Dynamic Strain Aging Phenomenon Research Articles

Theoretical Study for Dynamic Strain Aging in Niobium: Effect of Temperature and Strain Rate on the Flow Stress

A constitutive model for niobium with the effect of dynamic strain aging is proposed. The crystal structure of metals hugely influences the dynamic strain aging phenomenon and causes considerable alterations in the material’s macroscopic mechanical responses. Dynamic strain aging needs to be accounted for in a constitutive model to obtain accurate predictions of material’s thermo-mechanical behaviors during deformation. The proposed constitutive model attempts to describe the material’s flow stress responses during deformation by separating the flow stress contributions into the athermal component, thermal component, and dynamic strain aging component. Two different mathematical equations are proposed to model the dynamic strain aging component. The proposed model attempts to describe the mechanical response of niobium for a wide range of strain rates: from quasi-static loading ( $$\dot{\varepsilon } = 0.001\,{\text{s}}^{ - 1}$$ ) to dynamic loading ( $$\dot{\varepsilon } = 3300\, {\text{s}}^{ - 1}$$ ) across the temperature ranges 77 K–800 K.

Uniaxial ratcheting deformation of 316LN stainless steel with dynamic strain aging: Experiments and simulation

Dynamic strain aging (DSA) widely exists in austenitic stainless steel at elevated temperature. The materials will be drastically strengthened by this phenomenon. A series of symmetric strain-controlled and asymmetric stress-controlled cyclic experiments were conducted at different temperatures from 293 K to 823 K for 316LN stainless steel. The DSA phenomenon was observed in all the tests under elevated temperatures and it became more significant with the increase of temperature until reached the maximum at 823 K. There were a series of manifestations of DSA such as the anomalous cyclic hardening with temperature increasing in the strain-controlled tests and the quick-shakedown of ratcheting strain in the stress-controlled tests. An appropriate constitutive model to describe the cyclic behavior at different temperatures is necessary. The proposed kinematic hardening model is based on Ohno-Wang model and modified by introducing a hardening index into dynamic recovery term. The index accounts for DSA hardening degree of material under high temperature, therefore the performance mentioned above can be simulated well by this proposed model. By relating the parameters with temperature and plastic strain amplitude, a unified visco-plastic constitutive model was proposed. Simulation results of the proposed model agree much better with experimental values.

On Temperature Dependence of Microstructure, Deformation Mechanisms and Tensile Properties in Austenitic Cr-Mn Steel with Ultrahigh Interstitial Content C + N = 1.9 Mass.%

The microstructure, deformation mechanisms, tensile properties and fracture micromechanisms of ultrahigh-interstitial austenitic Fe-22Cr-26Mn-1.3V-0.7C-1.2N (mass.%) steel were investigated in wide temperature interval. After conventional homogenization and solid-solution treatment, the steel possesses complex hardening which includes grain boundary, solid-solution and dispersion strengthening. In the temperature interval of −60 to +60 °C, steel demonstrates striking temperature dependence of a yield strength which could be enhanced by the increase in solid-solution treatment temperature. The variation in test temperature does not change the dominating deformation mechanism of the steel, dislocation slip and insufficiently influences tensile elongation and fracture micromechanisms. The insignificant increase in the fraction of brittle cleavage-like component on the fracture surfaces of the specimens in low-temperature deformation regime is promoted by increase in planarity of dislocation arrangement and the gaining activity of mechanical twinning. In high-temperature range (200–300 °C) of deformation, a negative strain-rate dependence, serrations on the stress-strain diagrams and improved strain-hardening associated with a dynamic strain aging phenomenon have been observed.

