The sheared fracture surface of plane carbon steel has been examined by using optical and electron microscopy in order to study the change of dimple pattern with shearing edge displacement. The results obtained are as follows: (1) The elongated dimple pattern predominates on the sheared fracture surface. (2) The average dimple size is larger in the annealed steel than in the quenched and tempered steel. (3) The dimple size of the annealed steel increases with increasing shearing edge displacement. (4) In the case of S30C annealed steel, the average dimple size increases with decreasing the rate of strain hardening.
This paper presents an investigation on the effect of hydrostatic pressure on the strength of brittle materials. Pyrex glass was taken as the test material. Hollow and solid cylinders of Pyrex glass, naked or coated with thin rubber films, were twisted under hydrostatic pressures up to 1000kg/cm2. The torsional strength of the coated specimens increased with the superimposed hydrostatic pressure, while that of the naked ones exhibited no significant change. It was observed that fracture started from a surface flaw. The effect of hydrostatic pressure on the torsional strength of glass may be explained using the concept of critical stress intensity factor for a part-through surface crack.
Mechanical properties of vascular walls are very important in the field of medical research since cardio-vascular diseases are closely related with them. They also may provide some suggestion in the field of engineering because vascular walls are considered to be one of the ideal composite materials. In order to examine them, the authors made an apparatus for testing the mechanical behavior of vascular walls, and its details are described in the present report. With this apparatus, oscillating pressure superimposed upon a constant pressure can be loaded on the specimen. Its intraluminal pressure and diameter can be measured simultaneously and continuously. From its performance test, it was confirmed that the testing apparatus can be used efficiently for examining not only the static but also the dynamic mechanical properties of vascular walls. Vascular walls are generally constituted of three structural components. Therefore, it is necessary to determine the volume or area fraction of each component occupied in a wall exactly before discussing their mechanical properties in terms of vascular structure. The following method is proposed here for their determination. Some thin slices are sectioned out from a specimen whose shape and structure have been fixed under a constant pressure level. Each sectioned slice is stained by such a way as only one of the three components is distinguishable in the section. Area fraction is calculated from the density distribution profile obtained by scanning the photograph of the stained structure by a microphotometer. Sufficiently good results have been obtained by this method. It is expected that some generalized constitutive laws of vascular walls may be established by using the apparatus and the method presented in this report.
Specimens of 0.03%C steel with a crack of the length 1.5 or 3mm were subjected to the cyclic tension-compression of amplitude 10 or 13kg/mm2 or to the monotonic tensile stress 10 or 13kg/mm2. In each case, the following three parameters defining the plastic deformation ahead of the crack tips were measured by means of optical microscopy and the back-reflection X-ray microbeam diffraction method, i. e., (i) the depressed zone size, (ii) the slip band zone size and (iii) the distribution of the excess dislocation density in the vicinity of the crack tips. The plastic deformation in cracked plates was compared in terms of these microscopic parameters. The results obtained are summarized as follows: (1) The size of the depressed zone formed ahead of the crack tips under monotonic loads was accurately predicted by Dugdale's equation. The increase in the excess dislocation density was detected in the depressed region, the maximum value being reached at a small distance away from the crack tips. The maximum stress in the depressed region evaluated from the excess dislocation density was smaller than the lower yield strength of the material. (2) As to the plastic deformation due to cyclic tension-compression, the depressed zone was observed in the specimen under a high stress intensity factor, but not under low stress intensity factors. The antinucleation in the depressed zone under low stress intensity factors may be caused by the following reasons: (i) the strain rate in the cyclic tests is higher than that in the monotonic tests, (ii) the work-hardening of the material at the crack tip due to cyclic stress is higher than that due to monotonic stress, and (iii) the compressive residual stress exists near the tip of fatigue cracks. The excess dislocation density took the maximum value at the crack tip, and its value is several times as large as that under monotonic stress. The flow stress of the material at the crack tip under cyclic stress is nearly twice as high as that under monotonic stress. (3) Slip bands were not observed in the vicinity of the crack tips of the specimens that were deformed under monotonic loads, while they were observed near the tip of fatigue cracks. The zone of slip bands near the crack tips does not correspond to the monotonically deformed zone, but to the cyclically deformed zone.
Axial load fatigue tests were carried out on the plain specimens made of S50C carbon steel under loads of random and constant amplitudes with mean stresses 0 and 20kg/mm2. Furthermore, in the case of mean stress 20kg/mm2, the fatigue deformations of specimens were also measured under respective loads. The testing machine was an electro-hydraulic servo type equipment and the signals for random loading tests were supplied by the pseudo-random noise generator, which generated the repeated noise signals with a continuous analog waveform of approximately gaussian distribution in known sequence. It was observed that the endurance limits under random and constant amplitude loads nearly coincided to each other when they were compared on the basis of the maximum peak stress σpmax, and that the increases of fatigue deformation under random and constant amplitude loads showed the tendencies similar to the ordinary creep curves. Some discussions were made on the behaviors of fatigue strains by comparing the values of initial strain, ε0, strain rate A and final strain εN obtained under respective loads.
