A modified torsional kolsky bar for investigating dynamic friction

1999 ◽  
Vol 39 (4) ◽  
pp. 295-303 ◽  
Author(s):  
S. Rajagopalan ◽  
V. Prakash
Keyword(s):  
Kolsky Bar ◽  
Dynamic Friction ◽  
Torsional Kolsky Bar

An Elastic-Plastic Stress Analysis of the Specimen Used in the Torsional Kolsky Bar

1980 ◽  
Vol 47 (2) ◽  
pp. 278-282 ◽  
Author(s):  
Eric K. C. Leung
Keyword(s):  
Numerical Solutions ◽  
Elastic Stress ◽  
Dynamic Testing ◽  
Kolsky Bar ◽  
The Finite Element Method ◽  
Governing Equations ◽  
Elastic Plastic ◽  
Applied Torque ◽  
Torsional Kolsky Bar ◽  
Tubular Specimens

This paper examines the stress concentration, the yielding process, and the growth of the elastic-plastic boundary as a function of applied torque in tubular specimens with a short thin-walled section. Although the analysis is entirely quasi-static, it can, under the proper circumstances, be applied to the deformation of short specimens as generally used for dynamic testing in the torsional Kolsky bar. In the analysis, the governing equations for both elastic and elastic-plastic analyses are presented, the latter taking into account work hardening. Numerical solutions of these equations employ the finite-element method. The elastic stress distribution in the specimen and the elastic-plastic enclaves are presented for various loading stages.

A novel dynamic friction experiment using a modified kolsky bar apparatus

2000 ◽  
Vol 40 (2) ◽  
pp. 138-153 ◽  
Author(s):  
H. D. Espinosa ◽  
A. Patanella ◽  
M. Fischer
Keyword(s):  
Kolsky Bar ◽  
Dynamic Friction

Dynamic Constitutive and Failure Behavior of a Two-Phase Tungsten Composite

1997 ◽  
Vol 64 (3) ◽  
pp. 487-494 ◽  
Author(s):  
M. Zhou ◽  
R. J. Clifton
Keyword(s):  
Shear Band ◽  
Shear Bands ◽  
Kolsky Bar ◽  
High Rate ◽  
Failure Behavior ◽  
Localized Deformation ◽  
Two Phase ◽  
The Matrix ◽  
Torsional Kolsky Bar ◽  
The Impact

The constitutive response and failure behavior of a W-Ni-Fe alloy over the strain rate range of 10-4 to 5 X 105 s-1 is experimentally investigated. Experiments conducted are pressure-shear plate impact, torsional Kolsky bar, and quasi-static torsion. The material has a microstructure of hard tungsten grains embedded in a soft alloy matrix. Nominal shear stress-strain relations are obtained for deformations throughout the experiments and until after the initiation of localization. Shear bands form when the plastic strain becomes sufficiently large, involving both the grains and the matrix. The critical shear strain for shear band development under the high rate, high pressure conditions of pressure-shear is approximately 1–1.5 or 6–8 times that obtained in torsional Kolsky bar experiments which involve lower strain rates and zero pressure. Shear bands observed in the impact experiments show significantly more intensely localized deformation. Eventual failure through the shear band is a combination of grain-matrix separation, ductile matrix rupture, and grain fracture. In order to understand the effect of the composite microstructure and material inhomogeneity on deformation, two other materials are also used in the study. One is a pure tungsten and the other is an alloy of W, Ni, and Fe with the same composition as that of the matrix phase in the overall composite. The results show that the overall two-phase composite is more susceptible to the formation of shear bands than either of its constituents.

The Rheology of Lubricants at High Shear Rates

1993 ◽  
Vol 115 (4) ◽  
pp. 640-647 ◽  
Author(s):  
R. Feng ◽  
K. T. Ramesh
Keyword(s):  
Kolsky Bar ◽  
Shear Stresses ◽  
Test Duration ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Concentric Cylinders ◽  
Annular Layer ◽  
Short Test ◽  
Torsional Kolsky Bar

A modified torsional Kolsky bar is used to shear a thin annular layer of lubricant held between concentric cylinders. The shear rates obtained range from 4 × 103 to 4 × 104 s−1; the duration of the shear pulse is about 400 microseconds. The shear stress history and the corresponding shear-rate history are deduced using standard torsional Kolsky bar techniques. This experimental technique provides the capability of measuring the shear stresses sustained by fluids at very high shear rates, while the short test duration ensures a minimal rise in temperature due to the associated shear heating. Results are presented for a synthetic lubricant (5P4E) and a mineral oil (HVI650). The lubricants are both observed to be rate-sensitive over the entire range of shear rates examined; the rate-dependence of the shear response is strongly non-Newtonian at high shear rates. Softening during the test is observed for both materials; this softening appears to be largely driven by a thermal mechanism.

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