Maroš Tunák

Directional Defects in Fabrics

This paper deals with a procedure that recognizes common defects occurring in woven fabric. Images of woven fabric are considered as having a directional texture due to their periodical nature. We used a statistical approach based on the analysis of periodicity of texture images in horizontal and vertical directions. These periodicities correspond to the periodicity of second-order grey level statistical features obtained from a grey level co-occurrence matrix. A set of five significant features is extracted from the matrix: energy, correlation, homogeneity, cluster shade and cluster prominence. The presence of a defect over texture causes regular structure changes and consequently, statistical changes. Detection algorithm is based on the sliding window technique; the window is moved over the whole image area. We counted the test statistic for every window and the multivariate control charts are used as a tool for judging the existence of defects. The results show that the statistical approach is suitable for detection of directional defects or changes in regular structure in analysed simulated and real fabrics.

Prediction of hybrid woven fabric electromagnetic shielding effectiveness

This paper deals with experimental verification of numerical models of fabric shielding effectiveness especially via analysis of leakage through the apertures (pores) in the textile structure. Equations for both solid shield and non-compact material were adopted from the literature, whereas an aperture equation based on waveguide conception was used. The experimental sample set was woven fabrics made of hybrid yarns composed of polypropylene fibers with different contents of staple stainless steel metal fibers in their structure. Geometrical characteristics of the aperture structure used for prediction were estimated with the aid of image analysis. Electric conductivity of the hybrid fabric was determined by measuring volume resistivity and plane-wave electromagnetic shielding properties of the sample set were measured by means of the coaxial transmission line method. The effect of metal fiber content on geometrical characteristics (e.g. area of pores, number of pores, cover factor), volume resistivity and electromagnetic shielding effectiveness was investigated. Results obtained by modeling of sample shielding effectiveness and experimental results achieved by measuring of shielding effectiveness were compared and discussed. It was confirmed that electromagnetic shielding effectiveness increased with a higher amount of metal fibers in the hybrid yarn structure. It was verified that the proposed numerical model is usable for predicting electromagnetic shielding effectiveness based on knowledge of dimensions of the structure apertures (pores), thickness of the fabric and volume resistivity of the material.

Estimation of fiber system orientation for nonwoven and nanofibrous layers: local approach based on image analysis

Analysis of textile materials often includes measurement of structural anisotropy or directional orientation of textile object systems. To that purpose, the real-world objects are replaced by their images, which are analyzed, and the results of this analysis are used for decisions about the product(s). Study of the image data allows one to understand the image contents and to perform quantitative and qualitative description of objects of interest. This paper deals in particular with the problem of estimating the main orientation of fiber systems. Firstly, we present a concise survey of the methods suitable for estimating orientation of fiber systems stemming from the image analysis. The methods we consider are based on the two-dimensional discrete Fourier transform combined with the method of moments. Secondly, we suggest abandoning the currently used global, that is, all-at-once, analysis of the whole image, which typically leads to just one estimate of the characteristic of interest, and advise replacing it with a “local analysis”. This means splitting the image into many small, non-overlapping pieces, and estimating the characteristic of interest for each piece separately and independently of the others. As a result we obtain many estimates of the characteristic of interest, one for each sub-window of the original image, and – instead of averaging them to get just one value – we suggest analyzing the distribution of the estimates obtained for the respective sub-images. The proposed approach seems especially appealing when analyzing nonwoven textiles and nanofibrous layers, which may often exhibit quite a large anisotropy of the characteristic of interest.

In-plane shear behavior of 3D spacer knitted fabrics

The shear behavior of 3D spacer knitted fabrics was investigated by using a picture frame fixture. Three different methods were used to find the shear angle during loading rate of 10 mm/min. All the tests were recorded by a CCD monochrome camera. The images acquired during loading process were used for analysis in order to obtain the full-field displacement and shear angles at chosen points on the surface of test specimen. An experimental and analytical investigation of picture frame shear fixture was conducted to determine its suitability for measuring intra-ply shear properties of 3D knitted spacer fabrics. In this work, a fixture was designed to analyze the in-plane shear behavior of these fabrics. The nonlinear behavior of shear force versus shear angle and the deformation mechanism were analyzed. The curves for shear force versus shear angle and position of buckling for in-plane shear test are recorded by considering two different frame lengths in order to compare with each other. Load–displacement curves of intra-ply shear tests are also analyzed. In addition to this, a program was developed in MATLAB using Hough transform to analyze the shear angle in the real-time image taken during displacement of specimen at various positions. The results of image analysis were compared with the actual experimental results. These findings are important requirements for further improvements in designing of picture frame fixture and to study the in-plane shear properties of 3D fabrics.

A new method and apparatus for evaluating the electromagnetic shielding effectiveness of textiles

Textile structures with electromagnetic shielding ability are widely used to attenuate the strength of electromagnetic fields, and their functionality is evaluated through direct measurement of their electromagnetic shielding effectiveness. Depending on the size of the shield and measured frequency range, various test methods can be used. There is still a need for development of a rapid testing procedure designed for special materials where only small samples are accessible. The paper presents a new convenient shielding effectiveness measuring procedure based on the modified shielded box method. The design, construction, and testing results of a new device are described in this paper. The proposed method is primarily designed for rapid comparative measurements of newly fabricated samples of relatively small size. Replacement of existing measurement standards is not the goal of this proposal. The main advantages of the new device and methodology are a small required sample size, no necessity of sample preparation to special shapes or dimensions, rapid measurements, and simple and cheap equipment in comparison with standardized equipment. To prove usability of the proposed method the electromagnetic shielding effectiveness of a textile sample set was tested with the help of the new method and the obtained results were statistically compared with those gained by the coaxial transmission line method based on ASTM D 4935-10. The agreement between results from the proposed and comparative methods was verified for textile samples with low and intermediate electric conductivity. Suitability, scope of application, benefits, and limitations of proposed measuring system are discussed.

