New test methods to evaluate the performance of dermatological braided sutures from both the doctor and the patient sides

Test methods and instrumentations to measure suture tensile performances have been limited to single‐pull to failure and knot‐pull strength. Though useful, these tests do not thoroughly represent the stresses that sutures experience during wound healing. This paper proposes new test methods to evaluate the performance of dermatological sutures using slippage ratio and recovery deformation based on a realistic representation of suture geometry in wounds. For demonstration purposes, we compared three dermatological knots: square, surgeon’s square, and surgeon’s granny. Our results confirmed that the knot design and the generated internal forces in the knot led to significant change in suture behavior during the tying and healing process. Suture performance depended greatly on the intensity of internal forces and the ability of knot packing. Among the studied knots, the square knot had the lowest slippage ratio because it showed the best aptitude to tightening, while the surgeon’s knot exhibited the highest deformation recovery due to its lower locking ability.     

The Effect of Variation of the Isocyanate Content on the Refractometric Determination of the Concentration in Polyurethane Treatment Baths

A knot not previously used in the textile industry, the double-harness bend, is described and its performance in torque-unbalanced weaving yarn reported.

It is shown that the knot can be tied in three distinct ways, which behave differently under stress when tied in torque-unbalanced yarn. The performance of the knots is compared with that of the fisherman's knot, and it is shown that the best of the double-harness bends is likely to offer improved weaving.     

Influence of Twisting on Linen Fancy Yarn Structure

A study is reported for analysis of periodical effects of linen fancy yarns made in twisting process. The results indicate that the investigated variables are significant in determining the kind of decorative effect. It was concluded that the mathematical model that expresses the relationship between number of combination of two effects: loop/knot and plain knot in the unit of fancy yarn length and technological parameters of fancy yarn manufacture is informative. The received results enable to forecast the geometry of fancy yarn’s effects also permits to design new fancy yarns with optimum structure.     

Tensile behavior of staple fiber yarns part II: model validation

The theoretical models of tensile behavior of staple fiber yarns derived in Part I of this work are compared and validated with experimental results. It is observed that the stress–strain curve of yarn always lies under the stress–strain curve of fiber. The well-known Gégauff’s theory is found to overestimate fiber stress utilization in yarn. The partial generalization of helical model by taking fiber orientation into account results in satisfactory agreement with the experimental results. Clearly, fiber orientation plays an important role in deciding the fiber stress utilization in yarns. The lower is the variability of fiber direction in relation to the corresponding helical direction of fibers, the higher is the fiber stress utilization in yarn.     

The influence of two bar warp-knitted structure on the fabric tensile stress relaxation Part II: (locknit,satin, loop raised)

When strain is applied constantly, there is a decreased stress with time in viscoelastic materials, which is called stress relaxation. During the manufacture and application of clothing and footwear, materials experience various long-lasting deformations, and relaxation process in materials arises. Thus, with theoretical and experimental study of the factors affecting stress relaxation, the ability to design and produce appropriate clothes will be increased. In the first part of this research, we studied the stress relaxation behavior of warp-knitted structures which have longer underlaps in back bar (reverse locknit, three- and four-needle sharkskin, and queens’ cord). Following the previous research, the aim of this study was to investigate the effect of fabric structure, strain percentage, and course density on the stress and stress relaxation of the warp-knitted structures which have longer underlaps in front bar (locknit, three- and four-needle satin, and loop raised). The results reveal that the fabric structure, strain value, and fabric density are important factors affecting the stress and stress relaxation percent of the fabrics. By increasing the strain and the length of underlap in the front guide bar, stress and stress relaxation percent will be increased. Also, fabrics with higher course density show higher stress and stress relaxation percent. Among the mechanical models used to describe the stress relaxation behavior of the fabrics, the three-component Maxwell’s model with parallel-connect nonlinear spring showed the best agreement with the experimental stress relaxation curves of the analyzed fabrics.     

