Correlação de estrias de fadiga com espectro de cargas em liga de Al aeronáutica SAE-AMS 7475 T 7351. / Correlation of fatigue striation spacing to loading history in aeronautic Al alloy, AMS 7475 T7351.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

This work discusses the relationship between striation spacing, i.e. the microscopic crack propagation rate, SL (local) e SP (projected), as measured in post-mortem fractographic inspection of fatigue fractured surfaces, and the macroscopic crack propagation rate, da/dN, as monitored during fatigue crack growth tests. Compact tensile specimens C(T) were extracted in LT orientation from the core of a laminated plate of a SAE-AMS 7475-T7351 Al alloy and subsequently fatigue tested either at constant load or at constant ΔK, at room temperature, according to ASTM-E647. For constant amplitude loading fatigue tests, da/dN- ΔK data points were obtained for Regions II and III of crack growth curve. For constant ΔK fatigue tests, four ΔK levels were selected to give crack growth rates typically ranging from 0.15 to 2.4 μm/cycle. Additionally, KIC fracture toughness tests were performed in both LT and TL directions, according to ASTM E1820. SEM fractographic analysis was conducted on constant ΔK fatigue specimens, in order to determine striation spacing created during the fatigue test. Macro- and microscopic crack growth rates were compared and good correlation have been obtained for data within the range from 0,1 to 1,0 μm/ciclo. Using the technique proposed by Berkovitz, loading history was estimated by the K-factor parametrization and the results were compared to the true loading spectrum imposed by the testing machine. Using the local striation spacing SL and for ΔK values lower than 23 MPam 1/2 (Paris region), the estimated loading exhibits an error less than 15%. Propagation life estimated by local striation spacing (microscopic crack growth rate) was compared to the true propagation life obtained from macroscopic crack growth rate values and the absolute difference between them was less than 15,7%. These results suggest that both life and loading history can be adequately estimated using the local SL striation spacing values.

ASSUNTO(S)

espaçamento inter-estrias de fadiga investigação de falha parametrização fator k liga de alumínio mechanical properties striation spacing curvas da/dn accident failure investigation espectro de carga k-factor parameterization aluminum alloy análise quantitativa fratográfica load spectrum quantitative fractography da/dn curve propriedades mecânicas

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