High strain rate characterization of low-density low-strength materials

Sawas, O.; Brar, N. S.; Brockman, R. A.

doi:10.1063/1.55507

Cited by 7 publications

(4 citation statements)

References 1 publication

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“…This formulation and a detailed derivation of the procedures are presented in Refs. [13][14][15]. The following are the major steps of this method as applied to the identification problem:…”

Section: Viscoelastic Properties Of the Polymeric Pressure Barsmentioning

confidence: 99%

Dynamic characterization of compliant materials using an all-polymeric split Hopkinson bar

Sawas

Brar

Brockman

1998

Experimental Mechanics

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ABSTRACT--The split Hopkinson bar is a reliable experimental technique for measuring high strain rate properties of highstrength materials. Attempts to apply the split Hopkinson bar in measurement on more compliant materials, such as plastics, rubbers and foams, suffer from limitations on the maximum achievable strain and from high noise-to-signal ratios. The present work introduces an all-polymeric split Hopkinson bar (APSHB) experiment, which overcomes these limitations. The proposed method uses polymeric pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials, thus providing both a low noiseto-signal ratio data and a longer input pulse for higher maximum strain. The APSHB requires very careful data reduction procedures because of the viscoelastic behavior of the incident and transmitter pressure bars. High-quality stress-strain data for a variety of compliant materials, such as polycarbonate, polyurethane foam and styrofoam, are presented.

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Section: Viscoelastic Properties Of the Polymeric Pressure Barsmentioning

confidence: 99%

Dynamic characterization of compliant materials using an all-polymeric split Hopkinson bar

Sawas

Brar

Brockman

1998

Experimental Mechanics

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“…Application is only possible if a related re-evaluation of the measured strain signals, accounting for the dispersion and attenuation effects, is performed. Examples of the application of polymer bars to circumvent the problem with low transmitted signals can be found in work by Sawas et al [12], Sharma et al [13] and Sogabe et al [14]. For extremely low-impedance materials like weak foams, even PMMA bars lead to an inappropriate impedance mismatch.…”

Section: Acoustic Impedance and Signal-to-noise Ratiomentioning

confidence: 99%

Characterization of low-impedance materials at elevated strain rates

Hiermaier

Meenken

2009

The Journal of Strain Analysis for Engineering Design

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Experimental characterization of materials at elevated strain rates of the order of 10(3) s(-1) is typically performed by Hopkinson-bar-type facilities. The specific nature of Hopkinson bar tests is that a specimen is loaded by waves. As both the input and output bars are often made from high-impedance metallic materials, the ratio between transmitted and reflected wave components is very poor in the case of low-impedance specimen materials such as rubbers and foams. That poor wave transmission brings with it a limited quality of the signal-to-noise ratio. Changing the bar materials (e.g. to polycarbonate) is of little help because of the related viscous effects. A further deficiency of the wave-driven Hopkinson bar test for many rubber and foam applications is the comparably small amount of compression that is achievable. Maximum compressions of 95 per cent and above, often expected for damping and energy absorption applications, are out of the range of most Hopkinson bar set-ups. In order to overcome these deficiencies, first a split Hopkinson pressure bar (SHPB) facility was equipped with polyvinylidenefluoride (PVDF) thin-film sensors. Second, a direct-impact set-up for low-impedance materials was developed and calibrated at the Ernst Mach Institute (EMI). With the PVDF gauges, the range of application both for the SHPB and for the new set-up was enhanced. This is demonstrated with an SHPB-based investigation of stress homogeneity in polyurethane (PU) specimens. The direct-impact facility made it possible to derive the stress-strain relations for PU-rubber up to strain rates in the range of several 10(3) s(-1). Maximum compressions of more than 95 per cent were achieved. The paper describes the limitations of a classic SHPB set-up applied to low-impedance materials. The problem of stress homogeneity is addressed, and a set-up for a new direct-impact facility is presented. As an example application, a Confor-Blue foam, typically used for automotive crash-test dummies, is characterized at strain rates between 160 and 1115 s(-1)

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“…A set of linear viscoelastic wave propagation equations can be derived by this method. This technique was applied in the split Hopkinson pressure bars made of cast polycarbonate [15,16] and Plexiglas [17]. Both of these were designed to determine the dynamic behaviour of low-strength materials, such as plastics, under compression tests.…”

Section: Introductionmentioning

confidence: 99%

Dynamic characterization of micro-scaled samples using the Hopkinson tensile bar technique

Leung

2008

The Journal of Strain Analysis for Engineering Design

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Due to the increase in the applications of foils, fibres, and yarns under dynamic loading, characterizing the behaviour of small-scaled material samples at high strain rates has become important. However, owing to the low mechanical impedance and the small size of such samples, the conventional split Hopkinson bar technique encounters serious problems, such as high noise-to-signal ratios, an undistinguishable transmitted signal, a short loading time, and difficulty in achieving large strain. A mini-split Hopkinson tensile bar (mini-SHTB) system has been developed to measure the constitutive relation of micro-scaled material specimens under high strain rates. The system employs polymeric bars of small diameter to achieve a closer impedance match with the specimens. This match ensures a lower noiseto-signal ratio in the transmitted signals and hence allows correct interpretation of the transmitted strain profiles. A series of experiments were carried out on different types and forms of material, such as aluminium foil, cellulose nitrate foil, badminton racket string, and so forth, to verify the applicability of the apparatus. Strain rates in the order of 10 2 were attained under this mini-SHTB system. The results confirm that the tensile stress-strain behaviour of small-sized specimens, with low mechanical impedance and under high strain rates, can be determined effectively and efficiently using this technique.

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High strain rate characterization of low-density low-strength materials

Cited by 7 publications

References 1 publication

Dynamic characterization of compliant materials using an all-polymeric split Hopkinson bar

Dynamic characterization of compliant materials using an all-polymeric split Hopkinson bar

Characterization of low-impedance materials at elevated strain rates

Dynamic characterization of micro-scaled samples using the Hopkinson tensile bar technique

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