Abstract
Fatigue strength of welded joints under repeated load must be more carefully investigated than it is done for static strength. Particularly in the welding of high tensile strength structural steel advanced technique and the utmost care are required in order to obtain as much confidence as in the welding of mild steel.
Recently, longitudinal welding joint of thin plate has been used for bridge structures on economical reasons for example box girder and steel slab, so that the authors carried out these tests to determine the fatigue strengths of longitudinal butt welds of several types.
In these tests, two types of specimens were used, one consists of two high tensile strength structural steel plates welded by the longitudinal single-V butt welds, and the other of a high tensile strength plate and a mild steel plate welded in the same way.
In each of the both types, three groups of specimens were tested, the first group specimens were welded by using D 5216 electrode, the second by D 4316 electrode, and the third by D 4301 electrode; all plates used were of 8mm thickness and the surface of the plate for all specimens were kept at the condition as they were delivered.
The fatigue tests were carried out by using the Losenhausen fatigue testing machine (UHS type), at the room temperature (approximately 18°C) and the repeated stress of the tests were taken as pulsating stress 0-+σmax.
Some of the experimental results are as follows.
A little differences were recognized between the two types of specimen, i. e. longitudinal butt welded joint of two high tensile strength structural steel plates and that of high tensile strength steel plate and mild steel plate.
It was seen from these results that the D 4301 electrode used in these tests were sufficiently reliable for the fatigue failure.
By the inspection of the fatigue fractured surfaces, it seems to be clear that the greater part of fatigue failure started from the welding defects, blow hole, slag inclusion etc.
The fatigue failure of specimens for high tensile strength structural steel connected with mild steel were occured either in the welding part or in the mild steel part.
