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Hot deformation behavior of the maraging stainless steel is studied in temperature range from 900 to 1150 °C and strain rate from 0.1 to 10 s−1. When the deformation temperature is 900−950 °C, the abnormal stress increase is observed at the end of the flow curves. Transmission electron micrographs reveal that the Laves phase at the interface between prior austenitic (γ) and high‐temperature ferrite (δ) impedes hot deformation. The microstructure analysis shows that the dynamic recrystallization (DRX) mechanism of γ and δ is discontinuous DRX and continuous DRX, respectively. When the specimens are deformed at 950 °C, the extent of DRX at a strain rate of 5 s−1 is higher than at 0.1 s−1. This anomaly is due to adiabatic heating causing the actual deformation temperature at high strain rate (ε.$\overset{.}{\epsilon}$) to be higher than at low ε.$\overset{.}{\epsilon}$, indicating that DRX is more influenced by temperature compared to ε.$\overset{.}{\epsilon}$. The influences of adiabatic heating and friction are corrected. Strain‐dependent constitutive equation is developed based on the revised flow curves, yielding an average absolute relative error of 4.69% and a correlation coefficient of 0.99; the prediction accuracy exceeds 90% when the relative error is within 10%. [ABSTRACT FROM AUTHOR]

A split Hopkinson pressure bar was used to perform dynamic compression experiments on HS-Q&P steel at the strain rates of 0-12000 s-1. The deformation behavior of the specimen during dynamic compression was studied by SEM, EBSD, XRD characterization methods. The results show that the deformation behavior of the experimental steel at different rates is similar and is divided into three stages. First, there is a slight increase in stress at the platform, but the increase is more reflected in the strain. The adiabatic heating effect that occurs during the compression process will bring a softening effect. The strength and plastic deformation ability of the experimental steel can be improved by the retained austenite. The volume fraction of retained austenite in steel reduced by the transformation induced plasticity (TRIP) effect is the same as the volume fraction of martensite increased and proves the TRIP effect is the main strengthening mechanism in the steel. At the same time, it is observed by SEM that the retained austenite is transformed into acicular martensite by the TRIP effect. As the strain rate increases, the lattice distortion becomes more and more serious, and some deformation twins can be observed in the EBSD maps. At different strain rates, 〈001〉oriented grains are more likely to produce deformation twins.

Complex concentrated alloys (CCAs) are structural and functional materials of the future with excellent mechanical, physical, and chemical properties. Due to the equiatomic compositions of these alloys, cost can hinder scalability. Thus, the development of CCA-based coatings is critical for low-cost applications. The application of cold spray technology to CCAs is in its infancy with emphasis on transition elements of the periodic table. Current CCA-based cold spray coating systems showed better adhesion, cohesion, and mechanical properties than conventional one-principal element-based alloys. Comprehensive mechanical behavior, microstructural evolution, deformation, and cracking of cold spray CC-based coatings on the same and different substrates are reviewed. Techniques such as analytical models, finite element analysis, and molecular dynamic simulations are reviewed. The implications of the core effects (high configurational entropy and enthalpy of mixing, sluggish diffusion, severe lattice distortion, and cocktail behavior) and interfacial nanoscale oxides on the structural integrity of cold spray CCA-based coatings are discussed. The mechanisms of adiabatic heating, jetting, and mechanical interlocking, characteristics of cold spray, and areas for future research are highlighted. [ABSTRACT FROM AUTHOR]

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The six-hourly ERA-interim reanalysis data were used to analyze the intraseasonal oscillation (ISO) characteristics of the zonal wind in the exit region of the East Asian subtropical westerly jet (EAJ) during the winter (November to April). The results indicate that from East Asia to the North Pacific, the zonal wind in the upper troposphere shows significant 10–40-day oscillations, propagating eastward toward the jet exit region. The strength of the intraseasonal zonal wind anomaly increases from the lower troposphere to the upper troposphere, reaching a peak between 300 and 200 hPa. The zonal wind ISO in the jet exit area is closely related to the intraseasonal inverse temperature tendency between the north and south of the jet exit in the troposphere. In the acceleration (deceleration) phase of the intraseasonal west wind, the air temperature decreases (increases) in the north of the exit and increases (decreases) in the south of the exit. The intraseasonal temperature tendency is stronger in the north of the EAJ exit than that in the south. In the north of the EAJ exit, the intraseasonal temperature tendency is decided by the temperature advection, where the whole troposphere is controlled by the north wind in the west wind acceleration phase and controlled by the south wind in the west wind deceleration phase, so the intensity of temperature advection is strong. However, adiabatic heating plays a decisive role in affecting the temperature evolution in the south of the jet exit area, and the intraseasonal meridional wind is the opposite between the mid-upper troposphere and the lower troposphere, resulting in weak temperature advection and the weak temperature tendency. Therefore, although the zonal wind ISO in the jet exit area is the result of the joint action of the ISOs in different latitudes, the influence of mid-high latitudes is particularly important. [ABSTRACT FROM AUTHOR]

