High Strain Rate Effects Research Articles

Investigation the effect of strain history on crystallographic texture evolution based on the perspective of macro deformation for high speed machining Ti-6Al-4V

Control of texture evolution of machined surface is an important goal to achieve specific property of workpiece in one macroscopic direction or plane. The present work aims to explore the comprehensive effect of localized strain on the texture variation during high speed orthogonal cutting Ti-6Al-4V. The strain distribution on machined surface is firstly calculated based on finite element (FE) model. Then electron backscattered diffraction experiments are performed to observe the texture variation formation of Ti-6Al-4V machined surface. The FE simulation results show that the strain distribution of machined surface fits with a negative exponential function and the direction of maximum shear strain towards cutting direction varies in the range of 25°–40°. Experimental results show that the grain misorientation distribution exhibits a peak at the angle of 30–45°, which is consistent with the inclination angle of the maximum shear strain in Ti-6Al-4V machined surface. Pole figures and orientation distribution function maps present that C fiber deformation texture is generated evolving from initial texture component of {10−10}〈0001〉. Pyramidal slip system 〈c+a〉 of α-Ti phase begins to be activated under the effects of high strain rate and cutting temperature with the increasing of cutting speed. The findings suggest that lattice rotations leading to the changes of orientation are the direct consequences of imposed deformation strain on machined surface. The results also provide a new avenue for optimizing cutting parameters to control texture variation of Ti-6Al-4V.

A comparative study on Johnson-Cook and modified Johnson-Cook constitutive material model to predict the dynamic behavior laser additive manufacturing FeCr alloy

An accurate prediction of flow behavior of metals considering the combined effects of strain, strain rate and temperature is essential for understanding flow response of metals, and a key requirement for numerical modeling and simulation of machining. Thus, the effects of high strain rate and elevated temperature on the deformation behaviors of FeCr alloy specimen, obtained by laser additive manufacturing (LAM), were investigated by Split Hopkinson Pressure Bar tests with the strain rates of 1000–8000 s−1 and temperature range of 20–800 °C. Strain rate softening effect was found at high strain rate and discussed. Based on the experimental results, the Johnson-Cook model and modified Johnson-Cook model were established for the LAM FeCr alloy. The predictions of these constitutive models were compared using statistical measures like correlation coefficient and absolute average error. Analysis of statistical measures reveals that J-C model has more deviation from the experimental values. Whereas, the predictions of modified J-C model are very close to the experimental results, which is better model for predicting the dynamic behavior of the LAM FeCr alloy.

Rigid block and spring homogenized model (HRBSM) for masonry subjected to impact and blast loading

In the present study, a simple and reliable Homogenization approach coupled with a Rigid Body and Spring Model (HRBSM) accounting for high strain rate effects is utilized to analyse masonry panels subjected to impact and blast loads.The homogenization approach adopted relies into a coarse FE discretization where bricks are meshed with a few elastic constant stress triangular elements and joints are reduced to interfaces with elasto-plastic softening behaviour including friction, a tension cut-off and a cap in compression. Flexural behaviour is deduced from membrane homogenized stress-strain relationships by on-thickness integration (Kirchhoff– Love plate). Strain rate effects are accounted for assuming the most meaningful mechanical properties in the unit cell variable through the so-called Dynamic Increase Factors (DIFs), with values from literature data. The procedure is robust and allows obtaining homogenized bending moment/torque curvature relationships (also in presence of membrane pre-compression) to be used at a structural level within the HRBS model, which has been implemented in a commercial software. At structural level, the approach resorts to a discretization into rigid quadrilateral elements with homogenized bending/torque non-linear springs on adjoining edges.The model is tested on a masonry parapet subjected to a standardized impact and on a rectangular masonry slab subjected to a blast load. In both cases, a number of previous results obtained by literature models are available for comparison, as well as experimental data. Satisfactory agreement is found between the present results and the existing literature in the field, both experimental and numerical.

