Fabric Properties Textile Apparel Manufacturinginfohouse.p2ric.org/ref/07/06964.pdf · The apparel segment of the U.S. textile industrial complex is ... model for measuring fabric

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Characterization and Control of Fabric Properties in Textile and ApparelManufacturing

PIs: P. Banks-Lee, N. C. State; D. R. Buchanan, N. C. State; T. G. Clapp, N. C. State; J.W.Eischen, N. C. State; T. K. Ghosh, N. C. State; B. S. Gupta, N. C. State; T. J. Little, N. C. State;A. Seyam, N. C. State.

Post-Doctorate Research Associates: Dr. M. Gunner(EE), Dr. F. Sun

Graduate Students: G. Barrett(EE), S. Deng(ME), Y. G. Kim(ME), D. Kong(TAM), H.Li(TAM), T. McDevitt(ME), N.Timble(FPS)

Team Leader: T. G. Clapp

RELEVANCE TO NTC GOALS:

The apparel segment of the U.S. textile industrial complex is under tremendous pressurefrom foreign competition. The apparel industry is trying to respond to this pressure by changingits production philosophy to accommodate the consumer demand for ever increasing stylevariation and retailer demands for more frequent Just-In-Time (JIT) deliveries of smaller orders.The apparel industry must be able to respond to these demands to remain competitive in the U.S.and abroad.

Apparel manufacturing in a Quick Response (QR) environment must have the ability toquickly optimize its processes when faced with rapidly changing fabrics with variable materialproperties. This variability is inherent (statistical) within a given fabric and between differenttypes of fabric. In order to deal successfully with this challenge, it is necessary to understandhow important material properties permeate through the manufacturing chain. We must developtechnologies to measure these important properties quickly and reliably (not dependent ontraditional laboratory techniques and constraints). It is important to lay the groundwork fordealing with property variability in the design of apparel fabrics as well as in the manufacturingand finishing of these products.

An interdisciplinary team of researchers from Textile Engineering (TE), ElectricalEngineering (EE), Mechanical Engineering (ME), and Textile Technology (TT) are conductingresearch to collectively address the following research themes: 1) model fabric behavior, 2)on-line characterization of material properties, and 3) on-line manufacturing control. Newdevelopments in computer modeling and sensor technology are being applied to address thesethemes.

GOALS:

LONG TERM: Develop new technologies and methods to characterize fabric properties on-line(during processing) and control textile and apparel manufacturing processes to optimize qualityand productivity in a Quick Response or Just-in-Time manufacturing environment. Educategraduate and undergraduate students to help strengthen and lead U.S. fiber, textile, and apparelcompanies into the 21st century.

SHORT TERM: Using common fabrics a basis, 1) validate 3-D fabric deformation models, 2)refine and validate a theoretical model for predicting visco-elastic behavior of fabrics in rollform, 3) develop and validate a theoretical model for measuring fabric stiffness on-line, 4)develop sensor technology to characterize fabric on-line during high speed sewing, and 5)quantify fabric frictional behavior and mechanical properties as a function of orientation.Involve at least three undergraduates in research activities, and graduate at least two Ph.D. andtwo Master’s students.

National Textile Center Annual Report: September, 2994 219

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TECHNICAL QUALITY AND ACCOMPLISHMENTS

An interdisciplinary team of researchers from Textile Engineering, ElectricalEngineering, Mechanical Engineering, and Textile Technology have collectively addressed thefollowing research themes: 1) model fabric behavior, 2) on-line characterization of materialproperties, and 3) manufacturing control. The depth of the research is reflected by thesessubmitted. These are listed below. A brief summary of each of the five research tasks is alsoprovided.

Thesis Completed and in Preparation

1.

2.

3.

4.

5.

6.

7.

8.

Kim, Y. G., “Fabric Manipulation Simulation Including Material Non-linearityand Contact”, PhD Dissertation, Completed June 10, 1993.

McDevitt, T., ‘Flexible Fabric Mechanics analysis Using Large DeflectionBeam Theory”, MS Thesis, completed August 1993.

Kong, D., “Development of a Control System for Fabric Roll-MakingOperation”, MS Thesis August 1993.

Timble, N., ” Structural Factors Affecting Inter-facial Forces Between Fabrics,PhD Thesis”, submission in Final Form expected by October 25, 1993.

Li, H., “Simulated Roll-Like Loading in Laboratory and it’s effects on FabricProperties” complete.

