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The mechanical behaviors of CL65 wheel rim material from tread to depth under different temperatures (25-600 °C) and strain rates (0.001-7000 s−1) were investigated by utilizing quasi-static tensile and split Hopkinson pressure bar tests. The Johnson–Cook model of CL65 wheel steel was fitted, and the corresponding dynamic mechanics of wheel steel was discussed. The results show that the stress–strain curves of CL65 wheel rim steel were strain rate dependent and temperature dependent that the stress increased with the increase in strain rate and decreased with the rise of test temperature. With the elevated distance from the tread, the pearlite grain size, interlamellar spacing, and volume fraction of pre-eutectoid ferrite increased, resulting in an increase in ductility of quasi-static tensile and a decrease in the strength of the materials. In addition, the thin cementite layers showed more substantial toughness than the thick cementite layers. During the plastic deformation, high temperature promoted the fragmentation and dissolution of cementite lamellae, significantly impacting the thin cementite layer more than the thick cementite, which reduced the hindrance of dislocation movement during the plastic deformation, leading to weaker strain rate sensitivity and stronger temperature sensitivity in the material near the wheel tread (Zone 1) than in the deep material (Zone 2 and Zone 3). [ABSTRACT FROM AUTHOR]

Solid‐state welding of Al 1043 sheets is achieved via high‐pressure torsion (HPT) processing to produce bulk nanostructured Al disks. A homogeneous nanostructure without segregation is observed, with grain sizes of ≈430–470 nm. Miniature tensile testing, coupled with the digital image correlation (DIC) technique, is employed to determine the room‐temperature tensile deformation behavior, particularly the nonuniform behavior with necking, of the HPT‐bonded ultrafine‐grained (UFG) aluminum, comparing it with annealed coarse‐grained counterpart. The HPT‐bonded UFG Al exhibits a large fraction of post‐necking strain, which is supported by the estimated high strain rate sensitivity value of m = 0.085, suggesting the delay of local necking leading to tensile fracture. Detailed DIC analysis reveals prolonged diffuse necking, thus delaying local necking, in the HPT‐bonded UFG Al, while the annealed samples show high fractions of local necking during the nonuniform deformation. Moreover, the DIC data illustrate that local necking predominantly occurred at a limited neck zone, maintaining a plateau strain distribution at the out‐of‐neck zone throughout necking deformation toward tensile failure for both annealed and UFG aluminum. The DIC method offers an alternative means to demonstrate the transition in necking behaviors of materials by estimating the plastic lateral contraction exponent. [ABSTRACT FROM AUTHOR]

The present work deals with the hot deformation behavior of commercial Nb alloy C-103 and its microstructure evolution during uniaxial compression tests in the temperature range of 700-1100°C and the strain rate range of 0.001-0.4 s-1. Strain rate sensitivity, calculated from the compression tests data, was almost constant and showed a negative value in the temperature range of 700-900°C but increased significantly beyond 900°C. Dynamic strain aging was found to have a predominant effect up to 900°C, beyond which dynamic recovery and oxidation influenced the compressive properties. The microstructure of the deformed samples showed indications of dynamic recrystallization within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. The 950-1000°C temperature range and strain rate range of 0.001-0.1 s-1 were suggested as suitable hot deformation conditions. The constitutive equation was established to describe the alloy's flow behavior, and the average activation energy for plastic flow was calculated to be 267 kJ/mol. [ABSTRACT FROM AUTHOR]

The current SAC(Sn–Ag–Cu) solder often experiences rapid degradation of mechanical properties at high temperatures and is prone to fracture under dynamic loads, thus failing to meet the interconnection requirements of industrial electronic products that operate under high power and vibration loads. In light of this, this paper aims to enhance the overall performance of the alloy by reducing the fraction of the second phase in SAC305 alloy, altering the type of second-phase particles, and strengthening the matrix β-Sn phase. Additionally, based on thermodynamic calculations of phase diagrams, the internal phases and elemental solid solubility of the alloy under different temperature conditions are accurately designed, thereby improving the alloy's strength while maintaining its elongation almost unchanged. The experimental results indicate that the designed Sn1.0Ag0.7Cu–3Bi4In1.5Sb alloy exhibits a higher rate sensitivity factor m (0.0559), which is more than double that of the Sn1.0Ag0.7Cu–5Bi4In3Sb alloy (0.0239). This improvement is primarily attributed to the enhanced interaction between the matrix β-Sn and the solid solution effect. Larger compound phases, such as Cu6Sn5 and Ag3Sn, only play a role in the low-rate loading region. Additionally, the alloy demonstrates strong temperature dependence, which is also related to the dissolution of the In element in the matrix β-Sn. The solid solution of the In element significantly enhances the high-temperature elongation rate of the alloy, increasing from 11.9% at low temperatures to 21.3% at high temperatures. The successful development and implementation of this research provides a new solution for interconnection of electronic devices under high-speed dynamic loading and high-temperature service.