Effect of high strain rate on compressive behavior of strain-hardening cement composite in comparison to that of ordinary fiber-reinforced concrete

This paper presents an experimental study on the effect of high strain rate on the compressive behavior of two strain-hardening cement-based composites (SHCCs), compared to that of fiber-reinforced high-strength concretes (FRHSCs) with similar compressive strengths. One of the SHCCs was reinforced with 2% of polyvinyl alcohol (PVA) fibers by volume (SHCC-PVA) and had a compressive strength of 64MPa. The other was reinforced with 0.5% of steel plus 1.5% of polyethylene (PE) fibers by volume (SHCC-ST+PE) and had a compressive strength of 83MPa.Split Hopkinson pressure bar and hydraulic machine experiments were conducted to determine the behavior of the SHCC and FRHSC at strain rates from 30 to 300 and 10−4 to 10−1s−1, respectively. The Dynamic Increase Factor (DIFfc), the ratio of the material strength under dynamic loading to that under static loading, was determined for the materials considered. The fracture patterns of the specimens, matrix, and fibers were carefully examined. The results indicate that the fiber content has a significant effect on the DIFfc values. In addition, it is shown that the equations in CEB-FIP 1990 and fib 2010 codes are not applicable for SHCC and FRHSC beyond a transition strain rate of 30s−1.

Nano-milling on monocrystalline copper: A molecular dynamics simulation

ABSTRACTNano-milling is a promising technique for making miniaturized ultraprecision components. However, its underlying material removal mechanism is unclear and the accurate prediction of its performance is lacking. This study performs a systematic molecular dynamics analysis to reveal the material removal in the nano-milling of monocrystalline copper. It was found that the grooves by nano-milling, regardless of the machining parameters used, have two common features: (i) the groove top edge distortion is due to the effects of surface energy and high strain rate and (ii) the groove profile at the outlet side of the tool rotation aligns more closely with the designed geometry as a result of the atom flow variation and residual stress distribution. A dimensional analysis showed that the cutting speed factor and groove dimension factor significantly influence the specific energy and material removal rate in nano-milling. The groove quality can be improved by increasing the groove dimension factor or by decreasing the cutting speed factor. Finally, a machinability chart was developed for quality nano-milling processes.

Effect of high strain-rates on the tensile constitutive response of Ecofriendly Ductile Cementitious Composite (EDCC)

Abstract Eco-Friendly Ductile Cementitious Composites (EDCCs) are a newly developed class of engineered cementitious composites that contains reduced amounts of cement and very high volumes of fly ash (or other SCMs) and show very high ductility and elastoplastic response in pure tension. These characteristics make EDCCs a promising material for seismic retrofit applications. This paper describes an experimental program where the effects of higher rates of loading on the tensile behaviour of EDCC are assessed. Strain-rate ratios of the orders of 103 (static to dynamic) are investigated. The rate of loading is chosen to coincide with strain-rates normally observed during earthquakes. The EDCCs tested are fiber reinforced concrete materials having a total fiber volume of 2%. Non-oiled Poly-Vinyl Alcohol (PVA) fibers and Poly-Ethylene Terephthalate (PET) fibres are used in the EDCC mixes in three different combinations: 2% PVA, 2% PET, a hybrid mix of 1% PVA + 1% PET fibers. For the quasi-static tests, a normal closed-loop test set-up is used. For the dynamic tests, a newly designed test setup using an air gun is utilized. This investigation discloses that the approximate static to dynamic ratio for the tensile strength of EDCC varies between 0.75 and 1.00 in magnitude; and, the strain capacity varies between 1.0 and 3.0 for this material. Results demonstrated that EDCCs are highly strain-rate sensitive materials and their performance during an earthquake should not be assessed from routine quasi-static tests.

Simulation of Fracture in the Taylor Test Using Continuum Damage Mechanics Model

Impact problems lead to dynamic fracture and the study of this fracture is always a challenge. Impact problems are characterized by large plastic deformation, high strain rates and thermal softening. The strain rate regime of 103s−1 and beyond is generally regarded as the high strain rate range where the strain rate and thermal effects become important and need to be considered. The effects of high temperature and high strain rate on the fracture patterns in Taylor rod of IS2062: 2006 GR E410W A steel are studied by using the developed damage growth law at high temperature and high strain rate based on continuum damage mechanics model. The stress and strain fields are obtained by using the commercial finite element software ABAQUS/Explicit where the damage growth law (at high temperature/strain rate) is incorporated through an external user defined material subroutine (VUMAT). The critical damage criterion is used to predict the fracture initiation. After that, the spread of fracture is simulated by tracing the path of the failed elements.

