DETERMINATION OF MECHANICAL PROPERTIES OF THIN FILMS AND FUNCTIONAL GRADIENT MATERIALS USING INVERSE TECHNIQUE
This paper describes a method for evaluating material properties of multi-layered systems and functional gradient materials using data obtained from indentation testing. The measurement data collected from the penetration force-depth curves in the test are employed for identifying elastic moduli of thin films and functional gradient materials. An indentation problem is first analyzed on the basis of the three-dimensional axisymmetric theory of elasticity. Analyses of elastic contact problem, which an elastic axisymmetric indenter is penetrated into multi-layered systems and into functional gradient materials, are presented. An inverse analysis for determining Young’s moduli, Poisson’s ratios and radii of the contact area is performed under the assumption that the elastic moduli of the substrate and the indenter, and thicknesses for layers are known. When complex method is used for minimizing an objective function composed of errors, effective sampling of data obtained by penetrating indenters with various radii of curvature into the coated substrate and functional gradient materials is presented. INTRODUCTION Modern electric devices and mass storage devices have frequently multilayered structures to achieve a high performance and functionality. Furthermore, such devices are coated often by metal thin films to protect from the damage of external dusts and environment. It is important to estimate their mechanical properties for improving the reliability of devices and machines. Generally, mechanical properties of thin films deposited on a substrate are different from those of bulk. Hence, we need to know in-situ the mechanical properties of deposited films. However, it is very hard to carry out a test for evaluating the mechanical properties of films in a sub-micrometer thickness. Ihara, et al. estimated the material properties of a thin film using surface wave spectroscopy. Matui, et al. examined the accuracy of identified elastic moduli in a multilayered system. Kishimoto, et al. idetified the elastic properties for a bar of functional gradient materials. Indentation test is one of methods for evaluating the mechanical properties of thin films, which is the one estimating elastic moduli of thin films using experimental data of the force and the depth of an indenter penetrated into a multi-layered system. In the present paper, when data of the indentation force and depth are used, a method for identifying the mechanical properties of thin films and the distribution function of mechanical properties in functional gradient materials will be presented. ANALYSIS OF INDENTATION PROBLEMS In the present analysis, an axisymmetric elastic indenter with a cross section of f(r) will be penetrated into an elastic half-region composed of layers with various mechanical properties as shown in Figure 1. This contact problem is analyzed using the theory of threedimensional axisymmetric elasticity. Then, displacements and stresses in the layers, the indenter and the elastic half-region can be deduced by substituting Boussinesq’s potential functions, ψ and φ 3 , into the following relationships (Miyamoto 1977, Gladwell 1980).
Seismic response to a prescribed seismogram of a body embedded in a multilayered half space
Abstract While the actual problem is composed of an active fault surface, a soil site and a body embedded at that site; the proposed method provides an alternative smaller linear problem by replacing the propagating rupture on the fault surface by a fictitious focal point and a seismograph station in the vicinity of the given soil site. The Green's function for each of three fundamental problems of isotropic elastic and viscoelastic spaces undergoing harmonic vibration is derived. Infinite elements are adopted in the far field, and finite elements in the near field. The three fundamental problem solutions are used as the shape functions of infinite element nodal lines. The three concentrated orthogonal force components at the focal point are determined in such a way that the Fourier transforms of the three orthogonal acceleration components measured at a seismograph station are checked. For seismic analysis of a finite embedded body, consider the differential between the actual system and the seismic free field, which is the embedding half space without any embedment and being excited by the fictitious focal point forces. All along the analysis has been carried out in the frequency domain. An appropriate inverse Fourier transform algorithm will properly yield all results as time functions.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.