The present work deals with the hot deformation behavior of commercial Nb alloy C-103 and its microstructure evolution during uniaxial compression tests in the temperature range of 700-1100 °C and the strain rate range of 0.001-0.4 s-1. Strain rate sensitivity, calculated from the compression tests data, was almost constant and showed a negative value in the temperature range of 700-900 °C but increased significantly beyond 900 °C. Dynamic strain aging was found to have a predominant effect up to 900 °C, beyond which dynamic recovery and oxidation influenced the compressive properties. The microstructure of the deformed samples showed indications of dynamic recrystallization within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. The 950–1000 °C temperature range and strain rate range of 0.001-0.1 s-1 were suggested as suitable hot deformation conditions. The constitutive equation was established to describe the alloy's flow behavior, and the average activation energy for plastic flow was calculated to be 267 kJ/mol.

Strain rate plays a nonnegligible role in the plastic deformation behavior of metallic materials with heterogeneous nanostructure, while little research focuses on the topic. In-situ compression tests at various strain rates were conducted on the micropillars located at different depths from the gradient lamellar Ni. These tests intended to reveal the strain-rate dependence of micropillars with different lamellar thicknesses and illustrated the competitive relationship between strain rate and intrinsic grain size on the plastic deformation behavior of metallic materials. In addition, due to the strain rate sensitivity related to not only intrinsic size but also external size, single Ni micropillars with different diameters were also compressed at various strain rates in order to clarify the competitive relationship between intrinsic size and external size on the strain rate sensitivity. It is found that lamellar thickness rather than strain rate has more effect on plastic deformation, and external size exhibits a more obvious impact on the strain rate sensitivity. The plastic deformation behaviors of different micropillars are mainly explained by transitions in the effect of lamellar grain boundaries on the dislocation motion at various strain rates and over different lamellar thicknesses, resulting in the change of dislocation multiplication and annihilation rate.

An important goal of industrial development is to improve the forming and thermomechanical processing technologies, both in order to get the best characteristics of finished products and to reduce energy costs and material consumption. The key step in solving such problems is the correct formulation of a material constitutive model. The temperature and strain rate attained in particular metal forming processes can vary significantly and have a strong influence on the structural evolution of the material and, consequently, on the resulting physical and mechanical properties. However, there are almost no processes in which the temperature and strain rate are constant and equal at all points of the processed product. In this regard, it is relevant to build constitutive models that correctly account for the influence of changing temperature and strain rate on the material response. Based on our previous review, we propose here a modified two-level statistical model that correctly accounts for the temperature and strain rate effects on intragranular dislocation slip and the associated material response. The model parameters are determined for an fcc polycrystal of Al 2024-T351 alloy using literature data on the compression behavior of this alloy at different temperatures and strain rates. A detailed description is given for an algorithm developed to identify the model parameters using data from constant temperature and constant strain rate experiments. The proposed model showed adequate results for loading conditions with changing temperature and strain rate. [ABSTRACT FROM AUTHOR]

Although the strain rate sensitivity of polymers processed by traditional technologies like injection molding has been extensively studied in the literature, limited research studies exist examining this sensitivity for fused deposition modeling (FDM). As such, in an exploratory approach, this study illuminates the strain rate sensitivity of five thermoplastic materials under various tensile test speeds, from 2.5 to 400 mm/min. This study aims to analyze strain rate influence on mechanical characteristics of FDM 3D-printed materials, particularly CPE+ and nylon. PLA, ABS, and PC are also used as additional materials for comparison purposes. The influence of strain rate on tensile strength, yield strength, toughness, and fracture morphology is examined. The outcome of this investigation can be used to better understand how FDM parts, made of various thermoplastic materials, behave when dynamic loading is present. [ABSTRACT FROM AUTHOR]

In this study, the effect of cyclic compression on the micromechanical properties of a Zr-based metallic glass (MG) was investigated via nanoindentation. Cyclic compression significantly softened the surface of the sample, with a maximum hardness loss of 19.93%. The number of cyclic compression passes had a greater effect on the hardness of the sample than the cyclic compression load. The elastic modulus exhibited a nonlinear variation upon increasing the cyclic loading or number of passes at a lower loading rate due to the coupling effect of loading rate and cyclic compression treatment. Then, the serration behavior and strain rate sensitivity analysis were applied. The calculated m-values obtained for MGs were all negative and gradually tended to zero upon further cyclic compression treatment. This demonstrated the weakening effect of cyclic compression on the strain rate sensitivity of MG, and the underlying mechanism was discussed. This study provides a process reference for studying the fatigue failure behaviors of MGs from the perspective of mechanical properties, which is useful for understanding their fatigue generation. [ABSTRACT FROM AUTHOR]

