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In the photoreaction of Escherichia coli IM303 (superoxide dismutase (SOD)-deficient mutant) and MM294 (wild-type strain) with TiO₂ particles, the viability of strain IM303 decreased linearly with photoreaction time, while the time profile of the viability of strain MM294 exhibited a curved form. Using strain MM294 with varied initial SOD activities, the TiO₂ photoreaction tests were conducted at incident light intensities of I₀ = 4,8 and 14 W m^-2, and the time profiles of bacterial viabilities were analyzed on the basis of the series-event model. The value of n (corresponding to the step number in the series reaction kinetics described by the model) increased with an increase in initial SOD activity (A_SOD,0), giving a mean value of A_SOD,0/n = 7.1 × 10^-9 U cell^-1 under the conditions examined. SOD activities in the cells of strain MM294 with A_SOD,0 = 1.9 × 10^-8 and 4.0 × 10^-8 U cell^-1 decreased with the progress of photoreaction conducted at I₀ = 14 W m^-2. The transition of intracellular SOD activities expressed was in agreement with the observed data by considering the changes in bacterial cell populations with varied SOD activities based on the proposed model.© 2002 Society of Chemical Industry

We propose the extended Hamilton's principle to investigate the dynamic plastic behavior of a beam or a plate under an impact loading. Material is assumed to be rigid perfectly plastic. The impact loading is given in the form of initial velocity. Good agreement between our numerical solutions and experimental results done by Parkes and Jones indicates that the proposed variational method is a powerful approximation method for the dynamic plasticity analysis. The effect of strain-rate sensitivity on the permanent deflection of a plate is investigated in some detail. Instead of nonlinear differential equations, nonlinear algebraic equations are solved in the proposed method.

The machinability of two classes of high-temperature composites (SiC whisker/2124 aluminium and SiC whisker/Al2O3) with an abrasive waterjet (AWJ) was investigated. The as-machined surfaces of the composites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and profilometry to determine the surface finish. Microhardness measurements were also performed on the as-machined metal matrix composites. AWJ appears to be a quite promising machining method due to its fast speed and economical operation. It gives relatively smooth surfaces coupled with minimum subsurface microstructural damage.

Stress relaxation, a decrease of energy by plastic flow, interfacial sliding, local diffusion and bulk diffusion, has been studied for an inclusion bearing material. The complete relaxed state is found by minimizing the total energy, using a variational method. A relaxation process or the combination of two processes imposes a subsidiary condition that matches the physics of the process. The complete relaxation occurs when total stresses are uniformly hydrostatic in a plastic region. In interface-related phenomena, the complete relaxed state is as follows: tangential traction vanishes for interfacial sliding; normal traction is constant for local diffusion; and total traction is constant and normal to the interface for the combination of interfacial sliding and diffusion. When bulk diffusion is allowed, normal traction vanishes. If sliding is further allowed, an inclusion becomes stress free. By examining subsidiary conditions, the effectiveness of two processes can be compared.

Photocatalytic sterilization of Escherichia coli (bacterium) or Saccharomyces serevisiae (yeast) was conducted with a rectangular bubble-column photoreactor (40 mm in width, 40 mm in breadth, and 250 mm in height) containing slurried TiO2 semiconductor particles. The profiles of cell deactivation with sterilization time could be expressed in fair agreement with experimental data, based on a series-event model and a second-order kinetics with respect to the concentrations of microbial cells and oxidative radicals generated by photoexcitation of TiO2 particles. Sterilization rate constants for the microbes were determined under various conditions of TiO2 concentrations (0−5 × 10^-1 kg/m³) and average light intensities (0−223 W/m²) in the photoreactor. Linear relationships were obtained between the rate constants and average light intensity at TiO2 concentration of 1 × 10^-2 kg/m³. When incident light intensity was kept constant (27 W/m² for E. coli or 238 W/m² for S. cerevisiae), the correlations between the rate constants and TiO2 concentration were interpreted considering a fraction of TiO2 particles adhered to the cells in slurry.

The longitudinal Young's modulus of an aligned short-fiber reinforced composite with fiber-end cracks extending into the matrix is predicted theoretically in this paper. The analytical technique is based upon a modified Eshelby's equivalent inclusion method where infinite number of three kinds of ellipsoidal inhomogeneities are embedded in the matrix. The results indicate the importance of two parameters in affecting the stiffness of the composite: the size of the fiber-end crack, and the ratio of the number of fibers with fiber-end cracks to the total number of fibers.

