Non-uniform Temperature Distribution Research Articles

Integrating Taguchi Method and Gray Relational Analysis for Auto Locks by Using Multiobjective Design in Computer-Aided Engineering

In automobiles, lock parts are matched with inserts, and this is a crucial quality standard for the dimensional accuracy of the molding. This study employed moldflow analysis to explore the influence of various injection molding process parameters on the warpage deformation. Deformation of the plastic part is caused by the nonuniform product temperature distribution in the manufacturing process. Furthermore, improper parameter design leads to substantial warpage and deformation. The Taguchi robust design method and gray correlation analysis were used to optimize the process parameters. Multiobjective quality analysis was performed for achieving a uniform temperature distribution and reducing the warpage deformation to obtain the optimal injection molding process parameters. Subsequently, three water cooling system designs—original cooling, U-shaped cooling, and conformal cooling—were tested to modify the temperature distribution and reduce the warpage. Taguchi gray correlation analysis revealed that the main influencing parameter was the mold temperature followed by the holding pressure. Moreover, the results indicated that the conformal cooling system improved the average temperature distribution.

An accurate thermoelastic model and thermal output error analysis of a hemispherical resonator gyroscope under varying temperatures

This paper proposes an accurate thermoelastic model of a hemispherical shell resonator (TM-HSR) taking into consideration thermal stress and reveals the effect of its thermal deformation on the hemispherical resonator gyroscope (HRG) output error for the first time. First, a set of thermoelastic dynamic equations of the TM-HSR are derived by leveraging the thermoelastic shell theory, and the relationship between temperature and the equivalent thermal load is determined. Next, an approximate analytical solution of thermal deformation of HSRs is derived using Bubnov-Galerkin method and its accuracy is evaluated by comparing its result with ANSYS simulation results of HSRs with different structures. The approximate analytical solution is found to be very accurate, which is important for temperature testing of HRGs and application to various vibratory sensors with hemispherical shell structures. Subsequently, the effects of thermal deformations under uniform and nonuniform temperature distributions on the HRG output error are revealed by using a thermal output error model. Comparative simulation and experimental results demonstrate the effectiveness and practicability of the proposed model. The proposed model can be used for accurate error analysis and developing a compensation scheme for the thermal output error of HRGs.

Energy harvesting and stability analysis of centralized TEG system under non-uniform temperature distribution

Thermoelectric generator (TEG) systems are gaining much attraction due to utility in heat recovery, surface cooling, concentrated solar thermal, and sensor applications. In series–parallel configurations, TEG modules due to Heterogeneous temperature difference (HeTD) show the non-linear behavior. Due to non-uniform temperature distribution (NUTD), multiple maximum power points (MPP) appears on the P-V curve. It is crucial to drive the system at true global maximum power point (GMPP) among multiple MPP’s. Existing classical techniques exhibit slow tracking, low efficiency, and undesired fluctuation in output voltage transients. To address these shortcomings our control technique based on improved Moth Flame Optimization (IMFO) is employed for the maximum power point tracking (MPPT) control under dynamic operating conditions. Comparison of the proposed technique is made with other well-known meta-heuristic techniques including particle swarm optimization (PSO), cuckoo search (CS), Artificial Bee Colony (ABC), and recently developed Dragon Fly Optimization (DFO). The comprehensive case studies with statistical and quantitative analysis are performed to confirm the superior performance of IMFO for NUTD condition, fast varying temperature condition, and stochastic operations. To experimentally validate the performance of the IMFO algorithm a low-cost TEG emulator setup is designed. The IMFO based control is implemented on a low-cost microcontroller achieving effective real-time control application in hardware. The proposed IMFO algorithm attains up to 6 W more power and takes 59% less time to track and settle at GMPP with minimum fluctuation. Results also validate that IMFO extracts 5.2% more electrical energy in comparison to competing techniques. In light of comprehensive analysis, it is safe to conclude that the proposed IMFO performs excellently for TEG MPPT control.