Initiation of motion in a supercritical natural circulation loop is explored over a wide range of heater power, in an endeavor to correlate the inherent microdynamics with the regimes of heat transfer. It is impossible to predict the first direction of bulk movement, as well as the time required to attain that from quiescent condition, in a symmetric orientation, necessitating comprehensive computation. Development of recirculation vortices at both ends of the heating section, owing to the discontinuity in thermal boundary condition there, is earmarked as the first reason of instigating motion. Temperature of supercritical fluid outside the vortex fronts is found to increase uniformly till the merger of both the vortices, and it is accredited to the appearance of piston effect. Realization of such adiabatic heating in closed loops is a novel identification. Rayleigh-Taylor-type instability appears interior to the heater, resulting in chaotic patterns in the fluid segment entrapped between the two propagating fronts, forcing the system to deviate from symmetry, and accordingly enforcing the first direction of motion. Adiabatic heating is more prominent at lower powers, while the greater rate of temperature rise at higher powers allows an early dominance of buoyancy, with the thermodynamic state of the system quickly veering away from the critical point. Every loop undergoes a pair of flow reversals following the first motion to adapt to the high level of initial buoyancy and large circulation rate. While the system promptly achieves a steady-state at lower powers, it may continue to exhibit chaotic oscillations with repetitive flow reversals at higher powers, without attainment of any steady-state. • Numerical simulation of initiation of motion in symmetric supercritical loop. • Discontinuity in thermal boundary condition at heater ends initiates recirculation. • Uniform near-linear temperature rise over bulk of loop owing to adiabatic heating. • Rayleigh-Taylor-type instability between two propagating fronts instills asymmetry. • Buoyancy-dominance at higher powers, leading to chaotic oscillations and reversals. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of strain rate on the work hardening, strain-induced martensite transformation, strain partitioning, and crystallographic variant selection in a medium-Mn steel. Uniaxial compression tests were performed under quasi-static and dynamic loading conditions at the strain rates of 1 0 − 3 , 1 and 1 0 3 s − 1 . Besides, to determine the contribution of temperature rise due to adiabatic heating at a higher strain rate, compression tests were carried out at 409 K (estimated temperature rise) under quasi-static conditions. The work hardening rate was higher at high strain rates and it rapidly decreased at all strain rates up to a true plastic strain of ∼ 0.05. Beyond the true plastic strain of ∼ 0.05, the work hardening rate increased at a low strain rate up to a true plastic strain of ∼ 0.15 while at a high strain rate, it remained relatively constant and gradually decreased beyond a true plastic strain of ∼ 0.15. From the analysis of microstructures obtained from electron backscatter diffraction, it was observed that the strain-induced transformation of retained austenite to α ′ -martensite is significantly impeded at higher strain rates and in the sample tested at 409 K at low strain rates. The higher stability of retained austenite is attributed to the adiabatic heating which decreases the chemical driving force for retained austenite to martensite phase transformation and increases the stacking fault energy. Analysis of the misorientation axis and angle evolution revealed that while the Kurdjumov–Sachs relationship was followed under quasi-static conditions, it deviated at higher strain rates. Analysis of crystallographic variants related to strain-induced martensitic transformation at a true plastic strain of ∼ 0.15 revealed that the samples deformed at a lower strain rate did not show any noticeable variant selection. However, in samples deformed at a higher strain rate, a significant variant selection was observed. It is reasoned that the martensitic transformation nucleates initially on favorably oriented habit planes of retained austenite grains at all strain rates and other variants get activated with an increase in strain. As the transformation is impeded beyond a critical strain at a higher strain rate, the variants activated at lower strains remains predominant. [Display omitted] • Post-critical strain, lower work hardening is observed in high strain rate condition • The strain induced α ′ martensite transformation is suppressed at higher strain rates • High strain rates and the associated adiabatic heating stabilize retained austenite • Adiabatic heating lowers the driving force for transformation and enhances the SFE • At high strain rates, transformation is restricted to favorably oriented habit planes [ABSTRACT FROM AUTHOR]

In this work , in - situ high-energy X-ray diffraction was used to analyze the effects of strain rate and austenite (γ) grain orientation on the strain-induced martensitic transformation in metastable austenitic stainless steel 301LN. The diffraction measurements were carried out at strain rates ranging from 10−3 s−1 to 1 s−1 continuously without interrupting the experiment and thus creating nearly adiabatic conditions at the highest studied strain rate. The results indicate that <100>γ fiber-oriented grains preferentially transform at the strain rate of 10−3 s−1 when the true strain is above 0.10, whereas the <111>γ fiber-oriented grains transform only at later stages of plastic deformation. The phase transformation rate of the <111>γ and <100>γ fiber-oriented grains decreases with increase in strain rate. A theoretical model based on stacking fault width as a function of external stress and temperature (stacking fault energy) was used to predict lower-bound estimates for the critical tensile stress needed to start ε-martensite and α'-martensite phase transformations. The model can predict the experimentally observed phase transformation behavior of the <111>γ fiber orientations at all strain rates but is unable to predict the decrease of phase transformation rate of <100> fiber-oriented γ grains with increase in strain rate, which could be related to change in dislocation structure. • The α'-martensite volume fraction decreases from 0.86 to 0.26 when strain rate is increased from 10−3 s−1 to 1 s−1. • The development of <111> and <100> double fiber texture parallel to the tensile direction was observed in parent austenite (γ) grains. • The phase transformation rate, especially in the <111>γ fiber, is sensitive to changes in SFE. • The calculated macroscopic critical stress levels required for formation of wide stacking faults at different SFE values were compared with experimental observations. [ABSTRACT FROM AUTHOR]

Identification and understanding of persistent regional heat wave are essential for adaption and alleviation of its severe effects on human health and ecological environment, particularly under the situation of rapid global warming. Based on Climate Prediction Center global daily maximum temperature from 1979 to 2019, considering extreme, persistence and regionality of heat wave, summer regional pentad heat wave (RPHW) is defined by summer daily maximum temperature above 35°C with no less than 3 days in a pentad, which is also required to cover more than 2% grids over the eastern China. It breaks down the continuity constraints in both time and space in previous regional heat wave definitions that mainly indicate the synoptic phenomena. Besides, our RPHW is much useful in examining climatic features of regional heat wave, since it filters out the weather noises to some extend in terms of a pentad window. Three categories of RPHW are identified by K-means cluster analysis over the eastern China, i.e., North-Central China (NCC), Central China (CC), and South China (SC). Generally, intensity and area of RPHW are positively proportional to each other, and more RPHW appears in SC but with weaker intensity, whereas less RPHW locates in NCC and CC with stronger intensity. While RPHW in CC and SC mostly appears in middle-late summer, RPHW in NCC mainly occurs in early-middle summer which is transferred from the middle-late summer before the late 1990s. Most RPHW persists for one pentad and occasionally for five or six pentads at most. And both frequency and accumulated days of RPHW have been significantly increased since the late 1990s, particularly in CC and SC. Significant high-pressure anomalies are accompanied with the RPHW in China, which favor more incoming net solar radiation, increasing surface soil temperature, and more upward surface longwave radiation and sensible heat flux as well, eventually forming the RPHW. Specifically, the RPHW in NCC and SC are mainly caused by diabatic heating from the land surface and adiabatic heating due to the anomalous subsidence movement, respectively; however, both the diabatic heating and the adiabatic heating are responsible for the RPHW in CC.

