Rate Temperature Sensitivity Research Articles

Modeling of strain hardening behaviors of 6061 aluminum alloy considering strain rate and temperature effects

This paper focuses on the plastic strain hardening behaviors of 6061 aluminum alloy (AA6061), considering its dependence on strain rate and temperature. Quasi-static tensile tests were conducted over a wide temperature range (20 °C-300 °C), and the digital image correlation technique was used to capture the deformation process of specimens. Additionally, the uniaxial compressive mechanical response of AA6061 was tested utilizing quasi-static compression and split Hopkinson pressure bar experiments over a wide range of strain rates (0.001 s−1–6000 s−1). Experimental results showed that the flow stress decreased and increased nonlinearly with temperature and strain rate, respectively. A modified Johnson–Cook (MJC) model was developed by incorporating a temperature-dependent strain softening term, along with corrections to the temperature and strain rate product terms, to reproduce the nonlinear dependence. Furthermore, the MJC model was proven to be able to accurately reproduce the deformation of the specimens tested in Taylor impact experiments (strain rates up to 105 s−1), suggesting its effectiveness for interpolating and extrapolating stress-strain relationships. This model provides applicable modeling for materials with nonlinear rate sensitivity and temperature sensitivity, and it is expected to be applied in engineering problems involving ultra-high strain rates.

3D Effects of detonation re-initiation after diffraction at a back-facing step

Detonation diffraction at a backward facing step and subsequent re-initiation at the bottom wall at near critical detonation transmission conditions is studied in a square 7.6 cm channel. The experimental techniques used for this purpose include ultra high-speed schlieren video from the side and the top views. Direct photography is also performed in the top view configuration with a soot foil placed at the bottom wall after the step. The process of detonation re-initiation is studied for 2H2+O2+2Ar and CH4+2O2 mixtures that are characterized by a very regular and irregular detonation cellular structure, respectively. For both mixtures detonation re-initiation begins at discrete points where the descending transverse reflect from the bottom wall; the spacing of re-initiation points matches the wave number, suggesting the three-dimensional interaction of descending and lateral transverse waves on the reflecting wall trigger detonation re-initiation. The subsequent growth of these re-initiation kernels differs between mixtures. For regular cell mixtures, the detonation evolution is gradual and follows the lateral transverse wave along the bottom wall; whereas for irregular cell mixtures, explosive of hot spots grow independently of the lateral transverse waves. The observed initiation processes underscore the critical role of three-dimensional effects for both regular and irregular cell mixtures. The abrupt detonation initiation observed for methane-oxygen can be attributed to the high effective activation energy, i.e., high reaction rate temperature sensitivity.

Soil particle size-dependent constitutive modeling of frozen soil under impact loading

In this study, the soil particle size dependence of the impact dynamic mechanical properties of frozen soil was investigated using a split Hopkinson pressure bar, and the meso-deformation mechanism of frozen soil was analyzed via electron microscopy. Under impact loading, the dynamic stress-strain curves of frozen soil showed strain hardening, strain softening, strain rate-temperature sensitivity, and soil particle size dependence, and the soil particle size dependence of frozen soil was considered to be significantly influenced by non-uniform meso-deformation, which primarily appeared in the form of microcracks surrounding the coarse particles. A constitutive model comprising a multiplicative hardening law was proposed, and soil particle size dependence was introduced through the equivalent strain gradient of the soil cell element. The impact compression process of frozen soil was simulated in ABAQUS/Explicit using the proposed model, and the mechanism of frozen soil deformation was summarized by the finite element analysis: the stress concentration around coarse particles induces the initiation of microcracks, the propagation of microcracks forms a crack network, eventually leading to the softening behavior of frozen soil.

Nitrogen carrier gas for the separation of trace explosives on CI-GC/MS.

