Hereunder is given a report of a new apparatus developed for measurement of fatigue in liquid medium. It is based on Torsion Rheometer (Toyo Seiki Seisakusho Ltd.), and the torsional vibration with constant angular amplitude in liquid medium is made possible. Using a round plastic bar specimen, its change in stiffness during the fatigue was carefully followed continuously by measuring the torsional moment with wire strain gauges. In addition to the torsional fatigue in liquid medium with this apparatus it is possible to evaluate durability by measuring the change of the specimen in stiffness degraded separately. As the results of the experiments it is known that this apparatus is applicable to evaluation of durability in torsional fatigue in liquid medium, but in case there is no remarkable change in stiffness we must keep down the drifting of electronic device as small as possible. This apparatus is applicable to torsional fatigue testing in the atmosphere, water, oil, and chemical reagents at various degrees of temperature.
It is the object of this work to provide a picture of convenient apparatus which enables evaluation of fatigue of plastics in the presence of chemicals. The apparatus is substantially of ASTM D 671-63T (A) Type, and is equipped with devise for trickling liquid chemicals upon the specimen, with an electronic system for continuously recording the dynamic load, and with three pulleys for reducing the speed. The trickling of chemicals is processed by conveying the liquid from the storage tank to a burette and adjusting the stopcock so as to make the liquid drop on the middle portion of the specimen at a controlled rate. The portion is wound with suitable cloth to insure uniform contact of the liquid with the specimen. In the experiments with polyacetal and polyamide in various concentration of hydrochloric acid, the apparatus proved efficient in evaluating fatigue of plastics under the influence of the liquid chemicals.
In order to clarify the fatigue crack initiation mechanism of the annealed and the surface-rolled low carbon steels, the fatigue deformation and crack initiation processes in both the materials have been observed by the X-ray microbeam technique and the electron microscopic replica method, and discussion has been made on the experiment. The following results have been obtained. (1) The behaviors of crystal deformation during fatigue are various in each crystal grains, according to their crystal orientations. But generally, in annealed specimens, total misorientation and micro lattice strain increase highly in the initial stage of fatigue process, and keep on increasing slightly till 80% is reached in fatigue life, but in surface-rolled specimens on the contrary, they decrease. They show also quite different surface structural changes in both the specimens. (2) The formation of distinct subgrain is found after the increase of total misorientation and of micro lattice strain and before fatigue crack initiation in annealed specimens, and is found after their decrease and before fatigue crack initiation in surface-rolled specimens. And in the case of low stress fatigue the presence of subgrain is not so evident as in high stress fatigue. (3) The fatigue crack initiation mechanism is the same both in annealed specimens and in surface-rolled ones. The fatigue crack in both the specimens is formed by jointing the pores in the slip band region on the specimen surface which are considered to have been generated by the diffusion of vacancies, and this jointing action is accelerated by the stress concentration due to the notch-peak formed in the slip band region. On the other hand, the distinct subgrain becomes clear in both the specimens at the fatigue crack initiation. And this fatigue crack is considered to run along the distinct subgrain boundary.
In recent years active researches have been made of nondestructive testing of Fiberglass Reinforced Plastics (FRP), and the following methods have so far been employed for the purpose. (1) The use of X-Rays (2) The use of Ultrasonic Waves (3) The utilization of Temperature (4) The transmission of Light Waves (Infra-Red Rays) (5) Knock Of these the X-ray and the ultrasonic wave methods have been found as respectively useful, and the light wave method, though its practical application has been but little known, has been found as equipped with the following advantages. (1) That it requires simple apparatuses. (2) That it is of easy procedure. (3) That it permits good transmission. These advantages will recommend the light wave method to recognition as most suitable in our present experiment. That was the way the light wave method was adopted for the nondestructive besting of FRP, and the results of its measurements with respect to its strain, glassfiber direction and the number of layers are reported hereunder. The diffraction patterns that were recorded as they took place under stress were given out as the strain of the FRP. The light wave transmission method has given due to the glassfiber direction in the FRP and to the number of its layers by making the light pass through the material. The light wave transmission method is thus confirmed by these results of the experiment as an effective device for nondestructive testing of FRP.
The nondestructive test of Fiberglass Reinforced Plastics (FRP) under stress has called much attention of scientists for investigation of its disintegration by fatigue because the phenomenon of stress-whiting takes place in the test. This phenomenon will thus present significant source for researches. The light wave transmission method will prove more effective than the ultrasonic wave transmission method because the stress-whiting occurs by random reflection. In our experiment, therefore, the light of electric bulbs with tungsten filaments was passed through FRP under stress, and the decrease of the transmitted light was measured. As the relation between the number of cycles and the amount of the transmitted light was obtained in this way, it provides clue to suggest the mechanism of fatigue of FRP. Moreover1) it revealed also the number of the layers and the direction of the glass fiber. The light wave transmission method is thus shown as both practical and effective as well as easily available for nondestructive test of FRP.
The physical properties and characteristics in processing blends of PVC and a copolymer of vinyl chloride and cetyl vinyl ether were studied, and compared with PVC homopolymer. The impact modifier of methyl methacrylate-butadiene-styrene terpolymer gave higher impact strength to the blend than PVC. The impact modifier gave less effect of impact strength on vinyl polymer as the temperature of mixing stock rose. The mixing stock of the blend had less temperature rise due to the lubricant action of the copolymer in the blend. Therefore, it was considered that the effect of the impact modifier on the blend was larger than that on PVC. In injection molding, from the measurements of molding area diagram, the blend had optimum conditions in processing over a wider region than PVC. This was explained by the results that the blend had less pressure loss through injection nozzle and less temperature rise of resin stock due to lubricant action of the component. The draw down of parison in blow molding was measured in case of the blend and PVC. As the temperature of extrudate did not rise, the draw down of the blend was accordingly less than that of PVC.
Hereunder is presented a report of measurements that were carried out of various flow properties in concentrated solutions of polyvinyl alcohol (PVA) by the extrusion technique using short capillaries. As a result, (1) logarithmic plots of the apparent viscosity (ηa) against Newtonian shear rate (γNW) were well approximated with straight lines of slope -2/3 in the shear rate range where ηa decreased with increasing γNW (102-105sec-1). The slope was independent of molecular weight, of concentration of PVA, and of temperature. (2) End correction coefficient for extrusion of concentrated solution of PVA from short capillaries were determined. On the basis of the result, contributions of the Couette correction and recoverable shear strain were discussed. (3) The logarithmic plot of true shear viscosity (ηta) against true shear rate (γtw) was in good agreement with the logarithmic plot of absolute value of the complex dynamic viscosity (|η*|) and angular frequency (ω). (4) It was deduced that an anomalous increase in ηa with the increase of ηNW in a very high shear rate range might be due to the increase in elastic strain in the flowing solution. (5) The applicability of the theory of large deformation was tested employing Zapas' equation together with the relaxation spectra of concentrated solutions of PVA. The calculated shear viscosity was in good agreement with true shear viscosity. (6) The elastic shear strain was estimated from the viscosity data for the aqueous solutions of PVA. With this and the measured diameter of ballooning was determined the coefficient in Spencer's formula which correlated the magnitude of the ballooning and the elastic strain.