The Effect of Functionally Graded Materials into the Sandwich Beam Dynamic Performance

752

FGMs composed of two material constituents mixed

together with locally prescribed volume fractions have

been the focus of the majority of the literature concerning

FGMs and will be the focus of the study. Most authors

deal with epoxy and nylon. Hajime et al. [3] studied the

damping p ropert ies of carbon fi ber-re inforce d i nte rle aved

epoxy composites. Several types of thermoplastic-elasto-

meric films, such as polyurethane elastomers, polyethyl-

ene-based ionomers and polyamide elastomers, were

used as the interleaving materials. The damping proper-

ties of the composite laminates with/without the interleaf

films were evaluated by the mechanical impedance me-

thod. Also, the effects of the lay-up arrangements of the

carbon-fiber prepregs on the damping properties of the

interleaved laminates were examined. The stiffness of the

films at the resonant frequency of the laminates was an-

other important parameter that controlled the loss factor

of the interleaved laminate.

Khondker et al. [4] showed that the presence of fiber/

matrix interfaces strongly influences the overall me-

chanical properties of composites. Polyamide materials

were chosen and combined with Aramid fiber in an at-

tempt to achieve better interfacial bonding. Aramid/epo-

xy knitted composites were also fabricated to compare

them with aramid/nylon thermoplastic composites. Proc-

essing time, tensile modulus and strength of Aramid/

nylon composites have increased and decreased, respec-

tively. Aramid/nylon knitted composites have revealed

comparable strength property in the course direction,

albeit they have inferior tensile strength in the wale di-

rection when compared to that in Aramid/epoxy compos-

ites. In Aramid/nylon knitted composites, while tensile

modulus exhibited an increasing trend, there were clear

drops in tensile strengths with longer molding time. This

indicates that there could be an optimum molding condi-

tion at which maximum tensile properties can be ob-

tained.

In the work carried out by Meng-Kao et al. [5], the

faces of sandwich beams were graphite/epoxy laminates.

Epoxy and phenol resins served as a matrix material, and

multi-walled carbon annotates (MWNTs) provided rein-

forcement of the fabricated MWNT/polymer nanocom-

posites as core materials for sandwich beams. The finite

element method was used for free vibration analysis of

the sandwich beams; the natural frequencies and mode

shapes of the sandwich beams were calculated numeri-

cally. The experimental and numerical investigation of

the dynamic properties of sandwich beams with MWNT/

polymer nano composites as core materials, concluded

that the face laminate dominates the stiffness of the sand-

wich beams, and that the natural frequen cies of sandwich

beams were affected directly by the face materials and

decreased with increasing fiber orientations of the graph-

ite/epoxy face laminate.

A large number of investigators address the problem

of free vibration with free vibration analysis of FGMs.

Khalili et al. [6] studied the free vibration of three-lay-

ered symmetric sandwich beam which is investigated

using dynamic stiffness and finite element methods. To

determine the governing equations of motion by the pre-

sent theory, the core density has been taken into consid-

eration. Natural frequencies and mode shapes are com-

puted by the use of numerical techniques. After valida-

tion of the present model, the effect of various parame-

ters such as density, thickness and shear modulus of the

core for various boundary conditions on the first natural

frequency is studied. The study concluded that the face

properties like density, thickness are remained constant,

but the core properties are varied. Irrespective of the

boundary conditions, increasing the core/face density

ratio decreases the first natural frequency of the beam.

Galal et al. [7] studied the free vibration characteris-

tics of laminated composite beams (LCBs) which are one

of the bases for designing and modeling of industrial

products. In this study, the flexural vibrations of LCBs

are analyzed analytically using Bernoulli-Navier hy-

pothesis theory. The commercial finite element program

ANSYS 10.0 is used to perform a dynamic modeling to

the laminated beams. Mindlin eight-node isoperimetric

layered shell elements (Shell 99) are employed in the

modeling for describing the bending vibrations of these

laminated sandwich beams. The study concluded that

out-of plane bending frequencies decrease, in general, as

the fiber angle increases, in the case of the effect of fiber

orientation.

Simsek et al. [8] investigated the free vibration char-

acteristics and the dynamic behavior of a functionally

graded simply supported beam under a concentrated

moving harmonic load. Trial functions denoting the

transverse and the axial deflections of the beam are ex-

pressed in polynomial forms. The constraint conditions

of supports are taken into account by using Lagrange

multipliers. It is assumed that material properties of the

beam vary continuously in the thickness direction ac-

cording to the power-law form. The study concluded that

the effects of the different material distribution, velocity

of the moving harmonic load, the excitation frequency on

the dynamic responses of the beam are discussed. It is

observed from the investigations that the above-men-

tioned effects play very important role in the dynamic

behavior of the FG beam.

Xian-Kun et al. [9] deals with the small- and large-

amplitude vibrations of compressively and thermally

post-buckled sandwich plates with functionally graded

material FGM face sheets in thermal environments. Both

heat conduction and temperature-dependent material

properties are taken into account and the material proper-

ties of both FGM face sheets and a homogeneous sub-

Open Access MSA