Strain Rate Tension Research Articles

Rate-dependent constitutive behavior and mechanism of CMDB under tension loading

The composite modified double-base propellants (CMDB) were experimentally investigated for mechanical behavior under wide tension strain rate loading from 0.0001 s−1 to 2500 s−1, based on Instron mechanical machine and modified Hopkinson tension bar technique. Stress-strain curves were obtained for its strain rate effect and integrality evaluation. The results indicated that CMDB presents high rate-dependence with flow stress distinctly increase as loading strain rate increasing. A succinct constitutive formulation is established with only five parameters, to characterize well the rate-dependence and strain hardening behavior. The fracture morphologies were investigated by scanning electron microscopy, and it is indicated that they are also rate-dependent: the cavitation and matrix damage induced from matrix deformation work less but more RDX particles fractures with strain rate increasing. Equivalent unit cell model with brittle cracking was established to simulate the mechanical behavior and failure characteristics of CMDB. The results reveal that with increasing loading strain rates, CMDB presents a tough-brittle transition, with less cavitation and matrix damage induced by matrix deformation, while more RDX particles fracture. Series of simulated results confirm qualitatively the experimental observations, and the obtained stress contours facilitate to validate the observed characteristics and propose reasonable mechanisms.

Evaluation of the mechanical properties of porcine kidney.

With the development of medical diagnosis and treatment, knowing the mechanical properties of living tissues becomes critical. The aim of this study was to investigation material properties of the fresh porcine kidney and the parametric characterization of its viscoelastic material behavior. The material investigation included uniaxial tension tests in different strain rates, relaxation tests, as well as hydrostatic compression tests on the samples extracted from the fresh porcine kidney cortex. Tension tests and relaxation tests were performed by a planar dog-bone specimen with a micron loading testing machine. Hydrostatic compression tests were performed on the kidney cylinder sample which was placed in a compression chamber. Furthermore, a nonlinear viscoelastic model recently proposed by us was employed to characterize the tension data at different strain rates and relaxation test data. The the experimental and numerical results show that the stress-strain relations of the porcine kidney cortex at different strain rates in tension are presented for the first time and a higher strain rate results in higher ultimate strength and initial Young modulus but a lower rupture strain. A damage-dependent visco-elastic model is employed to model the tension data at different strain rates and relaxation data and exhibits a good agreement with the experimental data, which also demonstrates that the damage has an obvious influence on the stress-strain relation. Through comparison with the existing reference covering the uniaxial compression data, it seems that the mechanical behavior of the porcine kidney cortex manifests a stress state-dependent mechanical behavior. The ultimate strength and rupture strain are larger in compression than that in tension.

Effect of strain rates on mechanical behavior, microstructure evolution and failure mechanism of extruded-annealed AZ91 magnesium alloy under room-temperature tension

Loading rate is usually considered as a significant factor affecting formability of AZ91 magnesium alloy structural components. Herein, uniaxial tensile tests are conducted on extruded-annealed AZ91 alloy under room temperature with strain rates ranging from 1 × 10−4 s−1 to 1 × 10−2 s−1. Mechanical properties, microstructure characteristics, and fracture morphologies tensioned at these different strain rates are investigated. Extruded-annealed AZ91 alloy exhibits a positive strain-rate dependence of strength and a negative strain-rate dependence of elongation. With strain rate increasing, strain rate sensitivity basically decreases while strain-hardening rate increases. At higher strain rate, the larger strength is mainly attributed to the more rapid accumulation of dislocation and the larger dislocation density, and the lower elongation is mostly owing to the more elevated level of inhomogeneous deformation related with dislocations accumulation. As strain rate increases, the area fraction of basal texture increases while that of prismatic and pyramid texture decreases in tensioned samples, which is associated with the dominant room-temperature deformation mode of basal-slip and twinning co-induced lattice rotation. With tension strain rate increasing, there are three kinds of fracture modes including ductile facture with more and deeper dimples at low strain rate, ductile-brittle facture with some dimples and cleavage planes at mediate strain rate and brittle facture with dominant cleavage planes at high strain rate.

Methodologyfor Molecular Dynamics Simulation of Plastic Deformation of a Nickel/Graphene Composite.

