Elevated Temperature Exposure Research Articles

Machine learning enhanced modeling of steel‐concrete bond strength under elevated temperature exposure

AbstractThis study uses machine learning techniques to investigate the bond strength between steel and concrete under various elevated temperature scenarios. Five distinct machine learning algorithms, including Random Forest (RF), XGBoost, AdaBoost, Decision Tree, Linear Regression, and hyperparameteric optimisations, were used to predict changes in bond strength. The models underwent rigorous optimisation using GridSearchCV to achieve optimal performance. In this study, we evaluated several metrics such as Mean Squared Error, Root Mean Squared Error, Mean Absolute Error, and coefficient of determination (R2) Score to compare and assess the models' prediction capabilities. After optimisation, results indicate that the RF model exhibited exceptional performance in estimating bond strength across different temperature conditions, demonstrating minimal errors and a high R2 Score. Visual comparisons of actual and predicted values further confirmed the efficacy of the RF model in capturing complex fluctuations in bond strength. The findings of this study underscore the potential of machine learning models, particularly the optimized RF method, in accurately predicting bond strength under varying thermal conditions, with promising implications for engineering and construction practices.

Interface bonding characteristics of 3D printed ultra-high performance concrete after elevated temperatures

This study explored the influence of elevated-temperature exposure and interlayer time intervals on the interface bonding strength of hybrid-fibre 3D printed ultra-high-performance concrete (3DP-UHPC), and analysed the potential mechanisms driving these observed results. A relationship model for the bonding strength of hybrid fibre 3DP-UHPC in elevated-temperature environments was proposed. Results revealed that at 800 °C, localized damage occurred in 3DP-UHPC, but the addition of 0.5 % polypropylene fibres delayed the occurrence of spalling behaviour and enhanced its elevated-temperature resistance. Furthermore, as the time interval increased, the bonding strength of 3DP-UHPC gradually decreased, particularly at temperatures above 400 °C, where the melting and volatilization of polypropylene fibres negatively affected the bonding strength. The study suggested that polypropylene fibres inhibited spalling behaviour of 3DP-UHPC after elevated temperatures through moisture loss and thermal stability. However, they may also lead to interface weakening, resulting in a decrease in bonding strength. These findings provide important guidance for further development and design of 3DP-UHPC structures in elevated-temperature environments.

Effect of elevated temperature and hydrocortisone addition on the proliferation of fibroblasts.

Hyperthermia along with hydrocortisone (HC) are proven teratogens that can negatively influence embryo development during early pregnancy. Proliferation of cells is one of the main developmental processes during the early embryogenesis. This study was focused on testing the effect of elevated temperature and HC addition on proliferation of cells in invitro cultures. The V79-4 cell line was treated with HC and cultured invitro at 37°C or 39°C, respectively. To reveal the effect of both factors, the proliferation of cells cultured under different conditions was evaluated using various approaches (colony formation assay, generation of growth curves, computation of doubling times, and mitotic index estimation). Our results indicate that a short-term exposure to elevated temperature slightly stimulates and a long-term exposure suppresses cell proliferation. However, HC (0.1mg/ml) acts as a stimulator of cell proliferation. Interestingly, the interaction of HC and long-term elevated temperature (39°C) exposure results in at least partial compensation of the negative impact of elevated temperature by HC addition and in higher proliferation if compared with cells cultured at 39°C without addition of HC.

Application of metaheuristic algorithms for compressive strength prediction of steel fiber reinforced concrete exposed to high temperatures

