- 1 Definitions
- 2 Measurement Of Fabric Stiffness (IS – 6490 – 1971)
- 3 Measurement Of Drape Coefficient (IS-8357-1997)
Fabric stiffness indicates the resistance of the fabric to bend. It is a key factor in the study of handle and drape.
The drape is an ability of a fabric to assume a graceful appearance in use.
3) Drape Co-efficient
The drape coefficient is the ratio between the projected area of the draped specimen and it’s undraped and after the deduction of the area of the supporting disc.
Where, AD – Area of specimen
Ad – Area of supporting disc
As – Actual projected area of specimen
4) Bending Length
It is the length of fabric that will bend under its own weight to a definite extent.
5) Bending Modulus
This value may be used to compare the stiffness of the material in fabrics of difference thickness value.
6) Flexural Rigidity
It is the measure of stiffness associated with the handle. It is also called as Flex – stiffness.
7) Crease Recovery
The resistance to creasing should be distinguished from the ability to recover from the crease.
Measurement Of Fabric Stiffness (IS – 6490 – 1971)
A rectangular strip of fabric is mounted on the horizontal platform and slide until the fabric overhang like a cantilever as shown in the figure.
The length of overhang l when it is depressing under its own weight and the angle between the line joining the tip to the edge of the platform is measured and from these values, the bending length is calculated.
Bending length = C = l * f (θ)
Shirley Stiffness Tester
It consists of the platform, having smooth low friction, flat surfaces such as polished metal or plastic. The platform is supported by two side pieces made of plastic.
Index lines are engrooved on these side pieces, incline at an angle of 41.5o below the plane of platform surface at this angle f (θ) = 0.5. A mirror is attached to the instrument to enable the operator to view box.
Index lines from a convenient position. A scale is supplied with the instrument to measure bending length and it graduated in cm of bending length. It also serves as a template for cutting the samples of size.
The sample is conditioned in a standard testing atmosphere and using template specimens are cut to the size 6-inch x 1 inch or 25 mm x 150 mm.
Four specimens in warp way and weft way are prepared for the specimen is cut in such a way that this should not contain same warp or weft threads. Selvedges, end pieces creased or folded places must be avoided.
- Prior to test maintain the standard testing atmospheric conditions of 27*C temperature and 65% Relative Humidity.
- The specimen is placed on a platform with the template at the top of it so that the leading edges co-inclined.
- Both core slowly pushed forward until the leading edges of the specimen and the template project beyond the edge of the platform with the eye in position so that the index lines co-inclined the sliding of the specimen is stopped when it cuts both index lines.
- If the specimen has a tendency to twist the reference point at the center of the leading edge is taken.
- The bending length can be read from the scale.
Measurement Of Drape Coefficient (IS-8357-1997)
Drapability of fabric can be determined using the instrument “Drapemeter” and it expressed in terms of ‘drape coefficient’
A circular specimen of diameter 10 inches is supported on a circular disc of 5-inch diameter.
The unsupported area of the fabric drapes over the edge of the disc.
When the fabric is supported, it will assume the folded configuration due to gravity and the shape of the projected area will not be circular but something like the shape of the figure.
Measuring the following areas the drape coefficient F can be calculated.
- AD-Area of specimen
- Ad-Area of supporting disc
- As-Actual projected area of the specimen.
The drape coefficient F is the ratio between the projected area of the draped specimen and it’s undraped after the deduction of the area of the supporting disc.
Drape Coefficient= F = (As-Ad)/(AD-Ad)
How Drapability of Fabric Can be Improved?
The drapability of fabric can be improved by following way-
- By providing the more float length by reducing the number of interlacements in the weave repeat.
- By reducing the number of picks per inch.
- The fabric of satin/sateen is used for the curtain.
- The fabric of sari is having fewer picks per inch.