Konstrukciju ilgizturība un sabrukums

.

Damage Identification in a Plate-Like Structure using Modal Data

In this paper an on-going research effort aimed at detecting and localizing damage in plate-like structures by using mode shape curvature based damage detection algorithms is described. Two alternative damage indexes are examined. The first one uses exclusively mode shape curvature data from the damaged structure. This method originally was developed for beam-like structures. In this paper the method is generalized to plate-like structures that are characterized by two-dimensional mode shape curvature. To examine limitations of the method, several sets of simulated data are applied and damage detection results are compared to the damage identification method that requires mode shape information from both the healthy and the damaged states of the structure. The modal frequencies and the corresponding mode shapes for the first 15 modes of a plate are obtained via finite element models. Simulated test cases include damage of various levels of severity. In order to ascertain the sensitivity of the proposed method to noisy experimental data, numerical mode shapes are corrupted with different levels of random noise

Исследование деформативности композитов и устойчивости ребристых оболочек из них методом конечных элементов

Advisor: Рикардс, Ролан

Young’s Modulus Identification by Using Cylindrical Specimens

A method for determining the Young’s modulus of polymeric materials from deformation diagrams of thin-walled circular cylindrical shells in compression in the region of geometrical nonlinearity has been elaborated. A numerical solution is found by the finite-element method (ANSYS.) The existence of a unified deformation diagram in generalized coordinates is established, from which the flexural Young’s modulus is determined. To validate the method, the Young’s modulus of specimens was found experimentally

Inner Layer Material Identification of Two Layer

For the identification of the elastic modulus of the inner layer E2 the TWCS method (Method for the Identification of the Elastic Properties of Polymer Materials by Using Thin-Walled Cylindrical Specimens) is considered. The method is based on the solution of the problem of compression of a thin-walled cylindrical tube by two parallel planes. The contact problem is solved by using the Finite Element Method. The deformation of a thin polymer shell is characterised by great displacements and relatively low elastic deformations in a large range of movement of parallel planes. In this paper the cylindrical shell consisting of two layers with different elastic modulus is considered. The outer layer (bandage) of the cylindrical shell is made from a rigid polymeric material with relatively high Young's modulus (10J MPa). The inner layer is made from a softer polymer - Young's modulus 102 MPa or even 10 MPa. Poisson's ratios of both layers are 0.35. The average radius R, the length L, the Young's modulus of the outer layer E\ and the thickness of both layers t\ and tj of the cylindrical shell are assumed to be known. The parameter to be identified is the elastic modulus of the inner layer £2- According to the above mentioned method at first the so-called reduced elastic modulus Epriv (modulus of inelastic buckling) is determined from the compression experiment of a cylindrical shell. The cylindrical shell is assumed to be single-layered with thickness t=t\+t2. Then the step-down ratio for the elastic modulus K=E\/Epnv is introduced. Further a Finite Element model for the problem of compression of a two-layer cylindrical shell is built by using software package ANSYS. The Finite Element model is built by using SHELL181 element which allows multi-layer properties. Further the series of calculations of the cylindrical shell with different elastic modulus of the inner layer are carried out. Obtained results are tabulated and then on the basis of theses tables the graph of the dependence of the relative Young's modulus E\/Epi^ from the logarithm of the ratio of the elastic modulus of layers lg{E\IEi) is constructed

Kompozīto materiālu un konstrukciju parametru identifikācija

Kompozīto materiālu un konstrukciju parametru identifikācija ... ..

Finite Element Modeling of Thin Polymer Shell

Standard methods for determining the elastic modulus of polymer materials are based on tension, compression and bending tests of specially prepared specimens. Contrary to steel, the linear elastic area of deformation of polymer materials in standard experiments is rather small. This is the reason for a noticeable measurement error in the results obtained by such methods. The method of determination of the elastic modulus described in this study is based on the solution of the problem of compression of a thin-walled circular cylindrical shell by two parallel planes with regard to the geometrical and physical nonlinearity. The account of nonlinear effects in determination of elastic modulus makes it possible to use a considerably greater range of the loading curve in the elastic region of deformation compared with that in standard methods of testing specimens for tension, compression, and bending. The contact problem is solved by the finite-element method (ANSYS). To solve the nonlinear problem by the finite-element method, a macros-program was elaborated, which specifies the geometry, physical law, and properties of the material, boundary conditions, loading, division into finite elements, and the step scheme of the solution. The deformation of a thin polymer shell is characterized by great displacements and relatively low elastic deformations in a large range of movement of parallel planes. The solution obtained by finite element method allows making the universal loading diagram in dimensionless coordinates in the given range of thicknesses and elastic module. Equation of the universal loading diagram allows us to solve the inverse problem of determination of the elastic modulus according to experimental points on the loading diagram