Buckling Analysis of Twisted Cantilever FGM Plates with and Without Cut-OutS.

The use and applications of composites are expanding these days.Due to light weight,high specific strength and stiffness,composite materials are being widely used as a part of wind turbine blades and ship building.For high temperature applications,Functionally Graded Materials (FGM) are preferred over laminated composites because of its good performance in the thermal field.Chopper blades, turbine cutting blades,marine propellers,compressor blades, fan shape blades,and mostly gas turbines use pre-twisted cantilever plates.Often they are subjected to thermal environments,and thus FGMs are a decent option to metal plates.Composite structures with cut-outs are usually employed in engineering structures.In structural components cut-outs are provided sometimes to lighten the structure and for proper ventilation.Cut-outs in aircraft components (for example,fuselage,ribs and wing spar) are required for inspection,access,fuel lines and electric lines or to minimize the general weight of the aircraft.Study of buckling of cantilever twisted functionally graded material plates with and without holes and with varying applied in-plane loads is dealt in the present work.The analysis is carried out by using ANSYS.An element having six degrees of freedom per node SHELL-281 is used.The FGM plate is assumed to be a laminated section containing a number of layers with a steady variation of the material property through the thickness,where each layer is taken as isotropic. Material properties in each layer are determined using power law.Results obtained from convergence studies, carried out by using 12 number of layers and 12 by 12 mesh, are found to be quite accurate.Buckling behavior of cantilever twisted FGM plates with and without cut-outs and for different non-uniform applied in-plane loads are studied for the effect of various parameters like material gradient index,aspect ratio, side to thickness ratio, diameter of cut-outs and twist angle

On the thermal buckling behaviour of laminated composite plates with cut-outs

In this work, the thermal buckling behaviour of laminated plates with rectangular cut-outs is studied using the finite element method. Based upon the classical plate theory, the used finite element is a combination of a linear isoparametric membrane element and a high precision rectangular Hermitian element. After validating the results obtained by the finite element, a parametric study is made using three types of materials commonly used in the industry, namely: the T300/5208 Graphite/Epoxy, the AS4/3501-6 Graphite/Epoxy and the E-glass/Epoxy. The study was about the effect of the size of the cut-outs, the boundary conditions, the stacking sequence and the stress resultants distribution on the critical buckling temperature. The study showed that the critical buckling temperature is strongly affected by the discussed parameters

Free Vibration of Laminated Composite Plates with Cut-Out

The laminated composite plate are basics components of structure used in various field of engineering such as turbine blades, airplane wing and helicopter blades as well as many others in civil, automotive and ship industries etc. due to their excellent high stiffness to weight ratio and strength to weight ratio. Cut-outs are provided in structure for venting, reducing weight and passage of electrical wires. Most of the structures are subjected to severe dynamic loading during their service life. This may lead to change the dynamics response of the structure. The presences of cut-outs not only reduce the strength of composite plate but also alter the dynamics characteristics of composite plate. Therefore, it necessitates predicting the dynamics responses of laminated composite plates with cut-outs with cost effective and good accuracy of these complex structures. This present paper deals with combined numerical and experimental approach on dynamics characteristics of laminated composite plate with square cut-outs. The laminated composite plates are made by using hand lay-up method. Bidirectional glass fibres are used as reinforcement and polyester resin as matrix for composite plate. The experimental dynamics test has been carried out by using different dimensions of plate with various design parameters such as cut out ratio (D/d ratio), position of cut out, aspect ratio (a/b ratio), no of layers, ply orientations under different boundary conditions. The natural frequencies of composite plate with cut-outs are determined numerically using ANSYS 14.5 software. The convergence study is done for numerically obtained results and compare with other existing literature. The experimental values are also compared with the result obtained from ANSYS 14.5 software. It was seen that the fundamental frequency decreases with increase the cut-out ratio (d/D ratio) under CFFF and SFSF boundary conditions. But fundamental frequency decreases with increase the cut-out ratio (d/D ratio) up to 0.2 under CFCF boundary condition. Further fundamental frequency increases on increase of cut-out ratio (d/D ratio)

Measuring the notched compressive strength of composite laminates: Specimen size effects

Large fibre reinforced composite structures can give much lower strengths than small test specimens, so a proper understanding of scaling is vital for their safe and efficient use. Small size (scale) specimens are commonly tested to justify allowable stresses, but could be dangerous if results are extrapolated without accounting for scaling effects. On the other hand large factors are sometimes applied to compensate for uncertainties, resulting in overweight designs. The most important variables of scaling effects on the strength of composites with open holes have been identified from experimental tests as notch size, ply and laminate thickness. In this study, these have been scaled both independently and simultaneously over a large range of combinations. The specimens are fabricated from commercially available (Hexcel Composites Ltd.) carbon/epoxy pre-impregnated tapes 0.125 mm thick (IM7/8552). The material is laid up by hand in unidirectional [04]ns with n = 2, 3, 4, and 8 (i.e., 2, 3, 4 and 8 mm thick) and multidirectional laminates; two generic quasi-isotropic lay-ups, one fabricated with blocked plies [45n/90n/−45n/0n]s and the other with distributed layers [45/90/−45/0]ns with n = 2, 4 and 8 are examined. It is shown that the critical failure mechanism in these laminates is in the form of fibre microbuckling or kinking. The unnotched compressive strength in unidirectional specimens thicker than 2 mm is found to be limited by the stress concentration developed at the end tabs and manufacturing induced defects in the form of ply waviness, fibre misalignment and voids rather than specimen size (scaling). In the open hole specimens, for both lay-ups, the strength reduction observed is due to hole size effect rather than specimen thickness or volume increase. The open hole (notched) compressive strength results obtained compare favourably to predictions by a linear softening cohesive zone fracture model developed in earlier work by the second author

