ABSTRACT
Bulge test performed on the circular membrane of isotropic material provides an equibiaxial tensile stress state at the top of the inflated cap. It is supposed that a spherical shape exists in the neighborhood of summit and stress-strain state thus can be determined easily from measured inner pressure, membrane radius and stretch at the top. The inner force per unit length T can be determined from the equilibrium equation
2T R
p= , (1)
where p is the inner pressure and R is the radius of the spherical surface. However, the shape of the anisotropic bulge is rarely spherical. The basic structure of the fabric reinforcement has in general two main directions (warp and weft or course and wale) which results in orthotropic response and in the bulge cap shape resembling an ellipsoid. It is therefore possible to accept as a good approximation stresses for the membrane in the form of the ellipsoid (Chi-Teh Wang, 1953):
T p
T Tm c
c = −
⎛ ⎝⎜
⎞ ⎠⎟2 2κ
κ κ
,, (2)
1 INTRODUCTION
Application of textile technologies such as knitting, weaving, and braiding to thin NiTi wires enables to extend outstanding structural and functional properties of these wires to more complex structures (Heller et al. 2011). Moreover, through variation of textile morphology one is able to tailor macroscopic thermomechanical behaviour of such structures. Functional plain weft knitted NiTi textiles-elastomeric composites represent such a concept of functional NiTi textiles to be used in smart structures and systems. The experimental research and the modelling of smart elastomeric composites reinforced by SMA woven or knitted fabrics have been launched to determine the deformation behaviour of the material and then to identify material parameters of the appropriate constitutive equation. Preliminary results of the experimental research of the elastomeric composites reinforced by different types of SMA knitted and woven fabrics were presented (Marvalova et al. 2011).
