Theoretical analysis and numerical calculation have been carried out for the simple shear deformations of plastic materials which have the Tresca type yield condition and endow the combined work-hardening. At first, the constitutive equations and the evolutional equations of a scalar and a tensor internal state variable are solved analytically for the simple shear deformation. Then, the solutions are calculated numerically for a special material function. The shear and normal components of stress and translation and the scalar internal state variable are depicted via the shear angle. The results show the isotropic work-hardening as well as the translational one.
The dependence of strain rate on deformation strength was investigated on various pre-strained specimens of carbon steels under plane strain. The strain rate was from 4×10-3 to 2×104sec-1. In the range of high strain rate, a newly developed Stress-Strain Curve Direct View Device was used for the measurement of deformation strength. Furthermore, Digital Memory Scopes were utilized to obtain highly accurate experimental data. The results obtained are summarized as follows: (1) The deformation strength σ in plane strain is related to strain ε, strain rate ε and temperature T by σ(ε, ε, T)=k0εn1εn2exp(α/T) where n1 is the strain hardening exponent, n2 the strain rate exponent, α the temperature dependence index and k0 the strength constant. (2) The carbon equivalent value of yield stress Cy and the strain hardening exponent n1 and the temperature dependence index α are related each other. If Cy is known, the deformation strength in plane strain can be estimated from the average value of n2 of all kinds of steel by using this correlation.
The strain distribution and the strain concentration factor in friction welded specimens were examined by copper-electroplating technique. The influence of strain concentration on the fatigue damage by cyclic stressing was investigated. The tests were carried out by rotary bending, using specimens of mild steel with a smooth welded joint. The results obtained are summarized as follows: (1) The strain distribution in the friction welded specimen is affected by the micro-structure of the material. The strain becomes minimum at the weld interface, and increases with an increase in distance from the interface. (2) The strain concentration factor is maximum in the parent material and minimum at the weld interface. The difference, however, is not so remarkable. (3) The slip-lines in the specimen appear more densely in order of magnitude of the concentrated strain. The fatigue fracture of the specimen occurs at the location where the strain concentration factor is maximum and the fatigue crack propagates more rapidly.
The fatigue crack propagation rate and crack closure behavior under repeated two- and three-step loadings at low stress intensity level were investigated on an aluminum alloy A5083-O. The crack opening point, Kop, was found to be constant and was nearly equal to that for KH in Kmax-Kop relation for constant amplitude loading tests, where KH was the highest K value in repeated multiple-step loading tests. Based on the effective stress intensity range, ΔKeff, which is calculated considering the above mentioned behavior of Kop, the fatigue crack propagation life can be conservatively estimated by the linear accumulation law of crack propagation length adopting ΔKeff-dl/dn relation for constant amplitude loading tests.
Six kinds of metal (three ferrous and three non-ferrous) were tested under rotating and flexural bendings by applying n1 cycles of an overstress and n2 cycles of an understress alternately, to investigate the role of understress in fatigue damage accumulation. Fatigue life calculation for such a case gives nonconservative side estimation when the original S-N curve determined by the constant stress amplitude tests is used. This is because an understress, when preceded by an overstress, contributes to damage, which otherwise does not cause damage. The original S-N curve is to be modified to make an estimate coincide well with the test results. In case of ferrous metals downward extension of the inclined part of the original S-N curve fits the test data well so long as the value of n2 is large compared to n1. A steeper slope, however, seems necessary for a modified S-N curve as n2 becomes smaller. As for non-ferrous metals downward translation of the original S-N curve, by keeping its shape and slope, leads to good agreement with test data. The meaning of S-N curve modification is interpreted by the combination of increased damage accumulation brought about with the increased plastic strain range accompanying stress change and the counteracting phenomenon such as plastic strain concentration in crystals or the strengthening effect like strain aging especially under low stress amplitudes, which interferes with linear accumulation of fatigue damage at the higher and the lower stress amplitudes.
