As the shrinkage and integration of electric devices, an interfacial fracture between thin films with several nanometers becomes most important. This paper aims that the mechanism of damage process along the interface between multi-layered films during nanoscratch tests. Using the edge of indenter of Berkovich type, nanoscratch test was conducted in sub-micron films of Si3N4/Cu/TaN fabricated on silicon substrate. Initiation of damage takes place near the Si3N4/Cu interface which has poor interfacial strength before fracture of Si3N4. Damaged spot appears under the scratched line and its size is within several nanometers. Measured critical values in nanoscratch tests and three dimensional non-linear finite element analysis reveal that shear stress concentration appears backward the indenter and it agree with the behavior of spot-like damage area from observation by means of microscope qualitatively. In order to examine the validity of damage mechanism, another nanoscratch test in the opposite direction of scratch was carried out. The value of critical load takes the larger one than that in the original test due to the difference of the shape of indenter, but the stress analysis reveals that initiation of spot-like damage takes place when the values of peak stress acting on the interface reach the same in both tests.
A specimen which substrate was quenched after TiN coating was prepared, and the effects of heating time in the post quenching on the mechanical properties of TiN film were investigated. The residual stress and the hardness of TiN film were decreased with increasing the heating time in the substrate post quenching. The adhesive strength and the substrate hardness were increased by the substrate post quenching. With increasing the heating time, they once increased and then became constant from a heating time. In order to improve the adhesive strength and the substrate hardness with minimizing the decreases of the residual stress and TiN hardness, it is necessary to quench the steel substrate in the minimum heating time in which the adhesive strength and the substrate hardness are improved.
This paper proposes a new approach to estimate the damage pattern of a notched cross-ply laminate using an embedded Fiber Bragg Grating (FBG) sensor. The damage pattern near the notch was investigated by finite element analysis with cohesive elements for the onset and the extension of various cracks. Then, the reflection spectrum of the FBG sensor was analyzed from the strain distribution obtained in the damage analysis. Based on the above analysis, the damage pattern is optimized as an inverse problem in the damage analysis, while the spectrum shape is adopted as the objective function. In the estimation scheme, the strain distribution of the FBG sensor is calculated by the damage analysis using the damage pattern expressed by the residual strength distribution of the cohesive elements. We estimated the damage patterns of the notched cross-ply laminate from the reflection spectra obtained in the analysis and those measured in the experiment. The estimated damage patterns agreed well with those corresponding to the input spectra.
The use of thin actuator plates bonded to surfaces of laminated composites to suppress the growth of delamination cracks is investigated. A composite beam analysis was performed to estimate the effect of actuation strains on the strain energy release rate of delamination cracks. When compared at the same value of actuation strain, the increase in the apparent crack growth resistance is larger for smaller FRP thickness and for smaller value of the critical strain energy release rate of FRP without actuators, Gcr, under both mode I and II loadings. Mode I delamination suppression tests of unidirectional CFRP laminates were conducted by using thin SMA actuators. The value of the apparent crack growth resistance, Glapp, under actuation strains of about 0.1% was 2.5 times larger than fracture toughness of CFRP and was also about 1.5 times as large as that just before actuation.
In order to establish some basic concepts on the development and design of smart blades of FRP, the influence of the pre-twist angle and the stacking sequence on the twist of anti-symmetric laminate blades under centrifugal force was analyzed by FEM (Finite Element Method).It was found that the twist direction of a blade depends only on the anti-symmetric stacking sequence and that the twist angle depends on the pre-twist.Two stacking sequences were investigated.It was shown that, for different sequences, to twist-backward is easy however to forward-twist is hard as the pre-twist angle increases.Furthermore, it was demonstrated that the twist angle of blade depends more on the coupling of the stacking sequence than it does on the pre-twist.
A new strength reliability model of fiber-reinforced ceramic matrix composites is proposed, in which both the processes of multiple matrix cracks and fiber breaks are taken into account, based on Markov process model. It is assumed that damages due to the cracks and breaks accumulate discretely and independently in the composite in accordance with change in transition probabilities with an increase in matrix and fiber stresses, respectively. Both the processes were finally described by simultaneous ordinary different equations, and the probabilities being in states were solved numerically. The results show that, first, the proposed reliability model can predict means and variances in fiber and matrix stresses, with an increase in strain. Next, this model predicts well strength data, obtained experimentally from various ceramic matrix composites. In addition, when the composite stress is subject to the mixed rule, the mean and variance in the composite stress can be obtained from the first-order second-moment method. The analyzed stress-strain curve of the composite can be simulated well, as been in actual behavior. According to this modeling, combination of large scatter matrix strength to small scatter fiber strength, brings an increase in strength of the composites.
Rudnicki and Rice invistigated the localization of deformation into a shear band resulted from an instability in constitutive description of homogeneous deformation in pressure sensitive dilatant materials. Their analytical method has been used very often for the prediction of shear banding in soil. In their analysis the equilibrium is considered between multiple solutions in the perpendicular direction to a shear band, but the essential requirement is ignored that these multiple solutions are under identical boundary condition. This paper shows concretely the disturbance of boundary condition appeared in the onset of instability in their method. This disturbance results in the fact that their method cannot give useful prediction for ductile fracture in soil.
