Increasing Strain Rate Research Articles

Hot deformation behavior of 30MnB5V steel: Phenomenological constitutive model, ensemble learning algorithm, hot processing map and microstructure evolution

The hot deformation behavior of 30MnB5V steel was experimentally investigated and theoretically analyzed using phenomenological constitutive models and an ensemble learning algorithm. Hot compression experiments were conducted with an MMS-200 thermo-mechanical simulation machine on the 30MnB5V steel at strain rates of 0.01–10 s−1 and temperatures of 950–1150 °C. The characteristics of the true stress-strain curves under different conditions and the corresponding microstructural evolutions were examined in detail. The results indicate that raising the temperature or lowering the strain rate promotes dynamic recrystallization. As temperature decreases or strain rate increases, the degree of recrystallization softening declines, and stress-strain curves transition from recrystallization to sustained work hardening or dynamic recovery types. Subsequently, the strain-compensated Arrhenius model, modified Johnson-Cook (J-C) model, and Bayesian-optimized LightGBM (BO-LightGBM) model were constructed sequentially to predict the flow stress of the tested steel. The accuracy of the three models was evaluated using the coefficient of determination (R2), mean absolute error (MAE), root mean square error (RMSE), and mean absolute percentage error (MAPE). The results reveal that the accuracy of the BO-LightGBM model is significantly higher than that of the Arrhenius model and the modified J-C model. Finally, three-dimensional power dissipation maps and hot processing maps were established under various strain conditions. The results suggest that the tested steel demonstrates good workability at deformation temperatures of 1075–1125 °C and strain rates of 0.03–0.22 s−1.

Two-stage work-hardening of a transformable B2-enhanced metallic glass composite by molecular dynamics simulation

The crystalline-amorphous interfaces play vital roles in affecting martensitic transformation, shear band nucleation and interface stability. Though both quasi-static and dynamic mechanical behaviors of shape memory enhanced bulk metallic glass composites have been studied via experiments, the atomic-level interactions among martensitic transformation, localized shear softening and interfacial strain concentration imposed by strain rate remain elusive. We employ molecular dynamics simulations to study strain rate effect on uniaxial compression behavior of transformable B2–CuZr enhanced bulk metallic glass composite. As strain rate increases, the proportion of martensitic transformation accelerates. During the competition among martensitic transformation induced-hardening, shear induced-softening and interface debonding, a two-stage work-hardening is observed, which is in agreement with experimental findings.

Dynamic mechanical properties and energy dissipation analysis of rubber-modified aggregate concrete based on SHPB tests

The fluctuation of the waveform curves in the Split Hopkinson Pressure Bar (SHPB) test can provide a more intuitive reflection of the material's dynamic deformation process, with different strain rates resulting in varying damage states and σ-ε curves. A Φ120×100 mm size SHPB experiment was conducted to study the dynamic mechanical properties of new rubber-modified aggregate concrete (RAC). Based on the different characteristics of waveform and σ-ε curves, combined with high-speed photography technology, the typical failure modes and dynamic compressive strength of rubber-modified aggregate concrete under different loading rates were analyzed. Furthermore, the energy dissipation capacity and mechanism of rubber-modified aggregate concrete at different stages was discussed. The reflected wave of RAC shows a "double-peak" trend of "first high and then low" instead of "first low and then high" of normal concrete due to its exceptional capacity of energy absorption and dissipation. As strain rate increases, a plateau period appears in the reflected wave before first peak. The evolution process is dominated by the energy storage mechanism until it hits the limit, then by the energy dissipation mechanism. These findings can help us design and use RAC materials under dynamic stress.

