A model for fatigue crack propagation during high cycle fatigue

This paper deals with the prediction of high-cycle fatigue behaviour for four different materials (a 7075-T6 alloy, a Ti-6Al-4V alloy, JIS S10C steel and a 0.4%C steel) using Chapetti´s approach to estimate the fatigue-crack propagation curve. In the first part of the paper, a single integral equation for studying the entire propagation process is determined using the recent results of Santus and Taylor, which consider a double regime of propagation (short and long cracks) characterized by the model of El Haddad. The paper?s second part includes a comparison of the crack propagation behaviour model proposed by Navarro and de Los Rios with that advanced in the first half of this work. The results allow us to conclude that the approach presented in this paper is a good and valid estimation of high-cycle fatigue-crack propagation using a single equation to describe the entire fatigue-crack regime.Fil: Balbi, Marcela Ángela. Universidad Nacional de Rosario; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Effect of holding time at an intercritical temperature on the microstructure and tensile properties of a ferrite-martensite dual phase steel

To analyze the influence of the initial microstructure in the production of a dual phase (DP) steel on the mechanical properties, a commercial DP steel was subjected to two heat treatments (HT): step quenching (SQ) and intermediate quenching (IQ). SQ samples were austenitized at 930 °C for 20 min, then annealed at 830 °C for 5, 15, 30, 60 and 120 min and finally water quenched. Shorter annealing times show allotriomorphic ferrite and martensite while at longer time polygonal ferrite is formed. Tensile tests showed that yield and tensile strength are higher than those of the commercial DP steel and besides, the uniform elongation is smaller. IQ samples were water quenched after austenitization and then annealed at 830 °C for the same holding times and water quenched again. The microstructure consists of martensite dispersed in a ferrite matrix. The remarkable results are that these samples had similar tensile properties to that of the as-received DP steel. Tensile properties were analyzed as a function of the characteristic microstructure and the assessment of the alloying elements partition during the different HTs. Evaluation of the Kolmogorov-Johnson-Mehl-Avrami theory indicates that the transformation in SQ and in IQ samples corresponds to a diffusional process.Fil: Balbi, Marcela Ángela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Alvarez, Iris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Armas, Alberto Franklin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Microcrack growth and fatigue behavior of a duplex stainless steel

The kinetics of microcrack growth during cycling has been studied in a S32205 duplex stainless steel in the as-received and aged (100 h at 475 °C) conditions. Cylindrical specimens with a shallow notch were subjected to a constant plastic strain range of 0.3% in both thermal conditions. The characteristic features of surface damage and crack growth showed striking differences in microcrack density, nucleation location and propagation rate between the two thermal conditions even though the fatigue lives are comparable. In the as-received material, microcrack density is low and they nucleate mainly at grain and phase boundaries or second-phase particles. In the aged condition, slip markings first appear in the ferritic phase and they are the preferred site for microcrack nucleation. Crack propagation takes place along slip markings in adjacent grains for crack lengths less than 100 μm. A comparison between fatigue life and the relevant parameters of a microcrack growth law was made.Fil: Balbi, Marcela Ángela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Avalos, Martina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: El Bartali, A. Ecole Centrale de Lille; FranciaFil: Alvarez, Iris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Initiation and growth of short cracks during cycling in an aged superduplex stainless steel

The kinetics of short crack growth during cycling has been studied in a superduplex stainless steel in aged condition. After few cycles, slip lines appear distributed in both phases but the preferred phase for microcrack nucleation is the ferrite. Contrary to the exponential behavior observed in the as-received material, the growth rate of microcracks in aged condition follows a rather linear law. Internal dislocation structures were studied in the near surface region; microbands that sometimes extend over several grains were found at approximately 45º of the tensile axis on ferrite grains. The origin of the microbands has been analyzed and correlated with the microcracks.Fil: Balbi, Marcela Ángela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Hereñu, Silvina Andrea Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Proriol Serre, I.. Université de Lille; FranciaFil: Vogt, J. B.. Université de Lille; FranciaFil: Armas, A. F.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Alvarez Armas, I.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentin