Cushioning materials generally absorb kinetic mechanical energy under compression actions at a relatively constant stress over a large range of displacement. However, cushioning materials widely used today are polyurethane (PU) foams with low moisture transmission. As a new class of three-dimensional textile structures, warp-knitted spacer fabrics not only have much better moisture transmission property than PU foams, but also have the similar cushioning performance if appropriate structural parameters are adopted. This paper reports an experimental study on the compression behavior of a series of warp-knitted fabrics made for cushioning applications. These fabrics were produced on a double-needle bar warp knitting machine of gauge 18 by varying different structural parameters including spacer yarn inclination angle and fineness, fabric thickness, and outer layer structure. Both the compression stress-strain curves and energy efficiency diagrams from the testing results were used to analyze the compression behavior of these fabrics and the effect of each structural parameter. The results indicate that warp-knitted spacer fabrics are an ideal class of the energy absorbers for cushioning applications and their energy-absorption capacity can easily be tailored to meet specific end-use requirements by simply varying their structural parameters with the help of efficiency diagrams.

This paper presents a study of the impact compressive behavior of warp-knitted spacer fabrics developed for human body protections. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel warp knitting machine by varying their structural parameters, including spacer monofilament inclination and fineness, fabric thickness, and surface layer structure. A drop-weight impact tester was used to test these fabrics with predefined impact energy. The impact process of a typical spacer fabric was analyzed based on its impact contact force-displacement curve, energy absorbed-contact force curve and transmitted force-time curve. The effects of the structural parameters on the impact compressive behavior of the warp-knitted spacer fabrics were also discussed. The relationship between the peak transmitted force and peak contact force was established for these fabrics. The study shows that the warp-knitted spacer fabrics can be used as a type of effective material for human body protection due to their high energy absorption capacity and reduction of the contact peak force. The study also shows that all the structural parameters significantly affect the impact compressive behavior of the warp-knitted spacer fabrics in terms of peak contact force, peak transmitted force, and energy absorbed at different impact compressive stages. According to the results obtained, the warp-knitted spacer fabrics studied can reduce about 33.16% of the peak contact force.

The paper reports an experimental study on the influence of spacer fabrics' structures, that is, different surface stitches, fabric thicknesses, and diameters of spacer yarns, on the impact and compression-after-impact properties of warp-knitted spacer fabrics. Low-velocity impact tests, damage deformation characterizations, and compression tests after impacts were performed on six spacer-fabric specimens knitted on a double needle bar Raschel knitting machine. The impact method was flat-sphere (a flat striker contacted with a fabric wrapped on a hemispherical steel anvil). Deformation processes of typical spacer fabrics, force–displacement/time and energy–time curves, impact damage, and residual strength were analyzed and discussed; moreover, peak force, absorbed energy, damage depth, and the drop-off rate of residual strength were involved to estimate impact and compression-after-impact properties of the spacer fabrics with different structures. The results show that with the closed surface structure and coarser spacer yarns, the fabrics have the characteristics of lower peak forces, higher energy-absorption ability, lower damage depths, and higher drop-off rates of residual strength. Fabrics with higher thickness are of the features above but they do have lower drop-off rates

Abstract:The purpose of this research is to study the effect of both transverse impact, and ratio of outer diameter to thickness of outer steel tube (D/t), on the residual axial bearing capacity of concrete-filled circular steel tubular columns (CFCSTCs). A total of sixteen samples, including four samples left untreated for comparison, are experimentally studied to investigate the effect of both drop-hammer transverse impact height (H), and D/t ratio, on the residual axial bearing capacity of CFCSTCs. The failure mode, load-displacement curves, load-strain curves, and residual axial bearing capacity of those samples are extensively investigated. A finite element analysis (FEA) model is established to predict the effect of D/t ratio on the residual axial bearing capacity of CFCSTCs. The results indicate that the H and the D/t ratio have noticeable effects on the axial compression performance of CFCSTCs. Failure mode of samples is commonly local buckling. In addition, maximum reduction of the axial bearing capacity of columns reaches about 35% compared with that of untreated columns. The results also show that the bearing capacity of the column increases with a decreasing D/t ratio of the same diameter (D).

Seamless garments are popular knitted products nowadays. They are widely used as power stretchable underwear, outerwear and sportswear for which the use of high elastic yarns is indispensable . For seamless garments knitted with circular seamless machines, polyurethane (PU)/polyamide (PA) core-spun yarn is commonly used as the base yarn in a plating fabric to enhance the elasticity of the garment. However, the use of PU/PA core-spun yarn has encountered some problems, such as the difficulty in size control and the ageing of PU elastic yarn. In this study, the polytrimethylene terephthalate (PTT)/polyester (PET) bi-component filament was used to replace the PU/PA core-spun yarn for the development of seamless garments due to its excellent extensibility and elastic recovery property. The manufacturing processes, including knitting, pre-treatment, dyeing and finishing, were developed, and the end-use performance of the fabrics, which were respectively produced with the PTT/PET bi-component filament and PU/PA core-spun yarn as the base yarn and PA fiber as the face yarn for seamless garments, was compared based on the five different mechanical and physical properties. The results show that the fabric made of the PTT/PET bi-component filament has much better dimensional stability, much better elastic recovery property and much better wrinkle resistance than those of the fabric made of PU/PA core-spun yarn. It is expected that this study could help us to further exploit the use of the PTT/PET bi-component filament in the development of seamless garments in the future.