The influence of initial static shear on the torsional performance of BFRP bars-RC beams with different sizes

To reveal the influence of the initial static shear on the torsional performance of Basalt Fiber Reinforced Polymer Bars-Reinforced Concrete (BFRP bars-RC) beams, in this study, 52 BFRP bars-RC beam models with geometric similarity using a three-dimensional mesoscale numerical simulation method were established. The effects of initial shear static loadings (F0 = 0, 0.25Vu, 0.5Vu, and 0.75Vu) on the failure modes, torsional strength, ductility, and size effect of BFRP bars-RC beams under various equivalent strain rates were quantitatively analyzed. The results show that, regardless of whether the beams have initial damage, their load-bearing capacity and deformation ability increase as loading strain rates increase. For beams with initial damage, the increased degrees in load-bearing capacity relative to their respective initial static shear decreases as the initial static shear level increases but then increases as the subsequent loading strain rate increases. Increasing the beams’ initial damage degree makes the beams’ ductility worse. In addition, the more severe the beams’ initial damage, the more significant the strength size effect. However, increasing the strain rate can weaken the beams’ strength size effect.

Experimental study on dilatancy behavior of soft rock under dynamic loading

Correct understanding of rock dilatation plays a non-negligible role in the safety of rock engineering and the efficiency of geological resources extraction. Although the significance of dilatation under quasi-static loading or unloading conditions is well-studied, its behavior under dynamic loads remains poorly understood. This is largely because conventional dynamic testing system fails to capture the volumetric strain evolution of rock under confinement. This study develops a transparent confining chamber in SHPB system with which high-speed 3D-DIC is capable of measuring both axial and circumferential strain history of dynamically compressed rock. The progressive failure stages and volumetric change of red sandstone under confining pressure of 3.5 MPa and strain rates of 129∼292 s−1 were studied and compared with those in quasi-static case. Results show that, the normalized stress thresholds of crack initiation and dilatancy in dynamic cases are much smaller than those in the quasi-static one. The volumetric variation of soft rock is characterized by four distinct stages: elastic contraction, pre-peak dilatancy, strain-softening dilatancy and strain-recovery dilatancy. The pre-peak elastic contraction is negligible compared to the post-peak dilation, and the ultimate dilation observed in dynamic compression is significantly greater than that in quasi-static compression. Increasing strain rate delays the onset of dilatancy, decreases the dilatant rate but remarkably extends the strain-softening dilatant process which is dominant in total dilation. A rate-dependent piecewise model incorporating key strain thresholds and a dilatancy rate factor was established to characterize the dynamic dilatancy behavior. The research results provide a new insight and possible method in dilation prediction for underground engineering subjected to dynamic loading.

On energy mechanism of rate-dependent failure mode evolution in plain weave composite

The intricate failure modes and the yet unclear rate dependency of carbon fiber reinforced plain weave composite materials pose a challenge to mechanics researchers. This study establishes an energy-based evolution mechanism for the compressive failure modes of plain weave composite materials as the strain rate varies. This mechanism illustrates how the rate dependency of failure modes arises from the competitive relationship between strain potential energy and deformation kinetic energy. At low loading rates, the specimen exhibits a progressive crushing failure mode characterized by low peak stress and significant geometric deformation. As the loading strain rate increases, the energy required for this geometric deformation also increases. When the energy expenditure surpasses that needed to elevate the stress level of the specimen, it transitions to an instantaneous failure mode with high peak stress. In this mode, the specimen fractures into multiple small fragments immediately upon failure, lacking the large geometric deformations observed at lower rates. Through calculating this energy mechanism, a transition strain rate of 180 s−1 was determined for both failure modes. The accuracy of this mechanism was further verified by tests conducted near the critical strain rate. The energy-based evolution mechanism for failure modes provides a simplified and concise framework for simplifying complex models of composite material failures.

Effects of strain rate and low temperature on dynamic behaviors of additively manufactured CoCrFeMnNi high-entropy alloys

