Browsing by Author "Dharmadasa, BY"

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item: Conference-Abstract
Finite element simulation of thin folded membranes
Dharmadasa, BY; Mallikarachchi, HMYC
Deployable gossamer structures use thin filmed membranes folded into different patterns. Predicting the membrane behaviour and the stress propagation in these structures is complex due to non-linear characteristics at fold-lines. This paper investigates some of the current idealization methods (perfect hinge, perfect weld) and proposes a novel method, where connectors with rotational elasticity are defined. Furthermore a thorough investigation on key factors affecting the output is carried out. The results have proved that the novel simulation approach proposed is more accurate and careful selection of key factors could make the simulation efficient.
item: Article-Full-text
Formation of plastic creases in thin polyimide films
(2020) Dharmadasa, BY; McCallum, MW; Mierunalan, S; Dassanayake, SP; Mallikarachchi, CHMY; Jiménez, FL
We present a combined experimental and analytical approach to study the formation of creases in tightly folded Kapton polyimide films. In the experiments, we have developed a robust procedure to create creases with repeatable residual fold angle by compressing initially bent coupons. We then use it to explore the influence of different control parameters, such as the force applied, and the time the film is being pressed. The experimental results are compared with a simplified one-dimensional elastica model, as well as a high fidelity finite element model; both models take into account the elasto-plastic behavior of the film. The models are able to predict the force required to create the crease, as well as the trend in the residual angle of the fold once the force is removed. We non-dimensionalize our results to rationalize the effect of plasticity, and we find robust scalings that extend our findings to other geometries and material properties.
item: Thesis-Full-text
Simulation of fold-line stiffness in deployable membranes
Dharmadasa, BY; Mallikarachchci, HMYC
New designs for space structures such as solar sails and star shades are based on architectures that follow folding and packaging ofthin membranes. By leveraging recent advances in origami science, it is possible to design structures in which folded thin membranes deploy following a predetermined and robust path. Design and product optimization of deployable space structures are limited by complex environmental conditions experienced by them. However virtual simulations can be the perfect solution provided proper idealization techniques are followed. Presence of fold-lines alter the geometrical and mechanical properties ofthin membranes which have not being accounted in previous virtual simulations. Two major characteristics identified was the self-opening of the membrane to an equilibrium angle (defined as neutral angle) and the rotational spring stiffness ofthe membrane at the fold-line. An experimental study was devised to investigate the variation of fold-line stiffness while varying the neutral angles and membrane thickness for Kapton HN polyimide. A linear empirical relationship between resistive moment and fold-angle is proposed for each thickness. Self-opening and subsequent unfolding of a single fold was modelled using commercial finite element package, Abaqus/Explicit. Fold-line characteristics were represented with rotational spring connector elements defined between two shell portions. Compared to common idealization approaches (perfect hinge and perfect weld), rotational spring connectors were able to accurately predict the deformation profile and unfolding forces. Finally, the developed fold idealization technique was applied in an experimental case study of a deploying solar sail. It was shown that neglecting foldline stiffness underestimate the deploying force ofthe sail.