Strain Rate Conditions Research Articles

Effects of Different Strain Rates on the Impact Properties of Recycled Aggregate Concrete Modified With Nanosilica Solution and Polyvinyl Alcohol Fiber

The recycled aggregate (RA) was modified by 2% nanosilica solution, and the split Hopkinson pressure bar (SHPB) test device was used to study the dynamic impact properties of the modified recycled aggregate concrete (RAC) mixed with polyvinyl alcohol (PVA) fibers. The RA replacement percentage, the amount of PVA fiber, and the strain rate were variables. The failure pattern, the stress–strain curve of the nanosilica solution, and PVA fiber-modified RAC were shown under different strain rate conditions. Dynamic peak stress, peak strain, and dynamic increase factor (DIF) of the specimens are discussed. The results showed that the stress and dynamic peak strain value of the specimen increased with the increase of the strain rate; moreover, with the increase of the RA replacement percentage and the PVA fiber content, the dynamic peak stress of the specimen decreases, while the dynamic peak strain and the DIF value increase. The incorporation of nanosilica-modified RA is beneficial to the improvement of the impact performance of RAC, and the incorporation of an appropriate amount of the PVA fiber effectively improves the deformability of RAC.

Analysis of compressive dynamic behaviors of plain concrete and lightweight aggregate concrete

In this paper, 8 loading strain rates were configured to carry out experimental research on the compressive dynamic behaviors of plain concrete (PC) and lightweight aggregate concrete (LWAC) by utilizing a hydraulic servo machine. The compressive failure modes and stress-strain curves of PC and LWAC under various loading states were generated from the experiments. The peak stress and peak strain values extracted from the stress-strain curves, as well as the elastic modulus, were comparatively analyzed between the two types of concrete. The experimental findings indicate that the failure mode of PC under the static strain rate mainly manifest as the damage to bonding materials, while the failure under dynamic strain rates involves part of coarse aggregates. For LWAC, the failure modes under both static and dynamic loading mainly manifest as the damage to shale ceramisite. As the strain rate increases, the peak stress and elastic modulus of both PC and LWAC increase significantly. Compared with PC, the strain rate effect on LWAC is more obvious. The peak strain of both PC and LWAC varies insignificantly across different strain rates, even though the changing trend shows a discrete pattern. In addition, on the basis of the experimental results, the relationship equations between the strain rate and the related mechanical parameters were established for both PC and LWAC. It is found that the values of peak stress and elastic modulus and the logarithmic value of the corresponding strain rate after non-dimensional treatment fit a linear relationship. The findings provide theoretical insights into the research and engineering application of LWAC.

A Two-phase Constitutive Model with Damage for Tungsten Heavy Alloy

Tungsten heavy alloy is a kind of two-phase alloy composed of high-strength tungsten phase and binder phase with good-plasticity. Its mechanical properties and damage evolution are affected by both phases. The static and dynamic mechanical tests of 92.5W-4.9Ni-2.1Fe-0.5Co are carried out. According to the characteristics of stress-strain curves, KHL model is selected as the constitutive model of the material. Then, combined with Eshelby equivalent inclusion theory and Mori Tanaka mean field theory, the stress-strain relationship of each phase in tungsten heavy alloy is studied by introducing representative volume element (RVE). The damage evolution model considering the strain rate effect is proposed, and according to the different loading states, a two-phase constitutive model with damage is established. By compiling the UMAT subroutine, the test conditions of different strain rates are calculated in ABAQUS software. The simulation results are in good agreement with the test results, and the validity of the proposed model is verified.