There is a kind of bone damage called “diffuse damage”, which initiates before “linear cracks” initiate. Huja and Burr reported that the diffuse damage was related to the bone remodeling. However, studies about quantification of the diffuse damage have not fully been done. In this study, the diffuse damage was produced by the static or cyclic three-point bending. The occurrence and progression of diffuse damage were observed as an increase in fluorescence intensity by the confocal laser scanning microscope (CLSM), and a change in stiffness from the initial condition was evaluated. The beam specimens were prepared from the adult porcine femoral plexiform bone. By static bending, the diffuse damage estimated as an increase in fluorescence intensity increased rapidly just after the relationship between stress and strain became non-linear. In addition, by SEM image of diffuse damage, it was suggested that microstructure of diffuse damage was not crack-like structure. By cyclic bending with low strain amplitude of 2 500 microstrain, the stiffness of all specimens was finally lost up to 10%, but in some specimens, the stiffness was increased at the initial stage before stiffness loss.
Bio-compatible piezoelectric materials are becoming increasingly important for actuators and sensors in medical devices, that is Bio-MEMS such as health monitoring systems and drag delivery systems. In this study, we challenged to search new piezoelectric materials with bio-compatibility by first principles calculation. Firstly, constituent atom of bio-compatible piezoelectric materials have been specified by HSAB method from the viewpoint of interaction energy with in vivo molecules. Secondly, in order to create a perovskite-type crystal structure with good piezoelectric response, the combination of bio-compatible atoms was selected to satisfy geometric stable condition defined by tolerance factor. As a result, we discovered 7 kinds of new piezoelectric materials. One of them, MgSiO3 is known to be a mineral with perovskite-type crystal structure, but it has never been applied to piezoelectric materials. Therefore, we focused on MgSiO3 as a candidate for biocompatible piezoelectric materials, and then the stable cubic and asymmetric tetragonal structures of MgSiO3 were analyzed by first principles DFT. Finally, structural phase transition of MgSiO3 has been investigated on the assumption of linear structural change from cubic structure to tetragonal one. DFT calculation indicated that MgSiO3 can change spontaneously to tetragonal structure with electric polarization, and that MgSiO3 can present a good piezoelectricity.
This paper is concerned with an application of the boundary element method using the dual reciprocity method to analyze nonlinear transient heat conduction in anisotropic solids. In this study, as the fundamental solution of this problem is not obtained, the concept (Analog Equation Method) proposed by Katsikadelis and Nerantzaki is applied. A standard linear partial differential operator in which the fundamental solution can be obtained extracts from a nonlinear partial differential equation. One can consider the remainder as a body force and solve the equation using DRM. Mathematical formulations of this approach for two-dimensional problems are presented in detail. Two schemes are discussed in this paper : The “isotropic” scheme, in which the operator of steady-state heat conduction in isotropic solids extracts, and the “anisotropic” one, where the operator of the steady-state heat conduction in anisotropic solids does. The proposed solution procedure is applied to a couple of typical examples, and the validity and other numerical properties of the proposed BEM are demonstrated through discussons of the results obtained.
In this study, the thermal singular stresses in a elastic half-plane containing an infinite row of parallel cracks perpendicular to the boundary is considered. The half-plane is subjected to a uniform heat flux and a uniform mechanical load, and the temperatures on the crack surfaces and free surface of the half-plane are maintained at uniform temperatures, respectively. The Fourier transform techniques are used to formulate the problem in terms of singular integral equations. The singular integral equations are solved by using the Gauss-Jacobi integration formula. Both the cases of an internal crack and an edge crack are studied. Numerical calculations are carried out, and the effects of the geometric parameters on the temperature-thermal stress distributions and the thermal stress intensity factors are shown graphically.
In this paper we examine the basic characters of Particle Swarm Optimization (PSO), and apply it the mixed design variable problems. Some models of PSO have been proposed, but the basic characters of PSO are not well described. PSO is mainly a method to find a global or quasi-minimum for a nonlinear and non-convex optimization problem of the continuous design variables, and few researches of PSO about optimization problems with the discrete design variables have been reported. In this paper we also show the penalty function approach to treat the discrete design variables.To treat the discrete design variables as penalty function, it is possible to treat all design variables as the continuous design variables. As a result, the penalty parameter for the penalty function is needed. Additionally, we also present how to determine the penalty parameter for the penalty function. Through typical mathematical and structural optimization problems, the validity of proposed approach is examined.
Difficulty in quality assessment of adhesive interface between granular inhomogeneous materials and a disk plate has been pointed out in nondestructive ultrasonic inspection because of the effect of multiple-reflection at the contact point of each granular particle. A simulation technique is presented in this paper for estimating the adhesion quality of a CBN grinding wheel at the interface between the granular material and the disk plate. The grinding wheel was transposed to one dimensional serial model consisted of each segment of particle with random acoustic impedances at the interface. The propagation of incident ultrasonic waves in the grinding wheel was calculated and echoes from adhesive interface were analyzed. The domestic echo waveform from the adhesive interface was specified and learned by a neural network corresponding adhesion quality and the characteristic of the echo waveform. The effect of the grinding wheel structure to the accuracy of presumption was investigated by using the network. It was revealed that the neural network is effective to assess the adhesive quality of such inhomogeneous structural materials.
Vibration-damping properties have been studied for steel and CFRP (Carbon Fiber Reinforced Plastics) plates coated with viscoelastic elastomer which are applied for ship's hull materials with the aim of reducing the vibration noise. In the present. study, vibration loss factor of the coated materials and original components have been measured by the standard method as determined in JIS G 0602. The loss factor and the Young's modulus of the elastomer in a range of the frequency of the decrease object for reducing the vibration noise have been computed by the conversion frequency nomogram. In this calculation, the temperature-frequency conversion rule is used, which is obtained from the measurement of the loss factor and the resonance frequency characteristics. As a result of above experiments and calculations, a method for reducing the radiation noise by coating hull with elastomer is proposed.