Effect Of Strain Rate Research Articles

A phenomenological constitutive model of Novel Rheo Gravity Die Cast Al-15Mg2Si-4.5Si-0.01Sr-0.015B composite

The present study discusses the high temperature deformation behaviour as well as phenomenological constitutive model development of the novel Rheo gravity die cast (RGDC) Al-15Mg2Si-4.5Si-0.01 Sr-0.015B composite. Within the scope of the study, uniaxial isothermal compression tests are performed on the RGDC Al-15Mg2Si-4.5Si-0.01 Sr-0.015B composite, covering a range of strain rates from 10−3 to 10 s−1 and deformation temperatures spanning from 250 °C to 450 °C. Analysis using X-ray Diffraction (XRD), Energy dispersive spectroscopy (EDS) and Electron Probe Micro Analyzer (EPMA) revealed the presence of distinct phases within the material, including primary Al, Mg2Si, and elemental Si. The study employed three different constitutive models i.e., the Johnson-Cook (JC), modified Johnson-Cook (mJC), and sine hyperbolic Arrhenius (shA) types, to predict the flow stress of the material as a function of strain, strain rate, and deformation temperature. The results indicated that the sine hyperbolic Arrhenius type model and the modified Johnson Cook model effectively accounted the coupling effect of strain, strain rate, and deformation temperature, which affect the flow stress. Statistical analysis, specifically Pearson coefficient correlation (R), average absolute relative error (AARE) and standard deviations, established a reasonable agreement between the predicted flow stress values and the experimental flow stress data. Furthermore, it is observed that the sine hyperbolic Arrhenius type model exhibited superior accuracy compared to the modified Johnson Cook model, particularly at higher strain levels.

Injection moulding process parameter and strain rate dependence mechanical properties measurement and theoretical estimation of EVA polymer foam

Abstract In this study, the combined experimental and theoretical estimation on elastic characteristics of EVA (ethylene-vinyl acetate) copolymer material is demonstrated. Strain rate dependence stress–strain behavior of EVA in raw and foam material form are measured by the quasi static and dynamic compression test. Simultaneously, the influence of different mould temperature and injection pressure on mechanical properties of EVA foam are investigated. According to the usage scenario of EVA foam in sport footwear application, the EVA foam is generally deformed under higher strain rate as compared with the quasi-static compression condition. For this reason, the stress–strain behavior of EVA foam under high strain rates of 2.66 × 10−3 and 2.66 × 10−2 s−1 are estimated. The analytic results revealed that the strain rate slightly enhanced the modulus of EVA foam, and the foregoing strain rate effect is substituting into the classic Young's modulus estimation equation of closed cell cellular solid. Accordingly, the strain rate dependence Young's modulus of EVA foam is successfully estimated by both experiment and theoretical estimation.

Application of concrete damage evolution equation considering confining pressure and strain rate effects in projectile penetration

Repeated loading and unloading tests were carried out on concrete under different confining pressures and strain rates to characterize the damage using the decrease in elastic modulus, and a damage evolution equation considering the effects of confining pressure and strain rate was established. At the same time, the yield criterion and equation of state of the Holmquist–Johnson–Cook (HJC) model were modified by combining the experimental data of high confining pressure. The modified model was validated by performing single-element numerical simulations for different stress states. Then, experiments were carried out on the penetration of tungsten alloy projectiles into concrete slabs, with penetration velocities ranging from 172 m/s to 302 m/s. The depth of penetration and crater area were obtained. Numerical simulations were subsequently carried out using the proposed model. The results showed that this model can describe the behaviour of concrete under dynamic loading. Finally, the damage evolution mechanism of concrete during the penetration process is analysed in conjunction with the proposed damage evolution equation.

Effect of strain rates on the forming properties of DP Steel at high-temperature

Dual Phase steel grade, with its remarkable combination of features including formability and resistance to high temperatures, has been a revolutionary alloy in modern industry. It is a useful material that may be applied to many different tasks. It presents us with the task of examining its characteristics in response to changes in critical parameters such as temperature and loading rate during stretching operations. Understanding the formability behavior of DP steel sheets, which have a thickness of 1 mm, at various increased temperatures and strain rates was the main goal of the investigation. We investigated and examined the tensile characteristics at 650 and 750 degrees Celsius in the first investigation. On the other hand, because of flow stresses in the material at higher temperatures, elongation has decreased in value as deformation rates have increased. In addition, we plotted the FLDs experimentally and examined the formation behavior while performing the Nakazima Test on specimens with a thickness of 1 mm. Furthermore, a limiting dome height (LDH) study was conducted on a laboratory scale. In terms of temperature, the LDH was shown to be higher at 750 and at 0.001/s

