Masao Yoshiki

An analysis of brittle-fracture propagation

Brittle-fracture propagation tests were carried out to find relations among the speed of crack propagation, the dynamic-stress distribution, the test temperature and the applied stress. These tests were performed at low temperatures so that the behavior of the crack propagation was fully elastic. The test results were compared with the theoretical calculations and some considerations were made on the surface plastic work.

The Thirty-Fifth Thomas Lowe Gray Lecture: Design and Construction of Large Tankers in Japan

This lecture first presents an outline of research work by which many troublesome problems in the design and construction of large tankers were solved, and secondly introduces the largest tanker ever built in Japan, the Nissho Maru, of 130 000 deadweight tonnage.With regard to design of such tankers, two points, that is,(1)reduction in length of ship (L), and(2)increase in depth (D),should be taken into account from the standpoint of weight saving and of easy fabrication.Researches into structural problems of tank parts and into the dynamic pressure of cargo oil tank, due to ship motions, are described briefly, and show that the maximum impulsive pressure in model tests may be up to 5 times the static fluid pressure and may be observed at the tank top when the natural period of fluid in the tank is resonant with the oscillation period of the ship.Special care should be taken in the detailed design of longitudinals, struts and so on, otherwise cracks will initiate easily at the point of stress concentratio...

Study on the Mechanism of Propagation of Brittle Fracture

Tensile tests of rimmed steels with specimens having brittle pre-cracks of various length at their one side were performed at temperature ranges of 10°C and -50°C.The size of test specimens were 70mm width and 500mm length, and the length of pre-crack varied between 0.5mm and 25mm.The preparation of specimens were done in the following way. First, large size specimens of about 100mm width with a machined notch at their one side were prepared. Then, inserting a spltting wedge at the machined notch, a small hammering to the wedge was given to produce a brittle crack at sufficient low temperature by immersing the specimen in liquid oxygen. Any desired length of brittle crack was obtained by controlling the intensity of hammering and by trimming off the marginal side of specimen having pre-crack.The test results show that the breaking stress under constant temperature were inversery proportional to the square root of the initial crack length approximately, and the length of short fibrous crack formed at the tip of the brittle pre-crack decreased as the test temperature lowered.A new theory on the mechanism of brittle fracture propagation is proposed, using the yielding stress curve, the brittle fracture stress curve, and the fibrous fracture stress curve of the material, and satisfactory coincidence is found between the proposed theory and experimental results.

On the Corrosion of Ship Structural Steel

In order to study the effects of prestrain and welding on the corrosion of ship structural rimmed steel, we have performed some experiments to decide the degree of corrosion by measuring the electrical resistance increment of test pieces.The results obtained are as follows:(1) Steel becomes more sensitive to corrosion as the amount of pre-strain increases.(2) Particularly, the corrosion of steel which contains weldment is seriously precipitated.(3) The effects of pre-strain on the corrosiveness of steel have been reduced by welding which produces a large quantity of heat such as union melt welding.(4) The rim part of steel in more anticorrosive than the core part.

On the Slamming Test of a Wooden Model Ship

The authors performed towing test of a wooden model ship under regular waves and measured the pressure distributions at foreward bottom of the model when she was slamming, by using 19 specially designed pressure gauges.The maximum pressure observed reached about 4 to 5 times of static pressure under regular waves and position of maximum pressure located about 0.1L from F. P., and dynamical pressure became practically zero at about 0.25L from F. P..According to the experimental results, maximum pressure seemed to be related to the relative normal velocity of ship to wave rather than pitching or heaving velocity. And this result is expected from rough theoretical consideration written in Appendix and this maximum pressure can also be estimated from the pressure measured by falling test of flat or wedge shaped body on the surface of water.Slamming appeared when the ratio of length of wave to that of ship became about 1.1 to 1.2 in this test.

On the Bracketless System of the Bottom Longitudinals

In this paper we deal with the strength of the doubling liners applied to the bracketless system of the longitudinals proposed by Isherwood, when the liners are bent by the action of longitudinals which resists the external pressure. In the Isherwoods paper, the doubling liners were considered only from the viewpoint of the continuity of the longitudinal strength of ship at the bracketless ends of longitudinals. As the results of our calculation, the bending stress at the doubling plates reaches greater value than the longitudinals, so that it is necessary to decide the scantling of the doublings more carefully considering the bending action together with the longitudinal strength.