Anisotropy in geometrical and tensile properties of plain weave fabric: verifying a semi-empirical model

Geometrical and mechanical behaviors of fabric are extremely anisotropic. Exploit of fabric in multiplicity applications is dependent on its behavior in differ directions. Thus, attempts had been made to study the behavior of fabric in off and on axis systematically. For this purpose, authority of a semi-empirical model, based on earlier work, was experimentally investigated. The model consists of a numerical way to estimate yarn path under axial and normal tension simultaneously. A test method to evaluate flattening of yarn was presented in this study. Moreover, to reduce stress concentration at the sample’s corners a modified griper was applied. On the basis of initial data of fabric and flattening behavior of constitutive yarns, the fabric geometry and tensile force–strain (TF–S) curve of a strip fabric in arbitrary direction are capable to estimate using stated model. The variations in density of warp and weft yarns, shear angle, and TF–S curve of a fabric in different directions were measured and are compared with theoretical values. It was found that the stated model is applicable to predict fabric geometry and tensile behavior of a plain weave fabric under stress in arbitrary direction. Experimental results indicated that the strength of fabric at 45 degree was 22.59% higher than the strength of fabric in average of principal directions. On the basis of semi-empirical model, it is anticipated that the maximum strength of presented fabric would be occurred at 60 degree with 27.99% higher than the strength of fabric in average of principal directions.     

Model for the prediction of the tensile strength and tensile stiffness of knot clusters within structural timber

In the present paper, a model for the prediction of the local strength and stiffness properties is developed. Compared to existing models, here the local material properties are described according to their morphological characteristics; i.e. the timber boards are subdivided into sections containing knots (knot sections) and sections without knots (clear wood sections). The strains of the corresponding sections are measured during non-destructive tensile tests using an optical camera device. Based on these measurements the tensile stiffness of each particular section is estimated. For the estimation of the tensile strength, destructive tensile tests are performed. Herewith, the tensile strength of the entire timber board is measured. The strength of the other knot clusters are estimated using censored regression analysis. Taking into account the results of the experimental investigation, material models are developed to predict the tensile strength and the tensile stiffness of knot clusters.     

The influence of two bar warp-knitted structure on the fabric tensile stress relaxation Part I: (reverse locknit,sharkskin, queens’ cord)

Time-dependent mechanical behavior of textiles has particular importance. One of such behaviors is the stress relaxation. If a fabric is under tension over a period of time, some of the stresses in it will be relieved. During the manufacture and application of clothing and footwear, materials experience various long-lasting deformations, and relaxation process in materials arises. For example, if medical pressure garments such as compression stockings are under tension over a long period of time, some of their stresses will be relieved, with a consequent reduction in the skin and garment interfacial pressure. Thus, with theoretical and experimental study of the factors affecting stress relaxation, the ability to design and produce appropriate clothes will be increased. The aim of this study was to investigate the effect of fabric structure on the stress relaxation of two bar warp-knitted fabrics (reverse locknit, sharkskin, queens’ cord), as well as to find the effect of strain value and loading direction on the stress relaxation of the fabrics. The results reveal that the fabric structure, strain, and loading direction are important factors affecting the stress and stress relaxation percent of the fabrics. By increasing the strain and the length of underlap in the back guide bar, stress will be increased, but stress relaxation percent will be decreased. Also, stress relaxation percent in wale direction is more than course direction for reverse locknit and sharkskin3, but this is reversed for sharkskin4 and queens’ cord. Finally, among the mechanical models used to describe the stress relaxation behavior of the fabrics, three-component Maxwell’s model with parallel-connect nonlinear spring showed the best agreement with the experimental relaxation curve of the analyzed fabrics.     

山羊绒纤维的拉伸性能

研究了山羊绒纤维的拉伸性能以及单纱的拉伸松弛性能,并与细支羊毛纤维进行对比。研究结果表明:山羊绒纤维的比强度、拉伸模量,松弛时间高于羊毛;在较小定伸长条件下,山羊绒纱线拉伸应力松弛速率慢于羊毛纱线,即山羊绒纱线比羊毛纱线难定形,这些力学性能的差异是由于山羊绒纤维α-结晶度高于羊毛;在80~130℃干热条件下,山羊绒纱线的拉伸应力松弛速率及其定形率均随温度的提高而提高;当温度高于120℃时,提高不显著。     