A concrete constitutive model considering coupled effects of high temperature and high strain rate

Concrete in RC structures is possibly exposed to fire and blast due to occasional accidents or attacks during the service life. To predict the dynamic responses of RC structures under fire and blast precisely, the Drucker–Prager (DP) constitutive model was modified to consider the coupled effects of high temperature and high strain rate for concrete. The piecewise function for the complete stress–strain curve of concrete at the ambient temperature was extended for damage and high temperatures. The yield criterion with the exponent form and the associated flow rule were employed into the model to describe the plastic behaviors of concrete at high temperature. A new coupling function was proposed to determine the coupled effects of high temperature and high strain rate on concrete strength on base of the test data. The proposed model was implemented into the commercial FE software ABAQUS through VUMAT. A fine numerical analysis on the existing SHPB test at high temperature was conducted to validate the proposed model, and a good agreement with the test data was observed.

Mechanical properties of an epoxy-based adhesive under high strain rate loadings at low temperature environment

Abstract The tensile properties of an epoxy-based adhesive subject to high strain rate loadings at low temperatures were studied. Tensile split Hopkinson bar incorporating with an environmental chamber was utilized to conduct tensile property tests. Mechanical Parameters, like strength, Young's Modulus, strain to failure and fracture energy at low temperatures (−20°C and −40 °C) with different strain rates were investigated. The results show that at room temperature (RT), the strength and stiffness both increase significantly with the increase of strain rate. However, the increment of strength at low temperatures is insignificant. Interestingly, at RT and −20 °C, strain to failure increase with the increase of strain rates. From the stress-strain curves, strain softening phenomenon at high strain rates are observed at RT and −20 °C.This could be explained by the localized temperature rise in the specimens when the strain rate reaches high. At −40 °C, strain to failure decreases with the increase of strain rate and strain softening disappears. The larger temperature difference between the environment and the localized temperature rise in the specimens may reduce the strain softening phenomenon. Effects of high strain rate on tensile properties of epoxy adhesive at low temperatures are different from that on polyurethane-based adhesive in the literature.

Numerical study on electrohydraulic forming process to reduce the bouncing effect in electromagnetic forming

Electromagnetic forming (EMF) is a high-speed forming process that forms a blank by using Lorentz force. Because it is a high-speed process, the effects of high strain rate can enhance the formability of the blank. However, when the blank is deformed into a complex shape, bouncing occurs at the surface of the blank, thereby generating wrinkles in the metal. Therefore, electrohydraulic forming (EHF) is proposed in this paper to overcome the bouncing effect. EHF is a high-speed forming process that employs high voltage discharge in water. The shockwave resulting from the electric discharge propagates to the blank through the water and deforms the blank into the shape of the die. A numerical simulation of the EHF process was performed using the LS-DYNA program to examine the forming procedure in detail. In the simulation, an arbitrary Lagrange–Eulerian multimaterial formulation was used to describe the interaction between the fluid components. Furthermore, a coupling mechanism was used for modeling the fluid–structure interaction. The numerical results of EHF were compared to those of EMF. This comparison showed that the EHF process can overcome the bouncing effect and deform a blank into a complex shape.

Investigating the Behavior of Light-Frame Wood Stud Walls Subjected to Severe Blast Loading

AbstractAn understanding of the behavior of wood stud walls in a region corresponding to hazardous-blowout damage levels is currently lacking. The focus of the current study is on investigating the flexural response of full-scale wood stud walls subjected to pressure-impulse combinations that would yield severe damage levels. Static material properties were determined and used as input in an analytical model that considers the nonlinear behavior of stud-to-sheathing joints, as well as high strain-rate effects. Experimental results showed that premature sheathing failure could occur prior to full flexural stud response, and that sheathing panel debris could be generated. The use of thicker sheathing and screws shifted the failures to the studs, while decreasing the amount of debris. Welded wire mesh was successfully used as a reinforcement of the sheathing or as a catcher system while maintaining the residual axial capacity of the studs. A single-degree-of-freedom material-predictive model was successfully...

Effect of high strain rate on glass/carbon/hybrid fiber reinforced epoxy laminated composites

Abstract Composites are efficient to deal with tensile loads than metals. Now-a-days, metals are replaced with composites owing to their higher strength to weight ratio and are extensively used in aircraft wing and fuselage structures. These structures are subjected to high strain rates during impact loadings, such as bird hit or run-way debris impact. In order to design robust composite structures, it is important to understand the strain-rate-dependent behavior of composite materials. In this study, influence of strain rate on the tensile properties of glass/epoxy, carbon/epoxy and hybrid (glass-carbon/epoxy) composites are experimentally and theoretically investigated in the range of strain rates from 0.0016 s −1 to 542 s −1 . Drop mass setup is used for high strain rate tests. Quasi-static tests are performed on Instron universal testing machine in accordance with ASTM D638 . The results indicate that the tensile strength and tensile modulus of GFRP and hybrid composites increase and percentage of failure strain for GFRP, CFRP and Hybrid composites decreases with the increase in strain rate, whereas tensile strength and tensile modulus of CFRP composites remains approximately constant. The scanning electron microscopy is used for analyzing the failure modes of the failed region (surface) of the tested specimens. Non contact DIC system is used to capture the strain field with the help of high speed camera.