Fluctuations in ultra high purity (UHP) helium supply has the potential to negatively impact critical research efforts. Disruptions have increased significantly with suppliers prioritizing delivery to medical facilities. Due to the greater demand for helium, supply issues are likely to continue through the coming years. Many gas chromatography (GC)-based analytical methods rely on the supply of UHP helium, including those developed for the quantification of trace explosives. Vapor validation is critical in establishing sensor performance, limits of detection, and instrument performance. An alternate carrier gas must be established to maintain these critical functionalities. To circumvent the UHP helium disruptions, UHP nitrogen was explored as a replacement carrier gas in negative mode chemical ionization-gas chromatography/mass spectrometry (CI-GC/MS). Although, hydrogen is considered an acceptable alternative to helium in most GC-based separations, its' use as a replacement was omitted due to reactivity resulting in degradation of the CI-MS detector and incompatibility with the programmable temperature vaporization inlet on the GC used in this work. Herein discusses the method development of nitrogen carrier gas in the separation of an explosives mixture. Adjustments in flow rate, initial oven temperature, and ramp rate were made to achieve comparable analysis to that of helium. By lowering the flow rate and initial oven temperature peak resolution and sensitivity increased when using nitrogen carrier gas. Development of this method allows for continual laboratory output in times of helium scarcity.

Dynamic mechanical properties of FGH4097 powder alloy and the applications of its constitutive model

As a typical multiphase alloy, FGH4097 has good lasting strength (thermal stability and thermal fatigue properties), excellent wear resistance and heat resistance. It has been widely used in aerospace and other hot-end parts manufacturing fields. Most of the existing researches on the mechanical properties of FGH4097 alloy are carried out at low strain rate. There is no effective research on high temperature dynamic mechanical properties of FGH4097. Through the impact compression test of FGH4097 under different strain rates and different temperature conditions by the split Hopkinson compression bar equipment, the corresponding true stress-true strain curve was obtained, the strain rate sensitivity and temperature sensitivity of the material were analyzed. The specific heat capacity of FGH4097 alloy at different temperatures was measured by a laser thermal conductivity meter, and the adiabatic temperature rise of the alloy at different temperatures and strain rates was studied. The isothermal true stress-strain curve of the alloy was obtained by calculating the thermal softening coefficient. Two constitutive equations, Johnson-Cook and Power-Law, were introduced to fit and characterize the dynamic mechanical properties of FGH4097 alloy at different strain rates and temperatures, and the corresponding material constitutive models were obtained. Comparing the fitting accuracy of the two models, it is found that the fitting accuracy of the Power-Law model is higher, with an average error of less than 8%. The cutting simulation of FGH4097 alloy was carried out by AdvantEdge software, and the effects of strain and strain rate on the machinability of FGH4097 alloy were investigated.

Dynamic behavior and microstructural evolution of TiAl alloys tailored via phase and grain size

As a kind of promising aerospace material, TiAl alloys need to withstand extreme conditions such as high-rate impact loads and high temperatures. The mechanism on the failure and fracture of TiAl alloys under extreme conditions is related with the microstructure, including phase and grain size. In the present research, two kinds of TiAl alloys tailored with different microstructures, near lamellar (NL) and near gamma (NG), were fabricated by thermo-mechanical treatment. Microstructural characterization was analyzed by XRD and EBSD. The dynamic behavior of the TiAl alloys under different temperatures ranging from 293 K–873 K was investigated by a split Hopkinson pressure bar. The strain rate sensitivity and temperature sensitivity was analyzed. The microstructural evolution was concerned to understand the failure mechanism of the two kinds of the TiAl alloys. The NG-TiAl had the homogeneous deformation with synergy effect between homogeneous equiaxed grain and lamellar structure, and no failure occurred in NG-TiAl. However, the NL-TiAl showed heterogeneous deformation with both “orange peel effect” and cracks, which was attributed to large equiaxed grain and brittle γ-lamellae with similar orientation. Further, the cracks were easily nucleated and propagated from the interface between γ-lamellae structures, especially in the γ-lamellae structures parallel with the loading direction. Finally, the modified Johnson–Cook constitutive model was proposed to describe the deformation behavior, in which both strain rate hardening and temperature softening terms were expressed as a function of strain and strain rate.

