This paper deals with the method to measure the scratch resistance of the plastic plates. We studied about the relation between the amount of scratches left on the plastic plates when injured by means of the Mar resistance tester and the ratio of their gloss diminution measured by the gloss meter. As the result, we learned that the rate of gloss diminution on the plastic plate due to the artificial scratches by Mar resistance tester, were related only to the amount of scratches on it when the ratio of the gloss diminution was more than 45%, and that the initial conditions of the plate (color, surface gloss etc.) did not affect it. And we found that there was linear relation between the breadth of the scratch groove made on the plastic plate by the Clemens tester and the rate of the gloss diminution of the plate injured by Mar resistance tester. Thus we learned that the scratch resistance of the plastic plate could be found by measuring the breadth of the scratch groove marked on it by the Clemens tester. The above mentioned facts have been confirmed as the result of having tested the plate artificially scratched, but the test of the naturally scratched plate showed nearly the same result as the above mentioned one.
The effects of stress history and corrosive environment on fatigue crack propagation under stress amplitude, both constant and continuously varying, respectively, are hereunder discussed, and the following facts have been made clear: In air the crack rate under the continuously decreasing stress becomes smaller than the expected one based on the linear cumulative damage hypothesis. This is due to the deceleration effect corresponding to the delay in crack propagation found under the high-low two-step stress history. On the other hand, there is no effect of stress history to be observed on the crack growth under the continuously increasing stress. Accordingly, ∫(dn/N)>1 is concluded under the stress varying up and down periodically because of the deceleration effect of the crack propagation. In saline the same deceleration effect is observed under the continuously decreasing stress as is in air. On the other hand, when the stress amplitude is increased, the acceleration effect of the crack propagation is observed, though it tends to diminish at a smaller increasing rate of the stress amplitude under the continuously increasing stress. In consequence, ∫(dn/N)>1 is concluded under the stress varying up and down with the long period because of the more effective deceleration effect than the acceleration effect, whilst ∫(dn/N)≈1 is obtained under the stress up and down with the short period because of the mutual offset of the acceleration effect and the deceleration effect.
In discussing the fatigue crack propagation, the stress state and the structure of the material ahead of the crack tip will attract the interest of many researchers. In the present paper, as the first step to evaluate the strength of material at crack tip, the tensile deformation of low carbon steel has been examined by the X-ray micro beam technique and the micro Vickers hardness. The tensile true stress and the natural strain are correlated with the excess dislocation density obtained from the X-ray micro beam observation and micro Vickers hardness. The results obtained are summarized as follows; (1) The excess dislocation density Dm is proportional to the natural strain ε during the deformation from Lüders elongation to about 10% strain, as ε=7.8×10-11Dm. When ε exceeds 10%, Dm does not increase so much as expected by the above equation. (2) The true stress σ is related to Dm in the manner expressed by the equation during the strain ranging from Lüders elongation to about 20% strain, σ=11+5.8×10-4√Dm, where the first term of the right hand side of the equation is considered to be the frictional stress of this material. (3) On the other hand, the frictional stress is found to be derived from the true stress-strain curve by taking the value of stress at zero, the strain obtained by extrapolating the linear work hardening portion just after Lüders elongation of the true stress-strain curve. (4) Micro Vickers hardness HV is related to the natural srain ranging from Lüers elongation to about 10% strain, as HV=84+1.7×102√ε It is worthy of note that the hardness 86 of annealed material is nearly equal to the value 84 which is given by substituting ε=0 into the equation. (5) The following linear relation is established between HV and the true stress σ during the strain ranging from Lüders elongation to about 20% strain. HV=56+2.6σ When the hardness of annealed material is substituted into the equation, the corresponding stress of 11kg/mm2 is obtained which is the same value as the frictional stress given in item (2). This suggests that the initial locking of dislocations in annealed material used in this study which causes yield drop in the stress-strain curve has no influence on micro Vickers hardness. The above mentioned relations will be successfully applied to the investigation on the strength of materials, particularly the strength of small area in specimens such as crack tip of fatigued specimens.
The peak shift and line broadening on 0.06%C steel deformed by tension were measured by means of X-ray diffractometer. These values depended on their diffraction plane. In this paper, the change in peak shift and line broadening on the diffraction line was discussed with reference to its elastic anisotropy. The results are as follows. (1) The change in peak shift on the diffraction line was accounted for by considering that the mean residual stress in the grains in which X-ray diffraction occurred was constant. (2) Also the change in line broadening was accounted for by considering that the distribution of micro-stresses in each grain or between the grains in which X-ray diffraction occurred was almost the same. (3) It seems that it was either because the principal stresses in each grain were γ1≈γ2, or because the specimen in this work had texture, that there was but little line broadening due to the difference in the direction of action of the principal stresses. (4) The mean residual stresses measured from peak shift agreed with that which was obtained by the sin2φ method.
The preparation of graphites has been worked by pyrolysis of propane gas on a directly heated substrate in the vapor phase stirred by a fan. Its formation process and structural features (microstructure, density, and crystal structure) were examined on several samples deposited under various conditions at deposition temperatures of 1440, 1730, 2025°C, gas pressures of 10, 25, 50mmHg, and gas flow rate of 640cm3/min. The effect of stirring vapor phase is appreciable at high temperatures and high pressures. The convection of the decomposed gases or gaseous products disappears in the stirred vapor phase. It follows that the abnormal behavior observed in the pressure range of 20∼30mmHg as described in a previous paper is restored to its normal behavior. The formation process in the stirred vapor phase is discussed in relation to the change in the structural features under the gas pressure.
The principle of stress measurement by X-rays is based on the Hooks law which consists in the relation between the peak shift of the X-ray diffraction line and the magnitude of the stress, applied or internal. It has been noted as a unique method of nondestructive stress measurement of local stress. The X-ray stress measurement is applied in very wide fields of material engineering studies. The stress measured by X-rays, however, depends on the local value of the lattice strain observed in the certain diffracted crystal plane satisfying the Bragg's condition. In this connection, there are some problems regarding the character of X-ray stress measurement, for example, the generation of the lattice strain obtained from the peak shift of certain diffraction line is closely related to the crystal grain size, the deformation mechanism, the crystal anisotropy and other complicated factors. As mentioned above, the X-ray stress measurement of coarse grained materials is inadequate sometimes for the ordinary way as offered by Glocker and Macherauch etc. In other words, the stress measurement of coarse grained specimens is essential from the standpoint of the practical application of the X-ray method. For these reasons, the authors attempted to measure the lattice strain and analyse the stress with coarse grained crystal of aluminum, using the oscillating crystal method, and discussed the errors in the measured value. In this paper, the practical significance of the oscillating crystal method is made clear, and besides, it is concluded that the method is more useful than the divergent X-ray method for the stress measurement with coarse grained materials in the engineering sense. Moreover, when the micro-beam technique is introduced to this method, it is possible to measure the extremely localized stress such as tip of crack or one grain in industrial material. The results are as follows. (1) This camera can be applied to any size of grain under suitable geometrical conditions. (2) To correct systematic errors, it is necessary to use the standard specimens which have two or more diffraction lines on a film. (3) The errors of lattice strain were less than 6×10-5 for undeformed Aluminum. (4) The principal residual stress of a coarse grain in the specimen of 7% deformed Aluminum is σ1=2.5kg/mm2, σ2=0.1kg/mm2 and σ3=-1.7kg/mm2, and their directions agree respectively with that of the tensile axis, of the thickness and of the width.