High-Speed Tension Tests at Elevated Temperatures—Parts II and III

1941 ◽  
Vol 8 (2) ◽  
pp. A77-A91
Author(s):  
A. Nadai ◽  
M. J. Manjoine
Keyword(s):  
Strain Rate ◽  
Pure Iron ◽  
High Speed ◽  
Elevated Temperatures ◽  
Testing Machine ◽  
Constant Strain Rate ◽  
Observation Data ◽  
Continuous Increase ◽  
Wide Range ◽  
Plastic Forming

Abstract The authors discuss the results of an investigation on the resistance to plastic forming of several metals over a wide range of rates of deformation at various temperatures. To carry out the tests, two machines were built: One, a high-speed testing machine, was described in Part I of this report; the other, a constant-strain-rate machine, is dealt with in this presentation. The general trend of the test results for aluminum and copper indicates a continuous increase of the yield stresses with the strain rate. The speed relation for pure iron and the iron alloys seems to be much more complicated. The resistance to deformation at a given speed of straining exhibits a minimum and a maximum at certain temperatures. This maximum, known as “blue brittleness,” shifts to higher temperatures with increasing speeds of straining; it appears at 200 C for short-time tension speeds and shifts to 550 C for the high speeds. In the high-speed tests a local temperature rise of 50 C, due to the conversion of the work of deformation into heat, was observed in a specimen of pure iron. At very rapid rates of deformation remarkably high ultimate stresses were found for aluminum and copper when tested at temperatures approaching their melting points. A theory for the necking of a bar, based on the speed law, predicts the observed shapes of broken bars which were drawn down to a point. Observation data are furnished for an evaluation of the forces required for very rapid plastic forming of the metals at high temperatures, particularly through rolling.

scholarly journals Influence of Deformation Controlled Strain Rate on Tensile and Compression Behaviour of Magnesium and Steel Wire

2017 ◽  
Vol 892 ◽  
pp. 89-96 ◽  
Author(s):  
Thorsten Henseler ◽  
Madlen Ullmann ◽  
Grzegorz Korpala ◽  
Klaudia Klimaszewska ◽  
Rudolf Kawalla ◽  
...  
Keyword(s):  
Strain Rate ◽  
Elevated Temperatures ◽  
Steel Wire ◽  
Testing Machine ◽  
Constant Strain Rate ◽  
Strain Curve ◽  
Compression Testing ◽  
Uniaxial Tensile ◽  
Flow Curves ◽  
The Difference

This article demonstrates the difference in the flow curves of an AZ31 magnesium alloy and S235JR structural steel wire caused by non-linear strain rates during uniaxial tensile and compression testing at elevated temperatures. Throughout tensile deformation, the traverse velocity of the testing machine has to be adapted according to the current elongation of the specimen, thus accelerating, to ensure a constant strain rate during the admission of the stress-strain curve. The equivalent is necessary during compression testing, where the traverse velocity of the testing machine needs to decelerate ensuring a constant strain rate. Nevertheless, tensile and compression tests are performed with constant traverse velocity, which lead to divergent flow curves in comparison to deformation controlled traverse velocities. The results of the research show the difference in flow behaviour of magnesium and steel wire, when the temperature and strain rate are varied in conjunction with constant and deformation controlled traverse velocities.

Pressing Process of Al-W Alloy Powder and Constitutive Model the Pressed Billet at Elevated Temperatures

2014 ◽  
Vol 685 ◽  
pp. 11-17
Author(s):  
Yao Jin Wu ◽  
Yong Xue ◽  
Zhi Ming Zhang ◽  
Ya Wei Huang ◽  
Qian Qian Wang ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Alloy Powder ◽  
Elevated Temperatures ◽  
Testing Machine ◽  
Constant Strain Rate ◽  
Thermal Simulation ◽  
Powder Pressing ◽  
Simulation Testing ◽  
Relation Model

Al-W alloy billets were produced by powder pressing at room temperature and subsequent hot pressing. Quantities of billets were compressed at constant strain rate and temperature with 60% height reduction on Gleeble-3800 thermal simulation testing machine to study the plastic flow behaviors of the test alloy. The temperature of the compression processes ranged from 450 to 570oC. The strain rate was varied between 0.001 and 1s−1. The regularity of flow stress for the test alloy varied at elevated temperatures was studied. The activation energy during hot deformation is 757.943 kJ/mol by calculated, and the Arrhenius constitutive relation model was established. Keywords: Al-W alloy, powder metallurgy, thermal simulation, constitutive model

scholarly journals High Strain-Rate Compressive Properties of Carbon/Epoxy Laminated Composites – Effects of loading direction and temperature

2018 ◽  
Vol 183 ◽  
pp. 02011
Author(s):  
Kenji Nakai ◽  
Tsubasa Fukushima ◽  
Takashi Yokoyama ◽  
Kazuo Arakawa
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Elevated Temperatures ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Slenderness Ratio ◽  
Testing Machine ◽  
Negative Temperature ◽  
Hopkinson Pressure Bar ◽  
Instron Testing Machine

