High Strain Rate Effects Research Articles

The Effect of High Strain Rate on Properties and Microstructure of the Fully Austenitic High Mn Steel

In the paper, results of impact bending tests of a high-manganese steel of X30MnAlSi26-4-3 grade are presented. The tests were carried out using a flywheel machine, suitable for dynamic tensile tests and impact bending tests in the range of linear velocity of the forcing element from 5 ÷ 40 m/s. The obtained test results were compared with the results of impact resistance of the studied steel determined using Charpy machine. Structural investigations were carried out using light microscope and scanning transmission electron microscopy. Creating a mechanical twins at different strain rates was analyzed. The surfaces of fractures formed in the break point during bending tests were analyzed, and they indicate a presence of mixed transcrystalline fractures with a predominance of plastic fractures. Substructure studies revealed the presence of mechanical twinning induced in a high strain rate for the X30MnAlSi26-4-3 steel.

Effects of Low Temperature and High Strain Rate on the Tensile Behaviors of High-Performance Energetic Composite

To further study the effects of low temperature and high strain rate on the tensile behaviors of hydroxyl-terminated polybutadiene (HTPB) propellant, an INSTRON testing machine was applied for carrying out the uniaxial tensile tests at low temperatures and room temperature after storage at low temperatures. The strain rates are in the range of 0.40 to 85.71 s −1 . Scanning electron microscope (SEM) was used for examining the failure mechanisms of HTPB propellant under the test conditions. The results reveal that HTPB propellant is still capable of large deformation at lower strain rates and low temperatures in the glass transition and glass state. The characteristics of stress-strain curves at room temperature after storage at low temperatures are the same with that directly obtained at room temperature. The effect of strain rate on the elastic modulus E at various temperatures is almost the same. However, the effect of strain rate on the maximum tensile stress σ m becomes weak with decreasing temperature. Furthermore, the strain e m is nearly independence of the strain rate at higher strain rates and the lowest test temperature in glass state. Continuously decreasing temperature can more easily cause the extensive brittle fracture of AP particles, even at lower strain rates. The temperature changes from room temperature to low temperature and then from low temperature to room temperature in a short time cannot influence the failure mechanism of HTPB propellant at room temperature and high strain rate.

Combined effects of high temperature and high strain rate on normal weight concrete

Concrete in structures is possibly exposed to fire and blast due to occasional accidents or terrorist attack during the service life. Yet, there are few experimental studies on the responses of normal concrete structures subjected to high temperature and high strain rate loading simultaneously, although some high strain rate experiments were performed before or after fire exposure. This paper reports an experimental study of the combined effects of high temperature and high strain rate on normal concrete material, which is a preliminary basis for calculating and assessing the performances of RC structures in blast and fire. The dynamic properties of normal concrete at elevated temperature from 20 °C up to 950 °C were systematically studied using a specially manufactured microwave–heating automatic time-controlled Split Hopkinson Pressure Bar (MATSHPB) apparatus. The concrete specimens were first efficiently heated in a specially designed industrial microwave oven, and then rapidly loaded after quickly rolling to the SHPB system. Quasi–static and low strain rate tests at elevated temperatures were also carried out for comparative analysis. In contrast with previous experimental research, the test results showed that the dynamic strength and stress–strain curve of normal concrete at high temperature still experienced remarkable strain rate effects. Moreover, the failure appearances of normal concrete subjected to both high temperature and high strain rate loading were significantly different from those of concrete at ambient temperature. In contrast with quasi-static test data, a new empirical model on dynamic increase factor of strength and secant elastic modulus of concrete at elevated temperature (DIFTS, DIFTE) were established that can be used in a very wide range of application.

Microstructure, texture and mechanical properties of 5A02 aluminum alloy tubes under electromagnetic bulging

The microstructure, texture and mechanical properties of annealed 5A02 Al alloy tubes after electromagnetic bulging have been systematically studied using transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and uniaxial tensile test. Microstructural characterizations showed that the formation of dense dislocation bands and dislocation walls in the bulged samples is due to the effect of high strain rate of electromagnetic forming and solute–dislocation interactions in the Al alloy. The texture examination revealed that the volume fraction of α-fiber texture increases after deformation, while the brass texture component in β-fiber increases, and the copper and S texture components decrease with increasing strain, indicating the occurrence of texture rotation from the initial state to a more stable orientation. In addition, the lack of cross-slip activity and high strain rate accompanied by the electromagnetic deformation in the studied Al alloy also play a role in the texture evolutions. Finally, mechanical properties of the post-bulged samples were examined by uniaxial tensile test, which shows a significant increase in yield strength and fracture strength, but decrease in fracture elongation. The enhancement of strength was discussed on the basis of the dislocation boundary strengthening mechanism, which was in good agreement with the experimental results.