The six-hourly ERA-interim reanalysis data were used to analyze the intraseasonal oscillation (ISO) characteristics of the zonal wind in the exit region of the East Asian subtropical westerly jet (EAJ) during the winter (November to April). The results indicate that from East Asia to the North Pacific, the zonal wind in the upper troposphere shows significant 10–40-day oscillations, propagating eastward toward the jet exit region. The strength of the intraseasonal zonal wind anomaly increases from the lower troposphere to the upper troposphere, reaching a peak between 300 and 200 hPa. The zonal wind ISO in the jet exit area is closely related to the intraseasonal inverse temperature tendency between the north and south of the jet exit in the troposphere. In the acceleration (deceleration) phase of the intraseasonal west wind, the air temperature decreases (increases) in the north of the exit and increases (decreases) in the south of the exit. The intraseasonal temperature tendency is stronger in the north of the EAJ exit than that in the south. In the north of the EAJ exit, the intraseasonal temperature tendency is decided by the temperature advection, where the whole troposphere is controlled by the north wind in the west wind acceleration phase and controlled by the south wind in the west wind deceleration phase, so the intensity of temperature advection is strong. However, adiabatic heating plays a decisive role in affecting the temperature evolution in the south of the jet exit area, and the intraseasonal meridional wind is the opposite between the mid-upper troposphere and the lower troposphere, resulting in weak temperature advection and the weak temperature tendency. Therefore, although the zonal wind ISO in the jet exit area is the result of the joint action of the ISOs in different latitudes, the influence of mid-high latitudes is particularly important.

Here, we present a systematic experimental study and accompanying theoretical analysis of the dependence of ductile fracture on strain localization, strain hardening rates, deformation-induced thermal softening, and transient heat conduction under spatially uniform as well as spatially heterogeneous deformation. Spatially uniform cases are studied via standard dogbone shaped specimens subject to uniaxial tension. Spatially heterogeneous deformation is studied via the so-called Sandia Fracture Challenge (SFC) specimen, which is a standard compact tension specimen modified with three machined holes in front of a blunt notch (Boyce et al. in Int J Fract 186(1–2):5–68, 2014). We utilize the same precipitation hardened martensitic stainless steel used in the first SFC experiments, i.e. 15-5 PH with an H1075 heat treatment. We also study 15-5 PH in Condition A and with the H900 heat treatment, each of which has a different hardening behavior and ductility. We find that the ductility does not correlate with the deformation to first crack initiation in the SFC specimen. Instead, hardening rates are better correlated. Moreover, a re-examination of (Boyce et al. in Int J Fract 186(1–2):5–68, 2014) finds that an accurate calibration of the hardening rates is strongly correlated with accurate blind predictions of ductile fracture in the SFC specimens. Given that thermal softening can greatly affect hardening rates, we provided a thermographic analysis of deformation-induced heating and transient heat transfer in both the dogbone shaped samples and the SFC specimens. Transient heating in stainless steels is found to have first-order effects on the strain at the onset of necking, strain to fracture, as well as strain localization and ductile fracture in complex geometries even under so-called quasi-static loading rates. [ABSTRACT FROM AUTHOR]

Analysis of three different equations of state suitable for describing fluids near the thermodynamic critical point is performed. Numerical simulation of the piston effect (adiabatic heating) with the use of the equations of state is carried out. The range of temperature distances to the critical point in which the calculated time of the piston effect is equal to the analytical time is defined. The reasons of discrepancy between the calculated and analytical times of the piston effect beyond the range defined is discussed. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructural evolution under dynamic loading conditions are of paramount importance in the development and utilization of interstitial high-entropy alloys (iHEAs). This study focuses on the investigation of a currently trending material, C-doped TRIP-assisted HEA Fe 49.5 Mn 30 Co 10 Cr 10 C 0.5 (at.%). By subjecting the alloy to uniaxial quasi-static and dynamic tensile loading, the study systematically elucidates mechanical property testing under different strain states, characterizes the microstructural evolution during deformation, analyzes deformation mechanisms, and delves into the essence of mechanical responses. Particularly, by employing digital image correlation (DIC) techniques, local severe deformation regions under high-speed deformation conditions are sampled to investigate microstructural changes under extreme deformation conditions. The results indicated that, in comparison to quasi-static tensile deformation, the dynamic tensile deformation of the HEA demonstrated a slight increase in yield strength, a decrease in ultimate tensile strength, and a trend toward an increase in total elongation. Specifically, at a strain rate of 103 s−1, the tensile strength was ∼825.5 MPa, and at a strain rate of 10 s−1, the elongation was ∼57.7 %. In quasi-static deformation, the TRIP and TWIP effects served as the primary deformation mechanisms. In dynamic deformation, the proportion of ε-martensite phase transformation was significantly reduced, with deformation twinning (DT) and dislocations becoming the dominant mechanisms, originating from the impact of adiabatic heating on the stacking fault energy (SFE). Furthermore, in the locally severe deformation region, multiple twinning systems were activated, coupled with a substantial accumulation of dislocations. A minor presence of dual-oriented martensite also contributed to this complex mechanism. Additionally, the carbides formed through C-doping exerted a significant hindrance on dislocation slip during high-speed deformation and under high-strain conditions. Simultaneously, they promoted the activation of multiple twinning systems, making an indispensable contribution to maintaining the strain hardening rate (SHR) of the HEA. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive evaluation of artificial neural networks (ANNs) for predicting adiabatic compression heating in high-pressure processing (HPP) and high-pressure thermal processing (HPTP). The ANNs were thoroughly compared with experimental data, as well as data predicted by a previously developed approach. This previous approach used numerical methods to extract relevant material properties from experimental data, which was then used for compression heating predictions by solving an ordinary differential equation. The new work showcases the efficacy of ANNs in accurately predicting compression heating effects. The results indicate that ANNs offer a robust, flexible, and efficient approach for modelling adiabatic heating, with significant implications for the design and optimisation of HPTP treatments. The study underscores the transformative potential of AI in advancing food preservation technologies. • Artificial Neural Networks excel in predicting compression heating for liquids and solids. • Excellent agreement of predictions with experimental data. • Enhanced previously developed numerical approach significantly. [ABSTRACT FROM AUTHOR]

