内圧作用下における曲げ加工された銅配管の低サイクル疲労破壊現象

概要

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It is well known that fatigue strength of bended copper pipes under internal pressure is decreased by flattening and change in thickness at the cross section. It is important to understand fatigue fracture phenomenon of bended copper pipes, because they are significant members utilized in air-condition equipments and hot-water supply systems. In this paper, fatigue tests of bended copper pipe specimens were carried out under internal pressure and stress conditions of these cross sections were calculated by finite element method (FEM), in order to clarify fatigue fracture phenomenon of bended copper pipes.The conclusions are obtained as follows :(1) Origin of fatigue fracture of bended copper pipes was the same as position of maximum stress range (ΔSMAX) obtained by FEM.(2) In tested copper pipe specimens, ΔSMAX/Δσ at the cross section was strongly affected by flattening ratio (DoS/DoL), and ΔSMAX/Δσ was less affected by change in thickness ratio (Tout/Tin). Where, Δσ is an elastic stress range of Lamé's equation.(3) Fatigue fracture phenomenon of bended copper pipes under internal pressure was similar to low-cycle fatigue fracture phenomenon of strain controlled type at stress concentration parts.