Effect of high temperature compression deformation strain rate on the microstructure and corrosion behavior of 2205 duplex stainless steel

Purpose – The aim of this paper was to investigate the effect of strain rate on microstructure and corrosion behavior of 2205 duplex stainless steel, after high-temperature compression tests. Design/methodology/approach – The specimens were prepared using a Gleeble3800 thermo-simulation machine over a range of temperatures from 850 to 1,250°C and strain rates from 0.005 to 5 s−1, and the corresponding flow curves and deformation microstructure obtained were further analyzed. To evaluate the effect of strain rate on corrosion behavior, potentiodynamic polarization tests and double-loop electrochemical potentiodynamic reactivation (DL-EPR) were used to characterize the electrochemical performance. Findings – Compared with strain rate of 0.5 s−1, the worst corrosion resistance behavior from the potentiodynamic polarization test results after deformation at 0.005 s−1 was attributed to more austenite (γ) and ferrite (δ) grain boundaries or δ/γ phase interface formation due to the better effect of γ dynamic recrystallization (DRX) or δ dynamic recovery (DRV). Increasing strain rate to 5 s−1 lowered the corrosion resistance, due to the increase in dislocation density. At the low strain rate of 0.005 s−1, the susceptibility to intergranular corrosion (IGC) was comparatively high after deformation at 1050 and 1150°C with more γ/γ grains and δ/γ phase boundary formation, which was lowered with the strain rate increase to 0.5 s−1, due to suppressing effect of γ DRX. Originality/value – The paper provides the scientific basis for the practical application of hot working of 2205 duplex stainless steel.

Journal of Dynamic Behavior of Materials: A New Forum for Knowledge Exchange on Dynamic Material Response, High Strain-Rate Effects, Shock, and Materials Under Extreme Loading

We are excited to introduce the Journal of Dynamic Behavior of Materials (JDBM) as the new journal of the Society for Experimental Mechanics (SEM). We wish to invite you to submit your best work on the study of the dynamic behavior of materials to the journal and help in getting the word out to your colleagues. Information on the journal can be found at http://springer.com/40870. The field of dynamic behavior of materials is undergoing a revolution with increasing interdisciplinary focus and unprecedented new level of diagnosis at the bench scale and numerous user facilities. Classic loading techniques including split Hopkinson pressure (Kolsky) bar, gas/ powder guns, and high-explosives are being pushed to increased levels of precision, linked with new and novel diagnostics enabling previously unattainable levels of in situ measurement combined with advanced high resolution and three-dimensional post-mortem observation. National User Facilities are enhancing their capacities for studying materials in extremes with new facilities being developed ranging from SLAC’s Linac Coherent Light Source, the Dynamic Compression Sector at the Advanced Photon Source at Argonne National Laboratory, the Z-Machine at Sandia National Laboratories, the National Ignition Facility at Lawrence Livermore National Laboratory, and Matter-Radiation Interactions in Extremes at Los Alamos National Laboratory. An exciting collaboration at GSI in Darmstadt is incorporating expertise from pRad and LANSCE at Los Alamos National Laboratory in the USA and the Institute for Theoretical and Experimental Physics in Russia using the PRIOR microscope with great potential for studying dynamic materials processes. The Diamond Light Source located at the Harwell Science and Innovation Campus in the UK has been offering great levels of postmortem investigation of damage from dynamic loading. Exciting capabilities exist at these and other facilities around the world to advance the state-of-the-art for studies of dynamic behavior of materials. Advances in modeling & simulation of dynamic loading and material response have paralleled these experimental advances. Continued evolution in computing hardware is enabling calculations with extraordinary fidelity in representation of highly coupled complex physics. Great advances have been made in density functional theory, molecular dynamics, and dislocation dynamics based material models. Simulations based on these theories have historically had to be performed at very high strain-rates and in very short time and length scales. Advances in these models and the hardware on which these simulations are performed have brought them into line with the regimes of many platforms for dynamic experiments. New theories and models of material behavior are being developed to take advantage of understanding material at the mesoscale. Continuum level constitutive models are being proposed and developed with greater levels of physical underpinning and predictive ability. The state-of-the art in modeling & simulation and experiments along with the interdisciplinary approach to modern science and engineering have lead to significant payoff from hybrid experimental-computational approaches. Advances in simulation are enabling the development and optimization of experiments, with better understanding of the underlying physics and data capture. Conversely, advances in experimentation are pushing better models, codes, and simulations. The JDBM offers a single source to bring this broad, vibrant international community together. This peer E. N. Brown (&) Los Alamos National Laboratory, Los Alamos, NM 87545, USA e-mail: en_brown@lanl.gov

