The development of tensile shearing bond strength in 35 kinds of cold setting epoxy resins have been investigated according to ASTM D 1002-64. The experimental conditions were as follows: The adherend was an atmospheric corrosion resisting steel, the curing period was 1, 2, 4 or 8 days, and the curing was made under the atmospheric condition at 4°C in 65 per cent R. H. or the underwater condition at 4°C. The results show that the tendency of the strength development can be classified into three types; the increase curve type, the decrease curve type and the convex curve type. The latter two types basically belong to the same category because the decrease curve type also must have a peak. Their characteristics have to be improved by the addition of flexibilizer. In all cases, the strength reached a constant level at about 8 days' curing. The value of the strength at the constant level varied from 2 to 124kg/cm2 with the average value of 58kg/cm2 in the case of atmospheric curing, while it varied from 1 to 111kg/cm2 with the average value of 39kg/cm2 in the case of underwater curing. 28 kinds of the epoxy resin systems showed higher strength values in the case of atmospheric curing than those in the case of underwater curing, but other 7 kinds of epoxy resin systems showed the reverse results. The total average of the ratio in the strength between underwater curing and atmospheric curing for all the samples was about 65 per cent.
It has been found in this study that a correlation exists, at 1 per cent level of significance, between logarithmic viscosity and consistency or the degree of easiness of taking out from a vessel for 35 kinds of epoxy resin system of liquid resins and hardeners at 4 and 20°C. The relationship, which can be expressed by the equation “Y=AX+B”, indicates that a good workability is obtainable at the viscosity under 50000cps. The usable minimum temperature was obtained by either interporation or extraporation of the straight line in the plots of logarithmic viscosities against the reciprocal of absolute temperatures to the value of log 50000cps. 10 kinds of the liquid resins and 18 kinds of hardeners have the usable minimum temperature under 9°C. The relation between viscosity and consistency or workability reveals that the widely-used liquid resins such as Epikote 828 have very poor workability at temperatures below 9°C but their workability can be improved sufficiently by the addition of a reactive diluent. In case of hardeners, some kinds of improved aromatic polyamines and some kinds of improved aliphatic polyamines have good workability at temperatures below 9°C. Furthermore, 10 kinds of liquid resins and 10 kinds of hardeners have good workability at temperatures below 9°C, because both the viscosity and its temperature dependence were small enough for these materials.
Although the polymer impregnated concrete (PIC) has such excellent characteristics as high strength, small water permeability, high corrosion resistance and no shrinkage, it has such weak points as low impact strength, no plastic range in strain and low toughness. In the present paper, the mechanical properties of fiber reinforced polymer impregnated concrete have been investigated by using several fibers, made of glass, polypropylene and metal, and MMA-and SM-monomers. The main results obtained are as follows: Among the five kinds of fiber examined, piano wire with 0.2mm diameter and 35mm length was most effective. The strengths of FPIC reinforced by the piano wire were 2003kg/cm2 for compressive, 536kg/cm2 for flexural, 195kg/cm2 for tensile, and 186kg/cm2 for Charpy's impact strength, whereas those of plain mortar cured in water were 593, 73, 36 and 8.7kg/cm2, respectively. And from the fact that the tensile maximum strain at the ultimate strength obtained in repeated bending test for PW-PIC beam 2500×10-6, it is deduced that FPIC-material has large toughness and has far more useful properties than PIC.
An investigation has been carried out to find the effect of diffusion treatment on the fatigue strength of nickel plated steel. The results obtained are summarized as follows; (1) S-N curves indicated that the fatigue strength of the plated steel was slightly lower than that of the bare steel but the fatigue life of the diffusion treated steel was longer. (2) Macroscopic observations on the plated steel revealed that the fatigue crack nucleated under the plated layer, while in the diffusion treated steel the crack nucleation occurred at the surface. (3) By fractographic observations, the stage II type fatigue striation was noticed at the fracture surface of the bare steel, whereas the stage I type patterns, flat and grain boundary facets of the stage I type patterns were noticed in the diffusion treated steel. (4) A possible reason for the fatigue life recovery of diffusion treated steel is considered that the stage I period is prolonged by the effect of the solid-solution strengthening by inter-diffusion of iron and nickel.