In this study, some features of molecular dynamics simulation for evaluating the mechanical properties of a Ni/graphene composite and analyzing the effect of incremental and dynamic tensile loading on its deformation are discussed. A new structural type of the composites is considered: graphene network (matrix) with metal nanoparticles inside. Two important factors affecting the process of uniaxial tension are studied: tension strain rate (5 ps and 5 ps) and simulation temperature (0 and 300 K). The results show that the strain rate affects the ultimate tensile strength under tension: the lower the strain rate, the lower the critical values of strain. Tension at room temperature results in lower ultimate tensile strength in comparison with simulation at a temperature close to 0 K, at which ultimate tensile strength is closer to theoretical strength. Both simulation techniques (dynamic and incremental) can be effectively used for such a study and result in almost similar behavior. Fabrication technique plays a key role in the formation of the composite with low anisotropy. In the present work, uniaxial tension along three directions shows a big difference in the composite strength. It is shown that the ultimate tensile strength of the Ni/graphene composite is close to that of pure crumpled graphene, while the ductility of crumpled graphene with metal nanoparticles inside is two times higher. The obtained results shed the light on the simulation methodology which should be used for the study of the deformation behavior of carbon/metal nanostructures.

Fast nonlinear mechanical features decoupling to identify and predict asphalt-based composites

Nonlinear matrices employed in asphalt-based composites exhibit a prominent nonlinear elastic-viscoplastic-viscodamageable mechanical response. The constitutive model for this type of matrices requires a significant experimental effort to identify the material constants. To alleviate the characterization effort without losing reliability in the mechanical prediction, this paper presents a fast procedure decoupling the elasto-viscoplastic response from the viscodamageable one and facilitating the identification of the material constants via efficient optimization. This procedure relies on a combined experimental–numerical also applicable to other rheologically complex materials like polyurea, thermoplastics or elasto-viscoplastic polycrystals. The experimental part is deliberately designed to only conduct cost- and time-effective monotonic loads at different strain rates in tension and compression. These pure monotonic results are used in the constitutive model to predict more complex loading conditions such as multiple load–unload–reload (LUR) cycles. To do this, an elasto-viscoplastic constitutive model suitable to describe creep-like phenomena and large irreversible deformations is proposed. This model incorporates pressure and strain rate sensitivity, which is essential to capture the compression–tension asymmetry in asphalt-based composites. A rate-dependent damage model is proposed to describe the degradation rate of the elasto-viscoplastic part. The stress and the consistent tangent modulus are derived. The model implementation for user-defined finite element subroutines are given for explicit or implicit solvers. The proposed decoupling facilitates an efficient identification of the constant parameters via an in-house Nelder–Mead-based optimization method. To accelerate the identification, all the stress–strain curves, either in tension or compression, are simultaneously used with applying physically-based constrains. The framework is validated with asphalt matrix at room temperature (24 °C) and verified under LUR conditions at different rates. The identified model predicts correctly the experimental observations, proving its applicability to investigate particle-based composites with highly nonlinear matrices.

In situ transient Laue x-ray diffraction during high strain-rate tension.

In situ transient synchrotron Laue x-ray diffraction based on high-energy and broadband x rays under high strain-rate tensile loading was developed at a superconducting wiggler beamline at the Beijing Synchrotron Radiation Facility. A split-Hopkinson tensile bar is utilized to realize this dynamic loading condition, while the transient Laue x-ray diffraction captures the transient internal structure of monocrystalline materials. Plastic deformation of a monocrystalline nickel specimen was investigated to prove the ability of this instrumentation in the characterization of a dynamic response of monocrystalline materials during a high strain-rate impact process with 5 µs time resolution.

Effect of cold-form and tensile strain rate on mechanical properties of Q345 steel at elevated temperatures

In recent years, cold-formed steel has been extensively used, and the mechanical properties of cold-formed steel at elevated temperatures have been received considerable attention. However, little research on mechanical properties of the corner parts at elevated temperatures has been published. Meanwhile, the tensile strain rates adapted in the previous research on cold-formed steel are different, and the effect of this factor on mechanical properties was rarely investigated. In order to get a deeper understanding of the mechanical properties of cold-formed Q345 steel at elevated temperatures, an experimental investigation on flat and corner parts in cold-formed Q345 sections with two nominal thickness of 1.5 mm and 2.5 mm under three different tensile rates, 0.06/min, 0.6/min and 1.2/min, was carried out at elevated temperatures ranging from 20 °C to 800 °C. The effects of tension strain rate, cold-forming and thickness on mechanical properties of Q345 steel were systematically studied. Then the test results were compared with the prediction results provided by the current design standards and the other researchers. Furthermore, prediction equations were proposed to determine the mechanical properties of cold-formed Q345 steel.