The demand for steel fiber-reinforced concrete (SFRC) in construction has surged, particularly due to its enhanced fire resistance, leading to extensive research on its residual properties after elevated temperature exposure. However, conducting experimental tests can be a time-consuming process, demanding significant resources in terms of time, cost, and human resources. In contrast, machine learning (ML) models can rapidly simulate outcomes, enabling researchers to explore a wide range of scenarios efficiently. The previous literature studies used either ensemble or individual models; however, this study made a unique approach to utilize hybrid models, which are more precise compared to the other types of ML models. Accordingly, a data-rich framework containing 304 data samples was utilized in this study to develop an efficient and robust predictive model for the compressive strength (CS) of SFRC at higher temperatures. Support vector regression (SVR) in combination with three distinct optimization algorithms, specifically, particle swarm optimization (PSO), the firefly algorithm (FFA), and grey wolf optimization (GWO) were utilized to develop the hybrid models. In addition, typical ML techniques such as random forest (RF) and decision tree (DT) were used for comparative analysis. Among the five models, the SVR-FFA hybrid model showcased superior predictive accuracy, with the SVR-GWO model following closely. The correlation coefficients (R) for both models exceeded 0.99. The SVR-FFA model demonstrated relative root mean square error (RMSE) and mean absolute error (MAE) values of 0.0375 and 0.0248, respectively, while the SVR-GWO model exhibited corresponding values of 6.0560 and 5.1326. The SHapley Additive exPlanation (SHAP) technique revealed that the influence of temperature is more significant compared to the heating rate. Moreover, a considerable enhancement was observed in CS as the steel fiber volume fraction (Vf) reached 1.5%; on the other hand, no further improvement was noticed when Vf exceeded the 1.5% threshold. The proposed hybrid models are robust and accurate methods to estimate the CS of SFRC in field applications.

Effects of elevated temperature exposure on the mechanical properties of recycled fine aggregate concrete

ABSTRACT In this work, a compound waste material was made up of raw construction waste concrete, waste tiles, and waste bricks was mixed at a weight ratio of 6:3:1. They were ground into recycled fine aggregates (RFA). RFA substituted the local river sand in proportions of 0%, 30%, 50%, 70%, and 100% for preparing recycled fine aggregate concrete (RFAC) with varied water-to-cement ratios. It intended to explore concrete’s mechanical properties and ultrasonic pulse velocity changes before and after high temperatures (300–800°C). The loss on ignition (LOI) of concrete was simultaneously determined to compare the performance in resisting elevated temperature. Test results presented that the higher the replacement ratio of RFA, the gradually higher the reduction in the concrete splitting tensile, compressive, and residual compressive strengths and ultrasonic pulse velocity after elevated temperature exposure. A rapid reduction was especially found at the heated temperature of exceeding 440°C. Furthermore, the old cement paste adhered to the surface of the raw construction waste had a relatively higher LOI. This led to the consequence that the RFAC had an increased LOI with the increment of the RFA replacement ratio, while the LOI of RFAC dropped with the increment of the originally heated temperature.

Thermal stability and strength degradation of lithium slag geopolymer containing fly ash and silica fume

This paper investigates the thermal stability of lithium slag geopolymer (LSG) containing fly ash (FA) and silica fume (SF) exposed up to 900˚C. The effects of elevated temperatures on the microstructural evolution were investigated by thermogravimetric analysis (TGA), X-ray Diffraction (XRD), mineral analysis, surface porosity, and compressive strength of LSG modified by optimum incorporation of fly ash and silica fume. The results indicated that elevated temperature exposure significantly affects compressive strength, surface porosity, void size, weight loss, and phase transformation of fly ash incorporated lithium slag geopolymer (LSGFA) and silica fume incorporated geopolymer (LSGSF). The maximum loss in compressive strength of 44.07% was observed in LSGFA compared to 31.50% loss in LSGSF after exposure at 900˚C. The weight loss of LSGSF was higher than that of LSGFA between 500 and 800˚C and 800–1000˚C indicating a higher degree of dehydroxylation, crystal phase transformation, and viscous sintering observed in the former mix. A larger shrinkage cracking was observed in LSGSF by self-desiccation of the aluminosilicate paste matrix by dehydroxylation of mordenite molecules. Therefore, the degradation of compressive strength is governed by the combination of the crystallization of aluminosilicate gel and the formation of voids.