Numerical investigation into dynamic responses of RC columns subjected for fire and blast

Structures may be exposed to fire and blast due to accidents (i.e. explosion of flammable gas in industrial structures) or terrorist attacks during the service life. Performances of RC structures subjected to extreme conditions of fire and blast, thus, have drawn much attention from academia. In this paper, the coupling effect of high temperature and high strain rate in concrete was firstly studied based on the experimental data to improve the damage plasticity concrete model in ABAQUS. Secondly, the transient heat transfer effects in different fire scenarios and following fire resistances of RC columns with constant axial forces were numerically investigated on the basis of the improved concrete model, which are validated by the corresponding test data, and the residual axial loading capacity of RC columns was quantitatively calculated. By incorporating the different merits of implicit algorithm applied to heat transfer analyses and explicit algorithm usually used in blast analyses, a numerical approach to analyze the responses of RC columns subjected to the coupling loadings of fire and blast was finally developed. Mid-span displacements and damage of the RC columns subjected to fire and explosions were quantitatively calculated and discussed. The proposed approach was demonstrated to be effective in predicting the responses of RC structures subjected to coupling loadings of fire and blast.

The Effect of High-Strain Rate on Friction and Wear Behaviors of AZ31 Magnesium Alloy

In this study, wear behaviour of AZ31 magnesium alloy shocked by Hopkinson pressure bar was measured, the microstructure morphology was observed and the effect of high strain rate impact on wear resistance and wear mechanism of the alloy were analysed. The results show that: the wear property of AZ31 is improved by the impacted in a reasonable strain rate, but when the strain rate is high enough, it will cause the alloy inactivation. The wear mechanism of the alloy is main grain-abrasion wear, accompanied with the other form of wear, and there will be adhesive wear with the increase of the strain rate.

Experimental and Computational Study of the Shearing Resistance of Polyurea at High Pressures and High Strain Rates

Mechanical response of polyurea, a nanophase segregated elastomeric co-polymer, is investigated using all-atom, equilibrium, molecular-dynamics methods and tools. Specifically, the effects of high pressure (1-30 GPa) and high strain rate (105-106 s−1) on the shearing resistance of polyurea are examined. Such loading conditions are encountered by polyurea coatings subjected to impact by high-velocity projectiles, shell shrapnel, and improvised explosive device fragments. Computed results are compared with their experimental counterparts obtained using the so-called pressure-shear plate impact experiments. Computed results have also been rationalized in terms of the nanosegregated polyurea microstructure consisting of rod-shaped, discrete, the so-called hard domains embedded in a highly compliant, the so-called soft matrix. By analyzing molecular-level microstructure and its evolution during high-rate deformation and under high imposed pressures, an attempt is made to identify and quantify main phenomena in viscous/inelastic deformation and microstructure-reorganization processes that are most likely responsible for the observed mechanical response of polyurea.

Effect of High Tensile Strain Rate on the Evolution of Microstructure in Fe-Mn-C-Al Twinning-Induced Plasticity (TWIP) Steel

Fe-17.8Mn-0.52C-0.5Al TWIP steel has been investigated under high-strain rate conditions. Twinning along with stacking faults and high dislocation densities in the austenite matrix has been evaluated by X-ray diffraction line profile analysis and transmission electron microscopy. The samples strained at 100 s−1 show a gradient in the evolution of the dislocation density along the gage length except the fracture end where the density shows a decrease. In case of the samples strained at 1 s−1, the evolution of density shows attainment of a near-saturation stage. Electron backscatter diffraction analysis shows that the decrease in the dislocation density as well as near-saturation stage is due to dynamic recovery as well as dynamic recrystallization at region near the fracture end. The dynamically recrystallized grains are related to the deformed matrix through twin relationship.

Comparison of Dynamic Mechanical Properties between Pure Iron (BCC) and Fe-30Mn-3Si-4Al TWIP Steel (FCC)

Dynamic mechanical properties and microstructures of pure iron and Fe-30Mn-3Si-4Al TWIP (TWinning Induced Plasticity) steel were conducted by SHPB (Split-Hopkinson Pressure Bar), OM (Optical Microscopy) and TEM (Transmission Electron Microscope), at the strain rate ranging from 102 to 105 s-1 and at room temperature. The effect of high strain rate on the mechanical responses of pure iron and Fe-30Mn-3Si-4Al TWIP steel belonging to BCC (Body Centered Cubic) and FCC (Face Centered Cubic) structures respectively was evaluated. The comparison of deformation mechanism was analyzed between them and it concluded that dislocation gliding is a major deformation mechanism in pure iron with BCC structure and deformation twinning plays a significant role in Fe-30Mn-3Si-4Al TWIP steel with FCC structure.

