Defining, measuring and calculating the change-in-length properties of synthetic fiber rope

The change-in-length properties of synthetic fiber ropes are important for engineered applications. Unlike most other engineering components, typical synthetic fiber ropes have nonlinear, nonconstant change-in-length properties. These properties depend on variables such as rate and duration of tension application, and magnitude and number of previous tension applications. The length of a synthetic rope typically increases with each tension cycle. Thus strain-the ratio of change in length under tension to length before tensioning-has two different references. When overall change in length is of interest, strain must be referenced to the untensioned rope length before it was placed in service. But when rope stiffness under tension is of interest, the strain must be referenced to the untensioned length immediately before application of that tension. A clear unambiguous vocabulary of synthetic rope change in length properties is necessary. Different vocabularies were used in several recent rope test standards and design guidelines. This paper intends to explain the various vocabularies, propose a common vocabulary, and explain several pertinent concepts