Two step interval tests have been carried out on notched specimens of four kinds of metals under rotating and flexural bending conditions. n1 cycles of overstress σ1 and n2 cycles of understress σ2 were alternately applied. Both the crack initiation and final fracture lives were relatively longer compared with the fracture life of the unnotched specimen when n2 was larger than n1, though the lives become shorter as n2 decreases. In some cases specimens failed much earlier than expected from the Corten-Dolan modification line for a fairly small value of n2, and the regression line for the test data curved downward. The longer life of the notched specimen for a larger value of n2 seems due to retardation of crack initiation and propagation brought about by the compressive residual stress induced at the notch root and the crack tip after the stress amplitude was changed from σ1 to σ2. For a material in which repeated plastic strain range is rather small, retardation of crack initiation and propagation was not observed. This seems due to small compressive residual stress produced at the time of stress change from σ1 to σ2.
Influence of thermal ageing on the low-cycle fatigue life of SUS 321 stainless steel was investigated in the temperature range from room temperature up to 800°C. A large influence was observed when the fracture mode was intergranular. The aged specimens had always longer fatigue lives than the solution-treated specimens. This difference in fatigue life was caused by the difference in intergranular crack propagation rate. On the other hand, when the fracture mode was transgranular, the influence of ageing on the fatigue life was scarecely observed in the total strain range vs. fatigue life relationship. In the plastic strain range vs. fatigue life relationship, however, a little influence was observed, which was caused by the difference in the cyclic hardening behaviors between the aged and the solution-treated specimens.
The purpose of this study is to obtain the relationship between the internal failure mechanism and the whole deformational property of concrete specimens in uni-axial compression. As one of the methods to obtain such relationship, a numerical simulation analysis seems to be effective. In the present study, the finite element method was employed and a concrete specimen was divided into finite elements. Each finite element represents one of the failure patterns when its stress condition was satisfied in the element. The accumulated behavior of finite elements under increasing loading was discussed. The macroscopic numerical result showed good simulation of the behavior of concrete specimens. It gave valuable informations about the effects of material constants on the stress-strain relationship of concrete specimens.
One of the problems of underground storage of L.N.G. is a rock stability at low temperature or after having been at low temperature. In this study, the physical and the mechanical properties of rocks which had been at low temperatures of 0, -40, -80, -120, and -160°C were investigated. The physical and mechanical tests were carried out at room temperature. The main results obtained are as follows: (1) Both the compressive and the tensile strength of these rocks are smaller than those which had not been at low temperatures. (2) The microscopic observation revealed an increase of microcracks in Granite with decreasing temperature, as indicated by the test results of Young's modulus and Poisson's ratio. (3) The results of the X-ray diffraction show that cracks seem to grow at the interface between Quartz and Biotite, or between Quartz and Albite in Granite and Andesite. (4) The coefficient of thermal expansion changes with cooling temperature.
Single- and bi-crystal specimens of high purity aluminum were deformed in tension at 78K and 283K, and the electrical resistivity changes were measured in association with plastic deformation. The crystal orientation and testing temperature dependencies have been investigated on the single-crystal specimens. The bi-crystal specimens were studied with respect to the effect of grain boundary on the deformation. The results obtained are as follows: (1) For the bi-crystal specimens, the electrical resistivity changes show that the grain boundary effect extends to 2 or 3mm distance from the boundary at the early stage of deformation. This is consistent with the results of the slip line observations. The contribution of the grain boundary to the plastic deformation decreases with increasing strain and becomes constant after ε=10%. (2) For the single-crystal specimens, the ratio of electrical resistivity change (Δρ/ρ) does not depend on the crystal orientation at 283K, while it shows the crystal orientation dependency at 78K. The ratio (Δε78K-Δρ283K)/Δε78K also shows the crystal orientation dependency: the ratio was 50 to 60% for the specimens having a multiple slip orientation, but was less than 50% for those having a single slip orientation. (3) The orientation dependency of the τ-γ curve for single crystals was found only at 78K. This suggests that the activity of second slip system is closely connected with the thermal vibration of dislocations and the annihilation of excess vacancies, which were produced during deformation.
