PSI - Issue 19

Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000

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ScienceDirect

Procedia Structural Integrity 19 (2019) 194–203

Fatigue Design 2019 The Effect of Machined Surface Layer on Low Cycle Fatigue Lives of Austenitic Stainless Steel Fatigue Design 2019 The Effect of Machined Surface Layer on Low Cycle Fatigue Lives of Austenitic Stainless Steel

Shota Hasunuma a *, Takeshi Ogawa a a Aoyama Gakuin University, Kanagawa, 252-5258, Japan Shota Hasunuma a *, Takeshi Ogawa a a Aoyama Gakuin University, Kanagawa, 252-5258, Japan

Abstract Low cycle fatigue tests were performed for austenitic stainless steel, SUS316L, in order to investigate the effect of machined surface layer. For changing the machined surface layer, round bar specimens were machined by different condition of turning. Then, fatigue tests were carried out for the specimens machined by the different conditions. In addition, in order to separate the effect of surface shape and material property variations, we prepared the specimens, whose machined surface layers were removed completely or partly by polishing. Fatigue test results show that plastic deformation caused by machining as well as residual stress had small influence on fatigue lives. On the other hand, scratches reduced the fatigue lives. If there were scratches on specimen surface, many cracks initiated from the valley of scratches in a row. The cracks grew rapidly to be a semicircular crack almost as large as the scratch in early stage of fatigue life. But, fatigue lives of a specimen which had a few small scratches was similar to that of a specimen whose scratches were removed. Finally, fatigue crack propagations were predicted based on elasto-plastic fracture mechanics. We can predict safety side fatigue lives assuming a semicircular crack shape. Abstract Low cycle fatigue tests were performed for austenitic stainless steel, SUS316L, in order to investigate the effect of machined surface layer. For changing the machined surface layer, rou d bar specimens were machined by ifferent conditi n of turning. Then, fatigue tests were carried out for the specimens machined by the different conditions. In addition, in order to separate the effect of surface shape and material property variations, we prepared the spe imens, whose machined surface layers were r moved completely or partly by polishing. Fatigue test results show that plastic deformation caused by machining as well as residual stress had small influence o fatigue lives. On the other hand, scratches reduc d the fatigue lives. If ther were scratches on speci en surface, many cracks i iti ted from the valley of scratches in a row. The cracks grew rapidly to be a semicircular cr ck almost as large as the scratch in early stage of fatigue life. But, fatigue lives of a specimen which had a few small scratches w s similar to that of a specimen whose scrat hes were r moved. Finally, fatigue crack propagations were predicted based on elasto-plastic fracture mechanics. We can predict safety side fatigue lives assuming a semicircular crack shape.

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. Keywords: Machined surface layer ; Stainless steel ; Low cycle fatigue ; Fatigue lide prediction ; Keywords: Machined surface layer ; Stainless steel ; Low cycle fatigue ; Fatigue lide prediction ;

1. Introduction The fatigue design of a petrochemical or electric power plant uses a design fatigue curve. A design fatigue curve is determined from the relationship between the fatigue life and stress or strain while considering a safety factor. It is thus important to determine the design fatigue curve properly for both safety and cost. The safety factor of a pressure 1. Introduction The fatigue design of a petrochemical or electric power plant uses a design fatigue curve. A design fatigue curve is determined from the relationship between the fatigue life and stress or strain while considering a safety factor. It is thus important to determine the design fatigue curve properly for both safety and cost. The safety factor of a pressure

* Corresponding author. Tel.: +81-42-759-6210. E-mail address: hasunuma@me.aoyama.ac.jp * Correspon ing author. Tel.: +81-42-759-6210. E-mail address: hasunuma@me.aoyama.ac.jp

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.021