The effect of hydrostatic pressure on the mechanical behavior of a syntactic foam which is composed of glass micro-spheres embeded in epoxy resin matrix was investigated up to the high pressure of 3000kg/cm2. The behavior of the syntactic foam tested under hydrostatic pressure was typically brittle, although the matrix material behaved in a ductile manner. The tensile strength increased linearly with the increase of pressure. The increasing rate of the tensile strength with pressure was larger than that for the matrix material. However, a transition of the mechanical properties occurred around the pressure of 1500kg/cm2 and above this pressure the tensile strength dropped and the elongation value increased discontinuously. This transition phenomenon was considered to be related to the breakdown of the glass micro-spheres by hydrostatic pressure. The above trends of the behavior of syntactic foam under hydrostatic pressure were not altered by the change in volume fraction of the micro-spheres, although the transition pressure was affected a little. Penetration effect of the pressure medium used was small on the mechanical properties of the syntactic foam.
Optical absorption spectra have been obtained on Cr3+ in alkali borate, alkali silicate and alkaline earth borate glasses. The assignments for bands ν1∼ν5 were made on the basis of octahedrally coordinated Cr3+ in the glasses and their band positions were determined. The values of three parameters, namely the crystal field strength, Dq, the Racah B and Racah C parameters, were calculated. The results indicate that; (1) Dq value of alkali borate glasses increases with increasing concentration of alkali oxide up to about 15mole% but it changes anomalously in the composition range of 15∼20mole%. (2) Dq value of alkaline earth borate glasses increases with increasing concentration of alkaline earth oxide. (3) On the contrary, in alkali silicate glasses the value decreases with increasing alkali oxide content. (4) As for the effect of kind of ion an increase of Dq value of the glass is in the order Li2O>Na2O>K2O and CaO>SrO>BaO for the same molar concentration of the oxide
The elastic constants of As2Se3-X(X=S, Te, Tl) and As2Se3-As2S3 glasses have been determined by means of the ultrasonic interferometry technique. The data obtained for isotropic wave velocities, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, Debye temperature are listed in Table II and Table III together with the density and thermal expansion coefficient. It can be seen that the values of isotropic wave velocity for As-Se glasses are lower than those for oxide glasses4). The effect of the third component X(X=S, Te, Tl) on the elastic constants is shown in Fig. 2. Assuming that As2Se3-X glass is a composite of two phases, i. e., As2Se3 and X glassy phases, the experimental data for bulk modulus Ks can be roughly calculated from the formula of the type Ks=y1K1+y2K2 or 1/Ks=y1/K1+y2/K2 where K1, K2 and y1, y2 are the bulk modulus and the volume fraction of each phase, respectively.
The state of stress under tension-shear load was investigated experimentally and analytically on the single spot welded lap joint of single shear splice. Specimens were made from mild steel sheet of 1.0mm thickness. The stress distributions on the surfaces of the specimen were examined experimentally by the brittle coating and strain gage methods. According to the experimental results, the state of stress in the joint under tension-shear load appeared to be determined by the following factors. (i) Plane stress distribution near the weld nugget caused by the local transmission of load. (ii) Bending in the longitudinal direction resulted from the offset of lapped plates. (iii) Bending in the transverse direction, occured secondarily by the superposed effect of factors (i) and (ii). To clarify the state of stress owing to factor (i), the plane stress distribution was examined by the experiments on the middle plate of single spot welded double shear lap joint in tension, which was not affected by bending. Two-dimensional analysis by the finite element method was also made of the assumption of the idealized“Plane Model”. In connection with the state of stress due to longitudinal bending (factor (ii)), two-dimensional finite element analysis was employed on the“Section Model”of single spot welded single shear lap joint. Finally, the experimental stresses on the single spot welded single shear lap joint were compared with the analytical values, which were obtained by superposition of the stresses computed by Plane and Section Models. The results obtained are as follows: (1) In the stress measurement on the single spot welded single shear lap joint, the peak stress at 3mm distant above the nugget edge attained the value 3.9 or -1.3 times of the nominal tensile stress on the inner or outer surface of lapped plate, respectively. (2) The plane stress distribution computed by Plane Model agreed fairly well with the experimental result observed on the middle plate of double shear lap joint. In the finite element analysis by Plane Model, the lapped plates of the joint were doubly defined in the same plane. (3) The stress concentration factor deduced from the plane stress distribution was 2.2∼2.3 at the nugget edge of the joint, where the width of joint was 25mm and the nugget diameter was 5φ. (4) At the representative positions on the inner and outer surfaces of single shear lap joint, the superposed values of the stresses computed on the factors (i) and (ii) corresponded well with the axial stresses obtained from the experiments.
This paper describes the compaction of AE-concrete pavement having 30cm in depth by a surface vibrator. The test results are summarized as follows: (1) It is possible to consolidate AE-concrete having 30cm in depth with a surface vibrator by choosing the optimum vibrating condition for each mix proportion of concrete. (2) The optimum condition of compaction by a surface vibrator seems to have good correlation with the settlement time measured by the consistency test with a vibrator used for road concrete. (3) As the optimum condition, the frequency of 7000vpm and the acceleration of 20g are found to be suitable for the concrete having the settlement time of 25sec., the frequency of 5000vpm and the acceleration of 15g for the one with the settlement time of 15sec., and the acceleration of more than 5g and the amplitude of 0.6 to 1.4mm for the one with the settlement time below 10sec.