Time-varying non-uniform temperature distributions in concrete box girders caused by solar radiation in various regions in China

Non-uniform temperature distributions of concrete box girders are induced by solar radiation depending on the structural shapes and shadows cast on them. Using a real-time shadow-selection algorithm and finite element method, the thermodynamic analysis of concrete box girders is carried out to simulate their time-varying temperature distributions. The theoretical results of the finite element model (FEM) are verified by measured data. Based on this, a series of FEMs of concrete box girders are established considering regional influences, and the temperature gradients of concrete box girders in different climatic zones in China are studied. The most unfavorable temperature gradient of concrete box girders in China is obtained, and it is important for design and not only for health monitoring. Moreover, comparing the temperature gradient modes in the specifications of various countries, the temperature gradient of concrete box girders in the China Highway Bridges Design Code is conservative for structural design. Furthermore, the influences on structural temperature distributions of varying environmental factors induced by regional influences are explored, including atmospheric transparency coefficient (ATC) and solar radiation absorptivity (SRA).

Approximate Bayesian neural Doppler imaging

Aims. The non-uniform surface temperature distribution of rotating active stars is routinely mapped with the Doppler imaging technique. Inhomogeneities in the surface produce features in high-resolution spectroscopic observations that shift in wavelength because of the Doppler effect, depending on their position on the visible hemisphere. The inversion problem has been systematically solved using maximum a posteriori regularized methods assuming smoothness or maximum entropy. Our aim in this work is to solve the full Bayesian inference problem by providing access to the posterior distribution of the surface temperature in the star compatible with the observations. Methods. We use amortized neural posterior estimation to produce a model that approximates the high-dimensional posterior distribution for spectroscopic observations of selected spectral ranges sampled at arbitrary rotation phases. The posterior distribution is approximated with conditional normalizing flows, which are flexible, tractable, and easy-to-sample approximations to arbitrary distributions. When conditioned on the spectroscopic observations, these normalizing flows provide a very efficient way of obtaining samples from the posterior distribution. The conditioning on observations is achieved through the use of Transformer encoders, which can deal with arbitrary wavelength sampling and rotation phases. Results. Our model can produce thousands of posterior samples per second, each one accompanied by an estimation of the log-probability. Our exhaustive validation of the model for very high-signal-to-noise observations shows that it correctly approximates the posterior, albeit with some overestimation of the broadening. We apply the model to the moderately fast rotator II Peg, producing the first Bayesian map of its temperature inhomogenities. We conclude that conditional normalizing flows are a very promising tool for carrying out approximate Bayesian inference in more complex problems in stellar physics, such as constraining the magnetic properties using polarimetry.

Comparison Study on Welding Temperature and Joint Characteristics of AZ31 Magnesium Alloy by Ultrasonic and Heat Pipe Assisted FSW

As an important factor in friction stir welding (FSW) process, temperature directly affects the microstructures and mechanical properties of welded joints. The present work aims to investigate the welding temperature and joint characteristics of AZ31 magnesium alloy under three FSW conditions: conventional friction stir welding (FSW), ultrasonic assisted friction stir welding (UaFSW), and ultrasonic and heat pipe assisted friction stir welding (UHaFSW), respectively. The results show that the welding temperature distributions and the characteristic of “non-uniformity” are presented in the FSW and UaFSW joints along the welding and horizontal directions. Compared with conventional FSW, UaFSW can effectively balance and improve the non-uniform temperature distribution in the joints, resulting in the significant decreases in the peak temperatures and durations of high temperature. Hence, the grains are refined in the microstructure of the nugget zone in the UHaFSW joints, which enhances their microhardness and tensile properties. Based on these results, it can be concluded that UHaFSW could be an effective method to improve the mechanical properties of AZ31 magnesium alloy welded joints.

