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CONTENTS
Volume 2, Number 4, December 1994
 

Abstract
Some structures under the action of some specific loads can be treated as consisting of rigid and deformable parts. The paper presents a way to include rigid elements into a finite element model accounting for geometrical and material nonlinearities. Lagrange multipliers technique is used to derive equations of motion for the coupled deformable-rigid system. Solution algorithm based on the elimination of the Lagrangian multipliers and dependent kinematic unknowns at the element level is described. A follow-up paper (Rojek and Kleiber 1993) complements the discussion by giving details of the computer implementation and presenting some realistic test examples.

Key Words
nonlinear finite element analysis; rigid body dynamics; inelastic structures.

Address
Institute of Fundamental Technological Research, Polish Academy of Sciences, Swietokrzyska 21, Warsaw 00-049, Poland

Abstract
This is the second part of the paper(Rojek and Kleiber 1993) devoted to nonlinear dynamic analysis of structures consisting of rigid and deformable part. The first part contains a theoretical formulation of nonlinear equations of motion for the coupled system as well as a solution algorithm. The second part presents the computer implementation of the equations derived in the first part with a short review of the capabilities of the computer program used and the library of finite elements. Details of material nonlinearity treatment are also given. The paper is illustrated by discussing a practical problem of a safety cab analysis for an agricultural tractor.

Key Words
nonlinear finite element analysis; rigid body dynamics; rigid-deformable systems.

Address
Institute of Fundamental Technological Research, Polish Academy of Sciences, Swietokrzyska 21, Warsaw 00-049, Poland

Abstract
The differential equations governing free, in-plane vibrations of linearly elastic arches with variable cross-sections are derived and solve numerically for quadratic arches with three types of rectangular cross sections. Frequencies, mode shapes, cross-sectional load distributions, and the effects of rotatory inertia on frequencies are reported. Experimental measurements of frequencies and their corresponding mode shapes agree closely with those predicted by theory. The numerical methods presented here for computing for computing frequencies and mode shapes are efficient and reliable.

Key Words
circular arch; free vibration; mode shape; quadratic arch; rotatory inertia; variable cross-section.

Address
Department of Civil Engineering, Duke University, Durham, NC 27708-0287, U.S.A.
Department of Civil Engineering, Wonkwang University, Iri, Junbuk 570-749, Korea

Abstract
The stability behaivour of symmetrically laminated rectangular composite plates with loaded ends clamped and unloaded edges simply-supported, and subjected to uniform in-plane compression is investigated. A numerical and experimental investigation is presented in this contribution. The stacking sequence of the laminated glass/epoxy composite plates is symmetric about the middle surface and consists of 8-ply [0, 90, +45, -45]s lamination. Numerical predictions were obtained through the use of the finite element method. The above plates were modeled with 8-noded isoparametric layered shell elements. The effect of the input parameters such as the degree and forms of prescribed initial imperfection and the incremental step size required for incremental loading, on the convergence of the solution is thoroughly examined. Experimental results are presented for 10 test panels. All test panels were made from glass/epoxy unidirectional pregregs and have aspect ratio of 5.088. The laminate thicknesses were found to vary from 1.054 mm to 1.066 mm. Comparison of experimental data with predicted results show good correlation and give confidence in the finite element model.

Key Words
finite element method; large deflection; laminated composite plate; compression; buckling; post-buckling.

Address
School of Mechanical and Production Engineering, Nanyang Technological University, Nayang Avenue, Singapore 2263, Singapore

Abstract
This paper is concerned with the elastic buckling of cylindrical hells with internal rigid ring supports. The internal supports impose a zero lateral deflection constraint on the buckling modes at their locations. An automated Rayleigh-Ritz method is presented for solving this buckling problem. The method can handle any combination of end conditions and any number of internal supports. Moreover, it is simple to code and can yield very accurate solutions. New buckling results for cylindrical shells with a single internal ring support, and under lateral pressure and hydrostatic pressure, are given in the form of design charts. These results should be valuable to engineering designers.

Key Words
buckling; cylindrical shells; internal ring supports; Rayleigh-Ritz method.

Address
Department of Civil Engineering, National University of Singapore, Kent Ridge 0511, Singapore

Abstract
The residual stress distribution in a unidirectional graphite/epoxy laminate induced during the fabrication process is investigated at the microstress level within the scope of linear viscoelasticity. To estimate the residual stresses, the fabrication process is divided into polymerization phase and cool-down phase, and strength of materials approach is employed. Large residual stresses are not generated during polymerization phase because the relaxation modulus is relatively small due to the relaxation ability at this temperature level. The residual stresses increase remarkably during cool-down process. The magnitude of final residual stress is about 80% of the ultimate strength of the matrix material at room temperature. This suggests that the residual stress can have a significant effect on the performance of composite structure.

Key Words
residual stress; unidirectional laminate; fiber; matrix; viscoelasticity; polymerization phase; cool-down phase.

Address
Mechanical Systems Engineering Department, Korea Atomic Energy Research Institute, Taejon 305-606, Korea

Abstract
An improved finite element-transfer matrix method is applied to the transient analysis of plates with large displacement under various excitations. In the present method, the transfer of state vectors from left to right in a combined finite element-transfer matrix method is changed into the transfer of generally incremental stiffness equations of very section from left to right. Furthermore, in this method, the propagation of round-off errors occurring in recursive multiplications of transfer and point matrices is avoided. The Newmark-

Key Words
finite element; transfer matrix method; dynamic analysis; large displacement; micro-computer.

Address
Department of Physisc, SuZhou University, SuZhou, JiangSu 215006, China

Abstract
The durability of concrete is related to the permeation characteristics of its near surface. An attempt was made to use the permeation characteristics namely, absorptivity, permeability and diffusivity, to predict the freeze/thaw resistance of concrete. Test results indicate that in general, there was a trend that freeze/thaw resistance of concrete was enhanced with improved absorptivity and diffusivity whilst the freeze/thaw resistance of normal concrete was ground to have the best relationship with its intrinsic permeability. The latter method is therefore proposed to be adopted to predict freeze/thaw resistance of normal concrete. Since Figg air test is an inexpensive and simple test method that measures indirectly the intrinsic permeability of concrete, it is further proposed that it could be used as a quality control tool to assess, non-destructively, the freeze/thaw durability potential of in-situ concrete.

Key Words
intrinsic permeability; Figg air test; freeze/thaw resistance; concrete.

Address
Hong Kong Polytechnic
Dundee University
British Board of Agrement
Hong Kong Polytechnic


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