For mild steel sheets for the press work, it is necessary to have good deep-drawing quality, well-finished surface and to be free from stretcher straining which is apt to appear on the surface of steel pressings after a slight drawing.
In general, it is well-known that the magnitude of the stretcher strain depends on the yield-point elongation of steel sheet, thus, a larger elongation leading to severer stretcher straining. This yield-point can be shifted by slightly working the steel before pressing, i, e., by temper rolling.
Recently, it has been proved by many investigators that residual stress in temper-rolled sheet influences on the rate of strain aging, the yield-point elongation of mild steel, and the stretcher straining.
The present investigation was carried out to ascertain the effect of percentage reduction on the residual stress distribution, yield strength, yield ratio, Erichsen value and hardness.
0.07% C-mild steel sheet was used in these experiments. Temper rolling was carried out on a 100mm. dia. experimental mill at a rolling speed of 30cm/min. without tension, the reductions given to sheets varying from 0% to 4.5%. Determination of the residual stress was done by the usual method of etching away from one side of the sheet, and the original residual-stress distribution was calulated by measuring the change in the curvature of the specimen as the thickness is reduced.
The outline of these results was as follows. (a) At about 0.2% reduction, the temper-rolled mild steel sheet have the minimum of yield strength, the maximum of Erichsen value and therefore the maximum formability. (b) In the reduction range from 0% to 0.3%, skin residual stress is compression and above this range is tension. For explaining the cause of this phenomenon, it may be taken that in the smaller range than 0.3% reduction, mild steel sheet is rolled on the extreme surface layer only, but in larger range, the core is deformed more severely than the rolled surface layer.

View full abstract

In this paper, we explain the method for analysing the structural changes of material by means of measuring the specific volume or gravity. As materials are to be affected in their specific volume or the gravity by the change of phase caused by heat treatment, aging and so on, and if the specific volume or the gravity reflects very sensibly the phase changes, we may be able to analyse the material conveniently by means of the precision chemical balnace only, without using special apparatus.
So, we describe the measuring method, and by examining the data of the measurement, we know that the specific volume or the gravity well corresponds to the internal change.
The results are consistent with the change of length ascertained by means of the dilatometer (it is natural that the change of specific volume of materials is affected by the third degree as compared with the length), and agree with the changes of the lattice constant observed by the X-ray analysis (it means that the lattice constant decreases with microscopic volume and the increases with expansion, and the change of the specific volume macrocopically corresponds to the microscopic change).
We think the above justifies the analysis, and introduce some examples applied to the industrial method of the material analysis. That is: (1) Applying it on the analysis of the internal change in steel, iron and brass caused by heat treatment, there is a change peculiar to material in specific volume, so we can exactly know the internal change in composition. (2) And using the analysis of the aging in aluminium and its alloys, we can obtain the data as an aid for analysing the aging mechanism.

View full abstract

There are two kinds of rubber vibration isolators such as bonded and unbonded among the compression type. We compared these two types in vibration tests, in which correction of shape effect was made by applying Hattori-Takei's formula. In addition to this the authors checked the accuracy of successive approximation method by this formula. In this calculation one constant called shape factor... (cross sectional area)/(free surface area) was taken. When rubber is deformed the cross sectional area and free surface can roughly be obtained. If the rubber is compressed between lubricated metals the cross section varies uniformly along to its axis, enabling the calculation of true section and surface. In order to compare the characteristics, we took three cases as follows:
(A) Bonded type.
(B) The contents and dimensions of rubber are the same to (A). The used unbonded specimens are held between two metal parts polished by No. 0 sand paper.
(C) The specimen is the same to (B), prouided it is lubricated with silicone in the contact faces between rubber and metals.
Using these types of isolators, we obtained many data in various mean stresses from experiments, and calculated characteristics in other mean stress from zero stress, and came to the following conclusions.
(1) The stiffness by the statical tests, (A) is the largest and (C) is the smallest.
(2) In (A) its complex modulus and loss factor are the largest, and in (C) they are the smallest.
(3) The amplitude dependencies are similar in these three cases.
(4) Calculated values by the successive approximation method are larger than (A) and smaller than (B), and (C) is quite another.
(5) Hattori-Takei's formula is applicable so long as statical deflection by mean stress is not too large.
(6) The differences between (A) and (B) are taken as chiefly due to the penetration of metal into rubber and sliding deformation of rubber on contact faces with metals as well.

View full abstract