Investigation of Indoor Asymmetric Thermal Radiation in Tibet Plateau: Case Study of a Typical Office Building

The unique climate in cold plateaus leads to long and cold winters, which result in the characteristics and creation of an indoor thermal environment different from that of plain areas. However, there is a lack of detailed research on and evaluation of indoor temperature distributions. This study took an office building in Lhasa as an example to study the indoor non-uniform temperature distributions with radiator and solar radiation. The indoor and outdoor thermal environment parameters were tested. Next, a numerical model was established and verified. On a typical winter weather day, although the average indoor air temperature and radiation temperature in Lhasa are higher than those in Beijing (both are cold areas), the temperature in both is lower than comfortable levels. The indoor vertical air temperature differences are below 3 °C, with a 5% dissatisfaction most of the time. Solar radiation and radiators seriously affect the uniformity of the indoor thermal environment. The radiation asymmetry in Lhasa is significant, and the maximum radiation temperature asymmetry can reach 8.73 °C. In addition, the setting of north-facing windows should be avoided as far as possible in Tibetan areas. Suitable design and evaluation standards should pay attention to the obvious phenomenon of uneven indoor temperature distribution.

Numerical investigations on the aerodynamics and flue gas recirculation of cyclone-fired coal boiler

Cyclone-fired boilers have gained wide applications due to their ability to burn low ash fusion temperature coals that are unsuitable for pulverized coal (PC) firing. In comparison to PC boilers, cyclone-fired boilers exhibit significantly different aerodynamics and the molten slag layer plays a critical role in the operation of boilers. However, by far there are still lack of CFD models that are able to provide effective guidance to the design and operation of cyclone-fired boilers. In this paper a CFD model that was designed to solve the practical problems of cyclone-fired boilers was developed in which the capture of coal particles by the molten slag layer was considered through a slag layer capture model to remove the captured particles from calculation and release the combustion heat of the remaining combustibles. This model was then employed to investigate the aerodynamics and flue gas recirculation (FGR) optimization design of a 550 MW cyclone-fired boiler. The results demonstrated the highly nonuniform characteristics of furnace aerodynamics of cyclone-fired boilers due to the strong swirling flows created by the cyclones that frequently leads to the formation of localized high temperature zones and severe boiler fouling problems. Thus, it is critical to adapt the FGR design with the nonuniform furnace flow and temperature distributions. The simulation results showed that with the adapted FGR design the high temperature zones in the furnace could be effectively eliminated. This study is instrumental for the design of FGR system of cyclone boilers to avoid the potential severe boiler fouling problems.

Adjoint-Based Boundary Condition Sensitivity Analysis

Turbine performance in modern aeroengines is heavily affected by the nonuniform temperature distribution generated in the combustor. The conventional method to study the effect of nonuniform boundary conditions (BCs) is to compare flowfields and performance metrics with the nonuniformity at several typical positions. A much more efficient and intuitive method to analyze the BC sensitivity is proposed in this paper. An inlet guide vane is analyzed as a demonstration. The sensitivity analysis is achieved by pointwise derivatives of objectives with respect to inlet BCs, which are obtained by discrete adjoint method. Furthermore, to study the variation of gradients, a random sampling method that is based on the Gaussian process is proposed to explore the high-dimensional parameter space. When the gradient is invariant within the parameter space, the relationship between objectives and BCs is linear, and the effect of any perturbation of BCs can be directly predicted. In this case, the computational cost of the sensitivity analysis is drastically reduced to one computational fluid dynamics and one adjoint simulation. Interestingly, some gradients are nearly invariant across the parameter space. When the gradient varies, the active subspace method is introduced to reduce the number of dimensions. Then, several models, including the kriging, gradient-enhanced kriging (GEK), and Taylor expansions, are compared to predict objectives. The ordinary kriging model is recommended for its accuracy and stability. The GEK model can also predict the gradient and is a good choice for small BC variations. The method presented here offers a paradigm that extends the gradient-based sensitivity analysis to the global sense, which is suitable for high-dimensional problems such as BCs and spatially varying model parameters.

Full-scale fire tests in the underwater tunnel section model with sidewall smoke extraction

The Hong Kong–Zhuhai–Macau Bridge (HZMB) is a 55-km bridge-tunnel system, including a 6.7-km undersea tunnel that adopts the sidewall smoke extraction system. To evaluate the potential tunnel fire hazards, a 1:1 full-scale HZMB tunnel section model (16 m × 7.2 m × 150 m) was constructed, and eight full-scale tunnel fire tests were conducted with the sidewall smoke extraction. The temperature distribution and smoke movement under different vent arrangements and fire sizes (1.2–6.6 MW) were quantified. Results indicated that the fire HRR was mainly affected by the size of the liquid-fuel pool but insensitive to the arrangement of ventilation. The correlation between HRR and diesel pool-fire area can be fitted by a linear function of HRR=1.24AF-0.87 MW. The sidewall smoke extraction generated a tilted fire plume and non-uniform temperature distribution at the transverse direction, whereas the temperature decay still followed the exponential decay for the far fire field region. The decay factor increases with the increase of the HRR and increases when distributing the ventilation capability into two vent groups. A relatively slow smoke motion (0.8–1.2 m/s) and good smoke stratification were demonstrated in the tests, indicating a robust condition for safe evacuation. This research deepens the understanding of fire and smoke characteristics in tunnels with the sidewall extraction and highlights the importance of full-scale test data in the development of the smart tunnel-fire protection system.

Method for Determining Adiabatic Film Effectiveness in Presence of Thermal Boundary Layer

Abstract In this paper, we present a new method for determining adiabatic film effectiveness in film cooling experiments with nonuniform inlet temperature distributions, in particular the situation of an inlet thermal boundary layer. This might arise in a quasi-steady experiment due to loss of heat from the mainstream flow to the inlet contraction walls, for example. In this situation, the thermal boundary layer would be time-varying. Adiabatic film effectiveness is generally normalized by the difference between mainstream and coolant gas temperatures. Most importantly, these temperatures are generally assumed to be spatially—and, possibly temporally—uniform at the system inlet. In experiments with nonuniform inlet temperature, the relevant hot gas temperature for a particular point of interest on a surface is not easily determined, being a complex function of both the inlet temperature profile and the flow field between the inlet and the point of interest. In this situation, adiabatic film effectiveness cannot be uniquely defined using conventional processing techniques. We solve this problem by introducing the concept of equivalent mainstream effectiveness, a nondimensional temperature for the mainstream that can be used to represent the thermal boundary layer profile at the inlet plane, or the effective temperature of the mainstream gas—which we refer to as the equivalent mainstream temperature—entrained into the mixing layer affecting the wall temperature at a particular point of interest. By using data from two or more time instants during an experiment, we simultaneously solve for equivalent mainstream effectiveness and true adiabatic film effectiveness, that is, the adiabatic film effectiveness that we would measure in an experiment with both steady and uniform inlet temperature. This is an important transformation because the true adiabatic effectiveness has a clear physical interpretation and is a more transportable quantity between systems (comparisons between different experiments, between experiment and computational fluid dynamics (CFD), etc.). The proposed method is experimentally demonstrated using full-surface infrared (IR) thermography measurements of a cooled rotor blade platform, operated in a transonic linear cascade facility at matched engine conditions. Film effectiveness measurements processed in the conventional way suffer from inlet thermal boundary layer effects, rendering them both time-varying (as heat is released to the walls of the tunnel) and, in certain regions, nonphysical in magnitude. The proposed technique renders the same data insensitive to time, and everywhere within physically reasonable limits. By demonstrating independence to the particular (time-varying) inlet temperature profile, we demonstrate the advantages of the proposed technique.

