Test Temperature Research Articles

High-temperature mechanical properties and microstructure of 2.5D C/C–SiC composites applied for the brake disc of high-speed train

This paper uses chemical vapor infiltration method to prepare 2.5D C/C-SiC composites, and conducts various tests to reveal its high-temperature mechanical properties and failure mechanism. The results show that the test temperature significantly affects the mechanical properties. As the test temperature increased from room temperature to 800 °C, the tensile strength of the 2.5D C/C-SiC composite dropped from 127.67 ± 20.87 MPa to 94.74 ± 28.15 MPa, and the performance dropped by 25.79 %. The compressive strength dropped from 326.92±17.37 MPa to 192.31 ± 29.15 MPa, resulting in a performance decrease of 41.18 %. The bending strength dropped from 355.74 ± 40.80 MPa to 235.88 ± 23.52 MPa, and the performance dropped by 33.69 %; the interlaminar shear strength dropped from 9.77 ± 2.79 MPa to 7.80 ± 3.26 MPa, and the performance dropped by 20.16 %. High-temperature oxidation will lead to interface degradation, destroy the composite matrix and carbon fiber structure, change the interface bonding strength, and ultimately lead to a decline in composite performance.

Experimental constitutive relationships for high-temperature deformation of as-cast Al–Si binary alloys

ABSTRACT As-cast binary Al–Si alloys containing ∼2 to 30 wt.% Si were deformed by differential strain rate and differential temperature test techniques at 600–840 K and strain rates 10−4–10−2 s−1 to find the parameters of the constitutive relationships for high-temperature deformation. The maximum strain rate sensitivity index (m) of flow stress was found to be 0.28 in the eutectic Al-12Si alloy. The Arrhenius plot for activation energy for deformation (Q) exhibits bilinear behaviour, with Q being greater at higher test temperatures than at lower temperatures. The magnitude of Q varies as a function of Si content: 95.7 ± 9.8 kJ/mol for Al-2Si to 311.4 ± 98.1 kJ/mol for Al-12Si alloy. Also, the constant initial strain rate tests performed at selected strain rates and temperatures revealed flow hardening at small strains followed by flow softening. Deformation of Al–Si alloys is suggested to be controlled by the dislocation climb mechanism through the participation of both the grain interior and grain boundaries by consideration of effective stress instead of applied stress.

Study on the Application of Kramers-Kronig Relation for Polyurethane Mixture.

Polyurethane (PU) mixture, which is a new pavement mixture, exhibits different dynamic properties compared to a hot-mixed asphalt mixture (HMA). This paper analyzed whether the Kramers-Kronig (K-K) relation and thermorheologically simple properties applied to the PU mixture. Based on the results, the PU mixture exhibited thermorheologically simple properties within the test conditions. The time-temperature superposition principle (TTSP) was applicable for the PU mixture to construct a dynamic modulus master curve using the standard logistic sigmoidal (SLS) model, the generalized logistic sigmoidal (GLS) model, and the Havriliak-Negami (HN) model. The Hilbert integral transformed SLS and GLS models for the phase angle can accurately fit the measured phase angle data with newly fitted shift factors and predict the phase angle within the viscoelastic range. The core-core and black space diagrams both displayed single continuous smooth curves, which can be utilized to characterize the viscoelastic property of the PU mixture. The K-K relation is applicable for the PU mixture to obtain the phase angle master curve model, storage modulus, and loss modulus from the complex modulus test results with the test temperatures and loading frequencies. The phase angle of the PU mixture at extremely high or low test temperatures cannot be derived from the dynamic modulus data.

Effect of UV ageing on debonding of double glass laminates based on different crosslinking and thermoplastic PV encapsulants

