Hot Isostatic Pressing (HIP) is a powerful tool to produce functionally graded materials (FGMs). The Partially Stabilized Zirconia (PSZ)/stainless steel, TiAl (α/α+γ), and W/Cu FGMs can combine incompatible functions of heat resistance and toughness in structural uses. In functional uses, the graded C/C composite for the heat receiver, the Ir/W/Ta emitter electrode for the thermionic converter, and one step formation of a graded thermoelectric conversion unit of SiGe with electrodes are developed using HIP. These recent developments of FGMs by HIP are reviewed.
Assuming the structural units in Na2O-B2O3-GeO2 glass being composed of structural units of the Na2O-B2O3 and Na2O-GeO2 systems (sub-systems), glass transition temperature Tg was estimated from the viscosity-temperature relationship based on the sub-system concept. The distribution of Na2O component among the B2O3 and GeO2 components is determined according to the assumption that Na2O activity in the Na2O-B2O3 system is equal to that in the Na2O-GeO2 system and the ratio of the Na2O activity coefficients γ1 in the Na2O-B2O3 system over that γ2 in the Na2O-GeO2 system is constant throughout the composition of the Na2O-B2O3-GeO2 system. The calculated and the observed Tg was in reasonable agreement within the experimental scatters.
An effort was made to develop carbonized TiO2-woody composites which can effectively remove and decompose harmful air pollutants in environments. As an example of an air pollutant, formaldehyde (HCHO) was selected for evaluating the carbonized TiO2-woody composites. The composites were composed of carbonized wood as an adsorbent and the anatase-form of titanium dioxide (TiO2) as a photo-catalyst. They showed a much higher decomposing ability toward formaldehyde, when compared with the performance of non-composite controls composed of a simple physical mixture of carbonized wood and TiO2 granules. This indicates that synergetic effects existed in the carbonized TiO2-woody composites for photo-catalytic environmental cleaning. The topochemical mechanism inducing such synergetic effects is discussed in relation to the distribution of TiO2 granules in the composites.
A general approach to the study of the structure of all known forms of the solid state and of biological structures is possible on the basis of the concept “module” that is more general and unambiguous than “the lattice”. The potentialities of modular design for the deliberate selection of structural components and the estimation of the opportunities of their self-organization due to formation of perfect coherent boundaries between their regularly oriented crystallites in nanocomposites were shown by the examples of two-dimensional Penrose mosaics and three-dimensional biomimetic composite amorphous-Al2O3-hydroxyapatite-collagen-“bound water”.
This paper describes elastic behavior and failure mechanisms of plain-knit fabric composites. A single-ply glass-fiber knit fabric impregnated with epoxy resin was used to fabricate composite specimens. Tensile tests were then carried out in two directions: the wale and the course directions of the fabric. During the test, the fracture behavior of the composite specimen was identified by a video camera which caught the loop images from the beginning to their failure. Tensile properties were also experimentally determined. Furthermore, a three-dimensional (3-D) finite element model of a knitted loop was proposed for prediction of tensile moduli as well as failure mechanisms of the plain-knit fabric composite. The validation of the loop model was estimated by comparison of the experimental results with the predicted ones.
In order to investigate the effect of molecular weight on fatigue characteristics in the ultra-high molecular weight polyethylene (UHMWPE), tension-tension fatigue tests of notched specimens were carried out in the present study. The effects of testing parameters were investigated and fractography was also discussed. The fatigue strength does not increase with increasing molecular weight. The fatigue strength might be influenced by the high degree of crystallinity in spite of the decreased tie molecular density. Almost no effect of frequency on the number of cycles to failure can be observed. However, the higher the frequency is, the higher the crack tip temperature. At high stress ratio, number of stress cycles to failure (S-N) curves shift to the side of high number cycles to failure.
This work presents theoretical and numerical investigation on crack identification using piezoelectric materials embedded in structures. At first, a crack estimation model was designed by using piezoelectric materials. A simplified analysis was employed by separating the solving procedure for this model to two steps: fracture mechanics analysis and piezoelectric analysis. Two hypotheses named as the MLTNM hypothesis and the constant strain hypothesis were adopted. By means of these two analysis steps, the effect of the crack on the potential distribution can be obtained. Then taking use of a finite element program, comparisons between theoretical and numerical results were examined. The theory was also used to find the relationship between the crack parameters and the potential distribution. Numerical simulations of crack identification were made. The applicability of the use of piezoelectric materials to crack identification was demonstrated.
The effect of porosity on the elastic constants for X-ray stress analysis in sintered alumina was analyzed on the basis of three micromechanical models: Reuss' model, Voigt's model, and the self-consistent model (SC model). The mechanical Young's modulus decreased with decreasing bulk density or increasing porosity, while Poisson's ratio was nearly constant. The experimental value of X-ray elastic constant, E'X /(1+v'X) (E'X=Young's modulus, v'X=Poisson's ratio), decreased with decreasing bulk density or increasing porosity. SC model gave the best estimation for the effect of bulk density on the X-ray elastic constants. The prediction based on SC model requires the mechanical elastic constants of sintered alumina as a composite and the X-ray elastic constants of diffracting phases. It is not necessary to know the properties of secondary phases. When the mechanical elastic constants of ceramics are not known, the bulk density can be used to estimate the mechanical elastic constants, and then the X-ray elastic constants.
Simplified theoretical formulae based on shot peening parameters and materials properties have been developed to predict the maximum and the peak depth of the compressive residual stress produced by shot peening. These formulae are based on the motion equation for a shot and the analytical model proposed by Li, who utilized the Hertz theory of elastic contact and a simplified elasto-plastic theory. Experimental verifications were carried out under various shot peening conditions. Shots were made of cast steel, fused Zirconia, and glass, each having its own range in diameter. Actual residual stress distributions were measured by the X-ray diffraction method. The maximum and peak depth of the compressive residual stress predicted by the proposed formulae agreed well with the experimental values in a wide variety of shot peening conditions.