VERIFICATION OF THE SHB TEST RESULTS BASED ON THE ONE-DIMENSIONAL STRESS WAVE THEORY

2008 ◽  
Vol 22 (09n11) ◽  
pp. 1068-1073
Author(s):  
TOMOKAZU MASUDA ◽  
KENJI SAITO ◽  
IZUMI MORITA ◽  
SHUSHI IKEDA ◽  
KOICHI MAKII ◽  
...  
Keyword(s):  
Strain Rate ◽  
Stress Wave ◽  
High Speed ◽  
Wave Theory ◽  
High Speed Photography ◽  
Strain Rates ◽  
One Dimensional ◽  
Strain And Strain Rate ◽  
Deformation Behaviors ◽  
The One

In order to evaluate dynamic deformation behaviors under high strain rates, Kobe Steel has developed and applied a Split-Hopkinson Bar (SHB) apparatus. This paper discusses the validity of the strain measurements and strain rates measured by this SHB apparatus. The strain waves that propagated in the incident and transmitted bars and the specimen are captured using a high-resolution type high-speed photography in detail. The strain wave propagated many times in the incident and transmitted bars and the specimen when the specimen was not broken. The amount of the deformation of the specimen decreases with the propagation frequency of the incident wave. On the other hand, to improve accuracy at the strain and strain rate calculated by the one-dimensional stress wave theory, Young's modulus, the longitudinal wave speed, and the density were accurately determined. It was understood that the calculation value showed the strain and strain rate captured with the high-speed photography are a good agreement. As a result, the validity of the measurement accuracy of this SHB could be shown.

Investigation of the axial compressive behavior of Kevlar fibers using the dynamic loop test

2019 ◽  
Vol 89 (18) ◽  
pp. 3825-3838
Author(s):  
Ahmad Abuobaid ◽  
Raja Ganesh ◽  
John W Gillespie
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Failure Strain ◽  
Kink Band ◽  
Test Method ◽  
Strain Rates ◽  
Compressive Failure ◽  
Band Formation ◽  
Rate Dependent ◽  
Strain And Strain Rate

A dynamic loop test method for measuring strain rate-dependent fiber properties was developed. During dynamic loop testing, the fiber ends are accelerated at constant levels of 20.8, 50 and 343 m/s2. The test method is used to study Kevlar® KM2-600, which fails in axial compression due to kink band formation. The compressive failure strain and strain rate at the onset of kink band formation is calculated from the critical loop diameter ( D C), which is monitored throughout the test using a high-speed camera. The results showed that compressive failure strain increases with strain rates from quasi-static to a maximum strain rate of 116 s−1 by a factor of ∼3. Kink angles (φ) and kink band spacing ( D S) were 60 ° ± 2 ° and 16 ± 3 μm, respectively, over the strain rates tested. Rate-dependent mechanisms of compressive failure by kink band formation were discussed.

One-Dimensional Dynamic Compressive Behavior of EPDM Rubber

2003 ◽  
Vol 125 (3) ◽  
pp. 294-301 ◽  
Author(s):  
B. Song ◽  
W. Chen
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Dynamic Stress ◽  
Split Hopkinson Pressure Bar ◽  
Constant Strain Rate ◽  
Strain Rates ◽  
Hopkinson Pressure Bar ◽  
Stress Strain ◽  
Epdm Rubber ◽  
One Dimensional

Dynamic compressive stress-strain curves at various strain rates of an Ethylene-Propylene-Diene Monomer Copolymer (EPDM) rubber have been determined with a modified split Hopkinson pressure bar (SHPB). The use of a pulse-shaping technique ensures that the specimen deforms at a nearly constant strain rate under dynamically equilibrated stress. The validity of the experiments was monitored by a high-speed digital camera for specimen edge deformation, and by piezoelectric force transducers for dynamic stress equilibrium. The resulting dynamic stress-strain curves for the EPDM indicate that the material is sensitive to strain rates and that the strain-rate sensitivity depends on the value of strain. Based on a strain energy function theory, a one-dimensional dynamic constitutive equation for this rubber was modified to describe the high strain-rate experimental results within the ranges of strain and strain rates presented in this paper.

