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Determination of subsurface hardness gradients in plastically graded materials via surface indentation / Michael A. Klecka in Transactions of the ASME . Journal of tribology, Vol. 133 N° 3 (Juillet 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 133 N° 3 (Juillet 2011) . - 05 p. Titre : Determination of subsurface hardness gradients in plastically graded materials via surface indentation Type de document : texte imprimé Auteurs : Michael A. Klecka, Auteur ; Ghatu Subhash, Auteur ; Nagaraj K. Arakere, Auteur Année de publication : 2012 Article en page(s) : 05 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Ductility  Fatigue  Functionally  graded  materials  Hardness  Indentation  Machine  bearings  Materials  testing  Plasticity  Steel  Surface  hardening  Wear  resistance Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Graded materials with high surface hardness and ductile cores are popularly used in high performance bearing applications to resist surface wear and fatigue damage. The gradient in hardness with depth is commonly determined using micro-indentation on the cross section of the material which contains the gradation in microstructure or composition. In the current study, a novel method is proposed to predict the hardness gradient profile using solely surface indentations at a range of loads. The method does not require the graded material to be sectioned, and has practical utility in the surface treatment industry. Two case hardened steels, M-50 NiL and Pyrowear® 675, and a through-hardened M50 steel, are used as model materials to illustrate the concepts. For a material with a decreasing gradient in hardness, higher indent loads result in a lower measured hardness due to the influence of the softer subsurface layers. A power-law model is presented which relates the measured surface indentation hardness under increasing load to the subsurface gradient in hardness. It is shown that the response of the material is not influenced greatly by the absolute surface hardness value, but instead sensitive to the sharpness of the gradient in subsurface hardness beneath the indented region. The proposed approach is not specific to case hardened steels and can be used to determine the subsurface hardness gradient for any plastically graded material (PGM). DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Determination of subsurface hardness gradients in plastically graded materials via surface indentation [texte imprimé] / Michael A. Klecka, Auteur ; Ghatu Subhash, Auteur ; Nagaraj K. Arakere, Auteur . - 2012 . - 05 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 133 N° 3 (Juillet 2011) . - 05 p. Mots-clés : Ductility  Fatigue  Functionally  graded  materials  Hardness  Indentation  Machine  bearings  Materials  testing  Plasticity  Steel  Surface  hardening  Wear  resistance Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Graded materials with high surface hardness and ductile cores are popularly used in high performance bearing applications to resist surface wear and fatigue damage. The gradient in hardness with depth is commonly determined using micro-indentation on the cross section of the material which contains the gradation in microstructure or composition. In the current study, a novel method is proposed to predict the hardness gradient profile using solely surface indentations at a range of loads. The method does not require the graded material to be sectioned, and has practical utility in the surface treatment industry. Two case hardened steels, M-50 NiL and Pyrowear® 675, and a through-hardened M50 steel, are used as model materials to illustrate the concepts. For a material with a decreasing gradient in hardness, higher indent loads result in a lower measured hardness due to the influence of the softer subsurface layers. A power-law model is presented which relates the measured surface indentation hardness under increasing load to the subsurface gradient in hardness. It is shown that the response of the material is not influenced greatly by the absolute surface hardness value, but instead sensitive to the sharpness of the gradient in subsurface hardness beneath the indented region. The proposed approach is not specific to case hardened steels and can be used to determine the subsurface hardness gradient for any plastically graded material (PGM). DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

Material-dependent representative plastic strain for the prediction of indentation hardness / Nathan A. Branch in Acta materialia, Vol. 58 N° 19 (Novembre 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6487–6494 Titre : Material-dependent representative plastic strain for the prediction of indentation hardness Type de document : texte imprimé Auteurs : Nathan A. Branch, Auteur ; Ghatu Subhash, Auteur ; Nagaraj K. Arakere, Auteur Année de publication : 2011 Article en page(s) : pp. 6487–6494 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Representative  plastic  strain  Hardness  Plastic  deformation  Finite  element  modeling Résumé : The definition of representative plastic strain induced by a Vickers indent has received considerable attention in recent years. Previous reports have attempted to define a universal value that was independent of a material’s plastic response. However, the work presented here will show that a material-dependent representative plastic strain is valid in the conversion of flow stress to indentation hardness. This representative plastic strain is the volume average plastic strain within the plastic zone of Vickers indentation. The increase in indentation hardness within the plastic zones of macro-indents was experimentally determined by micro-Vickers indentation and then compared with that predicted by finite element modeling, which utilizes the proposed representative plastic strain. It was further shown that the representative plastic strain defined here is independent of yield strength, elastic modulus and magnitude of prior plastic deformation for both linear and power law strain hardening materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005240 [article] Material-dependent representative plastic strain for the prediction of indentation hardness [texte imprimé] / Nathan A. Branch, Auteur ; Ghatu Subhash, Auteur ; Nagaraj K. Arakere, Auteur . - 2011 . - pp. 6487–6494. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 19 (Novembre 2010) . - pp. 6487–6494 Mots-clés : Representative  plastic  strain  Hardness  Plastic  deformation  Finite  element  modeling Résumé : The definition of representative plastic strain induced by a Vickers indent has received considerable attention in recent years. Previous reports have attempted to define a universal value that was independent of a material’s plastic response. However, the work presented here will show that a material-dependent representative plastic strain is valid in the conversion of flow stress to indentation hardness. This representative plastic strain is the volume average plastic strain within the plastic zone of Vickers indentation. The increase in indentation hardness within the plastic zones of macro-indents was experimentally determined by micro-Vickers indentation and then compared with that predicted by finite element modeling, which utilizes the proposed representative plastic strain. It was further shown that the representative plastic strain defined here is independent of yield strength, elastic modulus and magnitude of prior plastic deformation for both linear and power law strain hardening materials. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410005240