The objective of this study is to clarify the effect of the chemical displacement reaction between Sn-Pb solder and ZnCl2 binary system fluxes containing fluorides or iodides as a second component on the spreadability of Sn-Pb solder. The results obtained are summarized as follows. (1) When ZnCl2 binary system fluxes containing fluorides such as AgF, BiF3 and NiF2·4H2O or iodides such as AgI, BiI3 and NiI2·6H2O were used, a remarkable chemical displacement reaction between Sn-Pb solder and the fluxes took place and the spread area of the solder with these fluxes was larger than that with pure ZnCl2 flux. (2) When ZnCl2 binary system fluxes containing fluorides such as ZnF2, MnF2, KF, NaF, LiF and BaF2 or iodides such as ZnF2 and CdF2 were used, the chemical displacement reaction hardly took place and the spread area was almost the same as that with pure ZnCl2.
In this report, the spreadability of Cd on Cu and brass base plates was examined by using various ZnCl2 binary system fluxes. When pure ZnCl2 was used as a flux, Cd showed a remarkable secondary spreading, yielding an increase in spread area. Moreover, the second component chloride added to ZnCl2 caused chemical displacement reactions with Cd as well as with base plate, and thus affected the spread area. Therefore, the spreading characteristic of Cd on Cu and brass plates with ZnCl2 binary system fluxes may be classified in four types.
Complex formations between cationic polyelectrolyte (polyaminesulfone and 6, 3 ionene) and inorganic solute (potassium ferrocyanide, ammonium reineckate, phosphomolybdic acid and silicotungstic acid) were investigated by conductometric and turbidity measurements. These complexations proceeded in non-stoichiometry. The reaction stoichiometry seems to be affected by the size of anion, the flexibility of polycation, and the ionic distance along the axis of polycation. Vapor adsorptions of water and organic vapors on the complexes were measured by using a quartz spring balance. The amounts of adsorption were small, compared with those of polyelectrolyte complexes composed of polycation and polyanion. It seems that the adsorption depends on the ions which are present in excess above equivalence.
In order to clarify the discrepancy of the fatigue life of welded joint specimens and that of welded structures, it is indispensable to detect the fatigue crack initiation life. For this purpose, the fatigue testing machine was stopped automatically by means of an electrical signal which was generated when the grille of copper foil on welded joints broke. Fracture of the grille corresponded to the crack initiation on the toe of weld of welded joints, because the grille adhered strongly on the weld zone through insulation coated on the weld zone. The grille was put in place by the vacuum deposition. The depth of the crack at the time of fatigue crack initiation was 0.2∼2mm on the fracture surface. This was well distinguishable by a colored part which appeared by heating the specimen after the fatigue testing machine was stopped. The above described treatment of specimens was found not to influence the fatigue life. So, this method is regarded as an effective way for detecting the fatigue crack initiation life. It was also revealed that the aspect ratio decreased with the increment of stress range. The smallest value of the aspect ratio was 0.05.
A position-sensitive proportional counter suitable for the X-ray stress analysis has been developed and residual stress in austenite steel was measured with an apparatus which uses this PSPC system. The detector was designed to have a good angular resolution overall the counter length for diffracted X-ray beams and a high counting rate. The mean angular resolution measured was about 0.2° in 2θ (FWHM), and the maximum allowable counting rate reached about 40000cps. The time required for the data accumulation was shortened to about one-tenth of that of the conventional counter method. It is generally said that the X-ray stress measurement of austenite steel should be performed on its γFe(311) diffraction plane by using Cr-Kβ radiation and the measurement on γFe(220) should be avoided because the strain sensitivity on γFe(220) diffraction plane is less than that on γFe(311) one. However, the precision of stress determined on γFe(220) was better than that on γFe(311), if Bragg's angles were measured at many ψ angles.