The article presents a simulation of metal hardness determination by the Rockwell method. The authors describe a physical model of an indenter and the examined sample built by means of the Nastran FX 2010 program using the finite elements method. The modelling included subsequent stages of indenter loads that follow the procedure used in the method. The verifying calculations were made for the results of C45 steel hardness of approx. 20 HRC. Two methods of hardness measurements were analyzed. A diamond cone was used as an indenting tool in one method, a steel ball in the other. As a result of calculations, spatial maps of elastic and plastic strains and stresses were obtained throughout the process. The hardness results obtained from computer simulations and those from experiments involving C45 steel are similar. metal hardness, Rockwell method, finite elements method, Nastran FX 2010, elastic strains twardość metalu, metoda Rockwella, metoda elementów skończonych, Nastran FX 2010, odkształcenia sprężyste
Artykuł dotyczy oszacowania dynamicznej twardości metali na podstawie badań przy użyciu wgłębnika. Jako porównawczą miarę tej właściwości zaproponowano wartości ilorazu energii kinetycznej młota i objętości wgłębienia. Zdefiniowano warunki pomiarów.
EN
A comparative measure of dynamic hardness of metalsThe paper deals with the assessment of dynamic hardness of metals on the basis of tests conducted with an indenter. As a comparative measure of this property, the dynamic indentation hardness is proposed which can be evaluated as the ratio of kinetic energy of the hammer and the indentation volume. The conditions of reliable measurements are defined.
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Colinear impact and dynamic hardness is analysed at spherical contact and moderate strains. A consistent three-dimensional contact theory based on viscoplastic material behaviour is laid down involving elements of self-similarity, stationary boundary conditions and cumulative superposition. Universal relations between impact velocity and the resulting contact region, impression depth and duration of impact are derived. Deformed surface shapes are shown to be self-similar for power law material behaviour and their relation to piling-up and sinking-in is explained in detail. The coefficient of restitution at rebound is estimated to first order. The concept of dynamic hardness is not unequivocally defined in general and various definitions in the literature are discussed in relation to true material rate sensitivity. Theoretical and numerical predictions of the present model are compared with pertinent experimental findings for different metals. Particular features such as lip formation, plastic zone size and maximum penetration depth are elucidated.
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