To evaluate the potential of novel thermoplastic polyolefin (TPO) encapsulants as alternative for peroxide crosslinking ethylene vinyl acetate (EVA) copolymer and polyolefin elastomers (POE), compressive shear glass laminates were prepared and characterized using EVA and POE benchmark grades and TPO film adhesives (TPO-3.5, TPO-F and TPO-UV). The specimens were exposed to Xenon arc light with an UV irradiation of 40 W/m2, a black panel temperature of 65 °C and relative humidity of 10 % for up to 3,000 h. Visual, optical, mechanical and chemical changes were assessed by light microscopy, UV–visible–near infrared (UVVISNIR) spectroscopy, compressive shear testing, as well as differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) on fractured surfaces. In contrast to EVA and POE laminates, enhanced birefringence was detected due to a higher degree of crystallinity of the TPO encapsulants. Nevertheless, the investigated TPO double-glass laminates revealed a significantly better ultimate mechanical shear performance at 60 °C, also after UV exposure for 3.000 h. TPO-3.5 was the best-performing grade after 3,000 h followed by TPO-UV, TPO-F, EVA and POE. While the aged and fractured EVA, POE, TPO-F and TPO-UV laminates exhibited carboxylic acid signatures differing in intensity, no carboxylic acid residues were detected on the fractured TPO-3.5 surface. TPO-3.5 is characterized by a lower melt flow index and hence, a higher average molar mass compared to TPO-F and TPO-UV. For the crosslinked EVA and POE, the test temperature was already within the melting range of the non-crosslinked, polyethylene rich phase of these peroxide crosslinked encapsulants.

The influence of solid solution hydrogen and precipitated hydride on the creep behavior of Zircaloy-4

The effect of hydrogen on the creep rates of Zircaloy-4 claddings especially in the low hydrogen concentration remains largely unexplored while creep is considered a main mechanism for spent nuclear fuel failure along with hydride-induced mechanisms. Here, we study the influence of hydrogen on the creep behavior of low burnup Zircaloy-4 cladding from a microstructural perspective. The creep tests at 450°C and 120 MPa reveal that specimens with hydrogen contents below the terminal solid solubility for dissolution (TSSD) at the test temperature exhibited decreased creep resistance as hydrogen concentration increased, while those with hydrogen contents above the TSSD demonstrated increased creep resistance with higher hydrogen concentration. The lowest creep resistance occurs at the hydrogen concentration corresponding to the TSSD. Additional microstructural analyses using electron backscattered diffraction (EBSD) show the increasing intra-granular/inter-granular hydride ratio in the post-crept specimens as the hydrogen concentration decreases, suggesting that hydrogen atoms in solid solution aid creep progression. Also, an increased amount of twin boundaries is observed in post-crept specimens with hydrogen concentration above TSSD. These results suggest that creep assessment in spent nuclear fuels may require caution especially in low-burnup regime.

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.

Enhanced asphalt dynamic modulus prediction: A detailed analysis of artificial hummingbird algorithm-optimised boosted trees

This study introduces and evaluates a novel artificial hummingbird algorithm-optimised boosted tree (AHA-boosted) model for predicting the dynamic modulus (E∗) of hot mix asphalt concrete. Using a substantial dataset from NCHRP Report-547, the model was trained and rigorously tested. Performance metrics, specifically RMSE, MAE, and R2, were employed to assess the model's predictive accuracy, robustness, and generalisability. When benchmarked against well-established models like support vector machines (SVM) and gaussian process regression (GPR), the AHA-boosted model demonstrated enhanced performance. It achieved R2 values of 0.997 in training and 0.974 in testing, using the traditional Witczak NCHRP 1-40D model inputs. Incorporating features such as test temperature, frequency, and asphalt content led to a 1.23% increase in the test R2, signifying an improvement in the model's accuracy. The study also explored feature importance and sensitivity through SHAP and permutation importance plots, highlighting binder complex modulus |G∗| as a key predictor. Although the AHA-boosted model shows promise, a slight decrease in R2 from training to testing indicates a need for further validation. Overall, this study confirms the AHA-boosted model as a highly accurate and robust tool for predicting the dynamic modulus of hot mix asphalt concrete, making it a valuable asset for pavement engineering.

