Elevated Temperature Tests Research Articles

Synergistic effects of nano titanium dioxide and waste glass powder on the mechanical and durability properties of concrete

This study investigates the combined use of waste glass powder and nano titanium dioxide (TiO2) on the mechanical and durability properties of the concrete. Waste glass being one of the major municipal wastes going into the landfill sites can be used as a pozzolanic material in the concrete, in this study cement is replaced with waste glass powder by 10% along with nano TiO2, it is used as an addition to cementitious material by 0.5%, 1% and 1.5%. Fresh and mechanical properties like setting time, workability, compressive strength and flexural strength is evaluated along with durability properties such as sorptivity, acid, sulphate and chloride attacks, elevated temperature test. Scanning electron microscope is done to understand the morphology of the blended concrete. Combined use of glass powder and nano TiO2 is found beneficial in mechanical and durability parameters whereas addition of nano TiO2 has resulted in decreased workability of the concrete.

Recycling of activated carbons from spent supercapacitors to refabricate improved supercapacitors

The growing market of commercial electric double-layer capacitors (EDLCs) will lead to a vast accumulation of waste as they arrive out of operation. Recycling the spent electrode activated carbon is a closed-loop solution to provide environmental and economic advantages for EDLC use. However, effectively regenerated methods of high-purity activated carbons are still lacked despite their considerable expense. Herein, a simple steam physical activation method is developed to regenerate high-class activated carbons from spent EDLCs. The process is first demonstrated that can effectively eliminate few electrolytes and complex organics as well as regenerate electrode carbon materials. The activation-recycled carbon materials preserve the physicochemical properties of fresh activated carbons and enhance their mesopore ratios, which contributes to improved EDLC performance, obviously surpassing recycled carbon materials by calcination method, including superior specific capacitance of 103.3 F g−1 at 0.5 A g−1, rate performance and cycling stability, equal to fresh activated carbons. Moreover, the assembled activation-recycled carbon material EDLC delivers low self-discharge rate (89 % of initial voltage after 72 h), wide temperature range (−40 to 85 °C), excellent cycling stability (92.2 % capacitance retention after 10,000 cycles) even at elevated voltages (3.0 V) and temperature (65 °C) test. The present work provides an effective and economic method of recycling high-grade activated carbons for sustainable EDLCs.

Assessment of aluminium alloys’ formability by elevated temperature testing

Abstract This work presents an investigation of the warm formability of AA7075-T6 aluminium alloy sheets using both experimental and numerical methods. Forming limit diagrams (FLDs) can be created by plotting the failure criteria on a graph with two axes representing major and minor strains. Sheets with a grid can be used to quantify both large and minor strains. General techniques available for the grid involve regular patterns of circles in this experiment. Experiments were conducted at various temperature levels, including room temperature, 100, 120, 140, 160, and 180 °C, as well as different strain rates. The investigation has revealed a significant impact of temperature on formability, while the effect of forming speed is quite insignificant across the whole range studied. At an ageing temperature of 140 °C, the distribution of precipitates is evenly balanced, resulting in improved mechanical strength. To offer accurate numerical models for warm-forming processes, a proposed constitutive model is introduced for aluminium alloy sheets. The present model incorporates plastic anisotropy and the effects of temperature and strain rate dependence. An investigation was conducted on the stress-strain behaviour of thin sheets composed of AA7075-T6 aluminium alloy under elevated temperatures and different strain rates. The objective was to ascertain the appropriate fitting parameters. It was associated with ABAQUS finite element modelling. The recommended material model was utilized to build finite element models, which were subsequently compared to the experimental data. The findings obtained from simulated isothermal uniaxial tensile tests were compared to the empirical measurements. The models used in the tensile test accurately predicted the material’s mechanical response. The predicted failure location, punch forces, and strain distributions for all three forming processes were found to be in close agreement with the experimental results. During deep draw operation, the warm forming limit curves were utilized to precisely predict both the pierce depth at which failure occurs and the precise location where the failure initiates.