Thermal impact on superplasticizer-free metakaolin-nano-silica binary and ternary mortars

ABSTRACT Binary and ternary blended mortars were prepared by replacing ordinary Portland cement with varying percentages of MK (10%, 15%, 20%) and NS (1.5%, 3%, 4.5%) to study their performance under elevated temperatures. Superplasticisers were not used to ensure an unadulterated assessment of thermal performance. Heat resistance was evaluated based on the area under the relative residual compressive strength curve concerning temperature. After heat treatment, surface cracking, spalling frequency, and weight loss were assessed. Morphological changes due to elevated temperature exposure were observed through SEM analysis. The findings indicate that the ternary mortar mix with 10% MK and 1.5% NS exhibited the highest thermal resistance. Increased MK and NS proportions resulted in decreased thermal resistance. The mortars remained crack-free until 350°C, with spalling observed at 650°C. Mortar MK10NS3 displayed higher spalling frequency due to its denser pore structure, showcasing the potential of MK and NS in enhancing thermal resistance.

Epoxy-Printed Circuit Board Interfacial Fracture Reliability Under Three-Point and Four-Point Bend Loading After Sustained Elevated Temperature Exposure

Abstract The survivability and reliability of commercial electronic components under very high thermo-mechanical loads are improved using underfilling and potting methods. Potting protects from operating conditions such as moisture, water, or corrosive agents. Furthermore, potting offers damping against shock and vibrations, heat dissipation, and structural support. Being one of the most cost-efficient methods, potting greatly increases reliability and therefore reduces costs for replacements and repairs. It also addresses trapped hot air issues better than other restraint technologies. In potted electronic assemblies, interfacial delamination at the epoxy and printed circuit board (PCB) interface has been one of the major failure modes. Interfacial delamination happens at the epoxy/PCB interface under dynamic shock loads, which leads to failures at the solder interconnects of the electronic components. Sustained operation and storage at elevated temperatures change the interfacial characteristics at the epoxy/PCB interface. This research is focused on interfacial failure mechanics at epoxy/PCB interfaces with high-temperature isothermal aging. In the selection of the epoxy potting material and the reliability assessments of the supplemental restraint systems, fracture parameters such as steady-state strain energy release rate stress and fracture toughness are critical. Rectangular beam specimens of the epoxy/PCB interface are fabricated for different potting compounds, and the fracture behavior is studied under quasi-static monotonic three-point and four-point bend loads. One of the main differences between three-point and four-point bend loading is that the maximum bending stress occurs at the midpoint under the point of loading of the specimen in three-point bending, whereas the peak stress is distributed over the section of the specimen between the loading points in four-point bending. Four different potting compounds with diverse properties have been studied. The recommended curing schedule from the manufacturer has been chosen and followed for all the potting compounds. The epoxy/PCB interfacial samples are aged at a high temperature of 100 °C for 30–180 days. Damage has been assumed to happen at the epoxy/PCB interface under dynamic loads. The critical load of crack initiation for the epoxy/PCB interface has been determined from the experimental findings, and it is used in the computation of fracture toughness values. The fracture toughness values are compared for the various epoxy/PCB systems based on the number of days of thermal aging and the method of flexure testing. A cohesive zone model has been constructed for predominantly mode-I delamination with four-point bend stress to predict the interfacial delamination behavior at the epoxy/PCB interfaces. It has been assumed that the bulk material is linear elastic during the bending load. The cohesive zone has been modeled at the interface, where the interfacial fracture has been assumed to occur. The fracture behavior in the simulation is predicted based on the fracture parameters determined through the experiment. The computed cohesive zone parameters are unique to the interfaces, and they can be used across various applications with the same epoxy/PCB interface to predict interfacial delamination and to select a more suitable potting material.

