Effect Of Temperature History Research Articles

Thermo-mechanical behaviour of a kaolin-based clay soil

The thermal behaviour of KSS, a low-plasticity artificial clay made with kaolin clay, silt and sand, was investigated in a series of temperature-controlled oedometer tests, at temperatures between 5°C and 70°C, and at vertical pressures up to 2·4 MPa. The experiments investigated the effect of overconsolidation ratio (OCR), pressure level and repeated thermal cycling on thermally induced volume change. Thermal volumetric strains were found to be dependent not only on OCR but also on pressure level, contradicting previous experimental findings and highlighting the importance of even a small dependency of compression index Cc on temperature. Furthermore, thermal volumetric strains were irreversible on heating and cooling even for highly overconsolidated samples. Although irreversibility at high OCR values has been attributed to particle rearrangement and plastic accommodation in the past, an alternative explanation is put forward here, as yielding on the Hvorslev surface is expected to occur on unloading under one-dimensional (1D) conditions. The tests also revealed evidence of thermal creep for the initially normally consolidated samples. The influence of both current temperature and temperature history on the reloading response of mechanically overconsolidated KSS was tested and quantified in terms of their effect on the measured pre-consolidation pressure. The results from these tests were compared to results from the available literature referring to clays of similar and higher plasticity and the comparison highlighted that although soil plasticity can explain the observed quantitative differences between high-plasticity soils to a large extent, mineralogy, in addition to structure, may also play an important role for low-plasticity soils.

Insights into the gradient microstructure and mechanical properties of Ti-6.5Al–2Zr–Mo–V alloy manufactured by electron beam freeform fabrication

Herein, the Ti-6.5Al–2Zr–Mo–V (TA15) alloy with gradient characteristics is fabricated via electron beam freeform fabrication (EBF3) technology. The gradient microstructure and mechanical properties are investigated in detail. Specifically, the microstructural evolution containing the morphology and size along the building direction and its impact on microhardness and tensile properties are systematically illustrated. Besides, the numerical simulation is developed for the establishment of the EBF3 temperature field thermal cycling profile to further elaborate the effect of temperature and thermal history on the microstructural evolution. The results reveal that the columnar to equiaxed transition and coarsening of the prior β grains, as well as successive increase and decrease of thickness of α lamellae along the building direction. The formation of fine lamellar α colony within the layer band is associated with the survived α phase when the peak temperature is just below Tβ. The gradient microstructure endows the TA15 deposit with different mechanical properties. Specifically, the microstructure with fine α lamellae manifests marginally higher microhardness in the layer-band-free region. The elemental dilution, loss and partitioning result in relatively low microhardness in the region with fairly fine α lamellae immediately adjacent to the substrate. The top region of the TA15 deposit, characterized by fine basket-weave microstructure, is imparted with better comprehensive properties relative to the middle and bottom regions, i.e., 1007.4 ± 30.8 MPa, 915.31 ± 28.7 MPa, and 12.08 ± 1.96% for tensile strength, yield strength and elongation, respectively. The integrated effect of coarsened prior β grains and refined α lamellae allow the middle and bottom regions to exhibit similar tensile properties.

Towards neural network‐based numerical friction models

AbstractFriction contacts can be found in almost all mechanical systems and are often of great technical importance. However, they are usually difficult to describe, and their behavior and influence on the whole system are hard to predict accurately. Modern product design and system operation strongly benefit from numerical simulation approaches today, but reliable friction models still represent a major challenge in this context.To tackle this problem, we employ neural network regression to capture the characteristics of frictional contacts and make them accessible for numerical methods in a minimal intrusive fashion. In particular, we test our approach using a Finite Element model of a 2D cantilever beam subject to stick‐slip vibrations induced by a moving conveyor belt at its free end. As a reference solution, we perform a transient analysis based on a simple analytical friction model, where the kinetic friction force only depends on the normal load and the relative sliding velocity. We take the same friction model, add some artificial noise to mimic uncertainties coming with experimental measurements, and pick a limited set of data points to train a regression neural network. The machine learning friction model is then deployed in the Finite Element code to predict the kinetic friction force acting on the beam tip during the slip phases.The deflection curves obtained by the transient numerical analysis using the new neural network friction model agree well with the reference solution based on the underlying analytical model. The results indicate that data‐driven approaches may also be capable of capturing more complex frictional contacts, including effects of temperature, humidity, and load history. The trained neural network friction models can then be employed in numerical simulations in a minimally intrusive manner. This approach opens up new possibilities to predict individual mechanical system behavior as accurately as possible.

