Mechanical properties of some polymers and composites at Strain Rates of 1000/s

On présente les résultats des essais dynamiques de trois polymères (polycarbonate, polyamide et polyéthylène téréphtalate), d'un plastique renforcé à la fibre de verre, et d'organoplastique de trois types de renforcement chacun. Les essais de compression des éprouvettes à la vitesse de déformation d'environ 103 s-1 sont effectués suivant la méthode de Kolsky avec la barre d'Hopkinson. Pour tous les matériaux, les diagrammes dynamiques de compression et les histoires de la vitesse de déformation sont obtenus. On note l'accroissement du module d'élasticité et des efforts de rupture avec l'accroissement de la vitesse de déformation. Pour le plastique renforcé par fibres de verre et pour l'organoplastique, ces paramètres sont aussi affectés par le type du renfort.Dynamic compression test results are presented for three polymers (polycarbonate, polyamide, and polyethylene terephtalate) and for two composite materials, a plain weave glass/epoxy with three different stacking sequences, and an aramid/epoxy (organoplastic material). Compression tests at a strain rate of about 103 s-1 were conducted using the Kolsky method with the split Hopkinson pressure bar (SHPB). Dynamic compression diagrams and strain-rate histories were obtained for all the materials. An increase in the modulus of elasticity and in the fracture stress with strain rate was observed. For the glass-reinforced plastic and organoplastic, these parameters are also affected by the reinforcement geometry

A MODIFIED KOLSKY METHOD FOR THE INVESTIGATION OF THE STRAIN-RATE HISTORY DEPENDENCE OF MECHANICAL PROPERTIES OF MATERIALS

Une modification assez simple de la barre d'Hopkinson fendue (SHB) est présentée. Elle permet des extensions considérables de la méthode de Kolsky dans l'étude de l'influence de la vitesse de déformation et de l'histoire de la vitesse de déformation sur les propriétés physiques et mécaniques des matériaux. Le développement de cette modification du SHB permet de conduire des essais incrémentaux avec chargement dynamique cyclique. Des exemples démontrant ces possibilités sont décrits.A fairly simple modification of the split Hopkinson bar (SHB) method is presented that extends significantly the scope of the Kolsky method in studying the effects of strain rate and strain-rate history on the physical and mechanical properties. The developed modification of the SHB method makes it possible to conduct incremental tests with alternating dynamic loading. Examples illustrating the possibilities of the modifications described are included

Dynamic compressibility of clay and loam

The results of investigation of dynamic compressibility of clay and loam at strain rate 10$^{3}$ s$^{ - 1}$ and higher are presented. At strain rate $\sim$10$^{3}$ s$^{ - 1}$ the experiments were carried out by using modification of Split Hopkinson Pressure Bar (SHPB), plate impact experiment was used at strain rate $\sim$10$^{4}$ s$^{ - 1}$ and higher. Shock adiabats were determined by reflection method. As the result of the experiments dynamic compressibility curves, hydrostatic curves and dependence of shear strength from pressure were obtained at uniaxial strain conditions. The joint use of these complementary methods has allowed to extent a range of loading conditions. The results obtained can be useful for formulation of equations of state for clay and loam

Mechanical characterization of rocks at high strain rate

The paper presents the dynamic characterization in tension and compression of three rocks, Carrara marble, Onsernone gneiss and Peccia Marble, at high strain-rates. Two versions of a Split Hopkinson Bar have been used. The version for direct tension tests is installed at the DynaMat Laboratory of the University of Applied Sciences of Southern Switzerland, while the traditional version in compression is installed at the Laboratory of Dynamic Investigation of Materials of Lobachevsky State University. Results of the tests show a significantly strain-rate sensitive behaviour, exhibiting dynamic strength increasing with strain-rate. The experimental research has been developed in the frame of the Swiss-Russian Joint Research Program

Mechanical Response of HPFRCC in Tension and Compression at High Strain Rate and High Temperature

The mechanical response of High Performance Fibre Reinforced Cementitius Composite (HPFRCC) has been analyzed at high strain rates and high temperature. Two experimental device have been used for compression and tension tests : the traditional Split Hopkinson Pressure Bar for compression and the JRC- Split Hopkinson Tension Bar for tension. The HPFRCC was thermally damaged at 3 temperature (200°C, 400°C and 600°C) in order to analyze the dynamic behaviour of this material when explosions and fires take place into a tunnel. Results show significant peak strength increases both in tension and in compression. The post-peak strength in tension is dependent on the thermal damage of the material. Its strain rate sensitivity and thermal damage have been illustrated by means of a Dynamic Increase Factor. These results show that it is necessary to implement new expression of the DIF for the HPRFCC, therefore more and more accurate and experimental studies using Kolsky-Hopkinson Bar methods are needful

Experimental and numerical analysis of high strain rate behavior of aluminum alloys AMg-6 and D-16

Results of experimental investigation and numerical modeling of high strain rate behavior of aluminium alloys AMg-6 and D-16 are presented. Using Split Hopkinson Pressure Bar (SHPB) parameters of Johnson-Cook's model and other models from LS-DYNA library were determined in strain rate range 10$^{2}$-10$^{4}$ s$^{ - 1}$. For verification of the models a comparison of the results of numerical modeling and model experiments was carried out. Modificated Taylor's test and modification of SHPB test for high-speed penetration were carried out as model experiments

The influence of temperature, strain rate history and shock preloading in the region of phase transition for armco-iron

The influence of temperature, strain rate history, and shock-wave prestraining on the mechanical behavior of Armco-iron (Fe) is presented. Shock-wave prestraining of iron above the polymorphic ($\alpha{-}\varepsilon$ transition is seen to result in significant changes in the stress-strain response of Fe. The increase in the constitutive response of Fe is seen to correspond to an increase in hardness in the preshocked Fe. A high degree of correlation in the experimental results independently obtained in Russia and USA is presented. The observed mechanical property effects in preshocked Fe are correlated to the microstructure evolution in iron following explosive prestraining