Effect of elevated temperature exposure on the flexural behavior of steel–polypropylene hybrid fiber-reinforced concrete

Effect of elevated temperature exposure on the flexural behavior of steel–polypropylene hybrid fiber-reinforced concrete

Numerical analysis of dynamic compressive properties of basalt fiber engineered cementitious composites after elevated temperature

The basalt fiber engineered cementitious composites (BF-ECC) was a superior cementitous material when used for tension loading. And it can prevent the development of wide cracks. In this paper, the dynamic compressive mechanics of BF-ECC after elevated temperature exposure(100 °C, 200 °C, 400 °C and 600 °C) is investigated. Parameter analyses are conducted to investigate the effect of the temperature and strain rate. In addition, a dynamic constitutive model including the damage factor function and the temperature effect function is constructed. It is extended and applied to the rate-type constitutive relation of BF-ECC materials after elevated temperature, and the numerical analysis results are compared with the experimental results to verify the applicability of the model.

Indirect Tensile Properties of Basalt Fiber-reinforced Recycled Aggregate Concrete after Elevated Temperature Exposure

Indirect Tensile Properties of Basalt Fiber-reinforced Recycled Aggregate Concrete after Elevated Temperature Exposure

Effects of one-sided thermal shock and hold on alumina-based oxide/oxide ceramic matrix composites for temperatures in excess of 1200 °C

Nextel™720/alumina based ceramic matrix composite plates were subjected to one-sided thermal shock and 30-minute hold at 1100 °C, 1250 °C, 1400 °C and 1550 °C. Post exposure, the plates were evaluated for physical, structural, and microstructural changes using state-of-the art characterization techniques as well as standard mechanical testing procedures. Physically, no significant mass or dimensional changes were noted, while the surface roughness decreased on the exposed side for all the cases. Structurally, both the tensile and flexural strengths decreased for the 1550 °C case, but not for the other temperatures. In addition, short-beam strength tests showed no effect on interlaminar strength as a result of the elevated temperature exposures for the 30-minute duration considered. Microstructurally, SEM/EDS evaluations showed no significant change in the microstructure or element composition on the exposed and back sides. However, mercury intrusion porosity measurements did show a change in pore size distribution due to the combined effect of matrix shrinkage and further matrix microcracking. Combined results show that the operational limit of the composite can be pushed significantly beyond 1200 °C for shorter (in minutes) durations provided it is structurally viable for the application sought.

Mechanical properties and microstructure of nano-modified geopolymer concrete containing hybrid fibers after exposure to elevated temperature

Geopolymer concrete (GPC) has a promising future as an eco-friendly material for refractory engineering applications. It is significant to investigate the changes in mechanical properties of nano-modified geopolymer concrete containing hybrid fibers (NHF-GPC) after exposure to elevated temperature for construction fire-resistant design. In this study, the macro-mechanical property tests and micro tests were carried out on geopolymer concrete containing hybrid fibers with different nano-SiO2 (NS) contents (0–2 %) after exposure to different elevated temperatures (200–800 °C). The coupling relationships of compressive, tensile and flexural strengths of NHF-GPC with temperature and NS content were established separately. And the relative sound velocity and damage degree were selected as acoustic parameters to construct a relationship model with the compressive strength loss rate. The results indicated that the compressive, tensile and flexural strengths of NHF-GPC were enhanced at 200 °C, while higher temperatures significantly reduced the mechanical properties of NHF-GPC. At the same temperature, the compressive, tensile and flexural strengths of NHF-GPC all increased and then decreased with increasing NS content, and reached the peak at a NS content of 1.5 %. The matrix became denser at 200 °C, while at greater than 200 °C, the water evaporated, the number of microcracks increased abruptly, and the porosity enlarged. The mass loss of NHF-GPC after elevated temperature mainly occurred below 600 °C, when there was no new material phase generated inside the matrix. And the established model can be used for the identification on the strength damage degree after elevated temperature exposure of NHF-GPC, and it can offer a conceptual foundation for the assessment of elevated temperature damage and the life prediction of GPC in the practical applications.