The tensile deformation behavior of an Mn–N bearing lean duplex stainless steel (LDSS) with metastable austenite was investigated at the strain rate range of 10−4 - 100 s−1. The mechanical response and microstructural evolution at various strain rate was characterized and in particular, the influence of strain rate on the work hardening, strain-induced martensitic transformation (SIMT) and fracture mechanism was focused on. The results show that the deformation of austenite dominates the overall work hardening and damage mode of the test LDSS. At the strain rate of 10−4 s−1, the test LDSS exhibits excellent strength-ductility combinations with ultimate tensile strength (UTS) of 928 MPa and total elongation (TEL) of 59 %, which are attributed to the occurrence of the SIMT with a typical sequence of γ→ε→α′ and resultant transformation induced plasticity (TRIP) effect. However, the increasing strain rate suppressed the TRIP effect, causing a negative correlation between UTS/TEL and strain rate, because the elevated temperature rise (Δ T) resulting from the adiabatic heating effect promoted increased austenite stability and decelerated SIMT kinetic. Especially at the case of 100 s−1, the higher T a (average temperature ∼ 23 + 38 = 61 °C), which is close to the M d temperature (the critical temperature up to which martensite formation can be forced by mechanical stress, ∼ 60 °C), leads to a significant increase in stacking fault energy (SFE) within the austenite. Consequently, the microstructural evolution during austenite deformation does not exhibit pronounced SIMT but rather maintains limited twinning. Although the samples deformed at various strain rates exhibit a dimple-type fracture mechanism, the secondary cracking on the fracture faces becomes more pronounced (i.e., reduced fracture resistance) with the decreasing strain rate. Crack initiation frequently appears at the interface of γ/α (or α′/α) for all strain rate cases because of the strain partitioning among constituents, moreover, at lower strain rates (≤10−2 s−1), the cracks inside of the α′-martensite are another damage site, which is responsible for the degradation of fracture resistance. • Pronounced strain rate-dependence in the tensile deformation behavior of LDSS. • Adiabatic heating effect alters the stacking fault energy, subsequently influencing the deformation mechanism. • Strain rate did not alter the fracture mode but rather influenced the damage evolution. • Lower strain rate sample exhibited excellent mechanical properties and damage tolerance due to the TRIP effect. [ABSTRACT FROM AUTHOR]

We investigated the early-stage development of cyclones occurring in the strong baroclinic regions in the Northwest Pacific and the Northwest Atlantic based on European Center for Medium-range Weather Forecasts Re-Analysis-Interim (ERA-Interim) data. The composite background conditions corresponding to the cyclones on the onset day are characterized by upper troposphere divergence of westerly jet ahead of a trough, low troposphere convergence of westerly jet behind a trough, and strong meridional air temperature gradient (baroclinicity) both in the Northwest Pacific and the Northwest Atlantic, but with stronger baroclinicity in the Northwest Pacific. The composite velocity and temperature fields of the cyclone on the onset day show a clear horizontal front and a westward and northward vertical tilting of cyclonic circulation to the cold zone. The composite Northwest Pacific cyclone filed on the onset day has a warm core, whereas the composite Northwest Atlantic cyclone field has a cold core in the low troposphere. The leading adiabatic processes that contribute to the developing of the cold core cyclone in the Northwest Atlantic on the onset day is the temperature advection, while stronger vertical motion induces stronger adiabatic warming in the Northwest Pacific cyclones, which has a significant contribution to the development of warm core cyclones on the onset day.

The "Western Tibetan Vortex" (WTV)—also termed the Karakoram Vortex—dominates the middle-to-lower troposphere and the near-surface air temperature variability above the western Tibetan Plateau (TP). Here, we explore the thermodynamic mechanisms through which the WTV modulates air temperature over the western TP by diagnosing the three major terms of the thermodynamic energy equation—adiabatic heating, horizontal temperature advection, and diabatic heating—that maintain the atmospheric thermal balance. We composite these major terms to examine the differences between anti-cyclonic and cyclonic WTV events. Our theoretical approach demonstrates that adiabatic sinking-compression (rising-expansion) provides the overwhelming control on both the middle-to-lower tropospheric and lower stratospheric temperature increases (decreases) under anti-cyclonic (cyclonic) WTV conditions over the western TP high mountain area in all four seasons. This also explains the mechanisms behind the anomalous temperature "dipole" found between the mid-lower troposphere and lower stratosphere when the WTV was initially identified. Spatially, adiabatic heating effects are centred on the central western TP in summer and the south slope centring at 70°–80°E of the TP in other seasons. The other two terms, horizontal temperature advection and diabatic heating, have localized importance over the edges of the western TP. In a case study over the Karakoram area, we further demonstrate that adiabatic heating (rising-expanding-cooling/sinking-compressing-warming) is the dominant thermodynamic process controlling Karakoram air temperatures under WTV variability, except for at the very near surface in autumn and winter. Our analysis methods can be applied to investigate the thermodynamic processes of other atmospheric circulation systems or climate variability modes. [ABSTRACT FROM AUTHOR]

