Method and device for tensile testing of cable bundles
Inventors
Robertson, Lawrence M. • Ardelean, Emil V. • Goodding, James C. • Babuska, Vit
Assignees
National Technology and Engineering Solutions of Sandia LLC • United States Department of the Air Force
Publication Number
US-8286498-B1
Publication Date
2012-10-16
Expiration Date
2030-08-09
Interested in licensing this patent?
MTEC can help explore whether this patent might be available for licensing for your application.
Abstract
A standard tensile test device is improved to accurately measure the mechanical properties of stranded cables, ropes, and other composite structures wherein a witness is attached to the top and bottom mounting blocks holding the cable under test. The witness is comprised of two parts: a top and a bottom rod of similar diameter with the bottom rod having a smaller diameter stem on its upper end and the top rod having a hollow opening in its lower end into which the stem fits forming a witness joint. A small gap is present between the top rod and the larger diameter portion of the bottom rod. A standard extensometer is attached to the top and bottom rods of the witness spanning this small witness gap. When a force is applied to separate the mounting blocks, the gap in the witness expands the same length that the entire test specimen is stretched.
Core Innovation
The invention improves a standard tensile test device to accurately measure the mechanical properties of stranded cables, ropes, and other composite structures by attaching a witness to the top and bottom mounting blocks holding the cable under test. The witness consists of a two-part structure: a top rod with a hollow opening in its lower end and a bottom rod with a smaller diameter stem on its upper end that fits into the hollow, forming a witness joint with a small gap.
A standard extensometer is attached to the top and bottom rods of the witness spanning the gap. When a force is applied to separate the mounting blocks, the gap in the witness expands by the same length that the entire test specimen stretches, thereby measuring the elongation of the entire cable specimen length rather than just a short portion. This yields a more accurate strain measurement for composite cables, which cannot be reliably tested by placing extensometers directly on the cable due to surface irregularities, twisting, and non-isotropic structure.
Claims Coverage
The patent includes two independent claims defining a method and an improvement to a standard tensile test device, each encompassing the use of a witness structure and measurement of cable elongation via displacement of the witness rods.
Use of a witness structure attached to mounting blocks
The method involves securely fastening a witness comprised of a top rod with a hollow end and a bottom rod with a stem that fits into the hollow end, both attached to the respective top and bottom mounting blocks so they can move freely together or apart directly with the mounting blocks' movement.
Measurement of elongation via displacement of witness rods
Applying a force separating the mounting blocks causes displacement between the top and bottom witness rods, which is measured by an extensometer as the elongation of the entire cable specimen, from which mechanical properties can be determined.
Integration of the witness and extensometer into a standard tensile test device
An improvement to a standard tensile test device by adding the witness attached to mounting blocks, with an extensometer measuring the separation between the witness rods, ensuring the measured displacement corresponds to the increased length of the entire cable specimen.
The claims collectively cover the inventive use of a two-part witness structure integrated with mounting blocks and an extensometer to accurately measure the total elongation of composite cable specimens during tensile testing, improving upon prior art methods that measured only a small portion of the specimen.
Stated Advantages
Provides a more accurate measurement of the elongation and strain of the entire cable specimen rather than a small portion, improving reliability for composite cables.
Avoids errors caused by placing extensometers directly on non-uniform, twisting cable surfaces where knife edges might slip.
Eliminates inaccuracies due to compliance in grips and fixtures by measuring displacement directly across the witness instead of relying on cross-head displacement.
Documented Applications
Measurement of mechanical properties of stranded cables, ropes, and other composite cable structures.
Testing of electrical power and signal cables found on precision spacecraft or other systems requiring accurate structural modeling.
Interested in licensing this patent?