A numerical study on the high-velocity impact behavior of pressure pipes

Pressure pipes are widely used in modern industry with some in potentially dangerous situations of explosion and impact. The security problems of these pipes when subjected to impact have attracted a lot of attention. A non-linear numerical model has therefore been developed to investigate the dynamic behavior of pressure pipes subjected to high-velocity impact. A high strain rate effect on the pipe response is considered here and the fluid and pipe interaction is modeled to include the coupling effect between the deformation of the pipe and its internal pressure. Low-velocity and high-velocity impact experimental results are used to verify the numerical model, and a reasonable agreement between the numerical and experimental results has been achieved. The effects on the dynamic behavior of the pipes of the nose shape of the projectile, the diameter of the spherical projectile, and the pipe wall thickness and internal pressure, are investigated quantitatively. During high-velocity impacts, the increase of pressure in the pipes decreases their resistance to perforation. A rise in internal pressure increases the elastic resistance of the pipes toward impacts without crack formation.

Nano-Impact Tests with Ultra-High Strain Rate Loading Using Graphene and Ion Impact

Strain rate is essential in study of the physics of fluids and solids undergoing deformation. State-of-art high strain rate tests have mainly been in macro-scale with an upper limit of [Formula: see text]. A graphene-based layered system is proposed to conduct nanometer-scale high strain rate testing. The process is investigated by molecular dynamics simulations. Accelerated single ion or group of ions are used to impact on the proposed system to generate ballistic or plate-like impact scenarios. The effects of impact energy, shape of impact absorber and the impaction location are investigated. The graphene layer is the key of the proposed system to spread the load and protect the sample. The results indicate that ion group and single ion impacts produce strain rates of [Formula: see text]–[Formula: see text] and [Formula: see text]–[Formula: see text], respectively. Ion group impact produces a more significant signal than single ion impact on the sensing nano-layer in the system. The ultimate strength of an Al-Cu alloy sample during ion impact is estimated to be 215[Formula: see text]MPa to 251[Formula: see text]MPa, significantly lower than predicted by the Johnson–Cook model because of the rapidly increased temperature and melting in the sample. The results demonstrate new possibilities for understanding high strain rate effects at nano-scale.

고속 변형률속도 효과를 고려한 폭발하중을 받는 보강형 방폭벽 구조의 동적 특성

본 연구는 폭발하중을 받는 보강판으로 구성된 방폭벽 구조에 대하여 유한요소 동적해석을 수행하였다. 수치 시뮬레이션은 서로 다른 재료로 구성된 경우에 대하여 비교 검증하였으며, 폭발 시뮬레이션 데이터를 기반으로 폭발하중에 대한 방폭벽의 동적거동을 상세 규명하였다. 충격흡수력이 좋은 고망간 강재로 구성된 방폭벽의 경우 충격에 대한 성능이 상대적으로 우수한 것으로 나타났다. 본 연구에서는 LS-DYNA 프로그램을 적용하여 유한요소 충격해석을 수행하였으며, 고속 변형률 속도 효과를 추가로 고려하여 고망간 강재로 보강된 방폭벽에 대하여 확장하였다. 다양한 매개변수를 적용한 수치해석 결과는 폭발 시뮬레이션으로부터 보강된 방폭벽 구조의 동적 효과를 비교 분석하여 서로 다른 재료의 적용효과를 보여준다. A finite element dynamic simulation is performed to gain an insight about the stiffened blast wall structures subjected to blast loading. The simulation was verified using qualitative and quantitative comparisons for different materials. Based on in-depth examination of blast simulation recordings, dynamic behaviors occurred in the blast wall against the explosion are determined. Subsequent simulation results present that the blast wall made of the high performance steel performs much better in the shock absorption. In this paper, the existing finite element shock analysis using the LS-DYNA program is further extended to study the dynamic response of the stiffened blast wall made of the high-performance steel considering high strain-rate effects. The numerical results for various parameters were verified by comparing different material models with dynamic effects occurred in the stiffened blast wall from the explosive simulation.

