Scope
This test method covers the determination of the stiffness of fabrics by the circular bend procedure.
This test method is generally applicable to all types of fabrics, including woven, knitted and nonwovens, of any fiber content.
Significance and Use
Test Method D4032 for testing stiffness of fabrics is considered satisfactory for quality control testing. It may also be used for acceptance testing of commercial shipments since the test method has been used extensively in the trade. In cases of differences in values reported by purchaser and seller using Test Method D4032 for acceptance testing, the statistical bias, if any, between the laboratories of the purchaser and seller should be determined with each comparison being used on the testing of specimens taken homogeneously from a lot of material of the type being evaluated. Specimens should be randomly assigned in equal numbers to each of the laboratories.
The circular bend procedure gives a force value related to fabric stiffness, simultaneously averaging stiffness in all directions. The stiffness tests in Test Methods D1388 are of the single directional type.
The circular bend procedure is simple to perform and may be used for knitted, woven or nonwoven fabrics, provided gage capacity is in keeping with fabric range tested.
Summary of Test Method
A plunger forces a flat, folded swatch of fabric through an orifice in a platform. The maximum force required to push the fabric through the orifice is an indication of the fabric stiffness (resistance to bending).
Apparatus
Circular Bend Stiffness Tester
- Platform, 102 by 102 by 6 mm (4 by 4 by 1/4 in.) smooth-polished chrome-plated steel plate with a 38.1-mm (1.50-in.) diameter orifice. The lap edge of the orifice should be at a 45-degree angle to a depth of 4.8 mm (3/16 in.).
- Plunger, 25.4 mm (1.00-in.) diameter, mounted concentric with orifice, 6.4 mm (0.25 in.) clearance on all sides. The bottom of the plunger should be set at 3 mm (1/8 in.) above the top of the orifice plate. From this position, the downward stroke length is 57 mm (2-1/4 in.).
- Force-Measurement Gage, dial or digital type.
- Dial gages with maximum reading pointer in different capacities ranging from 12 to 50 lbf, 0.5 to 25 kgf, or 5 to 200N with 100 graduations minimum; or
- Digital gage with maximum reading "hold" feature and capacity of 100 lbf, 50 kgf, or 500N, with 1000 graduations minimum.
- Actuator, manual or pneumatic.
- Specimen Marking Template, (102 by 204 mm) 4.0 by 8.0 in.
- Stop Watch, for checking stroke speed.
Sampling
- Lot Size -- For sampling purposes, a lot is defined as a single shipment of a single style of fabric. A lot may constitute all or part of a single customer order.
- Lot Sample -- Take a lot sample as directed in the applicable materials specification. In the absence of such a document, select random rolls, etc. of fabric for the lot samples.
- Laboratory Sample -- As a laboratory sample, take from the outside of each roll in the lot sample a full width swatch of fabric 1 m (1 yd) long after discarding a full width length of at least 1 m from the very outside of each roll. If necessary, discard more than 1 m from the outside of a roll in order to obtain a swatch that is free of abnormal deformations, wrinkles, or creases. Handle swatches carefully and as little as possible to prevent lowering specimen stiffness.
Number and Preparation of Test Specimens
Using the specimen-marking template, mark and cut five test specimens from staggered areas of each swatch in the laboratory sample. The short side of the specimen must be parallel to the machine (length) direction of the fabric. Cut no specimens closer to the selvage than one-tenth of the fabric width. Lay each specimen face down and fold the specimen once to form a square 4 by 4 in. (102 by 102 mm). After folding, use the template and hand pressure to flatten the crease. Handling of specimens must be kept to a minimum and to the edges to avoid affecting stiffness properties.
NOTE: Fabrics may also be tested face-to-face when the technical back is used
for the outer surface or when there are significant differences in face and back surface properties. In reporting, indicate that the fabric was tested face-to-face.
Conditioning
Bring the specimens to moisture equilibrium, as directed in Practice D1776.
Procedure
- Test the adequately conditioned specimens in the standard atmosphere for testing textiles, which is 21 ± 1° C (70 ± 2° F) and 65 ± 2% relative humidity.
- Set the tester on a flat surface with dial at eye level.
- Select a gage with a capacity in which results will fall within 15 to 100% of dial gage force or 1.5 to 100% of digital gage force.
- Check tester plunger speed control for full stroke length.
- Pneumatic Actuator -- Set the air pressure control to the actuator at 324 kPa (47 psi). Using a stopwatch, adjust the pneumatics to provide plunger speed of 1.7 ± 0.15 s under no load conditions.
- Manual Actuator -- Using a stopwatch, establish and confirm a plunger speed of 1.7 ± 0.3 s.
NOTE: The use of the pneumatic actuated tester gives a more controlled
result than the manual actuated tester, which is subject to operator variances
in the speed at which the plunger if operated.
- Center a double-ply specimen on the orifice platform below the plunger.
NOTE: If 3.2 mm (1/8 in.) clearance under plunger prevents ease of
entry of specimen due to fabric thickness, the clearance may be in-
creased to 6.3 mm (1/4 in.) maximum. In reporting, the results should
indicate the plunger clearance.
- Check the gage zero and adjust, if necessary.
- Set the maximum force reading switch.
- Actuate the plunger for the full stroke length. Avoid touching the specimen during testing.
- Record maximum force reading to nearest gage graduation.
- Continue as directed until all specimens have been tested.
Calculation
Average the individual specimen readings and round to the nearest gage increment.
Report
State that the specimens were tested as directed in Test Method D4032. Describe the material or product sampled, and the method of sampling used.
Report the following information:
- Average force in gage units.
- Number of specimens tested.
- Actuator type.
- Gage type and capacity.
- How fabric was folded, if not standard (back-to-back).
- Plunger clearance, if not standard.
From: 1992 Annual Book of ASTM Standards.
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