Research On Geometric Structure Development And Performance Of Warp-knitted Spacer Fabrics With Negative Poisson's Ratio

The warp-knitted spacer fabric has a three-layer structure of upper,middle and lower,which has excellent anti-compression and energy-absorbing properties when used in products such as seat cushions.When making products such as seat cushions,ordinary spacer fabrics need to be stretched and fixed,and the fabric will also be stretched during the process of being compressed by the human body.Stretching causes the fabric to become thinner,less energy absorption,less supportive and less comfortable in the product.When the material with negative Poisson's ratio is stretched by external force,the material becomes thicker and the energy absorption is enhanced.This paper aims to develop a class of spacer fabrics with a negative Poisson's ratio in the thickness direction to make the fabric thicker when stretched,with better compression resistance and energy absorption properties.A new mathematical theoretical model with thickness composed of upper and lower layers and intermediate spacer layers was designed,and two spacer fabrics with a thickness of 6.2 mm and 2.9 mm were knitted by machines that meet the demands of the job.The upper and lower layers of the two fabrics are composed of rigid and flexible parts,which are then connected by intervening monofilaments.The flexible parts extend when it is stretched,and the monofilaments rotation.Tension,compression and simultaneous tension and compression tests were performed on both fabrics.The behavior of the negative Poisson's ratio in the thickness direction of the fabric under single stretching and cyclic stretching was studied;three geometric models of spacer fabrics were established to predict the negative Poisson's ratio of the fabric using different assumptions;The single and cyclic compression resistance,compression resilience under different tensile states were analyzed.Finally,a spherical compression test was performed on the spacer fabric to simulate the interaction of the fabric with the human body when it was used as a seat cushion,and the comfort of the fabric was tested and analyzed.The single and cyclic stretching fabrics to obtain the minimum negative Poisson's ratio values for the 6.2 mm and 2.9 mm thick fabrics are-1.3 and-2.5,respectively.The negative Poisson's ratio of fabrics is positively correlated with tensile strain.And when the fabric is stretched laterally,only the negative Poisson's ratio effect is exhibited in the thickness direction.When the fabric is cyclically stretched laterally,The thickness increase of the fabric decreases with the number of times,and the Poisson's ratio gradually stabilizes at a negative value when the tensile strain is 10%,20%,30%,and 40%.The results of the Three different deformation models established show that reducing the thickness of the fabric and the angle between the monofilament and the surface layer,and increasing the number of chains in the rigid part can improve the negative Poisson's ratio effect of the fabric.Among them,the change of monofilament has the most obvious influence on the results.The results of simultaneous tension and compression tests on the fabric showed that compressive resistance and compressive resilience of fabrics are positively correlated with fabric tensile strain,and the compressive resilience could reach 50%.The fabric comfort measurement results show that the thermal conductivity and air permeability of the fabric are positively correlated with the Poisson's ratio.When the human body puts pressure on the seat cushion,it will have a stretching effect on the fabric.When an ordinary seat cushion is subjected to greater pressure,the fabric is compressed,and their thermal conductivity and breathability change in the opposite direction.The fabric has application value in products such as seat cushions.we have weaved fabric that it is in the horizontal stretch thickness direction is changing.When used in seat cushions and other products,the fabric is stretched,its compressive stress increases,and the energy absorption effect is better.Its air permeability and thermal conductivity are positively correlated with tensile strain.The fabric meets the application requirements of a seat cushion.