Takeshi Kanazawa

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 Notch Sensitivity of Mild Steel (The 2nd. Report)

It is familiar that stress concentration and triaxiality have great influence upon the transition temperature of notch sensitivity of mild steel. So I performed impact tests of various notched specimens, and studied the influence of the followings : i.e. (1) Notch radius, and Thickness of specimens, (2) Notch angle, and Notch depth, (3) Side notches, A 13mm. thickness rimmed steel was used for the tests.Using the theory of the notch sensitivity of mild steel stated in the 1st. report, I obtained curves of mean energy transition temperatures vs. stress concentration and triaxiality matching very well with the experimental results. And also I verified that there is a certain relation between the absorbed energy at 0°C and the temperature on the 2.6kg-m/cm2 (15Ft-Lb energy of the standard specimen) absorbed energy level.Some detailed discussion about absorbed energy will be left to the next report (the 3rd. report).

On the Forced Vibrations of Clamped Elastic Circular Plates. (No. 2)

In this article, we investigated the forced vibrations of clamped elastic circular plates under any eccentric forces, and the behaviours of elastic shock waves transmitted in the plates due to any eccentric shocks.We solved the problem by means of the forces or shocks expanded in the normal functions with the initial conditions; w=0, dw/dt=0 at t=0. As the particular cases, the distribution of forces or shocks were (i) uniform in the circle with radius a0 and eccentricity e.(ii) concentrated at the point having eccentricity e.and their time factor were(i) t/β for 0≤t≤β, 2β-t/β for β≤t≤2β, 0 for t≥2β or t≤0 (single trigonometric shock)(ii) e-ptsin(ωt-mk) for mk≤t≤mk+π/ω0 for mk+π/ω≤t≤(m+1)k(continous shock)(iii) sinωtThus we had the deflection of the plate and the bending moment at any time.

On the Notch Sensitivily of mild Steel (3rd Report)

In the 1st and 2nd report, we have obtaind the formula showing the transition temperature of notched specimen in terms of the ratio of notch radius to thickness of specimen, of notch depth and of notch angle, and the validity of the formula have ascertained by many experiments performed by Bagser, Thomas and Boodberg, etc.Furthermore, in the 2nd report, we have checkd the theoretical relation by Charpy impact test.In this paper, using the same steel as in the 2nd report, we have investigated the effect of notch radius, notch depth and thickness of specimen etc. on the transition temperature, and it has been found that the effect of these factors are expressed by the theoretical formula, as in the case of Charpy impact test.We have also studied the relation between these factors and absorbed energy, at constant temperature, and nominal maximum fibre stress, and we have obtained the facts that absorbed energy drops as increase of notch depth and thickness of specimen, and decrease of notch radius, and the nominal maximum fibre stress drops as increase of notch depth.

On The Rectangular Plates Under Lateral Impact

The rectangular plates under lateral impact of an isosceles triangular type were studiedanalytically. The maximum deflections and the maximum bending moments under varionsimpact durations, and their ratios to those under statical loads, etc. were evaluated numerically.Thus many interesting characters of the behavior of the rectangalar plates underimpact were brought to light.