Effects of temperature on the time-dependent compression and shear behaviour of a soft marine clayey soil

The thermal effects on geomaterials, especially on clayey soils are getting increasing concerns in many geotechnical applications. To study the effects of temperature on the stress-strain behaviour of Hong Kong marine deposits (HKMD), a series of temperature-controlled experiments were carried out. Oedometer and constant-rate-of-strain consolidation tests under temperatures from 10 °C to 60 °C were conducted on both intact and reconstituted HKMD considering different temperatures and stress paths. The effects of temperature history on the compression curves, thermally induced strain, and the characteristics of creep are revealed and discussed. The concept of virgin heating is proposed for interpreting the thermal plastic deformation. With increasing temperature, the creep coefficient is found to decrease while the creep strain rate increases. Consolidated undrained triaxial tests were performed on intact and reconstituted HKMD under different strain rates and temperature conditions. Under constant temperature, the undrained shear strength of HKMD is not significantly influenced by temperature. In triaxial tests subjected to step-changed temperature, the undrained heating causes a significant reduction of effective stress and rise of porewater pressure in HKMD. Finally, microscopic investigations with mercury intrusion porosimeter and scanning electron microscope are presented and discussed in this paper. It is found that the micropores of HKMD are evolutional with temperature.

Investigating the Effect of Temperature History on Crystal Morphology of Thermoplastic Composites Using In Situ Polarized Light Microscopy and Probabilistic Machine Learning.

Processing parameters including temperature history affect the morphology of semicrystalline thermoplastic composites, and in turn their performance. In addition, the competition between spherulite growth in resin-rich areas, and transcrystallinity growth from fiber surfaces, determines the final morphology. In this study, growth of crystals in low volume fraction PEEK-carbon fiber composites was studied in situ, using a polarized microscope equipped with a heating and cooling controlled stage and a probabilistic machine learning approach, Gaussian Process Regression (GPR). GPR showed that for spherulites, growth kinetics follows the established Lauritzen-Hoffman equation, while transcrystallinity growth deviates from the theory. Combined GPR model and Lauritzen-Hoffman equation were used to deconvolute the underlying competition between diffusion and secondary nucleation at growth front of spherulites and transcrystalline regions.

Thermal Stress of Early-Age Concrete Made with Different Cement Compositions

A temperature stress testing machine (TSTM) was used to investigate effect of cement composition and temperature history on thermal stress of concrete. Results show that the benefit of higher amount of C3S on concrete strength enhancement was compromised by the relatively higher temperature rise at early age, leading to a lower temperature difference. However, by means of a delicate design of cooling history, the deficiency of concrete with higher amount of C3S can be compensated and the cracking sensitivity was closer to that of concrete with lower amount of C3S.

Effect of temperature history during additive manufacturing on crystalline morphology of PEEK

Additive manufacturing parameters of high-performance polymers greatly affect the thermal history and consequently quality of the end-part. For fused deposition modeling (FDM), this may include printing speed, filament size, nozzle, and chamber temperatures, as well as build plate temperature. In this study, the effect of thermal convection inside a commercial 3D printer on thermal history and crystalline morphology of polyetheretherketone (PEEK) was investigated using a combined experimental and numerical approach. Using digital scanning calorimetry (DSC) and polarized optical microscopy (POM), crystallinity of PEEK samples was studied as a function of thermal history. In addition, using finite element (FE) simulations of heat transfer, which were calibrated using thermocouple measurements, thermal history of parts during virtual 3D printing was evaluated. By correlating the experimental and numerical results, the effect of printing parameters and convection on thermal history and PEEK crystalline morphology was established. It was found that the high melting temperature of PEEK, results in fast melt cooling rates followed by short annealing times during printing, leading to relatively low degree of crystallinity (DOC) and small crystalline morphology.