With the increasing demand for high-performance alloys in extreme environments, there has been an active development of new materials. High-entropy alloys (HEAs) are considered a promising choice due to their exceptional properties. Even though HEAs exhibit remarkable mechanical properties, only a limited number of studies have explored the mechanical properties and microstructures of additively manufactured HEAs under extreme conditions. In this work, the dynamic mechanical properties at high strain rates and different temperatures (i.e., 293 K and 77 K), as well as quasi-static mechanical properties for the CoCrFeMnNi HEAs fabricated by selective laser melting (SLM) are investigated. Microstructure observations have demonstrated that the as-printed sample displays a single face-centered cubic (FCC) phase with a columnar dendrite feature. Within dendrites, a large number of dislocations and substructures appear due to the applied high cooling rates during the SLM process. The as-printed sample exhibits a significant strain rate dependence from quasi-static to dynamic loading during deformation. Compared to the quasi-static mechanical properties, the as-printed HEA reveals higher dynamic yield strength (e.g., ∼1081 MPa and ∼1020 MPa along the build and scanning directions under 2800 s−1, respectively), more pronounced strain-hardening behavior, and larger remarkable plasticity under dynamic loading at cryogenic temperatures. When subjected to increasing strain rates ranging from 0.001 s−1 to 3500 s−1 at 293 K, the yield strength of the as-printed HEAs exhibits a notable enhancement, increasing from ∼517 MPa to ∼723 MPa along the BD direction, and from ∼545 MPa to ∼667 MPa along the SD direction. The corresponding variation in the strength of the BD samples is more pronounced than that of the SD samples. The enhancement in strength should be attributed to the differences in the features of grain orientation and dislocation distribution along different build directions, as well as the strain rate dependence. During plastic deformation, the dominant mechanisms of dislocation slips and deformation twins (DTs) are transformed into multi-stage-twin-controlled ones at cryogenic temperatures, which is beneficial to improve the strain hardening rate and plasticity. The present studies provide a deep understanding of the deformation mechanism of HEAs under extreme conditions and help promote the application of HEAs in the future.

Study on the dynamic fracture behavior of anisotropic CCNBD shale specimens under different impact angles

Drilling and fracturing are the key technologies for shale gas extraction, while most of the loads generated during rock drilling or fracturing are dynamic. In this study, dynamic impact experiments were conducted on the cracked chevron-notched Brazilian disc shale specimens with different chevron-notched crack (CNC) inclinations (β) and layer inclinations (α) by the split Hopkinson pressure bar. The results show that the dynamic peak load and dissipated energy increases with the increase of β, α, and strain rate, but their changing trends are different. The generation and expansion of cracks during the specimen failure process are mainly affected by β. As β increases, the failure type of the specimen can be divided into pure mode I fracture, mode I-II mixed fracture, pure mode II fracture, mixed tension-shear failure, and Brazilian splitting failure. The increase in strain rate will lead to a decrease in the time for crack initiation and propagation as well as an increase in secondary cracks. In addition, the mode I fracture toughness (KⅠC) and mode II fracture toughness (KⅡC) both grow with the increase of α and strain rate. The KⅡC predicted by the generalized maximum tangential stress criterion (GMST) exhibits more accurate.

Strain rate dependence of mechanical behavior in an AlSi10Mg alloy with different states fabricated by laser powder bed fusion

The strain rate dependence of mechanical behavior in an AlSi10Mg alloy with different states fabricated by laser powder bed fusion (LPBF) was investigated systematically via thermodynamic calculations, microstructure characterization and mechanical characteristic evaluation in the present study. The results show that there is a close relationship among the material state, microstructure and dynamic mechanical behavior. Before tensile deformation, the as-built specimen possesses a fine equiaxed grain structure and a typical cellular structure surrounded by continuously distributed particles; the annealed specimen has coarser equiaxed grain structures and particles, but no cellular structure is present. Both the as-built and annealed specimens exhibit weak strain rate sensitivity, and the strain rate sensitivity parameters are 0.01 and 0.024, respectively. Under specific strain rate conditions, the as-built specimen has a higher strength and lower elongation than the annealed specimen. After tensile deformation, there is a significant increase in the dislocation density. Independent of the material state, the dislocation density increases with increasing strain rate. Compared with the as-built specimen, the annealed specimen has a stronger strain rate sensitivity because of the greater dislocation density variation.