The high strain-rate compressive characteristics of a cross-ply carbon/epoxy laminated composite in the three principal material directions or fibre (1-), in-plane transverse (2-) and throughthickness (3-) directions are investigated on the conventional split Hopkinson pressure bar (SHPB) over a range of temperatures between 20 and 80 °C. A nearly 10 mm thick cross-ply carbon/epoxy composite laminate fabricated using vacuum assisted resin transfer molding (VaRTM) was tested. Cylindrical specimens with a slenderness ratio (= length/diameter) of 0.5 are used in high strain-rate tests, and those with the slenderness ratios of 1.0 and 1.5 are used in low and intermediate strain-rate tests. The uniaxial compressive stress-strain curves up to failure at quasi-static and intermediate strain rates are measured on an Instron testing machine at elevated temperatures. A pair of steel rings is attached to both ends of the cylindrical specimens to prevent premature end crushing in the 1-and 2-direction tests on the Instron testing machine. It is shown that the ultimate compressive strength (or failure stress) exhibits positive strainrate effects and negative temperature ones over a strain-rate range of 10–3 to 103/s and a temperature range of 20 to 80 °C in the three principal material directions.

scholarly journals Avrami Kinetic-Based Constitutive Relationship for Armco-Type Pure Iron in Hot Deformation

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 365 ◽  
Author(s):  
Yan Zhang ◽  
Qichao Fan ◽  
Xiaofeng Zhang ◽  
Zhaohui Zhou ◽  
Zhihui Xia ◽  
...  
Keyword(s):  
Kinetic Equation ◽  
Strain Rate ◽  
Strain Hardening ◽  
Pure Iron ◽  
Constitutive Relationship ◽  
Structure Evolution ◽  
Wide Range ◽  
Z Parameter ◽  
Time Exponent ◽  
Fractional Softening

The work presents a full mathematical description of the stress-strain compression curves in a wide range of strain rates and deformation temperatures for Armco-type pure iron. The constructed models are based on a dislocation structure evolution equation (in the case of dynamic recovery (DRV)) and Avrami kinetic-based model (in the case of dynamic recrystallization (DRX)). The fractional softening model is modified as: X = ( σ 2 − σ r 2 ) / ( σ d s 2 − σ r 2 ) considering the strain hardening of un-recrystallized regions. The Avrami kinetic equation is modified and used to describe the DRX process considering the strain rate and temperature. The relations between the Avrami constant k ∗ , time exponent n ∗ , strain rate ε ˙ , temperature T and Z parameter are discussed. The yield stress σ y , saturation stress σ r s , steady stress σ d s and critical strain ε c are expressed as the functions of the Z parameter. A constitutive model is constructed based on the strain-hardening model, fractional softening model and modified Avrami kinetic equation. The DRV and DRX characters of Armco-type pure iron are clearly presented in these flow stress curves determined by the model.

The mechanical properties of pure iron tested in compression over the temperature range 2 to 293 °K

1967 ◽  
Vol 261 (1121) ◽  
pp. 253-287 ◽  
Keyword(s):  
Mechanical Properties ◽  
Flow Stress ◽  
Strain Rate ◽  
Single Crystals ◽  
Yield Stress ◽  
Low Temperatures ◽  
Pure Iron ◽  
Constant Strain Rate ◽  
Frictional Stress ◽  
Strain And Strain Rate

The mechanical properties of pure iron single crystals and of polycrystalline specimens of a zone-refined iron have been measured in compression over the temperature and strain rate ranges 2.2 to 293 °K and 7 x 10 -7 to 7 x 10 -3 s -1 respectively. Various yield stress parameters were determined as functions of both temperature and strain rate, and the reversible changes in flow stress produced by isothermal changes of strain rate or by changes of temperature at constant strain rate were also measured as functions of temperature, strain and strain rate. Both the temperature variation of the flow stress and the strain rate sensitivity of the flow stress were generally identical for the single crystals ( ca. 0.005/M carbon) and the polycrystalline specimens ( ca. 9/M carbon). At low temperatures, the temperature dependence of the yield stress was smaller than that of the flow stress at high strains, probably because of the effects of mechanical twinning, but once again the behaviour of single and polycrystalline specimens was very similar. Below 10 °K, both the flow stress and the extrapolated yield stress were independent of temperature. The results show that macroscopic yielding and flow at low temperatures are both governed by the same deformation mechanism, which is not very impurity sensitive, even in the very low carbon range covered by the experiments. The flow stress near 0 °K is ca. 5.8 x 10 -3 u where [i is the shear modulus. On the basis of a model for thermally activated flow, the activation volume at low temperatures (high stresses) is found to be ca. 5 b 3 . The exponent in the empirical power law for the dislocation velocity against stress relation is ca. 3 near room temperature, but becomes quite large at low temperatures. The results indicate that macroscopic deformation at low temperatures is governed by some kind of lattice frictional stress (Peierls-Nabarro force) acting on dislocations.