Effect of cutout on stochastic natural frequency of composite curved panels

The present computational study investigates on stochastic natural frequency analyses of laminated composite curved panels with cutout based on support vector regression (SVR) model. The SVR based uncertainty quantification (UQ) algorithm in conjunction with Latin hypercube sampling is developed to achieve computational efficiency. The convergence of the present algorithm for laminated composite curved panels with cutout is validated with original finite element (FE) analysis along with traditional Monte Carlo simulation (MCS). The variations of input parameters (both individual and combined cases) are studied to portray their relative effect on the output quantity of interest. The performance of the SVR based uncertainty quantification is found to be satisfactory in the domain of input variables in dealing low and high dimensional spaces. The layer-wise variability of geometric and material properties are included considering the effect of twist angle, cutout sizes and geometries (such as cylindrical, spherical, hyperbolic paraboloid and plate). The sensitivities of input parameters in terms of coefficient of variation are enumerated to project the relative importance of different random inputs on natural frequencies. Subsequently, the noise induced effects on SVR based computational algorithm are presented to map the inevitable variability in practical field of applications

Effect of cut-out on modal properties of edge cracked temperature-dependent functionally graded plates

Modal analysis is employed to analyze the vibration of temperature-dependent of Functionally Graded Plates (FGP) under a thermal environment in order to determine the natural frequencies and mode shapes. Theoretical formulation of various materials’ properties is done using the rule of mixtures. The natural frequencies and mode shapes of simply supported and clamped square plates are investigated as a function of crack, cutout, crack and cutout and temperature dependent properties. The Ansys program is employed for the purpose of analyzing the natural frequency and mode shape of a plate. Non-dimensional results are compared for temperature-dependent and temperature-independent FGP and subsequently validated according to known results obtained from the literature. Numerical results indicate the effect of crack, cutout, gradient index and temperature fields on the vibration characteristics and mode shapes. This study proves that natural frequency decreases with increasing gradient index (n) increasing the temperature and simultaneous presence of crack-cutout. In addition, clamped plates have a higher frequency than simply supported plates in all cases. Increasing temperatures lead to a maximum decrease in frequency at clamped FGP

Metallic tube type energy absorbers: a synopsis

This paper presents an overview of energy absorbers in the form of tubes in which the material used is predominantly mild steel and/or aluminium. A brief summary is also made of frusta type energy absorbers. The common modes of deformation such as lateral and axial compression, indentation and inversion are reviewed. Theoretical, numerical and experimental methods which help to understand the behaviour of such devices under various loading conditions are outlined. Although other forms of energy absorbing materials and structures exist such as composites and honeycombs, this is deemed outside the scope of this review. However, a brief description will be given on these materials. It is hoped that this work will provide a useful platform for researchers and design engineers to gain a useful insight into the progress made over the last few decades in the field of tube type energy absorbers

Stress and buckling analysis of multilayered composite plates with different cut - outs using finite element method

This study is a numerical analysis where multiple layers of plates with different orientations were combined to form a composite plate. Within this study, the concept of in-plane tensile loading and buckling upon an orthotropic multi-layered plate with different cut-outs is discussed. The finite element method is used to conduct modeling and analysis of the composite plate where the plate has different geometric shape cut-outs to test for parameters such as deflection, stress-strain distribution, buckling, and other effects of cut-outs on the cross-section of the plate

Application of Vibration Correlation Technique for Open Hole Cylinders

As non-destructive method for axial buckling load determination - Vibration Correlation Technique (VCT) showed major advantages for a range of industrial application. Particular technique for validation of structural limit state in accordance to numerical model prediction for large (true) scale structures are getting the required momentum. The Vibration Correlation Technique (VCT) allows to correlate the ultimate load or instability point with rapid decrement of self-frequency response. Nevertheless this technique is still under development for thin-walled shells and plates. The current research discusses an experimental verification of extended approach, applying vibration correlation technique, for the prediction of actual buckling loads on unstiffened isotropic cylindrical shells with circular cut-outs, loaded in axial compression. Validation study include several aluminium cylinders which were manufactured and repeatedly loaded up to instability point. In order to characterize a correlation with the applied load, several initial natural frequencies and mode shapes were measured during tests by 3D laser scanner. Results demonstrate that proposed vibration correlation technique allows one to predict the experimental buckling load with high reliability, by loading up to % of ultimate load. Additional experimental tests including geometric imperfections from initial manufacturing and postbuckling mode shape are currently under development to further validation ofproposed approach