The fatigue crack propagation was investigated macroscopically on aluminum alloy 2014 treated at three different heating conditions. The fatigue fracture surface at a notch front was observed with an electronmicroscope and the appearance of shear zone and crack initiation in the notched specimen was discussed fractographically. The fatigue limits of T4 and T6 specimens with solution treatment were higher than that of O specimen without such treatment. All the materials followed the Paris' formula, but a parameter representing the easiness of crack initiation from a notch, which corresponds to the threshold stress intensity factor, was found to increase by the treatment. It was observed by electoronmicroscopy that facets and smooth patterns appeared at the 1st stage of crack propagation on the fatigue fracture surface of T4 and T6 specimens, and a river pattern showing cleavage fracture and striations characteristic of fatigue fracture surface appeared at the 2nd stage of crack propagation.
The strength development properties of epoxy resin mortars were investigated according to ASTM C 190 (tensile), ASTM D 695 (cylinder, compressive) and JIS R 5201 (a little modified, bending). The experimental conditions were as follows: the binder content is 15per cent; the aggregate is sea sand under 2.5mm produced in Nishikioka district; the water content of sand varies in the amount of 0, 1, 2, and 3per cent; the curing time is 1, 2, 4, 8 or 16 days; and three kinds of binders are used in the experiments. All the experiments were conducted in a low temperature room controlled at 4°C, 70per cent R.H. The results obtained were as follows: (1) In case of 3 per cent of water content of sand. The bending and tensile tests showed low strength not suitable for practical use, but the compressive test yielded the strength higher than 300kg/cm2. The addition of 15 per cent of calcium oxide powder to the binder resulted in a rather harmful effect on all the three kinds of strength. (2) In case of 1 or 2per cent of water content of sand. The bending, tensile, and compressive strengths of Epikote 815/Epomate RX3 type epoxy resin mortar developed with considerably good tendencies, and they were exceedingly improved by the addition of 15per cent of calcium oxide powder to the binder. (3) In case of 0per cent of water content of sand. The equilibrium strengths were obtained in the curing times of 1∼4 days (compressive), 2∼4 days (bending) and 2∼16 days (tensile) for these 3 kinds of epoxy resin mortars. It was found that the strength development was improved with decreasing the water content of sand.
The constitutive equations of the cubic anisotropic plastic materials are generalized to satisfy the principle of material frame-indifference. The constitutive equations obtained in accordance with the requirement for the plastic flow state are assumed to hold in all states, i.e., the natural unstrained state and the plastic flow state. As an example, the simple extension of the materials is analyzed, and the stress-extension relation is obtained. The result shows a gradual transition from the elastic state to the plastic flow state. The comparison between cubic anisotropic and isotropic materials is discussed briefly.
In the evaluation of the photo-oxidation of plastic materials, little discussions have been made on the correlation between the physical properties and the change of chemical structure during the photo-oxidation. We have previously studied the kinetics of the photo-oxidation of poly (vinyl alcohol) and reported that the scission and crosslinking of polymer chain are frequently accompanied with the formation of carbonyl groups. The present report deals with the correlation of the carbonyl group content of the photo- oxidized poly (vinyl alcohol) with the temperature dependence of the electrical conductivity and the frequency of the scission of the polymer chain. The results obtained are as follows (1) The absorption peaks of intramolecular band (3275cm-1), α, β-unsaturated aldehyde (1682cm-1), ester (1165cm-1) and trans ethylene (965cm-1), all of which are absent in case of solid phase photo-oxidation, are observed during the liquid phase photo-oxidation. The easiness of formation of carbonyl groups is in the order of ketonic, aldehydic, acidic and esteric type in the first stage of the photo-oxidation, and in the order of aldehydic, ketonic, acidic and esteric in the later stage. (2) In the liquid phase photo-oxidation, dehydration occurs first and the photo-oxidation is remarkably accelerated by the chain scission and crosslinking which have resulted from the formation of carbonyl groups. Also, the keto-enol tautomeric structure appears as the photo-oxidation proceeds. (3) Scission of polymer chain is considered to be random from the results of the change in the number average of polymerization degree with time. (4) The rate of mean molecular scission exhibits two stages in the course of photo-oxidation, being closely related to the formation of carbonyl groups (aldehydic, ketonic and acidic type). (5) A good correlation exists between the mean molecular scission and the carbonyl concentration. As the activation energy of chain scission is in fair agreement with that of the formation of carbonyl groups, the chain scission seems to be associated with the formation of carbonyl groups. (6) The temperature dependence of volume electrical current exhibits a three-step change. The variation of volume electrical current calculated from this change is found to be related with the carbonyl concentration. This may arise from the generation of electron carriers as carbonyl groups are formed and their migration along the π-electron system with the hopping mechanism. This result seems to indicate the possibility of electronic conduction in addition to the usual ionic conduction in the photo-oxidized poly (vinyl alcohol).