Mechanical properties of partially damaged structural steel induced by high strain rate loading at elevated temperatures – An experimental investigation

In structural engineering practice, understanding the behaviour of steel under extreme loading conditions is essential for accurate prediction of material response when subjected to a combination of severe load scenarios such as collision by heavy objects and a following fire. Hitherto, the combined effects of high strain loading and subsequent elevated temperature have not been widely investigated on the mechanical properties of structural steel. A comprehensive test program is carried out to investigate the post-impact fire properties of Grade 350 steel under well-defined conditions, the results of which are reported in this paper. Coupon specimens have undergone interrupting high strain rate (HSR) tensile loading at impact level, controlled locally at different levels of elongation, to account for different deformation states. Three different damage levels are introduced with respect to the displacement corresponding to the ultimate stress (fu). Subsequently, the partly damaged specimens are subjected to steady-state quasi-static tensile loading to failure at temperatures ranging from ambient to 600 °C. The overall stress–strain relationship, as well as the mechanical properties of pre-damaged steel, are presented at elevated temperatures and compared to those of each individual loading scenario. The test results demonstrate that the effects of these combined actions are profoundly different from those in which the structure is subjected to either high strain rate or thermal loading individually. It is shown that the strength and ductility of mild steel is significantly dependent on the rate of loading, the pre-deformation history and the temperature to which it is subsequently exposed. This necessitates the development of models which take into account the coupled effect of high strain rate and temperature in rational fire analysis and design of steel structures.

Dynamic interface model for masonry walls subjected to high strain rate out-of-plane loads

The present study proposes a dynamic constitutive material interface model that includes non-associated flow rule and high strain rate effects, implemented in the finite element code ABAQUS as a user subroutine. First, the model capability is validated with numerical simulations of unreinforced block work masonry walls subjected to low velocity impact. The results obtained are compared with field test data and good agreement is found. Subsequently, a comprehensive parametric analysis is accomplished with different joint tensile strengths and cohesion, and wall thickness to evaluate the effect of the parameter variations on the impact response of masonry walls.

On the calculation of cumulative strain around full‐flow penetrometers in steady‐state conditions

SummaryAn approximate solution for the effects of high strain rates, and gradual strength degradation, on the penetration resistance of penetrometers can be obtained by combining the strain‐path method with the classical upper bound theorem. The stream path calculations require the integration of the material constitutive equation along the streamlines. Unless the geometry is simple so that the integration can be evaluated analytically, numerical procedures are required to backtrack streamlines. The strain at any location is calculated by finding the streamline that passes through the given point and integrating the strain rate along that streamline from its inlet boundary. Thus, the calculations can be complicated, and errors can be accumulated during the calculation procedure.This paper presents an efficient approach for evaluating cumulative strains around penetrometers without the need to backtrack individual streamlines. In this approach, the strain components are treated as field variables. The global solution is obtained using the streamline upwind Petrov–Galerkin method. The new method together with an Eulerian‐based finite element formulation was used to study the cone penetration test and evaluate the effect of strain softening on the cone resistance. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of High Strain Rate on Adiabatic Shear Sensitivity and Microstructures in Pure Titanium

As a model material, commercial pure titanium was rolled to plates with different dislocation boundaries. The dynamic mechanical response of Ti specimen was analyzed during impacted with Split Hopkinson Pressure Bar (SHPB) at different strain rates, and microstructure evolution was investigated using optical microscopy and transmission electron microscopy. It was found that adiabatic shear sensitivity was decreased with increasing strain rates for all as-annealed, 25% and 50% cold rolled states. To the contrary, for 70% cold rolled state the adiabatic shear sensitivity was increased with increasing strain rates. The microstructure of adiabatic shear bands (ASBs) were developed from elongation morphology to fine equiaxed grains in the specimens of 25% cold rolled state, and ASBs became broader with increasing strain rate.