This study investigates the effects of matrix strength on the high‐rate tensile resistance and strain rate sensitivity of strain‐hardening fiber‐reinforced concretes (SHFRCs) under direct tensile loading. Two types of deformed steel fiber, hooked and twisted, were reinforced in two matrices, high‐performance concrete (HPC) with compressive strength of 84 MPa and ultra‐high‐performance concrete (UHPC) with compressive strength of 180 MPa. Additionally, an artificial neural network (ANN) based model was proposed to estimate the strain rate sensitivity of SHFRCs subjected to dynamic direct tensile loading. The results showed that HPC produced relatively lower post cracking strength but much higher strain capacity at a high strain rate than UHPC. Moreover, HPC was found to be more strain rate sensitivity than UHPC. Furthermore, the proposed ANN model was an efficient tool for predicting the strain rate sensitivity of SHFRCs. Based on the sensitivity analysis, the contribution of each influence factor on the final strain rate sensitivity of SHFRCs can be determined. [ABSTRACT FROM AUTHOR]

Perforation of the skin by fragment impact is a key determinant of the severity of an injury and incapacitation during modern asymmetric warfare. Computational models validated against experimental data are thus desired for simulating the responses of a skin simulant against fragment impact. Toward this end, experiments and concurrent computational modeling were used to investigate the dynamic responses of the skin simulant against fragment impact. Fragment simulating projectiles (FSPs) of masses 1.10 g and 2.79 g were considered herein, and the responses of the skin simulant were investigated in terms of the threshold velocity, energy density, peak displacement, and failure mechanisms. The results illustrate numerous salient aspects. The skin simulant failure involved cavity shearing followed by elastic hole enlargement, and these results were sensitive to the strain rate. The best agreement between the simulated and experimental results was achieved when the input stress–strain curves to the simulation were based on the full spectrum of strain rates. When a single stress–strain curve corresponding to a specific strain rate was used as the input, the threshold velocity and peak displacement of the skin simulant were either underpredicted or overpredicted depending on the strain rate considered. The threshold velocity was also sensitive to the input failure strain; here, the best agreement was obtained when the failure strain was based on the theoretical limiting strain. When the FSP materials were changed to plastics, the threshold velocities increased by up to 33%; however, the energy densities and generated stresses exceeded the contusion and laceration thresholds of the skin.

The evaluation of the hot workability of the super duplex stainless steel (SDSS) material still lacks scientific and theoretical basis, leading to the frequent occurrence of unacceptable defects in its forgings. In this study, a novel method for estimating the hot workability of S32906 SDSS was proposed and verified through forging. Firstly, the flow behavior and microstructural characteristics were demonstrated by conducting isothermal compression tests at the deformation temperature from 1000 °C to 1250 °C and the strain rate from 0.01 s−1 to 10 s−1. The influence of microstructure on flow and work hardening behaviors was correlated and displayed. Then, based on the deformation characteristics presented through the variations of strain rate sensitivity (SRS) and deformation temperature sensitivity (DTS) coefficients, the SRS and DTS maps were constructed and overlaid for obtaining the hot working window. Ultimately, a large plate type forging of S32906 SDSS applied in engineering was used to verify the applicability of the obtained window. The new method can provide an in-depth understanding of hot workability and enable control of the forming and microstructural properties for this unique material.

The superplastic forming (SPF) process is the large plastic deformation ability of metals and alloys. However, SPF ability can only be achieved under certain conditions including ultrafine grain (UFG) microstructure, high temperature, and very small strain rate. In this work, the high-strength aluminum alloy AA7075 was selected for the experimental process due to its outstanding industrial application. First, thermomechanical processing (TMP) is performed to create a fine stable grain size for the studied alloy. The UFG microstructure was obtained after TMP with an average grain size of about 10 μm. Subsequently, the tensile test method and the bulging free -forming (BFF) method were used to evaluate the superplastic properties of the AA7075 aluminum alloy sheet fabricated by TMP. These two method s are performed at temperatures of 500ºC and 530ºC with strain rates from 10-4 (s-1) to 10-3 (s-1). The relative elongation and the strain rate sensitivity are the evaluation criteria. At the temperature of 530ºC and strain rate of 10-3 (s-1), the maximum relative elongation and flow stress were achieved at 280% and 7.6 MPa, respectively. The value of the coefficient m ranges from 0.3 to 0.6. The obtained results confirm the SPF properties of the aluminum alloy sheet AA7075. [ABSTRACT FROM AUTHOR]

Nanoindentation tests were conducted on in-situ Al3Ti particulate reinforced Al-7Si alloy to investigate the strain rate sensitivity at room temperature. The indenter was loaded to a fixed maximum load with different loading strain rates. Hardness was investigated based on continuous stiffness measurement. Results show that the eutectic Si in Al3Ti particulate reinforced Al-7Si is modified to short fibrous morphology due to addition of Sr. Al3Ti particulate reinforced Al-7Si exhibits dependence on loading strain rate in terms of hardness. T6 heat treatment spheroidizes eutectic Si phases into round Si particles. Microstructure uniformity of materials is enhanced and the strain rate sensitivity becomes less pronounced. Strain rate sensitivity of the specimen is improved after cryogenic treatment, along with the refinement of α-Al grains and eutectic Si. [ABSTRACT FROM AUTHOR]

