Postbuckling analysis of variable angle tow composite plates

A geometrical nonlinear analysis of a symmetric, variable angle tow (VAT), composite plate structure under inplane shear load is investigated in this work. The nonlinear vonKarman governing differential equations (GDEs) based on stress function and displacement function are derived for postbuckling analysis of symmetric VAT plate structures. A numerical methodology based on the differential quadrature method (DQM) is developed for solving the GDEs of VAT plates. The methodology is applied to solve the postbuckling problem of VAT plates with linear fibre angle orientations under simply supported plate boundary conditions. To show the accuracy and robustness of DQM, results are compared with commercial finite element analysis. The postbuckling behaviour of VAT plates under positive and negative shear is studied for different VAT fibre orientations, aspect ratios and their performance is compared with straight fibre composites. In addition, the influence of the direction of shear on the postbuckling behavior of VAT plates under axial compression is studied.

Buckling analysis and optimisation of variable angle tow composite plates

An adaptive Ritz formulation for progressive damage modelling in variable angle tow composite plates

Variable Angle Tow reinforcement design for locally reinforcing an open-hole composite plate

Global buckling and wrinkling of variable angle tow composite sandwich plates by a modified extended high-order sandwich plate theory

Manufacturable insight into modelling and design considerations in fibre-steered composite laminates: State of the art and perspective

This study presents an optimization framework to enhance the thermal buckling temperature of a variable angle tow (VAT) laminated composite plate. A finite element model is formulated using first-order shear deformation theory and eight-nodes iso-parametric elements. The developed model is validated by comparing the results of the present model with the existing benchmark solution. A genetic algorithm is employed to optimize the fibre’s path using MATLAB. The effect of geometric and material characteristics, such fiber orientation, aspect ratio, boundary conditions, material anisotropy, and thermal expansion coefficients is extensively examined. The results show that finite element-based optimization can improve the critical buckling temperature by up to 111.76%. These insights are valuable for the efficient structural design of variable-angle tows composite plates, offering potential benefits for various engineering applications.

Thermo-mechanical buckling analysis of symmetric VAT composite laminates with temperature-dependent material properties

The functional advantages of tailored stiffness, often seen in nature, are also utilized in composite structures. Advancements in the multiaxis tow placement and automated fiber placement (AFP) machines led to the development of variable angle tow (VAT) composites, also referred further as variable stiffness composites (VSC). These composites are shown to effectively enhance the stress distribution and buckling load capacity of structures with greater flexibility on the design space. This review systematically presents the status of recent research on the topic of VSCs. Various manufacturing techniques of VSC are discussed; constraints and the defects associated with the manufacturing processes are enlisted. The review highlights the optimization studies based on the fiber profile and macro-scale stiffness invariants. Several studies existing in the domain of buckling, vibration, and aeroelastic tailoring of angle tow composites are summarized to connect the important aspects of analysis and present a holistic approach for future studies in this area.

The purpose of this study is to analyze the effect of delamination on the flutter characteristics of a cantilevered variable angle-tow (VAT) nanocomposite plate. A multi-scale three-phase composite material composed of curvilinear graphite fibers and epoxy resin matrix reinforced with multi-walled carbon nanotubes (MWCNTs) is considered for the study. A FE model for a delaminated composite plate is developed in MATLAB. To perform flutter analysis, the FE model is then linked to MSC. Nastran via Direct Matrix Abstraction Program (DMAP) module and the flutter problem is solved by the p-k method. The numerical investigation is carried out on both symmetric and unsymmetric VAT plates with delamination.

Lateral-torsional buckling of fixed circular arches having a thin-walled section under a central concentrated load

In order to employ the classical Rayleigh-Rite and the popular finite element methods to model different structural regions so that each is used to its fullest advantage, a coupled Rayleigh-Rite and finite element formulation using the penalty function method is presented. The formulation is based on a constrained variational principle. Along the interface of two different regions, deformations obtained from the Rayleigh-Ritz method are set equal to deformations obtained from the finite element method. The potential energy of the Rayleigh-Rite and finite element regions with these deformation constraints is used to derive a coupled stiffness matrix. This coupled stiffness matrix contains stiffness contributions from each region and an interface stiffness contribution from the constraints. The derivation is given for one dimensional coupling of a beam and two dimensional coupling of an equivalent plate with membrane finite elements to model a wing-like structure with box beam and leadingltrailing edges. Displacements and stresses using the coupled analysis are compared with those of using a single finite element analysis. Results indicate that using the coupled RayleighRite and finite element analysis produces results with a level of accuracy approaching that of a finite element analysis, while providing enhanced modeling flexibility.

<p>The current design codes for punching shear resistance of flat slabs are based on empirical formulations derived from test results of isolated slab-column connections, where the compressive membrane action was ignored. Testing continuous slab systems is very uneconomical and in most cases not possible. In this paper, finite element analyses (FEA) are performed to investigate the structural performance of continuous slabs. A previously tested and analysed isolated slab with larger in-plane dimensions and different boundary conditions is considered. The FEA results indicate that the shear capacity of the continuous slab is much higher compared to the capacity of the isolated slab. The numerical models are used to examine the effect of low reinforcement ratio in the response of the continuous slabs. Finally, a comparison between analytical results and code provisions indicates the conservatism of the design codes.</p>

Variable angle tow steering technology is capable of manufacturing complex aviation parts with a trajectory of intricate curvature planned based on stress or profile characteristics, which greatly improves the forming efficiency, design flexibility and mechanical properties of composite structures. In view of the forming defects such as buckling and wrinkles caused by the lateral bending of fiber prepreg tow, a theoretical buckling model based on the Rayleigh Ritz method, the principle of minimum potential energy and the viscoelastic foundation is established, in which the adhesion coefficient is characterized by the degree of intimate contact to introduce process parameters. On the basis of the contact mechanics analysis, the distribution of the compaction pressure and bending stress is studied to improve the theoretical model, and the critical buckling load and the minimum radius of the tow under the normal and tangential contact conditions are determined precisely. Finally, the finite element models of compaction and variable angle steering placement are proposed, and the theoretical model and simulation model are verified by corresponding trials. It is demonstrated that defects can be effectively suppressed through optimizing process parameters.

Axial vibration analysis of an optimized MEMS gyroscope is investigated in this paper. For this purpose; a model of rotating, axially functionally graded (tapered) nano-rod is represented. Along with classical continuum mechanics, Eringen’s non-local theory is adopted. Using Hamilton’s variational approach along with coupled displacement field concept which is derived from Babaei and Yang, governing equations of motion are derived. Rayleigh–Ritz approximate method is used to solve the equation for both clamped–clamped and clamped-free rod model. Verification of current results is ratified by comparison with results available in technical literature. Incorporation of taper parameter, non-local effect and rotation effects reveals predictable patterns along with unpredictable chaotic behavior of the optimized gyroscope. Such outcomes report necessity of precise and case-by-case perusal as for some specific values of taper and non-local parameters; system results unpredictable responses. In such chaotic regimes, pattern detection based on response of the gyroscope is impossible and a kind of real-time monitoring and analysis is required. Excluding critical values of the mentioned parameters of non-locality and taper; generally rotations around a fixed axis leads to lessening the oscillations, enhancing the non-locality yields weak vibrations, and intensifying the taper effects makes the system oscillate with greater frequencies wherein for quite high values of taper parameter, gyroscope model behavior turns out independent. It is good to mention that only case in which increment of taper parameter suppresses vibrations occurs when cross-section area of clamped-free nano-rod model is increasing. Eventually, influential factors of current model are revealed.