Residual Mechanical Properties of PBO FRCM Composites after Elevated Temperature Exposure: Experimental and Comparative Analysis

Residual Mechanical Properties of PBO FRCM Composites after Elevated Temperature Exposure: Experimental and Comparative Analysis

Mechanical properties of high-strength micro steel fibre reinforced concrete subjected to high temperatures

The concrete structure deteriorates as a result of numerous chemical changes that occur when subjected to extremely high temperatures. To reduce structural components, catastrophic failure due to elevated temperature exposure by adding fibres into the matrix, which increases the time inhabitants have to evacuate during accidental fires, is the principal purpose of this experimental work. In addition, whenever the structures are subjected to fire, one end of the structure may catch on fire while the other end may not, but both ends of the structure can get subjected to extremely high temperatures, analogous to the exposure to the furnace.After repeated heating and cooling, and concrete loses strength in application scenarios. Investigational work has been done on concrete with micro steel fibre with volume fraction varying from0 to 0.5%. For quality assessment, non-destructive testing (NDT) has been performed both before and after temperature exposure. A model has been developedthat can predict compressive strength values from the obtainedultrasonic pulse velocity values. According to this research, adding steel fibre demonstrated good strength results post-elevated temperature exposure. This research attempts to quantify the post-fire mass loss, strength degradation, and quality deterioration of high-strength micro steel fibre reinforced concrete after it has been exposed to elevated temperatures.

Effects of elevated temperature and copper exposure on the physiological state of the coral Galaxea fascicularis

The co-occurrence of elevated seawater temperature and local stressors (heavy metal contamination) affects the ecophysiology of phototrophic species, and represents a risk to the environmental quality of coral reefs. Therefore, we investigated the effects of both Cu alone and Cu in combination with elevated temperature (ET) on the physiology of the coral Galaxea fascicularis, and measured the parameters related to the photo-physiology and oxidative state. G.fascicularis is one of the dominant coral species in the South China Sea which exhibits strong adaptability to environmental stress. We exposed the common coral species G.fascicularis to a series of environmentally relevant concentrations of Cu at 29 °C (normal temperature, NT) and 32 °C (elevated temperature, ET) for 96 h. Single polyps were used in the experiments, which reduced individual variability when compared to the coral colonies. The results suggested that: i) Cu or ET had significant negative effects on the actual operating ability of photosystem Ⅱ (PSII), but not on the maximal chlorophyll fluorescence in darkness (Fv/Fm). ii) Symbiodiniaceae density was significantly reduced by high Cu concentrations, for Cu-NT and Cu-ET, a high concentration of Cu (40 μg/L) significantly impacted Symbiodiniaceae density, causing a 75.4% and 81.0% decrease, respectively. iii) the content of malondialdehyde (MDA) in coral tissues increased significantly under Cu-ET. iv) a certain range of copper concentration (25–30 μg/L) increased the pigment content of the Symbiodiniacea. Our results indicated that the combined stressors of Cu and ET made the coral tissue sloughed, caused the coral tissue damaged by lipid oxidation, reduced the photosynthetic capacity of the Symbiodiniacea, and led to the excretion of Symbiodiniacea.

Impact of Stress Phenotype, Elevated Temperature and Bacterin Exposure on Male Atlantic Salmon (Salmo salar) Growth, Stress and Immune Biomarker Gene Expression.

In this study, post-smolt male Atlantic salmon, previously identified as low (LR) or high responders (HR) based on post-stress cortisol levels, had their head kidney and liver sampled at 12 and 20°C prior to injection (time 0) and after (i.e., at 12 and 24 hpi, respectively) they were injected with either Forte Micro (a multi-valent vaccine containing bacterin, to capture peak antibacterial responses) or an equal volume of phosphate-buffered saline (PBS). Real-time quantitative polymerase chain reaction (qPCR) was then used to measure the expression of 15 biomarker genes in the head kidney and 12 genes in the liver at each temperature/sampling point. Target transcripts were chosen that were related to growth, stress and innate antibacterial immune responses. Many temperature, phenotype and injection effects were found for individual genes within these 3 broad categories, and multivariate statistical analyses (i.e., PCA and PERMANOVA) were used to look for overall patterns in transcript expression. These analyses revealed that HR salmon at 20°C mounted a more robust response (p < 0.05) for the 10 head kidney immune-related transcripts when injected with Forte Micro than LR salmon. In contrast, the 7 liver stress-related transcripts displayed a greater response (p = 0.057) in LR vs. HR fish with Forte Micro at 12°C. Overall, while this research did find some differences between LR and HR fish, it does not provide strong (conclusive) evidence that the selection of a particular phenotype would have major implications for the health of salmon over the temperature range examined.