Hybrid Effect of Metakaolin and Nano-Silica on Mechanical and Durability Parameters of Mortar

The incorporation of pozzolanic materials such as nano silica and metakaolin in cementitious materials has gained significant attention in recent years due to their potential to improve the mechanical and durability properties of cement-based composites. This thesis investigates the hybrid effect of nano silica and metakaolin on the mechanical and durability properties of cement mortar. The research work involved the preparation of cement mortar specimens with varying proportions of nano silica and metakaolin, which were then subjected to a series of mechanical and durability tests. The mechanical tests included compressive strength, while the durability tests included water absorption and elevated temperature test. The study showed that the addition of both nano silica and metakaolin to cement mortar resulted in a significant improvement in the mechanical properties of the mortar. Additionally, the hybrid effect of nano silica and metakaolin resulted in enhanced durability of the cement mortar, with a significant reduction in water absorption and improved temperature resistance. The findings of this study will have significant implications for the development of sustainable and durable cementitious materials. The use of pozzolanic materials such as nano silica and metakaolin can reduce the consumption of cement and the associated carbon footprint while also improving the durability and long-term performance of cement-based composites. Overall, this study suggests that the incorporation of nano silica and metakaolin can lead to significant improvements in the mechanical and durability properties of cement mortar, making it a promising material for use in various construction applications.

Bond line shear strength of structural wood adhesives at high temperatures up to wood carbonization – A classification approach

The European timber fire design code EN 1995-1-2 presently specifies that adhesives for timber construction products shall provide integrity throughout the intended fire exposure time, yet no test or requirement specifications are given. Contrary, in North America elevated temperature tests are mandatory and product standards for glued and cross laminated timber demand sufficient bond line shear strength up to 220 °C. This paper deals with block shear compression tests at ambient and elevated temperatures for development of a high temperature resistance classification system for structural wood adhesives. The investigations comprised 1200 specimens made from Norway spruce bonded with twelve brands from five adhesive families. Polycondensation (pcon) resins encompassed phenolic resorcinol formaldehyde, melamine urea formaldehyde and melamine formaldehyde adhesives. Polyaddition (padd) adhesives comprised five one-component polyurethanes and an emulsion polymer isocyanate. The focus was on the strength-temperature (fv-T) relationship of bonded and solid wood reference specimens at 180–270 °C. The pcon adhesives showed almost throughout a fv-T relationship close to solid wood up to 270 °C. Contrary, the padd adhesives revealed massive strength degradations vs. solid wood from 180 °C onwards. An adhesive test, evaluation and classification procedure with four classes T270 to T200 was derived. It is based on a comparison of the temperature-dependent shear strength decline in bonded samples vs. solid wood reference samples beyond 180 °C. Class T270 adhesives are proposed being suited for the linear charring model of EN 1995-1-2 as PRF adhesives without additional fire resistance testing of components deemed necessary today.

Development of large-size dissimilar stainless steel/α-Ti alloy joints by diffusion bonding using vacuum hot press: Interface microstructure and tensile response in the temperature range of 77–773 K

In the present study, dissimilar metal joints of SS321 and Ti–5Al-2.5Sn (α-Ti alloy) are produced by diffusion bonding at temperatures of 850, 900, and 950 °C under 10 MPa pressure for 30 min duration using a vacuum hot press (VHP). The interface of the joints was characterized through scanning electron microscopy coupled with energy dispersive spectroscopy and electron backscattered diffraction analysis for examining microstructure, morphology, and microchemistry across the interface. The effect of change in the heating process during diffusion bonding on the growth kinetics of interface layers was investigated. The interface of the joints comprised of intermetallic phases of σ phase, χ phase, (Fe,Cr)2Ti, FeTi and β-Ti. The joint produced at 900 °C has exhibited a maximum tensile strength of 315 MPa, 253 MPa, and 208 MPa at the test temperatures of −196 °C (77 K), room temperature (300 K), and 500 °C (773 K), respectively. Reduction in joint strength was noticed at test temperatures of RT and −196 °C for the samples bonded at a higher temperature of 950 °C due to the increased widths of the intermetallic phases at the interface. The effect of the bonding temperature on the tensile strength of the joints at an elevated test temperature of 500 °C was found to be negligible; however, the joints displayed good retention of strength along with substantial strain hardening followed by ductility at 500 °C. Fracture surfaces of RT and −196 °C tested samples showed the mixed mode of featureless smooth and cleavage fracture, whereas the 500 °C tested sample displayed planar interface failure. The zone of failure of the joints was noted to be around the interphase layer made of (Fe,Cr)2Ti + FeTi intermetallics.