Research on the deformation law of ultra-thin fiber metal laminates under the synergistic effect of nano-reinforcement and scale effect

At present, titanium alloy/carbon fiber reinforced polymer (TA1/CFRP) laminates, representing the latest fourth generation of fiber metal laminates (FMLs), are predominantly applied in the field of aerospace. The miniaturization of traditional FMLs in thickness or plane size to the micron level for the study of structural properties of ultra-thin laminates will further expand the application of FMLs in the field of micro-devices. Given that carbon nanotubes have a strengthening mechanism in polymers. However, most existing studies have focused on the effect of carbon nanotubes on the properties of macro-scale FMLs, while the enhancement mechanism of the interfacial and mechanical properties of ultra-thin micro-scale FMLs has not been studied, leaving the mechanism still unclear. Based on this, this paper explores the interfacial deformation mode, damage fracture and performance enhancement mechanism of the ultra-thin TA1/CFRP laminates by comparing the parameters of tensile strength and elongation under quasi-static conditions and different process parameters of multi-walled carbon nanotubes content, test temperature, geometry size and grain size. Meanwhile, the correlation law between high-speed tension and quasi-static tension is determined, a 29.3 % increase in tensile strength as the strain rate rises from 0.001 s−1 to 100 s−1, yielding the basic deformation law of ultra-thin FMLs.

Effects of incident heat flux on heat release rates and temperatures in cone calorimeter tests of polyurethane foam

Effects of incident heat flux on heat release rates and temperatures in cone calorimeter tests of polyurethane foam

Investigation of the elevated temperature tribological property and wear mechanism of Fe‐15Cu‐0.8C materials containing Mo‐coated MoS2 powders

In this work, MoS2 solid lubricant was introduced in the form of Mo‐coated MoS2 powder, to enhance the antifriction properties of sintered ferrous antifriction materials (FAMs). The microstructure, phase composition, and tribological properties of Fe‐15Cu‐0.8C‐3.75 (Mo‐coated MoS2) (MC1) were investigated and compared with Fe‐15Cu‐0.8C (M0) samples, with a discussion on the wear mechanism at a wide temperature range of room temperature (RT) to 600 °C. The study revealed that the addition of Mo‐coated MoS2 powders effectively prevents the decomposition of MoS2 during sintering, enhances the bonding strength between MoS2 and the substrate, and significantly improves the hardness of the sintered Fe‐15Cu‐0.8C samples. In comparison to the sintered Fe‐15Cu‐0.8C samples, the sintered Fe‐15Cu‐0.8C‐3.75(Mo‐coated MoS2) samples exhibit good antifriction properties with a frictional coefficient of 0.23 at 600 °C and a wear rate of 6.3 × 10‐7 mm3/N·mm at 300 °C. Introducing Mo‐coated MoS2 significantly reduces the average friction coefficient and wear rate of the sintered FAMs at elevated temperatures, attributed to the formation of FeMoO4. The antifriction performance of MC1 samples notably decreases with increasing test temperatures. The main wear mechanism is oxidative wear above 300°C.This article is protected by copyright. All rights reserved.

Thermal activation and dislocation dynamics in Ti–6Al–4V alloy

The tensile stress relaxation behaviour is experimentally investigated for Ti–6Al–4V alloy across a temperature range of −60, −30, 20, 120, and 230 °C. Interestingly, the results revealed that the alloy exhibited the lowest resistance to stress relaxation at 20 °C, i.e., room temperature. This resistance was found to increase with both increasing and decreasing test temperatures. The apparent activation volume values, which indicate the dislocation mean free path, increase with strain due to a decrease in activable dislocation segments. Furthermore, these values were found to be proportional to the test temperature, resulting from higher dislocation mobility at moderate temperatures (230 °C and 120 °C) than at lower temperatures. Our experimental and analysis results indicate that dislocation-mediated plastic deformation predominates in all tested temperature conditions. However, the transition from planar to wavy dislocation configuration, observed through Transmission Electron Microscopy (TEM) between temperatures of −30 and 20 °C, along with the change in activation volume, suggests a critical temperature at which dislocation mechanism changes in the Ti–6Al–4V alloy. A rapid exhaustion of a substantial amount of mobile dislocation density, which significantly contributes to time-dependent deformation was observed at 230 °C. These findings provide valuable insights into the mechanisms underlying the stress relaxation behaviour of Ti–6Al–4V alloy at different operational temperatures, offering practical implications for improved alloy design and manufacturing processes.

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.