Evolutions of mechanical properties of AISI 304L stainless steel under shear loading

The evolutions of microstructure and mechanical properties during shear punch testing (SPT) of an AISI 304L metastable austenitic stainless steel were studied at deformation temperatures ranging from 0 °C to 550 °C and strain rates in the range of 10-3 s-1 to 1 s-1. Based on the X-ray diffraction (XRD) phase analysis and metallographic observations, it was inferred that by increasing the deformation temperature from 0 °C to 200 °C, the amount of transformed strain-induced martensite decreases at all strain rates, leading to the weakening of the transformation-induced plasticity (TRIP) effect. However, depending on the strain rate, at temperatures higher than 200 °C, an anomalous trend in shear strength was observed, i.e. the shear strength rose by increasing the deformation temperature at low strain rates, due to the dynamic strain aging (DSA) phenomenon. Strain rate sensitivity studies in conjunction with the microstructural evolutions revealed four temperature-dependent regimes: 0–200 °C, 200–300 °C, 300–500 °C and higher than 500 °C, where the respective strain rate sensitivity index (m) becomes positive, zero, negative, and then positive again. These regimes were rationalized based on the TRIP effect, DSA phenomenon, and thermally-activated dislocation glide.

An evolving plasticity model considering anisotropy, thermal softening and dynamic strain aging

Comprehensive experimental characterization and numerical prediction have been performed to investigate the thermal effects on the anisotropic flow behavior of two high-strength steels in this study. For the experimental investigation of the anisotropic plasticity under the influence of temperature, uniaxial tensile tests have been conducted along three different loading directions covering the temperature range from 123 K to 773 K under the quasi-static loading condition. The results show that the thermal effects on the flow behavior are non-monotonic because not only the typical thermal softening but also the dynamic strain aging phenomena are observed. Moreover, the thermal effects on the anisotropy behavior are not constant but strain and material dependent. Regarding the numerical description, a generalized evolving plasticity model considering the evolution of thermal effects on flow behavior is proposed. With all material parameters systematically calibrated following a straightforward approach, the model is used to describe the temperature dependence of anisotropic plastic flow behavior of the investigated materials. The predictive capability of the model is validated by experimental results across a large temperature range even with the activation of complicated deformation mechanisms such as dynamic strain aging.

Experimental and Constitutive Model Study on Dynamic Mechanical Behavior of H96 Brass Alloy

To study the mechanical response of H96 brass, the quasi-static and dynamic compression experiments were performed by the universal-testing machine and the split Hopkinson pressure bar system. The selected temperature range was 293 K ∼ 873 K, the selected strain-rate range was 0.001/s ∼ 6000/s and the strains were up to 0.6. It was shown that, this alloy has remarkable strain hardening character, and this alloy is sensitive to strain-rate and temperature. In addition, the Dynamic Strain Aging phenomenon of this alloy occurs under the condition of 473 K and 0.001/s. According to the testing results and the thermal-activation dislocation mechanism, a plastic flow constitutive model was brought forth. This constitutive model can predict and describe the plastic flow behavior of H96 brass alloy in a wide range of temperature and strain rate.

Uniaxial Ratcheting Assessment of 304 Stainless Steel Samples Undergoing Step-Loading Conditions at Room and Elevated Temperatures

AbstractThe present study evaluates ratcheting response of 304 stainless steel samples subjected to various step-loading conditions at room and elevated temperatures using the kinematic hardening rules of Ohno–Wang (O–W), AbdelKarim–Ohno (AK–O), and Ahmadzadeh–Varvani (A–V). The hardening rules were employed along with the visco-plastic flow rule to account for the time-dependent response of 304 stainless steel samples. Ratcheting over low–high–low loading sequences consistently showed a small drop in ratcheting strain over the third loading step. This is mainly due to plastic strain accumulation over the first two loading steps preventing ratcheting strain to drop significantly with a drop in the mean stress. Moreover, dynamic recovery terms in these models were further modified through the inclusion of an exponential function developed by Kang to address the dynamic strain aging phenomenon. Low ratcheting rate and shakedown shortly after a few stress cycles within loading steps as operating temperatures varied between 400 and 600 °C were attributed to dynamic strain aging phenomenon in SS304 steel alloy. Progressive ratcheting response and their stress–strain hysteresis loops were highly influenced at various operating temperatures, stress levels, and stress rates. Coefficients in the dynamic recovery term of the A–V model controlled ratcheting progress and hysteresis loops agreeable with those of experimental data over consecutive loading steps. Choices of material constants and the number of segments defined from stress–strain curve based on the O–W and AK–O models noticeably influenced the ratcheting response of steel samples. Predicted ratcheting values by means of the A–V, O–W, and AK–O models were discussed and compared with those of the experimental data.