Effect of temperature history on the irradiation behavior of vanadium alloy irradiated with the MARICO-II rig in a fast reactor, JOYO

The irradiation behavior of vanadium alloys was examined to evaluate the effect of temperature history during reactor operation. Irradiation experiments were performed in a fast reactor, Joyo, with an irradiation-temperature-controlled irradiation rig, MARICO-II. In-core irradiation rigs that control the irradiation temperature and are not influenced by reactor power were used. Irradiation conditions with or without the MARICO-II rig were performed. Significant differences in irradiation hardening and swelling behavior in undersized vanadium binary alloys were visible between temperature-controlled and conventional rigs. The temperature history affects the microstructural evolution, especially the nucleation and growth of voids during startup and shutdown procedures. No difference was observed in the vanadium alloys with oversized solute atom because the vacancy migration was suppressed by tight binding between oversized solute atoms and vacancies during irradiation. V–4Cr–4Ti–(Si,Al,Y) alloys showed significant irradiation hardening at high-temperature irradiation even though the contribution of dislocation and precipitates for irradiation hardening was insufficient to satisfy the measured irradiation hardening. The significant irradiation hardening in the V–4Cr–4Ti–(Si,Al,Y) alloys may be caused by transmission-electron-microscope-invisible clusters including minor elements (Si, Al, Y) that were formed at a high temperature during irradiation.

Environmental history affects the growth and photosynthesis of a green‐tide macroalgae Ulva prolifera

In order to understand how the environmental history (low-light and low-temperature history) influences the photosynthetic physiology and metabolism of Ulva spp., we cultured Ulva prolifera seedlings under low-light (LL: 30–50 µmol m−2 s−1) and low-temperature (LT: 10°C) conditions for 3 and 8 days firstly; then, both the LL- and LT- grown seedlings were transferred to optimal conditions (25°C; 120–130 µmol m−2 s−1) for 3 days. During the stress and recovery period, the seedlings grown under 25°C and 120–130 µmol m−2s−1 were set as the control treatment (noted as 25–25°C). The results showed that compared with the control treatment, U. prolifera exhibited pronounced over-compensatory growth induced by low temperature, rather than the low light, but there were no significant differences between 3 and 8 days for low-temperature pretreatments. Based on the results, we cultured this species under 10, 12, 15 and 10–12–15°C firstly and then transferred them to 25°C, in order to study the effects of the low temperature history. It was found that compared with 25–25°C, the growth of thalli was significantly increased by low temperature history, except for that pre-acclimated to 15°C. The reasons for this increase varied, but not included the chlorophyll a (Chl a), water content, soluble sugar and soluble protein (SPs), because the Chl a content was significantly decreased by low temperature history, especially pre-acclimated to 10°C and 10–12–15°C. There were no significant effects of low temperature history on the water content and soluble sugar, while compared with 25–25°C, lower temperature history decreased SPs content, except for pre-acclimated to 10°C. Our results suggest that environmental history, especially low temperature history, plays an important role in the rapid growth of Ulva species.

Modeling of the precipitation kinetics and morphology evolution of lamellar α in Ti-alloys during non-isothermal treatments

The non-isothermal diffusional phase transformation plays an important role in adjusting materials microstructure. In the modeling of non-isothermal transformation, actual temperature history has a remarkable effect on the precipitation kinetics of new phase. When morphology anisotropy effect is considered, taking actual temperature history effect into account is very difficult for guaranteeing the accuracy of kinetics prediction. In order to solve this problem, a new non-isothermal transformation model in combination with cellular automaton (CA) method with mixed-controlled mode was proposed. In this new model, actual temperature history effect was characterized by the effects of cooling path and additive isothermal path on the nucleation and growth of new phase. Firstly, the cooling path with the consideration of supercooling effect was introduced into the created isothermal transformation theory model. Secondly, the temperature-time path (i.e. additive isothermal path) in CA model was calibrated by using the solute concentration model from experiments. With the use of this new model, the precipitation kinetics and morphology evolution of the lamellar α for IMI834 titanium alloy during continuous cooling from single-phase region was predicted. The predicted results were in good agreement with experiments. It was also revealed that the dominant role of mixed-controlled mode for lamellar α precipitation was gradually changed from the diffusion control to the interface control with the increase of cooling rate.

