates bamboo and pine strips in hybrid bamboo–timber composite members. An interleaved configuration of the hybrid bamboo–timber composites is proposed to enhance stress transfer and interfacial bonding. Such a design can mitigate global hygroscopic and thermal mismatch effects, including composites panel warping and continuous interfacial shear, through redistributing differential strains into small, localized scales. To minimize manufacturing energy demand, cold hydraulic pressing was used to prepare the specimens with bio-epoxy and polyvinyl acetate adhesives (PVAs). The list of experimental tests includes compression parallel to the grain, compression perpendicular to the grain, and flexure. The experimental results revealed that the developed bamboo and bamboo–timber composites outperform the reference materials consisting of commercial engineered bamboo and natural softwood. In particular, the average modulus of elasticity of the hybrid specimens bonded with bio-epoxy adhesive reaches 11.6 GPa (CoV = 13.8%), which is 40 percent greater than that of the tested commercial engineered bamboo specimens (CoV = 15.7%), emphasizing a stiffer and more reliable engineered bamboo. In the case of flexural testing, the hybrid bamboo–timber specimens reach the highest modulus of elasticity, while the engineered bamboo bio-epoxy test series exhibited a modulus of rupture that was 36% higher than that of the commercial engineered bamboo material with a CoV equal to 8%. Full article

Metal additive manufacturing (MAM) enables the fabrication of geometrically complex and high-performance components but is accompanied by steep thermal gradients, repeated thermal cycling, phase transformation, residual stress, and deformation. These effects can reduce dimensional accuracy, manufacturing stability, fatigue resistance, and service reliability. This review systematically examines residual-stress and deformation behavior in MAM from the perspectives of formation mechanisms, influencing factors, measurement and prediction methods, mitigation strategies, and service-related consequences. The temperature gradient, mechanical constraint, and phase transition mechanisms are discussed as quantitatively coupled rather than independent processes. Comparative attention is given to process-specific differences, alloy-dependent thermophysical and metallurgical behavior, multi-track and multi-material interactions, and complex geometries. Destructive and non-destructive measurement techniques are compared in terms of penetration depth, spatial resolution, uncertainty, and cross-validation. Thermo-mechanical finite element, inherent strain, analytical, reduced-order, machine-learning, physics-informed, and digital-twin approaches are evaluated according to accuracy, efficiency, transferability, and applicability. Mitigation strategies are further compared considering residual-stress reduction, deformation control, manufacturing cost, and mechanical-property retention. Finally, challenges associated with uncertainty quantification, service environments, post-machining stress redistribution, and closed-loop control are identified. This review provides an integrated framework for selecting measurement, prediction, and mitigation approaches for reliable and high-precision MAM. Full article

Coal phase-out regions concentrate the distributional risks of the energy transition, yet the tools used to identify energy-poor households in these territories still rely mainly on income and welfare criteria. This study asks whether such criteria can identify the households that suffer. Drawing on a survey of 706 households across six municipalities of Western Macedonia, Greece, the core territory of the national lignite phase-out, we validate a four-item Thermal Stress Index (polychoric ω = 0.885; loadings = 0.71–0.88; no differential item functioning by gender, income, or survey wave) and test nine hypotheses and one descriptive benchmark on prevalence, mechanisms, typologies, and targeting. Winter thermal inadequacy reaches 22.9%, which sits above the 19.0% national EU-SILC figure, reported as descriptive context. Dwelling energy features dominate all socioeconomic predictors of severe thermal stress (pseudo-R-squared 0.482 against 0.024), and no direct tenure association remains once envelope quality is included, while the protective association of income operates primarily through dwelling quality and is not observed across the range of inefficient dwellings. Latent class analysis identifies a hidden energy poverty class, 19.5% of households with severe experiential deprivation, above-average income, and no payment problems. A machine learning targeting audit shows that administrative criteria alone identify severely stressed households and show no discriminative capacity for identifying severely stressed households (AUC = 0.517), whereas adding dwelling and financial-strain information raises discrimination to an area under the curve of 0.938. Finally, in this sample, income-based screening is weakly associated with the households reporting severe thermal deprivation. Full article