This paper examines the effective longitudinal Young’s modulus of composites containing misoriented short fibers. The analysis is based on the Eshelby’s equivalent inclusion method and the average induced strain approach of Taya, Mura, and Chou. The present approach is unique in that it takes into account the interactions among fibers at different orientations. Numerical results are presented to demonstrate the effects of fiber elastic property, aspect ratio, volume fraction, and orientation distribution function on composite Young’s modulus. Fiber orientation distribution has a more significant effect on composite longitudinal Young’s modulus than fiber volume friction, within the range examined.

For plane strain finite deformation plasticity, several finite-element methods are examined and their corresponding computational efficiency and accuracy are compared by means of an example of pure bending. Then, employing one of the more efficient methods, the state of stress and deformation at the center of a rectangular bar, deformed in uniaxial extension, is studied. On the basis of this information, then the growth process of a (micro) void in a unit cell located at the center of the necked bar, is examined, revealing that the internal fracture at microscopic scales, seems to occur by the formation of shear bands inclined at about 45° with the axis of (macroscopic) extension, a fact which has been observed in ductile fracture of two-phase alloys. Finally, void growth parameters (i.e. those which characterize the geometry of the void) are computed and the results are compared with those obtained from a solution given by McClintock, arriving at a reasonably good agreement.

A formulation to compute the effective thermal expansion coefficients (αc) of an anisotropic short fiber-reinforced composite and the thermal stress (σ) induced in and around the fiber is developed. The formulation is based on the Eshelby’s equivalent inclusion method. Main emphasis is placed on short Carbon fiber/Aluminum. The thermal stress due to a uniform temperature rise ΔT is computed at points just outside the fiber. The effects of various parameters on αc and σ are also investigated.

The stresses induced in and around a coated short-fiber composite are investigated by use of the Boussinesq-Sadowsky stress function. The coated fiber is assumed to consist of two confocal spheroids and it is embedded in an infinite body. The major parameters in this analysis are the fiber aspect ratio, the coating thickness-to-fiber radius ratio, the coating-to-matrix stiffness ratio and the fiber-to-matrix stiffness ratio. It is found in the analysis that the stiffness and thickness of the coating and the fiber aspect ratio have some effect on the stress field in and around the coating in a coated short-fiber composite.

This paper examines an important aspect of the hygrothermal effect in fiber composite materials, the deformation induced by matrix shrinkage. The physical problem is simulated by prescribing a constant axial eigenstrain to the fiber material and the boundary-value problem is then solved in the context of an “inclusion” problem. The complete stress field due to a cylindrical inclusion with constant axial eigenstrain in an infinite elastic body are obtained by representing the eignestrain and displacements in Fourier integral forms. The solutions for stresses are expressed in terms of gamma and hypergeometric functions. The results are also compared with the existing solution of a special case.

One of the experimental findings on short-fiber reinforced composite materials is that the fiber-ends act as a crack initiator. The effect of the fiber-end crack on the overall stiffness and the strength of the composite are investigated here. A particular emphasis is placed upon the weakening longitudinal Young’s modulus by the fiber-end crack which is assumed to be penny-shaped. The energy release rate of the penny-shaped crack at the fiber-end under a uniaxial applied stress is also calculated for a fracture criterion. It is assumed in our theoretical model that short-fibers are all aligned in the loading direction and the penny-shaped crack at the fiber-end extends in the direction perpendicular to the fiber axis. Our analytical technique is a combination of Eshelby’s equivalent inclusion method and Mori-Tanaka’s back stress analysis so that our results are valid even for large volume fraction of fibers.

The second stage creep behavior of 6061 aluminum alloy and 15 percent Vf SiC Whisker/6061 aluminum composite was studied both experimentally and analytically. In order to obtain the accurate input data for the creep analysis, we have also conducted the experiment to measure various microstructure parameters. Based on these data and the Taya-Lilholt creep model, the second stage creep rates are calculated. A good agreement between the analytical and experimental results is obtained if the debonding at the matrix-fiber interface is considered in the analysis.