Functional polyester fabric/polypyrrole polymer composites for electromagnetic shielding: Optimization of process parameters:

Intrinsically conducting polymer polypyrrole/polyester textile composites were prepared by in situ chemical oxidative polymerization of polypyrrole on a polyester fabric. As an oxidizing agent ferric chloride was used, p-toluenesulfonic acid was used as a dopant. Polymerization conditions (concentration of monomer, polymerization time and temperature) were investigated and optimized by the help of Design of experiment methodology to obtain fabric with electromagnetic shielding efficiency at least 12 dB for frequency 1.5 GHz. Moreover, weight increase, macroscopic color shade of images and scanning electron microscopy images of samples were evaluated. It was found that all selected factors and their interactions have statistically significant effect on resulting electromagnetic shielding effectiveness, whereas monomer concentration has the highest positive influence. Experimental data were used to derive an empirical model linking the output and inputs. Optimized parameters (polymerization temperature 6.7℃, polymerization time 10 h and monomer concentration 5.8 g/l) for creating polypyrrole/polyester textile composite with electromagnetic shielding ability higher than 12 dB were successfully verified.

New objective system of pilling evaluation for various types of fabrics

Image analysis methods are widely used tools for an objective pilling evaluation. However, due to their intrinsic limitations, simple image analysis of digital photographs is not a suitable procedure for the pilling evaluation of fabrics with complex structures and distinct patterns. Generally, a fabric pattern or a complex fabric structure have presented significant problem to the pills detection. This paper describes a system of the objective pilling evaluation of unicolor fabrics and even fabrics with complex patterns. The main points of the pilling evaluation system include a 3D fabric surface reconstruction from shading based on gradient field method, using image analysis tools for the pills detection and an estimation of an objective pilling grade. In order to enable the estimation of the objective pilling grade, a relationship between the pilling grades obtained by a subjective method and selected pill characteristics was specified using a linear regression model. The method was tested on a set of different fabrics and estimated pilling grades were compared with subjective pilling grades of the samples. Results showed that the proposed method is suitable and reliable tool for the objective pilling evaluation of various types of fabrics.

Material, structure, chosen mechanical and comfort properties of kinesiology tape

Abstract The main objective of this paper is to determine material composition, structure, and chosen mechanical and thermo-physiological comfort properties of selected kinesiology tape. The results of experiments show that kinesiology tape is a non-linear elastic and porous composite material. Warp yarns are core-spun elastic yarns, while weft yarns are 100% cotton yarns. Fabric has a plain weave and its back side is equipped with an adhesive. Tensile strength of kinesiology tape ranges from 80 to 180 N depending on the tape width. In a relaxed state, porosity together with air permeability and other heat and mass transfer characteristics are mainly affected by the compact layer of adhesive on the surface of woven fabric. During tensioning, pores are expanding and therefore transfer of air and water vapor is significantly increased and at the same time heat transfer is reduced which can positively affect wearer comfort.

Comparative performance of flame retardancy, physiological comfort, and durability of cotton textiles treated with alkaline and acidic casein suspension:

The objective of the present study was to investigate the effect of coating of different concentrations and pH of aqueous casein suspension on thermo-oxidative properties, flame retardant behavior as well as physiological comfort of cotton fabrics. The flame retardant behavior was found to increase with increase in concentration of casein suspension in both alkaline and acidic pH conditions. The burning rate of 2.1 mm/s and 2.4 mm/s was measured for the samples of 150 g/L casein suspensions in acidic and alkaline pH, respectively. Moreover, better thermo-oxidative properties were obtained for the samples of casein suspension prepared in acidic pH than alkaline pH. The 150 g/L casein produced 19% and 28% residue, respectively for alkaline and acidic suspensions at 600℃. Furthermore, the phenomenon of intumescence was largely observed in case of samples coated with acidic casein suspension due to easier release of ammonia from protonated casein. These samples further exhibited relatively better durability against water washing and UV ageing as compared to those treated with alkaline casein suspension, however delivered poor physiological comfort properties due to blockage of fabric porosity by higher viscosity of casein in acidic pH.

Image analysis of jet structure on electrospinning from free liquid surface

The work analyses intra-jet distances during electrospinning from a free surface of water based poly(vinyl alcohol) solution confined by two thin metallic plates employed as a spinning electrode. A unique computer vision system and digital image processing were designed in order to track position of every polymer jet. Here, we show that jet position data are in good compliance with theoretically predicted intra-jet distances by linear stability analysis. Jet density is a critical parameter of electrospinning technology, since it determines the process efficiency and homogeneity of produced nanofibrous layer. Achievements made in this research could be used as essential approach to study jetting from two-dimensional spinning electrodes, or as fundamentals for further development of control system related to Nanospider™ technology.