In this work, the effects of strain rate and adiabatic heating on the strain induced martensitic phase transformation were uncoupled and individually evaluated. Tension tests were performed at different strain rates ranging from 2 × 10−4 s−1 to 1400 s−1, covering both isothermal and adiabatic conditions. The adiabatic temperature rise of a sample tested at a high strain rate was replicated with heating resistors in a normally isothermal low strain rate test. This test allows studying the mechanical behavior and microstructural evolution of the material at a very low strain rate at thermal conditions similar to that of a high strain rate test. The phase transformation rates from austenite to α′-martensite were measured with the magnetic balance method. The phase transformation rate drops significantly with increasing strain rate. At a higher strain rate, the α′-martensite nucleates primarily on a single habit plane parallel to the primary slip plane of the parent austenite, while at a lower strain rate the α′-martensite nucleation occurs on several habit planes. At the studied plastic strains, the strain rate seems to have a stronger effect on the α′-martensite formation than the adiabatic heating. This is supported by thermodynamic stacking fault calculations, which indicate that the increase in the stacking fault energy due to adiabatic heating at low strains is small and therefore unlikely the only reason for the reduced phase transformation rate. Therefore, the strain rate itself seems to have an important role in the strain induced martensitic phase transformation rate. Image 1 [ABSTRACT FROM AUTHOR]

To investigate the microstructure evolution of powder metallurgy (P/M) superalloys during high-strain-rate deformation, a P/M nickel-base superalloy is subjected to thermal compression at temperatures ranging from 1000 °C to 1100 °C and strain rates ranging from 1 s−1 to 10 s−1. The analysis regarding the flow behaviors and microstructure observation indicates that discontinuous softening is significant at high strain rates. Moreover, based on experimental measurement and theoretic estimation, the adiabatic heating under high-strain-rate deformation is hardly neglectable, which enhances the dynamic softening via dynamic recovery (DRV), dynamic recrystallization (DRX), and grain growth. In order to obtain refined and homogeneous grains, deformation at temperature range of 1025–1050 °C with strain rate rang of 1–10 s−1 or at 1000 °C/1 s−1 is suggested for high-strain-rate compression on the P/M superalloy, where DRX plays more dominating roles. • Discontinuous hardening and softening are observed at high-strain-rate compression. • The adiabatic heating under higher strain rate is more significant. • A processing window is preferred to obtain refined grains after high-speed deformation. [ABSTRACT FROM AUTHOR]

Abstract Fiber reinforced polymer matrix composites are increasingly being used to fabricate energy-absorbing aerospace structural components susceptible to impact loading, such as jet engine containment structures subjected to blade-out events. The development and certification of such structures necessitates a detailed understanding of the dynamic behavior of the constituent materials, particularly the strain rate, temperature, and pressure dependent polymer matrix, and their complex interaction. As the rate of deformation increases, the thermodynamic condition transitions from isothermal to adiabatic. The conversion of plastic work to heat causes local adiabatic heating in the polymer matrix, but the rapid nature of impact events does not allow sufficient time for heat to dissipate; ballistic impact events can therefore be regarded as fully adiabatic. Local adiabatic heating can significantly affect the high rate deformation response if thermal softening effects outweigh strain and strain rate hardening effects and therefore, must be explicitly modeled at the appropriate length scale. In this paper, an existing isothermal viscoplastic strain rate and pressure-dependent polymer constitutive formulation is extended to nonisothermal conditions by modifying the inelastic strain rate tensor components to explicitly depend on temperature based on the Arrhenius equation for nonisothermal processes. A methodology based on shifting neat resin dynamic mechanical analysis data is utilized to determine the polymer elastic properties over a range of strain rates and temperatures. Temperature rises due to the conversion of plastic work to heat are computed, assuming adiabatic conditions. It is demonstrated that the modified polymer constitutive model is capable of capturing strain rate and temperature dependent yield as well as thermal softening associated with the conversion of plastic work to heat at high rates of strain. The nonisothermal polymer constitutive model is then embedded within the Generalized Method of Cells micromechanics framework to investigate the manifestation of matrix thermal softening, due to the conversion of plastic work to heat, on the high strain rate response of a T700/Epon 862 unidirectional composite. Adiabatic model predictions for high strain rate composite longitudinal tensile, transverse tensile, and in-plane shear loading are presented. Results show a substantial deviation from isothermal conditions; significant thermal softening is observed for matrix dominated deformation modes (transverse tension and in-plane shear), highlighting the importance of accounting for local adiabatic heating in the polymer matrix in the high strain rate analysis of polymer matrix composite structures. [ABSTRACT FROM AUTHOR]

Electrodynamic actuators are used in hybrid switching systems where a very quick contact separation as well as operation repeatability and long-term reliability are required. The article presents selected results of thermal studies in the electrodynamic drive system. Study was carried out on the basis of the 3D electromagneto-thermal model implemented in the Ansys_Maxwell environment. The present model allows to determine the critical parameters related to the heating and to guarantee the correct and repeatable operation of the actuator. [ABSTRACT FROM AUTHOR]

Highlights • Nanomachining of glassy polymer is carried out below the depth of 200 nm. • Shear banding occurs when the depth of cut or cutting speed exceeds critical value. • Finite element analysis is conducted using a viscoplastic model accounting for adiabatic heating. • Adiabatic heating causes the formation of shear band in nanomachining of polymer. Abstract This paper discusses the shear banding phenomenon which took place during nanomachining of an amorphous glassy polymer. The nanomachining were carried out with varying machining conditions (depth of cut, machining speed), and the morphologies of the machined surfaces were characterized using atomic force microscopy. The experiments reveal the occurrence of shear band as the critical machining condition is reached. The shear banding was rationalized by the effect of adiabatic heating during machining. Finite element modelling of nanomachining was conducted using an existing elastic-viscoplastic model for this polymer, which accounts for the adiabatic heating due to plastic dissipation. The simulation was then compared with the experiment. It shows that the simulation can capture the main features of shear banding in nanomachining, indicating that the machining is controlled by a localized deformation mechanism. This work can be helpful in optimizing the processing parameters to improve the surface quality of optical products. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Micro-injection moulding (µ-IM) is a fabrication method that is used to produce miniature parts on a mass production scale. This work investigates how the process parameter settings result in adiabatic heating from gas trapped and rapidly compressed within the mould cavity. The heating of the resident air can result in the diesel effect within the cavity and this can degrade the polymer part in production and lead to damage of the mould. The study uses Autodesk Moldflow to simulate the process and identify accurate boundary conditions to be used in a gas law model to generate an informed prediction of temperatures within the moulding cavity. The results are then compared to physical experiments using the same processing parameters. Findings from the study show that without venting extreme temperature conditions can be present during the filling stage of the process and that venting solutions should be considered when using µ-IM.