Surface roughness characteristics of high–ductile thermo–mechanically treated steel rebar exposed to pitting corrosion and elevated temperature

Steel surface topography is critically impacted by pitting corrosion and elevated temperature exposure. The impacted surface topology could drastically reduce the mechanical performance of the steel, specifically concerning its fatigue behaviour. This study undertakes experimental investigations, including microstructural examinations, to explore the surface roughness characteristics of thermo–mechanically treated reinforcing bars subjected to pitting corrosion and elevated temperature. Variations in various surface roughness parameters such as amplitude, spacing, spatial and volume are reported. The study revealed that the surface roughness parameters varied significantly with increasing levels of pitting corrosion and exposure to elevated temperatures. Further, the microstructural examinations revealed the formation and growth of particles at rising temperatures that can promote initial fracture propagation at the steel sub–surface.

Engineering Attributes of Ternary Geopolymer Mortars Containing High Volumes of Palm Oil Fuel Ash: Impact of Elevated Temperature Exposure

Geopolymer mortars made from various waste products can appreciably reduce carbon dioxide emissions and landfill-related issues, making them viable substitutes for ordinary Portland cement, a workhorse in the concrete industry. Thus, a series of ternary geopolymer mortars were made and characterized to determine the effects of exposure to elevated temperatures (from room temperature up to 900 °C) on their engineered (residual compressive strength, weight loss, and slant shear bond strength) and microstructural properties. These mortars, which contain fly ash, ground blast furnace slag, and a high volume of palm oil fuel ash, were designed to activate via the incorporation of an alkali activator solution at a low concentration (molarity of 4). The elevated temperature-mediated deterioration of the ternary geopolymer mortar was quantified using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The results revealed an improvement in the ternary geopolymer mortars’ resistance against elevated temperatures when the palm oil fuel ash level in the mortar matrix was raised from 50 to 70% and when slag was replaced by fly ash. It was asserted that the proposed ternary geopolymer mortars may contribute to the advancement of green concretes demanded by the construction sectors.

Additive manufacturing of crack-free Al-alloy with coarsening-resistant τ1-CeAlSi strengthening phase

Wrought aluminium alloys popular for automotive and aerospace applications are susceptible to solidification cracking when fabricated via laser powder bed fusion (LPBF). Another long-standing and common issue for these alloys is microstructure coarsening and corresponding strength loss caused by elevated temperature exposure. To tackle these challenges, this study designs and develops a class of 1–4 wt% Ce modified Al6061 alloys. The best alloy, with 3 wt% Ce, achieves crack-free fabrication via LPBF due to a reduction in the solidification temperature range and a new solidification pathway that achieved 0.9 solid mass fraction at just 14 °C below the solidification onset. Furthermore, a fine microstructure consisting of coarsening-resistant τ1-CeAlSi eutectic forms, and after hot isostatic pressing, the tensile strength and elongation of the 3 wt% Ce alloy can reach 153 ± 6 MPa and 18.3% at room temperature and 89 ± 6 MPa and 32.5% at 200 °C, respectively. The observed ductility is attributed to nanoscale dispersion of discrete, coarsening resistant τ1-CeAlSi particles within grains and to the presence of large columnar α-Al grains. Meanwhile, solidification cracking was inhibited by continuous grain boundary τ1-CeAlSi eutectic accumulation, which converted to discrete nanoscale τ1-CeAlSi after hot isostatic pressing. This research uncovers a simple and effective approach of designing Al-alloys for LPBF with great potential for both room temperature and high temperature applications in automotive and aerospace industries.