An experimental assessment of friction effects in the split Hopkinson pressure bar using the ring compression test

The potential error due to friction in compression split Hopkinson pressure bar (SHPB) tests is assessed and conditions for minimising this error are investigated. Theoretical friction factors are inferred from ring compression tests. Experimental results are reported for mild steel, copper and aluminium ring specimens tested quasi-statically (∼10−2 s−1), using a servo-hydraulic test machine, and at high strain rates (∼103 s−1) on a SHPB. Specimens were tested dry, or lubricated using a molybdenum disulphide grease. The influence of surface finish and strain rate on the friction effect is discussed. The inferred friction factors are in the range m=0.08–0.14 (equivalent to Coulomb friction coefficients between μ=0.05 and 0.08). These results imply that the friction error in routine compression SHPB tests of metals lies between 2% and 3%.