Deng, S., “Nonlinear Fabric Mechanics Including Material Nonlinearity,Contact, and Adaptive Global Statics Algorithm,” PhD Dissertation, FinalDefense scheduled August 22, 1994.

Barrett, G. R., “On-line Fabric Identification and Adaptive Control of theSewing System for Improved Apparel Assembly.”

Farrington, C. E., “Deformational Characteristics of Plain Knitted Yarn LoopsUnder Shear Loading,” PhD Dissertation.

220 National Textile Center Annual Report: September, 1994

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RESEARCH SUMMARIES:

Deformational Characteristics of Plain Knitted Yarn Loops Under ShearLoading

Developing an automatic feeding or sewing mechanism requires an understanding of thebehavior of knitted fabrics under stress. A fabric which will be fed by an automatic feedingmechanism or will be sewn rarely experiences symmetrical loading. To date, however, mostanalyses made determine the structural behavior of knitted fabrics under no load or aresymmetrically loaded. Therefore, for practical applications, it is important to examine thebehavior of knitted fabrics under nonsymmetric loading conditions.

S. de Jong and R. Postle, authors of “A General Energy Analysis of Fabric MechanicsUsing Optimal Control Theory”, used an energy analysis based on Optimal Control Theory(OCT) to determine the key deformational characteristics of symmetrically loaded knitted loops.This approach assumes that yams in a knitted loop will take a shape such that their internalenergy is minimized while maintaining the force/couple equilibrium. By modifying this modelit is possible to analyze how a knitted fabric deforms under an uniform shearing load.

The first step in this project was to reproduce de Jong’s work. A computer program,written in C, was developed to determine the deformational behavior of a knitted quarter loopthat is symmetrically loaded. Certain algorithms were developed to reduce run time and increasesolution stability. This computer program will be the basis for any future research involving thenonsymmetric loading of knitted fabrics.

The second step was to modify the OCT algorithm to analyze the deformational behaviorof knitted loops under nonsymmetrical loading. This involved the expansion of the analysisfrom a quarter loop to a half loop. In addition, two subroutines were developed to solve the twopoint boundary problem, which arises from the expansion of the analysis to a half loop.

A review of the modified OCT analysis of plain knitted fabrics under a shearing loadconfirms the anisotropic behavior of knitted fabrics. A loop subject to counter-clockwiseuniform shear loading will skew in the counter-clockwise direction. To counteract this moment,the force exchange between interlocking yarns on the left side of the loop becomes higher thanthe force exchange between interlocking yarns on the right side of the loop. As the shearingload increases: 1) the loop becomes more skewed, 2) the tightness of the left side of the loopincreases due to a decrease in yarn curvature; and 3) the tightness in the right side of the loopdecreases as the yarn segment begins to straighten. Sewing or feeding mechanisms add this typeof shearing load to a fabric and therefore require further study.


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W

A) Symmetrically Loaded Knitted Loop. B) Nonsymmetrically Loaded Knitted Loop

On-line Fabric Identification and Adaptive Control of the Sewing Systemfor Improved Apparel Assembly

Analysis of current sewing techniques indicated that higher quality apparel assemblyrequired research into the fundamental aspects of sewing control. From this analysis, the twocourses of research to be followed were 1) the determination of methods for characterizing thedynamics of high speed sewing machine and fabric interactions, and 2) the determination ofmethods of adaptively controlling the sewing system based on the on-line evaluation of thefabric/machine interactions.

Needle bar forces occurring during high speed sewing can be used to identify fabricson-line. A neural network classifier for on-line identification of fabrics has been created. Theneural network acquires its data from a sewing machine equipped with force transducers. Thesetransducers measure the forces occurring at the needle during the sewing process. The neuralnetwork is trained to identify fabrics based on their force “fingerprint” (See Figs. 1 and 2). Byimplementing the neural network on a microprocessor, a practical way exist to identify not onlythe fabric type but also the number of plies sewn. Utilizing this type of classifier, the automatedapparel assembly station can adapt itself to changing sewing conditions and provide qualitychecks such as making sure all plies were sewn.