The Ti-6Al-4V alloy is widely used in aerospace and deep-sea applications due to its exceptional strength and corrosion resistance. However, its application is often constrained by high deformation resistance and a narrow hot-working temperature window, primarily attributed to its heat and mass transfer characteristics. To address these limitations, a novel Ti-6Al-1.3V-0.9Fe alloy was designed with an equivalent molybdenum content. In this study, Gleeble thermal simulation tests were conducted to investigate the impact of Fe on the hot deformation behavior under various conditions and to identify the optimal processing window for this alloy. The effects of deformation temperature and strain rate on the flow stress curves and peak stress were systematically analyzed, along with the role of Fe in microstructural evolution during hot deformation. The results demonstrate that the addition of Fe significantly refines the grain size of the Ti-6Al-1.3V-0.9Fe alloy. As expected, the flow stress decreases with increasing deformation temperature and increases at higher strain rates. Under high-temperature and low-strain-rate conditions, the alloy exhibits steady-state flow behavior, indicating improved hot workability. Based on the constitutive modeling, the apparent activation energy (Q) for hot deformation was calculated to be 503.81 kJ/mol. Finally, the optimal hot-working parameters for the Ti-6Al-1.3V-0.9Fe alloy were identified as a temperature range of 760 °C to 860 °C and a strain rate between 0.01 and 0.16 s⁻¹. Full article

Listeria monocytogenes is a foodborne pathogen capable of persisting under acid, osmotic, oxidative, thermal, and other environmental stresses. The glutamate decarboxylase (GAD) system is a major determinant of survival under acidic conditions. Previous work showed that the two-component system LiaSR negatively regulates the gadT2/gadD2 locus in L. monocytogenes 10403S, but the intervening regulator was unknown. Here, we combined transcription-factor mutant screening, promoter-reporter assays, RT-qPCR, Western blotting, acid-survival assays, and electrophoretic mobility shift assays to define this regulatory relationship. Deletion of mntR reduced P_gadT2-gfp activity, gadD2 transcript abundance, and GadD2 protein levels at pH 4.5, 7, and 9, whereas complementation restored expression toward the wild-type level. The ΔmntR strain also showed reduced survival under inorganic and organic acid stresses. LiaSR deletion increased P_mntR-gfp activity, and LiaR bound directly to P_mntR. Conversely, mntR deletion increased LiaR abundance, although MntR did not bind to P_liaSR, indicating indirect feedback regulation. The liaSR/mntR double mutant showed reduced gadT2/gadD2 expression under acidic conditions and impaired acid survival. Together, these findings support a LiaSR-MntR-gadT2/gadD2 pathway in which MntR promotes GAD-mediated acid resistance. Full article

High-purity quartz is a critical raw material for high-tech industries such as semiconductors and photovoltaics, yet its purity is severely constrained by gas–liquid inclusions within quartz crystals that are difficult to eliminate. The calcination–water quenching process is a key pretreatment step for removing inclusions and achieving deep purification, but its underlying mechanisms and the influence of process parameters on removal efficiency remain insufficiently understood. In this study, systematic calcination–water quenching experiments at different temperature gradients (500 °C, 700 °C, 900 °C, and 1100 °C) were conducted on high-purity quartz samples from Inner Mongolia and Angola. Comprehensive analytical techniques, including X-ray diffraction (XRD), major and trace element analyses, and polarizing microscopy, were employed to investigate the microstructural evolution, inclusion morphology, impurity element concentration changes, and phase transformation behavior before and after treatment. With increasing temperature, the quartz samples exhibited pronounced whitening and pulverization, accompanied by a significant reduction in the number of internal linear inclusions. Elemental analysis revealed that calcination–water quenching effectively removed certain alkali metals, alkaline-earth metals, and iron impurities, with 900 °C identified as the optimal calcination temperature; moreover, the sand-sized samples consistently showed better impurity removal efficiency than the lump-sized counterparts. XRD analysis was used to verify the phase transformation of quartz during calcination. Excessive temperatures (e.g., 1100 °C) led to a rebound in the content of some impurity elements. The calcination–water quenching process promotes inclusion decrepitation, exposure, and subsequent removal through the combined effects of volumetric strain induced by quartz phase transitions, thermal pressurization of inclusions, and thermal-shock stress from water quenching. This study establishes the optimal process window (hold at 900 °C for 2 h, sand-sized morphology) for the specific ore samples, elucidates the multi-factor synergistic mechanism of inclusion rupture, and provides both experimental and theoretical bases for the industrial purification of high-purity quartz. Full article