Hot Deformation Behavior of Cu-2.7Be Alloy during Isothermal Compression

The hot deformation behavior of Cu-2.7Be alloy was studied through isothermal hot compression experiments under various temperature and strain rate conditions. To predict and investigate the flow stress behavior, modified Johnson–Cook, Arrhenius-type, and artificial neural network models were used. The predictabilities of the models were assessed considering the parameters of average absolute relative error, correlation coefficient, and relative error. Among the three constitutive models, the ANN model was revealed to be the most accurate. According to the results of the dynamic material model theory, the hot processing of Cu-2.7Be alloys achieved its maximum efficiency (~60%) under a strain rate of 0.6 s−1, temperature range of 1023-1073 K, and the logarithm of strain rate in the range (− 1.25)-(− 0.25) s−1. Microstructural analysis indicated that the temperature and strain rate factors significantly affected the primary dynamic softening mechanism of the Cu-2.7Be alloys, following hot compression processing. At temperatures below 973 K, the Cu-2.7Be alloy primarily obeyed the dynamic recovery mechanism. Furthermore, the predominant mechanisms followed by the samples under the temperature/strain rate conditions of 973/0.1 and 1073 K/0.1 s−1 were continuous dynamic recrystallization and discontinuous dynamic recrystallization, respectively.

Mechanical characterization of Araldite LY 564 epoxy: creep, relaxation, quasi-static compression and high strain rate behaviors

A comprehensive mechanical characterization of a commercially available hot curing epoxy system (Araldite® LY 564 with Aradur® 2954, HUNTSMAN Corp.) is performed including compression tests at quasi-static and high strain rates, as well as creep and relaxation tests. High strain rate tests (770/s and 875/s) are conducted by using a split-Hopkinson pressure bar (SHPB) apparatus and compared with the quasi-static compression tests at three strain rates (0.001/s; 0.01/s; 0.1/s). Elasticity modulus and yield stress increase with increasing strain rate, for both quasi-static and high strain rate conditions. The change in the mechanical behavior from quasi-static to high strain rate conditions is quite prominent. While strain rate changes from 0,001/s to 875/s, elasticity modulus increases from 1465 to 3193 MPa (118% increase) and yield stress from 119 to 204 MPa (72% increase). The evident exponential hardening at the viscoplastic region seen on quasi-static stress–strain curves is not observed at high strain rates. Creep tests are performed for three different stress levels (50, 100 and 200 MPa) and 120 min (7200 s). In addition, relaxation tests are done for three different strain levels (3.16, 7.15 and 35.5%) also for 120 min (7200 s). Creep compliance and relaxation modulus are calculated and plotted. It is observed that creep strain values at the stress levels lower than the yield point are lesser compared to creep strain values around yield strength since rate dependency is increasing with increasing stress. Creep at the hardening region is not prominent due to polymer chain entanglement. Stress drop during relaxation is increasing with the increasing strain level.

A new phenomenological constitutive model for thermoplastics

A new phenomenological constitutive model is proposed to predict the mechanical behaviour of thermoplastics in the current research. The new constitutive model and the method to determine the parameters of the model are introduced. In the new model, a transition function is proposed to enable a smooth transition of the flow stress behaviours under both small-strain and large-strain conditions. In validating the model with testing data of Polyetheretherketone (PEEK) and Polycarbonate (PC), it is found that this new model is able to predict different phases of the flow stress behaviour of thermoplastics in consideration of the effect of strain, strain rate and temperature. Although the basic trends of tensile and compressive behaviours of PEEK and PC materials are different, the new constitutive model can be used to represent these behaviours effectively. In addition, the results show that the new model gives a favourable prediction of the PC material at high strain rate conditions. Compared with Johnson-Cook, Nasraoui et al., Duan-Saigal-Greif-Zimmerman (DSGZ) and Mulliken-Boyce models, the new model presents an improved level of accuracy on the mechanical behaviour of thermoplastics in a wide range of deformation conditions.

Stretch Forming Behavior and Constitutive Equation of a Modified 5083 Alloy with High Mg Content at Elevated Temperatures

For the purpose of applying a modified 5083 alloy (New 5083M alloy) with high Mg content in various automotive sheet parts, the stretch forming behavior of the 5083M alloy was studied in tensile mode at a wide range of processing conditions. The tensile tests were conducted by using a tensile test machine under the temperature ranges of 100–400 °C and the strain rate ranges of 0.001–1 s−1. The test results showed that the 5083M alloy has superior mechanical properties to that of the commercial 5083 alloy at elevated temperatures. The microstructure before and after the stretch forming was analyzed using optical microscope (OM) equipped with a polarizing filter and electron backscattered diffraction (EBSD) unit. Deformed microstructure was observed under low temperature conditions and dynamic recrystallized microstructure under high temperature conditions. However, regardless of microstructure evolution, developed deformation textures were distributed in orientation distribution functions (ODF) images. In addition, at high temperature and low strain rate condition, complex shaped cavities which were detrimental to mechanical properties appeared at the grain boundary and grain triple junction. Based on the test results data, a constitutive equation predicting the deformation behavior of the 5083M alloy was derived. The calculated curves by the constitutive equation were compared with the measured curves by experiment and agreed well.