Numerical simulation tool for wooden boards with a physically based approach to identify structural failure

Knots and the resulting fiber deviations are the main influencing parameters of the effective stiffness and strength behavior of wooden boards on a structural scale. Depending on the size, shape and arrangement of knots/knot groups, certain effective mechanical properties can remain unaffected or change significantly. For this reason, a reliable prediction of the mechanical behavior of wooden boards is a basic requirement for efficiently designed wood products and timber structures. Within this work, a Finite-Element simulation tool was developed, which is able to consider a realistic three-dimensional fiber course in the vicinity of knots and also accounts for density and moisture dependent strength and stiffness properties. The estimation of effective strength values within this tool is done by examining the qualitative stress changes in predefined volumes, and is based on the formation of failure zones predominantly caused by perpendicular-to-grain tension in the vicinity of knots. Comprehensive test series, comprising tensile and four-point bending tests were carried out and used for validation. In general, a very good correlation between numerical and experimental results was obtained.     

An improved method to analyze the tensile behavior of carpet yarn

Since the strain, friction, and vibration of carpet yarn have direct impact on the quality of tufted carpet, mechanical properties of yarn play an important role in carpet weaving. An improved method based on Boltzmann superposition principle for describing mechanical behavior of carpet yarn is presented in this paper, which greatly reduces the amount of calculation and further improves the fitting precision. To estimate the performance of the model, we carry out some experiments on carpet yarn specimens, and compared with a nonlinear viscoelastic model widely used in studying nonlinear material. The results showed that the improved method and the nonlinear viscoelastic model perfectly fit the stress relaxation experimental curves when the deformation of the specimens is small, however the improved method is more accurate than the nonlinear viscoelastic model based on single integral constructive equation when the models are used to predict the stress relaxation responses.     

A novel approach to the Poisson’s ratio of the yarn

Abstract

The Poisson’s ratio is a fundamental and inherent property of the materials in their reaction to loading. Determining the correct value of the Poisson’s ratio leads to more accurate predictions of the mechanical behavior of the material, especially in employing mechanical or numerical finite element modeling methods. In this study, seven different types of medium and coarse yarn were digitally filmed in seven sections from three various angles while tensile strength testing. Then, longitudinal and transverse strains and consequently, momentary deformation index and Poisson’s ratio of the yarns were calculated. Significance level of the mean Poisson’ ratio was also determined at different angles and sections using statistical comparison test. The results showed that the transverse strain has a convergent state at the end of the test and the start of the yarn breaking occurs at the convergence point. Additionally, in upper sections of yarn near to the movable jaw of the strength tester, the amount of the longitudinal strain increases which leads to reduce in momentary deformation index and Poisson’s ratio of the yarn. Moreover, a sectional mode to measure the Poisson's ratio was presented.     

A study of carboxylic acids and nano-TiO2 effects on stress relaxation of cotton fabrics

This study presents an evaluation on stress relaxation of cotton fabrics before and after performing the finishing process. The process includes a series of treatments on fabric samples through the Pad-dry curing method. A group of organic acids along with a proportion of catalyst and co-catalyst mixture constituted the treatment agents. Stress relaxation behavior of untreated and treated samples was assessed along two different directions of weft and warp using stress relaxation tester. In addition, an Italian Mesdan tensile tester was applied to measure physical and mechanical properties such as elongation, strength, Poisson’s ratio, and shear modulus. In the mean time scanning electron microscopy was applied to consider surface of samples before and after treatments. The results prove that the stress relaxation of treated samples has shown reasonably acceptable values when compared with those obtained for untreated one. Furthermore, the curve fitting of Maxwell’s model over the experimental data also justified that an interlaced model is more appropriate for explaining the stress relaxation in cotton fabrics. Beside the result of stress relaxation, Poisson’s ratio, and shear modulus illustrated remarkable increments. On the other hand, a reverse trend was observed for tensile properties in both directions. Orthotropic feature evaluation of fabrics toward both the direction of warp and weft also infers different response of stress relaxation in each direction.     

