RESISTÊNCIA À FADIGA POR FRETTING DA LIGA AA7050-T7451
FRETTING FATIGUE STRENGTH OF AN AA7050-T7451 ALLOY
Rossino, Luciana Sgarbi; Ashiuchi, Edgar; Manfrinato, Marcos Dorigão; Araújo, José Alexander; Bose Filho, Waldek Wladimir
http://dx.doi.org/10.4322/tmm.00603009
Tecnol. Metal. Mater. Min., vol.6, n3, p.167-173, 2013
Resumo
Foram realizados ensaios de fadiga por fretting na liga AA7050-T7451, com cargas de contato e tensões alternadas de fadiga constantes para todos os ensaios realizados. Foi apenas variada a tensão média aplicada, responsável pela variação da tensões cíclicas máxima e mínima obtidas para cada condição de ensaio. Tais resultados são comparados com as curvas de fadiga convencional obtidas para o material estudado. Como observado para os casos de fadiga convencional, o aumento na tensão média diminui a vida do material para os casos de fadiga por fretting. Existiram casos que, mesmo com a diminuição da tensão máxima cíclica para valores próximos a zero, ocorreu a iniciação de trincas devido ao carregamento severo de fretting. Cargas de fadiga com valores muito baixos para iniciar trincas foram capazes de propagá-las, causando ruptura do material. Para carregamentos cíclicos totalmente compressivos, ocorreu a iniciação de trincas, que não se propagaram e o material apresentou vida infinita. O fenômeno do fretting associado a um carregamento de fadiga reduz significantemente a vida de um componente.
Palavras-chave
Ensaio de fadiga, Fadiga, Freeting, Trincas
Abstract
Fretting fatigue tests were performed in an AA7050-T7451 alloy, with both contact load and fatigue alternate stresses kept constants. Only the applied mean stress, responsible for the maximum and minimum cyclic stresses are varied for each test condition. Such results are compared with the ones from the conventional fatigue tests obtained for the studied material. Similarly to the conventional fatigue results, it was observed that increasing the mean stress, lead to a reduced fretting fatigue life. There were cases that, crack nucleation took place due to the severity of the fretting loads, and they were propagated due to the applied fatigue stress, even with the maximum cyclic stress close to zero, which is considered too low to initiate a crack, leading the specimens to fracture. For cyclic loading totally compressive, again crack nucleation took place, due to the fretting loading, and the cracks did not propagated, leading the specimen to infinite life. The fretting effect in conjunction with fatigue loads significantly reduces the specimen life.
Keywords
Fatigue tests, Fatigue, Freeting, Cracks
Referências
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5 AMERICAN SOCIETY FOR TESTING AND MATERIALS. Designation ASTM E 1382-1397: Standard test methods for determining average grain size using semiautomatic and automatic image analysis. Ohio, 1994.
6 AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM E 466: Standard practice for conducting force controlled constant amplitude axial fatigue tests of metallic materials. Pennsylvania, 1996.
7 MARTINS, L. H. L., et al. Detailed design of a fretting apparatus and test n a 7050-T7451 Al alloy. Tribology – Materials, Surfaces and Interfaces, v. 2, n. 1, p. 39-49, Mar. 2008.
8 NOWELL, D. An analysis of fretting fatigue. Oxford. 1988. Thesis (Doctor Phil.) - University of Oxford, 1988.
9 SOUZA, S.A. Ensaios mecânicos de materiais metálicos: fundamentos teóricos e práticos, 5. ed. São Paulo: Edgar Blucher, 1982.
10 SHARP, M. L.; NORDMARK, G. E.; MENZEMER, C. C. Fatigue design of aluminum components & structures. New York: Mc Graw-Hill, 1996.
11 ARAÚJO, J. A.; NOWELL, D. The effect of rapidly varying contact stress fields on fretting fatigue. International Journal of Fatigue, v. 24, n. 7, p. 763-75, July 2002.
12 NICHOLAS, T. High cycle fatigue: a mechanics of materials perspective. Oxford: Elsevier Science, 2006.
13 HUTSON, A. L., et al. Effect of sample thickness on local contact behavior in a flat-on-flat fretting fatigue apparatus. International Journal of Fatigue, v. 23, suppl. 1, p. 445-53, 2001.
2 WATERHOUSE, R. B. Fretting fatigue. International Materials Reviews, v. 37, n. 1, p. 77-98,1992.
3 WARMUZEK, M. Metallographic techniques for alluminum and its alloys. In: AMERICAN SOCIETY FOR METALS. Metallography and microstructures. Metals Park, 2004. p. 711-751. (Metals handbook, 9).
4 ROSSINO, L. S. Estudo do comportamento em fadiga por fretting da liga de Al 7050-T7451. 2008. 232p. Tese (Doutorado em Ciência e Engenharia de Materiais) – Universidade de São Paulo, São Carlos, 2008.
5 AMERICAN SOCIETY FOR TESTING AND MATERIALS. Designation ASTM E 1382-1397: Standard test methods for determining average grain size using semiautomatic and automatic image analysis. Ohio, 1994.
6 AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM E 466: Standard practice for conducting force controlled constant amplitude axial fatigue tests of metallic materials. Pennsylvania, 1996.
7 MARTINS, L. H. L., et al. Detailed design of a fretting apparatus and test n a 7050-T7451 Al alloy. Tribology – Materials, Surfaces and Interfaces, v. 2, n. 1, p. 39-49, Mar. 2008.
8 NOWELL, D. An analysis of fretting fatigue. Oxford. 1988. Thesis (Doctor Phil.) - University of Oxford, 1988.
9 SOUZA, S.A. Ensaios mecânicos de materiais metálicos: fundamentos teóricos e práticos, 5. ed. São Paulo: Edgar Blucher, 1982.
10 SHARP, M. L.; NORDMARK, G. E.; MENZEMER, C. C. Fatigue design of aluminum components & structures. New York: Mc Graw-Hill, 1996.
11 ARAÚJO, J. A.; NOWELL, D. The effect of rapidly varying contact stress fields on fretting fatigue. International Journal of Fatigue, v. 24, n. 7, p. 763-75, July 2002.
12 NICHOLAS, T. High cycle fatigue: a mechanics of materials perspective. Oxford: Elsevier Science, 2006.
13 HUTSON, A. L., et al. Effect of sample thickness on local contact behavior in a flat-on-flat fretting fatigue apparatus. International Journal of Fatigue, v. 23, suppl. 1, p. 445-53, 2001.
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