Microstructure Evolution and Mechanical Properties of Medium Carbon Martensitic Steel during Warm Rolling and Annealing Process.

The microstructure evolution and mechanical properties of medium carbon martensitic steel during the warm rolling and annealing process were studied by scanning electron microscope (SEM), electron back scattering diffraction (EBSD), and electronic universal testing machine. The results showed that the microstructure of ferrite matrix with mass dispersive cementite particles was obtained by decomposition of martensitic in medium-carbon martensitic steel after warm rolling. The grain size of ferrite was ~0.53 μm, the yield strength and tensile strength were 951 MPa and 968 MPa, respectively, and the total elongation rate was 11.5% after warm rolling at 600 °C. Additionally, after the next 4 h of annealing, the grain size of ferrite and particle size of cementite increased to ~1.35 μm and ~360 nm and the yield strength and tensile strength decreased to 600 MPa and 645 MPa, respectively, with a total elongation increases of 20.9%. The strength of the material increased with increasing strain rate in tension, and the yield-to-tensile strength ratio increased from 0.92 to 0.94 and maintained good plasticity.

Dynamic increase factor (DIF) for concrete in compression and tension in FE modelling with a local concrete model

The dynamic increase factor (DIF) in the strength of concrete-like materials has been a subject of extensive investigation and debate for many years. It now tends to be generally accepted that the compression DIF as observed from standard sample tests is mainly attributable to the dynamic structural effect, whereas for concrete under tension the DIF is deemed to be governed by different mechanisms, probably more from the material and micro-fracture level. This paper presents a numerical study on the uniaxial compression and tension DIF, with a particular focus on how the DIF, irrespective of its cause, should be included in an appropriate manner in the finite element (FE) modelling with a local concrete model. The inevitable mesh-dependency issue due to numerical localisation and its implications on rate effects are examined in detail. A mesh-objective modification on the standard sample tested tension DIF is proposed with the aim to achieve relatively mesh independent analysis in the FE models where high strain-rate tension is involved. The results demonstrate that the proposed approach is effective, and reliable modelling results can be achieved with the proposed DIF modelling scheme for the local concrete model.

Пластическая деформация титанового сплава ВТ6 в сложном напряженном состоянии при высокоскоростном растяжении

The article presents the results of a studies on mechanical behavior of titanium alloy Ti-6Al-4V (Ti Grade 5) in the range of strain rates from 0.1 to 103 s−1. Tensile tests were carried out on flat and notched specimens using the Instron VHS 40/50-20 servo-hydraulic testing machine. High-speed video recording was carried out with a Phantom 711 Camera. The strain fields in the measuring area of the sample were investigated by the Digital Image Correlation (DIC) method. Analysis of the deformation fields of Ti-6Al-4V specimens under uniaxial tension at high strain rates revealed the presence of stationary localized shear bands at the initial stages of strain hardening. The evolution of the deformation fields in the studied loading regime indicates that in the localization bands the plastic strain is significantly higher than the average values in the gage zone of the specimen. It was found that the value of strain before fracture of the Ti-6Al-4V alloy in the zone of strain localization increases with the tension strain rate. The fracture of the titanium alloy is a result of cracks formation in the zone of plastic strain localization bands oriented along the surface of the action of the maximum shear stresses. The results obtained confirm the ductile nature of fracture of Ti-6Al-4V at strain rates from 0.1 to 103 s−1, at the triaxiality stress parameter 0.33 < η < 0.44, and at an initial temperature of 295 K. At the same time, Ti-6Al-4V alloy demonstrates a tendency to embrittlement with an increase in the triaxiality stress parameter to 0.497 at the same loading condition.