Development of Micro-mechanical Constitutive Model for Alumina at High Strain Rates Using Unified Mechanics Theory

Ceramic materials used in mechanical applications show variations in their properties due to the presence of cracks. Micro-cracks within the material (size, orientation and density) affect the ceramic material’s strength and other mechanical properties. This study developed a micro-mechanics-based model that accounts for the original orientation of micro-cracks and their propagation as wing cracks. Unlike other micromechanics-based models, the current model defines failure based on entropy associated with crack propagation within the material. Entropy is calculated from energy dissipation from crack propagation from the pre-existing flaws in the ceramic. The Unified Mechanics Theory (UMT) is used to define entropy-based damage in the ceramic material, in which a parameter called thermodynamic state index (TSI) is employed to describe the state of the material. A representative volume element (RVE) with a pre-existing flaw is used to calculate the energy dissipated during the wing crack propagation. The effect of various crack lengths and orientations is incorporated with a probability density function. The strain rate effects are implemented using dynamic crack growth law. The stress-strain curve at strain rate from quasi-static to high strain rate (10-3-106) is plotted for Alumina under dynamic compression.

Study on fractal and energy dissipation characteristics of rock impact fragmentation in Junggar basin

In order to study the rock energy absorption and crushing fractal characteristics under impact load, the dynamic impact tests of rock in J1b formation in Junggar Basin were carried out by split Hopkinson bar. The strain rate effect on the crushing energy consumption and failure mode were analyzed. Combined with fractal dimension calculation and energy density analysis, the energy density and fractal characteristics of rocks during the impact process are studied. The results showed that the strain rate and energy density of the specimens are in line with the power relationship, the energy density increases with the strain rate, and the fractal dimension increases significantly with the increase of the strain rate, the energy density and fractal dimension of the specimen under dynamic load conform to a power relationship. The more energy absorbed by the rock, the more obvious the fractal characteristics are. The energy density combined with the fractal dimension calculation of rock fragmentation can quantitatively study the energy absorption law of rock per unit time.

Effects of the temperature, strain rate, and loading conditions on the deformation behaviors and mechanical properties of the Ni/Ni3Al superalloy.

Using the molecular dynamics method, we comprehensively studied the effects of temperature, strain rate, and loading conditions on the deformation behaviors and the mechanical properties of the Ni/Ni3Al superalloy. Our investigation revealed that, an increase of the deformation temperature led to a significant improvement of plastic deformation capacity of the system, but the tensile strength and elastic modulus decreased. And the tensile strength and plastic deformation capacity of the system drastically increased with the strain rate. At high deformation temperature and strain rate, the loading conditions had a large effect on the deformation behaviors and the mechanical properties of the system. The difference of the mechanical properties of the system was mainly due to the different deformation mechanism of the system under different deformation temperature, strain rate and loading conditions. Our study offered a theoretical framework for explaining the difference of the mechanical properties for the Ni/Ni3Al superalloy at different service conditions.

Deformation behavior of super-austenitic stainless steel sandwich panels subjected to air blast and underwater explosion

Super-austenitic stainless steel is a class of high alloy steels with enhanced toughness, outstanding strength, and corrosion resistance. In this article, the structural integrity of super-austenitic stainless steel square sandwich panels subjected to surface and underwater explosions is investigated through numerical simulations, and the results are validated with experiments. Abaqus Explicit Solver is used to predict the face deformation and core crushing failure modes of the sandwich panels. Simulations are performed for three levels of impulse load by varying the explosive quantity. The fluid-structure interaction is established by CONWEP and UNDEX algorithms for air blasts and underwater explosions respectively. The dynamic deformation behavior of the sandwich panel is modeled using the Johnson-Cook (JC) plasticity model incorporating strain rate and temperature effects. Good agreement is witnessed between the numerical predictions and experimental observations. An increment in deformation of the face sheet, cell wall buckling, and core compaction is observed with the increase in the impulse. From a series of air and underwater explosion simulations, the advantage of using sandwich structures for blast mitigation is demonstrated. In addition, the significance of numerical simulations to limit experiments and predict the deformation of the sandwich panels is presented.

