Runjun Sun

Electromagnetic Shielding Effectiveness of Fabrics with Metallized Polyester Filaments

A preliminary study of the electromagnetic shielding effectiveness (EMSE) using metal coating films and a vacuum evaporation deposition technique with the woven fabrics made of metal/PET filaments is presented. Using coaxial transmission equipment, the EMSE of these films and fabrics was measured in the frequency range 2250—2650 MHz. The experimental results indicate that different coating materials have different EMSE, with a thicker coating film having a higher EMSE. In addition, a woven fabric with lower aperture ratio made from metal/polyethylene terephthalate (PET) filaments has higher EMSE, and the electromagnetic shielding of polarized electromagnetic waves possesses orientation effects. The paper provides theoretical guidance for designing flexible electromagnetic shielding products.

Color Variation on Spun-dyed Polyester Filaments during Processing

In this study, the color variation of spun-dyed polyester filaments was systematically investigated using various processing technology parameters including linear density, velocity of cross-flow air, different processing ways and different textured technology parameters. The results showed that these parameters had varying degrees of influence on the color of spun-dyed polyester filament in processing. The degrees of color variation were expressed using the CIE1976 L*a*b* system. As a result, it provided an important theoretical guidance for working out actual production technology and controlling color quality of spun-dyed polyester filaments based on actual industrial equipment and technological conditions.

Compressive deformation and load of a spacer filament in a warp-knitted spacer fabric

The compressive deformation and load of a spacer filament in a warp-knitted spacer fabric was analyzed theoretically in this work. It was found that the compression process of the spacer filament can be divided into four stages, including a Stiff Stage, an Elastic Stage, a Restful Stage, and an Ineffective Stage. Based on the theoretical analysis of the compressive displacement and the radius of the spacer filament at different stages, as well as the bending moment of the spacer filament during compression, the relationship between the critical compressive load at different stages and the structural parameters of the spacer filament in a warp-knitted spacer fabric was found. Furthermore, plane plate compression experiments for spacer filaments were designed and tested to verify the correctness of the theoretical analysis.

Visual Masking Performance of a Fabric

In this study, we investigated the main factors affecting the visual masking performance of a fabric, including the illumination level of the target, the cover factor of the fabric, the distance between the fabric and the target, and the illumination level of the fabric. It was found that among these four factors, the illumination level of the target had a significant effect on the visual masking performance. The masking performance of the fabric could be improved by decreasing the illumination level of the target and by increasing the illumination level of the fabric itself. For a nylon monofilament plain fabric, the masking performance of the fabric could be improved by increasing the cover factor of the fabric. In addition, the masking performance of a fabric could be improved slightly by increasing the distance between the fabric and the target.

Electromagnetic properties of three-dimensional woven carbon fiber fabric/epoxy composite:

To investigate the reinforcement architectures effect on the electromagnetic wave properties of carbon fiber reinforced polymer composites, three-dimensional (3D) interlock woven fabric/epoxy composites, 3D interlock woven fabric with stuffer warp/epoxy composites, and 3D orthogonal woven fabric/epoxy composites were studied by the free-space measurement system. The results showed that the three types of 3D woven carbon fiber fabric/epoxy composites had a slight difference in electromagnetic wave properties and the absorption was their dominant radar absorption mechanism. The electromagnetic wave absorption properties of the three types of composites were more than 90% (below −10 dB) over the 11.2–18 GHz bandwidth, and more than 60% (below −4 dB) over the 8–12 GHz bandwidth. Compared with unidirectional carbon fiber reinforced plastics, the three kinds of 3D woven carbon fiber fabric/epoxy composites exhibited better electromagnetic wave absorption properties over a broadband frequency range of 8–18 GHz. Therefore, the three kinds of 3D woven composite are expected to be used as radar absorption structures due to their excellent mechanical properties and outstanding absorption capacity. The total electromagnetic interference shielding effectiveness of the three types of 3D carbon fiber woven composites are all larger than 46 dB over the 8–12 GHz bandwidth, which is evidence that the three types of 3D carbon fiber woven composites can be used as excellent shielding materials for electromagnetic interference.

Study on the Thick Tip of Lamb's Wool of Superfine Merino Sheep

Superfine wool of Merino sheep has many distinct characteristics, especially its higher fineness. Generally, its mean diameter is about 16.5 µm and it is a good material for fine worsted fabrics. However, the region near the tip of a primary fiber has a coarser fiber diameter, with a value of 35—66 µm. The length of such a segment is usually up to 16—22 mm. The secondary fiber also has a small swelling segment near the tip, but the length of this segment is very short and difficult to determine. The existence of such fibers with thick tips would greatly decrease the final product quality. However, the fiber diameter of the wool becomes even and unchangeable along the fiber when a lamb is 4 months old. Therefore, we suggest that lambs wool should be sheared for other uses on lambs over 4 months of age.