The radiation belts and magnetospheres of Jupiter and Saturn show significant intensities of relativistic electrons with energies up to tens of megaelectronvolts (MeV). To date, the question on how the electrons reach such high energies is not fully answered. This is largely due to the lack of high‐quality electron spectra in the MeV energy range that models could be fit to. We reprocess data throughout the Galileo orbiter mission in order to derive Jupiter's electron spectra up to tens of MeV. In the case of Saturn, the spectra from the Cassini orbiter are readily available and we provide a systematic analysis aiming to study their acceleration mechanisms. Our analysis focuses on the magnetospheres of these planets, at distances of L > 20 and L > 4 for Jupiter and Saturn, respectively, where electron intensities are not yet at radiation belt levels. We find no support that MeV electrons are dominantly accelerated by wave‐particle interactions in the magnetospheres of both planets at these distances. Instead, electron acceleration is consistent with adiabatic transport. While this is a common assumption, confirmation of this fact is important since many studies on sources, losses, and transport of energetic particles rely on it. Adiabatic heating can be driven through various radial transport mechanisms, for example, injections driven by the interchange instability or radial diffusion. We cannot distinguish these processes at Saturn with our technique. For Jupiter, we suggest that the dominating acceleration process is radial diffusion because injections are never observed at MeV energies. Plain Language Summary: Space is filled with a radiation of protons and electrons moving with almost light speed. While in free space this is cosmic radiation of extreme energies, magnetized planets trap radiation particles of lower energies, typically in the megaelectronvolt range. These are the so called radiation belts that are found, for example, around Jupiter, Saturn, and Earth. All radiation particles initially start out from being almost at rest and are over time accelerated to almost light speed. The physical mechanisms responsible for this are the subject of ongoing research. Here we focus on the processes accelerating electrons around Jupiter and Saturn based on data from the Galileo and Cassini orbiters. During their life, electrons change their orbits around a planet, get closer to the planetary surface, and are exposed to stronger magnetic fields that these planets are producing. It is known that such changes in magnetic field exposure are in principle able to accelerate particles. Here we find that this exposure is indeed the main reason for acceleration of electrons at relatively large distances from Jupiter and Saturn, not other candidate processes that could in principle also have been responsible. Key Point: Electrons in Saturn's and Jupiter's magnetosphere, outside the most intense radiation belts, are accelerated through adiabatic transport [ABSTRACT FROM AUTHOR]

In conjunction with lubricant oil film dynamics, automotive piston's primary and secondary motion indicatively affect the engine noise and frictional losses (fuel economy). The escalation of oil film temperature due to adiabatic shear heating of low viscosity Newtonian lubricant oil film affects the load carrying capacity and viscosity of lubricating film and enhances friction losses, piston wear, and non-linear lateral motion of piston. In this study, a numerical model for piston dynamic and lubrication is presented, in which adiabatic heating effects are simulated in hydrodynamic mixed lubrication regime by coupling with 2D-energy equation. The thermo-hydrodynamic lubrication model is solved using finite difference formulation, while the piston dynamic model is solved using the modified Newton Raphson method. Furthermore, the effect of adiabatic shearing of lubricant and piston skirt design parameters on piston dynamics and lubrication performance are analyzed. Results show that the adiabatic heating significantly affects piston lateral motion and lubrication performance. Lubrication analysis is very beneficial in the improvement of engine design of piston skirt-liner and can help reduce the friction losses. [ABSTRACT FROM AUTHOR]

The effects of quasi-static and low-dynamic strain rate ( ε ̇ = 10 −4 /s to ε ̇ = 10 2 /s) on tensile properties and deformation mechanisms were studied in a Fe-25Mn-3Al-3Si (wt%) twinning and transformation-induced plasticity [TWIP-TRIP] steel. The fully austenitic microstructure deforms primarily by dislocation glide but due to the room temperature stacking fault energy [SFE] of 21 ± 3 mJ/m 2 for this alloy, secondary deformation mechanisms such as mechanical twinning (TWIP) and epsilon martensite formation (TRIP) also play an important role in the deformation behavior. The mechanical twins and epsilon-martensite platelets act as planar obstacles to subsequent dislocation motion on non-coplanar glide planes and reduce the dislocation mean free path. A high-speed thermal camera was used to measure the increase in specimen temperature as a function of strain, which enabled the use of a thermodynamic model to predict the increase in SFE. The influence of strain rate and strain on microstructural parameters such as the thickness and spacing of mechanical twins and epsilon-martensite laths was quantified using dark field transmission electron microscopy, electron channeling contrast imaging, and electron backscattered diffraction. The effect of sheet thickness on mechanical properties was also investigated. Increasing the tensile specimen thickness increased the product of ultimate tensile strength and total elongation, but had no significant effect on uniform elongation or yield strength. The yield strength exhibited a significant increase with increasing strain rate, indicating that dislocation glide becomes more difficult with increasing strain rate due to thermally-activated short-range barriers. A modest increase in ultimate tensile strength and minimal decrease in uniform elongation were noted at higher strain rates, suggesting adiabatic heating, slight changes in strain-hardening rate and observed strain localizations as root causes, rather than a significant change in the underlying TWIP-TRIP mechanisms at low values of strain. [ABSTRACT FROM AUTHOR]