Localized loading behavior of cold-formed stainless steel RHS under interior-one-flange load case at elevated temperatures

The localized loading behavior of cold-formed stainless steel (CFSS) rectangular hollow section (RHS) members at elevated temperatures is investigated in this paper. Fifteen localized loading tests conducted at various temperatures up to 800 °C were reported. The tests were carried out under the Interior-One-Flange (IOF) load case as specified in American Specification for the design of cold-formed stainless steel structural members. Tensile coupon tests were performed to obtain the material properties of the CFSS RHS at various temperatures. Detailed information on dimensions, temperature histories, failure modes, load-deformation curves, localized loading capacities of specimens at various temperatures were presented. In addition, a numerical investigation was supplemented, where a total of 192 finite element (FE) analyses were undertaken after validation of developed FE model against the elevated-temperature test results. The influence of various parameters on the localized loading capacities of CFSS RHS at different temperatures under IOF load case was revealed. The obtained results were utilized to assess the applicability of the localized loading design provision for CFSS RHS under IOF load case codified in the American Specification to elevated temperature conditions. Moreover, the results were also compared with predictions based on existing design rules in literatures for cold-formed RHS at elevated temperatures. Furthermore, reliability analyses were carried out to assess the reliability levels of the assessed design methods. It is shown that the existing design rules can generally provide conservative and reliable predictions of the localized loading capacities for the CFSS RHS under IOF load case at elevated temperatures.

Correlating microstructure and mechanical properties of harvested high dose Zorita light water reactor internals

In this study, microstructural studies and micro-mechanical testing of an ex-plant material harvested from the decommissioned pressurized water reactor (PWR) is carried out. Irradiated 304 stainless steel (SS) components were harvested by the Electric Power Research Institute, U.S. Nuclear Regulatory Commission, and members of the José Cabrera Nuclear Power Station (Zorita) in Spain. The bi-crystalline micro-tensile specimens, atom probe tomography (APT) tips, and transmission electron microscopy (TEM) lamellae were fabricated from the baffle plate materials irradiated to 0.05, 15 and 50 dpa to elucidate microstructural, microchemical, and local mechanical properties changes as a function of dose. TEM and APT studies reveal radiation induced Ni, Cr, and Si rich precipitates in the 15 dpa sample that become smaller and partially redissolve into the matrix of the 50 dpa sample (decreasing size and number density). Dislocation loop and cavity number density and size were quantified as a function of dose as well as swelling. Intergranular Ni and Si enrichments with concomitant Fe and Cr depletion were observed in the 15 dpa sample and were more pronounced in the 50 dpa sample. Micro-tensile testing performed in the scanning electron microscope (SEM) at room temperature and 300 °C shows that the material's local yield strength and ultimate tensile strength decreases with increased dose and elevated test temperature and provides further insights via localized strain mapping. Current and previous mechanical data was compared with calculated values using the dispersed barrier hardening model with inputs of dislocation loops, precipitates, and cavities from microstructural characterization.

Mission Results: Creating a 3D Map of a Very High Radiation Confined Space Using the LiDAR-Equipped Elios 3 Drone

A prototype configuration of an Elios 3 indoor inspection drone, made by Flyability, comprising a lightweight light detection and ranging (LiDAR) system and a wide-range, electronic dosimeter was developed and tested to quickly measure radiation levels and collect three-dimensional (3D) spatial data from within a very high radiation nuclear waste storage facility at the U.S. Department of Energy−operated Idaho National Laboratory (INL) site. The compact drone configuration was used for inspecting and collecting data from areas difficult or hazardous to access using conventional methods. Validation testing of the prototype drone configuration was performed, including maneuverability, radiation tolerance, dosimeter integration, and elevated ambient temperature testing. The drone configuration was shown to operate successfully in an ionizing radiation field as high as 100 Gy/h (10 000 rad/h), with an accumulated radiation dose of 40 Gy (4000 rad) and ambient air temperatures of 54°C (130°F). On November 16, 2022, the LiDAR and dosimeter-equipped prototype drone was used to successfully collect 3D spatial data and radiation measurements from within a very high radiation nuclear waste storage facility at the INL site, where it encountered radiation levels up to 7 Gy/h (700 rad/h). The mission, which included three flights of the prototype drone configuration, represents the first-ever drone flight within a very high radiation nuclear waste storage facility. On the third flight into the storage facility, the drone was unable to produce adequate lift necessary to fly back out of the facility. The lessons learned suggest the loss of adequate lift was due to the added weight of the dosimeter payload and the increasing temperature of the air inside the facility due to radioactive decay. Although the prototype drone was not retrievable, the drone’s wireless transmission system successfully transmitted the radiation measurements to engineers outside of the facility.

