ASTM D6775 - Textile Webbing Grips
Standard Test Method for Breaking Strength and Elongation of Textile Webbing
Wrap grips are necessary for any webbing or strap type textile material. Some manufacturers may also call this a ribbon or a capstan fixture. Basically it is any thin and wide material, tapes can also be tested as well.
By wrapping the webbing around the drum one can induce a perfect grip. The coefficient of friction will determine how many times the material must be wrapped around the center cylinder. The working principal of this fixture is to spread the strain over a longer area which reduces the propensity for it to break or slip at the wrong time.
Seatbelts are often tested to this standard, as well as any tie downs that may be used in the shipping and transportation industry. Safety straps and military equipment also use this type of woven textile material.
The wrap grip solution is also gaining popularilty amongst the bio-medical sector. Small redesigns of this setup can be used to pull tissues without fear of ripping the specimen at the fixture interface. The drum column distributes the strain over a wider area which reduces local stresses which could propagate a tear.
The width of the material being tested as well as the width of the drum are the two most important specifications along with the anticipated max load. Ultimate Tensile Strength and Elongation at break are the most common calculations, however more advanced analyses can be performed such as elongation modulus.