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Relation between the reduced and unreduced hardness in nanomicroindentation tests
Authors:S I Bulychev
Institution:(1) Moscow State Industrial University, 109280 Moscow, Russia
Abstract:Hooke’s law is generalized to the case of arbitrary elastic or plastic indentation 
$$\varepsilon = (2/\sqrt \pi )x(w_1 /\sqrt {A)} $$
, where ɛ=q/E r is the elastic strain, q is the average pressure over the contact area, E r is the reduced elastic (Young’s) modulus, A is the projected area of the contact, w 1 is the deformation in elastic indentation by a flat punch. On this basis a relation is obtained between the reduced hardness H and unreduced hardness H h, which depends on the ratio w s/w1=m s; w s is the elastic deformation along the perimeter of the indent, and m s≅0.78. It is shown that the correction ΔE r to the elastic modulus E r determined from the condition of linearity of the initial part of the unloading diagram, is ΔE r=0.27(ΔP/P m), where ΔP is the value used in the calculation of E r for the length of the linear part of the diagram, reckoned from the maximum load P m. It is shown that for metallic construction materials of medium hardness one has q=HM, where HM is the Meyer hardness. With increasing HM and increasing angle ϕ at the tip of the indenter, the ratio HM/q grows by an exponential law. Zh. Tekh. Fiz. 69, 42–48 (July 1999)
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