Kesan Parameter Bebanan Ke Atas Kadar Perambatan Retak-Lesu Di Dalam Kelakuan Keluli Tahan Karat 316

Abstract

This research was carried out to study the effect of loading parameter on fatigue crack growth behaviour of stainless steel 316 at room temperature using the center-crack tension M(T) specimens. The parameter involved were R-ratio and D s . For studying the effect of R-ratio, experiments were carried out with R-ratio of 0, 0.33 and 0.6 at constant D s of 100 MPa, whereas for studying the effect of D s , experiments were carried out with D s values of 100, 150 and 225 MPa at constant R-ratio of 0.1. The crack length was measured using a travelling microscope. Results showed that at a given value of cyclic stress intensity, D K the crack growth rate increased with increasing R-ratio but decreased with increasing D s . At the first stage, the value of D Kth decreased with increasing the value of R-ratio but increased as the value of D s was increased. At the linear region, the fatigue crack growth could be described with the Paris-Erdogon Power Law. The fatigue crack growth rate for various R-ratio occurred between 1x10-5 to 1x10-3 mm/cycle whereas, the effect of D s was occurred in a range of 1x10-4 to 2x10-3 mm/cycle. An increase in fatigue crack growth rate by factor 3.4 is observed at low D K of 12 MPa when R-ratio increased from zero to 0.6. At high D K values exceeding 25 MPa, it was found that da/dN converged to 3x10-4mm/cycles. The microscopic examination of the fracture surface was done using SEM. The tension fracture surface showed a ductile fracture where many microvoid coalesced and dimples were found. Fractography of the fracture surface showed striation at the second stage especially at high D K. At this stage crack occurred transgranularly with little intergranular crack but at the third stage crack occurred intergranularly