Experiments were conducted on Ti-based alloys including a commercially pure titanium (α phase), Ti-6Al-4 V (α + β phase) and TiNi (B19'-martensitic phase) alloys in order to investigate the phase transformation during high-pressure torsion (HPT) at room temperature. An allotropic α to ω phase transformation in the commercially pure titanium occurred during HPT processing but increasing the rotation speed led to a decrease in the volume fraction of the ω-phase. This procedure facilitates the loss of the β phase in the Ti-6Al-4 V alloy and promotes a B19' to B2 (austenite) phase transformation in the TiNi alloy. The results show that the bulk temperature increment in the processed specimens was not sufficiently high to affect phase transformations. However, the calculations by assuming adiabatic conditions revealed that the local temperature increment is responsible to encourage or suppress the phase transformation in the Ti-based alloys. This fundamental understanding of phase transformations during severe plastic deformation is useful for conducting microstructure engineering of Ti-based alloys by tailoring the microstructures containing different phases and thereby producing different mechanical and functional behaviors. • Different rotation speeds were applied for the HPT processing of Ti-based alloys. • Temperature increment samples was not sufficiently high to activate any reverse phase transformations. • Stabilization of phases can be prevented at high rotation speeds due to adiabatic shearing that produces local heating. • Heat generation prevented formation of the ω-phase in Ti and promoted reverse phase transformation in TiNi at high rotation speeds. [ABSTRACT FROM AUTHOR]

• Deformation behavior of transformative Fe 50 Mn 30 Co 10 Cr 10 complex concentrated alloy is studied under dynamic loading in contrast to its quasistatic response. • Alloy displays multistage strain hardening causing delayed damage localization under dynamic loading. • Multistage strain hardening is attributed to the favored bidirectional γ to ε phase transformation. • Alloy under quasistatic strain rate shows early fracture due to favored forward γ to ε transformation. High strain rate compression experiments performed on a non-equiatomic metastable fcc + hcp Fe 50 Mn 30 Co 10 Cr 10 high entropy alloy using split Hopkinson pressure bar setup shows improved flow stress and compression ductility compared to quasistatic deformed samples. The deformation response was characterised by the occurrence of hardening and softening stages compared to sustained strain hardening for quasistatic deformation. Detailed EBSD, BSE imaging analysis coupled with TEM shows significant bi-directional transformation (B-TRIP) and increased fcc γ phase stability in high strain rate regime while only forward (fcc to hcp) transformation dominates with increasing fraction of hcp ε phase in the quasistatic regime of deformation. Bidirectional transformation aided by adiabatic heating and heterogeneous deformation in the high strain rate regime leads to optimal stress and strain partitioning between the two phases and delays the initiation of damage at the interface. The presence of concomitant strain rate hardening and improvement in ductility in the dynamic deformation regime opens up avenues for microstructural tunability to achieve simultaneous improvement in strength and ductility using the metastability paradigm in complex concentrated alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

The strain rate effect (2.8 × 10 −5 –2.8 × 10 −1 s −1 ) on the tensile properties and microstructure evolution of a β-type Ti-10Mo-1Fe (wt%) alloy has been investigated. With increasing strain rate, the yield strength increased, while the ultimate tensile strength, total elongation and uniform elongation decreased. It was found that deformation at a lower strain rate led to an enhanced work hardening rate ( θ ). This is reflected in the decreasing strain rate sensitivity of flow stress, m , with increasing strain. Strain rate sensitivity was positive at a smaller strain level (< 0.13), and decreased to a negative at a larger strain. The strain rate dependence of work-hardening behavior has been investigated and discussed in terms of the microstructure evolution, such as {332}<113> twins and dislocations. Electron Backscattered Diffraction (EBSD) and X-ray diffraction (XRD) analyses revealed lower increasing rates of {332}<113> twins and dislocation density at higher strain rates, which may be caused by adiabatic heating. This may lead to the reduced work-hardening rate on deformation at the higher strain rates. [ABSTRACT FROM AUTHOR]

Transparent polymeric laminates are increasingly used for the substitution of conventional glass and laminated safety glass respectively and thus require reliable and efficient prediction and modeling techniques, in particular for numerical simulations. In the present work, the components of a polymeric laminate consisting of poly(methyl methacrylate) (PMMA) plies combined with a thermoplastic polyurethane (TPU) interlayer were subjected to experimental and numerical investigation. Uniaxial tensile tests and dynamic mechanical thermal analysis (DMTA) were used to determine the strain-rate and temperature dependent material behavior. Adiabatic heating of the interlayer was observed using infrared (IR) surveillance. Based on the experimental basis, viscoelastic material models were applied for both materials. The corresponding parameter identification was performed in two ways. One was based on the DMTA master curve, the other on uniaxial tensile test data. The material models were able to capture the temperature and time dependent behavior of both materials adequately and enable their usage in a laminated structure. [ABSTRACT FROM AUTHOR]

Aluminium alloys are widely used in the design of structural parts in the automotive and aircraft manufacturing because of their good specific mechanical properties. Many of the critical situations in these types of industries such as crash or impact phenomena as well as forming processes are related to high strain-rate deformations and adiabatic heating. Therefore, knowing flow and failure behaviour of materials under dynamic loading and applying reliable constitutive models is essential for designing the structural components safely. Johnson-Cook model is one of the most long-established constitutive relations in the dynamic field due to its simplicity and easy calibration. Nevertheless, empirical models do not collect and give information about the reason why materials behave in the way that they do, so micromechanical motivated continuum models are interesting for that. In the present work, authors analyse the mechanical dynamic behaviour of the aeronautical alloy Al2024-T3. An experimental study has been planned performing tests on sheet specimens at different strain-rates and temperatures to analyse the effect of these parameters. Low strain-rate experiments were conducted using a servo-hydraulic machine while high strain-rate tests were carried out using a split-Hopkinson tension bar. Testing temperatures were set at room and 373K by using a furnace made of resistors. The material behaviour is modelled using a micromechanical-based constitutive and a phenomenological failure model. Plastic flow of the material is defined by means of Orowan relation, where both temperature and strain-rate effect are included in the flow rule and the strain hardening law is just a function of equivalent plastic strain; while failure criterion is based on Cockcroft-Latham model. Strain fields on sample surfaces, which were used for obtaining the true stress-strain curves and performing a hybrid experimental-numerical failure calibration, were obtained by means of Digital Image Correlation technique. [ABSTRACT FROM AUTHOR]