Constraining models for methane oxidation based on long-term continuous chamber measurements in a temperate forest soil

Upland soils are thought to be a sink of CH4, the second most important anthropogenic greenhouse gas, owing to oxidation by methanotrophs. To better understand CH4 fluxes in upland forests, we quasi-continuously measured CH4 fluxes using an automated closed chamber system over seven years on a larch plantation in a volcanic soil in Japan. We hypothesized that the long-term data sufficiently can calibrate modules for CH4 fluxes, and aimed to predict future pathways of CH4 uptake and their uncertainties in the forest. Based on the observations, a thinning of the overstory only marginally influenced the CH4 fluxes measured by the chambers. Using the data with a Bayesian method, we calibrated four modules for CH4 fluxes in forest soils, which were embedded in the process-based ecosystem model VISIT. The modules well reproduced the observed seasonality, annual budgets, and interannual variability in the CH4 fluxes after calibrating the following parameters: the diffusion coefficient or base CH4 oxidation rate constant and temperature sensitivity. The CH4 fluxes were predicted to increase in the future under the RCP8.5 scenario but to decrease under the RCP 2.6 scenario. The contrasting trajectory was caused by rising and decreasing CH4 concentrations under the RCP 8.5 and 2.6 scenarios, respectively. Furthermore, the magnitudes of the future changes in the fluxes differed in each module because the responses to the changes in the CH4 concentrations were inconsistent among the modules. The observed CH4 fluxes increased with increasing atmospheric CH4 concentration (4.95 mg CH4 m−2 d−1 ppm−1), which was greater in magnitude than those in the modules. Considering the uncertainties in the modules and potential confounding effects in the observations, we conclude that further understanding the responses of CH4 uptake to rising CH4 concentrations is required.

Linking soil carbon availability, microbial community composition and enzyme activities to organic carbon mineralization of a bamboo forest soil amended with pyrogenic and fresh organic matter

Despite fresh and pyrogenic organic matter have been widely used as amendments to improve soil organic carbon (SOC) storage, mineralization that links to C quality and soil temperature, microbial community composition and enzyme activity remain poorly understood. This study aims to explore the effects of amendments (bamboo leaves and its biochar) and incubation temperature on mineralization, and disentangle the relationships of SOC mineralization with chemical composition of SOC, labile organic C, microbial community composition, and activities of enzymes in a subtropical bamboo forest soil. Results showed that cumulative soil CO2 emissions ranked as bamboo leaf (Leaf) > bamboo leaf biochar (Biochar) > Control, regardless of the incubation temperature. Compared to the control, the Leaf treatment markedly increased, whereas the Biochar treatment decreased, the temperature sensitivity of SOC mineralization (P < 0.05). The cumulative soil CO2 emission was positively correlated (P < 0.05) with water-soluble organic C (WSOC), microbial biomass C (MBC), O-alkyl C and alkyl C contents, and activities of β-glucosidase and dehydrogenase, but negatively correlated (P < 0.01) with aromatic C content, regardless of the incubation temperature. This indicated that the lower SOC mineralization rate and lower temperature sensitivity in the Biochar (cf. Leaf) treatment were intimately associated with the lower WSOC, MBC, O-alkyl C content, and β-glucosidase and dehydrogenase activities, and higher aromatic C content in the Biochar. The high relative abundance of bacteria relating SOC mineralization included Rhizobiales, Sphingobacteriales and JG30-KF-AS9, whereas that of fungi included Eurotiales, Sordariales, Agaricales and Helotiales. Our results revealed that the application of pyrogenic organic matter, as compared to the application of fresh organic matter, can reduce SOC mineralization and its temperature sensitivity in a subtropical forest soil by limiting the availability of C and microbial activity, and thus has a great potential for maintaining soil carbon stock in subtropical forest ecosystems.