The mechanical behavior of the unidirectional fiber reinforced plastics in the nonlinear viscoelastic region was studied on the basis of the nonlinear behaviors of fiber and matrix and the progress of debonding between these components. The fracture criterion of this composite was also determined using the following two conditions, (1) the normal stress in the fiber direction reaches a critical value, (2) the maximum resultant stress of normal stress and shear stress on a plane parallel to the fiber reaches a critical value. Experimental works for uniaxial and biaxial tensile tests were conducted by using the copper fiber-epoxy resin composites having various fiber volume fractions and fiber directions. The good agreements between the calculated and the experimental results were observed for both the stress-strain relations in the nonlinear viscoelastic region and the fracture criterion.
One of the purposes of the present study was to investigate the P-S-N diagrams at stress levels around the ordinary endurance limit, and to discuss the distribution of fatigue lives under constant load. Another purpose was to investigate the effect of variation of stress amplitude by comparing the P-S-N diagrams under the program load of two-stress repeated-block type with those under constant load. Carbon steel S50C and chromium-molybdenum steel SCM4 were used as the specimens and the tests were conducted under cantilever type rotating bending stress. The major conclusions obtained are as follows: (1) P-S-N curves do not reach a constant level but decrease even in the stress region below the ordinary endurance limit. And P-S-N curves tend to bend toward the left at stress levels around the ordinary endurance limit. (2) S-N diagrams are thought to be composed of three H-, F-, and S-curves, each of which represents the S-N relation based on the different failure mechanism. H-curve represents the S-N relation at stress levels well above the endurance limit, F-curve appears at stress levels around the ordinary endurance limit, and S-curve at still lower stress levels. (3) The effect of variation of stress amplitude on the fatigue life appears as the fall of the endurance limit, or the decrease of probability of survival at stress levels below the ordinary endurance limit.
The statistical fatigue properties were investigated for a commercial 0.45%C type carbon steel, most commonly used in mechanical constructions, in order to obtain quantitatively the scatter in fatigue lives and strengths. The fatigue tests were carried out in rotating bending for both smooth and notched specimens which had been subjected to different heat treatments so as to study especially the influence of the resilience of the material on the scatter in fatigue. Since the scatter in fatigue strength was expected to follow a normal distribution in the same manner as those in tensile strength and Vickers hardness, it was possible to obtain the probability fatigue curves (P-S-N curves) by the method proposed formerly3), which consists of shifting the median fatigue strength curve determined by Probit analysis. The variation coefficients of fatigue strength at 107 cycles were 2.1, 2.0 and 4.9% for the normalized, the 600°C tempered and the 350°C tempered smooth specimens, respectively, and 6.4 and 5.4% for the 600°C and the 350°C tempered notched specimens. From the variations in other mechanical properties and the results of microscopic observations of fatigue failure, it is considered that the variation of fatigue strength is particularly great for the 600°C tempered notched specimens, due principally to the variation introduced in the process of fatigue crack propagation.
The stationary viscoelastic properties of general purpose polystyrene (GPPS) and high impact polystyrene (HIPS) melts were measured by means of a screwless extruder. Since the cone rim pressure was not equal to the atmospheric pressure, some theoretical considerations were necessary to derive an approximate relation for calculating the first normal stress difference from the profile of Weissenberg's pressure and the value of pressure at the cone rim. Measurements of Weissenberg's pressure were performed in a stationary state which occurred at 7∼10min after the starting of the rotor and continued for about 5min. The first normal stress difference observed for low density polyethylene (M.I.=2.0, 190°C) showed a fairly good agreement with the literature values. The first normal stress difference for GPPS was slightly greater than that for HIPS at the same shear rate. Some flow properties were measured with an extruder-type rheometer according to both Bagley's and the pressure gradient methods, which gave the same results. The apparent viscosity of HIPS was somewhat greater than that of GPPS at the same shear rate. The rigidity, calculated from the first normal stress difference and the apparent viscosity for HIPS, was considerably higher than that for GPPS at the same shear rate. The correlation between the Weissenberg effect data and the exit pressure data was also examined.