Experimental investigation of mechanical properties of cold-drawn AISI 1018 steel at high-temperature steady-state conditions

Fire is one of the most serious problems that affect the integrity of building structures. It can cause significant degradation of the structural strength of steel over a short period prior to building collapse. This study conducted an extensive experimental program on the mechanical properties of AISI 1018 cold-drawn steel (CDS) at elevated temperatures using the steady-state method. The elastic modulus of CDS AISI 1018 underwent a reasonably rapid reduction at temperatures of 100–200°C. At higher temperatures up to 500°C, the steel exhibited slow reduction in its elastic modulus, whereas sharp reduction was observed at temperatures of 550–750°C. In contrast, slow reduction in mechanical strength was observed at temperatures of 100–200°C. At 300°C, the mechanical strength increased gradually until it achieved a peak at 500°C. This phenomenon was attributed to a dynamic strain ageing (DSA) effect that provided benefits in terms of increased mechanical strength and ductility, which were relatively higher than the mechanical strength at room temperature. Dimple fracture characteristics were observed in all samples tested at elevated temperatures. After raising the test temperature to 750°C, subsequent reduction in the area of the lamellar pearlite phase boundary led to a spheroidization process followed by increased ductility. Prescriptive model predictions based on the experimental data series were proposed and important features regarding the DSA phenomenon were highlighted regarding fire-safety design when using CDS AISI 1018 in building construction.

Material modelling for dynamic strain ageing phenomenon of alloy 20MnMoNi55

ABSTRACTDynamic strain ageing (DSA) is observed in the tensile behaviour of 20MnMoNi55. The DSA phenomenon contributes extra hardening for a certain combination of straining rate and temperature. At temperature ranging from 200°C to 400°C and a straining rate of 10−4–10−2 s−1, alloy 20MnMoNi55 exhibits DSA. In the present work, DSA stresses are calibrated as a function of strain, strain-rate and temperature. Modification of the Johnson–Cook material model by incorporating DSA has been attempted. The modified flow stress model is used in finite element computation to simulate the material behaviour for a wide range of temperature and strain-rates including the DSA regime. The simulated results are in good agreement with the experimental results.

Thermal-mechanical fatigue behaviour and life prediction of P92 steel, including average temperature and dwell effects

This study was devoted to an investigation of the effects of the average temperature and dwell on the thermal-mechanical fatigue (TMF) behaviour of P92 steel at elevated temperatures in the range of 350–650°C. The results revealed that increased average temperature decreased the in-phase TMF (IPTMF), out-of-phase TMF (OPTMF), and isothermal fatigue (IF) life values, and its effect was more significant in the range of 400–450°C. The effect of a short dwell time on the IPTMF life was dependent on the form of dwell, because tensile dwell decreased the IPTMF life and symmetric dwell increased the IPTMF life. Both creep stress relaxation (CSR) and dynamic strain ageing (DSA) were detected under IPTMF cycling. The application of dwell enhanced the CSR phenomenon. In contrast, the DSA effect was restrained, which was beneficial for fatigue resistance. The appearance of crack tip blunting and crack branching because of symmetric dwell indicated the retardation of crack propagation under the combined effects of enhanced CSR and the disappearance of the DSA phenomenon. In all cases, the transformation of lath structures into substructures was the dominant deformation mechanism. In addition, the equiaxial subgrain grew with increases in the strain amplitude and dwell time. Finally, the application of the current life models to P92 steel fatigue life prediction under both IF and TMF cycling were evaluated. Because of the insufficiency of the current models, a modified Coffin–Manson model is proposed by incorporating the mean stress and temperature into power law forms.