Hot Deformation Behavior and Processing Map of 5356 Aluminum Alloy

The hot compression deformation of 5356 aluminum alloy was performed with the deformation temperature 300∼500°Cand the strain rate 0.01∼10s−1 by using Gleeb1e-3500 thermal mechanical simulator. The microstructure of the alloy was analyzed by ZEISS metallographic microscope. The results show that the flow stress of 5356 aluminum alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. 5356 aluminum alloy is mainly dynamic recovery under low strain rate conditions, such as 0.01 S−1, 0.1 S−1. The alloy is discontinuous dynamic recrystallization under high strain rate conditions, such as 1 S−1, 10 S−1. The hot processing map of 5356 aluminum alloy was established with the strain of 0.2∼0.5, can provide an effective data reference for the development of high-end 5356 aluminum alloy wire continuous rolling process.

Effects of strain rate on austenite stability and mechanical properties in a 5Mn steel

The austenite stability and the mechanical properties in a typical medium Mn grade steel, i.e., 5Mn steel, were investigated under a wide range of strain rates through the combination of experimental and theoretical methodologies. The obtained results indicate that austenite is more stable at a high strain rate, which is due to the suppression of the austenite to martensite transformation. This suppression is attributed to the increased stacking fault energy and the high deformation energy barrier. Moreover, the suppression of martensitic transformation also leads to the decrease in the ultimate tensile strength and the uniform elongation. Owing to the increase in an adiabatic heating temperature, an increase in the uniform elongation is acquired at a high strain rate. The obtained fundamental study results shed light on a wide application of the medium Mn steel under different strain rate conditions.

Prestressed bridge deck responses to blast loads

Bridges are critical to most transportation systems, especially in times of crisis; however, as highly visible and accessible structures, they are also potential targets for terrorist attacks. An understanding of the performance of bridges subjected to blast loads is of critical importance to prevent progressive collapse of such structures that could lead to a catastrophic loss of life. The current research focuses on investigating the behaviour of bridge decks under blast loads from various explosions. The bridge in this investigation is the Sheikh Saad Bridge in Wassit Province, Iraq, whose deck is made of simply supported spans with two types of prestressed concrete girders. Both spans were accurately modelled using the finite element software Abaqus/Explicit, and both concrete and steel mechanical material properties were modified to match the properties under high strain rate conditions of the blast analysis. The latest element deletion technique of the built-in Concrete Damaged Plasticity (CDP) model (available since Abaqus 2019) was used to provide a realistic simulation of concrete damage and spalling. The model was separately subjected to various explosive charges placed at different locations above or below the bridge deck in order to determine the influence of size and location of blast on the bridge superstructure, detailed results and the relevant conclusions are thus presented. Overall, the modelling managed to successfully simulate the blast load response and the cracking propagation within the damaged deck components.

