Defining relationships between geometry and behavior of bistable composite laminates

Bistability is exhibited by an object when it can be resting in two stable equilibrium states. Certain composite laminates exhibit bistability by having two stable curvatures of opposite sign with the two axes of curvature perpendicular to each other. These laminates can be actuated from one state to the other. The actuation from the original post-cure shape to the second shape is called as ‘snap-through’ and the reverse actuation is called as ‘snap-back’. This phenomenon can be used in applications for morphing structures, energy harvesting, and other applications where there is a conflicting requirement of a structure that is load-carrying, light, and shape-adaptable. MW Hyer first reported this phenomenon in his paper in 1981. He found that thin unsymmetric laminates do not behave according to the predictions of the Classical Lamination Theory (CLT). The CLT is a linear theory and predicts the post-cure shape of thin unsymmetric laminates to be a saddle. MW Hyer developed a non-linear method called the “Extended Classical Lamination Theory” which accurately predicted the laminate to have two cylindrical shapes. Since then, a number of researchers have tried to identify the key parameters affecting the behavior of such laminates. Geometric parameters such as stacking sequence, fibre orientation, cure cycle, boundary conditions, and force of actuation, have all been studied. The objective of this research is to define a relation between the length, width and thickness of square and rectangular laminates required to achieve bistability. Using these relations, a 36 in × 36 in bistable laminate is fabricated with a thickness of 30 CFRP layers. Also, it is proved that a laminate does not lose bistability with an increase in aspect ratio, as long as both sides of the rectangular laminate are above a certain ‘critical length’. A bistable laminate with dimensions of 2 in × 50 in is fabricated. Further, for laminates that are bistable, it is necessary to be able to predict the curvature and force required for actuation. Therefore, a method is developed which allows us to predict the curvature of both stable shapes, as well as the force of actuation of laminates for which the thickness and dimensions are known. Finite Element Analysis is used to carry out the numerical calculations, which are validated by fabricating laminates. The curvature of these laminates is measured using a profilometer and the force of actuation is recorded using a universal test set-up.

Post-buckling analysis of non-uniformly heated functionally graded cylindrical shells enhanced by shape memory alloys using classical lamination theory

Thermal post-buckling analysis of functionally graded cylindrical shells enhanced by shape memory alloys under uniform and non-uniform heating is presented in this article. Nonlinear equilibrium equations are derived based on the classical lamination theory and von-Karman nonlinear kinematic relations and post-buckling field is investigated using Galerkin method. For temperature dependency of material properties, a numerical solution is applied to solve the nonlinear equilibrium equation using finite difference method to solve the nonlinear heat conduction equation and layered model to evaluate the thermal stress of hybrid cylindrical shells. A closed-form solution is also presented for temperature independency of material properties. Brinson model is adopted to describe the thermo-mechanical behavior of shape memory alloys. Numerical results are presented for evaluating the effects of shape memory alloy layer and functionally graded material cylindrical shells properties on suppressing of the post-buckling path of hybrid cylindrical shells.

Additive manufactured multi-material structure with directional specific mechanical properties based upon classical lamination theory

Purpose This paper aims to additive manufacture (AM) the multi-material (MM) structure with directional-specific mechanical properties based on the classical lamination theory of composite materials. Design/methodology/approach The polyjet three-dimensional printing (3DP) process is used to fabricate the MM structure with directional-specific mechanical properties. MMs within a layer are positioned and oriented based on the classical lamination theory to achieve directional-specific properties. Mechanical behavior of the AM structure was examined under various loading conditions to justify the directional-specific properties. Findings With MM processing capabilities of the polyjet 3DP machine, AM MM structures with directional-specific mechanical properties were fabricated. From experimentation, it was observed that the AM MM structure with a quasi-isotropic laminate has superior tensile and flexural strength, and the AM MM structure with an angle ply laminate has superior shear strength. Various mechanical properties determined through testing will be useful for the selection of an appropriate layup arrangement within a structure for appropriate loading conditions. Originality/value This study presents the innovative methodology for the fabrication of AM MM structures with tailor-made mechanical properties. The developed methodology paves way for using the polyjet 3DP MM structure for applications such as the complaint mechanism, snap fits and thin features, which require directional-specific properties.

Stress Analysis of Domestic Composite LPG Cylinder Using Classical Lamination Theory (CLT)

Conventional Steel Cylinders used for LPG cylinder for domestic applications are not manufactured in a single joint but are welded. While composite cylinders are manufactured in a single joint, Composite components cannot be welded like the steel cylinder. Composite Cylinders are winded using Filament Winding technique. Compared to Steel Cylinders, Composite Cylinders are costlier. As composite cylinders are safer than steel cylinder, composite Cylinders due to a rubber lining inside, they are 100% leak proof. If mass production of composite cylinders are done then the cost may get reduced. This paper summarizes the design and analysis of the manufacturing of Liquid petroleum gas (LPG) Cylinder using Glass Fibre Reinforced Plastic (GFRP) material. The stresses along all the directions of the ply sequence are also calculated using Classical Lamination Theory (CLT). The fibre stresses along all the directional angles were found to be under the required stress limits. The Metallic boss Calculation & angle variation at dome is the key parameter and is carried out and determined the tip radius.