Institute of Structural Macrokinetics and Materials Science Russian

1. XII EPNM Symposium «Explosive Production of New Materials: Science, Technology, Business, and Innovatios» DYNAMIC LOCALIZATION OF STRAIN: SPALLATION MECHANISM A.F. Belikova, S.N. Buravova, E.V. Petrov, and A.S. Shchukin Institute of Structural Macrokinetics and Materials Science Russian Academy of Sciences, Chernogolovka

2. 2 Condition of a problem The purpose of my report is to show the nature of adiabatic shear bands. The reason for deformation localization is the loss of plastic flow stability caused by heat release during transition of work of plastic deformation in the heat and further thermal softening of the material. The thermoplastic deformation localization model with 1944 has undergone virtually no changes so far Condition of localization such: attestation of changes occurring with the sample after explosive loading is performed at a high level. However, the study of the saved (recovered) samples does not allow to determine the cause, why these changes occurred. Question of the relationship between the structure after deformation and developing during deformation has not been studied. In our work study of the structure of the material is performed together with wave picture of the process

3. 3 Collapse of a thick-walled tubular sample Scheme of experiment. The interference of unloading waves, with tension stresses not exceeding the dynamic strength of the material, produces localized deformation bands under the impulsive load. The deformation and shear failure are two independent processes, as material deformation occurs at the shock loading stage, while shear bands appear at the unloading stage. 1. Explosive, 2. Sample, 3. Internal cavity, 4. Top and bottom covers A.F. Belikova, S.N. Buravova, Yu.A. Gordopolov / Technical Physics, 2013. Vol. 58. Issue 2. P. 302-304.

4. 4 Transformation of spall cracks into localized deformation bands tentatively proves the spall nature of the shear bands formation. Spall damaging:Radial,Plane, Needlelike, Circular,Angular. A.F. Belikova, S.N. Buravova, E.V. Petrov / Technical Physics, 2013. Vol. 58. Issue 8. P. 1152-1158.

5. 5 Transition region of the spall crack in band of localized deformation Feature of the transition zone spall crack band of localized deformation is a high density of etch pits (1) compared with the adjacent matrix material and the presence of micropores (2) in unstructured material. The size of the micropores varies in a wide range of 200 nm to 500 nm. Experimental measurements of the size of the germinal centers of damageability in the quasistatic tensile copper gives a value of 200 nm. (Betekhtin V.I.)

6. 6 Explosion welding Cause of the very thin shear banding in the weld joint is the formation of micro protrusions ahead of the contact point which under loading by clad plate penetrate into the target and create simple shear bands. Arising thus adiabatic shear bands are sources of material fracture during its operation.

7. 7 Conclusions: 1.The interference of unloading waves, with tension stresses not exceeding the dynamic strength of the material, produces localized deformation bands under impulsive load. Transformation of spall cracks into localized deformation bands proves the spall nature of shear band formation. 2. The deformation and shear failure are two independent processes, as material deformation occurs at the shock loading stage, while localized strain bands appear at the unloading stage. 3. Transition spall crack in shear bands is accompanied by the emergence of a huge number of nucleation damage centers, the microstructure of the copper sample is highly deformed structureless material. 4. This physical observation casts a doubt on the universality of a thermally induced loss of stability leading to shear localization.

8. Thank you for attention!

9. Scheme of experiment.