Nano-indentation technology can not only analyze the nano-hardness and elastic modulus, but also extract the creep properties. In the current study, the nanostructured La 2 (Zr 0.75 Ce 0.25) 2 O 7 (LCZ) coating were successfully constructed by atmospheric plasma spraying (APS). Furthermore, the indentation creep characterization of LCZ coating was systematically analyzed by nano-indentation. Results imply that power-law formula can well fit the curve relationship between indentation depth and time in the creep process of LCZ coating. The determined strain rate sensitivity of LCZ coating is 0.0134 ± 0.0045. The study provides support for further research on creep properties of nanostructured LCZ coating in the future. [ABSTRACT FROM AUTHOR]

The thermal stability and temperature dependent hardness of ultrafine-grained Cu-alloys CuSn5 and CuZn5 after high pressure torsion are investigated using the high temperature scanning indentation (HTSI) method. Fast indentations are carried out during thermal cycling of the samples (heating-holding-cooling) to measure hardness and strain rate sensitivity as a function of temperature and time. The microstructures after each thermal cycle are investigated to characterize the coarsening behaviour of both alloys.Results show that the thermal stability of the tested alloys can be expressed in terms of several temperature regimes: A fully stable regime, a transient regime in which growth of individual grains occurs, and finally a regime in which the microstructure is fully coarsened. The onset of grain growth is accompanied by high strain rate sensitivity on the order of 0.2–0.3. Furthermore, the obtained hardness and strain rate sensitivity values are in good agreement with continuous stiffness measurement (CSM) and strain rate jump (SRJ) experiments. This highlights the applicability of the HTSI method to the characterization of the thermomechanical properties of ultrafine-grained alloys.

An extruded Mg−6Gd−3Y−1.5Ag (wt%) alloy was processed by 6 passes of equal channel angular pressing (ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction (EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 µm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization (DRX). This microstructure contained fine grains with an average size of 1.3 µm, a high fraction of high angle grain boundaries (HAGBs), and nano-sized Mg5Gd-type particles at the boundaries of the DRXed grains, detected by transmission electron microscopy (TEM). High-temperature shear punch testing (SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity (SRS) index (m-value). While the highest m-value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m-values of 0.41 and 0.52 at 598 and 623 K, respectively, delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol−1 and m-values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding (GBS) assisted by grain boundary diffusion.

In the present study, the behavior of type A serrations according to strain rate was investigated using the room-temperature tensile flow curves of Fe-18Mn-0.55C (wt%) steel specimens. In the strain rate range from 1 × 10−1 /s to 5 × 10−5 /s, a critical strain (ecA) of type A serrations was reduced with decreasing strain rate, indicating a normal Portevin-Le Chatelier (PLC) behavior. However, at the slow strain rates ranging from 5 × 10−5 /s to 1 × 10−6 /s, ecA was increased again with decreasing strain rate, although dynamic strain aging occurred just after yielding. This inverse PLC behavior of type A serrations was explained by applying the concept of the drag force (Fd) by the Cottrell atmosphere on aged dislocations to the existing mechanism of negative strain rate sensitivity. Fd was reduced with decreasing strain rate from 5 × 10−5 /s to 1 × 10−6 /s, suppressing the formation of the PLC band for type A serration.

ABSTRACTFive different chocolate types (i.e. extra dark, dark, milk, white, and ruby) were characterized and compared for the acoustical and textural characteristics. Acoustic properties were described in terms of longitudinal and transversal wave velocities. These velocities were used for the evaluation of elastic constants namely Young modulus and Poisson ratio. The values of the Young moduli are significantly higher than those obtained using uniaxial compression and tensile tests. At the same time, the values of Poisson ratio are in reasonable agreement with results of these methods. Texture characteristics were evaluated using of the compression test at loading rates (crosshead velocity) 1, 10 and 100 mm/min. Results are presented in form of stress vs strain. The stress-strain dependences obtained from the compression test exhibited two different regions of the sensitivity of stress to the applied strain. The linear dependence stress- strain is taken as the evidence of the elastic behavior of the tested material. The extent of this region was given by the strain, which was the same for all tested chocolates. Its value increased with the loading rate. The stress-strain behavior in this region was only slightly dependent on the loading rate with exception of the ruby and dark chocolates. The stress-strain dependence in the following region was significantly dependent on the strain rate. Values of the strain rate sensitivity were evaluated. The order of the tested chocolates according to the values of stress at the given strain was identical with that obtained using of the elastic wave velocities.