Cyclic strain rate dependent behaviour of Alloy 617

This paper investigates the effect of strain rate on the properties of Alloy 617 under low-cycle fatigue (LCF) in room temperature (RT). The LCF life properties and the damage mechanism are studied for this Alloy over a range of strain rate (5E-4 ∼ 1E-2 s−1) under fully-reversed controlled total strain range of 1.2%. It is found that LCF life of Alloy 617 is strongly influenced by the time-dependent mechanism, in terms of slow strain rate test (SSRT). The relationship between total strain, plastic strain, and time to failure with strain rates are established and expressed by means of power law function to describe the fatigue life. Metallography examination is carried out on the fractured specimens with the help of electron microscope and the fractography is discussed to distinguish the effect of SSRT on the physical damage characteristic under LCF loadings.

The essence of the effect of strain rate on the mechanical behavior of the Fe14.6Ni (at%) elastocaloric refrigeration alloy: a molecular dynamics study.

In this research, a molecular dynamics (MD) model was adopted to investigate the essence of the effect of strain rate on the mechanical behavior of the Fe14.6Ni (at%) elastocaloric refrigeration alloy. The study showed that the mechanical behavior of the Fe14.6Ni (at%) alloy was dependent on the strain rate. Besides, the investigation of temperature demonstrated that the strain rate influenced mechanical behavior by changing the transient temperatures. Furthermore, it was found that the adiabatic temperature change (ΔTadi) was high and up to 51 K, which was a 1.57 times improvement. Finally, the conclusion was drawn that the strain rate influenced the mechanical behavior by changing the transient total kinetic energy and the phase content evolution processes, which was the essence of the effect of strain rate on the mechanical behavior. This work has clarified the essence and enriched the theory of the effect of strain rate on the mechanical behavior of elastocaloric refrigeration alloys.

Critical LME elongation: a criterion measured with Gleeble correlated to LME sensitivity during spot welding

Liquid metal embrittlement may appear on multiphase high strength galvanized steels during the spot-welding process. The aim of this paper is to describe a high temperature tensile test, performed with a Gleeble machine, to evaluate the LME sensitivity of a given coated steel in conditions similar to spot welding (time cycle). The critical LME elongation, corresponding to minimum of stress derivative during force decrease, has been found as being the most relevant parameter to measure the LME phenomenon. Relevant test parameters such as temperature, strain rate, applied thermal cycle, and effect of thermocouple welding have been studied on two steels. The first, TRIP 800 steel, presents a high sensitivity to LME between 750 °C and 900 °C while the second, DP600 steel, is not sensitive. Strain rate effect reveals a competition between LME crack propagation and ductile fracture. The study also shows the need to avoid welding thermocouple on Zn-coated side. Overall, the critical LME elongation from Gleeble test is well correlated to LME cracks number and depth in spot welding.

Complete constitutive model of CFRP including continuous damage in low strain rate compression and temperature generation in high strain rate impact

AbstractThis paper reports a method to construct the complete constitutive model of carbon fiber‐reinforced plastic (CFRP) by distinguishing the strain rate state and modifying the material stiffness. In quasistatic (low strain rate) compression, the initial nonlinear effect caused by the material defects was described by introducing an nonlinear increasing factor. In dynamic (high strain rate) impact, the nonlinear strengthening effect was described by introducing the dynamic amplification factors of stress and strain based on the reference state. Considering the instantaneous temperature rise obtained from the impact work–temperature generation equation and the influence of temperature on modulus and strength, the coupled thermomechanical constitutive models combining the strain rate effect and the temperature effect were established. The user‐defined material subroutines (VUMAT) were developed, and then these constitutive models were verified by finite element analysis (FEA). Finally, the developed material subroutine was applied to predict the impact penetration of CFRP laminates, and the results show that the opening holes, damage and energy dissipation are in good agreement with the reference experiment. This work comprehensively analyzed the construction method of CFRP constitutive models, which would provide a guidance for the coupled thermomechanical behavior under dynamic impact.Highlights An anisotropic continuum mechanical constitutive behavior considering strain rate effect and damage evolution behavior was established. A macroscopic anisotropic constitutive model including the coupled impact temperature generation‐mechanical behavior was established. Combined with the incremental finite element method, the three‐dimensional user‐defined material subroutines (VUMAT) were developed and verified. The thermomechanical impact penetration behaviors of CFRP laminates was predicted, and the stress field, temperature field and failure characteristics were visualized.

