Modelling and experimental validation of the effect of the elastic properties of fabrics on the durability of screen printed e-textiles

Fabrics are stiff in tension but highly compliant in compression in the plane of the textile. The effect of these differing elastic properties on the durability of electronics integrated in or on the fabric is still largely unknown because fabric properties are not easily characterised. Using a mathematical model combining classical beam theory (CBT) and Pierce's fabric cantilever test, this paper models the bending behaviour of a woven fabric and locates its neutral axis ( NA) as a basis for developing more durable printed e-textiles. The CBT model showed that the difference in the tensile and compressive moduli of a fabric reduces the bending resistance of the fabric and also moves its NA position away from the central axis on the fabric. Results obtained from a Pierce's bending test of four different textile blends of polyester, cotton and lycra indicate textiles can have anisotropic elastic moduli with different values in their warp and weft directions. This results in different NA positions that vary depending upon the direction of the bending forces. Empirical verification of these NAs was achieved by comparing the change in resistance of a set of screen printed piezoresistive strain gauges positioned on and away from the NA during positive and negative bending with a radius of 5 mm. The gauge positioned at a 1% distance from the NA position showed approximately 0.3% change in its electrical resistance in contrast to a 37% change in its resistance when it was located at a 65% distance away from the NA.