Explosive welding interface commonly show wavy shapes, makes microstructure anisotropic. The effects of microstructure and different loading directions on shear properties of bonding interfaces at dynamic loading conditions are still unclear. In this work, characteristics on transverse and longitudinal sections of TA2/Q235 welding interface was characterized by optical microscopy. It was found that the transverse sections of bonding interface showed wavy shapes with wavelength and amplitude of 1200 μm and 400 μm. The longitudinal sections of bonding interfaces were composed of wavy interface, dislocation shaped interface and stacking fault shaped interface, which was explained by non-equilibrium theory. A small-size S-shaped specimens was processed to investigate shear properties of bonding interface varied with orientation angles (0°, 45°and 90°) at both quasi-static (0.001 s−1) and dynamic (5000∼7000 s−1) loadings. Meanwhile, fracture mechanism of interfaces was analyzed by scanning electron microscopy coupled with energy dispersive spectrometer. The results indicated that the maximum shear strength of joining interfaces (380 MPa–410 MPa under quasi-static loading, and 450 MPa–600 MPa under dynamic loading) was obtained along 90° orientation angle. Fluctuation of explosive detonation pressure was the fundamental cause of the interface inhomogeneity, and strength of joining interfaces increases with increasing strain rates, indicating positive strain rate sensitivity. Fracture mainly occurred in bonding interfaces near TA2 side at quasi-state loading, and failure occurred in interface waves at dynamic loading because of TA2 showed more obvious strain rate sensitivity than Q235. Fracture morphology indicated the ductile-brittle mixed fracture occurred in both quasi-static and dynamic tests.

Since Fe–Mn–Si–Cr shape memory alloy (Fe-SMA) has been discovered, an improvement of the shape memory effect (SME) is challenged. Numerous attempts have been made thus far to improve SME. To effectively control such performance, it becomes imperative to comprehend the real-time behavior of the stress-induced martensitic transformation (SIMT), which is strongly related to SME, during deformation. In the past, the measurement of volume resistivity has been proposed and applied to capture the forward SIMT behavior during the tensile loading process at various strain rate. However, it is quite hard to find investigations of the reverse martensitic transformation after the loading, which is more essential for understanding SME. Therefore, a comprehensive evaluation of the whole SIMT process including the loading process at various strain rate is strongly required. In this study, an improved measurement of volume resistivity is established by introducing both the four-probe and active-dummy techniques with a development of a diameter measurement at high temperature. Then, the volume resistivity of Fe-SMA is measured during the whole deformation including loading under tension at various strain rate, unloading, and heating processes. Besides, the microstructures of Fe-SMA after unloading and heating processes are observed, respectively. Finally, the real-time whole martensitic transformation in Fe-SMA is first investigated with the novel optimization method. The negative strain rate of change in volume resistivity during whole processes can be found. More amount of austenite can be obtained at lower strain rate, resulting in a larger SME.

The mechanical properties and rate-sensitive deformation of T4 and T6 AA6063 aluminum alloys have been analyzed at 298 K, 78 K, and 4 K. The strength, ductility, and work hardening capacity of two alloys increase with decreasing deformation temperature. Plastic deformation of AA6063-T4 is accompanied by adiabatic flow stress instabilities at 4 K and the Portevin-Le Chatelier (PLC) effect at 298 K. The alloy shows a better synergy of flow stress and work hardening than the T6 condition, determined by the underlying microstructure. The limited ability of dislocation storage in T6 alloy arises from shearing β″ particles and the enhanced dislocation annihilation occurring in pure Al matrix. The failure of the alloys is promoted by void nucleation at intermetallic particles before the Considére criterion is fulfilled. AA6063-T6 exhibits positive strain rate sensitivity (SRS) at three temperatures. Dislocations-β″ particle interactions determine its SRS and are a rate-controlling process at 298 K. AA6063-T4 shows negative strain rate sensitivity (nSRS) at 298 K controlled by dislocation-solute interactions. Data for SRS and thermodynamic deformation parameters characterizing different mechanisms in T4 and T6 alloys between 4 K and 298 K are discussed. The results indicate that plastic deformation produces vacancies by jogs' dragging at 298 K, but this process does not occur at 78 K and 4 K.

We introduce a new nanoindentation method to continuously measure the hardness while sweeping through orders of magnitudes of strain rates within a single experiment. While nanoindentation already allows the determination of the strain rate sensitivity of materials by means of strain rate jump tests, these are typically limited to few discrete strain rates. With the new method, the strain rate sensitivity can be measured continuously as a function of the strain rate. Applications to fused silica, Zn-22 %Al superplastic alloy, single crystalline aluminum, various nanocrystalline metals and a palladium-based metallic glass are shown. Besides some discrepancy with the reference measurements, the new method seems only affected by the presence of a strong nanoindentation size effect. Provided this indentation size effect is not excessively large and can be corrected for accurately, the method proves robust, with no suggestion that the direction of the strain rate sweep affects the evaluation of the strain rate sensitivity.

