Dependence of Hertzian fracture angle on Poissons ratio and indentation techniques

Sub-parallel concentric conic fractures can be produced consecutively in Perspex by "liquid indentation". There is a linear relationshp between the conic angle, θ, of Hertzian fracture and the Poisson's ratio, Ν, of the material. This angle is about 10‡ higher than the calculated path of the principal stress trajectory for a given Ν. γ decreases with the increase of stress application rate. This dependence of θ is very marked in materials with high Poisson's ratios.