Hereunder is presented a report of the fatigue tests of notched specimens of 0.11% C steel that were conducted under both random and program loads. In performing these tests the electrodynamic type equipment that was previously constructed was reinforced with certain necessary device for the random load fatigue test. It was observed that the fatigue lives under the random and program loads considerably differed from each other, irrespective of the fact that the relative frequency distribution of peak stresses was approximately similar in both of the loads. However, the tendency was observed that in the range of longer life, the lives under both of the loads approached each other. The estimated life based on Miner's rule agreed approximately with the experimental value only in the range of shorter life for the program load. In other cases, the estimation always gave longer lives than the experimental values, and the discrepancy between these values was dominant especially for the random load. Further discussions were made on the relation between the estimated life and the experimental value under the random load, based on the compilation of the results so far reported.
This experiment was carried out in order to find out conditions for ausforming Mn-Cr-B spring steel. The steel was ausformed in either stable or metastable phase of austenite, and tempered at 480°C for one hour, and then its various properties have been investigated by subjecting the material to tension test, hardness test and optical microscopy. The results obtained are as follows: (1) The steel, as it is ausformed at 480°∼550°C, increases in yield strength and in tensile strength, but decreases considerably in elongation. In the relationship between tensil strength and elongation the ausformed steel is found second-rate to the steel conventionally treated. (2) The greater is the improvement that can be attained in hardening steel by raising the temperature in operation, when the process of ausforming it is carried on in the stabe phase of austenite. Though there is but small increase in strength after tempering it, there is scarcely any decrease in elongation. Though the relationship between tensile strength and elongation is nearly equal in both the kinds of steel after their heat treatment, the yield ratio in ausformed steel is higher than that in the steel convetionally treated. (3) Developing bainite in austenite in the course of ausforming steel has bad effect on elogation of the material, but it scarcely appears that developing pearlite in austenite will anywise affect elongation. (4) It is recommended that ausforming spring steel will be processed in the stable phase of austenite.
In this study an experiment is reported of subjecting Mn-Cr-B spring steel to thermomechanical treatment by gradually cooling the material. The steel was first austenitized at 850°C, which temperature was gradually lowered to 620°∼720°C. At these lowered degrees of temperature the steel was reduced in thickness, and there was its 50% plastic deformation. Then the steel was tempered at 480°C for an hour. Then the steel was tested respecting its mechanical properties by submitting the material to tension test, hardness test and fatigue test. The chief results obtained are as follows. (1) By this thermomechanical treatment about 13∼48% improvement in yield strength has been realized, keeping up higher rate of improvement than in tensile strength. The elongation is above 10%. (2) This thermomechanical treatment of the steel, while it makes no difference to the relationship between its strength and ductility, improves the relationship between the tensle strength of the material and its yield ratio, i. e. given the tensile strength of the material as balanced in both the kinds of treatment, its yield strength is higher in the thermomechanical treatment than in the conventional. (3) This thermomechanical treatment of the steel has raised its fatigue limit to approximately 15∼34%, or 0.2∼0.5kg/mm2 rise per 1% reduction over the fatigue limit of the steel treated by the conventional process. (4) This thermomechanical treatment of the steel at 650°∼720°C has prolonged its fatigue life about 7∼60 times as long as the steel in its pre-treatment state. (5) Developing pearlite in austenite, while it scarcely affects the mechanical properties of the steel, does greatly affect its fatigue life over the amplitude of high stress. For processing the ausform of spring steel, therefore, it recommended that the temperature for the treatment will be raised to over 650°C.
It is generally known that the biharmonic equation can be solved upon mutual analogy in the use of resistance simulator, and that the problems concerning the equations for thermoelastic two-dimensional surface in the multiply connected regions will be divided between Laplace's and Poisson's equations. In the present paper it is demonstrated theoretically that the problems concerning the equations of thermoelastic two dimensional surface in the multiply connected regions can be solved upon mutual analogy in the use of resistance simulator, and for its verification the estimation of stress distribution has accordingly been made in the circular ingot mould. The agreement of the measurement made by using resistance simulator with the theoretical values is found to have been sufficiently established for practical purposes. Although there is some difficulty in setting boundary conditions when this method is used, and in spite of the errors that inevitably arise in numerical differentiation of stress function, this method is commendable as being efficient for estimation of thermal stress distributed in the multiply connected regions.
In order to investigate the mechanism of the cracking of polymethyl methacrylate (PMMA) due to enviromental stress, the propagation of the artificially induced Griffith cracks under petroleum was studied. The stress changes due to the crack propagation were also examined by the photoelastic method and the fractured surfaces were observed in the light and by electro microscopic technique. The main results are summarized as follows: (1) The growth and propagation of cracks are studied in two distinct stages. At the first stage the crack grows at high speed immediately after coming in contact with petroleum, and gradually falls until it stands at constant speed at the second stage. (2) The energy on the fractured surface is estimated at 0.40×105 and 0.36×105erg/cm2 respectively under the plane stress and strain. This estimation is in coincidence with what has been derived from the Griffith crack length at the critical point where the constant of the velocity of crack propagation through the stages first and second has dropped to 0. (3) Of changes in stress patterns due to the crack propagation there have been but few cases recognized, but there have been crazings observed as made by high stress concentration at the tip of the Griffith cracks. The crack that grew at the first stage apparently passed through this crazing area. (4) The fractured surfaces are rough over extensive areas which tell of crack growth in the first stage, and a number of small parabolic marks indicate discontinuous crack initiation in the second stage.