Fracture behaviour assessment of the additively manufactured and HPT-processed Al–Si–Cu alloy

Ultrafine-grained Al–9%Si–3%Cu alloy was achieved by a combination of laser powder bed fusion (LPBF) additive manufacturing and high-pressure torsion (HPT) processing in this investigation. The alloy was initially deposited layer-by-layer using a bi-directional scan strategy in LPBF with a scan rate of 1000 mms−1, a layer thickness of 40 µm and a hatch spacing of 200 µm, leading to a melt pool morphology with an average width of 150 µm and differing lengths. This led to a grain size of 722 nm and a dislocation density of 1.1 × 1014 m−2. This as-deposited alloy was then processed using HPT at room temperature using an applied pressure of 6.0 GPa and at a speed of one revolution per minute for different numbers of turns: half, one, five and ten turns. The alloy after HPT processing showed ultrafine grains with a grain size of 66 nm, well-dispersed nanosized intermetallic particles with sizes of 50–90 nm, the disappearance of the pool morphology and a notable dislocation density of about 6.2 × 1014 m−2 for the ten turns HPT-processed alloy. The as-deposited and subsequently HPT-processed samples were tensile tested at 298 and 573 K at different strain rates between 10−4 and 10−1 s−1. The elongation-to-failure and tensile strength were recorded and the fracture surfaces were also inspected using scanning electron microscopy and then correlated with the manufacturing, processing and tensile testing conditions. The alloy performance in tensile testing has been evaluated at ambient and elevated temperatures in terms of structural evolution and fractography for the first time. Ultrafine α-aluminium grains and nanosized eutectic silicon particles obtained by room temperature HPT-processing of the alloy have significantly improved the mechanical properties and microstructural stability at ambient and elevated testing temperatures for the HPT-processed additively manufactured alloy compared to the as-deposited additively manufactured and counterpart conventional alloys. The HPT-processed tensile samples showed a significant tensile strength of 700 MPa at 298 K and elongation-to-failure of 220% at 573 K, which is higher than that seen in the as-deposited tensile samples where 400 MPa and 106% are observed under the same testing conditions. Fractographic observations demonstrated that mixed brittle and shear ductile fractures dominated in the as-deposited tensile samples at 298 K, and tension ductile fracture dominated at 573 K. However, the HPT-processed tensile samples exhibited tension ductile and shear ductile fractures at 298 K, and tension ductile fracture at 573 K. The ultrafine-grained microstructure produced by the HPT application in the LBPF-manufactured alloy controls effectively the fracture mechanisms, dimple morphology and thus strength and elongation in comparison with the as-deposited additively manufactured microstructure.

Artificial neural network evaluation of concrete performance exposed to elevated temperature with destructive–non-destructive tests

In this study, it is aimed to predict the performance of concretes obtained by using supplementary cementitious materials (SCM) before and after high temperature using artificial neural network. Thus, in addition to contributing to sustainable development and circular economy by using waste materials in concrete production, predicting concrete strength using artificial neural network without the need for experimental studies will provide a great advantage in practice. In addition, it will also contribute to the literature in terms of determining the optimum amount of metakaolin to be used with fly ash in concrete production. Metakaolin, silica fume and fly ash were used as SCM in different proportions in concrete mixes. Accordingly, a total of 22 concrete series were prepared, one of which was the control series. Porosity, ultrasonic pulse velocity, pressure and tensile strength tests were applied to the series at the end of 7th, 28th and 90th curing periods before high temperature. In order to determine the strength losses after elevated temperature, porosity and compressive strength tests were applied at temperatures of 400, 600 and 800 °C. Mineral additive series showed positive mechanical properties up to 20%. However, it has been observed that the use of fly ash after a certain rate causes a decrease in strength. After elevated temperature, strength loss was observed in all series due to the increase in temperature, while it was observed that the rate of being affected by elevated temperature decreased as the percentage of metakaolin increased. Optimum mineral additive usage percentages were determined as 10% fly ash and 15% metakaolin. On the other hand, the use of mineral additives above the optimum level caused the performance of the concrete to decrease. Then, the concrete compression strengths obtained at 7th, 28th, and 90th days and at 400, 600 and 800 °C temperatures are taken as the outputs of the ANN. The artificial neural network provided the closest results to experimental data. Moreover, to prove the predictive performance of ANN, a comparative analysis was made with GPR, SVM and LR and the smallest value of the RMSE value is obtained with the ANN model. Finally, a fivefold cross-validation criteria was used to objectively present the performance of the model.