Mechanical behavior and microstructure evolution during deformation of AA7075-T651

In view of developing a physics-based constitutive material model for AA7075-T651, the mechanical behavior and microstructure evolution of the material has been studied through compression tests using Gleeble thermo-mechanical simulator. The tests were performed at wide range of temperatures (room temperature (RT), 100, 200, 300, 400 and 500 °C) with two constant strain rates (0.01 and 1 s-1). The true stress-strain curves depicted an increase in the flow stress with increase in the strain rate and decrease in the deformation temperature, with an exception at RT. The effects of softening mechanisms, such as adiabatic heating, dissolution of precipitates, dynamic recovery (DRV) and dynamic recrystallization (DRX), on the flow stress level, strain rate sensitivity (SRS) and temperature sensitivity over the entire range of temperatures were analyzed. Pertaining to the microstructure analysis, the intermetallic particles present in the initial as-received (AR) material were identified as (Al,Cu)6(Fe,Cu) and SiO2 with the help of back-scattered electron (BSE) imaging and energy dispersive X-ray spectroscopy (EDS). The microstructure of the material after the deformation processes were analyzed and compared with that of the AR state using inverse pole figures (IPF), grain orientation spread (GOS) and grain boundary rotation maps generated from electron back-scattered diffraction (EBSD) scans. DRV was observed for deformation at 300 °C, whereas a combination of DRV and incomplete DRX took place for 400 and 500 °C depending on the strain rate. The fraction of recrystallized grains was higher in case of deformation at higher temperature and lower strain rate. Furthermore, the difference in microstructure evolution on different surfaces of the deformed samples as well as at different locations on individual surfaces was also investigated.

Adaptive evolution of microalgae Schizochytrium sp. under high temperature for efficient production of docosahexaeonic acid

Temperature is an important factor that not only affects cell growth, but also changes fatty acid composition in oleaginous microorganisms. Here, adaptive laboratory evolution (ALE) was performed in Schizochytrium sp. to enhance strain thermotolerance in docosahexaeonic acid (DHA) production. The adaptive strain showed higher growth rate and lower temperature sensitivity. Cell growth rate of the adaptive strain after 70 cycles at high temperature stimulation (ALE70) at 28 °C and 34 °C were 46.93% and 60.55% higher than that of original strain. Meanwhile, the reduction ratio of DHA yield from 28 °C to 34 °C of ALE70 decreased by 61.71%. Finally, lipid and DHA concentration at 34 °C reached 4.31 and 4.33 times of the starting strain. Further physiological analysis showed ALE70 generated less ROS, synthesized less HSP proteins, and produced more pigments, which might be related to the improved performance. This work increased the fermentation temperature by 5 degrees without affecting DHA production, which significantly reduced the energy consumption cost of the industrialization.

Low temperature mechanical behaviour of PVDF: cryogenic pre-treatment, quasi-static, cyclic and dynamic experimental testing and modelling

PVDF has historically drawn the interest of the scientific community because of its mechanical response to external stimuli. Recently, novel 3D printing techniques have been proposed to manufacture responsive PVDF components, leading to the reconsideration of this polymer in many applications (i.e., sensor-actuator or energy harvesting systems). During manufacturing and/or service conditions, PVDF structures can be subjected to large deformations that, eventually, can involve low temperature loading (e.g., piezoelectric sensors for aircrafts). In this work, a deep mechanical characterisation of PVDF specimens is carried out under low temperature conditions. To this end, we first evaluate potential effects of cryogenic pre-treatment going beyond the glass transition temperature of the polymer. Then, mechanical tests are conducted at different loading conditions and a wide range of testing temperatures from room to temperatures below glass transition: quasi-static compression tests, cyclic loading tests, and high strain rate tests. The complete set of experiments is analysed together to identify slow and fast relaxation mechanisms within the polymeric structure and motivate a new constitutive model. Finally, taking the experimental observations as formulation's basis, a thermodynamically consistent constitutive model is developed for finite deformations. This model describes the mechanical behaviour of PVDF as the combination of slow and fast response and accounts for strain rate dependency, temperature sensitivity, hysteresis and thermal evolution during the deformation process. The results from this work provide a full study of the mechanical behaviour of PVDF at low temperature, considering effects of both pre-treatment and testing temperature, and a new modelling tool to predict its response under a wide range of room-to-low temperature loading conditions.