Strain Rate Effects in CFRP Used For Blast Mitigation

The purpose of this research is to gain a better understanding of strain rate effects in carbon fiber reinforced polymer (CFRP) laminates exposed to blast loading. The use of CFRP offers an attractive option for mitigating structures exposed to blasts. However, the effect of high strain rates in CFRP composites commonly used in the civil industry is unknown. This research conducted tensile tests of 21 CFRP coupons using a hydraulically powered dynamic loader. The strain rates ranged from 0.0015 s−1 to 7.86 s−1 and are representative of strain rates that CFRP may see in a blast when used to strengthen reinforced concrete structures. The results of the testing showed no increase in the tensile strength or stiffness of the CFRP at the higher strain rates. In addition, the results showed significant scatter in the tensile strengths possibly due to the rate of loading or manufacture of the coupon.

High strain rate behaviour in tension of steel B500A reinforcing bar

In reinforced concrete structures under severe dynamic loading, as impact and blast, both concrete and reinforcing bars are subjected to high strain-rates. While the dynamic tensile behaviour of concrete is the subject of many researches, the behaviour of the reinforcing steel under high strain rate has been not completely considered yet. Such behaviour is of capital importance in the structural assessment under the abovementioned loading conditions. This is the reason why an experimental program on rebar, stirrup and wire steels under high strain rate in tension is running at the DynaMat Laboratory. In this study the effect of high strain rate on the mechanical properties of B500A steel reinforcing bars in tension has been analysed. The steel of three different bars having diameter of 6, 8 and 10 mm have been investigated. The experiments have been carried out by means of a Split Hopkinson Tensile Bar at 250, 500 and 1000 s−1. Finally the parameters of the well-known Johnson–Cook and Cowper–Symonds materials models have been obtained.

Finite Element Modeling of Crack Generation in Laser Shock Peening Processed Airfoils

Laser shock peening (LSP) is a surface treatment process for airfoils that is achieved by the induction of compressive stress. While LSP is a mature and reliable surface treatment process, slight anomalies during the process, or variations in material ductility and geometries, may cause unintended formation of small subsurface cracks in the resultant LSP processed material. In this study, we developed a 3D FEM model to simulate the formation and predict the sizes of cracks generated by inappropriate LSP processing in airfoil specimens in order to avoid producing such subsurface cracks. The Johnson-Cook plastic material model along with the consideration of effects of high strain rate was used to describe the plasticity of Ti alloys. The constants in this plastic model have been optimized with experimental data. The FEM model also includes both damage initiation and evolution criteria to simulate cracks generated by LSP process in the specimens. The simulated crack sizes and locations in the specimens have been validated by the experimental results.

Load Duration Effects in Wood at High Strain Rates

AbstractStrain rate can significantly affect the strength of materials. The split-Hopkinson pressure bar (SHPB) was initially utilized to study the effects of high-strain rate (∼103-1/s) on the behavior of metals. Subsequent modifications to the original technique allowed the study of brittle materials such as ceramics, concrete, and rock. Although material properties of wood for static and creep strain rates are readily available, data on the dynamic properties of wood are limited. Previous work using the SHPB technique with wood has considered only a few conditions, and tests to prove the applicability of the SHPB on wood have not been performed. In this study, tests were conducted using a large diameter [75-mm (3.0-in.)] SHPB. Hard maple specimens, consisting of sugar maple (Acer saccharum), black maple (Acer nigrum), and eastern white pine (Pinus strobus) specimens were utilized to represent a dense hardwood and a low-density soft wood. Specimens were machined to diameters of 63.5 and 75-mm (2.5 and 3...

High strain rate effects on direct tensile behavior of high performance fiber reinforced cementitious composites

Direct tensile behavior of high performance fiber reinforced cementitious composites (HPFRCCs) at high strain rates between 10s−1 and 30s−1 was investigated using strain energy frame impact machine (SEFIM) built by authors. Six series of HPFRCC combining three variables including two types of fiber, hooked (H) and twisted (T) steel fiber, two fiber volume contents, 1% and 1.5%, and two matrix strengths, 56MPa and 81MPa, were investigated. The influence of these three variables on the high strain rate effects on the direct tensile behavior of HPFRCCs was analyzed based on the test results. All series of HPFRCCs showed strongly sensitive tensile behavior at high strain rates, i.e., much higher post cracking strength, strain capacity, and energy absorption capacity at high strain rates than at static rate. However, the enhancement was different according to the types of fiber, fiber volume content and matrix strength: HPFRCCs with T-fibers produced higher impact resistance than those with H-fibers; and matrix strength was more influential, than fiber contents, for the high strain rate sensitivity. In addition, an attempt to predict the dynamic increase factor (DIF) of post cracking strength for HPFRCCs considering the influences of fiber type and matrix strength was made.