Dynamic compressive behavior of hybrid basalt-polypropylene fibers reinforced coral aggregate concrete

In this study, the effects of strain rate, fiber type, and hybrid fiber content on the dynamic mechanical properties of basalt-polypropylene fiber reinforced coral aggregate concrete (HBPRCAC) under impact loading are investigated using a split-Hopkinson pressure bar (SHPB) with a 75 mm diameter. The results demonstrated that the incorporation of basalt fiber (BF) and polypropylene fiber (PF), particularly when mixed, effectively reduced the failure of HBPRCAC. With an increase in strain rate, the failure of HBPRCAC exhibited a more severe pattern; even at low strain rates, cracks directly passed through the coral aggregate, causing damage. The failure modes of BF and PF were related to the strain rate. The probability of BF and PF being pulled out was higher at low strain rates than at high strain rates, where BF and PF predominantly exhibited snap failures. Additionally, the dynamic increase factor (DIF) of the dynamic compressive strength and dynamic modulus of elasticity for HBPRCAC demonstrated a decimal logarithmic linear increase with strain rate, while the dynamic critical strain and impact toughness of HBPRCAC exhibited a linear increase with strain rate. The mixed addition of BF and PF had varying effects on the strain rate sensitivity of HBPRCAC's dynamic mechanical properties, but the fiber mixing content was significantly positively correlated with the strain rate effects on the dynamic compressive mechanical properties of HBPRCAC. The dynamic compressive strengths of BPCAC-0.1 and BPCAC-0.2 at strain rates of 128–135 s−1 were increased by 78.66 % and 88.47 %, respectively, compared to those at strain rates of 33–36 s−1. The dynamic moduli of elasticity for BPCAC-0.1 and BPCAC-0.2 showed increases of 16.47 % and 13.06 %, respectively, compared to that of coral aggregate concrete. Moreover, the critical strain and impact toughness of BPCAC-0.2 were the highest at all tested strain rates.

Sustained Strain Applied at High Rates Drives Dynamic Tensioning in Epithelial Cells.

Epithelial cells experience long lasting loads of different magnitudes and rates. How they adapt to these loads strongly impacts tissue health. Yet, much remains unknown about their stress evolution under sustained strain. Here, by subjecting cell pairs to sustained strain, we report a bimodal stress response, where in addition to the typically observed stress relaxation, a subset of cells exhibits a dynamic tensioning process with significant elevation in stress within 100s, resembling active pulling-back in muscle fibers. Strikingly, the fraction of cells exhibiting tensioning increases with increasing strain rate. The tensioning response is accompanied by actin remodeling, and perturbation to actin abrogates it, supporting cell contractility's role in the response. Collectively, our data show that epithelial cells adjust their tensional states over short timescales in a strain-rate dependent manner to adapt to sustained strains, demonstrating that the active pulling-back behavior could be a common protective mechanism against environmental stress.

Hot deformation and constitutive modeling of a Ti-Al-Sn-Zr-Mo-Cr-Nb alloy

Titanium alloys are the ideal structural materials for automotive and aerospace industries, and hot deformation is widely used to modify the microstructure of the alloy. In this work, a Ti-Al-Sn-Zr-Mo-Cr-Nb alloy was hot deformed at various strain rates and temperatures. The deformation behavior, microstructure, processing maps, and constitutive modeling are investigated. The results show that the hot deformation behavior of the studied alloy is sensitive to the processing parameters, the revised Johnson-Cook model with an average relative error of 1.463 %, and a correlation coefficient of 0.991 can accurately describe the hot deformation behavior of the alloy. Based on the established processing maps, the safe processing areas are 1133–1213 K, 0.004–0.1 s−1 and 1093–1213 K, 0.001–0.004 s−1. With the increased deformation temperature, both the fraction and size of the equiaxed α and lamellar α phases are gradually decreased, and the spheroidization degree of the lamellar α phase gradually decreases too. The strain rates have different influences on the evolution of α and β phases. With the increased strain rates, the fraction of recrystallized and deformed β phase is remarkably decreased, the fraction of sub-structured microstructures of β phase is obviously increased, while the fraction of deformed structures of the α phase is less affected.

