A Study on Reduction of Friction in Impact Compressive Test Based on the Split Hopkinson Pressure Bar Method by Using a Hollow Specimen

2014 ◽  
Vol 566 ◽  
pp. 548-553 ◽  
Author(s):  
Nobuhiko Kii ◽  
Takeshi Iwamoto ◽  
Alexis Rusinek ◽  
Tomasz Jankowiak
Keyword(s):  
Impact Test ◽  
Split Hopkinson Pressure Bar ◽  
Strain Curve ◽  
Hopkinson Pressure Bar ◽  
Compressive Test ◽  
Friction Effect ◽  
Wide Range ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact

The split Hopkinson pressure bar (SHPB) technique is widely-used to describe the impact compressive behavior of different materials including metals. During the impact test, the specimen deforms in a wide range of impact strain rate from 102 to 104 s-1. It is a reason why the method is studied for many years even though the structure of the apparatus based on the SHPB is simple. Actually, the cylindrical specimens are widely used for a compressive test and it is clearly seen that stress measured by the test includes the increment of stress (an error) derived by friction effect between a specimen and pressure bars. Therefore, it is important that the measured stress should indicate similar value as the proper stress of the material by reducing friction effect during not only quasi-static but also the impact test. Various attempts to reduce a friction effect in past have been conducted. A method to reduce friction effect is in general a use of lubricants. However, it is ineffective because it can be considered that this method contributes to an attenuation of the stress wave for obtaining the stress-strain curve under impact loading. Thus, rise time of waves obtained by the experiment becomes longer compared with a case not to use lubricants. Recently, a study can be found using a ring specimen, however, the determined thickness of the specimen is quite thin and it can be considered that a buckling effect cannot be vanished. In this study, a use of hollow specimen is suggested to solve the problem related to reduce the friction effect by decreasing a contact area between a specimen and pressure bars instead of a cylindrical specimen. The compressive experiments at various strain rates are conducted by using a hollow specimen.

IMPACT TENSILE PROPERTIES IN AL-MG-SI BASE ALLOYS FOR AUTOMOTIVE USE

2008 ◽  
Vol 22 (09n11) ◽  
pp. 1123-1128 ◽  
Author(s):  
HIROYUKI YAMADA ◽  
KEITARO HORIKAWA ◽  
HIDETOSHI KOBAYASHI
Keyword(s):  
Plastic Strain ◽  
Tensile Properties ◽  
Intergranular Fracture ◽  
Impact Test ◽  
Alloy Composition ◽  
Split Hopkinson Pressure Bar ◽  
Hopkinson Pressure Bar ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact

Effect of alloy composition on impact tensile properties [Formula: see text] in Al - Mg - Si base alloys was investigated by means of the split Hopkinson pressure bar method. As a result of the impact test, it was proved that the nominal stress for 5% plastic strain was not changed by changing the strain rate regardless of the alloy composition. In the impact test, the elongation was decreased with increasing the amount of excess Si , while that was increased by the addition of Cu . Fractography revealed that the reduction of the elongation in the excess Si alloy was caused by the change of the fracture mode from the mixture of transgranular and intergranular fracture to the intergranular fracture.

scholarly journals Using the split Hopkinson pressure bar to validate material models

2014 ◽  
Vol 372 (2023) ◽  
pp. 20130294 ◽  
Author(s):  
Philip Church ◽  
Rory Cornish ◽  
Ian Cullis ◽  
Peter Gould ◽  
Ian Lewtas
Keyword(s):  
Split Hopkinson Pressure Bar ◽  
Strain Curve ◽  
Material Model ◽  
High Rate ◽  
Hopkinson Pressure Bar ◽  
Validation Data ◽  
Material Models ◽  
Wide Range ◽  
Split Hopkinson ◽  
Pressure Bar

This paper gives a discussion of the use of the split-Hopkinson bar with particular reference to the requirements of materials modelling at QinetiQ. This is to deploy validated material models for numerical simulations that are physically based and have as little characterization overhead as possible. In order to have confidence that the models have a wide range of applicability, this means, at most, characterizing the models at low rate and then validating them at high rate. The split Hopkinson pressure bar (SHPB) is ideal for this purpose. It is also a very useful tool for analysing material behaviour under non-shock wave loading. This means understanding the output of the test and developing techniques for reliable comparison of simulations with SHPB data. For materials other than metals comparison with an output stress v strain curve is not sufficient as the assumptions built into the classical analysis are generally violated. The method described in this paper compares the simulations with as much validation data as can be derived from deployed instrumentation including the raw strain gauge data on the input and output bars, which avoids any assumptions about stress equilibrium. One has to take into account Pochhammer–Chree oscillations and their effect on the specimen and recognize that this is itself also a valuable validation test of the material model.