Energy absorption and storage of nanofluidic solid–liquid composite material under high strain rates

Efficient energy absorption and dissipation are crucial for the development of novel protective materials under intensive dynamic loadings. Nanofluidic solid–liquid composite materials (NLCs) provide a promising pathway to engineer such materials owing to their rapid and reversible energy absorption and storage performance. In this study, we conducted systematic experiments on nanoporous SiO2 based NLCs to gain a better understanding of the dynamic mechanical behavior and the underlying energy absorption and storage mechanisms under compressions with varying strain rates. Our findings indicate that the energy absorption in terms of dissipation and storage under the repeat compressive loadings includes two stages. The initial stage indicates the maximum energy absorption capacity, which is efficiently improved by the adding electrolyte solution and the retreatment. The stable energy absorbing stage represents the reversible energy absorption and storage capacity of the NLCs. Based on the noticeable strain rate effect, a three-stage mechanism is proposed to explain the significant increase of energy absorption capacity with the varying compressive strain rates. The superior reusable energy absorption capacity of NLCs holds great promise for their use as excellent energy-absorbing materials under intensive impulsive loadings.

Maintain sort order of grain boundary to investigate the deformation mechanism of CoCuFeNiPd high–entropy alloys

Molecular dynamics simulations of tension tests on CoCuFeNiPd high–entropy alloys (HEAs) are performed to study the effects of grain sizes (d), temperatures, and strain rates on the mechanical properties. After a series of tension simulations with different grain sizes, the Hall – Petch (H–P) and inverse Hall – Petch relationships are discovered. Hall–Petch breakdown is observed at grain size (d) of 10 nm. In the inverse Hall – Petch region, the average flow stress (σ(ε)) decreases from 1.97 to 1.76 (GPa) when grain size is decreased from 10 nm to 4 nm. On the contrary, the average flow stress increased from 1.90 to 1.97 (GPa) as d reduced from 18 nm to 10 nm. The microstructural evolution of the CoCuFeNiPd HEAs model exhibits that the primary deformation process in the H–P relation (d > 10 nm) is dislocation slips. The grain boundaries (GB) prevent dislocation expansion in the H– P relation, causing mechanical strengthening. Meanwhile, the main deformation mechanisms for the inverse H–P (d < 10 nm) are grain rotation and GB migration, decreasing flow stress. In addition, Young's modulus of the HEAs model increases with grain size (d). The yield strength, flow stress, and Young's modulus of HEAs specimens tend to reduce at high temperatures. Additionally, the number dislocation length reduces at high temperatures due to the amorphization phenomenon. The results also showed that Young's modulus and yield strength increase when strain rates rise.

Ignition and energy release characteristics of energetic high-entropy alloy HfZrTiTa0.2Al0.8 under dynamic loading

Steel-like density HfZrTiTa0.2Al0.8 high entropy alloy (HEA) with a density of 7.78 g/cm3 is designed and fabricated as a novel energetic structural material (ESM). The microstructure, thermal analysis, compressive mechanical properties, ignition and energy release under dynamic loading are systemically investigated. The experimental results show that the HfZrTiTa0.2Al0.8 HEA has a single BCC solid solution structure, and spinodal decomposition with elements segregation in the nanoscale is observed. Thermal analysis shows the HEA keeps stable in the Ar atmosphere and the oxidizing reaction occurs in the Air atmosphere. The mechanical properties show brittle characteristics with maximum strength with 1520 MPa and fracture strain 0.07 and strain rate effect from 0.001s−1 to 3000s−1 is observed. Under high strain rate loading, the fracture-induced spark is observed, which is caused by an oxidizing reaction due to the rise. By direct ballistic test, the energy release velocity threshold is measured as 980 m/s, and the energy release intensity is more violent in higher velocity impact conditions. Moreover, the impact reaction degree is increased with increasing fragmentation degree and adiabatic temperature rise induced by impact. The designed HEA-ESM is a promising candidate that simultaneously possesses both high strength, high reactive heat and excellent energetic characteristics in the application field of high-strength ESM fragment.