A statistical analysis of thermal characteristics of 55-Ah large-format LIB pouch cell with different tab-type, tab size, and tab position

The non-uniform temperature distribution in large-format lithium-ion batteries (LIBs) can lead to thermal runaway or performance degradation. This study develops a three-dimensional electrochemical–thermal model of a 55-Ah large-format LiFePO4/graphite pouch cell and statistically analyzes the effects of width, height, and attachment positions of the nominal tab (NT), lateral tab (LT), and counter tab (CT) on the temperature distribution. The temperature difference that occurs across the cell is analyzed separately for each design factor through design of experiments (DOE) and analysis of variance (ANOVA). Accordingly, wider tabs reduce the maximum temperature and temperature difference irrespective of the tab type. Taller tabs yield higher maximum temperatures, resulting in a larger temperature difference. Attaching tabs to the edge of the cell increases the maximum temperature and temperature difference. The locations of the negative NTs and CTs do not affect the temperature difference. However, the location of the negative LT increases the minimum temperature, thereby decreasing the temperature difference. The ANOVA revealed that the p-value of the width, height, and attachment position of the positive tab is lower than 0.05 which means the factors strongly influence the temperature difference for all tab-types. Also, the attachment position of the negative tab affects only the LT-type.

Experimental and numerical study on the thermal environment of a data center

Data centers are energy-intensive facilities, and a suitable thermal environment is vital for the safe and reliable operation of information technology equipment and energy saving. In this case study, field experiments and thermal environment evaluation were conducted in an existing data center. However, some problems were reported, including the relative humidity of the rack inlet air exceeding 60%, hot-cold air mixing, non-uniform temperature distribution, local overheating, and a low average temperature difference between the return and supply air of computing room air conditioning units (CRACs). To overcome these dilemmas, three cost-efficient and convenient methods for improving the thermal environment were proposed, including installing blanking panels, closing unnecessary perforated tiles, and increasing the set return air temperature of CRACs. The temperature field and flow field were simulated using the software 6SigmaRoom to predict the effects of the optimization methods. Finally, after the optimization scheme was implemented, field experiments were performed again to examine the application effects of optimization measures. The results demonstrate that the temperature distribution was more uniform, and the thermal environment was considerably improved. Meanwhile, the average temperature difference between the return and supply air of CRACs increased from 6.7 °C to 8.8 °C, resulting in a decrease in the supply air volume of CRACs of about 10903.37 m3/h, and saving the energy consumption of the fans around 96 kWh/day.

Thermal performance of insulated gate bipolar transistor module using microchannel cooling base plate

• Microchannels were proposed for Insulated gate bipolar transistor module cooling. • The performance of two counter-flow microchannel base plate designs was studied. • Horizontal counter-flow microchannel showed a better thermal–hydraulic performance. • Longitudinal vortex generators enhanced heat transfer of the microchannel cooling. The insulated gate bipolar transistor (IGBT) module cannot meet industrial requirements under high-power density due to the high junction temperature and non-uniform temperature distribution. To overcome these problems, two novel microchannel designs (i.e. longitudinal counter-flow microchannel and horizontal counter-flow microchannel) were proposed for the base plate cooling of the IGBT module, in this study. A heat transfer model was developed to investigate the heat transfer performance, pressure drop, temperature distribution of a full-size IGBT module with the proposed microchannel cooling designs. The results showed that the horizontal counter-flow microchannel design had better heat transfer performance, lower pressure drop, more uniform temperature distribution and higher energy efficiency in comparison to the longitudinal counter-flow microchannel cooling design. To further improve the heat transfer performance, longitudinal vortex generators was applied in the horizontal counter-flow microchannel design. It was found that the Nusselt number of the horizontal counter-flow microchannel with longitudinal vortex generators reached 10.86, which increased by 61% compared with the basic horizontal counter-flow microchannel design.