The relationship between lower yield stress and strain rate has been measured on a low carbon steel at various temperatures. The results obtained are summarized as follows: (1) Deformation twins were observed in Lüders band under the condition of low temperature and high strain rate at which the lower yield stress value was over 50kg/mm2. The slope in the logarithmic plots of lower yield stress against strain rate in the range where the deformation twins were observed during propagating Lüders band was lower than that without a deformation twin. (2) In the range of temperature and strain rate where no deformation twin was observed, the relation between lower yield stress and strain rate in logarithmic plots was represented by a straight line having only one or two slopes over the strain rate of 10-5∼102 1/s at a constant temperature. (3) The fact that the slope of the above straight lines at a constant temperature depends upon the strain rate may be caused by the disagreement between the Lüders band front velocity and the cross head speed.
Aluminium is, in general, being used as a light structural material, but the demand for light structural materials with better mechanical properties than aluminium is increasing more and more recently. Such demand may be satisfied with the hybrid CFRP-Al construction. This paper is concerned with the bending strength and the fatigue strength of the hybrid CFRP-Al construction which is made of the combination of aluminium and carbon fiber reinforced plastics (CFRP). The results obtained are as follows: Hybrid-A, bonded with Redux BSL 408, has shown about 2 times the bending strength of aluminium, and hybrid-B, bonded with Redux BSL 308, has shown about 1.4 times. On the process of fatigue, the rigidity of aluminium decreases suddenly just before the rapid fatigue failure, but the rigidity of hybrid CFRP-Al gradually decreases with increasing the number of cycles to failure. As for the mode of fatigue failure, it is shown that the failure of aluminium is due to the separated breaking, but that of hybrid CFRP-Al is due to the interfacial failure at less than 104 cycles and to the development of microcracks formed in aluminium part at higher cycles. Both hybrid-A and-B have shown about 2 times the fatigue strength of aluminium, and therefore it is considered that the fatigue strength of aluminium is improved by the hybrid construction. It is also found that the calculated value of (σHy)f/(σc)f, the ratio of fatigue strength of hybrid CFRP-Al to that of aluminium, is in good agreement with experimental results.
The relation between TRIP phenomenon and the amount of residual austenite was examined by means of tensile test at various temperatures using Fe-30%Ni-0.2%C specimens containing 13%, 41%, 76% and 100% austenite. The main results are as follows: (1) The TRIP phenomenon was observed and the maximum elongation (δmax) increased linearly with volume fraction of austenite, when the amount of austenite was more than 41%. In case of 13% austenite, however, the TRIP was hardly observed. (2) The peak temperature of elongation by TRIP decreased with decreasing the amount of austenite. (3) In case of the tests at temperatures accompanying TRIP, the serrations caused by the formation of strain-induced martensite were observed in the stress-strain curves of the specimens containing more than 76% austenite. (4) When the austenite was more than 76%, the phenomenon that 0.2% proof stress drops at temperatures around Ms was observed.
Three kinds of theoretical methods based on (a) an extended empirical formula with a contiguity factor, (b) an approximate averaging method and (c) a finite element method, were proposed to predict the elastic constants of high performance carbon fiber reinforced plastics taking account of the anisotropy of carbon fiber itself. The fibers were assumed to be distributed in hexagonal or square arrays in the analyses (b) and (c). Experiments by three kinds of loading, that is, axial tension, circumferential tension and torsion, were carried out to measure the anisotropic elastic constants of two kinds of filament-wound cylindrical specimens reinforced by two different carbon fibers. Through these experiments, the anisotropy of carbon fiber was quantitatively estimated and the theoretical elastic constants based on these values agreed well with the experimental values obtained on the herically wound and laminate specimens. It can be concluded from this work that (1) the anisotropy of carbon fiber is extremely large, i. e., the transverse modulus is about one fifteenths to thirtieths longitudinal modulus, (2) the analysis assuming the square array of fibers give larger elastic rigidity than that for the hexagonal array, and (3) all of the three proposed theoretical methods give nearly the same values, so that the analytical method such as (a) or (b), which gives the solution in closed form, can be conveniently used in estimating the elastic constants of composites with arbitrary composition and in evaluating the quantitative effect of elastic characteristics of the constituent materials on them.
Although it is well known that brittle lacquer coating of air-drying type is superior in experimental stress analysis to the baking type, brittleness of the former is markedly dominated by both basic ingredients and solvents whose effects are rather complicated. Few studies have been made on solvents for lacquer coating, and recently it becomes more necessary that they should be of low toxicity and non-flammable in order to prevent peril in practical use. The authors have principally investigated, therefore, the dependence of the brittleness, which is proportional to the strain sensitivity of the coating, on several solvents having a variation in the properties such as solubility parameter, evaporating rate, azeotropy to water, noxiousness, blushing and others. As the result of the study the following facts have been obtained. The threshold strain sensitivity of the coating is essentially determined by the solvent used, so that it is impossible to improve the sensitivity even if the formula of basic ingredients is made to vary. The sensitivity is inversely proportional to the specific volume of the coating which decreases as the fine crystallization of abietic acid employed as a basic ingredient takes place. The coating using carbon disulfide does not show any crack development in the direction of the principal stress on the surface of the specimens, but it easily blushes during application. Low toxic and non-flammable trichloro-ethylene is most satisfactory among the solvents tested although it is inferior to carbon disulfide in regard to the strain sensitivity.