X-ray broadening measurements were performed on various fracture surfaces by using a parallel beam method. A large X-ray exposed area (2×5mm2: the counter method and 1mm in colimeter diameter: the film method) was employed to eliminate the crystalographic local data scattering which would appear if a small X-ray exposed area (such as the microbeam method) were used. The following results were obtained. (1) X-ray broadening can be expressed as a function of fracture stress intensity. In the case of fatigue crack propagation, the broadening depends on the stress amplitude rather than the maximum stress. In the case of program load fatigue, it depends on the stress amplitude that caused a larger crack propagation area. (2) A quantitative analysis can be carried out even though fracture is the intergranular crack type. Also, this method is applicable even for the fatigue fracture analysis on the surface having no striation. (3) This method is effective even for slightly corroded fracture surfaces on which only the corroded surface film is detectable by the scanning electron microscope.
The influence of deformation sub-structure on tensile properties was investigated on pure aluminum (99.9%) having the deformation sub-structure of various sizes formed by varying the amount of tensile prestrain. The results obtained are summarized as follows; (1) When the angle of misorientation between sub-grains varies with the sub-grain size, the flow stress increases parabolically with the inverse square root of the sub-grain size; and so Petch's relation does not hold true. (2) When the angle of misorientation between sub-grains is constant independently of sub-grain size, Petch's relation holds true between the flow stress and the sub-grain size. (3) The flow stress σf is proportional to the product of the square root of misorientation α and the inverse square root of the sub-grain size t, as expressed by a linear equation σf=σ0+KMα1/2t-1/2. (4) The flow stress σf increases with increasing excess dislocation density Db. This relation can be expressed by a linear equation σf=σ0+α'GbDb1/2 which is of the same form with that derived from the work-hardening theory. (5) The tensile strength could be expressed by a linear function of the inverse square root of the sub-grain size.
A stress measurement technique was developed in order to reduce the disturbance caused by electromagnetic field. Using this technique, a series of short circuit tests were carried out on 21000kVA two-pole turbine generators. The stress and displacement induced on the stator end windings were examined under various short circuit voltages. The mechanical strength of the stator end windings was discussed in comparison with the measured stress and the bending strength of stator windings and was also discussed in relation to the variations in tangent delta and breakdown voltage characteristics. The results obtained are as follows. (1) The stress measurement technique developed in this study is effective for the stress measurement on electric appliances which are exposed to strong magnetic field. (2) The stator end windings can be bent repeatedly tangentially in the direction to increase the stator end windings' curvature and radially in the opposite direction to the rotor. (3) The maximum amplitudes of stress and displacement of the stator end windings increase in proportion to the square of short circuit voltage. But they depend on the magnitude of the direct component in short circuit current and tend to increase with it. (4) When the direct current component appears relatively large, the predominant frequency of the stress and displacement is 60Hz, but with decreasing of direct current component 120Hz frequency becomes predominant. When it is small, 120Hz frequency is predominant. (5) It is considered that within this test condition there is no mechanical damage which would cause the reduction of electric characteristics under further service operation.
Recently, adhesive techniques are widely used for fiber reinforced plastics (FRP) constructions from the requirements of a large size structure and efficiency of constructions using a parts system. The adhesive strength of FRP has been examined for carbon and boron FRP, which have high strength and high rigidity, to meet the demand for the usage in an aircraft. But studies on the glass/polyester FRP adhesive constructions used widely in various areas have not been carried out extensively. This paper reports the adhesive strength and stress distributions of FRP adherents, which are constructed with glass/polyester FRP adhesive joints. The configuration of adhesive joints used was of a single lap construction and they were loaded with tension-shear to consider the pure shear stress at the adhesive layers. The measurements of stress distribution were made with electric strain gages and moiré method. The bending moment and yielding at FRP adherents were investigated on these FRP adhesive joints. Three kinds of adhesives used were hard type polyester (widely used for FRP adhesive constructions), soft type polyester and epoxy-polyamide, and the shear strength of these adhesives was examined. Then, the factors affecting the strength of adhesive FRP joints subjected to bending loads, such as the dimensions of adhesive joints and the shear strength of these adhesives, were discussed.
The relation between transition behaviour and temperature has been examined on a low carbon steel at various bending speeds. The results obtained are summarized as follows: (1) Three transition temperatures, TD, TG and TB, are noticeable in the bending resistance-temperature curves constructed from the load-deflection curves. (2) The shape of the bending resistance-temperature curve does not change with bending speed. However, the range of transition temperature shifts to high temperature with increasing bending speed. (3) The relation between the transition temperatures (TD, TG, TB) and bending speed, V is represented by the following equation, 1/Ti=ai-bilogV where a and b are constants and i is D, G or B. (4) Fracture loads, PD, PG and PB, seem to be independent of bending speed. (5) Micro-cracks may be formed by applying the stress above a certain value at the root of notch in the temperature range above TB, and it is considered that the brittle fracture occurs through the process of instant growth and coalecence of these cracks. (6) Micro-cracks can not be observed in the vicinity of fracture surface below TB.