A study of the rapid deformation behaviour of a range of polymers

1989 ◽  
Vol 328 (1597) ◽  
pp. 1-33 ◽  
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Deformation Behaviour ◽  
Testing Machine ◽  
Polymeric Materials ◽  
High Speed Photography ◽  
Frictional Stress ◽  
Strain Rates ◽  
Petroleum Jelly ◽  
Rapid Deformation

Polymers are increasingly being used in applications where they are rapidly deformed. However, compared with metals, relatively few studies of their mechanical properties at high rates of strain have been published. This paper describes an investigation of the rapid deformation behaviour in compression of a number of widely used polymeric materials. The necessity of properly characterizing polymers is discussed, as the variation of commercial grades bearing the same name is considerable, and furthermore these materials are much more susceptible to change during storage than say metals. The importance of thermal properties to rapid, and hence adiabatic, deformation is pointed out, and tables of such properties are presented. Extensive use was made of high-speed photography (interframe time 7 (is) to study qualitatively the behaviour of solid discs of polymers at strain rates of 2.5 x 10 3 s -1 . The framing speed was sufficiently fast to capture fracture initiation and subsequent failure of all the polymers studied, including polycarbonate (PC), which fails in an almost explosive manner. The darkening of heat-sensitive film in contact with deforming discs was also investigated. Quantitatively, this technique was used to check the applicability of Avitzur’s analysis (Avitzur ( Israel J. Technol . 2, 295-304 (1964)) of a deforming annulus to polymers. Agreement was found to be good and hence friction could be measured during deformation at high rates of strain for the first time. Studies were also carried out to determine the best lubricant for rapid compressive testing. Petroleum jelly was found to reduce the friction closest to zero. An optically identical system was set up in an Instron mechanical testing machine both to perform friction studies and to explore deviation from incompressible behaviour. Agreement with Avitzur’s analysis was found to be poorer, and no lubricant was found to reduce friction below about 3-4 %. PC, with a very high value of frictional stress, showed evidence of a change in volume. Allowances were made for the elastic indentation of the anvils. Higher strain rates were achieved by using an instrumented drop-weight machine and a direct impact Kolsky bar, both developed in this laboratory. Care was taken to eliminate sources of error, including friction and calibration errors. The strain rate sensitivity of the polymers ranged from 5—15 MPa per decade of strain rate. However, most showed some softening as the strain rate was raised from 10 3 to 10 4 s -1 , the exceptions being polybutylene teraphthalate (PBT) and polyvinylidene difluoride (PVDF).

Dynamic Behavior Characterization of Lead at High Strain Rates Using High Speed Photography for Finite Element Simulation

2005 ◽  
Author(s):  
G. S. Sohoni ◽  
M. V. Walame ◽  
V. Tandon ◽  
R. S. Mahajan ◽  
S. Raju
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Dynamic Stress ◽  
High Strain ◽  
Computational Techniques ◽  
High Speed Photography ◽  
Radial Deformation ◽  
Strain Rates ◽  
High Strain Rates ◽  
Stress Strain

This paper reviews experimental as well as computational techniques for determining stress-strain characteristics of materials at high strain rates. Quasi-static and dynamic compression tests were performed on standard Lead (Pb) specimens of three different L/D ratios, 0.8, 2 and 3. A Drop tower system was used to achieve different strain rates along with high-speed camera to capture the vertical and radial deformation of specimen and accelerometers to capture load data. The results obtained from the experiments were processed to generate dynamic stress-strain curve for Lead under different strain rate conditions. It was observed that the dynamic stress increases with increasing strain rate. The information gained is valuable for validating constitutive models.

