Revolution of technique to process fiberglass reinforced plastics is urgently required by the following situations. (1) The principal industrial concerns in Japan have begun to take interest in this field of industry to meet the expansion of its market. (2) The hand work must give place to mechanical operations in view of shortage of labor. (3) Automation is general tendency in the industrial world. In order to show how revolution is required to meet these situations the present state of fabricating technique of FRP is represented at length in this paper.
The relation of complex modulus of elasticity to the deflection or the strain of a viscoelastic cantilever under forced vibration was explained mathematically. The deflection of the beam was expressed as a complex number, and we could understand the amplitude and the phase difference from the applied force. With this deflection diagram, the loss factor of the tested material was defined. To find the viscoelastic properties of glass fiber reinforced plastics, the real part and the imaginary part of the complex modulus of elasticity were measured at various temperatures, using polyester resin reinforced with glass fiber roving cloth and polyvinyl chloride resin reinforced with glass fiber mat. The values of the loss factor of these materials were about 0.01∼0.2, under various conditions of this study. Generally, the viscoelastic behaviour of the materials became more viscous in accordance with the rise of temperature. The rich content of glass fiber made the materials more elastic and resistible against heat, and the value of loss factor decreased. These effects mainly depended upon the fibers lying parallel to the direction of the stress.
The fatigue tests have been carried out with glassfibre reinforced plastics composed of laminae of various types, such as chopped strand mat, cloth, and roving. The criterion of the fatigue failure is found to be the strain amplitude in the outmost layer. Provided that the rigidity of the FRP of combined laminae and the allowable strain amplitude of the outmost layer are known, the fatigue strength of the combined FRP is to be obtained, though the second layer seems to have a little effect. When the inner layer has considerably lower strength than the outmost layer, the fatigue failure is initiated in the inner layer even under bending fatigue. In this case, the criterion is the strength of the inner weak layer, but the adjoining layers have some effecct on the fatigue strength of the combined FRP. When cloths are used for the outmost layer and their warps have a large angle with the load direction, the layers are hardly expected to have strengthening effect.
Static tensile tests and low cycle fatigue tests up to 10000 stress cycles under pulsating tension were carried out on plate specimens of glass fiber reinforced plastics. The test plates (340× 280×3.12∼4.13mm) were made by laying up with hand 16ply plain woven cloth of glass fiber. The test pieces were cut off with a hand saw from these plates at first in line with the warp and then at its angle of 45°. The following results were obtained from these tests. (1) In the case of the test pieces loaded in line with the warp, the tensile strength does not vary if the breadth of the test pieces is more than 4mm, but in the test specimens loaded at the angle of 45° of the warp, the tensile strength increases linearly with the breadth up to 12mm, and is constant when the breadth is more than 12mm. (2) The S-N curves under low cycle faigue up to 10000 stress cycles can be represented by straight lines, and the fatigue strength at any cycles of N loaded in line with the warp is expressed in the following empirical formulas: for the plain specimen σ=σB-3.3log10N for the notched specimen σ=σBK-2.0log10N where, σB: tensile strength of plain specimens, σBK: tensile strength of notched specimens. (3) The fatigue notch factor considered for the fatigue strength at N cycles increases when the stress cycles decreases, and the fatigue notch factor at one cycle, i, e. at tensile strength reaches its maximum. (4) The fatigue notch factor for the specimens loaded in line with the warp reaches its maximum when the notched specimen has the radius of 6mm. (5) The fatigue notch factor for the specimens loaded at the angle of 45° of the warp is less than the unit.