High strain rate constitutive behavior of SAC105 and SAC305 leadfree solder during operation at high temperature

Industry migration to leadfree solders has resulted in a proliferation of a wide variety of solder alloy compositions. The most popular amongst these are the Sn–Ag–Cu family of alloys like SAC105 and SAC305. Electronics subjected to shock and vibration may experience strain rates of 1–100/s. Electronic product may often be exposed to high temperature during storage, operation and handling in addition to high strain rate transient dynamic loads during drop-impact, shock and vibration. Properties of leadfree solder alloys at high strain rates at low and high temperatures experienced by the solder joint during typical mechanical shock events are scarce. Previous studies have showed the effect of high strain rates and thermal aging on the mechanical properties of leadfree alloys including elastic modulus and the ultimate tensile strength. The ANAND viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components. In this study, SAC105 and SAC305 leadfree alloys have been tested at strain rates of 10, 35, 50 and 75/s at various operating temperatures of 50°C, 75°C, 100°C and 125°C. Full-field strain in the specimen have been measured using high speed imaging at frame rates up to 75,000fps in combination with digital image correlation. The cross-head velocity has been measured prior-to, during, and after deformation to ensure the constancy of cross-head velocity. Stress–strain curves have been plotted over a wide range of strain rates and temperatures. Experimental data for the pristine specimen has been fit to the ANAND's viscoplastic model.

Verification of FEM Modelling Capabilities Allowing for the Effects of Strain Rate

The effects of strain rate on the changes in material properties are commonly known [2,5]. This phenomena is also the subject of studies related to composite materials due to fact that composites are widely used as an energy absorbers in road safety structures [6]. Those effects are more often considered as required to be included in the design of structures subject to dynamic loads [1,3]. The example structure is the road infrastructure subject to high strain due to the vehicle impact characterized by a high strain rate [1].Various numerical methods are being employed at the design stage to reduce the costs of experiments on actual structures. One of the most important factors in preparation of the analysis is to select a suitable material model to allow for the effects of strain rate on the changes in material properties. One of the material models allowing for the effects of strain rate is the model developed by G.R. Johnson and W.H. Cook.The study aims to verify the FEM modelling capabilities of the effects characterized by the effects of high strain rate on the material properties. Thus, the strength tests required to determine the material constants for Johnson-Cook model were performed and modelled using FEM method and the results including the effects of strain rate on the mechanical properties were compared.

Experimental and Numerical Correlation of Impact of Spherical Projectile for Damage Analysis of Aero Engine Component

<p>Studies the impact response of flat Titanium alloy plate against spherical projectile for damage analysis of aero engine components using experimental and finite element techniques. Compressed gas gun has been used to impart speed to spherical projectile at various impact velocities for damage studies. Crater dimensions (diameter and depth) obtained due to impact have been compared with finite element results using commercially available explicit finite element method code LS-DYNA. Strain hardening, high strain rate and thermal softening effect along with damage parameters have been considered using modified Johnson-Cook material model of LS-DYNA. Metallographic analysis has been performed on the indented specimen. This analysis is useful to study failure analysis of gas turbine engine components subjected to domestic object damage of gas turbine engine. </p><p> </p>

A simplified approach to high strain rate effects in cold deformation of polycrystalline FCC metals: Constitutive formulation and model calibration

This work describes a macroscopic finite elastic–viscoplastic constitutive formulation that accounts for the individual contributions of strain hardening, strain rate induced hardening and viscous behavior in cold deformation of polycrystalline FCC metals. The constitutive modeling follows a Perzyna-type formulation within the thermodynamics with internal variables framework. The approach introduces a single phenomenological internal variable defining an effective microstructural feature, which comprises strain hardening contributions related to large strain processes. Internal variable evolution is based on physical considerations and gives rise to a modified Voce hardening law, which allows for predicting both the strain rate history effects and the linear hardening at large strains. Instantaneous rate-sensitivity is accounted for by a phenomenological overstress function. Material parameters are adjusted using experimental data available in literature for annealed high purity copper. Comparisons with experimental results and other viscoplastic models have demonstrated the model aptitude to properly predict high strain rate effects in cold deformation of polycrystalline FCC metals.

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.