The effects of strain and strain rate on residual microstructures in copper

1986 ◽  
Vol 44 ◽  
pp. 420-421
Author(s):  
M. F. Stevens ◽  
P. S. Follansbee
Keyword(s):  
Strain Rate ◽  
Applied Stress ◽  
Threshold Stress ◽  
Rate Sensitivity ◽  
Viscous Drag ◽  
Strain Rates ◽  
Strain And Strain Rate ◽  
Threshold Strength ◽  
Mechanism Transition ◽  
Intrinsic Strength

The strain rate sensitivity of a variety of materials is known to increase rapidly at strain rates exceeding ∼103 sec-1. This transition has most often in the past been attributed to a transition from thermally activated guide to viscous drag control. An important condition for imposition of dislocation drag effects is that the applied stress, σ, must be on the order of or greater than the threshold stress, which is the flow stress at OK. From Fig. 1, it can be seen for OFE Cu that the ratio of the applied stress to threshold stress remains constant even at strain rates as high as 104 sec-1 suggesting that there is not a mechanism transition but that the intrinsic strength is increasing, since the threshold strength is a mechanical measure of intrinsic strength. These measurements were made at constant strain levels of 0.2, wnich is not a guarantee of constant microstructure. The increase in threshold stress at higher strain rates is a strong indication that the microstructural evolution is a function of strain rate and that the dependence becomes stronger at high strain rates.

Constitutive Modeling for Elevated Temperature Flow Behavior of ZHMn34-2-2-1 Manganese Brass

2017 ◽  
Vol 872 ◽  
pp. 30-37
Author(s):  
Meng Han Wang ◽  
Kang Wei ◽  
Xiao Juan Li
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Flow Behavior ◽  
Peak Stress ◽  
Strain Rates ◽  
Hollomon Parameter ◽  
Prediction Ability ◽  
Absolute Relative Error ◽  
Deformation Behaviors ◽  
State Stress

The hot compressive deformation behaviors of ZHMn34-2-2-1 manganese brass are investigated on Thermecmastor-Z thermal simulator over wide processing domain of temperatures (923K-1073K) and strain rates (0.01s-1-10s-1). The true stress-strain curves exhibit a single peak stress, after which the stress monotonously decreases until a steady state stress occurs, indicating a typical dynamic recrystallization. A revised constitutive model coupling flow stress with strain, strain rate and deformation temperature is established with the material constants expressed by polynomial fitting of strain. Moreover, better prediction ability of the constitutive model is achieved by implementation of a simple approach for modified the Zener-Hollomon parameter considering the compensation of strain rate and temperature increment. By comparing the predicted and experimented values, the correlation coefficient and mean absolute relative error are 0.997 and 2.363%, respectively. The quantitative statistical results indicate that the proposed constitutive model can precisely characterize the hot deformation behavior of ZHMn34-2-2-1 manganese brass.

Research on Numerical Algorithm of Constitutive Equation under High Speed Deformation in Hadfield Steel

2012 ◽  
Vol 562-564 ◽  
pp. 688-692 ◽  
Author(s):  
Deng Yue Sun ◽  
Jing Li ◽  
Fu Cheng Zhang ◽  
Feng Chao Liu ◽  
Ming Zhang
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Deformation Behavior ◽  
High Speed ◽  
High Strain ◽  
Equivalent Stress ◽  
Hadfield Steel ◽  
Stress And Strain ◽  
Strain Rates ◽  
The Finite Element Method

The influence of the strain rate on the plastic deformation of the metals was significant during the high strain rate of loading. However, it was very difficult to obtain high strain rate data (≥ 104 s-1) by experimental techniques. Therefore, the finite element method and iterative method were employed in this study. Numerical simulation was used to characterise the deformation behavior of Hadfield steel during explosion treatment. Base on experimental data, a modified Johnson-Cook equation for Hadfield steel under various strain rate was fitted. The development of two field variables was quantified during explosion hardening: equivalent stress and strain rates.

scholarly journals Strain rate and thermal softening effects in shear testing of AA7075-T6 sheet