Laboratory Experiments on the Droplet Shattering Secondary Ice Production Mechanism

2020 ◽  
Author(s):  
Alice Keinert ◽  
Judith Kleinheins ◽  
Dominik Spannagel ◽  
Alexei Kiselev ◽  
Thomas Leisner
Keyword(s):  
High Resolution ◽  
High Speed ◽  
Cloud Model ◽  
Pure Water ◽  
Measuring System ◽  
Striking Difference ◽  
Observation Data ◽  
Experimental Conditions ◽  
Wide Range ◽  
Ice Production

<p>Supercooled drizzle droplets may produce multiple ice particles upon freezing. This mechanism could potentially explain the high ice number concentrations outside of temperature range where the well-known Hallett-Mossop mechanism of ice multiplication would take place. Limited experimental methods in the past prevented direct observations of the shattering droplets, resulting in a wide range of experimental results, unsuitable for the development of a sophisticated cloud model parameterization. Recently, we have revived experiments on secondary ice production by levitating individual drizzle droplets in electrodynamic balance (EDB) and observing the freeze-shattering with high-speed video microscopy and high-resolution infrared thermal measuring system. In this way we have been able to identify three additional SIP mechanisms (cracking, jetting and bubble bursts) associated with the freezing of drizzle droplets (Lauber et al., 2018). <br>Additionally, we have extended the range of experimental conditions to mimick the freezing of continental (pure water) and maritime (aqueous solution of analogue sea salt) drizzle droplets suspended in the updraft of cold moist air. We report a strong enhancement of shattering probability as compared to the previous studies conducted under stagnant air conditions. The high-definition video records of shattering events reveal the coupling between various microphysical processes caused by ice propagation inside the freezing drop and reveal striking difference between freezing of pure water and SSA solution droplets. Application of high-resolution infrared microscopy allowed us to record the evolution of the droplet temperature under realistic flow conditions and thus constrain the thermodynamic parameters controlling the pressure build-up inside the droplet. Based on these new observation data and theoretical model of freezing droplet, we discuss the physical mechanism behind the shattering of drizzle droplets and its implication for mixed-phase cloud modeling.</p><p>Lauber, A., A. Kiselev, T. Pander, P. Handmann, and T Leisner (2018). “Secondary Ice Formation during Freezing of Levitated Droplets”, Journal of the Atmospheric Sciences 75, pp. 2815–2826.</p>

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.

Strain-Rate Sensitivity of Concrete: Influence of Moisture Content

2006 ◽  
Vol 326-328 ◽  
pp. 1661-1664
Author(s):  
Gao Lin ◽  
Dong Ming Yan
Keyword(s):  
Moisture Content ◽  
Strain Rate ◽  
Earthquake Engineering ◽  
Testing Machine ◽  
Dynamic Strength ◽  
Rate Sensitivity ◽  
Tensile Tests ◽  
Hydraulic Testing ◽  
Wide Range ◽  
Compressive Tests

Understanding the behavior of concrete under dynamic loading conditions is an issue of great significance in earthquake engineering. Moisture content has an important influence on the strain-rate effect of concrete. In this study, both tensile and compressive experiments were carried out to investigate the rate-dependent behavior of concrete. Tensile experiments of dumbbell-shaped specimens were conducted on a MTS810 testing machine and compressive tests of cubic specimens were performed on a servo-hydraulic testing machine designed and manufactured at Dalian University of Technology, China. The strain rate varied in a wide range. The analytical formulations between the dynamic strength and strain rate were proposed for both compressive tests and tensile tests. It was concluded from the results that with the increasing strain rate, strengths of specimens with both moisture contents tended to increase and the increase seemed to be more remarkable for the saturated specimens; based on the experimental observation, a better explanation for the dynamic behavior is presented.

Simulation analysis of a method to improve data-transmission performance of Nanshan 26m Radio Telescope based on Software-Defined Networks

2021 ◽  
Vol 21 (11) ◽  
pp. 279
Author(s):  
Jie Wang ◽  
Hai-Long Zhang ◽  
Na Wang ◽  
Xin-Chen Ye ◽  
Wan-Qiong Wang ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Data Transmission ◽  
Network Architecture ◽  
High Speed ◽  
Astronomical Observation ◽  
Observation Data ◽  
Software Defined Networks ◽  
Continuous Increase ◽  
Network Bandwidth ◽  
Tcp Throughput

Abstract Data Center of Xinjiang Astronomical Observatory (XAO-DC) commenced operating in 2015, and provides services including archiving, releasing and retrieving precious astronomical data collected by the Nanshan 26m Radio Telescope (NSRT) over the years, and realises the open sharing of astronomical observation data. The observation data from NSRT are transmitted to XAO-DC 100 km away through dedicated fiber for long-term storage. With the continuous increase of data, the static architecture of the current network cannot meet NSRT data-transmission requirements due to limited network bandwidth. To get high-speed data-transmission using the existing static network architecture, a method for reconstruction data-transmission network using Software-Defined Networks (SDN) is proposed. Benefit from the SDNʼs data and control plane separation, and open programmable, combined with the Mininet simulation platform for experiments, the TCP throughput (of single thread) was improved by ∼24.7%, the TCP throughput (of multi threads) was improved by ∼9.8%, ∼40.9%, ∼35.5% and ∼11.7%. Compared with the current network architecture, the Latency was reduced by ∼63.2%.

Sign in / Sign up

Export Citation Format

Share Document