前言 我室1976年曾对φ720口径的90°弯头进行过强度试验研究,包括四项内容:(1)没有内压时弯曲应力及变形的测定;(2)有内压时弯曲应力及变形的测定;(3)纯内压时应力及变形的测定;(4)弯头塑性破坏的极限弯矩值测定。前三项内容的试验研究报告已在我院学报上发表,第(4)项内容则附在崔孝秉所写“薄壁弯头塑性破坏的极限弯矩问题”一文中发表(见本期学报29页)。 INTRODUCTION Our laboratory made an intensity test on φ720 90 ° elbow in 1976, including four items: (1) Measurement of bending stress and deformation without internal pressure; (2) Bending stress and deformation with internal pressure (3) Determination of stress and deformation at pure internal pressure; (4) Determination of ultimate bending moment of plastic failure of elbow. The first three items of the experimental research report has been published in the journal of our institute. The fourth item is attached to Cui Xiaobing, “The Problem of Ultimate Moment of Plastic Elbows in Thin-walled Elbows.” (See Current Issue 29 page).