Mechanical properties of technical plasticine under static and dynamic loadings

This paper presents experimental studies of the mechanical properties of technical plasticine - which is a composite material consisting of a matrix (a mixture of wax and oils) and particulate filler (talc, clay, pigments) - under tension, compression, shear and penetration of a spherical indenter. At a constant strain rate (tension, compression) “stress - strain” diagrams have been obtained and characterized by a small elastic zone and yield strains up to 15-20 %. On the basis of experimental data power law for dependence of yield strength vs the strain rate in the range of 0.0004... 80 s -1 have been obtained. Thus, the deformation of technical plasticine can be described by viscoelastic Norton-type model with a serial connection of elastic and viscous elements. Under the tensile and shear strain of the technical plasticine over 3…5 % it begins to rapidly accumulate scattered microdamages, which does not allow using shear test as a test for determination of the yield stress like in the known methods related to metals. The yield stresses under tension and compression are close at the same strain rates. A linear diagram “force - penetration depth” down to a depth of 3 mm are obtained at penetration of a spherical indenter with a diameter of 43 mm in a plasticine block of 75 mm thick. Thus, the plasticine hardness is constant at a certain strain rate. The authors have managed to get dynamic hardness as the energy of a falling body, divided by the volume of cavity in the plasticine. Static and dynamic penetration is a promising method for the study of plastic properties of materials because of its simplicity. However it is necessary to establish the correlation coefficient relating hardness and yield stress. For the considered material such ratio is 0.24 at the frictionless condition.