Fonksiyonel derecelendirilmiş ve çok katmanlı kompozit malzemelerde dalga yayılması

Gökmen^Aksoy, Hüseyin; şenocak, Erol
April 2010
ITU Journal Series D: Engineering;Apr2010, Vol. 9 Issue 2, p105
Academic Journal
Composite materials have been used by the engineers. Thus by using proper combination of different materials one can produce a material with an improved thermal, acoustical, mechanical or electrical properties according to the needs in design. Composite materials can be classified in three groups, which are fibrous composites, laminated composites and particulate composites. Many different approaches have been used for approximating the mechanical behaviour of composite materials. The mechanical behaviour of composite materials under static loads are well documented. On the other hand less is known about mechanical behaviour of composites under dynamic loads. Behaviour of composite materials, which are used in military equipments, under impact loads and modeling of this behaviour is gaining attention. In design and modelling of composite materials two main approaches have been used. One of these is to model the composite material as layered material. In modelling the layered media most of the attention is paid to the defining the effective material properties. Many theoretical and experimental studies have been done on this topic. The use of layered media in designing composite plates has some disadvantages. Sudden change in material properties causes stress concentration in the material which may cause failure. The later is functionally graded materials (FGMs). The material properties are continuous in FGMs. Therefore no stress concentration occurs. This property of FGMs makes it advantageous for many applications. Modelling of both FGMs and layered media are challenging task. Modelling of graded material increases the computational cost whilst modelling the layered media degrades the accuracy due to the sudden change of material properties. Thus degradation of numerical accuracy affects the conservation of energy, momentum and angular momentum. Conservation properties of numerical methods are important for many structural dynamics problems. Therefore in the recent years more attention paid to the research on the conservative numerical methods for time integration and discretization in space. In the field of computational mechanics researchers are focused on the conservation properties and stability of the time integration algorithms. Newmark time integration method is one of the most widely used time integration method in structural dynamics. On behalf of this, Newmark family of algorithms are not energy and angular momentum conserving. Energy preserving algorithms are developed by the researchers. Thus energy preserving schemes are lack of high frequency dissipation, which is necessary for damping high frequency oscillations in the numerical solution. Space-time finite element method is attractive for researchers due to the stability properties. …


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