This paper describes the irradiation effects on the tensile characteristics of welded polyethylene. Low density polyethylene plates, 2mm in thickness, were used in this experiment. These polyethylene plates were welded by means of a semiautomatic heating plate welding apparatus and exposed to various irradiation doses of neutron. Examination of X-ray diffraction pattern and measurement of X-ray diffraction intensity were made during tensile test of the welded part of neutron irradiated polyethylene. It was found that the irradiation effects on the welded part are similar to those on the base material of polyethylene and molecular orientation tendency during tensile test is restrained with increase of irradiation does.
Stress and deformation of metals during quenching were analyzed in the framework of thermoplasticity. The kinetics of phase transformation, such as the formations of martensite and pearlite from austenite were estimated by adopting the continuous cooling transformation diagram, and the dilatations due to the transformation as well as the temperature change were introduced to the constitutive equation of metals to take into account the effect of quenching. A finite element analysis was carried out for the calculation of stress and deformation, and the comparison of the calculated results with the experimental data for two types of steels were discussed.
Specimens of annealed and cold-rolled 99.99% pure aluminium were fatigued under completely reversed plane bending. The effect of stress amplitude on the crystal deformation during the fatigue process was investigated by using the X-ray microbeam diffraction technique and optical miroscopy. The results are summarized as follows: (1) Fatigue strength increases as the reduction of thickness increases. (2) Configuration of slip bands in the cold-rolled specimens, at high stress amplitudes, is similar to that in the annealed specimens. At low stress amplitudes, however, slip bands become coarse in the specimens of low reduction, and discontinuous or island-like in those of high reduction. (3) Both in the annealed and the cold-rolled specimens, substructures are developed during the fatigue process. The amount of crystal deformation is dependent on stress amplitude. In the annealed specimens, the total misorientation β and the excess dislocation densities (Db)max and (Db)min increase while the subgrain size t decreases with increasing stress amplitude. On the other hand, in the cold-rolled specimens, β, (Db)max and (Db)min increase and the subgrain size lessens only when stress amplitude exceeds a certain critical value, which augments with decreasing thickness. (4) In the annealed specimens the excess dislocation density in the grain (Db)min is correlated to stress amplitude by the following equation. σ=0.49+1.15×10-4√(Db)min In the cold-rolled specimens, when stress amplitude is higher than the value calculated by substituting the excess dislocation density in the grain (Db)min due to cold-rolling into the above equation, the dislocations in the subgrain being rearranged, “fatigue-induced recovery”takes place and furthermore the substructure is well developed. On the contrary, when stress amplitude is lower than that, only the rearrangement of the pre-existing dislocations in the subgrain comes to be the principal crystallographic deformation during the fatigue process and the fatigue-recovery is not so remarkable as at high stress amplitudes.
Low cycle fatigue tests at elevated temperatures under several types of saw-tooth wave strain cycling were carried out on two steels, a low carbon steel and an austenitic stainless steel, in order to investigate the effect of the difference in strain rate between tension going and compression going periods on the fatigue life. For both steels, the fatigue life was found to be longest under the strain cycling with equal tension going and compression going periods, and it became shorter as the difference between the two periods became larger. These results of fatigue life can be explained by the following damage concept. The fatigue damage in one cycle Δφ, which is defined as the inverse of the cycle number to failure, is given by the equation: Δφ=(Δφ'+Δφ")/2+η(Δφ'-Δφ")/2, where Δφ' and Δφ" are the values calculated from the tension going and compression going strain rates by using the relation between strain rate and fatigue life under triangular wave strain cycling. The intensity parameter η in the second term depends only on the condition whether the tension going period was longer or shorter than the compression going period.
In-phase- and out-of-phase-thermal fatigue tests under several combinations of the minimum and the maximum cycle temperatures were carried out on a low carbon steel and 304 stainless steel, in order to investigate the effect of the difference in temperature between the tension going and compression going periods on the fatigue life. In the study, the maximum cycle temperature T2 and the minimum cycle temperature T1 were regarded as the temperature in the tension going period and that in the compression going period, respectively, in the case of in-phase thermal fatigue, because a tensile plastic strain was induced at the temperature close to T2 and a compressive plastic strain at the temperature close to T1. For the similar reason, T1 and T2 were regarded as the temperature in the tension going period and that in the compression going period in the case of out-of-phase thermal fatigue. For both steels, the thermal fatigue life was found to be longest under the strain cycling at T1=T2 (i.e., isothermal fatigue), a larger difference in temperature between the two periods gave the shorter fatigue life. The results of the thermal fatigue life obtained were summarized by the following damage concept. The thermal fatigue damage in one cycle Δφ, which is defined as the inverse of the cycle number to failure, can be given by the equation: Δφ=(Δφ'+Δφ")/2+η(Δφ'-Δφ")/2, where Δφ' and Δφ" are isothermal fatigue damages at the temperatures equal to those in the tension going and compression going periods of thermal fatigue. The value of parameter η is about 7.9 in the case of in-phase thermal fatigue and about -4.2 in out-of-phase thermal fatigue, which seems to be independent not only of the cycle temperature condition but also of the material.
