In this paper, the relation between Kb value and hardness of aged Cu-Be alloys during the aging process is reported. Four aging temperatures of 250°, 280°, 290°and 310°C were selected, and specimens of A type (without cold rolling) and H type (38% cold rolled) were aged for various aging times. Electrical resistivity, Kb value and micro-Vickers hardness were measured on these aged specimens. Moreover, the integrated X-ray intensities were measured from the diffraction intensity curves of intermediate γ' phase and stable γ phase, and the half-value breadth for α matrix phase was determined during the aging process. It was found that a linear relationship holds between Kb value and hardness throughout the aging process. Furthermore, the optimum aging time to give the maximum Kb values was obtained for four aging temperatures.
The effect of several kinds of pre-treatments on the temperature of diffusionless reverse transformation from martensite to austenite was investigated on an Fe-33%Ni alloy. The main results obtained are as follows. (1) The T0 temperature (=(Ms+As)/2), at which the chemical free energies of austenite and martensite are equal in the alloy, was constant even if the Ms temperature was varied with different austenitizing treatments. (2) The As temperature (starting temperature of reverse transformation to austenite) increased markedly with deformation of martensite. It became clear that the reverse transformation was suppressed with deformation of martensite. However, the Af temperature (finishing temperature of reverse transformation) hardly changed with deformation. (3) Reverse transformation of the ausformed martensite was hardly affected by the degree of ausforming.
The effects of strain history both on the cyclic stress-strain relation and on the shape of hysteresis loop have been investigated on annealed S55C by the constant strain amplitude tests with different mean strains and the incremental step tests. The results are summarized as follows: (1) The cyclic stress-strain curves of the constant strain amplitude tests coincide with each other irrespective of the mean strain in the stationary state of fatigue process, or at a half of the fatigue life. They can be written as Δσ=KΔεpn, where K=338 and n=0.254, when Δσ is taken as the true stress range and Δεp as the logarithmic plastic strain range. The cyclic stress-strain relation in the incremental step tests also has a similar trend as above, being represented by the equation Δσ=KΔεpn, K=317 and n=0.232, when the stationary state is considered to be at half of the number of blocks to failure. (2) For the constant strain amplitude tests, the shape of hysteresis loop in the stationary state is represented, regardless of mean strain, as σ*=Kεp*n*, K*=KΔεpn-n* and n*=0.06Δεp-0.193, where σ* and εp* designate the true stress and the logarithmic plastic strain respectively, with the origin of the coordinates being located at one end of the hysteresis loop. On the other hand, for the incremental step tests, it is written as follows, since n* is observed to be nearly constant; σ*/Δσ=(εp*/Δεp)n*, n*=0.114 The equational difference of the shape of hysteresis loops in both cases has to be discussed carefully in view of some variations of the data obtained. However it may be considered very useful to adopt the latter equation for the incremental step tests, since the mechanical behavior of the material is fully defined from three constants of K, n and n*, which are easily obtained from one specimen.
This paper is concerned with the time- and temperature dependences on the compressive properties of the plain fabric glass cloth reinforced laminates (GRP) and on the tensile properties of the epoxy resins used as the matrices of the GRP. The results obtained are summarized as follows: (1) The master curves of the relaxation moduli for the epoxy resins and the creep compliances for the GRP can be constructed, using their thermo-rheological simple properties. As for the time- and temperature shift factors, they are in good agreement each other quantitatively. (2) It was found that the relation between the relaxation moduli of the matrix and the creep compliances of the GRP at low temperatures in the short time range can be uniquely determined by the rule of mixture for viscoelastic materials, independent of the conditions of their circumstance such as time and temperature. (3) The above-mentioned results (1) and (2) are similar to those obtained in the previous paper concerning with the flexural properties of the unsaturated polyester resins and GRP containing these resins. Therefore, these results seem to hold generally in the stress-strain relations of various GRP under any load conditions. (4) The time-temperature shift factors of the epoxy resin and the unsaturated polyester resin can be approximately expressed by the two Arrhenius equations having different activation energies. The boundary temperatures of the two equations are nearly equal to the glass transition temperatures of the resins.
