Improving cushioning properties of a 3D weft knitted spacer fabric in a novel design with NiTi monofilaments

Abstract

Cushioning pads alleviate the effects of mechanical stress on the human body due to impacts and daily activities. One relevant application for such pads is orthopedic insoles used for diabetic foot to improve energy absorption and reduce stress gradient by using suitable materials and structures. This article considers a novel design that improves the energy absorption capabilities of cushioning pads. Experiments were conducted to evaluate the properties of the designed weft knitted spacer fabrics. Six groups of samples were knitted in which steel, polyamide, and shape memory alloy materials were utilized as spacer monofilament. Stress–strain, energy absorption and efficiency diagrams were obtained following the quasi-static compression tests carried out on the samples. Three investigation groups were adopted to evaluate the effect of the spacer monofilament material, diameter, and slope on energy absorption capacity. It was determined that shape memory alloy monofilament with 0.1 mm diameter was the optimum configuration to be utilized as spacer yarn in a typical 3D weft knitted fabric. It was also concluded that higher-inclined spacer monofilament in spacer fabric was the optimum choice for knitting cushioning pads as it absorbed more energy. The energy absorption capacity of the optimum design of spacer fabric obtained in this study, increased by a factor of 2.4 compared with commercial polyamide pads. This design can be utilized in any cushioning pad exposed to high mechanical stress due to impact, sports and daily activities.

Force attenuation capacity of weft-knitted spacer fabric in low-velocity impact

“…Due to coarser monofilament yarns, the risk of needle breaks during the knitting process is high due to its high bending rigidity. As mentioned in previous work (Hamedi et al, 2018), bending rigidity (B) is calculated by equation (1): Where I is the moment inertia and E is the elasticity modulus. According to the above equation, the bigger the diameter of the spacer yarn in the fabric, the higher the bending rigidity due to enhancement in the moment of inertia and consequently the more difficult the knitting process.…”

“…Studies have been conducted to investigate the cushioning properties of spacer fabrics (Ertekin and Marmarali, 2012;Chen et al, 2015;Arumugam et al, 2017;Hamedi et al, 2018;Zhao et al, 2018). Understanding the impact behavior and wear comfort of spacer fabrics also becomes researcher's attention (Liu et al, 2012;Guo et al, 2013;Liu et al, 2014;Rajan et al, 2015;Wardiningsih et al, 2015;Wardiningsih and Troynikov, 2018b).…”

Mechanical and Thermal Behaviours of Weft-Knitted Spacer Fabric Structure with Inlays for Insole Applications

“…On the other hand, spacer fabric has better compression resistance and energy absorption when there is a smaller span distance between the spacer yarns, coarser monofilaments, and higher spacer yarn density [ 15 ]. Hamedi et al developed weft knitted spacer fabric to construct insole materials for diabetic patients by using a shape memory alloy, nickel-titanium, as the spacer fabric monofilaments [ 16 ]. However, spacer fabrics deform easily under high compression stress due to body weight and lose their cushioning properties after prolonged use.…”

Novel weft-knitted spacer structure with silicone tube and foam inlays for cushioning insoles

“…Spacer fabrics are 3D knitted fabrics known for their superior properties, such as good air and moisture permeabilities, cushioning performance, shock resistance, and pressure distribution, and ability to prevent ulcerations in clinical applications. [11][12][13] Their unique properties mean that spacer fabrics can be used for a wide range of products, for example, thermal insulated clothing, 14 mattresses, 15,16 protective clothing, 17 insoles 18,19 and wound dressings. 20 Nevertheless, there are also some limitations of spacer fabrics and concerns around their use in insole applications.…”