Thermo-viscoplastic behavior of 304 austenitic stainless steel at various strain rates and temperatures: Testing, modeling and validation

This paper presents a systematic study of the thermo-viscoplastic behavior of a 304 austenitic stainless steel (ASS). The experiments were conducted over a wide range of strain rates (10−3 s−1 to 3270 s−1) and temperatures (-163°C to 172°C), for which the deformation behavior of 304 ASS becomes more complex due to the strain-induced martensitic transformation (SIMT) effect. Dynamic tests at low/elevated temperatures were conducted using the Hopkinson technique coupled with a cooling device/heating furnace, and temperature distribution within the specimen was verified to be uniform. Experimental results showed that the strain hardening rate of 304 ASS was strongly affected by SIMT effect. For quasi-static tests (10−3 s−1 to 1 s−1) at low temperatures (-163°C to -20°C), the stress-strain relations exhibited an S-shape and a second strain hardening phenomenon. The strain rate sensitivity and temperature sensitivity of 304 ASS were also different from metallic materials deformed by dislocation glide. Several unexpected phenomena including the negative strain rate sensitivity and the changing temperature sensitivity from quasi-static to dynamic tests were observed. Based on experimental results, an extension of the Rusinek-Klepaczko (RK) model considering SIMT effect was used to simulate the deformation behavior of 304 ASS: it predicted flow stress curves of 304 ASS above -60°C correctly. In addition, to validate the extended RK model and the identified model parameters, numerical simulations of ballistic impact tests of 304 ASS plates at various temperatures were carried out, showing a good agreement with experiments.

Study on the constitutive model of porous titanium alloy

Porous titanium (Ti) alloys usually need high-speed precision machining before they are put into practical applications. Therefore, it is necessary to study the materials’ mechanical properties under conditions of larger strain rate and higher temperature in order to understand the processing mechanism and determine the appropriate processing parameters. In this study, the mechanical properties of porous titanium alloys of two porosities were first investigated by quasi-static compression tests and split Hopkinson pressure bar tests under different conditions. Then, the constitutive models of the flow stress were fitted. From the results of quasi-static compression tests, it was found that the static mechanical properties of porous titanium alloys decreased rapidly with increase in porosity. From the result of the split Hopkinson pressure bar tests, the strain rate sensitivity and temperature sensitivity of porous titanium alloys were determined. The mechanical properties of porous titanium alloys increased with strain rate increase in the range 1000–3000 s−1. The alloys exhibited a temperature-softening effect at 100°C, while they had a temperature-hardening effect at 300°C. The constitutive model could describe the strain-hardening rate of the material appropriately, but the accuracy of the simulated results needed to be improved compared with experimental values.

The initial level of heart rate variability determines the dynamics of the neuropathy of the autonomic nervous system and temperature sensitivity in rats with streptozotocin diabetes