The titanium alloy TC6 was laser peened without coating (LPwC) with a pulsed Nd:YAG laser (1064 nm) at power densities of 3, 6 and 9 GW cm − 2 . Microhardness data revealed that hardness does not linearly scale with power density. Residual stress analysis indicated that the profile has two distinct regions, one near surface (< 100 μm) showing thermal effects due to laser beam-material interaction and a far-surface region (> 100 μm) with decreasing compressive residual stresses with increasing power density. Transmission electron microscopy (TEM) showed high dislocation density with dislocation tangles and dislocation walls without dislocation cell or nanocrystals in the near surface region. Synchrotron radiation showed the increase in volume fraction of β phase with increase in power density in the far-surface region. Fatigue performance of the samples (number of cycles to failure) subjected to LPwC at a power density of 6 GW cm − 2 was found to have increased by a factor of 2–4, in the load range of 12.5–15 kN. Further, it was observed that in addition to the normally observed sub-surface crack nucleation of LPwC samples, additional formation of β phase in the far-surface region improves fatigue performance. [ABSTRACT FROM AUTHOR]

During mechanical joining processes, high equivalent plastic strains occur in the joint area (e.g., flat-clinching: φ eqv > 3.0). This causes a high deformation energy within the forming zone. In cold bulk forming, approximately 80% of the plastic energy is converted into heat due to internal friction at the grain boundaries. Compared to other forming processes, mechanical joining processes are characterized by short process times and high strain rates. Therefore, the converted heat cannot dissipate from the forming zone by heat radiation or heat conduction. For this reason, a significant heating of the joint area is expected. Within the scope of this work, the emerging heat shall be analyzed experimentally as well as numerically. There is an extremely high contact pressure in the joint area, which would result in a destruction of any thermocouple. Hence, it is not possible to determine experimentally the temperature within the forming zone. For this reason, a reference setup was developed for determining the increase of temperature during flat-clinching. This measurement serves as a basis for the verification of the numerical temperature calculation. During the numerical investigations, the influence of the component heating on the forming result and forming forces was analyzed and compared to simulations without consideration of the heating. [ABSTRACT FROM AUTHOR]

Laser peening without coating (LPwC) was performed on a Ti-2.5Cu alloy at wavelengths of 1064 and 532 nm and at a constant power density of approximately 7 GW cm −2 with overlap rates of 53%, 63% and 73%. Surface softening due to thermal interaction of laser beam with material was observed till a depth of 500 µm (at 532 nm) and 200 µm (at 1064 nm), based on hardness data. This was corroborated (rather weakly) by residual stress analysis. In addition, softening due to mechanical effects (adiabatic heating) was observed in the bulk. Although there was an increase in mechanical softening with increase in overlap rates at 532 nm, it was observed, upon comparison with peened samples at 1064 nm, that the mechanical softening is a function of wavelength of radiation used for peening. It was observed that the onset of softening was earlier if the wavelength was shorter. Further, evidence of hardening in the form of twinning was found for the 1064 nm case while it was absent for the 532 nm case, for 73% overlap. The workhardened depth was more than 1000 µm, not observed in earlier studies based on residual stress analysis. The direct consequence of softening effect was found in the fatigue results. The fatigue life extended by a factor of 1.4 and 2.3 for the samples peened at 532 nm and 1064 nm respectively, consistent with the observed wavelength dependent onset of softening. [ABSTRACT FROM AUTHOR]

In this study, A356 Al alloy composites reinforced with SiC particulates (SiC p ), whose SiC p volume fraction was quite high (about 56 vol%) for a candidate surface material of multi-layered armors, were fabricated by a liquid pressing process, and their dynamic compressive properties were investigated by using a split Hopkinson pressure bar. Defects such as misinfiltration or pores were eliminated, but about 2 vol% of eutectic Si particles and about 3 vol% of Fe-Al intermetallic compound particles were contained in the Al matrix. According to the dynamic compressive test results, dynamic compressive strength and strain were much higher than quasi-static ones because of strain-rate hardening effect and existence of molten Al matrix formed by adiabatic heating. The as-cast composite showed the best combination of dynamic strength and strain, together with the highest dynamic toughness, because the crack propagation was effectively blocked by the molten Al matrix and deformation band formation, while the T6-heat-treated composite showed the lowest compressive strain in spite of the highest strength. These findings suggested that the present Al-SiC p composites could be reliably applied to armors because the dynamic toughness or resistance to fracture was much higher under the dynamic loading than under the quasi-static loading. [ABSTRACT FROM AUTHOR]

The present study concerns the deformation and fracture behavior of two ferrite–martensite dual phase steels (FMDP660 and FMDP780) with different phase fractions subjected to different strain rate (0.001 s−1 to 1000 s−1) tensile testing. For both steels, the yield strength (YS) monotonically increased with strain rates, whereas the values of ultimate tensile strength (UTS), uniform elongation (UE) and post-uniform elongation (PUE) were maintained stable at the low strain rate range (0.001–0.1 s−1), followed by a significant increase with strain rate at high strain rate levels (0.1–1000 s−1). The FMDP780 steel with a higher fraction of martensite possessed a stronger strain rate sensitivity of tensile strength and elongation (UE and PUE) values at the high strain rate stage, compared with the FMDP660 sample. The change of UTS and UE with different strain rates and phase fractions was highly related to the strain hardening behavior, which was controlled by the dislocation multiplication in ferrite, as validated by transmission electron microscopy (TEM). The fracture surface of the two steels was characterized by dimpled-type fracture associated with microvoid formation at the ferrite–martensite interfaces, regardless of the strain rates. The change of the dimple size and PUE value of the two steels with strain rates was attributed to the effect of adiabatic heating during tensile testing.