How to Read a 5-Million-Cycle Torsion Test: Dresspack Life Is More Than One Number

Summary: The difference between torsion, flexing, specimen and complete-assembly life — with the test conditions, standards and scope of application.

1. One number cannot answer the whole life question

Customers often ask “how long will it last?” and suppliers often answer “5 million cycles”. But a dresspack is not a single material — it contains conduit, cables, connectors, mounting brackets and springs, and its life has to be examined part by part.

2. Torsion and flexing are two different tests

A torsion test measures repeated twisting through a defined angle; a flexing test measures repeated bending at a defined radius and angle. The two are not interchangeable, and neither alone can represent a complete assembly. Taking report ADTK20240624008F as an example, the torsion test used ±180° at 1.7 Hz with a 1.75 m specimen, and the flexing test used 180° at 1.7 Hz with a 600 mm specimen. The results: no abnormality was found after 5 million flexing cycles; the torsion specimen showed whitening at the mid-section, with no fracture recorded.

3. Specimen results are not complete-assembly results

No abnormality after 5 million flexing cycles, and whitening at the mid-section after torsion with no fracture recorded — these results describe the specified conduit specimen. They do not represent the service life of a complete dresspack across every model, every cable configuration and every motion path.

4. Five things to look at in a report

Look at the specimen, the test frequency, the angle, the bend radius and the termination criteria. If any one of these is missing, the number cannot be reproduced.

5. How to use the standards

Torsion test methods reference GB/T 37220-2018 and flexing test methods reference GB/T 5565.1-2017; ingress protection is verified to GB/T 4208-2017, and flame retardancy can be tested to GB/T 2408-2021. A report is evidence, not a marketing slogan.

6. What buyers should ask suppliers

Do not ask only “what is the service life”. Ask: what was the specimen, what were the test conditions, what is the report number, how is the complete assembly verified, and how is the solution adjusted for different working conditions. A supplier who can answer clearly has a more traceable solution.

Next step

Need help reading a dresspack test report? Send us the report or the test conditions and we will work through what it actually demonstrates.