ASTM D751 - Standard Test Method for Coated Fabrics

 

Theory:

 

The Standard Test Methods for Coated Fabrics is an umbrella ASTM for a long list of tests for coated fabrics. The literature recognizes rubber-coated fabrics, however the coverage is not limited to rubber, and extends to similar types of polymer coatings on textiles. 

 

Types of coatings that are commonly used include plastic material as well as teflon (PTFE). This allows the material to acquire multiple hybrid properties, such as a textile becoming stronger or more stain or wear resistant. Waterproof textiles are also usually tested to one or more of these standards.

 

This list explains the grips and equipment needed for each of the 20 different tests under ASTM D751.

 

1. Dimensions and Mass:

The length may be measured by a ruler or with the drum method where the length data is measured off a dial or indicator. The width can also be measured with a ruler or more accurate device. thickness is measured with a thickness gauge. The weight is measured on a scale with a smaller piece of the fabric. 

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2a. Breaking Strength - Grab Test Method

The grab method is similar to ASTM D5034. The test utlizes a tensile testing machine and a pair of vise grips with front grip inserts of 1x1" and back inserts of 1x2".  

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2b. Breaking Strength - Cut Strip Test Method

The strip method is similar to ASTM D5035. A UTM and vise grips with the same 1x1 and 1x2 inserts are used. 

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3. Elongation

The elongation is typically measured by the crosshead of the UTM, however extensometers can be used to acquire direct strain data from the specimen. 

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4. Bursting Strength

A puncture fixture similar to the one outlined in the ASTM D3787 Ball Burst Test is used in conjunction with a UTM. 

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5. Puncture Resistance

Another test using a puncture fixture. This test is similar to ASTM D4833 where a puncture implement with a chamfered edge is used to puncture through the sample. 

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6a. Tearing Strength - Pendulum Method

The pendulum method is similar to ASTM D1424 and uses an Elmendorf machine create a rotational tearing motion.

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6b. Tearing Strength - Tongue Tear Method

The tongue tear method is also described in similar detail in ASTM D2261. The vise grip faces must be 1x2" HxW or more.  

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7a. Trapezoidal Tear

Trapezoidal tear is also explained in more detail in ASTM D5587 and ASTM D4533 . A tensile tester and vise grips with 2x3" HxW grip inserts are used. 

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8a. Hydrostatic Resistance - Mullen Type Tester

A Mullen's style testing machine is different from a UTM/tensile tester. This small benchtop machine forces hydraulic fluid through a diaphragm of the coated fabric under inspection. The coated fabric diaphragm will burst, revealing its hydrostatic resistance.

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8b. Hydrostatic Resistance - Rising Water Column Tester

A rising water column tester is a simpler device compared to the Mullens tester. This type of test is also referred to as a Suter test. 

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9. Adhesion Coating to Fabrics

The adhesion test is used when the coating is stronger than the adhesive that binds it to the fabric. When this is the case, a T-Peel test may be used which is similar to ASTM D1876. The vise grip inserts should be 1x3" HxW.

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10. Strength of Coating

The strength of the coating on the fabric is measured by pretensioning the sample and then testing it using one of the above hydrostatic methods. The sample is pretensioned in a UTM with vise grips and inserts of 1x2" HxW.  The sample is stretched at a definied load for a set period of time before being hydrostatically tested. 

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11. Tack-Tear Resistance

The Tack-Tear test fixture is described in scant detail in the official publication. It involves a fixture that uses a row of needles or nails to grip into the sample. The apparatus is then pulled apart and tearing occurs along where the needles were gripped into the sample. 

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12. Low Temperature Bend Test

ASTM D2136 specifies the low temperature bend test. 

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13. Low Temperature Impact Test

Similar to above, the low temperature impact test is specified in ASTM D2137.

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14. Low Temperature Crack Resistance

Crack resistance is tested at low temperature by means of a chilling chamber. Square samples are put into the chamber for conditioning. Once the samples are cold enough, the samples are folded in half. A weighted roller is used to roll over the folded sample to push down on the crease. The samples are then unfolded and allowed to reach more normal temperatures. The remaining sample is then tested for Hydrostatic Resistance. The idea is to test for any cracks in the coating that may affect its permeability.

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15. Seam Strength

The seam strength test uses a machine that can pull at Constant-Rate-of-Extension (CRE). The CRE machine must use vise grip faces that are 1x3" HxW. ASTM D1683 covers a similar procedure for seam efficiency.

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16. Accelerated Heat Aging (Oven Method)

Accelerated heat aging using an oven is described in both ASTM D573 and ASTM D1349. The oven only cycles heat, the samples should not be exposed to light. After the sample has been heat aged it is tested using one of the above procedures.  

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17. Dead Load Seam Strength

Dead Load Seam Strength is similar to the seam strength test. Grips with faces of over 1x1" are appropriate. 

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18. Blocking Resistance at Elevated Temperatures

Blocking resistance is tested by folding a piece of fabric sample a couple of times and then placing it in between two glass plates. A weight is placed on top of the glass plates to maintain even pressure. The samples are then conditioned in an oven for a set temperature and time period.

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19. Crush Resistance

Crush resistance is a compression test similar to a shear test. A piece of coated fabric is pushed onto a small circular button. The button has space to puncture through the sample. This special crush resistance fixture is unique to this test.

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20. Wicking of Coated Cloth

Small wick sized samples are put into a beaker with a water soluble dye. The wicks stand in the beaker and the dye traverses up the fabric by means of wicking. After a set period of time the amount of wicking is measure. 

Solution:

Vise Grips are the standard solution for this test, however self-tightening wedge or scissor grips may be used as well as long as the grip face sizes are appropriate. There are a few types of grip faces that are available including blank, vulcanized rubber, pyramid, or wave. Textile tests are usually performed in rapid sequences and therefore it may be advantageous to use pneumatic grips, especially if the machine is running for several hours per day. The long term increases in productivity and efficiency out-weigh the initial cost.  Tests within D751 include puncture, seam strength, and tear tests. There are a total of 20 procedures listed, with most of them being variations of common fabric tests.

 

 

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