Experimental and analytical investigations of prefabricated segmental concrete beams post-tensioned with unbonded steel/FRP tendons subjected to impact loading

Studies of prefabricated segmental concrete beams (PSCBs) under impact loading are extremely scarce, especially those constructed with geopolymer concrete (GPC) and non-corrodible fibre-reinforced polymer (FRP) tendons. This study conducts experimental tests to explore the impact performance of PSCBs made of GPC and post-tensioned with FRP/steel tendons. An analytical model for predicting the impact response of PSCBs is also derived. The test results show that different from monolithic beams, the damage in PSCBs is mainly concentrated around segment joints due to joint openings that led to the beam failure by concrete spalling. The PSCBs with carbon-FRP tendons and steel tendons show similar damage patterns. Under a similar condition, the difference in the displacement response of these two beams is less than 4 %. A similar trend in the generated impact load and reaction force is also observed. These two beams reach the first peak and plateau region of impact load and the maximum reaction force at similar times. Overall, the PSCB with carbon-FRP and steel tendons exhibits comparable impact performances. These results manifest the applicability of carbon-FRP tendons in PSCBs against impact loads, as a feasible and durable alternative to conventional steel tendons. Furthermore, theoretical derivations are conducted to derive a simplified analytical model for predicting the impact response of simply supported segmental beams. This analytical model is based on a mass-spring-damper system and a nonlinear sectional analysis, considering the local response at the impact zone, global elastic and inelastic behaviours of segmental beams, imperfections in segment interfaces, nonlinear behaviours of material properties and strain rate effects. The proposed analytical model can facilitate the analysis and design of segmental beams.

The effect of temperature and strain rate on the grain boundary sliding in a CM247 LC Ni-based superalloy processed with laser based powder bed fusion

The current work explores the meso-scale deformation behaviour of an additively manufactured CM247 LC at room and high temperatures. In particular, the study focuses on assessing grain boundary sliding (GBS), which can play a crucial role in the high-temperature deformation of superalloys. Specific samples were produced using the Laser Based Powder Bed Fusion technique (PBF-LB), heat treated and tested under monotonic compression in a Gleeble® system. Compression tests were carried out in a wide temperature range at two strain rates and the effect of testing parameters on GBS activity was studied. A thorough microstructural characterization of the PBF-LB material using EBSD and TEM revealed a γ/γ’ microstructure consisting of columnar grains decorated with Hf-rich MC carbides without any segregations of alloying elements. Qualitative and quantitative analysis of GBS was performed using FEG-SEM and AFM, and contribution of GBS into plastic deformation was estimated. It was demonstrated that GBS is activated at 760 °C. A direct correlation between the contribution of GBS into plastic deformation and testing temperature was found, while strain rate has the opposite effect. The highest GBS contribution (∼32%) was recorded at 1093 °C/10−3 s−1. Finally, intergranular microcracking at triple junctions and along grain boundaries was observed when the material was tested at the highest temperatures (871 °C and 1093 °C). The effect of the temperature and the strain rate on the GBS activity in the PBF-LB material is discussed.

Study on morphology reconstruction of SiC ceramics ground by monolayer-patterned grinding wheel considering strain rate effect

Study on morphology reconstruction of SiC ceramics ground by monolayer-patterned grinding wheel considering strain rate effect

Strain-rate effect on the hydro-mechanical behaviour of unsaturated damaged Callovo–Oxfordian claystone

Strain-rate effect on the hydro-mechanical behaviour of unsaturated damaged Callovo–Oxfordian claystone

Effect of strain rate on the hardness of relaxor ferroelectric PMN-0.32PT single crystals

The relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) has been considered to be a potential choice for high performance actuators and sensors owing to their ultrahigh electromechanical properties. Recent experiments have shown that the hardness and indentation fracture toughness of PMN-PT varies with load and loading direction. However, it is not clear from these studies that how the loading rates would affect the indentation response of these materials. Therefore, nanoindentation experiments at different strain rates are performed on [001] and [011] oriented poled PMN-0.32PT single crystals. Results show that the hardness, H decreases with increase in strain rate. This behavior is in contrast to the trend reported for PMN-PT single crystal in the recent past. The indentation size effect (ISE) is noticed in both the orientation for all the strain rates. In order to analyze the observed ISE, various mechanistic models are used such as Meyer's law, Hays-Kendall (H-K) model, proportional specimen resistance (PSR) model, and modified PSR (MPSR) model. The analysis of nanoindentation data using MPSR model satisfactorily describes the ISE in terms of resistance offered by the specimen to indenter penetration, the interface friction, and surface residual stress.