Simultaneous enhancement of strength and ductility in a NiCoCrFe high-entropy alloy upon dynamic tension: Micromechanism and constitutive modeling

The deformation responses of NiCoCrFe high-entropy alloy (HEA) under quasi-static (1 × 10−4-1 × 10−1/s) and dynamic (1,000–6,000/s) tension were investigated. A good combination of high strength and ductility is obtained under dynamic tension. The yield strength and true ultimate tensile strength is increased from 217 to 830 MPa at 1 × 10−4/s to 440 MPa and more than 1,000 MPa at 6,000/s, respectively. In addition, the engineering fracture strains maintain 60%–85% over a wide range of strain rates. The enhancements of strength and ductility originate from (1) the significant strain-rate sensitivity (SRS) mainly due to the presence of short-range orders/clusters (SROs/SRCs) as well as phonon drag effect of dislocations, and (2) the extraordinary work-hardening capacity due to dynamically formed nanoscale twins upon high strain-rate tension. The temperature and strain-rate dependence of the yield strength of the alloy are well modeled based on the thermally activated mechanism. Additionally, considering nanoscale twin boundaries as local sites for nucleating and accommodating dislocations, the dislocation density evolution model is modified and subsequently introduced into Taylor hardening model to accurately capture the hardening behavior of the current NiCoCrFe HEA. Hence, the distinguished work-hardening capacity under dynamic tension can be mainly ascribed to the low dislocation recovery rate and remarkable twin-induced dislocation generation.

Strain-Rate-Dependent Tensile Response of Ti⁻5Al⁻2.5Sn Alloy.

This study is an experimental investigation on the tensile responses of Ti–5Al–2.5Sn alloy over a wide range of strain rates. Uniaxial tension tests within the rate range of 10−3–101 s−1 are performed using a hydraulic driven MTS810 machine and a moderate strain-rate testing system. The high-rate uniaxial tension and tension recovery tests are conducted using a split-Hopkinson tension bar to obtain the adiabatic and isothermal stress–strain responses of the alloy under dynamic loading conditions. The experimental results show that the value of the initial yield stress increases with the increasing strain rate, while the strain rate sensitivity is greater at high strain rates. The isothermal strain-hardening behavior changes little with the strain rate, and the adiabatic temperature rise is the main reason for the reduction of the strain-hardening rate during high strain-rate tension. The electron backscatter diffraction (EBSD) analysis of the post-deformed samples indicates that there are deformation twins under quasi-static and high-rate tensile loadings. Scanning electron microscope (SEM) micrographs of the fracture surfaces of the post-deformed samples show dimple-like features. The Zerilli–Armstrong model is modified to incorporate the thermal-softening effect of the adiabatic temperature rise at high strain rates and describe the tension responses of Ti–5Al–2.5Sn alloy over strain rates from quasi-static to 1050 s−1.

The high strain rate tension behaviour of pseudo-ductile high performance thin ply composites

In this study the effect of strain rate in tension on two different types of thin-ply pseudo-ductile laminates is reported. These comprised Unidirectional (UD) and quasi-isotropic (QI) hybrids made from low strain thin-ply carbon/epoxy and high strain glass/epoxy prepreg and all-carbon laminates made from thin-ply [±ϴ/0]s laminates referred to as angle-ply (AP) composites. Laminates were designed and subjected to a range of cross-head speeds from 2 mm/min (0.0003 s−1) to 10 m/s (100 s−1). The designed laminates were made from single or hybrids of low strain and high strain unidirectional prepregs, i.e. thin-ply Carbon/epoxy and Glass/epoxy, respectively. Dynamic stress-strain plots and details of the damage mechanisms were obtained for each sample and compared with the quasi-static test results. The investigated thin-ply UD and QI hybrid composite laminates showed excellent pseudo-ductility at different strain rates, whereas the AP laminates were strain rate dependent and pseudo-ductility decreased with increasing strain rate.

Deformation behaviour of re-entrant carbon honeycomb structures

Recent successes of researchers in the fabrication of new carbon structures of different morphologies and dimensions open up broad prospects for the development of carbon materials with qualitatively new properties. Such promising materials are cellular structures (or carbon aerogels) that have high deformability, good adsorption and conductivity characteristics. In this work, we consider a carbon structure consisting of re-entrant honeycomb cells, which allow the structure to be auxetic. The stability and deformation behaviour of re-entrant carbon honeycomb structures is studied by molecular dynamics simulation. The effect of structural parameters on the stability of carbon aerogel is discussed. It is shown that structural changes significantly depend on the strain rate and the loading direction. At a high strain rate in tension along the z-axis, all cells open slightly at the same time. On the contrary, at small strain rates, certain cells open, while others almost completely collapse, which is expected to result in changes in physical properties, for example, in conductivity. During tension along the x-axis, a transformation from a re-entrant honeycomb to a traditional honeycomb took place.