2018 ◽  
Vol 183 ◽  
pp. 02037 ◽  
Author(s):  
Taamjeed Rahmaan ◽  
Ping Zhou ◽  
Cliff Butcher ◽  
Michael J. Worswick
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Rate Sensitivity ◽  
Thermal Conditions ◽  
Shear Loading ◽  
Image Correlation ◽  
High Rate ◽  
Strain Rates ◽  
Shear Testing ◽  
Plane Shear

Shear tests were performed at strain rates ranging from quasi-static (0.01 s-1) to 500 s-1 for AA7075-T6 sheet metal alloy at room temperature. A miniature sized shear specimen was used in this work to perform high strain rate shear testing. Digital image correlation (DIC) techniques were employed to measure the strains in the experiments. At maximum in-plane shear strains greater than 20%, the AA7075-T6 alloy demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the AA7075-T6 alloy showed mild positive rate sensitivity. The strain to localization (using the Zener-Holloman criterion), measured using the DIC technique, decreased with strain rate in shear loading. The strain at complete failure, however, exhibited an increase at the highest strain rate (500 s-1). The current work also focused on characterization of the thermal conditions occurring during high rate loading in shear with in situ high speed thermal imaging. Experimental results from the highest strain rate (500 s-1) tests showed a notable increase in temperature within the specimen gauge region as a result of the conversion of plastic deformation energy into heat.

High-speed tensile fractures in granite and gneiss: an experimental study

2021 ◽  
Author(s):  
Beno J Jacob ◽  
Santanu Misra ◽  
Venkitanarayanan Parameswaran ◽  
Nibir Mandal
Keyword(s):  
Aspect Ratio ◽  
High Strain Rate ◽  
Strain Rate ◽  
High Speed ◽  
High Strain ◽  
Tensile Fracture ◽  
High Speed Photography ◽  
Fracture Networks ◽  
Compression Direction ◽  
Tensile Fractures

<p>Tensile fractures are ubiquitous in impact structures formed because of high strain rate deformations of the earth’s crust. At regions far from the point of meteorite impact, intense rupturing, fragmentation, and pulverisation are an implication of pressure waves limiting at the tensile strength of the host rock with little influence of shock deformation or shear failure. The branching and anastomosing of the fractures are controlled by the local stress state and anisotropy. Thus, a network of infilled fractures or impact breccia dikes is a common feature in the subsurface of impact sites.</p><p>We have investigated the failure processes under high strain rates responsible for the formation of Mode-I breccia dikes, at the laboratory scale. The control of planar fabric structures in the development of anastomosing tensile fracture networks was studied through high-strain-rate Brazilian disc tests on gneiss (foliated) and granite (isotropic) samples. A Split Hopkinson Pressure Bar, equipped with high-speed photography (~10<sup>5</sup> fps), was employed in the study. The gneissic foliation in the gneiss samples were oriented at θ = 0, 45 and 90° to the compression direction. The strength of granite lies between 24 and 26 MPa, and the gneisses failed in the range of 29-37MPa at about 70-90 μs. The fracture network formation was seen in the time series images. There is a stark disparity in the nature of failure of granite from gneiss and the geometry of clasts formed in each rock type. While granite samples fail with pulverised clasts localised along a single fracture spanning the diameter of the sample along the compression direction, the gneisses further developed a network of secondary fractures forming large elongate clasts. Preferential orientation of secondary crack growth in relation to the foliation is strongly influenced by <em>θ</em> in gneiss samples. The aspect ratio of the pulverised clasts (size < 10mm) formed in granite was about 1:2, whereas the gneisses produced larger clasts. The clasts in gneisses had an aspect ratio of 1:4 for <em>θ</em> = 45 and 90º, and 1:5 for <em>θ</em> = 0º.</p><p>The branching and anastomosing nature of fractures is similar in fracture networks observed from the field and in the experiments, thus providing an insight into the formation of high-speed impact breccia dikes in isotropic and foliated rocks. Our experiments demonstrate that monomict breccia dikes may by formed <em>in situ</em> inclusive of clasts, rather than by infilling in previously formed tensile fractures.</p>

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