Effect of strain wave shape on high temperature fatigue life of a type 316 steel and application of the strain range par
- PDF / 1,263,198 Bytes
- 9 Pages / 594 x 774 pts Page_size
- 93 Downloads / 153 Views
INTRODUCTION
EXPERIMENTAL PROCEDURE
C O M P O N E N T S of various machines and structures operating at elevated temperatures are subject to repeated thermal stresses resulting f r o m start-up and shut-down. Therefore the problem of high temperature low-cycle fatigue failure is of great importance to the design of the c o m p o n e n t s ) There are m a n y studies on high temperature lowcycle fatigue behavior of various heat-resisting steels for steam generator and pressure vessel of nuclear reactors, 2-6 for casing and rotor of steam turbines, 7-9 and for bucket and blade of gas turbines. ~~ It has become apparent that the fatigue lives depend not only on testing temperature and environment but also on strain rate and strain wave shape. 2-~7 In studies" on creep-fatigue interaction, it is important to quantify and predict the fatigue lives from an engineering point of view. Recently some useful methods for predicting fatigue life have been proposed. 18-24 A m o n g them the strain range partitioning method proposed by Manson, H a l f o r d and Hirschberg is of interest since it is possible to explain the variations in fatigue lives tested with different strain wave s h a p e s ? 4-28 The purposes of this study are to examine the effects of strain rate and strain wave shape on high temperature low-cycle fatigue life of a Type 316 stainless steel and to apply the strain range partitioning method to observed results. In applying this method there is a problem of how to partition the inelastic strain range. In this study a new technique of partitioning the inelastic strain range was proposed and used.
The material used was bar of commercial T y p e 316 stainless steel. The chemical composition is listed in Table I. It was solution-annealed at 1050 ~ and water-quenched. Tensile and creep rupture properties of this steel are shown in Table II. Fatigue specimens were machined f r o m the bar stock to the shape shown in Fig. 1. Strain-controlled low-cycle fatigue tests were carried out using a pushpull type, servo-controlled, hydraulic testing machine. Heating o f the specimen was by an electric resistance furnace. Testing temperatures were 600 and 700 ~ Details of the testing procedure have been given in Refs. 15, 29 and 30. Six types of strain wave shape shown in Fig. 2 were used to examine the effect of strain wave shape on the fatigue life. Figs. 2(a) and (b) show fast-fast and slowslow triangular waves at a strain rate (~) of 6.7 x 10-3s -~ and 6.7 x 10-Ss-~, respectively. Figs. 2(c) and (d) show truncated waves with a hold time at both the tension and compression sides and at the tension side only, respectively. The hold time was varied f r o m 2 to 60 min, and the r a m p rate was always 6.7 x 10-3s -~. Figs. 2(e) and (f) show fast-slow and slow-fast sawtooth waves at a tensile strain rate of 6.7 x 10-3s-I and a compressive strain rate of 6.7 x 10-~s-~, and vice versa, respectively. In addition triangular wave shapes at a strain rate of 2 x 10-2s -~, 6.7 x 10-4s -~ and 1.1 x 10-Ss -~ were used to investigate s
Data Loading...