AbstractThe effects of quasi-static strain rates on the tensile properties of two commercial ferrite-martensite dual-phase DP 600 and DP 800 steels were investigated using strip-shaped samples. The investigation was done by uniaxial tensile tests, covering applicable quasi-static strain rates. The two dual-phase steels show positive strain rate sensitivity. It is found that, as the flow stress increases, the strain-rate sensitivity exponent m decreases. The drop in the strain-rate sensitivity exponent m with strain is largely attributed to the decreased true strain rate caused by the increased instantaneous length of the specimen as the deformation progresses. To better describe the flow behavior of DP steels, a relationship combining the effect of both strain hardening exponent n and strain-rate sensitivity exponent m on the slope of the stress-strain is correlated. A good agreement between the extended Hollomon model and experimental tensile test data from stress-strain measurements is found.

The mechanical behavior, microstructures, as well as the crystallographic textures of the Ti57-Nb43 alloy were investigated on cylindrical specimens compressed at high temperatures, in the range of 700–1000 °C, and strain rates between 0.001 and 1.0 s−1. Hardening, followed by softening behaviors, were observed as a function of strain due to the occurrence of dynamic recrystallization/recovery in hot deformation. The modified five-parameter Voce-type equation described well the stress–strain curves, but, for the present alloy, it was also possible with only four parameters. A new two-variables polynomial function was employed on the four parameters that described well the flow curves as a direct function of temperature and strain rate. It permitted the reduction in the number of parameters and had the predictive capacity for the flow stress at any temperature, strain, and strain rate in the investigated range. The crystallographic textures were similar at all temperatures, with an increase in intensity from 900 °C. The textures could be characterized by a double <100> and <111> fiber and a unique component of (001) <110>, the latter inherited from the initial hot-rolling texture. Viscoplastic polycrystal self-consistent deformation modeling reproduced the measured textures showing that dynamic recrystallization did not alter the development of the deformation texture, only increased its intensity. [ABSTRACT FROM AUTHOR]

This research was devoted to unveiling the strain rate sensitivity (SRS) of G18NiCrMo3-6 cast steel in tension/compression asymmetry. For that purpose, detailed mechanical characterization tests were conducted providing a process window covering quasi-static and medium strain rate regimes (0.001, 0.1, 10 [s−1]) in tension and compression states. Through this experimental effort, the SRS of the material could be extracted by a function of strain and the strain rate which enabled us to create a mathematical expression to easily be implemented as a state variable for constitutive material modeling. Finally, a pressure- and rate-dependent constitutive material model on the basis of the Cocks'89 yield locus definition was created using a subroutine (UMAT) file and the material parameters were verified with respect to the experimental data. The UMAT file also takes into account the tension/compression asymmetry in yielding to handle the effect of the porous media plasticity concept. The predictions of the proposed material model are in line with the experimental outputs. [ABSTRACT FROM AUTHOR]

This study examines the changes in strain rate dependence and the deformation behavior of near-eutectic Sn-Bi alloys as a function of Sb concentration using nanoindentation. Alloying near-eutectic Sn-Bi solder with Sb has been shown to increase the strain to failure under tensile and shear conditions in solder ball geometries, with Sb additions remaining in solid solution up to 0.5 wt.% Sb. In this study, the resulting hardness of the three Sb-containing Sn-Bi alloys (Bi-42Sn eutectic, Bi-42Sn-0.5Sb, Bi-42Sn-1.0Sb) exhibits little solid solution hardening at room temperature, and the alloys all exhibited similar strain rate sensitivity behavior, independent of composition for this microstructure. Using nanoindentation and post-indentation microscopy to analyze the deformation behavior of these alloys, the out-of-plane deformation and slip behavior does change with composition. Solute Sb increases the strain hardening behavior at low strains while decreasing planar slip and out-of-plane deformation. The observed changes in deformation modes in this nanoindentation study with the addition of Sb as a solid solution alloy (less slip planarity, more uniform deformation, and more strain hardening) could play a role in previously observed changes in tensile failure modes without the formation of SbSn intermetallic compounds. [ABSTRACT FROM AUTHOR]

An extruded Mg−6Gd−3Y−1.5Ag (wt%) alloy was processed by 6 passes of equal channel angular pressing (ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction (EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 µm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization (DRX). This microstructure contained fine grains with an average size of 1.3 µm, a high fraction of high angle grain boundaries (HAGBs), and nano-sized Mg 5 Gd-type particles at the boundaries of the DRXed grains, detected by transmission electron microscopy (TEM). High-temperature shear punch testing (SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity (SRS) index (m -value). While the highest m -value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m -values of 0.41 and 0.52 at 598 and 623 K, respectively, delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol−1 and m -values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding (GBS) assisted by grain boundary diffusion. [ABSTRACT FROM AUTHOR]