A physically based constitutive model for dynamic strain aging in Inconel 718 alloy at a wide range of temperatures and strain rates

Dynamic strain aging has a huge effect on the microstructural mechanical behavior of Inconel 718 high-performance alloy when activated. In a number of experimental researches, significant additional hardening due to the dynamic strain aging phenomenon was reported. A constitutive model without considering dynamic strain aging is insufficient to accurately predict the material behavior. In this paper, a new constitutive model for Inconel 718 high-performance alloy is proposed to capture the additional hardening, which is caused by dynamic strain aging, by means of the Weibull distribution probability density function. The derivation of the proposed constitutive relation for the dynamic strain aging-induced flow stress, the athermal flow stress and the thermal flow stress is physically motivated. The developed model is applied to Inconel 718 high-performance alloy to demonstrate its ability to capture the dynamic strain aging behavior, which was observed in the literature across a wide range of temperatures (300–1200 K) and strain rates from quasi-static loading (0.001/s) to dynamic loading (1100/s).

Experimental study on the mechanical strength and dynamic strain aging of Inconel 617 using small punch test

In the present work, the mechanical strength and deformation characteristics of Inconel 617 were studied using small punch test at different temperatures and deformation rates. As temperature increases, small punch characteristic parameters decreases and three temperature intervals are defined. An important conclusion here is that dynamic strain aging phenomenon can be found at a high-temperature small punch deformation of Inconel 617 in a multi-axial stress state. Due to serration plastic flow, small punch characteristic parameters of Inconel 617 appear no significant changes in the temperature range from 300 °C to 700 °C. To describe dynamic strain aging behaviour, serration type, critical displacement, and maximum load drop are discussed. As the temperature increases or deformation rate decreases, the serration type of the load–displacement curve gradually changes from Type A to Type C, and maximum load drop increases. Meanwhile, critical displacement displays normal and inverse behaviour at different temperature ranges. Based on the deformation characteristics analysis, the mechanical strength of Inconel 617 in different aging states was analysed. Finally, the relationship between the mechanical strength, small punch characteristic parameters and hardness was established. The results show that small punch test is an effective method for reasonably estimating the mechanical strength and dynamic-strain aging behaviour of Inconel 617.

Characterization and Modeling of Hot Deformation Behavior of a Copper-Bearing High-Strength Low-Carbon Steel Microalloyed with Nb

This study investigates hot deformation behavior of a newly developed Cu-bearing high-strength low-carbon steel microalloyed with Nb (Nb-HSLC). A computational method based on experimental data was employed to design the chemical composition of the alloy. Compression tests were carried out in the temperature range of 850-1100 °C as well as strain rates of 0.001-10 s−1 using BAHR Dil 805 A/D thermo-analyzer equipment. The Arrhenius-type constitutive equations were used to model the hot working behavior of the designed steel. Effects of friction and temperature rise during deformation were corrected to obtain the actual stresses. The results showed that the peak flow stress was increased with increasing Zener–Hollomon parameter. The obtained flow curves at strain rates lower than 0.1 s−1 and temperatures above 950 °C represented the typical dynamic recrystallization (DRX) behavior, while the flow curves at temperatures lower than 950 °C at all strain rates were associated with continuous strain hardening. This feature is in good agreement with the precipitation temperature range of Nb(C, N) particles, i.e., 800-1000 °C. Moreover, the flow curves showed the serrations during hot deformation at strain rates of 0.001 and 0.01 s−1, indicating that the dynamic strain aging (DSA) phenomenon occurred at low strain rates. The best fit between “peak stress” and “deformation conditions” was obtained by a hyperbolic sine-type equation (R2 = 0.993). Therefore, the average activation energy was determined as 348 kJ mol−1. The agreement between the achieved model and experimental flow data was verified using the results of additional tests at a strain rate of 5 s−1. The maximum difference between the measured and predicted “peak stresses” was calculated as 5 Mpa.