Adaptive Controller Area Network Intrusion Detection System Considering Temperature Variations

Security threats increase as connectivity among vehicles increases. In particular, a lack of authentication, integrity, and confidentiality makes the controller area network (CAN) protocol, which is used in critical domains such as vehicle body and powertrain, vulnerable to threats. In this paper, we propose methods for CAN security enhancement that use a support vector machine (SVM) and the autocorrelation of the received signal to detect a malicious node. Robustness to temperature variation is also considered because autocorrelation is affected by temperature variation. There are two methods based on the degree of uniformity of the temperature distribution. If the temperature is uniformly distributed over the vehicle and the temperature sensor is embedded in the secure node, the first scheme (temperature measurement system) trains data in each segmented temperature range more precisely using multiple classifiers. If not (i.e., a nonuniform temperature distribution or an absence of a temperature sensor), the alternative scheme (all-temperature training system) trains data in all temperature ranges with a single classifier. The performances of the proposed systems are evaluated on a testbed. The proposed method can operate without modifying the CAN protocol because it is based on the characteristics of the physical layer. In addition, security can be enhanced redundantly by the system running independently without authentication protocols.

Temperature non-uniformity detection on dPCR chips and temperature sensor calibration.

A microfluidic-based digital polymerase chain reaction (dPCR) chip requires precise temperature control as well as uniform temperature distribution to ensure PCR efficiency. However, measuring local temperature and its distribution over thousands of μL/nL-volume samples with minimum disturbance is challenging. Here, we present a method of non-contact localized temperature measurement for determination of the non-uniformity of temperature distribution over a dPCR chip. We filled the dPCR chip with a PCR solution containing amplified DNA fragments with a known melting temperature (TM). We then captured fluorescent images of the chip when it was heated from 70 to 99 °C, plotted the fluorescence intensity of each partition as a function of temperature, and calculated measured TM values from each partition. Finally, we created a 3-D map of the dPCR chip with the measured TM as the parameter. Even when the actual TM of the PCR solution was constant, the measured TM value varied between locations due to temperature non-uniformity in the dPCR chip. The method described here thereby characterized the distribution of temperature non-uniformity using a PCR solution with known TM as a temperature sensor. Among the non-contact temperature measurement methods, the proposed TM-based method can determine the temperature distribution within the chip, instead of only at the chip surface. The method also does not suffer from the undesirable photobleaching effect of fluorescein-based temperature measurement method. Temperature determination over the dPCR chip based on TM allowed us to calibrate the temperature sensor and improve the dPCR configuration and precision. This method is also suitable for determining the temperature uniformity of other microarray systems where there is no physical access to the system and thus direct temperature measurement is not possible.

Experimental thermal and electrical performance analysis of a concentrating photovoltaic/thermal system integrated with phase change material (PV/T-CPCM)

Applying compound parabolic concentrator (CPC) and phase change materials (PCMs) in photovoltaic/thermal (PV/T) systems are effective methods to promote the electrical and thermal performance simultaneously. Much work has intensively investigated the performance enhancement of separate PV/T-CPC or PV/T-PCM system and conducted experiments under lab environment. However, there were few studies devoted to the thermal and electrical performance collaborative improvement especially at an actual outdoor environment. In this study, a compound parabolic concentrating PV/T system integrated with PCM (PV/T-CPCM) is constructed and different parameters are analyzed in an open-air environment. As solar irradiance and ambient temperature vary during the test period, PCM melts from solid to mushy state, and the temperature non-uniformity factor of PV modules/PCM drops from 4.28/1.34 to 1.42/0.66, indicating the PCM obviously improves the non-uniformity of temperature distribution. Set the pump state as OFF-ON-OFF, PV modules temperature firstly rises from 10.6 °C to 33.2 °C, then quickly drops down to 28.5 °C, and after that slowly drops down to 27.1 °C, showing the combination of PCM and liquid cooling is beneficial to further reduce the PV modules temperature. During the pump-on period, the instantaneous thermal, electrical and primary energy efficiency decrease from 19.6% to 5.0%, 4.8%–3.0%, 30.4%–16.8%, and the averaged values are 7.1%, 4.0% and 17.6%, respectively. The maximum primary energy efficiency of the PV/T-CPCM system is about 7.9% and 10.7% higher than that of the separate PV-CPC and PT-CPC system respectively, demonstrating that the PV/T-CPCM system owns superior heat-electricity cogeneration performance.