The frequently used metallurgical parameters such as activation volume, internal stress, strain rate sensitivity, and dislocation density are identified in ultrafine-grained (UFG) materials through erudite analytical relations. It is difficult to analyze such parameters optically since the material consists of highly distorted and inhomogeneous microstructure due to the large strain imposed during the constrained groove pressing (CGP) process. Hence, transient tests like stress relaxation tests are advantageous over the optical to use. Apart from the identification of parameters in low-carbon steel materials using uniaxial loading and stress relaxation tests, the relationship between the parameters is nobly investigated in as-received and UFG structure samples produced through the CGP process. In the relationship, the exponential-power law constitutive to describe the accurate stress–strain curves, identification of mobile and forest dislocation density during strain hardening, and exponential variation between grain size and activation volume are proposed. The replenishment or exhaustion of mobile and forest dislocation density significantly affects the metallurgical parameters during uniaxial tensile loading followed by stress relaxation testing. In this experimental and analytical work, the CGP process produces a UFG material that has lower activation volume and higher stress drop, mobile dislocation density, forest dislocations density, strain rate sensitivity, and internal stress. [ABSTRACT FROM AUTHOR]

Superplasticity of a coarse-grained cast Mg–2.5Gd–0.5Zr alloy was investigated by assessing the strain rate sensitivity index (m-value) through the shear punch testing (SPT) method in the temperature range of 623–748 K and shear strain rate range of 2.8 × 10−3–2.2 × 10−2 s−1. The initial as-cast grain size of about 150 μm was reduced to about 3.5 μm at the end of the test. This severe grain refinement caused by dynamic recrystallization (DRX) facilitated superplasticity in the studied cast alloy. According to the respective m-values of 0.51 and 0.53 obtained at 698 and 723 K, and the activation energy of 80 kJ mol−1, the prevailing mechanism of deformation was suggested as grain boundary sliding (GBS) controlled by grain boundary diffusion.

To overcome the limitation in formability at room temperature, manufacturers have developed magnesium alloys with remarkable properties by adding rare-earth elements. The rare-earth magnesium alloys behave differently from the conventional alloys, especially with respect to their coupled anisotropic and strain rate sensitive behavior. In the current work, such behavior of the rare-earth Mg alloy ZEK100 sheet at room temperature is investigated with the aid of the elastic viscoplastic self-consistent polycrystal plasticity model. Different strain rate sensitivities (SRSs) for various deformation modes are employed by the model to simulate the strain rate sensitive behaviors under different loading directions and loading rates. Good agreement between the experiments and simulations reveals the importance and necessity of using different SRSs for each deformation mode in hexagonal close-packed metals. Furthermore, the relative activities of each deformation mode and the texture evolution during different loadings are discussed. The anisotropic and strain rate sensitive behavior is ascribed to the various operating deformation modes with different SRSs during loading along different directions.

We propose and assess a new experimental technique to measure the fracture toughness of engineering materials and its sensitivity to strain rate. The proposed method is based on a ring expansion technique and it overcomes the limitations of current dynamic fracture tests, as it is not affected by transient stress wave propagation during loading and it results in spatially uniform remote stress and strain fields prior to fracture; the method is also suitable to achieve remote strain rates well in excess of 1000 s−1. We demonstrate the technique by measuring the plane-stress Mode I fracture toughness of PMMA specimens at remote strain rates ranging from 10−3 s−1 to 102 s−1. The experiments show an increase of the toughness of the material with increasing strain rate.

Knowing the mechanical behavior of silicon at elevated temperatures is crucial for many high-temperature applications and processes. This work aims to expand the knowledge of these properties, especially on length scales relevant to miniaturized silicon structures. Therefore, nanoindentation experiments were performed on two differently doped (1 0 0) silicon wafers with varying oxygen content, from room temperature up to 950 °C. Residual impressions were microscopically characterized via confocal laser scanning microscopy. From this dataset covering an exceptionally large temperature range the elastic modulus and hardness as well as strain rate sensitivity, activation volume, and energy were evaluated. Generally, a change in deformation behavior can be identified between 300 °C and 400 °C. Above this transition temperature, the hardness drops exponentially. Also, the material becomes strain rate sensitive. These observations support the assumption that the deformation mechanism shifts from high-pressure phase transformation to dislocation-controlled plasticity with increasing temperature. Furthermore, a change in strain rate sensitivity, activation energy, and activation volume above 800 °C implies a further shift in the rate-controlling mechanism of dislocation motion. Lastly, the more strongly doped sample with the higher oxygen content showing higher mechanical strength is discussed regarding solid-solution strengthening and dislocation locking by oxygen atoms.