The plastics reinforced with glass fibers have recently been attracting general attention as mechanical members. In this paper is presented the report of the study made of the plastics reinforced with woven glass cloth and subjected to the edgewise loading, with a view to finding the stress distribution on the interface of its fiber matrixes and its composite longitudinal stiffness. This analysis was made with the use of the two-dimensional model and the application of the finite element method, and in this connection the following assumptions have been made. (i) That these materials used in the present study are isotropic, homogeneous and elastic. (ii) That these materials are perfectly bonded together on the interface of their fiber-matrixes. (iii) That the state of plane stress has been maintained throughout. The results obtained by the finite element technique are compared with the results obtained by the rule of mixture. The results are as follows. (1) The maximum stress is induced on the concave side of the longitudinal fibers, and the stress concentration factors increase with increasing stiffness ratio Ef/Em and with increasing bent angle β of the longitudinal fibers. (2) The stress concentration factors on the interface of the transverse fiber-matrixes increase with decreasing Ef/Em and with increasing in β (Ef/Em>6). (3) The efficiency of the finite element method is confirmed in the experiment in which the stress and stiffness obtained by that technique agree well with the results obtained by the rule of mixture (β=0).
It is pointed out first what favorable effect the small quantity of glass fiber ingredient in the reinforced Nylon 6 will have on the material to arrest the propagation of fatigue crack in it, and then the problem what is to account for the said favorable effect is carefully examined, from the standpoint of fractography, by performing repeatedly the test of low cycle fatigue, which is due to the tensile loads, by the use of an apparatus for the test of constant load. The results obtained are as follows. (1) The fatigue crack in this case propagates itself slowly in match with the increasing ratio of glass fiber ingredient in the reinforced Nylon 6, no matter what sort of strain is repeated, unlike the crack propagation in the test of low cycle fatigue in the repeated bending by the use of the apparatus for the test of constant deflection. (2) The relationship between the rate of propagation of crack in these specimens and the factor for the stress intensity at the crack tip follows Paris's formula, and it is found in the light of this relationship that the glass fibers will have power to arrest the propagation of fatigue crack. (3) It is made clear by observation through the optical microscope that there are four typical patterns of fatigue fractured surface. These patterns of fatigue fractures together go to point to the condition that the glass fiber ingredient in the matrix functions to arrest the propagation of fatigue crack.
In order to inverstigate the properties of cohesive soil, a series of creep tests and triaxial compression tests of the material were repeatedly performed. The distinctive feature in these tests was in measuring the changes in the volume of the specimens under undrained condition, since the specimens were partially saturated. The following results were obtained. (1) There are several properties in respect of volumetric changes of the clay specimens that are clearly recognized as characteristics in common both of the triaxial compression tests and the creep tests, evidently so in particular during the unloading process of both these tests. (2) One characteristic of the volumetric change of the specimens is what will be called “the expansion point” which is apparent during the increasing process of the axial load, and which is considered to be the critical point in the transition of energy from the elastic state to the plastic state of the clay.
The present paper is concerned with the failure process of cement mortar under triaxial compressive stresses. To give the quantitative evaluation of process of failure of cement mortar with loaded history, the degree of failure α is defined as; α=1.0-uniaxial compressive strength of cement mortar specimen with loading history/uniaxial compressive strength of cement mortar specimen without loading history The surface of the same degree of failure of cement mortar is determined in the three dimensional stress space. The following conclusions are made on the degree of failure of cement mortar under high triaxial compressive stresses. (1) The surface of the same degree of failure closes on the space diagonal. (2) The right section of the surface changes its shape with an increase of hydrostatic pressure. When the hydrostatic pressure is low, the shape is slightly bulged from an equilateral triangle with apexes in the direction of principal stresses. With an increase of hydrostatic pressure it becomes almost regular hexagonal, and changes into the slightly bulged equilateral triangle of the reversed mode to the former. (3) The stress condition for the same degree of failure can be approximated by a single curve expressed as a function of the sum and the difference of the maximum and the minimum stresses.
Hereunder is presented the report on the investigation of the infrared absorption spectra in a variety of chalcogenide glasses. The absorption band at about 12.5-12.7μ observed for As-S glasses prepared by the evaporation and/or distillation methods (Refs. 12 and 14) was formally attributed to the vibration of As=S bond in AsS2.5 component and/or to the AsS component included in a glass (Ref. 13). The corrected assignment of the band in this region is given by the present investigation to be due to the vibration of As-O bond. On the basis of this assignment the oxidation process in the above evaporation and distillation procedures is suggested for the preparation of As-S glasses. Two absorption bands near 15 and 21μ for As-S glasses shifted respectively from 15.2 to 14.5μ and from 20.5 to 21.1μ as the arsenic content decreased, provided that the thickness of the glasses was controlled within 0.1-0.2mm. Correspondingly the relative intensity of the former band decreased and that of the latter increased. A possible structure coincident with these results is the formation of AsS2.5 component including the dative As→S bond in glasses in the AsS1.5-S system. The following absorption bands are attributed to the contamination with oxygen: about 12.6 and 16μ bands in As-Se and As-Se-Te glasses, 11.2-11.4 and 13.6-13.7μ bands in Ge-As-Te glasses, 10.2-10.4 and 13.9-14.5μ bands in Si-As-Te glasses. These bands, except the bands due to the Si-O bond in Si-As-Te glasses, can be eliminated by the melting procedure in carbon-coated silica glass ampule. The oxide-free As-Se, As-Se-Te and Ge-As-Te glasses show good transparency up to about 20μ, whereas As-S glasses up to about 13μ; the uniform transmission is limited by about 10μ for Si-As-Te glasses contaminated with oxygen because the reduction of SiO2 by carbon is thermodynamically impossible.