In the two previous papers, the authors discussed the effect of a single high tensile load applied prior to stress cycling or during stress cycling on fatigue strength. In the present study, the effect of periodic high tensile loads on the rotating bending fatigue strength of 0.33% carbon steel were investigated. The main conclusions obtained are summarized as follows: (1) In the case of the high tensile load σH=39.5kg/mm2 corresponding to the lower yield point of virgin specimen, the S-N curve bends slightly to the side of shorter life at the stress near the fatigue limit of virgin specimen. (2) In the case of the high tensile load σH=60.0kg/mm2 corresponding to 8.7% true strain of virgin specimen, the fatigue life is shorter than that of σH=39.5kg/mm2 and the S-N curve bends abruptly to the side of shorter life at the stress near the fatigue limit of virgin specimen. (3) The effects of frequency and sequence of high tensile loads are not found. (4) In the case of the high tensile load σH=39.5kg/mm2, the fracture surface of specimens exhibits fatigue fracture surface, while in the case of σH=60.0kg/mm2 it shows fatigue fracture surface above the S-N diagram's nose but local contraction fracture surface below that point. (5) In most cases the values of the cumulative cycle ratio are very small.
Up to the present, little is known on the effect of the surface layer hardened by machining on the fatigue strength of steel and the condition to remove such surface layer by low temperature annealing in vacuum. In the present study, the effect of annealing in vacuum on the rotating bending fatigue strength of three kinds of carbon steels (S15C, S35C and S55C) was investigated in order to clarify the above mentioned matters. The results obtained are as follows: (1) The surface layer hardened by machining seems to increase the fatigue strength at relatively large N, and decrease the fatigue strength at relatively small N. This tendency is remarkable in the case of S15C and S35C. (2) In order to remove the surface layer hardened by machining completely without any decrease in its fatigue strength (probably due to growth of grains) by low temperature annealing in vacuum, the annealing at a temperature a little higher than 650°C, 650°C and a temperature considerably lower than 650°C for 1 hour are suitable for S15C, S35C and S55C, respectively.
Mechanical degradation in polyacrylamide (PAA)/water mixtures have been studied by using a homomixer at room temperature. The degree of degradation was determined by measuring the number-average chain length at various stages of mechanical degradation. It was found that the rate constant of mechanical degradation (kS) decreases with the degree of polymerization of PAA at the initial stage of the degradation. From the effect of pH on the degradation of PAA, the maximum rate was obtained at pH 10-12. Mechanochemical polymerization in PAA/acrylamide (AA)/water mixtures have been also studied by stirring the mixtures vigorously with a homomixer. The initial rate of polymerization (Rp) was found to be expressed by Rp=k[PAA]2[AA].
Degradation of polyester resin mortar has been studied by using unsaturated polyester resins having different resistances against boiling water, and by measuring the change in flexural strength during the course of soaking in boiling water, in order to clarify the relation between the resistances of the polyester resin mortar and the unsaturated polyester resin used against boiling water. The results showed that the resistance of the resin mortar against boiling water depends mainly on that of the unsaturated polyester resin used, although some effects of adhesion of the unsaturated polyester resins to natural silica sand and calcium carbonate are also present.
The effect of incorporation of calcium carbonate (CaCO3) on degradation of mechanical properties of a cured unsaturated polyester resin (UP)-CaCO3 system in boiling water has been studied. The results showed that the incorporation of CaCO3 increased remarkably the retention of flexural strength but decreased the retention of flexural modulus of the above system under the soaking condition in boiling water, while the incorporation of CaCO3 decreased the initial flexural strength but increased remarkably the initial flexural modulus of the system. A mechanism of the degradation in boiling water was proposed that the decrease of flexural strength was mainly due to the degradation of UP component and that of flexural modulus was due to absorption of water into the interface between UP and CaCO3. Accordingly, the increase of CaCO3 content which caused dilution of UP content increased the retention of flexural strength but decreased the retention of flexural modulus due to the increase of the interface between CaCO3 and UP.
The effect of the amount of calcium carbonate (CaCO3) on water absorption of the cured unsaturated polyester resin (UP)-CaCO3 system in boiling water has been studied and the correlations between the retentions of flexural strength and modulus and the water absorption of the system were discussed. When the samples were soaked in boiling water, the water absorption decreased with an increase of CaCO3 content at first, became maximum at a certain CaCO3 content and then decreased with an increase of CaCO3 content. This phenomenon suggests the two effects of CaCO3 that the incorporation of CaCO3 lowers the water absorption at a short period of soaking but raises the water absorption at a long period of soaking. Both of the retentions of flexural strength and flexural modulus decreased with an increase in the water absorption, but the incorporation of CaCO3 reduced such decreasing tendency of the retention of flexural strength, while it promoted that of the retention of flexural modulus. From these results, it is proposed that the decrease in UP content resulting from the increase in CaCO3 in the system causes the reduction of water absorption by UP and suppresses the decrease in retention of flexural strength, while the increase in interfacial area by the increase in CaCO3 content promotes water absorption at the interface and, thus, accelerates the decrease in the retention of flexural modulus.
The effects of various fillers incorporated in the unsaturated polyester resin (UP)-filler system on resistance against degradation in boiling water have been studied. The results are summarized as follows. The incorporation of fillers in UP improved the retention of flexural strength of the system in boiling water, while it deteriorated that of flexural modulus in a short period of soaking in boiling water but improved that in a long period. The initial flexural strength was decreased markedly but the initial flexural modulus was considerably increased by the incorporation of fillers. The behaviors of the flexural strength and modulus of the system during soaking in boiling water could be explained by the combination of these two effects, that is, the latter effects are predominant in a shorter period of soaking but the former effects take over in the course of soaking. The incorporation of fillers in UP reduced the water absorption of the system. The increase in water absorption lowered both the retentions of flexural strength and modulus. The extent of the decrease in the retentions became smaller for the flexural strength but larger for the flexural modulus, compared with those of UP without fillers. The effects mentioned above varied depending upon the kinds of fillers used, but their tendency was similar. The above results of the degradation of the UP-filler system in boiling water can be explained by the same mechanism proposed in the previous paper by the present authors for the degradation of the UP-CaCO3 system.