ASTM D1388 Standard Test Method for Stiffness of Fabrics

Get Certified ASTM D1388 Testing for Reliable Fabric Stiffness Evaluation

The ASTM D1388 specifies controlled test methods for measuring the stiffness and bendability of textile fabric. The test is used to allow a laboratory to assess the ease with which a fabric will bend under its own weight and to give quantitative values for comparison of fabrics. There are two testing methods in the standard. As the Cantilever Test is easier to carry out than the Heart Loop Test, it is the preferred test; however, it is not suitable for all fabrics that tend to curl/twist at the cut edge, and for these fabrics the Heart Loop Test is recommended. The higher the bending length or flexural rigidity, the stiffer the fabric 

The ASTM D1388 standard:

• Determines the stiffness characteristics of fabrics.
• Measures the bendability of fabric samples.
• Computes flexural rigidity based on bending behavior measured.
• Checks bending under the weight of the fabric using the Cantilever Test.
• Applies the Heart Loop Test to an up-hung fabric loop which is suspended vertically.
• For woven, knitted, layered (both woven and knitted), pile, napped, blanket, and other applicable fabrics.
• Works with untreated, coated, sized, resin-treated, and otherwise treated fabrics.
• Uses standard units of measurement (SI units) 

What are the Uses of ASTM D1388 Testing?

ASTM D1388 is a test method that is useful for helping determine the bending and stiffness characteristics of textile materials. The outcomes are used by manufacturers and engineers to compare fabrics and determine the appropriateness of a fabric for a fabric application where fabric handle, drape, bending resistance, or structural behavior is important.

This standard:

• Measures the bending length of fabric.
• Measures the stiffness of fabric.
• Helps compare the stiffness of different fabrics.
• Assists in textile quality control and product development.
• Gives quantitative data to describe materials.
• Assists in the selection of fabrics to suit end uses.
• Accepts commercial fabric for shipment to customers for testing.
• Gives results which can be related to subjective measurement of fabric stiffness. 

Which Materials Can Be Tested Under ASTM D1388?

ASTM D1388 is applicable to most fabric types that can be prepared and tested in accordance with the procedures outlined. Woven fabrics, airbag fabrics, blankets, napped fabrics, knitted fabrics, layered fabrics, and pile fabrics are specifically mentioned in the standard. Fabrics may be resin-treated, heavily sized, coated, untreated, or otherwise treated. It can also be used for a number of nonwoven products such as hydroentangled, dry-laid, resin bonded, needle punched, thermal, and wet laid. The standards for medical textiles (surgical mesh, films and membranes) are referenced by ASTM D1388, which also requires reference to ASTM F3260. Technicians choose those samples that are representative of the laboratory sample and away from the sample edge. They remove folds, creases, wrinkles, oil, water, grease, and other contaminations from the specimens, which may affect their bending behavior. 

Why is ASTM D1388 Important?

ASTM D1388 allows you to measure fabric stiffness using a consistent method, not just handling or visual inspection. The test evaluates bending length, and the results are used to determine flexural rigidity in order to compare the behavior of fabrics under controlled conditions. The Cantilever Test is a convenient method for fabrics that do not curl or twist too much around the edges of the cuts. Fabrics that have a higher tendency to curl or twist can be used on the Heart Loop Test. However, the two options do not necessarily result in the same results in terms of numbers, and different fabrics do not necessarily rank in the same order. As noted in the standard, the laboratory must choose which of the two options is more suitable for the fabric being tested. 

ASTM D1388 Testing Process and Data Collection

The analyst selects appropriate fabric samples that represent the material and determines the test direction. The technician sizes and conditions the specimens according to the conditioning atmosphere used in the textile industry. The operator then checks the testing apparatus and loads the sample into the testing segment of the apparatus for the cantilever test. In the cantilever test, the technician moves the specimen forward from the edge of the platform. The unsupported part bends down under its own weight until it is in the given reference position. The operator determines the overhang and writes down the bending length. In the Heart Loop Test, the technician loops the fabric strip on the bars and hangs it up vertically. The fabric creates a heart loop under its own weight, and the operator measures the length of the loop. By measuring the bending length and using the fabric mass per unit area, the analyst is then able to determine flexural rigidity. The measurements are repeated in the necessary test directions in the laboratory, and the single values are recorded. The results are then compared with the analyst’s to determine whether there are any differences in the stiffness of the fabric or the bending properties.

Common Challenges and Troubleshooting

Representative specimens, correct specimen dimensions, proper conditioning, and stable test equipment are required to obtain accurate ASTM D1388 results. The bending property may be affected by folds, wrinkles, creases, or contamination, which can influence the result obtained. The test can also be affected by the curling or twisting of the fabric. The cantilever test is not appropriate for very limp fabrics or fabrics that have a strong tendency to curl or twist at the cut edge. In these situations, technicians have the option to use the Heart Loop Test and choose a proper specimen width.  One other factor to consider is specimen width. The width of the specimen does not necessarily affect bending length, except when the fabric is curled or twisted. Generally, a piece of fabric with a slight tendency to curl would require a 25 mm wide strip, and the wider the strip, the greater the tendency to curl. 

• Laboratory records the test direction and specimen ID.
• The bending length will be calculated based on the observed bending characteristics of the fabric.
• The fabric mass per unit area is used with the bending length to calculate flexural rigidity.
• A higher bending length or flexural rigidity is likely to indicate stiffer fabric.
• When the machine direction and cross-machine direction are tested, the results in both directions may be compared.
• Laboratories can compare results from various fabrics tested under the same conditions.
• The choice of test option is reported since the cantilever and heart loop procedures do not always yield the same numerical results or ranking. 

Link to ASTM D1388