In-situ synchrotron diffraction analysis of deformation mechanisms in an AA5083 sheet metal processed by modified equal-channel angular pressing

Severe plastic deformation (SPD) is a process to significantly improve the mechanical properties of materials by grain refinement. For forming at room temperature (RT), higher strengths can thus be achieved; for increased temperatures (HT), greater elongations can be achieved. This great potential has been chiefly applied only on laboratory scale due to a lack of industrial process design. Equal-channel angular pressing (ECAP) offers the possibility to integrate these advantages in industrial processes. This paper investigates a modified ECAP process for aluminum AA5083 sheet metal. Two passes of ECAP for sheet metal and an additional heat treatment were used. To study the material deformation on a micro-scale, in-situ synchrotron measurements at DESY (Hamburg) were performed to analyze the evolution of lattice strains and dislocation densities during tensile testing. The mechanical properties of the ECAP-processed sheet material reveal an increase in yield strength and a decrease in elongation at RT. Higher strains can be measured for the processed material at elevated test temperatures. In-situ diffraction results show a changed behavior of the ECAP sheet material compared to the reference material for both temperature regimes. These changes are based on the increased defect density in the material, which leads to increased strength at RT. At HT, dynamic recrystallization occurs during tensile testing, and the prevailing deformation mechanisms reconfigure. Electron backscatter diffraction (EBSD) and micrographs are used to interpret and supplement the observations. The findings provide the basis for the in-depth understanding of the deformation behavior of the material and help to apply the ECAP process on an industrial scale.

Investigation on Residual Mechanical Properties of Galvanized Iron Cold-Formed Steel Sections Exposed to Elevated Temperatures

Cold-formed steel (CFS) sections are used to construct medium and low-rise structures designed to carry small-scale loads. CFS sections are manufactured without the application of heat. Therefore, it is crucial to comprehend the properties of CFS sections which are exposed to fire or elevated temperatures. To simulate the real- time fire exposure, an ISO Standard fire curve was used to heat the CFS sections. The objective of the study is to assess the residual mechanical strength of exposed sections after the elevated temperature test. The study aims to compile data for forecasting the degeneration of elements and to ascertain whether the structural components can be reused or replaced. The CFS sections were subjected to different temperatures, and after heating, two cooling methods were used to bring down to room temperature. The characteristics of the retrieved specimens, taken from exposed CFS sections were assessed using a tensile coupon test. The residual properties such as ultimate strength, yield strength, and elastic modulus were examined and reported. The influence of heating and cooling is more pronounced from the test results. A reduction in the yield and ultimate strength was noticed, and it was found to decrease as the heating intensity increases for air and water cooling respectively. In the case of yield and ultimate strength, the strength reduction is critical beyond 60 minutes. The elastic modulus was also found to be reducing with a similar trend. Based on the test results, reduction factors are proposed for ultimate strength, yield strength and elastic modulus. Reduction factors obtained for yield strength under 60 minutes of heating for air and water cooling is 0.575 and 0.557 respectively. In 120 minutes, the values are 0.400 and 0.329. Reduction factors obtained for ultimate strength under 60 minutes of heating for air and water cooling is 0.586 and 0.566 respectively. For 120 minutes, the values are 0.331 and 0.313.

