Constitutive behavior of granular materials under high rate of uniaxial strain loading

Quasistatic and Dynamic Compressive Behavior of Gelatin

ASME 2010 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2010-19406 ◽

2010 ◽

Author(s):

Jiwoon Kwon ◽

Ghatu Subhash

Keyword(s):

Split Hopkinson Pressure Bar ◽

Rate Sensitivity ◽

Polymeric Materials ◽

Soft Materials ◽

High Rate ◽

Constitutive Behavior ◽

Hopkinson Pressure Bar ◽

Property Data ◽

Split Hopkinson ◽

Pressure Bar

Gelatin has been extensively used as a tissue stimulant. Determination of properties and tits constitutive behavior is crucial to successful use of gelatin in these applications. In this study, ballistic gelatin was used because the recipe to prepare the gelatin and its quasi-static strength (250 bloom) of this particular type of gelatin is well known [1]. Although the study for high rate deformation is important to understand the damage from blast impact, majority of the currently available material property data is in quasi-static range [2,3]. Generally, polymeric materials (including human tissue) exhibit highly rate sensitive response [4]. Therefore, the understanding of the constitutive behavior for these materials at high rate loading is essential. This study will provide the rate sensitivity of gelatin by comparing the response under quasi-static and dynamic loading. In order to investigate the dynamic behavior of gelatin, the split Hopkinson pressure bar (SHPB) was used in this study. Because use of a solid metallic bar to test such soft materials does not provide an adequate transmitted signal, a polymer split Hopkinson pressure bar (PSHPB) was used to reduce the impedance mismatch between bar and soft gelatin specimen. The nature of dispersion and attenuation was corrected using an iterative scheme developed earlier [5].

Download Full-text

Microgravity Experiments on Granular Materials

MRS Proceedings ◽

10.1557/proc-87-203 ◽

1986 ◽

Vol 87 ◽

Cited By ~ 4

Author(s):

Nicholas C. Costes ◽

V. C. Jano ◽

S. Sture

Keyword(s):

Granular Materials ◽

Constitutive Modeling ◽

Constitutive Equations ◽

Space Shuttle ◽

Stress Fields ◽

Constitutive Behavior ◽

Technological Gap ◽

Microgravity Experiments ◽

Constitutive Properties ◽

Induced Stresses

AbstractGravity induced stresses in terrestrial laboratory specimens comprising of relatively weak and soft granular materials, are often of the same magnitude as the external tractions that are applied during investigations of constitutive behavior especially at low intergranular stress levels. The presence of heterogeneous strain and stress fields within such a specimen makes it difficult if not impossible to obtain objective and unambiguous constitutive properties and to devise relevant constitutive equations. To fill this technological gap, microgravity experiments are now planned which will be performed during future flights of the Space Shuttle, in conjunction with ground-based tests. This paper deals with analytical and experimental issues related to constitutive modeling of granular materials.

Download Full-text

Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069272 ◽

1970 ◽

Vol 28 ◽

pp. 456-457

Author(s):

L. E. Murr ◽

G. Wong

Keyword(s):

Single Crystal ◽

High Vacuum ◽

Ultra High Vacuum ◽

High Rate ◽

Flash Evaporation ◽

Optimum Load ◽

Single Crystal Films ◽

Crystal Films ◽

A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

Download Full-text

Rapid Freezing of Freeze-Etch Specimens

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600003275 ◽

1980 ◽

Vol 38 ◽

pp. 752-755

Author(s):

A. Elgsaeter ◽

T. Espevik ◽

G. Kopstad

Keyword(s):

Low Temperature ◽

Metal Surface ◽

Relative Velocity ◽

Thermal Contact ◽

High Rate ◽

Rapid Freezing ◽

Temperature Decrease ◽

Freeze Etching

The importance of a high rate of temperature decrease (“rapid freezing”) when freezing specimens for freeze-etching has long been recognized1. The two basic methods for achieving rapid freezing are: 1) dropping the specimen onto a metal surface at low temperature, 2) bringing the specimen instantaneously into thermal contact with a liquid at low temperature and subsequently maintaining a high relative velocity between the liquid and the specimen. Over the last couple of years the first method has received strong renewed interest, particularily as the result of a series of important studies by Heuser and coworkers 2,3. In this paper we will compare these two freezing methods theoretically and experimentally.

Download Full-text