Using a high speed impact tensile testing machine with a large rotary disk installed in Tokyo Institute of Technology, the high speed impact tensile fracture was photographed at a speed of 5000∼7000 frames per second using HIMAC 16 HB (16mm, camera maximum speed 10000fps) high speed motion picture camera, with the test pieces made of mild steel. The following results were obtained from the experiment (1) Fractures at the impact velocity of 10, 15, and 20m/sec were clearly observed by the motion picture. (2) The specimens were pulled by impact tensile load without bending by the high speed impact tensile testing machine with a large rotary disk.
A repeated impact tension testing machine was designed by means of which a single pulse stress wave was made to pass through a specimen under one impact loading. By making use of it, the repeated impact strength of 0.01% C steel was investigated, and it was found that the failure and fracture of the material were influenced not only by the stress magnitude but also by its duration. The main test results are as follows. (1) The yielding occurred near both the ends of the specimen and the yielding zone spread toward the center with each passage of stress wave. (2) The total duration of stress required for breaking the specimen could be regarded nearly constant under the constant stress magnitude. (3) The elongation under repeated impact stress was larger than that under static tension.
The effect of heat treatment on the mechanical properties of 17-7PH (17% Cr, 7% Ni, 1% Al) stainless steel was investigated at room temperature. The specimens were given the following heat treatment conditions: (a) Solution treatment: 1050°C×15min, a.c. (b) Intermediate treatment: 760°C∼975°C×15min, a.c. (c) Subzero treatment: -78°C×8hr. (d) Aging treatment: 425°C∼575°C, 0∼70hr, a.c. The results obtained can be summarized as follows: (1) Austenite in the solution treatment could be transformed into martensite by intermediate and subzero treatments, so that tensile strength, yield strength, plane-bending fatigue limit and hardness increased, but elongation considerably decreased. (2) After subzero treatment, the mechanical properties of this steel increased a little with increasing intermediate temperature. (3) In the relation between aging conditions and hardness, the lower the aging temperature, the longer was the aging time that showed a maximum value of hardness, but its value rose high. (4) When the aging conditions continued within the temperature range of 425°C to 575°C for 2 hours, the maximum mechanical properties could be obtained at 500°C. In this case, there was hardly the effect of intermediate temperature except elongation. (5) When the specimens intermediate-treated at 950°C were aged at 500°C, these tensile strength, yield strength, fatigue limit and hardness were remarkably increased in the early stage of aging and showed the maximum values in 2 hours. But these elongation was nearly constant up to 7 hours. (6) In the condition of subzero treatment or aging treatment the ratio of the fatigue limit to the tensile strength was about one-third.
An unnotched specimen having the emery- or carborundum-paper polished surface is generally used in ordinary fatigue tests in order to avoid the effects of a hardened surface layer and the roughness induced in the machining process on the fatigue strength, but the surface has thin hardened layers owing to the mechanical polishing. In the present study 11 kinds of alminium alloys were examined to determine the fatigue strength of the specimens from which the hardened surface layers were removed by the electrolytic polishing method, and the effect of the annealing treatments after the mechanical polishing. The fatigue test was conducted on an Ono's rotating-beam fatigue tester and the fatigue strength was determined at 107 cycles. The specimen polished with carborundum-paper had hardened layer on the surface about 0.03mm deep. When the layers were removed by the electrolytic polishing, the fatigue strength dropped lower than the specimen polished with carborundum-paper. The reduction of fatigue strength of O, T4 and T6 treated alloys are 4.2-19.2%, 10.6-21.1% and 1.6-6.8%, respectively. In case of notched condition, the specimen electrolytically polished showed lower fatigue strength than that shown in the machined specimen, but no difference was detected in the fatigue strentgth in either of the surface conditions of 6061 alloy. The fatigue strength of the specimen polished with carborundum-paper had the highest value, which was followed in the declining order by the specimen electrolytically polished, that annealed in vacuum, and that atmospherically annealed.
The effect of glass volume fraction and Young's moduli of the constituents on the creeps of polyester resin filled with glass fiber particles in the deformation region in which the samples behave as a linear viscoelastic materials were studied by using elastic theory of isotropic heterogeneous elastic body. The variation in the creep curve with time is pertinewt only to the creeps of resin, therefore by substituting the value of creep compliance for Young's modulus of the resin, we can deduce creep compliance of FRP filled with rigid particles. The creep compliance of FRP calculated by using a linear viscoelastic operator shows good agreement with the measured value.
Polyesters from phthalic anhydride (I) and glycerol (II) (mole ratio of I/II=3/2 (A), 1/1 (B)), polyesters from I, II and diethylene glycol (III) (mole ratio of I: II: III=6:2:3 (C), 2:1:1 (D), 3: 2:1(E)) were prepared at 180°C under atmosphere of nitrogen, and acid values, softening points and reduced viscosities of these polyesters, were measured. The softening points of polyesters composed of (I) and (II) were higher than those of 3 component (I, II, III) polyesters. The softening points were lower in order of A, B, C, E, D and F. After curing of two aluminium plates bonded with the above polyesters at 140±2°C and 180±2°C for 1, 2, 3 and 4 hours, the comparative shear strength of the resins for bonding metals was measured. From the results it was concluded that the strength of the 3 component system was generally higher than that of 2 component ones, and strength after curing at 180°C was markedly higher than that after curing at 140°C. When curing temperature was 140°C, C, F, and D were stronger as compared with A, B and E. When curing temperature was 180°C, D and F were very strong and became weaker in order of C and E, and B and A had the lowest strength. For both the 2 and 3 component systems, it was concluded that the bond strength decreased as glycerin content increased.