BACKGROUND: The development of diabetes mellitus (DM) is accompanied by hyperglycemia, which leads to the development of neuropathy. We assume that the individual characteristics of the organization of the autonomic nervous system (ANS) in humans affect not only the ability to withstand stress, but can determine the course of diseases, including diabetes.&#x0D; AIMS: The study of the dynamics of heart rate variability and temperature sensitivity in rats against the background of hyperglycemia depending on the organization of the initial regulation of the heart under ANS.&#x0D; MATERIALS AND METHODS: 70 male rats were randomized by weight and level of total heart rate variability (HRV) on animals with initially low and high levels of total HRV. Diabetes was modeled by a single i.p. injection of streptozotocin (STZ). The control group received a single i.p. injection of citrate buffer (CB). Before the induction of diabetes, as well as on 21, 42 and 70 days after the injection of STZ, a comprehensive examination of rats condition was carried out: 1) assessment of HRV; 2) analysis of temperature-pain sensitivity; 3) assessment of glucose and ketone bodies in the blood. Similarly, animals in the CB group were examined.&#x0D; RESULTS: The change in HRV and temperature-pain sensitivity in rats depends on the initial level of HRV. In rats with low variability, the reaction time in the pain test increased by 832% from the 28th day of the experiment, from 21 days the bradycardia increased and the decrease in individual HRV indices at rest, but not the response of these parameters to cold stress.&#x0D; CONCLUSION: The development of ANSs lesion depends on the initial level of HRV. Low variability animals are more resistant to hyperglycemia: the normal ranges of CP reactions from the side of HR, the parameters of total HRV and the CVHS contribution to it are longer, but there is a loss of temperature sensitivity. Initially, highly variable rats with the development of diabetes do not lose temperature sensitivity, but demonstrate an imbalance in the regulatory circuits of heart rate and HRV.

Temperature sensitivity of biomass-specific microbial exo-enzyme activities and CO2 efflux is resistant to change across short- and long-term timescales.

Accurate representation of temperature sensitivity (Q10 ) of soil microbial activity across time is critical for projecting soil CO2 efflux. As microorganisms mediate soil carbon (C) loss via exo-enzyme activity and respiration, we explore temperature sensitivities of microbial exo-enzyme activity and respiratory CO2 loss across time and assess mechanisms associated with these potential changes in microbial temperature responses. We collected soils along a latitudinal boreal forest transect with different temperature regimes (long-term timescale) and exposed these soils to laboratory temperature manipulations at 5, 15, and 25°C for 84days (short-term timescale). We quantified temperature sensitivity of microbial activity per g soil and per g microbial biomass at days 9, 34, 55, and 84, and determined bacterial and fungal community structure before the incubation and at days 9 and 84. All biomass-specific rates exhibited temperature sensitivities resistant to change across short- and long-term timescales (mean Q10 =2.77±0.25, 2.63±0.26, 1.78±0.26, 2.27±0.25, 3.28±0.44, 2.89±0.55 for β-glucosidase, N-acetyl-β-d-glucosaminidase, leucine amino peptidase, acid phosphatase, cellobiohydrolase, and CO2 efflux, respectively). In contrast, temperature sensitivity of soil mass-specific rates exhibited either resilience (the Q10 value changed and returned to the original value over time) or resistance to change. Regardless of the microbial flux responses, bacterial and fungal community structure was susceptible to change with temperature, significantly differing with short- and long-term exposure to different temperature regimes. Our results highlight that temperature responses of microbial resource allocation to exo-enzyme production and associated respiratory CO2 loss per unit biomass can remain invariant across time, and thus, that vulnerability of soil organic C stocks to rising temperatures may persist in the long term. Furthermore, resistant temperature sensitivities of biomass-specific rates in spite of different community structures imply decoupling of community constituents and the temperature responses of soil microbial activities.

Characterization of Hot Deformation Behavior for Pure Aluminum Using 3D Processing Maps

AbstractThe hot compressive deformation behavior of pure aluminum has been investigated at different conditions of strain rate range of 0.005–10 s−1 and temperature range of 523–823 K. Based on dynamic materials model Malas criterion, processing maps were constructed to evaluate the efficiency of energy dissipation and flow instability regions. The optimized condition was around strain rate of 0.005–0.01 s−1 and temperature of 773–823 K with peak energy dissipation efficiency of 42 %. Meanwhile, the rule of strain hardening exponent, strain rate sensitivity exponent and temperature sensitivity exponent have been studied, then 3D processing maps considering the strain variable was developed, and the energy dissipation maps and the dynamic instability maps were changed with the strain increasing. Results showed that region at strain rate of 10 s−1 and the region at temperature of 823 K, strain rate of 0.005 s−1 showed high-energy dissipation rate. The 3D dynamic instability maps showed instability region of different parameters, the proper process parameters was ought to be kept away from this region. The conditions of the cracking microstructure occurred proving that the region was determined by the 3D instability maps.