Analysis of the Impact of the Frequency Range of the Tensometer Bridge and Projectile Geometry on the Results of Measurements by the Split Hopkinson Pressure Bar Method

2013 ◽  
Vol 20 (4) ◽  
pp. 555-564 ◽  
Author(s):  
Wojciech Moćko
Keyword(s):  
Test Bench ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Deformation ◽  
Spectral Width ◽  
Hopkinson Pressure Bar ◽  
Computing Environment ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact ◽  
Bench Model

Abstract The paper presents the results of the analysis of the striker shape impact on the shape of the mechanical elastic wave generated in the Hopkinson bar. The influence of the tensometer amplifier bandwidth on the stress-strain characteristics obtained in this method was analyzed too. For the purposes of analyzing under the computing environment ABAQUS / Explicit the test bench model was created, and then the analysis of the process of dynamic deformation of the specimen with specific mechanical parameters was carried out. Based on those tests, it was found that the geometry of the end of the striker has an effect on the form of the loading wave and the spectral width of the signal of that wave. Reduction of the striker end diameter reduces unwanted oscillations, however, adversely affects the time of strain rate stabilization. It was determined for the assumed test bench configuration that a tensometric measurement system with a bandwidth equal to 50 kHz is sufficient

Studies on the Dynamic Compressive Properties of Open-Celled Aluminum Alloy Foams

2006 ◽  
Vol 306-308 ◽  
pp. 905-910 ◽  
Author(s):  
Zhi Hua Wang ◽  
Hong Wei Ma ◽  
Long Mao Zhao ◽  
Gui Tong Yang
Keyword(s):  
Yield Strength ◽  
Strain Rate ◽  
Split Hopkinson Pressure Bar ◽  
Strain Rates ◽  
Hopkinson Pressure Bar ◽  
Aluminum Foams ◽  
Wide Range ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
Dynamic Loading Conditions

The compressive deformation behavior of open-cell aluminum foams with different densities and morphologies was assessed under quasi-static and dynamic loading conditions. High strain rate experiments were conducted using a split Hopkinson pressure bar technique at strain rates ranging from 500 to 1 2000 − s . The experimental results shown that the compressive stress-strain curves of aluminum foams also have the “ three regions” character appeared in general foam materials, namely elastic region, collapse region and densification regions. It is found that density is the primary variable characterizing the modulus and yield strength of foams and the cell appears to have a negligible effect on the strength of foams. It also is found that yield strength and energy absorption is almost insensitive to strain rate and deformation is spatially uniform for the open-celled aluminum foams, over a wide range of strain rates.

Wave Propagation in the Split Hopkinson Pressure Bar

1983 ◽  
Vol 105 (1) ◽  
pp. 61-66 ◽  
Author(s):  
P. S. Follansbee ◽  
C. Frantz
Keyword(s):  
Wave Propagation ◽  
Elastic Wave ◽  
Split Hopkinson Pressure Bar ◽  
Strain Curve ◽  
Leading Edge ◽  
Elastic Wave Propagation ◽  
Mathematical Treatment ◽  
Hopkinson Pressure Bar ◽  
Split Hopkinson ◽  
Pressure Bar

Elastic wave propagation in the split Hopkinson pressure bar (SHPB) is discussed with an emphasis on the origin and nature of the oscillations that often trail the leading edge of the pressure wave. We show that in the conditions of the SHPB test the pressure bars vibrate in the fundamental mode and that elastic wave propagation can be fully described mathematically. Excellent agreement is found between experimental results and predictions of the mathematical treatment. This suggests that dispersion effects in the pressure bars can be removed from the strain gage records, which reduces the magnitude of the oscillations in the resulting stress strain curve.