Asymmetric cyclic deformation behavior of SA 333 steel at elevated temperatures

Purpose The purpose of this paper is to study the effect of mean stress and stress amplitude on the asymmetric cyclic deformation behavior of SA333 Gr-6 C-Mn steel. Such type of loading may arise during the service period because of the load fluctuations, thermal gradients and sudden loading like seismic events. Tests were also carried out at different temperatures to understand the effect of it on sensitiveness of the materials deformation behavior. Design/methodology/approach Cylindrical specimen of 8-mm gauge diameter and 15-mm gauge length was fabricated from the pipe section along its axis. Stress controlled ratcheting tests were carried out by using triangular waveform for cyclic loading. The strain accumulations were measured using 12.5-mm gauge length extensometer. Ratcheting tests were carried out at fixed stress amplitude of 400 MPa and mean stress varying from 0 to 75 MPa, whereas at the fixed mean stress of 100 MPa and stress amplitude varies from 300 to 400 MPa at 300°C. To study the effect of temperature on ratcheting behavior, tests were carried out at a load of 100 MPa mean stress and 350 MPa stress amplitude, with a varying temperature between room temperature and 350°C. The stress rate of 115 MPas-1 was kept constant for all the tests. Findings Increase in mean stress and stress amplitude, ratcheting strain and plastic strain amplitude increases, whereas ratcheting life decreases. With an increase in temperature, ratcheting life increases and strain accumulation decreases up to 300°C, whereas on further increase in temperature, strain accumulation increases with reduction in ratcheting life. Minimum ratcheting rate was observed at 250°C and 300°C. The dynamic strain aging (DSA) phenomena lead to the hardening of the material. The investigated steel shows DSA temperature regime lies between 250°C and 300°C. The failure modes at 250°C and 300°C temperature was transgranular, whereas at 350°C complete ductile. Research limitations/implications The stress rate and loading condition may vary to study the ratcheting behavior. Practical implications From this study, the critical cyclic load may be determined. The DSA temperature regime of this material is determined at this stress rate. This could help to evaluate the cyclic deformation behavior of the material with temperature changes. Originality/value In this investigation, the DSA temperature regime has been determined where maximum ratcheting life, minimum strain accumulation and ratcheting rate were observed. The critical load where the minimum life of the material occurred at elevated temperature is 100 MPa mean stress and 400 MPa stress amplitude.

Constitutive model for metals with dynamic strain aging

In this paper, a modified constitutive relation to model the dynamic strain aging phenomenon is proposed based on the previous model of Voyiadjis-Abed. The dynamic strain aging phenomenon is typically observed in metals for a certain range of strain rates and temperatures. In quasi-static loading experiments which were performed by Abed et al. (2017) using a C45 steel for a large range of temperatures from 298 K to 923 K, a stress increase due to the dynamics strain aging was observed according to the temperature variation. Using both a phenomenological Johnson-Cook model and a physically based Voyiadjis-Abed model, this stress increase cannot be captured when dynamic strain aging is active. The Voyiadjis-Abed model is modified in the present work by means of a mathematical expression of the Weibull distribution that is derived based on a physically based mechanism of evolution of the dislocation density.

Effect of dynamic strain aging and precipitation on the hot deformation behavior of 253MA heat-resistant alloy

In this research, we performed an experimental investigation into the influence of dynamic strain aging (DSA) and precipitation behavior on the plastic deformation and microstructure evolution in alloy 253MA considering its service temperature. The serrated flow behavior, stress anomaly behavior and negative strain rate sensitivity are considered as the manifestation of DSA within a certain temperature range (TDSA), which can be classified as low (550–700 °C), intermediate (600–750 °C) and high temperatures (700–790 °C) at 0.001 s−1, 0.01 s−1 and 0.1 s−1, respectively. The activation energy of DSA was determined to be 242 kJ/mol, indicating that the diffusion of substitutional solutes, such as Cr and Ni, is mainly responsible for the DSA phenomenon. The characteristic of dislocation substructures is prone to change from linear structure to cellularization structure with a rising deformation temperature in the DSA regime. The stress anomaly behavior can be attributed to the rapid dissolution of σ phase. The initiation of dynamic recrystallization should contribute to the disappearance of DSA by suppressing the dynamical solute atom–dislocation interaction.