Effect of thermo-oxidative aging on compressive behavior of carbon fiber polymer matrix composites

The effects of reinforcement architecture on the compressive behaviors of carbon fiber polymer matrix composites (CF-PMCs) under thermo-oxidative aging conditions were investigated. Samples of three-dimensional and four-directional braided carbon fiber/epoxy composites (BC) and laminated plain woven carbon fiber/epoxy composites (LC) were subjected to isothermal aging at 80℃, 100℃, 120℃ and 140℃ in air circulating ovens for various durations up to 1200 h. The process resulted in progressive deterioration of the matrix reins and fiber/matrix interfaces, in the form of chain scissions, weight loss and fiber/matrix debonding, which significantly led to the decrease of the compressive strength. In addition, the compressive strength retention rates of BC were higher than those of LC at the same aging conditions due to the differences of their reinforcement architecture. On the one hand, LC lost more weight than BC because the percentage of exposure of fiber ends to air in the LC samples was five times more than that in the BC samples. Moreover, the BC samples could resist the compressive load as an integral structure and did not show delamination damage as in the case of LC samples, although the resin was damaged and the adhesive force between fiber bundles and resin decreased after thermo-oxidative aging. Therefore, adopting the three-dimensional and four-directional braided preform as the reinforcement of CF-PMCs is an effective way to improve their compressive strength under thermo-oxidative aging conditions.

Random process model of mechanical property degradation in carbon fiber-reinforced plastics under thermo-oxidative aging

The mechanical properties of carbon fiber-reinforced plastics used in aerospace are vulnerable to degradation under thermo-oxidative aging conditions. However, it is hard to establish a mechanical property prediction model for carbon fiber-reinforced plastics from thermo-oxidative aging mechanism point of view since the thermo-oxidative aging degradation processes are very complex. A mathematical model was proposed based on the theory of stochastic processes for predicting mechanical property degradation of carbon fiber-reinforced plastics under thermo-oxidative aging conditions in the present work. However, the predicted values calculated by the “random process model” were not in good agreement with experimental data. And then a “modified random process model” (namely a wider random process model) was established through Box–Cox transformation for random process model. The verification of the evaluation model showed that the modified random process model can nicely describe the mechanical performance degradation of carbon fiber-reinforced plastics with the increasing of aging time under certain aging temperatures. As the modified random process model was established without limiting the reinforced structure of carbon fiber-reinforced plastics, the described method provides an opportunity to rapidly predict the mechanical properties and the lifetime of any carbon fiber-reinforced plastics by testing the mechanical properties of carbon fiber-reinforced plastics before and after aging for a short period of time.

Factors Affecting on the Electricity Properties of a Metal/Pet Composite during Tensile Deformation

The effects of different factors on the electrical properties of a well-bonded metal/PET composite during tensile deformation were systematically analyzed, including metal materials, metal coating film thickness and environmental temperature. It was found that, before a crack appearance in the coated metal film, the critical elongation of a well-bonded metal/PET composite depended on the differences of modulus and Poissons ratio between the coated metal material and PET substrate. After cracking, the metal/PET composites with different metal films showed different elongations when there was a sudden increase in the resistance of the metal/PET composite; the thicker the metal film deposited on PET substrate was, the lower resistance the metal/PET composite had. The thickness of metal film had no obvious effect on the critical elongation of the metal/PET composites. In addition, the resistance of the metal/PET composite increased with the increasing environmental temperature.

Non-Fick effect of transient water transport in woven fabrics

This study investigated a new phenomenon of liquid water transport in woven fabrics by using a specially-designed liquid water transport detecting device. It was found that within 6 mm space from liquid water resource, transient transport of liquid water in a woven fabric appears to have non-Fick effect, that is, liquid water transport in a woven fabric processes obvious transient shock effect. After this transient period, water transport in the fabric follows the classical mass transfer theory, and tends to maintain a constant rate. The non-Fick effect of the water transport varied with fabric densities and yarn twists. In general, the lower the fabric density and the yarn twist are, the more obvious the non-Fick effect is. The non-Fick effect of transient transports of liquid water also behaved differently for fabrics made of different fiber materials.