抄録
Hereunder is given a report of the stress relaxation tests of mild steel that were made by Oding's eccentric ring method for a short time (1∼1200min) at 300∼600°C. In this method, the stress relieved is known by measuring the initial spacing of the gap (d0) of the ring specimen, the spacing of the gap (d) which is broadened before heating the specimen, and the gap spacing (d') retained after removing the wedge after heating at test temperature.
From these tests, the following results have been obtained.
(1) In Oding's ring test, “shape constant”A(δ=Aε, where δ=(d-d0)/d0, and ε is the average fiber strain defined in Fig. 1) should be kept as much in uniform as possible with each specimen, in order to apply the desired initial stress, and to know the stress being precisely relaxed. As a unique relation is found experimentally between A and the initial gap-spacing d0, the specimens with uniform A must be prepared by making their gap-spacing d0 as much in uniform as possible. (2)In the case of mild steel, the relation between the remnant stress σ and time t in the earlier stage of the relaxation process at 400∼600°C, is well expressed by
σ=σ0-m'(logt-C'),
where m' and C' are constants which vary exponentially with temperature, and m' increases with σ0.
(3) The relaxation data of mild steel at 500∼600°C, around σ0 of 18kg/mm2, seem to be well rearranged into a single master curve using the relationship
T(logt+6.5)/(1-8.5×10-4T)=F(σ/σ0)
where t is testing time (hr), and T temperatnre (°K).