This study proposes an empirical relationship between the hardness and tensile strength of a busbar to predict the tensile strength of a bended section in the busbar under different strains and strain rates. Moreover, this study theoretically confirms the contributions of the strain rate to the overall tensile properties of a pure copper (Cu) plate. A commercial pure-grade Cu plate was fabricated through warm rolling from a round billet, and a prototype specimen of a busbar was fabricated using a die-free core bending process. The tensile specimens were subject to a given nominal strain (5–40%) in a strain rate of 4.17 × 10–5 to 4.17 × 10−2 s−1, and their hardness was measured to construct an empirical relationship between their tensile strength and hardness. The empirical relationship could be described as a linear relation, in which the slope increases with increasing strain rate. Additionally, from the empirical relationship, the tensile strength and strain rate applied in the bending process of the busbar prototype could be indirectly evaluated through hardness measurement. The tensile strength of the Cu plate increased with increasing strain rate, and the strain required to reach a specific stress level significantly decreased as the strain rate increased. This increase in the tensile strength and decrease in the tensile strain with increasing strain rate is because while the strength coefficient and strain-hardening exponent increase as the strain rate increases, the strain rate sensitivity decreases. [ABSTRACT FROM AUTHOR]

Slow strain rate tensile (SSRT) experiments were applied to comprehensively examine the strain rate susceptibility of the stress corrosion cracking behaviour of commercial Zr702 used in the spent nuclear fuel reprocessing environment. Results revealed that layers formed on Zr702 in boiling HNO3 solutions was composed of monoclinic ZrO2 (m-ZrO2) and tetragonal ZrO2 (t-ZrO2). With strain rates above 10−4 s−1, oxide layers ruptured rapidly, evidenced by the drop down of opened circuit potential (OCP). However, the OCP curve displayed fluctuation with 10−5 s−1 during straining, indicating that oxide layer alternately ruptured and repaired, resulting in the thickening of the oxide layer and increasement of stress corrosion cracking susceptibility. [ABSTRACT FROM AUTHOR]

In the last three decades, several severe plastic deformation (SPD) procedures have been developed and applied in materials science to create bulk, ultrafine-grained (UFG) structures. As a consequence of the SPD, not only submicron and even nanometer grain sizes can be obtained, but also new grain boundaries with non-equilibrium structures in a material may be formed. Therefore, both the strength and ductility of the UFG materials can change significantly compared to the coarse-grained counterparts. This review is focused on unusual mechanical behaviors of UFG Al and Al alloys, associated with grain boundary structure and segregations which are responsible for the modification of the Hall-Petch relationship and the so-called size-effect for UFG structure. Unusually high strain rate sensitivity, intensive grain boundary sliding and superplasticity at low temperature are described and surveyed. In addition, innovation potential of these phenomena is also briefly considered. [ABSTRACT FROM AUTHOR]

This study presents that A1050 commercial-purity aluminum increases the tensile strength and ductility using the processes of accumulative roll bonding (ARB) and high-pressure sliding (HPS). Both processes yield a similar tensile strength exceeding 240 MPa after processing by ARB for 10 cycles and by HPS for the sliding distance of 15 mm, respectively. The stress-strain behavior is evaluated through microstructure observations and measurements of strain hardening rates. Significant grain refinement with well-defined grain boundaries is responsible for the strength increase. The grain refinement also leads to an increase in strain hardening rate and thus an increase in the ductility. [ABSTRACT FROM AUTHOR]

The effects of quasi-static strain rates on the tensile properties of two commercial ferrite-martensite dual-phase DP 600 and DP 800 steels were investigated using strip-shaped samples. The investigation was done by uniaxial tensile tests, covering applicable quasi-static strain rates. The two dual-phase steels show positive strain rate sensitivity. It is found that, as the flow stress increases, the strain-rate sensitivity exponent m decreases. The drop in the strain-rate sensitivity exponent m with strain is largely attributed to the decreased true strain rate caused by the increased instantaneous length of the specimen as the deformation progresses. To better describe the flow behavior of DP steels, a relationship combining the effect of both strain hardening exponent n and strain-rate sensitivity exponent m on the slope of the stress-strain is correlated. A good agreement between the extended Hollomon model and experimental tensile test data from stress-strain measurements is found. [ABSTRACT FROM AUTHOR]

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Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It was shown recently that the grain size contribution to the flow stress and strain rate sensitivity of pure metals having different structures can be estimated by a model of deformation for grain boundary sliding. The present research extends this earlier study by estimating the grain size contribution to the flow stress in the CrMnCoFeNi high entropy alloy. This alloy has attracted significant attention in recent years due to its remarkable mechanical properties which include a higher strength compared to f.c.c. pure metals due to a significant contribution from solid solution strengthening. The present work demonstrates that the flow stress of the CrMnCoFeNi alloy can be readily estimated from the sum of the contributions from solid solution and grain size strengthening. There are some unique experimental trends observed in this alloy and these provide supporting evidence for the assumption that the grain size strengthening is thermally-activated. The flow stress, strain rate sensitivity, activation volume and activation energy are predicted for different grain sizes and testing conditions as a function of the fundamental properties of this alloy and the results show excellent agreement with the reported experimental data.