Application of Laminated Composite Grids as a Reinforcing Element of Automotive Components

This paper intends to present the application of laminated grid structures as a new class of stiffeners for reinforcing body and chassis of transportation vehicles. A laminated grid plate is constituted from several grid plies with different orientations. Therefore, the grid layers with various fibers, patterns, and orientations can be used, resulting in laminates with enhanced stiffness and coupling effects. In this study, a hypothetical trunk floor is assumed as a sandwich panel with two skins and a composite laminated grid core, which is clamped along all edges. Three different grid structures are considered as the core to strengthen the trunk floor subjected to arbitrary lateral loads. Moreover, the first natural frequency of the plates are achieved. The Ritz method is employed to obtain the maximum deflection and free vibration frequencies of the trunk’s floor panel. The results indicate that employing the laminated grids considerably enhances the response of the panel in comparison with conventional grids

Influence of Employing Laminated Isogrid Configuration on Mechanical Behavior of Grid Structures

For a long time, a single grid layer, such as isogrid, have been utilized to strengthen a shell or plate or as an independent structural member for various applications. Laminated grid structures consist of several grid layers that can have different in-plane orientations or can be made from different materials. Therefore, using laminated configuration instead of conventional grids yields to an extensive variety of configurations with different coupling effects and cost. In the current paper, to evaluate the appropriateness of laminated isogrids, the vibration and stability behaviors of a conventional isogrid are compared with corresponding laminated isogrid plate. The first-order shear deformation plate theory as well as the Ritz theorem is utilized to achieve the critical buckling loads and free vibration frequencies of the plates. The influence of increasing the number of isogrid plies and changing pattern geometries on mechanical behaviors of the laminated isogrid plate is also investigated. The results imply that utilization of the laminated isogrids remarkably enhances the buckling load and free vibration frequency values of the plates

Symmetrical and Antisymmetrical Sequenced Fibers with Epoxy Resin on Rectangular Reinforced Structures under Axial Loading

In this study, Finite element Method (FEM) evaluation is performed for the compressive failure of reinforced structures with layered composite shells under axial loading. In addition, embedded delamination between the reinforcing layered composite shells and the core is considered as a defect. The layered composite shells are made of 12 plies of equal thickness of Kevlar, CFC, and E-Glass with epoxy resin. Considering the orientation and laminate, three different layered composite shells, (0°/90°/0°/90°/0°/90°), (45°/-45°/0°/90°/60°/-30°), and (60°/-30°/90°/0°/30°/90°), are considered for symmetrical and antisymmetrical sequences. These results are obtained through ABAQUS simulations and subsequent analysis. The results show that symmetrical and antisymmetrical sequences can be used as an index for quality control and as a safety factor of composite shells produced by the hand lay-up technique in certain industrial processes. The delamination growth is also investigated with the help of cohesive elements. Buckling phenomenon occurred abruptly due to the fast propagation of delamination, having face/core debond

Failure study of fiber/epoxy composite laminate interface using cohesive multiscale model:

In this study, finite element modeling is performed to investigate the compressive failure of the composite sandwich structures with layered composite shells. An embedded debond area between the layered composite shell and the foam core is assumed as a defect. The composite shells are several plies of equal thickness Kevlar, carbon fiber composite, and E-glass composite with epoxy resin. Three different lay-ups, namely, (0°/90°/0°/90°/0°/90°), (45°/−45°/0°/90°/60°/−30°), and (60°/−30°/90°/0°/30°/90°) are considered for symmetric and asymmetric sequences. The work focuses on the importance of cohesive zone model versus the previously conducted numerical simulation and experimental results for buckling of sandwich composite structures. This enables one to account for delamination growth between shells and core and improve the correlation results with those of experiments. It has been shown that not only the cohesive model is capable of demonstrating delamination propagation, but it also correlates very well with the experimental data. By compiling user-defined cohesive mesoscale model in Abaqus simulation, the local and global buckling of the face-sheets can be precisely detected and response of sandwich structure becomes mesh independent, while mesh size is reduced

Bree\u27s Diagram of A Functionally Graded Thick-walled Cylinder Under Thermo-mechanical Loading Considering Nonlinear Kinematic Hardening

n this paper, elasto-plastic analysis of a thick-walled cylinder made of functionally graded materials (FGMs) subjected to constant internal pressure and cyclic temperature gradient loading is carried out using MATLAB. The material is assumed to be isotropic and independent of tem- perature with constant Poisson\u27s ratio and the material properties vary radially based on a power law volume function relation. The Von Mises’ yield criterion and the Armstrong-Frederick non- linear kinematic hardening model were implemented in this investigation. To obtain the incre- mental plastic strain, return mapping algorithm (RMA) was used. At the end, the Bree\u27s inter- action diagram is plotted in terms of non-dimensional pressure and temperature which represents an engineering index for optimum design under thermo-mechanical loading

Performance Analysis of an Electromagnetically Coupled Piezoelectric Energy Scavenger