Effect of Center Crack on Mechanical Properties of Graphene

Graphene is a thin sheet with special properties and complicated mechanical behavior. It’s important to study graphene experimentally and theoretically. Stone–Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, effect of center cracks on graphene was discussed. At first, mechanical properties of non-defected graphene sheet was obtained using molecular dynamics simulation. Comparing result with theoretical and experimental studies showing good agreements and proofing the results. Then, 8 different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that increasing crack length lead to decreasing Young’s modulus of graphene from 870GPa to 670GPa. Also, fracture occurred in less tensile strain. In the following, structural molecular mechanics method was used to simulate cracked graphene sheets. The results showed good agreement between two methods.

Residual strain in graphene: study of temperature and crack effect

Graphene is a thin sheet with special properties and complicated mechanical behavior. It’s important to study graphene experimentally and theoretically. Stone–Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, residual strain in graphene was discussed. At first, stress-strain curve of non-defected graphene sheet was obtained using molecular dynamics simulation and effect of temperature on mechanical properties of graphene was obtained. Then, four different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that cracks lead to the graphene to fracture sooner. Also, increasing temperature lead to the Young’s modulus of graphene decreases and graphene fractured at lower strain. On the other hand, residual strain of non-defected and cracked graphene increased by increasing temperature from 200 K to 1200 K. It means that graphene had more plasticity behavior by increasing temperature.

Numerical modelling of concrete fracture processes under dynamic loading: Meso-mechanical approach based on embedded discontinuity finite elements

This paper deals with 2D numerical modelling of concrete fracture under dynamic loading. For this end, a mesoscopic modelling approach with an explicit representation of aggregates and different fracture types by rate-dependent embedded discontinuity finite elements is developed. The mortar fracturing is governed by pre-embedded multiple discontinuity finite elements. The aggregates may fail according to the principal stress criterion (mode I) with a single embedded discontinuity. The numerical examples demonstrate that the present model captures many of the experimentally observed features of concrete under low and intermediate strain rates in tension and compression as well as in dynamic Brazilian disc test on concrete. Particularly, the simulations corroborate the hypothesis that the dynamic increase of strength in uniaxial compression and in Brazilian disc test (i.e. the indirect tensile strength) is caused by structural effects due to lateral inertia while in uniaxial direct tension it is a genuine material effect.

Tensile Behaviour of Commercial Aluminium Alloys Used in Armour Applications at High Strain Rate

The use of aluminium alloys in the construction of defence vehicles is strongly increasing in these last decades due to their comparably promising potential of the weight-performance relationship at similar price range. In this paper, the mechanical properties at high strain rate in tension of several commercial aluminium (2xxx, 5xxx, and 7xxx) alloys are analysed and compared. The tests have been carried out by means of three different set-ups for quasi-statics, medium and high strain rates. For the high and medium strain rate range following test methods have been used respectively: the Split Hopkinson Tensile Bar and the Hydro-Pneumatic Machine installed in the DynaMat Laboratory of the University of Applied Sciences of Southern Switzerland-Lugano. The paper presents the changing stress at a given strain when increasing the strain rate from 10-3 to 103 s-1, the strain-rate sensitivity of the uniform and the fracture strain, the reduction of the cross-sectional area at fracture with increasing strain-rate.

Coarse-Grained Molecular Dynamics Simulation of Fracture Problems in Polycarbonate

A coarse-grained particle (CG) model was developed based on all-atom molecular dynamics simulation results, aiming at applying to deformation and fracture analyses of polycarbonate. After confirming the validity of the model, the developed CG model was applied to deformation analyses to investigate the effects of strain rate and multiaxial tension. The effect of strain rate was found to be consistent with an experiment. Two types of deformation behavior were observed according to the type of multiaxial tension.

Fragmentations of Solids Under Impact Tension

Materials usually break into many pieces (fragments) under high strain-rate tension. Understanding the fragmentation properties of solids is important to the researchers in fields of physics, mechanics, aerospace and defense engineering. In this paper, we reviewed the researches on tensile fragmentation undertaken since 1940s. Recent advances in the fragmentation studies from theoretical analysis, experimental investigation, and numerical simulation are addressed. Some suggestions were provided for the future development in this field.