Mechanics of Advanced Composite Structures
Volume:2 Issue: 1, Spring and Summer 2015

In this paper, Eringen’s nonlocal elasticity and Timoshenko beam theories are implemented to analyze the bending vibration for non-uniform nano-beams. The governing equations and the boundary conditions are derived using Hamilton’s principle. A Generalized Differential Quadrature Method (GDQM) is utilized for solving the governing equations of non-uniform Timoshenko nano-beam for pinned-pinned, clamped–clamped, clamped–pinned, clamped–free, clamped–slide, and pinned-slide boundary conditions. The non-dimensional natural frequencies and the normalized mode shapes are obtained for short and stubby nano-beams where influences varying cross-section area, small scale, shear deformation, rotational moment of inertia, acceleration gravity and the self-weight of the non-uniform Timoshenko nano-beam are discussed. The present study illus-trates that the small scale effects are more significant for smaller size of nano-beam, larger nonlocal parameter and higher vibration modes. Further, the compression forces due to gravity and the self-weight of the nano-beam also like the small scale effect are reduced the magnitude of the fre-quencies of the nano-beam.

In the current study, the effects of interactions of the moving loads and the attached mass-spring-damper systems of the composite plates on the resulting dynamic responses are investigated comprehensively, for the first time, using the classical plate theory. The solution of the coupled governing system of equations is accomplished through tracing the spatial variations using a Navier-type solution and the time variations by means of a Laplace transform. Therefore, the results are exact. The effects of various material, stiffness, and kinematic parameters of the system on the responses are investigated comprehensively and the results are illustrated graphically. Apart from the novelties presented in the modeling and solution stages, some practical conclusions have been drawn such as the fact that the amplitude of vibration increases for both the free and forced vibrations of the plate and the suspended mass, when the magnitude of suspended mass increases.

The molecular dynamic technique was used to simulate the nano-indentation test on the thin films of silver, titanium, aluminum and copper which were coated on the silicone substrate. The mechanical properties of the selected thin films were studied in terms of the temperature. The temperature was changed from 193 K to 793 K with an increment of 100 K. To investigate the effect of temperature on the mechanical properties, two different ways including step by step and continuous ways, were used. The temperature in the indentation region was controlled and the effect of temperature increase due to the friction between the indenter and the film was taken into account. The temperature effects on the material structure, piling-up and sinking-in phenomena were also considered. The results show that the elasticity modulus and hardness of thin films decrease by increasing temperature. These mechanical properties also decreased due to the increase in temperature, in the indentation region, which in turn was due to the interaction between the indenter and the thin film.

In this study, aluminum (Al) matrix reinforced with micro-particles (30 µm) and nano-particles (50 nm) boron carbide (B4C) were used to prepare Al-2.5%wt., B4C nano-composite and micro-composite, respectively, using mechanical alloying method. The mixed powders were mechanically milled at 5, 10, 15 and 20 hrs. The XRD results indicated that the crystallite sizes of both the micro-composite and nano-composite matrix decreased with increasing milling time, showing 55 nm and 40 nm, respectively. Mechanical testing results showed an increase in the flexural strength from 98 to 164 and 115 to 180 MPa, and an increase in the hardness from 60 to 118 and 75 to 130 HV for micro-composite and nano-composite, respectively. The results indicate that the strength and hardness of the nano-composite are higher than those of the micro-composite due to the presence of the fine particles.

This study deals with the applications of a trigonometric shear deformation theory considering the effect of the transverse shear deformation on the static flexural analysis of the soft core sandwich beams. The theory gives realistic variation of the transverse shear stress through the thickness, and satisfies the transverse shear stress free conditions at the top and bottom surfaces of the beam. The theory does not require a problem-dependent shear correction factor. The governing differential equations and the associated boundary conditions of the present theory are obtained using the principle of the virtual work. The closed-form solutions for the beams with simply supported boundary conditions are obtained using Navier solution technique. Several types of sandwich beams are considered for the detailed numerical study. The axial displacement, transverse displacement, normal and transverse shear stresses are presented in a non-dimensional form and are compared with the previously published results. The transverse shear stress continuity is maintained at the layer interface, using the equilibrium equations of elasticity theory.

This study presents a new approach to control the nonlinear dynamics of an adaptive absorber using shape memory alloy (SMA) element. Shape memory alloys are classified as smart materials that can remember their original shape after deformation. Stress and temperature-induced phase transformations are two typical behaviors of shape memory alloys. Changing the stiffness associated with phase transformations causes these properties of SMA. A thermo-mechanical model (based on the transformation strain which is a measure of strain indicating the phase transformation) is used to constrain the general thermo-mechanical features of the SMA. Here, the one-dimensional SMA model is adopted to calculate both the pseudo-elastic response and the shape memory effects. The dynamic behavior of shape memory alloys is then investigated, and a Newmark method is adopted to analyze the nonlinear dynamic equations. Results demonstrate that the vibration of an initial system can be tuned using the SMA absorber in a wide range of frequencies. Therefore, SMAs as adaptive tuned vibration absorbers provide an excellent performance to control vibrations.

The free vibration of the lattice cylindrical composite shell reinforced with Carbon Nano-tubes (CNTs) was studied in this study. The theoretical formulations are based on the First-order Shear Deformation Theory (FSDT) and then by enforcing the Galerkin method, natural frequencies are obtained. In order to estimate the material properties of the reinforced polymer with nano-tubes, the modified Halpin-Tsai equations were used and the results were checked with an experimental investigation. Also, the smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of the shell in order to obtain the equivalent stiffness of the whole structure. The effect of the weight fraction of the CNTs and also the ribs angle on the natural frequency of the structure is investigated in two types of length to diameter ratios in the current study. Finally, the results which are obtained from the analytical solution are checked with the FEM method using ABAQUS CAE software, and a good agreement has been seen between the FEM and the analytical results.