Temperature sensitivities of microbial plankton net growth rates are seasonally coherent and linked to nutrient availability.

Recent work suggests that temperature effects on marine heterotrophic bacteria are strongly seasonal, but few attempts have been made to concurrently assess them across trophic levels. Here, we estimated the temperature sensitivities (using activation energies, E) of autotrophic and heterotrophic microbial plankton net growth rates over an annual cycle in NE Atlantic coastal waters. Phytoplankton grew in winter and late autumn (0.41 ± 0.16 SE d-1 ) and decayed in the remaining months (-0.42 ± 0.10 d-1 ). Heterotrophic microbes shared a similar seasonality, with positive net growth for bacteria (0.14-1.48 d-1 ), while nanoflagellates had higher values (> 0.4 d-1 ) in winter and spring relative to the rest of the year (-0.46 to 0.29 d-1 ). Net growth rates activation energies showed similar dynamics in the three groups (-1.07 to 1.51 eV), characterized by maxima in winter, minima in summer and resumed increases in autumn. Microbial plankton E values were significantly correlated with nitrate concentrations as a proxy for nutrient availability. Nutrient-sufficiency (i.e., > 1 μmol l-1 nitrate) resulted in significantly higher activation energies of phytoplankton and heterotrophic nanoflagellates relative to nutrient-limited conditions. We suggest that only within spatio-temporal windows of both moderate bottom-up and top-down controls will temperature have a major enhancing effect on microbial growth.

The effect of pre-strain on tensile behaviour of 316L austenitic stainless steel

ABSTRACTThe effect of pre-strain on tensile behaviour of 316L austenitic stainless steel was investigated, focusing on strain rate sensitivity, temperature sensitivity and strain hardening. Experimental data showed that strain rate sensitivity, temperature sensitivity and strain hardening were weakening with pre-strain. Meanwhile, the variation of microstructure with pre-strain was observed by optical microscopy, scanning electronic microscopy and X-ray diffraction. Then, the mechanical properties of pre-strained material were correlated with the increase in dislocation density and mechanical twinning with pre-strain. Finally, an improved Arrhenius-PS model considering the effect of pre-strain was developed.This paper is part of a thematic issue on Nuclear Materials.

Temperature-Dependent SRS Behavior of 316L and Its Constitutive Model

The strain rate sensitivity (SRS) and temperature sensitivity (TS) of 316L austenitic stainless steel were investigated by constant strain rate test (CSRT) and strain rate jump test (SRJT) under four temperatures (293, 373, 473 and 573 K) and four strain rates (5 × 10−4/s, 1 × 10−3/s, 5 × 10−3/s and 1 × 10−2/s). The results show that temperature sensitivity (TS) indexes at different strain rates are coincidence to be negative, related to temperature softening. On the contrary, SRS indexes change from positive to negative with the increase in temperature associated with dynamic strain aging (DSA). Moreover, based on the comparison between CSRT and SRJT, SRS and TS indexes obtained by two methods agree well. It proves that the SRJT can describe the SRS and TS phenomenon of 316L efficiently. Furthermore, the effects of temperature and strain rate on fracture mechanism were discussed. At last, an improved Johnson–Cook model was proposed to consider the temperature-dependent SRS behavior of 316L.

氮添加对杉木林土壤有机碳矿化速率及酶动力学参数温度敏感性的影响

氮添加对杉木林土壤有机碳矿化速率及酶动力学参数温度敏感性的影响