Rheology of Felsic Granulite at High Temperature and High Pressure

AbstractRheological properties of continental lower crust (CLC) are essential for understanding many geodynamical processes in the Earth. Here we performed a series of deformation experiments on synthetic felsic granulite (65% plagioclase + 15% quartz + 9% clinopyroxene + 6% orthopyroxene + 5% amphibole) using a 5 GPa modified Griggs‐type deformation apparatus at 827–927°C and 1 GPa. All experiments have reached a steady‐state creep under conditions of constant pressure, temperature, and strain rate. Our data yield the following flow law:, whereis in s−1,σin MPa, andTin Kelvin. Microstructural observations show that plagioclase and pyroxene in deformed samples develop noticeable intracrystalline plasticity and shape preferred orientation (SPO). Electron backscatter diffraction (EBSD) measurements demonstrate more significant crystallographic preferred orientations (CPOs) of pyroxene and plagioclase in deformed granulites compared to those in hot‐pressed ones. By contrast, quartz develops nearly random fabrics probably due to the simultaneous activation of multiple slip systems during deformation. These features indicate that dislocation creep dominates the deformation of these minerals and felsic granulite, consistent with the obtained stress exponent. Our data imply that a CLC consisting of felsic granulite is weaker rheologically compared to the quartz‐dominated upper crust and the olivine‐dominated uppermost mantle, which supports the ‘jelly sandwich’ model for the strength of continental lithosphere. Additionally, extrapolations of flow laws of our felsic granulite and formerly‐reported mafic granulite strongly favor the hypothesis of delamination‐induced decratonization of the North China Craton.

High-temperature deformation behaviour of duplex stainless steel with hard boronised layer

In order to understand the high-temperature deformation behaviour of alloy having hard surface layer, thermo-mechanically treated duplex stainless steel (DSS) is boronised for 0.75–6 h at 1223 K and subsequently deformed under compression mode at the same temperature under strain rate condition of 1 × 10−3, 2 × 10−4 and 6 × 10−5 s−1 until strain of 0.4. The substrate microstructure is almost isotropic with grain size after boronising with layer thickness between 1.61 and 2.74 μm. X-ray diffraction results confirm the formation of boride on DSS surface. The surface hardness of DSS increases from 387 to 1000–2400 HV after boronising. Uniform boronised layer with thickness of 20–40 μm is formed at DSS surface. Compression results show that the flow stress of the deformation increases with the strain rate and boronising time. For the boronised samples, the flow stress range is between 5 and 89 MPa. To determine the actual effect of the boronised layer on the flow stress, the results are also compared with those from un-boronised samples having similar microstructure. The results suggest that at a constant grain size, even with the hardest layer, the effect of hard surface layer on the flow stress almost could be negligible when the deformation rate is slow, but at faster deformation rate, even in the layer with the least hardness, the flow stress shows a significant increase. It is also observed that the hard boride surface disintegration could be avoided at a sufficiently low deformation flow stress that could be attributed to superplasticity.

Influence of strain rate on the mechanical behavior of dry and hydrated chitosan-based dense materials for bioabsorbable implant applications

Chitosan has generated enormous interest in the scientific community because of its distinctive biological and physicochemical properties, which allow new advanced structures and applications. Porous chitosan scaffolds have been extensively studied and explored in bone generation, however it is still a challenge to obtain bioabsorbable orthopedic implants that involves pure 3D dense chitosan geometries due to the inherent difficulties in producing and shaping such structures.In this work, chitosan was blended with 10% glycerol and 10% glycerol + 10% biphasic mixture of calcium phosphate (70% hydroxyapatite with 30% β-tricalcium phosphate) to produce dense chitosan-based blocks, which were then shaped into rods. The introduction of plasticizer aimed to improve the materials ductility while the ceramic particles were used to increase stiffness and strength. The mechanical behavior of the two chitosan-based compositions was evaluated by uniaxial compression tests using a customized split-Hopkinson pressure bar (SHPB). The specimens were analysed in quasi-static conditions (less than 0.1 s−1) and medium strain rate conditions (200–800 s−1), both in dry state and in different hydrated conditions, in the latter case to approximate the in vivo implant conditions.The results showed promising results for the intended application. The chitosan blends present excellent ductility with an elastic perfect-plastic behavior in quasi-static conditions, with yield stresses around 40 MPa for the dry state, with a decay for 3 MPa after 48h hydration. An empirical model was proposed to describe the flow stress curves, with a good agreement with the experimental data, allowing future modelling of this material behavior.

Laser Metal Deposition of Inconel 718 Alloy and As-built Mechanical Properties Compared to Casting.