Temperature non-uniformity due to heat conduction and radiation in the pulse calorimetry technique

The paper presents an assessment of the unwanted temperature non-uniformity found in high temperature applications of the pulse calorimetry technique. Specimens in the form of a solid cylinder undergoes fast electrical heating and an intense heat radiation at high temperatures, coupled with the heat conduction the specimens? cold ends, make them having a highly non-uniform temperature distribution, both in their radial and axial directions. By using finite element method simulations of a typical pulse calorimetry experiment, the temperature non-uniformity across the specimen diameter and along the specimen effective length has been estimated for different specimen dimensions and materials, as well as for different heating rates. The obtained results suggest that an optimization of experimental parameters, such as the specimen diameter, specimen total and effective length and heating rate, is needed for minimization of the temperature non-uniformity effect.

Measurements of surface temperature distributions on coal dust particles

The rate of thermochemical conversion of solid fuel depends strongly on temperature. However, temperature can vary significantly across a single particle's surface and can locally change reactivity for combustion. To account for this phenomenon in numerical models, we carried out an experimental investigation of the temperature profiles for particles obtained from two chars prepared from hard coal and lignite. We used a custom-built, two-color pyrometer to measure surface temperature distributions for particles with an approximate diameter of 100 μm. We used CCD cameras as detectors what allowed for measure temperature with high resolution. The applied research method allowed for the analysis of thousands of individual particles in different conditions. We carried out experiments under O2/N2 and O2/CO2 atmospheres with the oxidizer concentration between 10 and 30% (vol%). We observed highly non-uniform temperature distributions on the surface of the reacting particles with differences greater than 100 K. The standard deviation of the surface temperatures increased with the mean temperature of the particles. The observed variations could be due to inherent particle heterogeneity for ash content, porosity, and shape. Non-uniform temperature profiles and reactivities may alter the Stefan flow at the outer surface of the particles, affecting the mass and heat transfer balance and changing the trajectory of the particles as they move through the combustion chamber. Therefore, the correction factors determined in this study may be applied to existing numerical models of solid fuel combustion.

Study of Alloy Hot Flow and Hardening Behavior Using a New Correction Method for Hot Uniaxial Tests

The precise characterisation of hot flow behavior of titanium alloys is of vital importance for practical hot forming processes. To precisely determine the hot flow behavior of titanium alloys under the forming conditions, Gleeble hot tensile tests are usually performed to simulate the forming processes by accurately controlling the deformation temperatures and strain rates under designed conditions. However, there exists a non-uniform temperature distribution during the Gleeble tests, which leads to inaccuracies in the determined hot flow behavior. To overcome such an issue, this paper proposed a new strain-based correction method for Gleeble hot tensile tests, enabling the mitigation of the non-uniform temperature-induced stress-strain curve inaccuracies. The non-uniform temperature zones have been successfully excluded in the calculation of the true strain levels. A series of hot uniaxial tensile tests of TA32 at temperatures, ranging from 750 °C to 900 °C, and strain rates, 0.01/s~1/s, were carried out. The obtained stress-strain correlations for a large gauge zone were characterized using the new correction method, which was further used to evaluate the hardening behavior of titanium alloys. The results have shown that the ductility, strain hardening component (i.e., n), strain rate hardening component (i.e., m) and uniform strain value (i.e., εu) are over-estimated, compared to conventional method. Higher strain rates and lower temperature leads to enhanced hardening behavior. This research provides an alternative correction method and may achieve more accurate stress-strain curves for better guidance of the hot forming process for titanium alloys.