The fracture strength of filament-wound composite structure can be determined by relating the fundamental strength of the unidirectional reinforcement materials to the three-dimensional stress components on a plane which contains fibers. The object of the present paper is to report the experiments intended to find the values of the fundamental strength of the unidirectional filament-wound materials which correspond to the three kinds of fracture mechanisms, glass-epoxy filament-wound composites have been used for specimens. There has yet been no established method for the experiments. Our experiments have therefore been carried out to find the fundamental strength against the tensile strength in line with the fibers, that against the tensile strength at right angle to the fibers and that against the shearing strength at the fiber-matrix interface. In the experiments concerning the shearing strength, special attention has been paid to examining the effects that the angle of the shearing to the fibers and the normal stress will have on the shearing strength. These are important factors for determining the exact fracture strength according to the three-dimensional stress analysis. The fundamental strength of the unidirectional composite materials will also give clue to determining analytically the fracture strength of the helically wound cylindrical tubes under axial tension, under internal pressure, and under torsion, showing good agreement with the experimental values of on the glass-epoxy specimens. The detailed description regarding these fracture strengths will be reported in the forthcoming papers.
The fracture strength of helical-wound composite cylinder under axial tension is discussed. The three-dimensional elastic stress components on the planes which do not intersect the fibers are analysed by use of the in-plane stress components in each layer. Then, in order to determine the tensile strength, they are related to the three kinds of fundamental strength of unidirectional fiber-reinforced composites obtained experimentally. The axial tension tests are carried out on glass-epoxy cylindrical composites which are helically wound at various sorts of winding angle. The experimental results on fracture strength including elastic moduli are found to be in good agreement with the analytical results which take into account the yielding of matrix before fracture. Based on the similar concept discussed here, the fracture strength under torsion and internal pressure can also be analysed showing good agreements with experimental results and they will be reported in the forthcoming papers.
In the previous paper of the author, the rolling friction under line contact and the lifetime of the rolling cylindrical body were discussed. In the present paper the experimental results of rolling friction in the case of point contact and the lifetime of the rolling body under static load and oil lubrication are presented on the basis of the information of the previous paper. In the present paper the characteristics of rolling friction in both cases of line and point contact is also reported by use of #60 spindle oil and jet fuel oil (JP-4), respectively. From the present study the following conclusions have been obtained; (1) The characteristics of friction under point contact and the lifetime of the rolling body are nearly the same as those under line contact. The strength of the oil film and the maximum pressure of rolling fatigue limit under point contact are larger than those under line contact. (2) In the case of point contact, there is small difference between the characteristics of rolling friction by use of #60 spindle oil and that of jet fuel oil, but larger difference in the case of line contact.
The present study has been made to clarify the effect of lubricant for press-fitting upon the rotatingb ending fatigue strength at the press-fit. White zinc paint, epoxy resins, molybdenumdisulfide are used for lubricants, and the shrink-fitted specimens have also been tested. The results obtained are as follows. (1) Molybdenumdisulfide is slightly effective to increase the fatigue limit based on the complete fracture, σw2. (2) Epoxy resin increases the fatigue limit based on the crack initiation, σw1, by about 30% as compared with the usual zinc paint.
To perform a series of X-ray studies on low-cycle fatigue, the failure process of a pre-pulled 0.16%C steel under constant strain cycling was observed with X-ray diffraction technique. The results obtained in this study are as follows: (1) The specimen pulled to 17% after preliminary annealing exhibited cyclic strain-softening in the first half of its fatigue process under the strain range of 2.0% without mean strain. (2) The integral breadth of diffraction peak decreased with the progress of strain-softening. It was established by a profile analysis of diffraction peak that the increase in particle size decreased its integral breadth. (3) During the process of strain-softening, the diffraction spots in the micro-beam Debye-Scherrer ring became fine and sharp. This microstructural change together with the result mentioned above in (2) revealed the fact that mechanism of strain-softening in low-cycle fatigue was the annihilation and rearrangement of dislocations produced by pre-tension. (4) The failure process of the cyclic-softened specimens consisted of two stages, the first was the stage of development of surface roughness, and the last of the growth and multiplication of the cracks. (5) Good correlation was found between the integral breadth and the extent of hardening in cyclic hardening and-softening processes. (6) The hypothesis, that the surface roughness increased, while the cracks decreased, the integral breadth, would account for the mode of change in the integral breadth occasioned by the low cycle fatigue both of the cyclic hardened specimens and of the cyclic softened specimens. It was possible on that account to make clue of the integral breadth to detecting the fatigue damage like surface roughness and cracks.