Influence of graphite nodules on fatigue limit of nodular cast iron

 

N. Costa ^1,2, N. Machado ², F. S. Silva¹

 

¹Universidade do Minho, Departamento de Engenharia Mecânica, Azurém, 4800-058 Guimarães, Portugal.

²MAHLE Componentes de Motores S.A. Murtede, Portugal.

nuno@dem.uminho.pt

 

ABSTRACT: This paper describes the fatigue behaviour of a nodular cast iron dispersed within martensitic matrix microstructure. Cyclic fatigue tests have been performed on nodular cast irons. The effects of both the microstructure and the graphite nodules geometrical features such as shape and size, on the fatigue behaviour of nodular cast iron were studied. The rule of size and position of graphite nodules on the fatigue limit has been established. On this study is verified if the (square root of the maximum graphite nodule area projected onto the principal stress plane) parameter model proposed by Murakami, quantitatively predicts with accuracy the fatigue life of the nodular cast iron.

In this paper, a high strength nodular cast iron, with rupture strength of about 1.300 MPa and Young modulus of about 165 GPa has been used. Comparison between experimental results and  parameter model has been assessed.

Keywords: Nodular cast iron, Fatigue strength, defects geometry, automotive.

 

RESUMO: Este artigo descreve o comportamento á fadiga do ferro fundido nodular com matriz martensitica. Testes de fadiga foram realizados em amostras de ferro fundido nodular. Foi estudado o efeito da microestrutura e dos nódulos de grafite (forma e tamanho), no comportamento á fadiga do ferro fundido nodular. Uma relação entre tensão limite de fadiga, tamanho e posição dos nódulos de grafite foi estabelecida. Neste estudo foi verificado se o modelo proposto por Murakami, (raiz quadrada da máxima área projectada dos nódulos de grafite no principal plano de tensão) prevê com exactidão a tensão limite de fadiga.

Neste artigo foi utilizado um ferro fundido nodular com tensão limite de rotura de 1.300 MPa e modulo de elasticidade de 165 GPa. Uma comparação entre resultados experimentais e o modelo proposto por Murakami, foi efectuada.

Palavras chave: Ferro fundido nodular, resistência á fadiga, defeitos geométricos, automóvel.

 

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