The compressive strength of β-Titanium alloy (15V-3Cr-3Sn-3Al) was investigated in the temperature range from 293K to 973K and at strain rates from 1.7×10-4S-1 to 5.6×10-2S-1. The strength generally decreased with a rise in temperature, but at certain temperatures it increased due to the aging effect which proceeds much more rapidly during deformation than the isothermal aging. There existed the temperature range where the strength actually is independent of temperature and slightly decreases with an increase in strain rate. Portvin le Chaterie effect was observed in this temperature range. Thermally activated strain rate analysis gives plausible explanation of the experimental results.
SMC (Sheet Molding Compound), which has such excellent characteristics as surface brilliance, formability and mechanical property, is usually formed by compression molding. This method has short cycle time of processing, but needs huge energy for forming because of formation of hydrostatic stress domain in the mold. So, roll forming is proposed for SMC so as to decrease the forming energy ay losing a formation of hydrostatic stress and to keep short cycle time. At first, the fundamental experiment is carried out to see the behavior of deformed material using a constant reduction on each forming condition. It is necessary to decrease the number of roll stand for making a compact roll forming system. But the condition for large reduction results in that the deformed material shows an instability behavior between roll stands. And, the condition for low reduction can improve the formability of the flange of channel shaped products. The tension brought in by the difference in driving speed makes material stable from the exit of one roll to the entrance of the next roll, and this tensile load affects the deformation of the materials. The result of this research is useful to decide the driving speed during reduction.
Time dependent behavior in viscoelastic media with arbitrary shaped tunnel is investigated by use of correspondence principle between elasticity and viscoelasticity. The analytical solutions for stress and displacement are obtained and a back analysis using the above result is shown. Then the viscoelasticity for the ground is adopted to be represented by typical rheology models such as Burgers or Standard model for deviatoric part and Elastic model for volumetric part about stress. Concrete numerical examples are shown by graphical representations.
The composite material plate used in this study is called super hybrid plate which is built up from many thin aluminum alloy sheets and unidirectional CFRP and KFRP layers. This plate can be formed plastically at room temperature under certain limiting conditions. Super hybrid plate is very flexible and has a wide plastic deformation range if it is not cured. Moreover, plastically deformed aluminum layers themselves may act as a mold for FRP layers. Therefore a new V-shape forming prosess was developed based on. these properties. First of all, a stacked material, consisting of aluminum and FRP layers, is pre-formed at room temperature, and then cured under an appropriate temperature and pressure by using hot-press. It became possible to form a shap V-bent with radius 2.5mm which is nearly equal to the plate thickness. On the other hand, this causes fluctuation of thickness of the formed article. To solve the problem the article formed at room temperature was cured in an autoclave with a simple device which can cancel the spring back of the article. As a result, the new V-shape forming process to get articles with no spring back and with exact 90 degree bending angle was developed.
Advanced fiber-reinforced composite materials have been used for structural members, because of their high specific strength and stiffness. In general, laminated cylindrical shells behave differently from isotropic and homogeneous orthotropic cylinders due to the effect of lamination constitution associated with their anisotropy and unsymmetric lamination. In this paper, the effect of lamination constitution on the buckling stress of carbon fiber/epoxy (CFRP) angle-ply laminated cylindrical shells under bending is reported. The effect of various factors, such as stacking sequence, number of layers, lamination angle, dimension of cylinders, and buckling modes, on the buckling value are analyzed by assuming the buckling patterns which satisfy the Flügge-type equilibrium equations. It is clarified that the buckling stress is significantly affected by the effect of lamination constitution.
An irreversible thermodynamic theory for elastic-plastic-damage materials by use of damage potential expressed in stress space is formulated and its validity is discussed. By expressing Gibbs thermodynamic potential and the dissipation potential in terms of a second rank damage tensor D, a scalar damage variable β, Cauchy stress σ and isotropic hardening parameter of plasticity r, constitutive and evolution equations for elastic-plastic-damage materials are first derived according to the constitutive theory of irreversible thermodynamics. Then, after discussing the essential features of the resulting equations, they are applied to the cases of uniaxial and torsional loadings. Finally, the changes in Young's modulus, Poisson's ratio and shear modulus due to damage development and the initial and the subsequent damage surface expressed in stress space are compared with the corresponding experimental results on the tubular specimen of spheroidized graphite cast iron.
In order to investigate the effect of testing rate on the mechanical properties of ceramics, impact lateral compression tests for Mullite circular tubes were carried out at a velocity of 0.6m/sec. The impact lateral compression strength of Mullite tube was obtained to be σfDy≅213MPa which is about 1.6 times greater than the static lateral compression strength. Dynamic and static FEM analyses were also performed to obtain the distribution of hoop stress, σθ, in Mullite tubes during deformation. The distribution of σθ at the maximum load in impact tests was quite similar to that in static tests, although the magnitude of σθ was different. To examine the relation between the increase of maximum load due to the increase of testing rate and the crack-rate sensitivity of the crack growth resistance of ceramics, a numerical simulation for lateral compression of ceramic tube was carried out. If it can be assumed that tube material is perfectly brittle and crack-rate sensitive, the increase of maximum load due to the increase of testing rate can be expected in lateral compression tests and the larger crack-rate sensitivity causes the greater increase of maximum load.
