A method for evaluating the distribution of electrical potential around multiple spherical defects was proposed. As the method is based on the known formulated solution for a single defect, the electric field could be analyzed efficiently in comparison with the other methods, such as finite element method. The electric field in a conductive material with multiple spherical defects at random locations was analyzed by the method. Result of the analysis showed that the increase in the potential difference normalized by the potential difference without defects, ΔV/V0, was in proportion to the product of the volumetric density of defects and the mean of cubed defect radius, nv[r3]m. This universal relationship held independently of the value of nv and the distribution of defect radius. Using the relationship, the damage due to the multiple defects can be evaluated from the increase in potential difference.
The response of a thin piezothermoelastic composite plate subjected to stationary thermal and electric fields is investigated. Solutions are obtained using the thin plate theory and the Rayleigh-Ritz method. As an analytical model, we consider a simply supported antisymmentric angle-ply laminate poezothermoelastic plate. The plate is exposed to an environment with a temperature rise on the upper surface only. To reduce the deflection produced by the thermal loading, electric potential is applied to the piezoelectric layer in the composite. Numerical results show the effects of the ply angle of the laminate configuration and the number of layers on the response of the thermal deflection and the applied voltage.
Real-coded Adaptive Range Genetic Algorithms (ARGAs) have been developed. The real-coded ARGAs possess both advantages of the binary-coded ARGAs and the use of the floating point representation to overcome the problems of having a large search space that requires continuous sampling. First, the efficiency and the robustness of the proposed approach are demonstrated by test functions. Then the proposed approach is applied to an aerodynamic airfoil shape optimization problem. The results confirm that the real-coded ARGAs consistently find better solutions than the conventional real-coded Genetic Algorithms do. The designed airfoil shape is considered to be the global optimal and thus ensures the feasibility of the real-coded ARGAs in aerodynamic designs.
Compliant mechanisms are a relatively new breed of jointless mechanisms in which the elastic deformation is intended to be a source of motion. In the past, flexible structural design optimization was cosidered only for the direction of the flexible point by using the material density or the homogenization method to identify the optimum layout. Here we shall extend this design theory to the case of a two dimensional design for compliant mechanisms which can specify the amount of deformation of the flexible portion. Finally, some examples are presented to confirm that the verification of optimal configuration using an image-based design method.
The axial impact crushing behavior of square tubes with and without stiffeners are studied by Finite Element method, and comparisons of mean axial crushing force between numerical solutions and theoretical prediction as well as qualitative comparisons of folding patterns between numerical simulations and experimental observations are made and discussed. Based on the numerical analyses, maximization problems of dynamic crushing energy absorption of square tubes with and without stiffeners, respectively, are solved using the crashworthiness maximization technique for tubular structures which combined the techniques of design-of-experiment, response surface approximation as well as usual mathematical programming. In addition, the energy absorbing capability of cylindrical tubes and square tubes with and without stiffeners are also compared.
Dynamic buckling experiments on thin cylindrical shells placed inside a rigid liquid container were carried out by using a shaking table. The shells represent the thermal baffles and the container represents the reactor vessel of a fast breeder reactor. The fluid pressure caused by the horizontal excitation distributes nonuniformly around the cylinders and causes external pressure buckling deformation on them. The buckling pressure on various types of test cylinders and seismic waves was measured, and it was confirmed to be higher than that predicted by static buckling analysis. It was also found that sub harmonic vibration occurs under a certain sinusoidal-wave excitation, and the response displacement increases suddenly at a lower pressure than the buckling pressure measured by seismic-wave-excitation tests. The test results indicated that in seismic design to prevent buckling of the thermal baffles, the static bucklimg analysis can be used as ling as sub-harmonic vibration does not occur.
In order to develop a methodology for creep life assessment of directionally solidifed Ni-base superalloy CM247LC, commonly used in advanced gas turbine blades, changes in electrochemical property of the alloy caused by creep have been investigated. Experimental results on electrochemical polarization measurements revealed that the peak current densities "Ip" and "Ipr", which appeared at a specific potential during potentiodynamic polarization reactivation measurements in a dilute glyceregia solution, increased linearly with the life fraction at an early stage of creep life and were uniquely correlated with a newly proposed Arrhenius-type parameter "(t/tr) exp (-Qc/RT)". The creep life fraction can be nondestructively evaluated by electrochemical polarization measurements and the above parameter.
A difference in fatigue strength depending on the rotational speed between air and water was found for the rotating-bending fatigue characteristics of a TiNi shape-memory alloy wire in our previous work. The heat transfer characteristics around a shape-memory alloy wire were measured using Reynold's analogy. The rise in temperature of the metal during the rotating-bending cycles was calculated considering the heat transfer result. As a result, the rotating-bending fatigue characteristics of a shape-memory alloy wire were explained well from the viewpoint of the heat transfer characteristics.
It is possible to strengthen metallic materials by using a cavitating jet to introduce compressive residual stress in the material surface, since the impact of collapsing cavitation bubbles peen the surface in the same way as shot peening. In order to demonstrate the improvement in the fatigue strength of a material by using a cavitating jet, an experimental study was carried out. Silicon manganese steel JIS SUP7 was chosen as a test material, since JIS SUP7 is used as a spring material after shot peening. The specimens were exposed to the cavitating jet with upstream pressure p1=20 MPa, downstream pressure p2=0.28 MPa, the cavitation number σ〓p2/p1=0.014, the nozzle throat diameter d=0.842 mm and the atandoff distance s=31 mm. The scanning speed v at which the compressive residual stress took the most significant value was 0.25 mm/s. The compressive residual stress was introduced in the entire surface peened by the cavitating jet under the above conditions. The fatigue strength of the specimen was investigated by a four point bending test. The minimum bending stress σm/n was fixed at 123 MPa and the amplitude of the load was varied. The fatigue strength of material peened by the cavitating jet is shown to be about 440 MPa, which is about 10% stronger than the strength without peening.
In the present paper, dynamic interlaminar fracture toughness of carbon fiber reinforced plastics (CFRP) is estimated by split Hopkinson's pressure bar test using end notched flexure (ENF) specimens. The dynamic deformation of the specimen is approximated by classical beam theory with Laplace transform. The Mode II fracture toughness of unidirectional CFRP is computed by the analyzed deflection of the specimen employing the scheme of J-integral with the measured impulsive load and reactions at the supported points. Through some numerical calculations, the validity of the J-integral for the dynamic ENF test is confirmed. The experimental results for carbon/epoxy laminates show that dynamic interlaminar fracture toughness of the unidirectional specimen has dependency on a deflection rate.
An epoxy matrix of Carbon Fiber Reinforced Plastics (CFRP) was modified using sub-micron Cross-linked acrylo Nitrile Butadiene Rubber (CNBR) particles to improve the mechanical properties of CFRP. The static tensile strength increased more than 15% in comparison with the strength of unmodified CFRP when the rubber content was 10 wt%. The Young's modulus little changed due to CNBR modification of the matrix. Fracture toughness and fatigue crack propagation resistance under Mode I loading were also improved due to CNBR modification. The impact resistance in the flat-wise direction was improved as well. Fatigue lives under tension-tension loading were significantly extended by CNBR modification at all stress ranges, although the slope of the S-N line of CNBR modified CFRP was almost the same as that of unmodified CFRP. Differences in fractured surface and internal damage accumulation process between two CFRPs were found. Fatigue lives also increased for center hole-notched specimens due to CNBR modification.