A lot of studies on fatigue by using X-ray diffraction methods have been conducted during these ten years. The X-ray diffraction makes it possible to measure not only macro-stress but also various parameters on microstructure such as micro-stress in materials. Therefore the use of X-rays is promising as source for creation of new and significant fields in the fatigue study, and its application by the persons concerned about this kind of problems is foreseen. The 2nd Division of the Committee for the X-ray Study on Deformation and Fracture of Solid Material in the Society of Material Science, Japan, have conducted a series of studies by collaboration of scientists with a view to achieving further development in this field of studies. The first report of the Division was presented in the Journal of Material Science, Japan, vol. 18, p. 679 and 685 (1969), as a survey of the investigation conducted. One of the suggestions given in the report was that the broadening of X-ray diffraction line would represent the state of fatigued metals well and possibly indicate the extent of fatigue damage. This suggestion has stimulated engineering interest. Therefore as many experimental results on the change in broadening of the diffraction line during fatigue have been gathered as possible, and examination has been made of its application to the nondestructive method indicating fatigue damage, for the second report of the Division.
It has been understood that the fatigue strength of machined materials increases by the hardening work in surface layers. In these hardened surface layers, microstructures, such as dislocation structure, might be variable with the extent of working. And there might be variation in surface structure during the fatigue. Therefore, in order to clarify the surface structural changes during the fatigue of the annealed low carbon steels and the surface-rolled ones under three different working conditions, in this paper, the observations on the notched part of the rotating bending fatigue specimen are performed by light microscope and electron microscope with replicas, and the properties of slip line and fatigue crack initiation have been made clear. The summarized results are as follows: (1) The morphology of slip lines are variable from the annealed specimens to the surface-rolled specimens. In the former the fine slip lines are formed near the grain boundaries, and in the latter the slip bands are formed locally in the ferrite grains. These slip bands increase in length and width as the number of cycles increases. (2) The higher the rolling pressure rises, the more preferential slip bands are formed in the ferrite grains. The microcracks in the highly rolled specimens tend to initiate within the slip bands before these slip bands interfere each other. (3) Under the same cyclic stress condition, the time of emergence of the slip lines is earlier in the surface-rolled specimens, but that of microcracks is slower than that in the annealed specimens. (4) The direction of the slip lines in the surface-rolled specimens is perpendicular to the maximum tensile stress axis. (5) The slip ratio during fatigue increase more slowly in the surface-rolled specimens than in the annealed specimens.
The correlation of temperature dependence between Vickers hardness and tensile properties was examined in tungsten, molybdenum and steels (SS41, Coltuf-28) in the range of 77°K to 773°K from the viewpoint of ductile-brittle transition property. As a result, it was found out that there was close correlation between the transition temperature due to the tensile properties and the junction point in the temperature dependence of Vickers hardness. The conclusion drawn from the comparison of the deformation found near tensile fracture surface with that found around Vickers impression, further leads to the idea that the junction points of higher and lower temperatures in the curves of the logarithmic hardness vs. the reciprocal absolute temperature express respectively their ductile-brittle transition points. It was also proved that the hardness test corresponds to the tensile test with larger strain rate, and using this relation it turned out that the difference between the transition temperature by hardness and that by tensile test could be illustrated.
There are two types of brittle lacquer coating, air-drying and baking. The air-drying type is generally less fit than the baking kind to bring out brittleness, while even the latter leaves the coating to lose its brittleness rapidly after heat treatment. Neither of these types is worth recommendation therefore to analyse stress distribution. In order to cope with the problem, another, and better, method has been suggested of applying the“solvent-cracking”which is often observed in high polymers where crack is occasioned at lower stress than in air. The experimental stress analysis made with this method has won higher credit than what is given to the ordinary method exercised in air. This method is rendered futile, however, when the machines or their parts are studied respecting stress analysis under varying dynamic load such as rotating, running and flying. For materials for stress analysis in general, therefore, lacquer coating of high sensitivity to strain even without heat treatment is required. (Strain sensitivity is in proportion to the brittleness of the coating.) The principle for improving the brittleness of the coating will be educed through the micro structure of the coating as previously reported. As the result of the study, the author has found an efficient method for lacquer coating using abietic acid and calcium abietate which have displayed high sensitivity at room curing temperature. The cracking properties and the composition of the new lacquer coating are described in the present paper.
Many non-Newtonian visoous fluids are recently used in practice, and in consequence the chances of handling these fluids have increased in many fields. However, at present the rheological equation is not yet established for the viscoelastic non-Newtonian fluids. Experimental studies are required, therefore, of viscoelastic flow concerning its stress analysis. One of the most efficient experimental methods is considered to be the photoelastic procedure, in view of the fact that the viscoelastic fluids with velocity gradients have birefringence effect. In this paper, the results of photoelastic measurements of viscoelastic flows through narrowed portions are reported. The flow was produced in rectangular vessels as two-dimentional flow by applying pressure to the fluid, and the narrowed portions were formed by applying triangular or rectangular projections to the two opposite walls. As the viscoelastic fluid, taking the homogeneity, fluidity and transparency as well as the birefringence effect of the material into consideration, Epikote fluid was employed. An ordinary photoelastic apparatus was used, and clear isochromatic and isoclinic patterns of stressed viscoelastic fluid were obtained. The experimental results may be summarized as follows. In general, the shear stress plays an important role for the mechanical degradation of highpolymer fluids. It is significant, therefore, to predict the amount of shear stress in the flow of such fluids, In the viscoelastic flows through the narrowed portions experimented in this study, the maximum shear stress appeared at the corner of each projection. Moreover, the shear stresses along the flow direction midway between both the projections showed peak values at the points a short distance ahead or behind the corners of the projections.
In order to study the stresses working transversely on the square arrays of circular fibers contained in composite materials, strips with a row of circular shaped inclusions subjected to normal loading were studied with respect to the stresses working transversely on the load. The stress distribution was analyzed by the finite-element method, and the results were compared with that obtained by the photoelastic analysis. The results are as follows. (1) It is confirmed that the stresses obtained by the finite-element method agree well with that obtained by the photoelastic method. (2) The maximum stress has been induced at the matrix-reinforcement interface, and the stress concentration factors have increased with increasing constituent stiffness ratio Ef/Em and with increasing volume content of reinforcement vf. (3) The stiffness of the composite transverse to the axis of the reinforcement has increased with increasing Ef/Em and vf.
The blends of PVC and a copolymer of vinyl chloride and cetyl vinyl ether were observed in comparison with PVC homopolymer to study their compression characteristics and fusion rate on mixing roll. Then the fusion rates of several polymers and the blend were measured by means of Brabender Plastometer. The results showed higher fusion rate of the blend as the content of the copolymer increased in the blend. Next, in order to find the factor in heat stability of polymers during the processing, torque values were measured in plastogram. The results indicated that the blend had equilibrium torque for long time because of less elevating of stock temperature. The heat stability of the blend was almost the same as that of PVC homopolymer. Plastogram also showed that PVC having high polymerization degree had short time keeping equilibrium torque, and this fact was closely related to heat stability in the processing. When the blend type had the same content of cetyl vinyl ether as the one copolymer type, the blend showed long time of equilibrium torque in plastogram. The copolymer component in the blend was considered to decrease the generation of friction heat during mixing. Finally the extruding rates of several polymers, were measured in which the blend type gave high rate by lubricant action of the copolymer component in the blend.