Issue 40

L. Zou et alii, Frattura ed Integrità Strutturale, 40 (2017) 137-148; DOI: 10.3221/IGF-ESIS.40.12 141 Given a neighborhood decision table , , , , U C D V f   , all reductions consist of B 1 ,B 2 ,…B n , the core of is defined as 1 n i i core B    . A kind of forward greedy reduction algorithm is used for the neighborhood decision table in this work, as is shown in the following Fig. 2, where ε is the threshold of the significance of attribute and its value is close to 0. Figure 2 : Reduction algorithm. Three Types of Fatigue Stress-life Relations Up to now, there are three types of mathematical expressions to describe the S-N curve, including Basquin [20], Langer [21] and three parameters stress-life model [22]. Among which, Basquin model is the most commonly used form, as is shown as , m S N C  (13) where, m and C are constants related to material types. Take logarithm on both sides, we get lg lg S A B N   (14) where ， A= lg / C m ， B= 1 / m  . Besides Basquin model, Langer model and the three parameters model are the other two models commonly used for fatigue analysis. The Langer model is shown as Eqs. (15) and the three parameters stress-life model is shown as Eqs. (16). mS e N C  (15) ( ) m f S S N C   (16) In this work, three types of the fatigue stress-life relations are all used for S-N curve fitting of the aluminum alloy welded joints. Then, statistical results of the three relations are compared and the best one is selected. N OVEL S-N CURVE MODELING METHOD Establishment of Fatigue Database fter a review of relevant literature [23, 24], fatigue data of aluminum alloy welded joints is collected and fatigue database is built up. The total number of samples in the database is 64, and S-N curves are fitted on basis of these samples. Totally, there are four types of welding methods including MIG, GMAW, TIG and Manual Arc, five kinds A