Bonding mechanism and fracture behavior of cold-sprayed Fe-based amorphous alloy on 6061 Al alloy

Using cold spray technology to prepare amorphous alloy coatings can effectively prevent crystallization, thereby preserving the excellent properties of amorphous alloys. However, interfacial bonding significantly affects performance, such as weak bonding impacting the durability and stability of the coating. Therefore, in-depth study of the interfacial bonding mechanism is crucial for a comprehensive understanding of coating properties. This paper uses cold spray technology to prepare Fe-based amorphous alloy coating on 6061 aluminum alloy substrates. The bonding mechanisms at the particle/substrate, particle/particle, and coating/substrate interfaces are studied, and the fracture behavior in the tensile bond strength test is analyzed. The results show that the heat accumulation and the increase in strain rate generated by the particles impacting the substrate cause the viscosity of the amorphous alloy to suddenly decrease from 1.2×103 g·cm−1 s−1 to 8.4×10−1 g·cm−1 s−1. Increased fluidity and micro-friction accelerate the mixing of elements and form a metallurgical bond at the particle/substrate interface. Meanwhile, the oxides at the particle/particle interface are extruded, and the exposed fresh metal is subjected to a huge shear rate to promote atomic fusion. Tamping of the subsequent particles leads to further deformation of the deposited particles, forming a stronger metallurgical bond and mechanical anchoring at the particle/particle interface. In addition, the continuous impact of particles triggers dynamic recrystallization of the substrate, and the average grain size decreases from 14.28 μm to 1.39 μm. This fine-grained structure strengthens the mechanical anchoring of the coating/substrate interface. Furthermore, the bonding strength measured by the tensile test is determined to be 18.51 MPa. The main reasons for the final fracture occurring in the coating are the coating pores, cracks formed by shear bands accumulated in free volume, and the low adhesion oxide layer at the particle interface.

Molecular Dynamics Simulations of Effects of Geometric Parameters and Temperature on Mechanical Properties of Single-Walled Carbon Nanotubes

Carbon nanotubes (CNTs) are considered an advanced form of carbon. They have superior characteristics in terms of mechanical and thermal properties compared to other available fibers and can be used in various applications, such as supercapacitors, sensors, and artificial muscles. The properties of single-walled carbon nanotubes (SWNTs) are significantly affected by geometric parameters such as chirality and aspect ratio, and testing conditions such as temperature and strain rate. In this study, the effects of geometric parameters and temperature on the mechanical properties of SWNTs were studied by molecular dynamics (MD) simulations using the Large-scaled Atomic/Molecular Massively Parallel Simulator (LAMMPS). Based on the second-generation reactive empirical bond order (REBO) potential, SWNTs of different diameters were tested in tension and compression under different strain rates and temperatures to understand their effects on the mechanical behavior of SWNTs. It was observed that the Young’s modulus and the tensile strength decreases with increasing SWNT tube diameter. As the chiral angle increases, the tensile strength increases, while the Young’s modulus decreases. The simulations were repeated at different temperatures of 300 K, 900 K, 1500 K, 2100 K and different strain rates of 1 × 10−3/ps, 0.75 × 10−3/ps, 0.5 × 10−3/ps, and 0.25 × 10−3/ps to investigate the effects of temperature and strain rate, respectively. The results show that the ultimate tensile strength of SWNTs increases with increasing strain rate. It is also seen that when SWNTs were stretched at higher temperatures, they failed at lower stresses and strains. The compressive behavior results indicate that SWNTs tend to buckle under lower stresses and strains than those under tensile stress. The simulation results were validated by and consistent with previous studies. The presented approach can be applied to investigate the properties of other advanced materials.

The Role of Deformation and Microstructure Evolution on Texture Formation of a TA15 Alloy Subjected to Plane Strain Compression.

In this study, the texture formation mechanism of a TA15 titanium alloy under different plane strain compression conditions was investigated by analyzing the slipping, dynamic recrystallization (DRX) and phase transformation behaviors. The results indicated that the basal texture component basically appears under all conditions, since the dominant basal slip makes the C-axis of the α grain rotate to the normal direction (ND, i.e., compression direction), but it has a different degree of deflection. With an increase in deformation amount, temperature or strain rate, {0001} poles first approach the ND and then deviate from it. Such deviation is mainly caused by a change in slip behaviors and phase transformation. At a smaller deformation amount and higher strain rate, inhomogeneous deformation easily causes a basal slip preferentially arising from the grain with a soft orientation, resulting in a weak basal texture component. A greater deformation amount can increase the principal strain ratio, thereby promoting other slip systems to be activated, and a lower temperature can increase the critical shear stress of the basal slip, further causing a dispersive orientation under these conditions. At a higher temperature and a lower strain rate, apparent phase transformation will induce the occurrence of lamellar α whose orientation obeys the Burgers orientation of the β phase, thereby disturbing and weakening the deformation texture. As for DRX, continuous-type (CDRX) is most common under most conditions, whereas CDRX grains have a similar orientation to deformed grains, so DRX has little effect on overall texture. Moreover, the microhardness of samples is basically inversely proportional to the grain size, and it can be significantly improved as lamellar α occurs. In addition, deformed samples with a weaker texture present a higher microhardness due to the smaller Schmidt factors of the activated prism slip at ambient loading.