The second course of research pursued was the determination of methods of adaptivelycontrolling the sewing system based on the on-line evaluation of the fabric/machine interactions.The fundamental knowledge gained from these investigations has led to a full report on a presserfoot force actuator and patent disclosure to the University. This control method stabilizes theforces applied to a fabric during feeding. By maintaining an optimai applied force, fabric may ‘beless likely to pucker during sewing. A prototype to demonstrate the fundamental operation ofthis device is currently being designed and built. The digital controller design method uses anellipsoid algorithm to optimize controller parameters. Time domain specifications are


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implemented as linear inequality constraints within the ellipsoid algorithm (See Figs. 3 and 4).The ellipsoid algorithm then searches for controller parameters that optimize some (usuallynon-linear) objective function subject to the constraints. In this manner, the controlled presserfoot behaves with certain specified time responses.

1.0

0.5

0.0

.

Figure 1. T&ical needle force waveforms for one stitch for five fabrics

Figure 2. Neural network misclassifications of fabric type as a function of training time


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Output and t3fott Cmstraints

0 1 0 2 0 TimZitep 4 0 5 0

Figure 3. A unit step respon.se of presser km1 force thalsatisfies the time domain constraints

6 0

6-

4-

2-

o-

ci

- 2 -

-4-

-6-

-8’ 1 1 1 I-6 -4 -2 0 2 4 6 8

X l

Figure 10. Convergtmcz of a two dimensional parameter *searchto an optimal feasible point using the ellipsoid algorithm


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Develop Models for Predicting Fabric Friction and Directional Variation in FabricMechanical and Viscwelastic Properties

Fabric Friction

The friction results obtained on fabrics varying broadly in structure and fiber material,and reported in previous reports, were rationalized using a modified version of Wilson’s modelwhich included fabric compressional coefficient, L, estimated experimentally, as a measure ofhardness, and apparent area of contact, Aa, estimated theoretically by Pierce’s model, as ameasure of the number of asperities of contact. Using these modifications, the foal models forthe constants C and n which characterize frictional behavior of fabrics by the equation (P/A) = C(N/A)” can be given as follows.

C = kSL-7 Aal-Y (1)n=B(l-y)+ y (2)

In these equations, S is the specific shear strength of the adhesion junctions, yis the factorrelated to the shape of the general pressure(P)-area(A) curve given by the relationship P=KAawhere a = p1 - l), and k and B are model constants.

Using these models (Equations 1 and 2) the effects of fabric structure parameters, picksper inch and yarn twist, on frictional behavior could be rationalized effectively. An example ofthe results which give a comparison between the experimentally determined and the theoreticallypredicted values of C(Equation 1) is shown in Figure 1. Currently, a paper is being written forsubmission to Textile Research Journal for publication on this work.

-0.5 - y = 0.27 + 1.17xR-square = 0.71, R =0.84

.

-0.6 -

Figure 1. Theoretical values of friction parameter, C , versus experimental values offriction parameter, C, for all the filament polyester model fabrics. (y = 0.90)

Fabric Mechanical and Viscoelastic Prouerties

The fabrics must endure stresses and strains of variety of levels during conversion into finalproducts as well as during end use, specially industrial. The sewability, seam quality, style and drapeof garments and performance in which fabrics are subjected to multidirectional forces areadditionally affected by the variation in mechanical and visco-elastic properties of fabrics. Theinformation available from such a study will allow us to understand and predict (1) the behavior ofa fabric when subjected to pull from different directions, and (2) style and drape, and performancein manufacturing of fabrics. The focus of activity in this area has been on measuring the variationin mechanical properties with direction and modelling the behavior using theoretical/empiricalapproaches.


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The tensile properties of five different fabrics, varying broadly in construction and yammaterial (Table l), were measured using ASTM method D5035 (Strip test method). The propertiesmeasured were in seven different directions ( O”, 15’, 30°, 45’, 60”, 75’, 90” >from the warpdirection).

The results obtained clearly show that the properties vary greatly with the direction of testingand the structure of the fabric. An example of results is given in Figure 1. Currently, the resultsobtained are being analyzed and modelled using a finite-deformation theory. Also, the impact the2.:: variation in mechanical properties has on fabric sewability and seam quality is being

.