Evolución microestructural y envejecimiento dinámico por deformación en la aleación Mg-6%Gd- 1%Zn durante ensayos a tracción y compresión a temperaturas intermedias

La aleación Mg-6%Gd-1%Zn muestra el fenómeno de serrado durante la deformación a temperaturas intermedias debido al proceso de envejecimiento dinámico provocado por la presencia de átomos de soluto en solución sólida y dislocaciones móviles. Aunque la aleación tiene una textura al azar, se observa un comportamiento diferente en tracción y en compresión. El límite elástico y el endurecimiento es mayor cuando la aleación se ensaya en compresión. Durante la deformación a temperaturas intermedias se ha observado la activación de dislocaciones tipo < a > y maclas de tensión, independientemente del signo de la carga. Sin embargo, la fracción en volumen de maclas es siempre mayor cuando el material se somete a compresión. A temperaturas intermedias, los átomos de Gd y Zn anclan tanto las dislocaciones como las maclas. Por encima de 250 ºC, el fenómeno de serrado desaparece y la presencia de precipitados g´ y g´´ en el plano basal aumenta el endurecimiento.

Mechanical properties and tensile deformation behavior of a reduced activated ferritic-martensitic (RAFM) steel at elevated temperatures

Here the tensile behavior of a 9Cr-1.7W-0.1C reduced activated ferritic-martensitic steel over the temperature region from room temperature (RT) to 600 °C was studied. The variation of the dislocation distribution under the interplay mechanism of dislocations with solute atoms and lath boundaries was found to be the main reason for the decreasing of plasticity in the intermediate temperature zone. Temperature and strain rate were confirmed to affect the interaction intensity of this dynamic strain aging (DSA) phenomenon on the tensile deformation behavior through changing the extent of dislocation pile-up on the lath boundaries. The variation of average rate of crack propagation in the fibrous region was determined to be related to the DSA effect on the dislocation mobility.

Understanding thermally activated plastic deformation behavior of Zircaloy-4

Understanding micromechanics of plastic deformation of existing materials is essential for improving their properties further and/or developing advanced materials for much more severe load bearing applications. The objective of the present work was to understand micromechanics of plastic deformation of Zircaloy-4, a zirconium-based alloy used as fuel cladding and channel (in BWRs) material in nuclear reactors. The Zircaloy-4 in recrystallized (at 973 K for 4 h) condition was subjected to uniaxial tensile testing at a constant cross-head velocity at temperatures in the range 293 K–1073 K and repeated stress relaxation tests at 293 K, 573 K, and 773 K. The minimum in the total elongation was indicative of dynamic strain aging phenomenon in this alloy in the intermediate temperature regime. The yield stress of the alloy was separated into effective and athermal components and the transition from thermally activated dislocation glide to athermal regime took place at around 673 K with the athermal stress estimated to be 115 MPa. The activation volume was found to be in the range of 40 b3 to 160 b3. The activation volume values and the data analyses using the solid-solution models in literature indicated dislocation-solute interaction to be a potential deformation mechanism in thermally activated regime. The activation energy calculated at 573 K was very close to that found for diffusivity of oxygen in α-Zr that was suggestive of dislocations-oxygen interaction during plastic deformation. This type of information may be helpful in alloy design in selecting different elements to control the deformation behavior of the material and impart desired mechanical properties in those materials for specific applications.

Effects of Loading Frequency on Fatigue Behavior, Residual Stress, and Microstructure of Deep-Rolled Stainless Steel AISI 304 at Elevated Temperatures

The effects of loading frequency on the fatigue behavior of non-deep-rolled (NDR) and deep-rolled (DR) austenitic stainless steel AISI 304 were systematically clarified at elevated temperatures, especially at temperatures exhibiting the dynamic strain aging (DSA) phenomena. Tension-compression fatigue tests were performed isothermally at temperatures of 573 K and 773 K (300 °C and 500 °C) with different loading frequencies of 5, 0.5, 0.05, and 0.005 Hz. For the DR condition, the residual stresses and work-hardening states will be presented. It was found that DSA would be detected at appropriate temperatures and deformation rates. The cyclic deformation curves and the fatigue lives of the investigated austenitic stainless steel AISI 304 are considerably affected by the DSA, especially on the DR condition having high dislocation densities at the surface and in near-surface regions. In the temperature range of the DSA, residual stresses and work-hardening states of the DR condition seem to be stabilized. The microstructural alterations were investigated by transmission electron microscopy (TEM). At an appropriate temperature with low loading frequency, the plastic deformation mechanism shifted from a wavy slip manner to a planar slip manner in the DSA regimes, whereas the dislocation movements were obstructed.