Perspectiva de la Congregación en el Estado.

with temperature around 20 ℃ and humidity around 65%. The force and pre- tension were in a unit of N/m, which means the force applied on fabric in a unit width (or the force applied on fabric in a unit circumference length for a fabric shell).

3.2.1 Fabric Assurance by Simple Testing (FAST) (De Boos and Tester, 1994)

The FAST tensile tester (FAST-3) is used to obtain the fabric shear properties by extending fabric strips cut in bias directions under a fixed extension force of 4.9N/m. Besides, the FAST bending tester (FAST-2) is used to evaluate fabric bending length and rigidity.

3.2.1.1 Shear modulus obtained in bias extension testing in the FAST-3 tester

Fabric specimens cut in bias directions (both 45˚ and 135˚) and having an

effective test area of 50mm in width and 100mm in length are extended under the load force of 4.9N/m, the corresponding extensions are used to calculate the fabric shear modulus according to the relationship between Young’s modulus in bias direction and the shear modulus shown in equation 5.14 in section 5.2.1.2

For each fabric, tensile elongations of three specimens in each of the two

orthogonal directions are measured, and the average shear modulus is obtained. 3.2.1.2 Bending length and bending rigidity measured in the FAST-2 tester Fabric bending length measured in the FAST bending tester, FAST-2, follows cantilever bending principle. Bending lengths of three fabric specimens having a size of 50mm in width and 200mm in length for each of the two orthogonal directions of each fabric are measured. During bending length test, a fabric

specimen is placed on a flat platform with an aluminium plate placed on the top of the fabric without covering the leading edge. The fabric strip is slowly moved until the leading edge block a light beam generated by instrument, and the fabric bending length at this moment is recorded. This process is repeated for another side of the same fabric end; two sides of the other fabric end are also tested. Therefore four readings are obtained for each fabric specimen, and average bending length of three specimens of each direction of a fabric are obtained and it is used to calculate the fabric bending rigidity according to the equation 6.3 shown in section 6.1.2 .

3.2.2 Kawabata Evaluation System for Fabric (KES-F)

There are four testers in the KES-F system to measure fabric mechanical properties: tensile & shear tester (KES-F1), bending tester (KES-F2),

compression tester (KES-F3) and surface tester (KES-F4). In this project, fabric shear modulus is measured in the KES-F1, and bending rigidity is measured in the KES-F2 and fabric roughness and friction coefficient are measured in the KES-F4. Three specimens are tested in each of the two orthogonal fabric directions; each fabric specimen has a size of 200mm x 200mm for all the tests conducted in the KES-F system. Average of three specimens in each direction are obtained (KES-F Manual).

3.2.2.1 Shear modulus obtained in the KES-F1

In the KES-F shear testing, a fabric specimen is held by two chucks having a gauge length of 50mm, and an extension force 4.9N/m is applied vertically onto fabric. A shear force is applied onto the fabric forwards and backwards within a maximum angle of 8˚. A shear force (N/m)-shear angle (degree) curve is obtained in this process In the KES-F system (Hu, 2000), average slope of force-degree curve between ±0.5˚ and ±2.5˚ is used to evaluate fabric shear rigidity. In this study, this slope is used to calculate shear modulus and shear rigidity according to equation 5.20 in section 5.2.2.

3.2.2.2 Bending rigidity obtained in the KES-F2

Fabric pure bending property is measured in the bending tester (KES-F2). A fabric specimen is mounted on two fabric clamps with a gap of 10mm between them. The fabric specimen is bent at a constant bending deformation rate of 5 mm-1/s by moving one of the clamps, and a bending moment – curvature curve is obtained. In the KES-F system, the average slope of the bending moment-curvature curve between 0.5cm-1 and 1.5cm-1 is used to evaluate fabric bending rigidity (Hu, 2000). In this project, bending rigidity obtained in the KES-F system is calculated according to the equation 6.5 in section 6.1.3.