Effect of Temperature History During Additive Manufacturing on Crystalline Morphology of Peek

Effect of Temperature History During Additive Manufacturing on Crystalline Morphology of Peek

On three-dimensional J-integral for finite deformation problems with continuous and discontinuous spatially mechanical property variations

In welded joints, which are widely used in various applications, the mechanical properties of material change discontinuously due to the effects of temperature history and weld between dissimilar materials. Therefore, it is necessary to develop a method for evaluating fracture mechanics parameter for structure with discontinuous changes in mechanical properties. One of the fracture mechanics parameters to evaluate crack propagation is the J-integral. The objective of this study is to establish an accurate mechanical strength evaluation method for problems with discontinuous changes in mechanical properties. For this purpose, we propose a three-dimensional J-integral which is applicable to large-deformation elastic-plastic problems that allow continuous and discontinuous changes of mechanical properties.

Development of LSTM networks for predicting viscoplasticity with effects of deformation, strain rate and temperature history

Abstract In this paper, long short-term memory (LSTM) networks are used in an original way to model the behavior of a viscoplastic material solicited under changing loading conditions. The material behavior is dependent on history effects of plasticity which can be visible during strain rate jumps or temperature changes. Due to their architecture and internal state (memory), the LSTM networks have the ability to remember past data to update their current state, unlike the traditional artificial neural networks (ANNs) which fail to capture history effects. Specific LSTM networks are designed and trained to reproduce the complex behavior of a viscoplastic solder alloy subjected to strain rate jumps, temperature changes or loading-unloading cycles. The training datasets are numerically generated using the constitutive viscoplastic law of Anand which is very popular for describing solder alloys. The Anand model serves also as a reference to evaluate the performances of the LSTM networks on new data. It is demonstrated that this class of networks is remarkably well suited for replicating the history plastic effects under all the tested loading conditions.

Comparison of tensile and compressive creep of hydraulic concrete considering loading/unloading under unified test conditions

In order to study the relationship between the magnitude of the tensile and compressive specific creep of concrete, and to compare the measured and predicted creep recovery based on the superposition principle. In this paper, combined with the concrete mix proportion of typical hydraulic engineering, creep tests of hydraulic concrete under loading/unloading with different loading ages (7, 28, and 60 days) are conducted under unified test conditions. Furthermore, the equivalent age theory is introduced to establish eight-parameter specific creep models of tension and compression considering the effect of temperature history, and an optimization algorithm is used to identify the parameters of the models. Finally, the recovery of specific creep under tensile and compressive different creep is discussed in detail based on the principle of superposition. The results show that the specific creep in tension is greater than that in compression in all three creep test groups, and the recovery of specific creep in tension and compression after unloading indicates that the predicted values of the recovery of specific creep obtained by superimposing compressive specific creep are in better agreement with the measured values.

Effect of temperature history on thermal properties of additively manufactured C-18150 alloy samples

The effects of thermal history on the thermal properties of C-18150 (Cu-1.5Cr-0.5Zr, wt%) parts made by the laser powder-bed-fusion (L-PBF) additive manufacturing (AM) process with three different fabrication orientations (horizontal, angled, and vertical to the build direction) were investigated. A significant difference in thermal properties between as-fabricated and fully heat-treated L-PBF C-18150 samples was observed, and the mechanisms of such behaviors are discussed.

Effects of Sintering Temperature History and Al<sub>2</sub>O<sub>3</sub> Concentration on Formation of Acicular SFCA with Fine Pores

Effects of Sintering Temperature History and Al<sub>2</sub>O<sub>3</sub> Concentration on Formation of Acicular SFCA with Fine Pores

Effect of Temperature History on the Thermal and Mechanical Properties of Fibrous Fumed Alumina Compacts

Effect of Temperature History on the Thermal and Mechanical Properties of Fibrous Fumed Alumina Compacts

Control effects of temperature and thermal evolution history of deep and ultra-deep layers on hydrocarbon phase state and hydrocarbon generation history

