Design strategy for auxetic dual helix yarn systems

Parametric sensitivity analysis to maximise auxetic effect of polymeric fibre based helical yarn

“…However, contradictory claims made by various authors as to which design configuration increases the auxetic effect have made it evident that further investigation is required to determine the optimal design parameters. Whilst previous studies have shown that lowering the starting wrap angle tends to result in a higher maximum NPR [13][14]17]; none have identified at which angle that assumption becomes untrue. This study aims to determine the optimal design configuration for maximising the auxetic effect by finding the starting wrap angle which results in the greatest NPR using finite element analysis (FEA).…”

“…The helical auxetic yarn (HAY) presented itself as the most fitting structure to be chosen for the study; as well as having the greatest potential to maximise the auxetic effect 3 [11][12][13][14][15][16][17][18][19]. The HAY has been shown to be capable of achieving a NPR of -6.8 [17], which is the highest published value of any auxetic material to date.…”

“…An array of HAYs that make up a fabric sheet all exhibiting a NPR would amplify the auxetic effect, thus increasing the desirable enhanced mechanical characteristics. Work published by previous authors up to now, has identified key parameters involved in manipulating the behaviour of the HAY, such as the starting wrap angle [13][14][15]17], tensile moduli of component materials [13,[15][16][17], and fibre diameter sizes [13][14]. However, contradictory claims made by various authors as to which design configuration increases the auxetic effect have made it evident that further investigation is required to determine the optimal design parameters.…”

“…Papers published on HAYs since they were first designed by Hook [7] have studied the design characteristics of the structure and focused on identifying the defining factors that contribute to the auxetic behaviour in the material [13][14][15][16][17]. This has been done mainly through simulated or experimental tensile testing; or by comparisons of both tests.…”

“…These were the factors considered in the modelling of the yarn. The factors are: wrap diameter, core diameter and starting wrap angle [13]. The material properties that affect a HAY's performance are: Young's modulus of both core and wrap; and Poisson's ratio of core and wrap.…”