3.2.2.3 Fabric surface friction coefficient and fabric roughness obtained in KES-F4

In the surface tester KES-F4, a fabric specimen is mounted on the equipment horizontally with one fabric end being fixed at a winding drum and the other end being connected to a tension devise of 400g (19.8N/m). Two metal sensors contact the fabric surface with the following constant normal forces: 50g for the friction sensor and 10g for the roughness sensor. During the rotation of the drum moving the fabric at a speed of 1mm/s, the fabric friction coefficient and its mean deviation is detected by friction sensor, and the geometrical surface roughness is detected by the roughness sensor.

3.2.3 Universal tensile tester (Titan)

Fabric elongations in unidirectional deformation under small extension force (2N/m and 4.9N/m) are obtained in a universal tensile tester, Titan, which is developed by James Heal Ltd, UK in this project. A fabric specimen with a width of 50mm is mounted on two fabric clamps with a gauge length of 50mm. The fabric specimen is extended at a constant speed of 0.2mm/s, and the fabric elongations when extension force is 2N/m and 4.9N/m are obtained in the force- extension curve recorded in Titan extension test.

3.2.4 Leeds University Fabric Handle Evaluation System (LUFHES) The LUFHES system described in section 2.2.3 is used to evaluate the shear modulus and buckling property (e.g. critical buckling force) of fabric cylindrical shell in biaxial deformation processes, as well as the fabric-fabric self-friction properties (Mao and Taylor, 2012).

Each fabric is tested in two directions: warp/wale/MD and weft/course/CD for woven, knitted and nonwoven fabrics, respectively. For each direction, three fabric specimens are evaluated. Woven, knitted and nonwoven fabrics tested in each direction are denoted with a different initial letter. For example, woven fabric W1 in

warp direction is denoted as W1-p and in weft direction as W1-t; knitted fabric K2 in wale direction is labelled as K2-w and in course direction as K2-c; nonwoven fabric N1 in machine direction is denoted as N1-m and in cross direction as N1-c. Before each test, usually a pre-tension of 2N/m is applied on fabric shells in their axial direction unless it is explicitly stated.

3.2.4.1 Shear modulus obtained in cyclic twisting test

In each fabric shell twisting test, each specimen is deformed in five twisting

cycles. In each cycle of the twisting buckling process, the bottom end of the fabric shell is twisted to 5˚ at the speed of 0.5˚/s and then return back to the starting position while its upper end is fixed.

During the cyclic twisting test, the torques required to twist fabric shell and recover deformed fabric shell are measured and corresponding torque-degree curve is obtained. The twisting torque measured is employed to obtain the shear modulus of fabric (equation 5.35 in section 5.2.3). In addition, various energies consumed to deform the fabrics during the fabric deformation process are obtained (see section 2.2.3.1).

3.2.4.2 Energies and compression buckling Young’s modulus obtained in cyclic axial compression buckling test

During each cyclic compression buckling test, each fabric shell specimen is

deformed and recovered for five cycles. In each cycle of the compression buckling test, the upper end of the fabric shell is moved downwards to compress the fabric shell for 15mm at the speed of 1mm/s and then return back to its starting position while the bottom end is fixed. Fabric shells are deformed to have identical

displacement (15mm) in each compression buckling-recovery cycle, dynamic forces required to compress the fabric shells and recover the deformed fabric shells in the compression buckling process are measured to obtain the

corresponding force-displacement curves. The fabric critical buckling force (see section 6.1.1) and various energies consumed during the fabric buckling-recovery process (see section 2.2.3.1) are calculated from these compression buckling force-displacement curves.

3.2.4.3 Extension and friction test in LUFHES

In the extension and friction test, the upper end of fabric shell is pressed on the fabric surface of the fabric strip attached on upper sample holder by a strip of elastic band of fixed length. During the extension and friction test, the upper sample holder with the fabric strip attached on is dragged out of the inner surface of the fabric shell at a speed of 1mm/s for 20mm. When the extension force

equals to or greater than the static friction force existed between the two fabric surfaces, the relative movement between them takes place in the axial direction and the fabric to fabric self-friction force between the two pieces of identical fabric specimens is measured, the dynamic friction force-displacement curve is thus obtained to calculate the dynamic friction coefficient and fabric roughness accordingly.