In the last years, powder-based Laser Metal Deposition (LMD) has been attracting attention as a disruptive Additive Manufacturing (AM) technique for both the fabrication and restoration of Inconel 718 components, enabling to overcome current limitations faced by conventional manufacturing processes in terms of manufacturing costs, tool wear, and lead time. Nevertheless, the uncertainty related to the final mechanical performance of the as-built LMD parts limits a wider adoption of such technology at industrial level. This research work focuses on the mechanical characterization of as-built Inconel 718 specimens through split Hopkinson tensile bar tests performed at different strain rate conditions. The influence of laser power on the final mechanical behavior of the as-built tensile samples is discussed and compared with the mechanical response of as-cast ones. The as-built specimens exhibit a high internal density (i.e., 99.92% and 99.90% for 300 W and 400 W, respectively) and a more ductile behavior compared to the as-cast ones for every evaluated strain rate condition. The strain hardening capacity of the as-built samples increases with the laser power involved in the LMD process, reaching an average Yield Strength of 703 MPa for specimens realized at 400 W and tested at 800/s.

Investigation on Mechanical Properties of GH4720Li at High Strain Rates at Wider Temperature Range

In this paper, the dynamic mechanical properties of GH4720Li nickel-base alloy under a large temperature range and high and low strain rates were studied by the hot compression test. The difference of mechanical properties of GH4720Li alloy under high and low strain rates was analyzed from the perspective of microstructure. The hot compression test experimental results showed that the true stress of GH4720Li alloy decreased at a low strain rate as the trial temperature elevated. Nevertheless, it was abnormal that the true stress increased at high strain rate condition as temperature elevated. By comparing the microstructure under high and low strain rates, it was found that the precipitates under low strain conditions contained a large amount of Cr (Mo). However, the content of Cr (Mo) in the precipitates at a high strain rate decreased, while the content of Fe increased. It would be concluded that Cr (Mo) would reduce the compressive strength and plasticity of GH4720Li alloy, while Fe would increase the compressive strength and plasticity of GH4720Li alloy. In addition, under the condition of a low strain rate, the shape of Cr (Mo) precipitates obtained at 20°C was lamellar, but it was spherical at 800°C. The compressive strength of GH4720Li composites with lamellar precipitates was higher than that of spherical precipitates.

Strain localization of a frozen sand under different test conditions

In this paper, a series of plane strain tests were conducted on a coarse frozen sand under different temperatures and loading conditions of constant strain rate and stress. With the overall strain fields obtained with particle image velocimetry (PIV) technique, the influence of loading conditions, temperature and strain rate on the strain localization characteristics of the frozen sand was analyzed. It is indicated that, under the same loading conditions, the temperature and strain rate have little influence on the shear band formation process. Both of the single and X shape shear band are observed under different test conditions. The X shape shear bands are more likely to be generated under strain rate lower than the magnitude of 10−3 min−1. When the sand samples are at failure, most part of the strain field is at dilatancy state. The shear band inclination angle and width are inversely proportional to the temperature and independent of strain rate and loading conditions. Further analysis indicated that, within the testing temperature range in this study, the widely accepted Coulomb's solution of unfrozen soils is applicable as the upper bound of the measured shear band inclination angle of the tested frozen sand, and the measured shear band width falls in the range of 10 to 20 times of mean particle size.

Analysis of two parameter identification methods for original and modified Johnson-Cook fracture strains, including numerical comparison and validation of a new blue-brittle dependent fracture model for free-cutting steel 50SiB8

A non-linear relation between fracture strain and temperature is observed in Split Hopkinson Tension Bar (SHTB) tests for free-cutting steel 50SiB8 at high strains and high temperatures, due to blue-brittleness. A fourth-degree polynomial function for the thermal parts of the original and modified Johnson-Cook (JC) fracture strain constitutive equation is suggested and the corresponding parameters are identified. Fracture modelling of 50SiB8 is not reported in literature. 50SiB8 is characterized under quasi-static, isothermal, high temperature and high strain rate conditions using smooth and notched tension specimens. For the calculation of the original and modified JC fracture parameters, two different parameter identification procedures, so-called forward and backward parameter identification methods are performed, compared with each other and explained in detail. For the stress triaxiality factor of the original and modified JC fracture model, the forward parameter identification method is suggested for the original JC fracture model, while backward parameter identification method is proposed for the modified JC fracture model. The effect of blue-brittleness in the temperature factor and the corresponding parameters are presented. Furthermore, FEM simulations of the original and the blue-brittleness based JC fracture model are compared with experiments. In the blue-brittle temperature range, the new adjusted JC model shows more accurate results, regarding fracture diameter and strain. Additionally, this work introduces a fracture model combining the Bai-Wierzbicki stress triaxiality dependent model, JC fracture models and the nonlinear temperature factor with blue-brittleness effect, while further experiments are required in order to determine its parameters.

