Standard Test Methods for Testing Fiber Ropes

 

Theory:

ASTM D4268 specifies a method for testing fiber based ropes. Ropes are really just a series of individual fibers which are wound or braided to create larger strands and eventually, a rope or cord. These types of materials are used in the transportation industry in order to secure cargo. Ropes are also used for sports such as mountain climbing. A tensile test is one of the simplest ways of testing a rope's performance and quality.

 

Geometry:

Standard samples for ropes can vary between different manufacturers. The cross-sectional area is the most important factor. Ropes from different stages of the winding process are usually taken and tested so as to reduce the amount of potential scrap material and ensure the proper quality. 

Solution:

Wrap grips are the best solution for ropes tensile testing because they reduce the propensity for the cord to slip during the pull. The wrap drum spreads the tensile stress over a wider area which helps with procedural consistency and better simulates actual working conditions. The amount of times the cord must be wrapped depends on the coefficient of friction of the rope. If the rope is made of nylon or a similar type of material, it will probably need to be wrapped several times.

Analysis:

The results for the ASTM D4268 test are simple for breaking force. Breaking force is the force at which the rope breaks. Ultimate Tensile Strength (UTS) can also be transcribed if the max force is larger than the breaking force.  

 

Elongation is also important and the modulus of elasticity can also be derived from this data as well. There are several elongation calculations which can be found in the official publication:

 

NE = nonelastic elongation

RE = residual elongation

CE = recoverable elongation

TE = total elongation

WE = working elongation

EX = extension