Effect of fission products on the thermal conductivity of ThO2-A molecular dynamics study

Thermal conductivity (k), as an important thermal property of nuclear fuels, would be deteriorated due to fission products. Therefore, to investigate the effect of fission products on the thermal conductivity of nuclear fuels is essential. Two typical fission products: Xe and Kr with 0–2 % concentration are considered in this work. The lattice constants (L) of ThO2 increase due to fission products at all testing temperatures. The extent of increase in L due to Xe interstitials is the maximum. The fission products significantly reduce the thermal conductivity of ThO2. The extent of reduction in thermal conductivity of ThO2 by the defects follows the trend Xe (interstitials) > Xe (substitutional defects) > Kr (substitutional defects) > Kr (interstitials). Finally, the full-filled Xe/Kr bubble has a nearly identical thermal conductivity as an empty void or half-filled Xe/Kr bubble. The underlying reason may be that the thorium atoms have a lower mobility than uranium atoms. These calculated values can be used to predict the thermal properties of the irradiated ThO2.

Effect of temperature on the uniaxial tensile properties of wood plastic composites: Experimental investigation and numerical analysis

Seven groups of uniaxial tensile experiments on wood plastic composites with a High Density Polyethylene (HDPE) matrix at different temperatures were completed in this paper. The test temperatures ranged from -60 °C to 60 °C, with a temperature difference of 20 °C for each group. All samples exhibited tensile brittle fracture. The test results showed that the tensile strength of the specimens decreased continuously with increasing temperature. Taking 0 °C as the reference temperature, the ultimate strength of the sample at -60 °C was 1.63 times that at 0 °C. When the temperature was 60 °C, this value was 0.41. Then, it can be calculated that the ratio of the strength of the sample at -60 °C to that at 60 °C was approximately 3.93, and the corresponding ratio of the elastic modulus was approximately 4.52. This shows that the mechanical properties of WPC are sensitive to changes in temperature. The variation coefficient of the average strength and elastic modulus of WPC for different specimens at different temperatures was less than 0.17, showing good stability due to the small dispersion of mechanical properties among different samples at any specific temperature.

Quasi-static tensile properties of DMLS TI6AL4V(ELI) specimens exposed to two different heat treatment processes and tested at different elevated temperatures

The use of Ti6Al4V components in the aerospace industry has increased in the past years s. Jet engine components made of Ti6Al4V such as compressor blades and exhaust ducts, as well as landing gear, hydraulic systems, and many airframe parts, are exposed to different temperatures while in service, which may affect their mechanical properties. Compressor blades are exposed to temperatures up to 400 °C, exhaust ducts up to 300 °C, and hydraulic systems in the range of −50 °C–135 °C, while landing gears and many airframe structures are exposed to temperatures in the range of −50 °C–70 °C. Therefore, it is of great importance to determine their stability at different temperatures. The results of a study aimed at investigating the effect of elevated temperatures on the mechanical properties and microstructures of DMLS Ti6Al4V(ELI) alloy are presented and discussed in this paper. A DMLS EOSINT M290 machine was used to manufacture test specimens, which were then machined to comply with ASTM E8 for tensile tests. Thereafter, tensile tests were carried out at different test temperatures till fracture. Fractography was then used to study the characteristics of the fracture surfaces. The results obtained in this work showed that temperatures between 175 °C and 325 °C have a significant effect on the mechanical properties and microstructures of the alloy.

High-temperature high cycle fatigue performance of laser powder bed fusion fabricated Hastelloy X: Study into the microstructure and oxidation effects

High-temperature fatigue properties are critical for laser powder bed fusion (LPBF) fabricated Nickel-based superalloy Hastelloy-X (HX) used in aero engines. In this study, superior high-temperature high-cycle fatigue properties of LPBF HX were achieved. The detailed investigations show that the grain boundary oxidation promoted by the different deformation modes between neighboring grains, despite the reduced oxygen-related damage in the coarser LPBF HX microstructures, are the potential causes for the inter-granular fatigue crack initiation and the subsequent crack coalescence. In the meantime, the crack propagation could be hindered by the refined carbides and annealing twins with Σ3 misorientation (60°/〈111〉) in LPBF HX. Furthermore, the recrystallized grains formed ahead of the crack tip due to the severe deformation within the plastic zone and high testing temperature have different crystallographic orientations, which leads to the crack propagation path changes and increases the fatigue crack propagation resistance.