Fatigue Properties at Elevated Temperatures of Secondary Tempered Nanostructured Bainite: A Study of Deformation Mechanisms

Nanostructured bainitic steel obtained through austempering or bainitic transformation of high Si steels consists of bainitic ferrite and carbon‐enriched retained austenite. Secondary tempering of those microstructures tailors their mechanical properties through its unique nanostructure and austenite stability. Herein, fatigue and tensile properties of a nanobainitic steel in different secondary tempering conditions are presented and the results are discussed based on the deformation mechanisms taking place due to the microstructure evolution during secondary tempering. Influence of secondary tempering and elevated testing temperature on tensile and fatigue properties at room temperature and 250 °C is presented. Based on the present deformation, mechanism results are discussed supported by microstructure evolution results obtained through dilatometry, X‐ray diffraction, and microscopy. Depending on secondary tempering temperature, main influencing mechanisms are martensite formation after secondary tempering during cooling, transformation‐induced plasticity effect, and precipitation hardening obtained by secondary tempering.

Dynamic imidazole-urea bonds for designing recyclable and crosslinked poly(imidazole-urea)

Covalent adaptable network (CAN) with the ability of structural rearrangement has attracted great attentions in recent years because it breaks the limitations in reprocessability and recyclability of traditional thermosetting polymers. Developing catalyst-free dynamic chemistry that proceeded in mild condition would make significant advances in the field of CAN and hold great promise for real applications. Here, we report a new class of highly dynamic imidazole-urea bonds for developing dynamically crosslinked poly (imidazole-urea) (PIU). The reversible reaction and the reaction kinetics between different imidazoles and isocyanate were first studied by model compounds. PIUs with varied crosslinking structures were then constructed from biobased histamine and commercially available isocyanates. Rheological and stress relaxation analysis revealed the rearrangement ability of PIUs at elevated temperature, while thermogravimetric and tensile tests showed their good thermal stability and mechanical properties. The reprocessed PIUs also demonstrated high recovery efficiency of mechanical properties after several cycles of reprocessing. It is expected that this study could broaden the scope of imidazole compounds for novel dynamic polymers.

Post-irradiation examination of commercial tantalum alloys following neutron irradiation

Post irradiation examination of two commercial tantalum alloys (based on Ta-8 %W) revealed significant irradiation hardening following neutron irradiation in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Tensile samples of commercial Ta alloys T-111 and ASTAR-811C were irradiated to a total neutron fluence (E > 0.1 MeV) in the range (2–4)x1021 n/cm2 (0.39–0.75 dpa) at an irradiation temperature near 900 °C. Tensile testing conducted at room temperature and at 800 °C revealed significant irradiation hardening under all test conditions. Samples that were tensile tested at room temperature exhibited brittle failure, whereas ductility was maintained for elevated temperature testing. The irradiation hardening and embrittlement noted for both alloys was attributed to irradiation-induced dislocation loop formation as confirmed through scanning transmission electron microscopy analysis. Corresponding energy dispersive x-ray spectroscopy revealed radiation-induced segregation of Hf in these loop populations. This Hf enrichment is shown to result in eventual co-precipitation of elongated (Hf,O)-rich precipitates along the dislocation loops. These results show that irradiation hardening is enhanced via irradiation-enhanced precipitation at elevated irradiation temperatures. Consequently, the minimum recommended operating temperature window for Ta alloys should be increased to account for observed hardening/embrittlement at irradiation temperatures as high as 900 °C (1,173 K).

Innovative Advances and Prospects in In Situ Materials Testing: A Comprehensive Review

Real-time analysis of materials in use is crucial in the in-situ field. In situ testing is essential for assessing materials in extreme conditions such as aviation, energy, and military applications. Advancement in situ testing methods have opened up research prospects. Strain measurement, deformation conduct mechanical characteristics, microstructure, spectral analysis, electrical chemistry, corrosion resistance, thermal resistance, elevated temperature testing, fatigue testing, nano mechanics, non-destructive evaluation, and in situ microscopy have advanced. These advances enable anatomical and practical material investigation, improving understanding of their function. Characterization methods include acoustic emission, neutron scattering, X-ray diffraction, synchrotron radiation, and scanning probe microscopy have improved in situ testing. With these technologies, scientists can build new materials with specified properties and research material behaviour fundamentals. In situ testing helps develop high-performance materials and understand how they react in extreme situations. In real-world applications, in situ testing improves material response comprehension and aids material design and optimization in several industries. X-ray diffraction, Synchrotron radiation techniques are suitable conducting in situ analysis on crystalline solids. While Scanning electron microscopy, electron microscopy and acoustic emission techniques can be used to determine properties up to nano level.