Grinding is the final precision machining step for bearing rings, which induces subsurface gradients in microstructure and mechanical properties. Rolling contact fatigue life and service reliability are directly determined by the gradients. Current research of the grinding metamorphic layer in bearing steels is synthesized in this review. The formation mechanisms, characterization approaches, and the influence of grinding parameters on metamorphic layers is covered. The coupled thermal–mechanical–phase transformation framework encompasses heat-driven phase transformation, high-strain-rate gradient plastic deformation, and their interactions, which collectively govern the formation of the three-layer gradient structure. When the surface temperature exceeds the austenitization threshold, the governing regime shifts from mechanically dominated to thermally dominated, producing an abrupt increase in white layer thickness and concurrent dark layer softening. The capabilities and limitations of characterization techniques for probing the gradient microstructure and residual stress profile are evaluated. The influence of grinding depth, wheel speed, feed rate, wheel characteristics, and cooling conditions on the metamorphic layer is analyzed. The areas requiring deeper investigation are identified. These insights aim to establish correlations between the grinding process and the surface integrity and service performance of bearing components, and to provide directions for future research on the grinding metamorphic layer. Full article

The characterization of high-temperature plastic deformation behavior in centrifugally cast alloys has historically been based on curve fitting of experimentally obtained creep data. Although this approach provides acceptable results within the range of experimental conditions used for curve fitting, performance predictions under conditions outside conventional tests—typically derived from constant temperature and stress—remain insufficiently accurate for petrochemical engineering applications. In this study, constant-load creep tests were performed across a stress range of 5–33 MPa at 950–1100 °C. The minimum creep rate was calculated from the creep curves and used to fit Norton-law parameters by log–log regression. A global Norton-law fit was first carried out for each temperature, and an additional segmented fit was then performed by separating the low- and high-stress domains. The results reveal a systematic variation in the apparent Norton stress exponent (n) with the stress range considered. This variation suggests that the creep response changes from one apparent stress domain to another, contradicting the assumption of a single-valued Norton exponent inherent in standard curve-fitting procedures. Although the experimental database was obtained from conventional constant-load and constant-temperature creep tests, the results are discussed in terms of their implications for creep modeling under non-stationary operating conditions, where local stress and temperature fields may evolve during service. Parameters fitted over a broad stress range may produce systematic local errors when applied to stress domains with different apparent sensitivities. Furthermore, it is well known that classical steady-state creep models may be insufficient when their fitted parameters are transferred to non-stationary loading conditions, where thermal transients during start-up and shutdown generate differential thermal strains and high local stress levels. Geometric constraints, combined with these peak stresses, may lead to values exceeding the yield strength, a condition under which classical methods fail to adequately describe material behavior and stress relaxation mechanisms. This manuscript directly addresses this limitation through the analysis of three heats of the same centrifugally cast alloy. Full article

Sludge-conditioning strategies are commonly optimized for filtration performance, with less attention paid to the rheological and textural properties of concentrated sludge and their relevance to low-temperature drying. Here, thermally modified drinking-water sludge (HDWS) was evaluated as a waste-derived mineral conditioner for filtration dewatering and low-temperature drying. The specific resistance to filtration (SRF) was lowest at 30% DS, whereas the 60% DS treatment reduced the moisture content to 35.66% after drying at 60 °C for 30 min, indicating that the optimum filtration condition did not deliver the best drying performance. Increasing the HDWS dosage from 0 to 60% DS reduced the Jenike shear stress from approximately 565 to 490 Pa and the apparent yield stress from approximately 670 to 380 Pa, while also decreasing adhesiveness and cohesiveness. At higher dosages, the sludge retained relatively high small-strain stiffness but exhibited lower nonlinear elastic and viscous resistance. These responses were consistent with weakened macroscopic bonding and altered deformation-dependent energy dissipation after HDWS addition. A possible contribution from mineral-particle contacts is suggested, although the underlying microstructural mechanism was not directly resolved. The 60% DS treatment shortened the time required to reach 20% water content to approximately two-thirds of that for raw sludge but reduced the cake calorific value from approximately 9.6 to 4.3 kJ g⁻¹. HDWS, therefore, exhibited process-specific trade-offs, and its dosage should be selected according to the targeted unit operation and downstream management route rather than regarded as a single overall optimum. Full article