Effect of strain rate on tensile characteristics and failure behavior of Al/steel welded joint producing by a laser-MIG composite heating source

Studies on dynamic tensile characteristics for Al/steel dissimilar materials are crucial to ensure the integrity and dependability of light-weight structures. In this study, the tensile characteristics and failure behaviors of Al/steel laser-MIG welded-brazed joints were studied. The dynamic fracture mechanisms of the joints are discussed. With the increase in strain rate, the fracture mode and tensile properties of Al/steel joints with reinforcement changed. The joints exhibited two failure modes of heat-affected zone failure at lower strain rates and interface failure at higher strain rates. When the strain rate was 1000 s−1, the increase in dislocation density in the weld reinforcement and diversion of cracks in the intermetallic compound layer significantly enhanced the joint’s properties. The tensile and yield strengths reached 222.6 and 166.6 MPa, 6.5 % and 17.9 % higher than those at a stain rate of 1 s−1, respectively. For Al/steel joints without reinforcement, as the strain rate increased, the crack gradually grew to the Al8Fe2Si phase, leading to a notable enhancement in the joint’s performance. At a strain rate of 500 s−1, the maximum strength of the joint reached 238.3 MPa, representing an increase of 58.9 % in comparison to the strain rate of 1 s−1.

Investigating mechanical properties and energy absorption of elastomeric polymer nanocomposites containing cellulose nanofibers in tensile, quasi-static compression, and high strain rate tests

In this study, mechanical properties and energy absorption of elastomeric nanocomposites reinforced with cellulose nanofibers are investigated from tensile, Quasi-static Compression (QSC), and Split-Hopkinson Pressure Bar (SHPB) tests. For this purpose, the design and preparation of rubber nanocomposites with different loadings of cellulose nanofibers (CNFs) were carried out, and the optimal cure temperature (T90) of the rubber compound containing cellulose nanofibers was determined from the rheometer test. In the continuation of this study, the effects of adding cellulose nanofibers on the tensile strength, elongation to break, and energy absorption of the proposed Nano-composites were investigated. The results showed that the nanocomposite containing 6 phr increases the ultimate strength and elastic modulus of 300% by 33.5% and 22.7%, respectively, compared to the control rubber (0 phr). Similarly, these numbers are about 10 and 65% for loading 12 phr cellulose nanofibers. From the results of the quasi-static compression test for different amounts of cellulose nanofibers at a strain rate of 50%, it was found that the lowest and highest compressive stress due to the resistance of elastomeric nanocomposites is related to the control sample (0 phr) and the 12 phr sample, respectively. Also, from high strain rate tests of Split Hopkinson Pressure Bar, it was found that the fracture mechanism of flexible composites containing cellulose nanofibers changes in response to a high-speed impact, and the samples respond to high-pressure impact with brittle fractures. It was also found that rubber nanocomposites reinforced with cellulose nanofibers are very sensitive to strain rates. As the strain rate increases, the energy absorption of rubber nanocomposites increases. The optimal loading (6 phr) of cellulose nanofibers in rubber compounds makes them suitable for energy absorption applications. Cellulosic nanofibers provide acceptable dispersion of nanomaterials through good interaction with natural rubber and lignin-carbon fillers. Therefore, through the physical interweaving of fillers with polymer chains, CNF provide better binding of polymer chains to improve properties.