Elevated temperature properties of foam concrete: Experimental study, numerical simulation, and theoretical analysis

Foam concrete, as an inorganic cellular material possessing exceptional thermal insulation and fire resistance properties, emerges as a promising candidate for thermal insulation. To achieve a more precise evaluation of its performance under elevated temperatures, the present study comprehensively investigates the thermal characteristics of foam concrete with a combined experimental, numerical, and theoretical approach. Firstly, a high-temperature test is conducted to investigate the influence of temperature and foam concrete density on its macroscopic appearance and internal temperature distribution. Meanwhile, the thermal conductivity of foam concrete at various densities and temperatures is directly measured with a thermal conductivity analyzer. Subsequently, to acquire comprehensive specific heat and thermal conductivity parameters of foam concrete, with a numerical model established within ABAQUS, the genetic algorithm is applied to identify these thermal parameters based on the measurement data from the elevated temperature test. In addition, CT scanning and 3D reconstruction of foam concrete before and after exposure to elevated temperatures are utilized to extract pore characteristics. This facilitates the thermal conductivity calculation using theoretical models, enabling the determination of the thermal conductivity of foam concrete above 600 °C. Through a comparison of the experimental, numerical, and theoretical results, it is recommended to consider the variation of specific heat in three dehydration stages due to the observed notable dehydration. Due to the effect of cracks, the numerically determined thermal conductivity is slightly higher compared to the experimentally and theoretically determined thermal conductivity. Based on the analysis, an improved formula predicting the specific heat of foam concrete, and a formula determining the thermal conductivity of foam concrete subjected to elevated temperature are proposed.

Experimental research on heat transfer and mechanical properties of concrete subjected to elevated temperature during the water-cooling process

In this study, a series of experiments, including elevated temperature tests, cooling tests with different regimes, and compressive tests, were conducted on concrete to investigate the heat transfer and mechanical properties of the concrete during the cooling process after being subjected to elevated temperatures. According to the temperature curves during the water-cooling stage, there were two parts in the cooling process with a demarcation temperature of 100 °C, and an apparent temperature plateau was found at around 100 °C. The higher temperature caused more severe damage to the concrete, and the temperature difference caused by the thermal shock had a significant effect on the mechanical properties of the concrete during the cooling process, especially at temperatures of 400 °C and 600 °C, indicating that concrete structures subjected to fire may suffer severe and rapid deterioration of their mechanical properties during the fire-fighting process. Finally, the two constitutive models deduced in this paper show better agreement with the experimental test results than the traditional constitutive model.

Characterizing stable nanocrystalline Cu-Ta behavior and failure dynamics under extremes of strain rate, strain, temperature and pressure by modified dynamic tensile extrusion

This work presents characterization of thermo-mechanically stable, bulk nanocrystalline (NC) Cu-Ta alloys under a combination of extreme states using high-temperature, dynamic tensile extrusion experiments. The NC Cu-Ta was subjected to high dynamic strain rates up to 105/s, large plastic strains of 100–500 %, and high homologous temperatures greater than 50 %TM. This combination of thermo-mechanical conditions provides a unique look at how these extremely stable microstructures can accommodate and reconfigure under situations where dislocation activity is the most extreme, given constitutive relationships between strain rate, dislocation nucleation, and plastic work. Elevated temperature tests results reveal NC Cu-1Ta alloys are capable of forming a coherent jet, (25 mm in length by 1.8 mm in diameter) as it accelerates out of the die after being dynamically extruded. Microstructural analysis reveals that unlike previous reports on conventional un-stabilized nano or near nano-grained Cu, NC Cu-Ta alloys behave differently. They do not undergo grain coarsening via a nucleation and growth process, but rather behave identically to that of coarse-grained Cu. The NC grains elongate along the extrusion direction and at the same time shrink in diameter and develop a <111> type texture. Ultimately, the occurrence of premature dynamic failure was attributed to the inherent constraints posed by processing defects during synthesis.