Processing routes, resulting microstructures, and strain rate dependent deformation behaviour of advanced high strength steels for automotive applications

Automobile industry is continuously striving to obtain light body-in-white structures to meet tightened regulations on flue-gas emissions/crash-testing parameters. ‘Advanced high strength steels (AHSS)’ find increased applications in the automotive industry because of improved crashworthiness/formability at reasonably low costs. AHSS category mainly includes transformation induced plasticity (TRIP) steels, twinning induced plasticity (TWIP) steels, dual phase (DP) steels, complex-phase (CP) steels, and quenching-partitioning (Q&P) steels. AHSSs provide superior strength-ductility combination than conventional high-strength steels by virtue of their multi-phase microstructures. Mechanical properties of AHSSs are greatly influenced by processing routes/derived microstructures. Furthermore, mechanical properties/tensile deformation behavior are also strain rate dependent. During an automobile crash, deformation occurs at strain rates which are exceedingly higher than quasi-static conditions. So, investigation of AHSS properties under both quasi-static as well as high strain rates conditions is important to check applicability for superior crash-resistance. The present work critically reviews details of processing routes, room temperature microstructures, mechanical properties, and finally strain rate dependence of tensile deformation behaviour of AHSSs. Finally, main gaps in existing literature/scope for future research with regards to high strain rate deformation dependent properties of this steel category are presented.

On the effect of the microstructure on the dynamic behaviour of Ti-6Al-4V

Aerospace components in jet engines need to outstand extreme conditions of high-temperatures and loads. Moreover, these components can sometimes undergo dynamic conditions if impact occurs during the flight. It is critical to understand the behaviour of aerospace alloys under these combined extreme conditions of high-temperature and dynamics loads. One of the most extended alloys used in the compressor and fan stages of commercial jet engines is Ti-6Al4V. The dynamic properties of Ti-6Al-4V are strongly dependent on the microstructure state and the temperature conditions. However, these dependencies are yet not fully understood. Moreover, this alloy can present a wide variety of microstructures depending on the component and manufacturing methods. In this work, we compare the response of five typical Ti-6Al-4V microstructures tested under static and dynamic conditions and different temperatures. The macroscopic response of the alloy is rationalised on the basis of its microstructural state using combined microscopy characterisation and computational modelling. To this end, computational plastic models are constructed and validated against experimental observations. In this way, the relationship between the mechanical properties of each microstructure and the temperature and strain rate conditions can be extracted to optimize the material state under specific dynamics in-service conditions.

The Study on Forming Property at High Temperature and Processing Map of 2219 Aluminum Alloy

2219 aluminum alloy is a kind of high-strength Al-Cu-Mn alloy that can be strengthened by heat treatment. Its mechanical property parameters and forming properties are greatly affected by the deformation rate, temperature and strain. Taking 2219 aluminum alloy extruded bar as the research object, the Gleeble-3500 thermomechanical simulator was used to analyze the thermal compression deformation behavior of 2219 aluminum alloy under different temperatures and strain rates. The results show that the deformation behavior of 2219 aluminum alloy under high temperatures is greatly influenced by the deformation temperature and strain rate, and the flow stress is the result of high-temperature softening, strain hardening and deformation rate hardening. According to the experiment results, the Arrhenius constitutive model and the exponential constitutive model considering the influence of temperature and strain rate, respectively, were established, and the predicted results of the two constitutive models were in good agreement with the test results. On this basis, the processing map of 2219 aluminum alloy was established. Under the same strain rate condition with an increase of the deformation temperature, the power dissipation efficiency increases gradually, and the driving force of 2219 aluminum alloy to change its microstructure increases gradually. At the same deformation temperature, the lower the strain rate, the less possibility of plastic instability.