The deliberate introduction of nonlinearities is widely used as an effective technique for the bandwidth broadening of conventional linear energy harvesting devices. This approach not only results in a more uniform behavior of the output power within a wider frequency band through bending the resonance response, but also contributes to energy harvesting from low-frequency excitations by activation of superharmonic resonances. This article investigates the nonlinear dynamics of a monostable piezoelectric harvester under a self-powered electromagnetic actuation. To this end, the governing nonlinear partial differential equations of the proposed harvester are order-reduced and solved by means of the perturbation method of multiple scales. The results indicate that, according to the excitation amplitude and load resistance, different responses can be distinguished at the primary resonance. The system behavior may involve the traditional bending of response curves, Hopf bifurcations, and instability regions. Furthermore, an order-two superharmonic resonance is observed, which is activated at lower excitations in comparison to order-three conventional resonances of the Duffing-type resonator. This secondary resonance makes it possible to extract considerable amounts of power at fractions of natural frequency, which is very beneficial in micro-electro-mechanical systems (MEMS)-based harvesters with generally high resonance frequencies. The extracted power in both primary and superharmonic resonances are analytically calculated, then verified by a numerical solution where a good agreement is observed between the results

Electrospun Nanofibers for Label-Free Sensor Applications

Electrospinning is a simple, low-cost and versatile method for fabricating submicron and nano size fibers. Due to their large surface area, high aspect ratio and porous structure, electrospun nanofibers can be employed in wide range of applications. Biomedical, environmental, protective clothing and sensors are just few. The latter has attracted a great deal of attention, because for biosensor application, nanofibers have several advantages over traditional sensors, including a high surface-to-volume ratio and ease of functionalization. This review provides a short overview of several electrospun nanofibers applications, with an emphasis on biosensor applications. With respect to this area, focus is placed on label-free sensors, pertaining to both recent advances and fundamental research. Here, label-free sensor properties of sensitivity, selectivity, and detection are critically evaluated. Current challenges in this area and prospective future work is also discussed

Flexural modes coupling in cantilever-type piezoelectric energy harvesters

The ability to harness the waste mechanical energy and convert it into useful electrical power has made kinetic energy harvesters a promising candidate to provide an everlasting energy source for wireless autonomous devices. Nonlinearities, whether introduced deliberately for the sake of bandwidth broadening or present intrinsically, can highly influence the dynamic response and output power behavior of these type of energy scavengers. This paper aims to investigate the effect of nonlinearity on multi-mode vibrational response of a harvester composed of a cantilevered piezoelectric composite beam with an attached mass of finite dimensions. To that end, first of all a 3-DoF lumped parameter coupled electromechanical model of the device is developed through a comprehensive mathematical approach and its mode shapes and natural frequencies are calculated. The perturbation method of multiple scales is then applied to obtain the steady state solutions to the extracted order-reduced governing equations of the system. Results indicate that a harvester with a cubic attached mass exhibits a simple Duffing-type resonance as the excitation frequency falls in the vicinity of each natural frequency. That occurs while for a U-shaped mass the vibration modes would be coupled through occurrence of an internal resonance. In this latter case, both flexural modes of the piezoelectric beam are stimulated by a single frequency excitation and contribute to the power generation leading to an enhancement of the total output power which is the major advantage of the proposed design in this paper compared to the other existing energy harvesters. The frequency response curves of the output power are found to be composed of four branches and include Hopf bifurcations and instability regions. To verify the results obtained from the analytical approach, they are compared to a numerical solution where a good agreement is observed between them

Multi-Objective Optimization of Composite Angle Grid Plates for Maximum Buckling Load and Minimum Weight Using Genetic Algorithms and Neural Networks

The present work describes an optimization process based on the ε-constraint method to find an optimum design to maximize the critical buckling load and minimize the structural weight of an angle grid plate. A comprehensive geometrical model is considered including all geometrical design variables of the grid. In order to achieve a precise and effective approximation of the buckling load, an artificial neural network (ANN) is employed. Training data for ANN is obtained by the Mindlin plate theory as well as the Ritz method. The ANN is combined with genetic algorithms (GA) to find the optimized design variables for an angle grid structure. The results provide a wide range of geometrical data for designers to choose the maximum buckling load at the minimum structural weight

Static and Dynamic Solutions of Functionally Graded Micro/Nanobeams under External Loads Using Non-Local Theory

Functionally graded materials (FGMs) have wide applications in different branches of engineering such as aerospace, mechanics, and biomechanics. Investigation of the mechanical behaviors of structures made of these materials has been performed widely using classical elasticity theories in micro/nano scale. In this research, static, dynamic and vibrational behaviors of functional micro and nanobeams were investigated using non-local theory. Governing linear equations of the problem were driven using non-local theory and solved using an analytical method for different boundary conditions. Effects of the axial load, the non-local parameter and the power index on the natural frequency of different boundary condition are assessed. Then, the obtained results were compared with those obtained from classical theory. These results showed that a non-local effect could greatly affect the behaviors of these beams, especially at nano scale