Grain boundary sliding (GB sliding) and grain boundary cracking in both isothermal fatigue under saw-tooth wave strain cycling and thermal fatigue were investigated on 304 stainless steel, in order to elucidate the physical meanings of the damage acceleration under these types of fatigue conditions found in the previous papers. In isothermal fatigue under saw-tooth wave and thermal fatigue, GB sliding was found to be accumulated in nearly proportion to the number of strain cycles, contrary to the case of isothermal fatigue under triangular wave where the accumulation of GB sliding was negligibly small. The direction of GB sliding accumulation both in isothermal fatigue under slow-fast saw-tooth wave and in-phase thermal fatigue was characterized as to induce the tensile residual strain of the specimen, while the direction both in isothermal fatigue under fast-slow saw-tooth wave and out-of-phase thermal fatigue was contrary. Grain boundary cracking was frequently observed in the vicinity of triple points or ledges on the grain boundary which accommodated the strain concentration due to GB sliding, and the higher amount of accumulation of GB sliding caused the earlier initiation of grain boundary cracking. Based on these metallurgical findings, it is concluded that the acceleration of fatigue damage is closely related to the accumulation of GB sliding.
Fatigue tests were carried out on S15CK tufftrided specimens at room temperature, 100, 300, 400, and 500°C under reversed axial stress. The results obtained were summarized as follows; (1) The fatigue limit of tufftrided steel at room temperature is about 1.4 times the value of untufftrided one. (2) The fatigue strength of tufftrided steel at 300°C is higher than that at room temperature, but when the temperature is over 300°C, the fatigue strength becomes lower that at room temperature. The fatigue strength at 500°C is close to that of untufftrided steel at room temperature. (3) The hardness of tufftrided steel increases after the fatigue test at every temperature tested. Especially, the increase in hardness is remarkable at the core of specimen. (4) The microstructural observation after the fatigue test at 300°C revealed a remarkable precipitation of nitride from the position 1mm inside of the surface to the center of core.
The effect of prestrain on the relationship between non-ductile transition temperature and bending speed has been examined on a low carbon steel. In this experiment, the V-notched specimens of sharpy type were used and they were prestrained by bending at room temperature before the test. The amount of prestrain at the notch root was estimated by the micro-hardness method. The results obtained are summarized as follows: (1) In the case of a constant bending speed, the non-ductile transition temperature rises with increasing the amount of prestrain at room temperature. (2) The relationship between the non-ductile transition temperature TB and the bending speed V is represented by the following equation, 1/TB=a-blogV where a is dependent on the amount of prestrain and b is a constant. (3) It is assumed that the cleavage fracture at the bending test is caused by the same dislocation piled-up mechanism as that of the tensile test6).
The effect of specimen length on tensile strength has been examined by the statistical theory of the tensile strength using a small size of data in the previous report. The results obtained are summarized as follows. (1) The mean value σM of tensile strength decreases with the increase of specimen length l, as represented by the following equation: where σM=αl-b σM=α1l-b for l≤ls σM=α2l-b2 for l>ls where α1, α2, b1 and b2 are constants which depend on the chemical composition of materials and metallurgical structure, and α1>α2 and b1>b2. ls is about 52mm in the present case. (2) The scattering range[(σmax)r, (σmin)r]of tensile strength decreases as l becomes longer or shorter than ls=52mm. (3) The length ls=52mm is equal to the length of the standard specimen. Accordingly, the scattering range is maximum for the standard specimen. Moreover, the minimum value of the tensile strength σ at ls is less than the minimum value of σ at any other l. Therefore, the tensile strength σ of a specimen is represented as σ≥((σmin)r)l=52, where ((σmin)r)l=52 is the minimum value of tensile strength at ls.
The distribution of ultimate breaking strength of cable has seldom been studied from the point of view of inherent casual factors which influence the nature of the resultant mathematical distribution. It has been pointed out only that the skewness of the curve representing the frequency distribution of breaking strength of cable is ordinarily negative presumably due to flaws in the cable. This paper gives a physical meaning to asymmetry of the frequency distribution from the theory of extreme values. Comparison is also attempted between the theory and experimental results.
The electrochemical measurements were conducted to investigate pitting of iron in dilute caustic soda solutions containing NaCl at 95°C. The rupture potential and the protection potential were obtained as a function of NaCl concentration. The static potential was also determined, and it was located in the pitting region of the potential vs. NaCl concentration diagram, when the NaCl concentration was higher than 0.05M.
The purpose of this study about the addition of both glycerol and sucrose to tobacco was to investigate the main effect of additive quantity of each additive as well as the interaction effect between both additives on three characteristics (fragility, filling capacity and equilibrium moisture content), and to compare the effect of simultaneous addition of both additives with that of individual addition of only glycerol or sucrose on the three characteristics. Experiments were carried out by changing such five factors, as the glycerol addition (0-4%), sucrose addition (0-8%), environmental humidity (43-80% RH), shreds length (0.71-12.7mm) and tobacco variety (Flue-cured and Burley), and by considering two subsidiary factors of glycerol and sucrose contents in tobacco shreds determined by chemical analysis. The important results obtained by the statistical analysis of these experimental data are as follows: (1) On the filling capacity and the equilibrium moisture content, the interaction effect between glycerol and sucrose was smaller than the main effect of glycerol or sucrose alone. (2) On the fragility, the main effect of glycerol was greater than that of sucrose or the interaction effect between glycerol and sucrose. (3) The effect of simultaneous addition of both glycerol and sucrose on the three characteristics can be regarded as the superposition of two individual effects of glycerol and sucrose. (4) In every case of the simultaneous addition of both glycerol and sucrose or the individual addition of only glycerol or sucrose, the effect of the addition was large on fragility, medium on filling capacity and small on equilibrium moisture content.