Tensile characteristics and stress relaxation analysis of woven fabrics in terms of fabric direction

Abstract

Woven fabrics in various end uses are subjected to tensile loads in different directions, so investigation of the effect of fabric direction on the tensile behaviour and the stress relaxation performance of fabrics is important and needs to be considered. In this study, the tensile and stress relaxation properties of woven fabrics with five various weave structures have been analysed, in different directions. It was concluded that the tensile properties of fabrics such as Young’s modulus, breaking load and elongation and also the work of rupture were significantly affected by the fabric direction and weave structure. Moreover, it was determined that the fabric tensile stress relaxation (%) was considerably affected by the applied strain level, fabric direction and weave structure in the confidence range of 95% and it might well be expressed as a Gaussian function of sample direction.     

A novel plied yarn structure with negative Poisson’s ratio

This article presents an experimental and geometrical study of a novel kind of plied yarn structure with negative Poisson’s ratio (NPR). The deformation mechanism of the yarn structure formed with two stiff yarns and two soft yarns to achieve NPR behavior was firstly introduced. Based on the proposed yarn structure, four kinds of yarn samples were then fabricated with two kinds of stiff yarns and two types of soft yarns and tested under the axial extension to verify their auxetic or NPR effect. A geometric analysis was finally conducted to theoretically calculate the Poisson’s ratio of the yarn structure and compared with the experimental results. The study shows that the proposed yarn structure has obvious NPR effect and the geometrical analysis can well predict its Poisson’s ratio in the higher axial strain range. It is expected that this study could promote further development of auxetic textiles with unusual behavior.     

4—THE FISHERMAN'S KNOT

An investigation of the fisherman's knot and its performance in torque-unbalanced weaving yarns is reported.

The term ‘fisherman's knot’ is shown to encompass three distinct knot structures. The physical characteristics of the structures are explored, and dramatic differences in their rates of slippage are shown to exist. Slippage is shown to occur predominantly via a change in knot structure rather than by yarn simply pulling through the structure.     

Effect of knots on the flatwise bending stiffness of lumber members

In machine stress-rating of lumber where flatwise bending stiffness is used as a predictor of strength, it is customary to assume that the effect of knots is accounted for by stiffness. However, only few data in the published literature can be used to substantiate this claim. The present study was undertaken to evaluate the relationship between stiffness and knot size for lumber members loaded in bending with a test geometry similar to that used by grading machines. Experiments were carried out with spruce lumber specimens containing a single centerline knot. A theory-of- elasticity based model was derived for analysis purposes. Theory and experiments agreed in showing that the effect of knots on flatwise bending stiffness is very small. This low sensitivity may explain why correlations between strength and machine measured stiffness are rather poor for commercial lumber. Implications of this finding on the practice of machine stress-rating of lumber are discussed.     

三原组织织物拉伸力学性能有限元仿真

为使织物在设计前就可预估其拉伸性能,对织物拉伸过程进行了有限元模拟和试验验证。通过超景深数码显微镜对织物试样的细观照片进行尺寸测量,得到纱线的几何结构参数,借助AutoCAD绘图软件建立了三原织物单胞物理模型;基于纱线拉伸试验和织物周期边界条件理论,利用有限元分析软件ANSYS研究了三原织物的拉伸性能;并将有限元仿真结果与拉伸试验结果进行对比。结果表明：织物经向拉伸时,经向平均应力、经向平均应变、纬向平均应变和泊松比的有限元模拟结果与试验结果的差异均在5%左右;经向弹性模量的有限元模拟结果与试验结果的差异也在10%以内;证明有限元仿真的可行性。     

成纱质量与配棉、纺纱工艺关系探讨

文中从成纱质量指标与配棉、纺纱工艺关系角度说明如何利用现有的原料和工艺生产出满足客户需求的纱线,主要以棉结、不匀、强力等质量指标为例,阐述了成纱质量的影响因素和生产中如何选用合理的上车工艺,同时根据客户质量指标评判企业是否能生产出合格的产品。当然,成纱的指标很多,各种影响因素也不尽然,因此,文中所述只是一个引子,由此能引发大家共同讨论。