Abstract:
The use of thin membranes is widespread in a variety of applications in a range
of industries owing to the lightweight nature and small packaged volume
attainable by them. When facilitating the storage of large areas of membranes
by foldingspeci cally in aerospace applications, the resulting creases alter the
physical state and material properties of the overall membrane structure. Even
though numerical modelling is preferred as a viable tool in replicating space
environments on earth in the form of reduced gravity and air drag, the
idealisations utilised in these analyses require validation via small-scale
experiments. The signi cance of this process is highlighted due to past
endeavours which failed to idealise the crease mechanics accurately, leading to
inaccurate predictions and eventual failure in complete missions. Moreover, the
use of virtual testing in this regard is limited by the unavailability of accurate
experimental data.
In this research, an attempt has been made to characterise the crease
mechanics of multiple creased thin Kapton 100 HN poyimide membranes using
an experimental study.A combination of specimens consisting of two and three
creases have been analysed in this regard, and momentangle responses were
plotted using results of physical experiments. The results indicated di erent
crease sti nesses for each crease in a parallel-creased specimen, with the highest
sti ness observed for a crease nearest to the pinned support. However, all the
sti ness values obtained herein were observed to be of a lower order than the
simulation and physical experimental results obtained by previous researchers
for membranes with a single crease, which could be attributed to the precise
measurements taken during the experimental study and the incorporation of the
e ect of self-weight of the membrane into its momentrotation response, which
was neglected in earlier studies. The time dependence of the opening behaviour
ii
was also studied, and it was identi ed that the membrane achieves a constant
opening angle in a shorter time duration on being loaded.
An improved experimental setup was designed and developed, on identifying
the limitations and inaccuracies observed in the experimental setup devised by
previous researchers. This ensured controlled displacement being o ered to the
membrane for capturing its deployment behaviour over a wider regime of
loading, along with precise force measurement. The setup included additional
measures to facilitate its usage for specimens of a wider range of dimensions,
and to ensure proper alignment of the membrane, thereby enhancing the
accuracy of the results obtained via the physical experiments which would then
be utilised for idealisation schemes of deployment simulations in virtual
environment.
Crease sti ness determined for single-creased membranes utilising the
improved setup was implemented in Abaqus/Explicit nite element package for
the purpose of predicting the deployment behaviour of membrane structures
with multiple creases accordingly. The crease-line was represented with
connector elements specifying the rotational elasticity, and was observed to have
negligible e ect on the deployment which contradicts the experimental
observations. Hence, further investigations are required for assessing the
accuracy of this claim.
A quasi-static simulation was carried out for a simple creased unit based on
traditional \Waterbomb" base for predicting the deployment behaviour
consisting of intersecting creases. The simulation developed in Abaqus/Explicit
environment was able to capture the deployment response observed in the
physical experiments, in terms of maximum deployment ratio and shape on
incorporating the e ect of gravity to the simulation.
Citation:
Dassanayake, D.M.S.P. (2019). Investigation of creases in ultra - thin membranes [Master’s theses, University of Moratuwa]. Institutional Repository University of Moratuwa. http://dl.lib.uom.lk/handle/123/16950