Deep and ultra-deep layers in the petroliferous basins of China are characterized by large temperature difference and complicated thermal evolution history. The control effects of temperature and thermal evolution history on the differences of hydrocarbon phase states and the hydrocarbon generation history in deep and ultra-deep layers are researched less and unsystematically. To deal with this situation, based on a large number of temperature and pressure data of deep layers and combined with the complicated historical situation of deep layer evolution in the oil and gas basins of China, the effects of temperature, heating time and pressure on the hydrocarbon formation temperature and phase state were analyzed, and the types of temperature and pressure relationships were classified. Finally, based on the classification of thermal evolution history of deep and ultra-deep layers, We discussed the control effects of basin thermal evolution history on the hydrocarbon generation and phase state, and the following research results were obtained. First, the hydrocarbon phase states of deep layers in different basins and regions are greatly different, and they are mainly affected by temperature, heating time, heating rate, pressure, source rock types and other factors. And temperature is the most important factor controlling hydrocarbon generation and phase state distribution. Second, under the conditions of rapid temperature increasing and short heating time, there still may be oil reservoirs and condensate gas reservoirs in deep and ultra-deep layers in the case of high temperature. Third, overpressure inhibits hydrocarbon generation and pyrolysis. Fourth, there is a close relationship between temperature and formation pressure of deep layers, which can be divided into three types, i.e., low–medium temperature and high pressure type, high temperature and high pressure type, and medium temperature and low–medium pressure type. Fifth, the thermal evolution history of deep and ultra-deep layers can be divided into four types, namely the late rapid subsidence, heating and low geothermal gradient type, the late rapid subsidence, heating and high geothermal gradient type, the middle–late rapid heating and late uplifting and cooling type, and the early great subsidence and rapid heating and middle–late great uplift erosion and cooling type. In conclusion, deep and ultra-deep layers in the basins with different types of thermal history are different in hydrocarbon phase states, accumulation stages and prospects.

Short-term temperature history affects mineralization of fresh litter and extant soil organic matter, irrespective of agricultural management

The influence of temperature on mineralization of plant litter and pre-existing soil organic matter (SOM) involves not only the prevailing temperature, but also how it has changed through time. However, little is known about how temperature variability through time influences mineralization processes. Here, we investigated how short-term temperature history affects the mineralization of SOM and plant litter in soils from different agricultural management systems. We used soils from a long-term experiment with conventional and organic management treatments to set up microcosms. The microcosms were exposed to eight days of contrasting temperature regimes (different mean temperatures and constant versus fluctuating temperatures). Microcosms were then returned to a common temperature of 16 °C, 13C-labelled plant litter was added to half of them, and CO2 efflux was measured over the following week. We found that SOM and litter mineralization were both sensitive to the temperature history, with lower mean temperatures during preliminary treatment associated with higher mineralization during the subsequent common-temperature incubation. This effect persisted through the week after temperature differences were removed. Different patterns of temperature fluctuation and agricultural management did not significantly affect mineralization during common-temperature incubation. The history sensitivity of litter mineralization, despite litter being added after temperature differences had ended, indicates that the temperature history effects may be driven by short-term microbial acclimation. We conclude that organic matter and litter mineralization, which are key processes in the carbon cycle, are sensitive to short-term temperature history. This suggests that future investigations of soil CO2 efflux may need to take recent weather effects into account.

Mechanical performance of welded hollow spherical joints with H-beams after elevated temperatures

Welded hollow spherical joints with H-beam (H-WHSJ), as a new connection pattern in space lattice structures, have been applied in practical engineering. This study aims to investigate the residual mechanical properties of H-WHSJ after loading in elevated-temperature environments and provide an important basis to evaluate the performance of space lattice structures after the occurrence of fire. The effects of temperature history, plastic residual deformation, sizes of WHSJ and H-beam, type of steel, and stiffening rib arrangement on the residual mechanical performance of H-WHSJs after exposure to elevated temperatures are determined via axial compression test by using 28 specimens and finite element (FE) parametric study. The major conclusions are as follows. (1) The residual characteristics of H-WHSJ after elevated temperature are rarely affected by temperature history, but mainly determined by the residual deformation at elevated temperature when the temperature is lower than 700 °C. (2) Plastic residual deformation can considerably reduce the residual bearing capacity (Nu,p) of the loaded H-WHSJ. In particular, Nu,p decreases by approximately 20% when the residual deformation is 6% of the hollow sphere diameter. (3) The formula to calculate the residual bearing capacity of H-WHSJ after loading in elevated-temperature environments has been proposed, and its prediction are in good agreement with the test and FE results.