In contrast to composites and woven fabrics, nonwoven materials have a unique web
structure, which is composed of randomly oriented fibres bonded in a pattern by
mechanical, thermal or chemical techniques. The type of nonwovens studied in this
research is a thermally bonded one with polymer-based bicomponent fibres. Such
fibres have a core/sheath structure with outer layer (sheath) having a lower melting
temperature than that of the core. In thermal bonding of such fibres, as the hot
calender with an engraved pattern contacts the fibrous web, bond points are formed
thanks to melting of the sheath material. Molten sheath material acts as an adhesive
while core parts of the fibres remain fully intact in the bond points. On the other
hand, web regions, which are not in contact with the hot engraved pattern, remain
unaffected and form the fibre matrix that acts as a link between bond points. With
two distinct regions, namely, bond points and fibre matrix, with different structures,
nonwovens exhibit a unique deformation behaviour. This research aims to analyse
the complex mechanical behaviour of thermally bonded bicomponent fibre
nonwoven materials using a combination of experimental and numerical methods.
A novel approach is introduced in the thesis to predict the complex mechanical
behaviour of thermally bonded bicomponent fibre nonwovens under various threedimensional
time-dependent loading conditions. Development of the approach starts
with experimental studies on thermally bonded bicomponent fibre nonwovens to
achieve a better understating of their complex deformation characteristics.
Mechanical performance of single bicomponent fibres is investigated with tensile
and relaxation tests since they are the basic constituents of nonwoven fabrics. The
fabric microstructure, which is one of the most important factors affecting its
mechanical behaviour, is examined with scanning electron microscopy and X-ray
micro computed tomography techniques. At the final part of experimental studies, mechanical response of thermally bonded bicomponent fibre nonwovens is
characterised with several mechanical tests. (Continues...)