scholarly journals OPTIMIZATION OF HOPKINSON BAR INSTRUMENTATION FOR TESTING OF CELLULAR AND LOW IMPEDANCE MATERIALS

2019 ◽  
Keyword(s):  
Hopkinson Bar ◽  
Low Impedance Materials

A split Hopkinson bar technique for low-impedance materials

1999 ◽  
Vol 39 (2) ◽  
pp. 81-85 ◽  
Author(s):  
W. Chen ◽  
B. Zhang ◽  
M. J. Forrestal
Keyword(s):  
Hopkinson Bar ◽  
Split Hopkinson Bar ◽  
Split Hopkinson ◽  
Low Impedance Materials

scholarly journals Investigating slow shock in low-impedance materials using a direct impact Hopkinson bar setup

2021 ◽  
Vol 250 ◽  
pp. 06009
Author(s):  
Puneeth Jakkula ◽  
Georg Ganzenmüller ◽  
Samuel Beisel ◽  
Stefan Hiermaier
Keyword(s):  
Dynamic Compression ◽  
Hopkinson Bar ◽  
Polyurethane Foams ◽  
Image Correlation ◽  
Dynamic Force ◽  
Strain Rates ◽  
Direct Impact ◽  
Compression Tests ◽  
Low Impedance Materials ◽  
Force Equilibrium

This work implements a direct impact Hopkinson bar, suitable for investigating the evolution of dynamic force equilibrium in low-impedance materials. Polycarbonate as the bar material favours for a long pulse duration of 2.6 ms for an overall length of only 5 m, allowing to compress large specimens to high strains. This setup is applied to polyurethane foams with different densities ranging from 80 - 240 kg/m3. Dynamic compression tests are performed at strain rates of 0.0017, 0.5 and 500 /s on the foams at room temperature. Depending on density, they show a saturation in increase of yield strength at strain rates of 500 /s, or even show a negative strain rate sensitivity for the lowest density. This behaviour is explained by comparing the dynamic force equilibrium to a phenomenon similar to shock in solid materials: For low densities and high rates of strain, homogeneous compression is replaced by a localized collapse front with a jump in stress across the front. Digital image correlation is performed to analyse elastic and plastic compaction waves by means of Lagrange diagrams.

scholarly journals The Symmpact: A Direct-Impact Hopkinson Bar Setup Suitable for Investigating Dynamic Equilibrium in Low-Impedance Materials

2021 ◽  
Author(s):  
P. Jakkula ◽  
G. C. Ganzenmüller ◽  
S. Beisel ◽  
P. Rüthnick ◽  
S. Hiermaier
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Hopkinson Bar ◽  
Dynamic Compaction ◽  
Strain Gauges ◽  
Negative Strain Rate Sensitivity ◽  
Compaction Waves ◽  
Low Impedance Materials ◽  
Force Equilibrium

Abstract Background Measuring the dynamic behavior of low-impedance materials such as foams is challenging. Their low acoustic impedance means that sensitive force measurement is required. The porous structure of foams also gives rise to dynamic compaction waves, which can result in unusual behavior, in particular if the foam material is so thick, that dynamic force equilibrium is not reached. Objective This work investigates comparatively large polyurethane foam specimens with densities in the range of 80 – 240 kg/m3 to deliberately achieve a state away from force equilibrium during high-rate compaction. The aim is to understand how an increase in strain rate leads to a reduction in strength for such materials. Methods A specialized direct-impact Hopkinson bar is employed. It uses polycarbonate bars to achieve the required long pulse duration of 2.6 ms to compress the large specimens into the densification regime. In contrast to existing setups, both striker and output bar are instrumented with strain gauges to monitor force equilibrium. The absence of an input bar allows monitoring force equilibrium more accurately. Special attention is paid to the calibration of strain gauges, taking non-linear effects, wave dispersion and attenuation into account. Digital Image Correlation is employed to analyze elastic and plastic compaction waves by means of Lagrange diagrams. Results Depending on density, the specimens show saturation of dynamic strength increase at high rates of strain $$\approx$$ ≈  500 /s, or even negative strain rate sensitivity in case of the lowest density. The occurrence of apparent negative strain rate sensitivity is accompanied by a localized structural collapse front, moving at a low velocity of $$\approx$$ ≈ 10 m/s through the material. This apparent strain rate sensitivity is a structural effect which is related to the thickness of the specimen. Conclusions The primary aim of material characterization using Hopkinson bars is to achieve a state of force equilibrium. For this reason, very thin specimens are usually employed. However, data gathered in this way is not representative for thick foam layers. Here, an increase of strain rate can lead to a decrease of strength if homogeneous deformation is replaced by a dynamic compaction wave. This behavior can occur at strain rates encountered under conditions such as automotive crash.

Methodological aspects of testing brittle materials using the split Hopkinson bar technique

Strain ◽  
2021 ◽  
Author(s):  
Anatoly M. Bragov ◽  
Leonid A. Igumnov ◽  
Aleksandr Y. Konstantinov ◽  
Leopold Kruszka ◽  
Dmitry A. Lamzin ◽  
...  
Keyword(s):  
Brittle Materials ◽  
Hopkinson Bar ◽  
Split Hopkinson Bar ◽  
Split Hopkinson ◽  
Methodological Aspects

scholarly journals Experiments and simulation of split Hopkinson Bar tests on sand

2014 ◽  
Vol 500 (11) ◽  
pp. 112018 ◽  
Author(s):  
P D Church ◽  
P J Gould ◽  
A D Wood ◽  
A Tyas
Keyword(s):  
Hopkinson Bar ◽  
Split Hopkinson Bar ◽  
Split Hopkinson

Experimental and numerical characterization of a polymeric Hopkinson bar by DTMA

2017 ◽  
Vol 103 ◽  
pp. 50-63 ◽  
Author(s):  
Marco Sasso ◽  
Michele Gabrio Antonelli ◽  
Edoardo Mancini ◽  
Mario Radoni ◽  
Dario Amodio
Keyword(s):  
Hopkinson Bar ◽  
Numerical Characterization

scholarly journals A numerical study of the impact perforation of sandwich panels with graded hollow sphere cores

2021 ◽  
Vol 13 (4) ◽  
pp. 168781402110094
Author(s):  
Ibrahim Elnasri ◽  
Han Zhao
Keyword(s):  
Boundary Conditions ◽  
Hollow Sphere ◽  
Sandwich Panel ◽  
Numerical Study ◽  
Sandwich Panels ◽  
Hopkinson Bar ◽  
Core Density ◽  
The Core ◽  
The Impact ◽  
Force Displacement

In this study, we numerically investigate the impact perforation of sandwich panels made of 0.8 mm 2024-T3 aluminum alloy skin sheets and graded polymeric hollow sphere cores with four different gradient profiles. A suitable numerical model was conducted using the LS-DYNA code, calibrated with an inverse perforation test, instrumented with a Hopkinson bar, and validated using experimental data from the literature. Moreover, the effects of quasi-static loading, landing rates, and boundary conditions on the perforation resistance of the studied graded core sandwich panels were discussed. The simulation results showed that the piercing force–displacement response of the graded core sandwich panels is affected by the core density gradient profiles. Besides, the energy absorption capability can be effectively enhanced by modifying the arrangement of the core layers with unclumping boundary conditions in the graded core sandwich panel, which is rather too hard to achieve with clumping boundary conditions.

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