Mechanical C haracterisationof T hrough-air Bonded N onwoven Structures Amit Rawal*, Stepan Lomov**, Thanh Ngo**, Ignaas Verpoest**and Jozef Vankerrebrouck*** *Current Address: The University of Bolton, Deane Road, Bolton BL3 5AB, UK ** Department of Metallurgy and Material Engineering, Katholieke Universiteit, Leuven, Kasteelpark Arenberg, 44, B-3001 Leuven, Belgium ***Libeltex bvba, Marialoopsteenweg 51, 8760 Meulebeke, Belgium downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Contents • Introduction • Objectives • Experimental Work • Micromechanical Model for Initial Tensile Behaviour of Through-air Bonded Structures • Results • Conclusions • Potential Outputs downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Introduction downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Definition of Nonwovens * A fabric consisting of an assembly of textile fibres (oriented in one direction or in a random manner) held together (1) by mechanical interlocking; (2) by fusing of thermoplastic fibres, or (3) by bonding with a rubber, starch, glue, casein, latex, or a cellulose derivative or synthetic resin. *www.nonwovens.com downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Classification of Nonwovens downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Importance of Mechanical Properties in Nonwoven Structures Thermal bonded structures undergo various modes of deformation during their end-use performance. For example, geotextiles when placed under the soil exhibit high levels of tensile and compressive modes of deformation. Characterisation of tension, shear, compressional and bending resistance is needed for accurate prediction of fabric draping during the formation of a three-dimensional (3D) shaped composite part for many automotive applications. downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Objectives downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
The main objective of the research work was to characterise the mechanical properties of thermal bonded nonwoven structures namely, tension, bending, shear and compression, including anisotropy in the properties, along with the fibre orientation distribution in the fabric. A simple micromechanical model has also been proposed to investigate the initial tensile behaviour of thermal bonded structures. downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Experimental Work downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Production of Through-air Bonded Structures C R1 R2 D Web Properties TB1 TB2 Type of Fibres PET PET PET PET (Bicomponent) (Normal) (Bicomponent) (Normal) Proportion (%) 50 50 50 50 Linear Density 2.2 3.3 4.4 12 (dtex) Computed 14.20 17.40 20.15 35.03 Diameter (µm) Average 48.83 58.38 47.80 61.20 Length (mm) downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Fibres Stress-Strain Curve 7 2.2 dtex 6 3.3 dtex 5 4.4 dtex Stress (cN/tex) 12 dtex 4 3 2 1 0 0 2 4 6 8 10 Strain (%) downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Properties of Through-air Bonded Nonwovens Fabric Sample Mass per unit area Thickness (mm) (g/m 2 ) IDs TB1 31.09 ± 0.082 0.44 ± 0.0012 TB2 28.46 ± 0.031 0.43 ± 0.0038 downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Measurement of Mechanical Properties • Tension: Fabric strips of 20x15 cm were tested on an Instron tensile testing machine under uniaxial loading in a “grab” test. Poisson’s ratio was also determined by measuring the contraction in the centre of the specimen relative to the strain in the test direction. • Shear: Picture frame was mounted on Instron tensile testing machine. • Bending: KES-F B2 (Bending Tester) was used and the fabric was bent between the curvature of –2.5 and 2.5 cm -1 . Three cycles were repeated for each sample in the machine (0° ) and cross- machine (90° ) directions. • Compression: KES-F B3 (Compression Tester) was used and the pressure was increased gradually up to 50 g/cm 2 . downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Measurement of Fibre Orientation Angles z YZ y x XZ Machine Direction Sectioning of fabric samples downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Measurement of fibre Orientation Distribution (Cont.) arccos( b / a ) � � � Z’ ’ � a p z’ Y’ b p x’ ’ � p y’ X’ Scheme for computing the fibre orientation angles 2D image analysis software provides the values of minor and major axes along with an in-plane fibre orientation angle � ´ downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Ambiguities, Errors and Corrections in 2D Image Analysis • Ambiguity : There are two possible values for fibre in the in-plane orientation angle ( ) � � as the fibres with orientations and + 180 � � � � have identical cross-sections. • Correction : Assuming the orientation distribution to be symmetrical, and the out- of-plane orientation angle is randomised by using the following equation. 1 , x 0 � � � sign ( x ) 0 , x 0 � ´ 1 = (sign (RAND (0,1)-0.5) � � ’ ������� � � � � � 1 , x 1 downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm � � �
Ambiguities, Errors and Corrections in 2D Image Analysis (Cont.) • Ambiguity : The probability of finding a fibre with defined orientation ( ) such that it has an � , � � � elliptical cross-section on the sectioning plane. • Correction : The “ probability of intersection ” between the fibre and the sectioning plane has been determined by dividing the fibre orientation distribution with cosine of the sectioning angle (Zak et al ., 2001). ( , ) XZ � � � � � i j XZ � � ijcorrected ’ cos � i Zak, G., Park, C. B. and Benhabib, B., Estimation of three-dimensional fibre-orientation distribution in short-fibre composites by a two-section method, Journal of Composite Materials , downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 35 , 316-339 (2001).
Ambiguities, Errors and Corrections in 2D Image Analysis (Cont.) • Error : Small errors in the measurement of elliptical axes for the fibres oriented nearly perpendicular ( ) to the sectioning plane can � � yield large errors in the measured value of � � (Mlekusch, 1999). • Correction : Fitting a normal distribution to the measured values of in-plane fibre orientation angles . Mlekusch, B., Fibre-orientation in short-glass-fibre composites II: Quantitative measurements by downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm image analysis, Composites Science and Technology , 59 , 547-560 (1999).
Micro-mechanical Model for Initial Tensile behaviour of Through-air Bonded Nonwoven Structures downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
A simple micro-mechanical model has been developed to predict the anisotropy of the tensile properties of through-air bonded structures. The model is based on the averaging schemes of bond distribution and fibre orientation proposed by Pan et al. (1993), Komori and Makashima (1977, 1978) and Lee and Lee (1985). downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Assumptions • Each fibre segment is straight before loading, i.e. local fibre crimp is neglected. • The constituent fibres of same type have identical properties and are elastic. • Bending, torsion and compression deformations of the fibre segments and compliance of bond are neglected. • Fibres do not slip past each other. downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm
Calculation of Number of Contacts Assuming the centre of fibre B ( ) is brought into contact � , � � � with the surface of fibre A ( ), � , � then the parallelepiped consisting of two rhombuses of length l and height 2 D , where D is the diameter of the fibre. 2 v ( , , , ) 2 Dl sin � � � � � � � � Contact of Fibre A with Fibre B (Komori and Makashima, 1977) 2 2 Dl sin � P � V cos cos cos sin sin cos( ) � � � � � � � � � � � � � where V is the total volume P is the probability that fibre A will contact with fibre B is the angle between the two neighbouring axes of fibres A and B � downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 1. Komori, T., and Makishima, K., Numbers of fibre-to-fibre Contacts in General fibre Assemblies, Textile Research Journal , 47, (1977).
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