Glass Ceramic Fibers Containing PbS Quantum Dots for Fluorescent Temperature Sensing

Glass ceramics (GCs) containing PbS quantum dots (QDs) are prepared for temperature sensing. Broadband emissions are detected in the GCs when PbS QDs are precipitated from the glasses, and emissions centers are modulated from 1250 nm to 1960 nm via heat treatments. The emission centers of GCs exhibit blue-shifts when environment temperatures increase from room temperature to 210 °C. Importantly, the shift values of emission centers increase linearly with the test temperature, which is beneficial for applications in temperature sensing. A temperature sensor based on PbS QDs GC is heat-treated at 500 °C for 10 h, possesses the highest sensitivity of 0.378 nm/°C, and exhibits excellent stability and repeatability at high temperatures (up to 210 °C). Moreover, GC fibers are fabricated by using the GCs as the fiber core. The sensitivity of the temperature-sensing sensor of the GC fibers is also demonstrated and the sensitivity is as high as 0.558 nm/°C. The designed PbS QDs GCs provide a significant materials base for the manufacturing of fluorescent temperature sensors and the GC fibers offer significant opportunities for temperature detection in complex, integrated and compact devices.

Effects of Quasi-Static Strain Rate and Temperature on the Microstructural Features of Post-Processed Microstructures of Laser Powder Bed Fusion Ti6Al4V Alloy

This study documents an investigation of the flow stress properties and microstructural features of Ti6Al4V (ELI) alloy produced using laser powder bed fusion (LPBF). Selected heat treatment strategies were applied to the material to obtain different microstructures. The influence of quasi-static strain rates and temperature on the obtained microstructures of this material and their strain hardening properties are documented in this study. All microstructures of the alloy formed in this study were found to be sensitive to quasi-static strain rates and temperatures, where their flow stresses increased with increasing strain rate and decreased for tests conducted at elevated temperatures. The strain hardening rates of the fine microstructures were found to be high compared to those of coarse microstructures. The strain hardening rates for the various forms of LPBF Ti6Al4V (ELI) examined here were found to diminish with increasing test temperature. Though the deformed surfaces of the built samples were largely dominated by adiabatic shear bands (ASBs), the absence of ASBs was noted for all samples tested at a temperature of 500 °C and an imposed strain of 30%.

Insights into hardening and strengthening in ultrafine Ti(C, N)-based cermets

Ultrafine Ti(C, N)-based cermets are vacuum-sintered by refining the particle size of raw materials and tailoring the WC/TaC ratio to achieve the improvements in comprehensive mechanical properties and cutting performance. The hardness, flexural strength and tool lifespan of ultrafine Ti(C, N)-based cermets are substantially higher than those of submicron Ti(C, N)-based cermets with the same composition because of the refined grains and the improved distributions of both metal phases and residual stress. The hardness attenuation behavior and strengthening mechanism in Ti(C, N)-based cermets at different test temperatures have been proposed. At 400 ℃, the hardness attenuation of Ti(C, N)-based cermets depends mainly upon the softening of metal phases. However, at 800 ℃, the hardness attenuation of Ti(C, N)-based cermets is mainly related to the reduced bearing capacity of hard ceramic phases and interfacial sliding. The addition of refractory TaC is beneficial for the improvement of high-temperature mechanical properties and the tool lifespan, attributed to the strengthening of the ceramic framework by tantalum atoms.

Comparative analysis of unloading compliance and normalization methods for fracture toughness assessment in 316L stainless steel at cryogenic temperatures

In the present study, the impact of test temperature, specimen geometry, and evaluation methodologies on the fracture toughness of 316L stainless steel was evaluated. Tensile and fracture mechanics tests were conducted utilizing a cryostat across a range of temperatures from ambient conditions to liquid hydrogen environments. The analysis of crack length prediction and resistance curve was performed using two fracture toughness evaluation methods: the unloading compliance method and the normalization method. The difference in fracture toughness by specimen thickness using the normalization method was within acceptable tolerances for all temperatures. However, fracture toughness evaluation using the unloading compliance method showed apparent negative crack growth at all temperatures, causing differences in J-integrals between specimen thicknesses and discrepancies between physical and estimated crack extensions. The application of the offset technique to the unloading compliance method significantly reduced these differences and made the J-integral of the normalization method and the unloading compliance method agree well. The substantial underestimation in the correction of the rotation angle at ambient temperatures was confirmed through real-time imaging of the crack tip with the unloading compliance method, which contributed to the large deviations between estimated and measured crack extensions.