Table 1. Fabric Specifications

FABRIC Fabric Counts Yarn Number (Denier) Weave FiberEPI PPI Warp filling

A 66 95 150 150 2f2hvillB 109 60 70 150 plainC 58 50 200 200 plainD 212 56 70 150 satinE 80 69 2/47* 1/34* 2/2 twill

* worsted count

polyesterpolyesternylonpolyesterwool

70I

---c- IabncA

- fatmcB- fatxlCC- mncD- labricE

ot I , ,, (,.%I, j , I

0 20 40 60 60 100

Angle from warp direction (degree)

Figure 1. Stress Variation with Change of Angle

226 National Textile Center Annual Reporf: September, 1994

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Computational/Experimental Determination of Fabric Drape and Motion

T, McDevitt- Flexible Fabric Mechanics Analvsis Using Large Defection Beam

Theorv

The primary objective of this research was to develop a computer method to simulate thequasi-static motion of fabric parts during certain manufacturing processes in the apparelindustry. Fabric parts are modeled as very flexible elastic beams that can accommodatestretching and bending in a single plane. Again, the equilibrium equations are solved using thefinite element method. In solving for drape shapes and fabric configurations duringmanipulation, numerical problems are encountered when the fabric begins to buckle or wrinkle.In this project, a technique know as arc-length control has been implemented to treat thesedifficulties, and be able to simulate very complex load deflection paths. Attention has also beenfocused on generating finite element meshes that adapt to the severity of the deformation.Generally speaking, a numerical method requires more refinement (nodes) in the areas where thestate variables (displacements) are varying the most rapidly. A method to distribute the finiteelement nodes to those regions of the fabric undergoing the most curvature has implemented.

S. Deng- 3D Fabric Drape Mechanics

This project is an ongoing extension of our capability to model three dimensional fabricdrape over complicated surfaces. The use of large displacement shell theory to model the fabricsbehavior has proved to be very successful. A very interesting aspect of this work is thediscovery of multiple numerical solutions for seemingly simple fabric shapes. The solutions ofthe highly nonlinear equilibrium equations is non-unique. The challenge is to determine whichof the several solutions is the physical realizable one, or whether multiple physical solutions arepossible. Figure 1 shows the drape of a fabric part over a pair of intersecting cylinders. Thisproblem demonstrates that the method can treat general part shapes and complex contactsurfaces, We are also able to simulate the drape of fabric parts that show a nonlinear momentcurvature relationship.

(a) Experiment Result(b) Linear Material Solution

Figure 1. Comparison of Numerical Solutions and Experimental Result for Fabric Draping OverIntersecting Cylinders


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Develop an “Intelligent” Closed Loop System to Control the Roll Making Process

A feed-back control system for fabric roll-making has been developed. The controlsystem, in principle, would allow production of fabric rolls with optimal levels of internalstresses. The system is also designed to minimize variation of stresses.

Traditionally, fabric rolls are produced without any particular concern for the windingtension or roll-size. Their levels are mainly dictated by the unit process or the experientialknowledge of the operator. Generally, the winding tension remains somewhat constant duringany process. It has been demonstrated in this research that in case of constant tension windingthe fabric inside the roll may actually buckle and may cause permanent deformation of thefabric. This is particularly undesirable for easily deformable or delicate fabrics such as certaintypes of fine woolen or knit fabrics. To demonstrate the levels of stresses developed in fabricrolls and their variation strain measurement systems for both compressive and tensile strainshave been developed. A miniature compression load cell has been used to, measure the radialcompressive stresses within a roll. The result shows initial rapid increase in compressive stressnear the core followed be a levelling off near the top. This suggests that after a certain numberof layers on the core the hoop stresses are not transmitted to the core from further layers. Maybethe intermediate layers together act as a non-deformable rigid cylinder. To measure the in-planestresses foil-type strain gages have been used. It was necessary to develop special mountingtechniques to obtain any meaningful measurement of strains in fabric layers. The results showthat in some layers the fabric is actually under in-plane compressive stresses, even though, theweb tension in the fabric at the time of winding was positive. These results substantiate earlierresults of theoretical analyses during this project.

1,6: Electric Cylinders 2,4: Guide Cylinders 3: Moving Cylinders5: Tension Measurement Cylinders

Figure 1. Tension Control System for Roll-making

In the control system developed in this project the winding tension is used as the controlparameter Since our last report the control system has been modified to eliminate noisevibrations and to improve stability of the control. Figure 1 shows the improved control system.In this, the vertical position of a control cylinder is precisely controlled to generate variouslevels of wrap angle which in turn determines the outgoing tension in the fabric. The measuredtension in the fabric web is used to control the position of the control cylinder. The controlcylinder is driven by two electric cylinders working in unison. A new and improved softwarefor the control system has been developed by using a graphical programming languageLabView2. Using this program the winding tension can be controlled as function of time.


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Fabric Properties Textile Apparel Manufacturinginfohouse.p2ric.org/ref/07/06964.pdf · The apparel segment of the U.S. textile industrial complex is ... model for measuring fabric