The drying shrinkage of cement mortars modified by polymer emulsions except polyvinyl acetate emulsion is generally known to be lower than that of unmodified cement mortars. The drying shrinkage depends on the polymer composition and content. The polymer emulsions used as cement modifiers in this study were polymerized in aqueous solution with ammonium persulfate as an initiator, and polyethyleneglycol and surfactant as stabilizers. The tests for the drying shrinkage were carried out by using specimens of 4×4×16cm size and the measurements were made by a dial-gauge. The first part of experiments were performed to determine the drying shrinkage of cement mortars modified with polyethylacrylate. The results used to discuss the relationships between the drying shrinkage and the polymer-cement ratio, water-cement ratio at a constant polymer-cement ratio and the evaporative water loss. The second part of experiments were performed to study the drying shrinkage of mortars with acrylic polymers or copolymers having various glass transition temperatures. The main results are as follows: (1) The cement mortars modified with polyethylacrylate were observed to expand during the initial period of curing, the magnitude of expansion depending upon the polymer-cement ratio, cement-sand ratio and humidity of curing. (2) The close relationship between the drying shrinkage of cement mortars with acrylic polymer or copolymer and the glass transition temperature of polymer was noticeable. (3) The very low drying shrinkage of cement mortar could be obtained by the modification with acrylic polymer or copolymer having very low glass transition temperature.
The rotating bending fatigue tests were performed on the electroless nickel plated steels at room temperature, and the effects of thickness of plating and baking temperature after plating on the fatigue strength were investigated. Furthermore, the characteristics of deposited film itself were discussed. The electroless nickel plating of the specimens used was carried out at 90°C, pH 6, in a plating bath of the following compositions; NiSO4·6H2O: 30g/l; NaH2PO2·H2O: 10g/l; NaC2H3O2·3H2O: 10g/l. The results obtained are as follows: (1) When the electroless nickel plating is carried out on carbon steels, their fatigue strength rather increases, contrary to the case of electro-deposit steels. This improvement is independent of the thickness of deposited film and carbon content of steels. The rate of increase in fatigue strength against non-plated specimens is about 16∼17% for both steels. (2) The electrolessly deposited nickel film shows very satisfactory adhesion to the substratum under fatigue fracture condition. The fatigue damage of plated steels is suppressed by deposited film. Consequently, the nucleation of fatigue crack is delayed, resulting in the increase in fatigue strength. (3) By baking treatment, the micro-hardness of deposited film increases, accompanied with structural changes. This increase is due to the precipitation hardening of Ni3P. At the same time, the tensile residual stress in deposited film is reduced. The rotating bending fatigue strength, however, is not affected. Therefore, it is not expected that the fatigue strength is improved by means of the baking treatment after the electroless plating.
Pulsating tension fatigue tests were made with spot welded and plain specimens of cold rolled steel sheets 1.0mm thick. The breadth of spot welded specimens was 25mm, and the joining types were (a) 1-spot welded single shear splice, (b) 2-spot welded single shear splice and (c) 1-spot welded double shear splice. The fatigue test results of the spot welded specimens were expressed in terms of nominal stress amplitude, which was deduced from the stress distribution of the critical section of each specimen under tension-shear load. Then, the“fatigue strength reduction factor” of a spot welded area, i. e. the ratio between the endurance limits of plain and spot welded specimens, was studied. Reference was also made to the previous results of plane bending fatigue tests with 2-spot welded specimens of single shear splice. The results obtained are as follows: (1) Fatigue fracture initiated in the base metal area adjacent to the nugget and developed transversely for all three welded specimens. (2) The nominal stresses, σn, of the spot welded specimens (a), (b) and (c) were estimated to be 4P/bt, 2.5P/bt and P/bt, respectively, where P is the tension-shear load, b the specimen breadth and t the sheet thickness. They correspond to the average stresses on the interfaces of the critical sections. (3) The fatigue test data of the welded specimens, when arranged on the relation between load amplitude Pa and cycles to fracture N, showed that the load amplitude equivalent to the endurance limit increased by the factor of about two in order of (a), (b) and (c). (4) In terms of nominal stress amplitude σna, the S-N relations of the spot welded fatigue specimens (a), (b) and (c) converged almost on the same level. (5) The slopes of S-N relation under pulsating tension load of the spot welded specimens were considerably steeper than that of the plain specimen, owing to the effect of the stress gradient in the critical area. They were nearly parallel to the slope of S-N relation obtained from the previous reversed plane bending tests on the spot welded specimens. (6) In both present pulsating tension and previous reversed bending tests, the “fatigue strength reduction factor”of the spot welded specimen expressed in terms of the nominal stress, attained to almost the same value (about 1.4), irrespective of the difference in joining type of specimens or loading.
The corrosion behaviors of iron, particularly the initiation and propagation of pits, in hot concentrated NaOH solutions saturated with NaCl have been studied by the electrochemical method and the dipping test. The anodic polarization characteristics of iron in concentrated caustic solutions are affected by the potential sweep rate, in such a way that the larger the sweep rate is, the larger the current density for maintaining passivation is. The data obtained by the steady-state potential step method are found to be most reliable. The threshold of potential for initiation of pitting was estimated as a function of the NaOH concentration. The results show that pitting can be initiated when the NaOH concentration is lower than 5M. On the other hand, pitting may not occur in the higher concentrated NaOH solutions saturated with NaCl, but the uniform corrosion of iron may take place in this case.