The purpose of this paper is to show a highly accurate inverse analysis for the problem of lozenge cavity with sharp corner under in-plane and out-of-plane loadings, which is based on the complex variable method using a conformal mapping technique. A method of inverse analysis for the magnitude and direction of initial stresses is represented by use of the exact elastic solutions. The results of inverse analysis are in agreement with the analytic results on high accuracy.
The surface of ring-like annealed mild steel specimens with diameter of 30mm and thickness of 8mm was coated with TiN film by an activated reactive evaporation (ARE) method. A pair of ring-like specimens contacted each other in the radius direction were set to the Nishihara type wear testing machine. They were rotated at the speed of 13.3rev./s under the condition of applied stress of 330 to 1100MPa and pure rolling contact with lubricant. The thin TiN film was uniformly produced on the surface of specimen by ARE method. This film adhered well to the surface of mild steel and it had enough bonding strength to mild steel even under pure rolling contact with lubricant. The annealed mild steel specimens coated with TiN had superior rolling contact fatigue strength than the uncoated ones. The fatigue life of the specimen coated with TiN was about eighteen times as large as that of the uncoated specimen under the same contact stress. TiN film on the surface of specimen was effective to suppress the generation of surface crack of specimens. The work hardening layer formed by repeated contact stress was near the surface of specimen and the degree of work hardening became larger with an increase in contact stress.
Fatigue crack growth tests on four kinds of γ-base TiAl alloys with different microstructures were carried out. The basic mechanism of fatigue crack growth and the effect of microstructure on fatigue crack growth properties were discussed in detail. It was found that microcrack nucleation in the near crack tip region, growth and coalescence to a main crack are the dominant mechanism of fatigue crack growth. The fatigue crack growth resistance of lamellar microstructure material was higher than that of duplex microstructure material, which in turn was higher than that of equiaxed microstructure material. In the lamellar microstructure materials, crack growth resistance was low when the orientation of lamellar lath coincided with the crack growth direction. These differences in crack growth resistance might be induced by the stress shielding effect due to bridging on the crack wake.
Rotating bending fatigue tests have been conducted at room temperature in air using the specimens of medium carbon steel (S45C) with sprayed coating of a cermet (WC-12%Co). The fatigue strength and fracture mechanisms were studied. The fatigue strength was enhanced by the cermet spraying and the fatigue limit of the sprayed specimens was 30-40% higher than that of the electro-polished specimens of the substrate steel. Fatigue cracks were initiated at defects between the substrate and sprayed coating. When the specimens were blasted by alumina grits before the cermet spraying, fatigue cracks were initiated at the alumina grits remained on the surface of the substrate. Therefore, fatigue strength was increased when the substrate was blasted by steel balls or the blasting was omitted. In these specimens, fatigue cracks were initiated at the debonding defects at the interface between the substrate and sprayed coating. When a crack was initiated in the sprayed coating by the increase of localized strain due to the crack initiation in the substrate, the crack growth rate in the substrate was accelerated by the stress concentration of the crack in the sprayed coating, which led to the decrease in the crack growth life of the specimen.
High strength steel is so sensitive to environment that it is liable to corrode in air. Therefore, it is necessary to consider the influence on fatigue crack propagation of high strength steel in air. In fact, the experiments in the past showed that the influence of moisture in air appeared as acceleration effect of da/dN. However, there are a large number of unknown factors about the details of the subject. In order to investigate the influencing factors of high strength steels on fatigue crack propagation characteristics at the stage 2, the fatigue crack propagation tests and SEM observations of fracture surface were carried out under the stress ratio R of 0.1 in air and dry air. The results obtained are: (1) The acceleration of da/dN by moisture in air is dependent upon the static mechanical properties and the length of stage 2b area. And the acceleration is due to the appearance of intergranular fracture due to hydrogen induced cracking. (2) The acceleration effect differs with the difference of frequency as a result of quasi-cleavage of fracture due to hydrogen induced cracking. (3) The acceleration of da/dN decreases with an increase in pre-austenite grain size.
In recent years, an increasing interest has been paid for the exact measurement of stress-strain relation at high rate of strain to check the result of precise formulation of rate-sensitive constitutive equations. In the strain rate range above 102/S, the split Hopkinson bar method is commonly used for this purpose. In this method, however, the both input and output bars should be long enough to prevent the disturbance caused by the wave reflection at the ends of those two bars. In this paper, the outline of a newly developed compact dynamic loading device using a stress sensing block which consists of a small cylindrical knob for stress measuring followed by a relatively large mass block, is drawn, and its application to the measurement of stress-strain relation at the strain rate of 103/S is discussed. With this device, the dimension of input and output bar system can be reduced to 1/2-1/3 of that of on ordinary split Hopkinson bar device, while the accuracy of the obtained stress-strain curve retains the same level of that obtained by the split Hopkinson bar device.
A new method of X-ray stress measurement was proposed for cubic polycrystals having the  fiber texture with the fiber axis perpendicular to the specimen surface. The relation between the strain measured by the X-ray method and the stress was derived on the bases of Reuss and Voigt models. The procedure to determine the residual stresses in aluminum thin films having the  fiber texture was presented. The X-ray strain was measured at the inclination angle ψ=0° and 70.5° for 222 diffraction, and ψ=29.5° and 58.5° for 311 diffraction. The values of in-plane stresses, σ11, σ22 and σ12, and out-of-plane stress, σ33, were determined from the measured strains. For the case of equi-biaxial stresses, i.e. σ11=σ22=σ, both models give the identical relation between the X-ray strain and sin2ψ. The stress can be determined from the slope of the linear relation.