Experimental Study of Impact Strength of Al-6063 Alloy Processed by Equal Channel Angular Extrusion

2014 ◽  
Vol 911 ◽  
pp. 158-162 ◽  
Author(s):  
Shamsuddin Sulaiman ◽  
J. Nemati ◽  
Hani Mizhir Magid ◽  
B.T.H.T. Baharudin ◽  
G.H. Majzoobi ◽  
...  
Keyword(s):  
Impact Strength ◽  
Equal Channel Angular Extrusion ◽  
Split Hopkinson Pressure Bar ◽  
Hopkinson Pressure Bar ◽  
Angular Extrusion ◽  
Split Hopkinson ◽  
Ram Speed ◽  
Pressure Bar ◽  
The Impact ◽  
Strength Improvement

In the present study, the impact strength of annealed Al-6063 alloy developed by equal channel angular extrusion (ECAE), up to 6 passes at a temperature of 200°C following route A with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels was investigated. The impact strength of extruded specimens is evaluated for different passes at a strain rate of 1800 s-1 using Split-Hopkinson pressure bar techniques. The results indicate that the major strength improvement occurs in the 5th and 6th passes while in primary passes, the strength improved but at a considerably lower rate. A total increasing in ultimate strength (UTS) and yield strength (YS) are 127% and 65% respectively and observed for the extruded material after 6 passes. Optical microscopic examinations show a grain refinement from 45 μm to 2.8 μm.

Modelling of Micro-Concrete Behaviour under Static and Dynamic Loading

2014 ◽  
Vol 584-586 ◽  
pp. 1089-1096
Author(s):  
Remdane Boutemeur ◽  
Mustapha Demidem ◽  
Abderrahim Bali ◽  
El Hadi Benyoussef
Keyword(s):  
Strain Rate ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Compression ◽  
Dynamic Tests ◽  
Hopkinson Pressure Bar ◽  
Proposed Model ◽  
Wide Range ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
Static And Dynamic Loading

The aim of this study is to present a model for assessing the dynamic compression behaviour of a micro-concrete. This model is based on the results of numerous tests providing the developments of the mechanical characteristics of the material on a wide range of strain rate from 10-4s-1to 10+3s-1.The Split Hopkinson Pressure Bar (SHPB) dispositive, based on the wave propagation theory in materials, has-been adopted to carry out the dynamic tests on the investigated material. The proposed model is composed of two terms, each characterizing the different contributions noted in the two major explored areas of strain rate.

scholarly journals Wave Attenuation and Dispersion in a 6 mm Diameter Viscoelastic Split Hopkinson Pressure Bar and Its Correction Method

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Haotian Zhang ◽  
Linjian Ma ◽  
Zongmu Luo ◽  
Ning Zhang
Keyword(s):  
Impact Velocity ◽  
Wave Attenuation ◽  
Split Hopkinson Pressure Bar ◽  
Small Diameter ◽  
Correction Method ◽  
Hopkinson Pressure Bar ◽  
Amplitude Attenuation ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact

The propagation characteristics of viscoelastic waves have been investigated with a 6 mm diameter split Hopkinson pressure bar (SHPB) made of polymethyl methacrylate (PMMA). The strain signals in SHPB tests were improved by the pulse shaping technique. Based on the experimentally determined propagation coefficients, the amplitude attenuation and wave dispersion induced by viscoelastic effects at different impact velocities were quantitatively analyzed. The results indicate that the high-frequency harmonics attenuate faster in a higher phase velocity. With an increase in the impact velocity, the amplitude attenuation of the viscoelastic wave changes slightly during propagation, while the waveform dispersion gradually intensifies. A feasible method by waveform prediction was proposed to verify the validity and applicability of the propagation coefficient. The results indicate that the strain obtained from the small diameter viscoelastic SHPB can be effectively modified by utilizing the propagation coefficient. Furthermore, it is preferred to adopt the propagation coefficient obtained at low impact velocity for correction when the impact velocity varies. Moreover, the PMMA-steel bar impact test was performed to further illustrate the accuracy of the propagation coefficient and the effectiveness of the correction method.

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