Concrete exposed to sub-zero and elevated temperatures exhibits strongly non-monotonic mechanical behavior governed by different physical mechanisms. Existing thermo-mechanical constitutive models commonly account for temperature-dependent degradation, but many are formulated for a specific temperature regime, and explicit treatment of reversible freezing-induced strengthening and irreversible high-temperature damage within a single constitutive structure remains limited. This study develops a unified thermo-elastoplastic damage model for concrete over the temperature range from −40 to 800 °C within the framework of irreversible thermodynamics. Plasticity is formulated in the effective-stress space, while compressive damage is driven by the damage energy release rate. Temperature effects are incorporated through evolution laws for compressive strength, elastic modulus, peak strain, and the shape parameters of the ascending and descending branches. Ice-induced strengthening is represented through reversible modifications of stiffness and strength thresholds, whereas high-temperature dehydration and microcracking are represented through irreversible thermal damage. The model was calibrated using published low-temperature compression data for C30–C50 concrete and complete high-temperature stress–strain curves for normal-strength concrete. The normalized curve-shape laws were subsequently assessed using high-strength concrete curves after normalization by their measured peak stress and peak strain, while selected components of the three-dimensional extension were assessed using residual HSC60 true-triaxial data. The calibrated model represented the freezing-point strength valley, sub-zero strengthening and embrittlement, non-monotonic strength evolution at intermediate temperatures, and progressive high-temperature ductilization. Complete high-temperature normal-strength concrete curves were reproduced with R² values of 0.94–0.99, while the normalized multiaxial strength assessment yielded an average relative error of approximately 8%. These results support the internal consistency of the formulation and the limited cross-strength-grade applicability of the normalized curve-shape laws, rather than unrestricted predictive capability. Further independent experiments are required before application beyond the material, moisture, thermal-history, and loading conditions represented by the available datasets. Full article

This study analyzed the effect of a processing sequence comprising precision casting, heat treatment, and high-temperature plastic deformation on the microstructure and mechanical properties of the Haynes 282 nickel superalloy. The starting material was prepared in an industrial VIM IC induction furnace under vacuum conditions; the quality of the resulting castings, phase composition, thermal effects, and the alloy’s behavior during uniaxial compression were then evaluated. Castings in the form of rods with diameters of 10, 12, and 16 mm were produced at a molten alloy temperature of 1550 °C and a ceramic mold temperature of 1250 °C. The lowest porosity values, ranging from approximately 0.036–0.16%, were obtained for the vacuum furnace cooling variant, which was selected for further testing. DTA analysis revealed characteristic thermal effects in the range of 935.9–1379.8 °C, which enabled the selection of supersaturation parameters and a safe range for deformation tests. After supersaturation and aging, the samples were compressed at temperatures of 700–1200 °C at strain rates of 0.001 s⁻¹ and 0.008 s⁻¹. An increase in temperature caused a systematic decrease in maximum stress and yield stress, with the highest plastic resistance observed at temperatures of 700–800 °C. In this range, the microstructure exhibited characteristics of strong strain hardening, high dislocation density, and strain localization. At temperatures of 850–1000 °C, a transition to conditions of intense dynamic recovery and dynamic recrystallization was observed, whereas above 1050 °C, grain growth following recrystallization dominated. The most favorable compromise between reducing deformation resistance, minimizing the risk of cracking, and maintaining a finer microstructure was achieved in the 900–1000 °C range. The results indicate that the combination of precision casting and controlled thermomechanical working can serve as the basis for further optimization of the manufacturing technology for Haynes 282 superalloy semi-finished products. Full article