Temperature and strain rate-dependent compression properties of 3D-printed PLA: an experimental and modeling analysis

PurposeThis study aims to investigate the compression characteristics of the 3D-printed polylactic acid (PLA) samples at temperatures below the glass transition temperature (Tg) with varying strain rates and develop a thermo-mechanical viscoplastic constitutive model to predict the finite strain compression response using a single set of material parameters. Also, the micro-mechanical damage processes are linked to the global stress–strain response at varied strain rates and temperatures through scanning electron microscopy (SEM).Design/methodology/approachTg of PLA was determined using a dynamic mechanical analyzer. Compression experiments were conducted at strain rates of 2 × 10–3/s and 2 × 10–2/s at 25°C, 40°C and 50°C. The failure mechanisms were examined using SEM. A finite strain thermo-mechanical viscoplastic constitutive model was developed to analyze the deformations at the considered strain rates and temperatures.FindingsTg of PLA was determined as 55°C. While the yield and post-yield stresses drop with increasing temperature, their trend reverses with an increased strain rate. SEM imaging indicated plasticizing effects at higher temperatures, while filament fragmentation and twisting at higher strain rates were identified as the dominant failure mechanisms. Using a non-linear regression analysis to predict the experimental data, an overall R2 value of 0.98 was achieved between experimental and model prediction, implying the robustness of the model’s calibration.Originality/valueIn this study, a viscoplastic constitutive model was developed that considers the combined effect of temperature and strain rate for FDM-printed PLA experiencing extensive compression. Using appropriate temperature-dependent modulus and flow rate properties, a single set of model parameters predicted the rise in the gap between yield stress and degree of softening as strain rates and temperatures increased.

Dynamic mechanical behaviors of foamed concrete using modified viscoelastic SHPB

This study aims to investigate the dynamic mechanical behaviors of foamed concrete (FC) utilizing a modified viscoelastic split Hopkinson Pressure Bar (VE-SHPB). The VE-SHPB proposed in this study enables impedance matching between bars and FC, enhancing measurement precision. Dynamic mechanical behaviors of FC with different densities (400, 700, 1000, 1300 kg/m3) under various incident pressure (0.2, 0.5, 0.8, 1.1 MPa) are examined using the VE-SHPB. The failure modes of FC are categorized into Spalling (Mode I), Disintegration (Mode II), and Comminution (Mode III) based on fracture states of post-impact. The mechanism of strain rate and density on failure mode, dynamic strength, dynamic increase factor (DIF), and energy consumption density are discussed. The results show that FC's dynamic mechanical properties increase with increasing strain rate, but present different strain rate sensitivities at different densities. The dynamic mechanical properties of FC are determined by both the pore structure and matrix properties. Notably, Mode II shows better ability of energy consumption, specifically FC with a density around 700 kg/m³ demonstrates higher energy absorption density.

Cryogenic deformation behavior, constitutive modeling and microstructure evolution of solution-treated 2195 Al–Li alloy at high strain rates

In this paper, the flow behavior, constitutive model and microstructure evolution of solution-treated 2195 Al–Li alloy at temperatures from 123 K to 298 K and strain rates from 2000 s−1 to 5000 s−1 were studied. Experimental results show that the flow stress of the solution-treated 2195 Al–Li alloy is more sensitive to deformation temperature than strain rate. As the temperature declines from 298 K to 123 K, the flow stress at 2000 s−1 and 5000 s−1 increases by nearly 32.8% and 34.5%, respectively; whereas as the strain rate increases from 2000 s−1 to 5000 s−1, the flow stress at 298 K and 123 K only increases by 5.1% and 6.5%, respectively. The average strain hardening rate tends to decline with the increase in strain rate and temperature, and its value at 123 K and 2000 s−1 is about 1.5 times greater than that at 298 K and 5000 s−1. To overcome the very limited applicability of the conventional Arrhenius model with strain compensation, an Arrhenius-based model (c-Arrhenius model) is developed by coupling an independent strain term and then derived by using normalized flow stress and linear regression. To quantify the strain rate effect and temperature effect, a Johnson-Cook-based model (c-Johnson-Cook model) with exponential terms is developed. These two new constitutive models are validated via a comparative analysis, showing good predictability and accuracy. A further microstructure observation shows that the dislocation density is the highest at a strain rate of 5000 s−1 and cryogenic temperature of 123 K, which is beneficial for subsequent aging strengthening.