Stress wave propagation in A1 single crystals

Transmitted wave profiles are presented for A1 single crystals that were loaded along crystallographic directions [100], [110] and [111] by a stress wave of the amplitude 1·85 GPa. The experiments were carried out with the Hopkinson Split Bar Technique. The observed wave profiles strongly depend on the specimen length. The constitutive relation of elastic-plastic-relaxing solid was proposed for the interpretation of obtained results. Mechanical properties can then be inferred by comparing observed rates of decay with theoretical models of stress relaxation.     

The dynamic (spall) strength of steels

Energy-based theory of dynamic fracture (spall) was examined for 21 steels (including different heat treatments). The explosive loading was used. Experimental results suggest that the present theory of this fracture should be modified in order to include the models of the observed microstructure changes. Two spall mechanisms of the spall transitions were found which were not reported up to present.     

Plastic wave front propagation in cylindrical bars

Making use of the dynamic, elastic-plastic finite element program, the elastic-plastic wave propagation in a cylindrical bar with a circular cross section is analysed for linear strain hardeningt Special attention is given to the influence of strain rate on. the axial stress distribution for variou. impact loading conditions. Comparison is made between numerical two-dimensional and analytical one-dimensional results for structural low alloy steel (C-Mo-Cr) having strain rate dependens dynamic mechanical properties. The implications of practical importance for experimental dynamic plasticity studies by means of Hopkinson Split Pressure Bar (HSPB) technique are discussed in detail.     

Response of Cu single crystals to high loading rates

The present paper deals with dynamic response of Cu single crystals to high loading rates. Cu crystals were loaded with transient stress waves along several crystallographic directions ([110], [100] and [¯135]). The response is expressed in terms of stress wave attenuation. The obtained results indicate that there are at least 2 basic regions where different mechanisms of plastic strain are working.The paper also involves a critical analysis of the used Hopkinson split bar technique. The analysis clearly indicates that the interpretation of experimental results can not be generally done by means of the function(). The obtained results may be described in terms of relaxation processes, analogously as in case of shock waves. This procedure also makes possible to describe the results in terms of dislocation dynamics. The possible connection between elastic precursor decay curves and the stress distribution in a specimen loaded with the Hopkinson split bar technique is briefly outlined.     

Supersonic crack propagation in basalt

Experimental results on crack propagation in shock loaded basalt are presented. The crack velocities greater than Rayleigh wave velocity which is believed to be the maximum admissible crack velocity were reported.     

Determination of dislocation damping in copper single crystals with stress pulse method

Dislocation damping in copper single crystals was determined by the stress pulse method. For this purpose very short stress pulses were used, maximum length 30 s, by which loading conditions of a metallic matrix in the frontal region of a propagating brittle crack were simulated. At loading by these very short stress waves, strain rates above 10⁴ s^–1 are achieved, however, the strain rate during loading is not constant. Therefore a technique was elaborated that enables to compare the measured results of mechanical characteristics with very short stress pulses ( const.) with results obtained on a device with a constant strain rate of the specimen. With the use of the dependence = ( ) the existence of damping mechanisms of a viscous character was proved and the damping coefficientB determined. These results agree with theoretical assumptions in [10,20] about the probable mechanical behaviour in the region of the propagating brittle crack.ikova 22, Brno, Czechoslovakia.