Incorporating Cyclic Fatigue Testing TBAR – Part 5

TBAR DSO Incorporating Cyclic Fatigue Testing – Part 5

Cyclic Fatigue Testing Machine

By Carter Penley

The last ‘TBARtm” article (Part ‘4’) discussed the affects of the composite materials and geometric shapes on ‘TBARtm” measurement, with more emphasis on materials.

            Part’4′ ended with the discussion concerning lightweight shafts; specifically the effects of the measurement equipment in reference to failing the shafts internal wall structure at the tip and/or butt section. The task at this point was to ensure that all shafts could be flexed, measured and successfully achieved without damaging the shaft. The ability of the measuring equipment to measure all shaft flexes and weights would guarantee that a linear standardization could be established and maintained throughout the “TBARtm system. This would allow for all TBARtm data acquired being accurate and consistent.

            It was even more obvious to Penley that the limiting factor for “TBARtm” measuring equipment and the range of testing requirements was going to be the structural design and materials factor of the lighter weight shafts. The fact that a golf shaft may or does fail during testing is not always an indication that the golf shaft will always fail during play. Although, I will concede that if a shaft tends to fail at or below the DSO (Design Service Objectives) safety factor(s) more often than not during what engineering considers “non-destruct tests” then there would be an engineering requirement to further investigate the design and materials selection.

            Testing criteria is developed and put into place to “fail products” not “pass products” therefore, we must be very careful of how robust a test might be. If we become too critical of the requirements and safety factors, we will tend to either over design greatly exceeding the DSO which will not only increase cost, but discourage testing all together. The latter is the most common result, especially for small or less-knowledgeable golf shaft manufacturing companies.

            These design limits can be analyzed, tested and demonstrated with the proper equipment to destruct testing as required, specifically using the dynamic method of cyclic fatigue testing. Penley, to our knowledge is one of the few if any golf shaft manufacturing companies to have designed and placed into service their own cyclic fatigue testing equipment and has incorporated fatigue testing as part of their design and test analysis and to form DSO criteria. This test is performed primarily to determine a golf shafts tip sections durability and ultimate strength. The process requires that the shafts tip section is deflected to a predetermined load and if passes then the golf shaft is prepared and affixed in the cyclic test machine and then cycled at the maximum load (deflection) to ~10,000 cycles or failure which ever occurs first.

            Cyclic fatigue testing is critical to the design analysis because the results are a design driver for the engineer and if there is a failure it requires a full analysis from initial design solution to full cyclic fatigue testing again prior to release to the public. The old method of taking a newly designed golf shaft out to the driving range and hitting it a few times and if the golf shaft does not break it is deemed a successful design, are over! Because of concerns over liability and lawsuits, not to mention the wide range and diversity of player abilities requires that a quality golf shaft manufacturer be able to emulate all critical variables through design analysis and in the laboratory and field testing before you go to market with your product.

            So not only is the reliability of the standard golf shaft important but for the lightweight golf shaft it is most important to incorporate non-destruct testing, such as required for “TBARtm” analysis and machining processes.

            Therefore, the “TBARtm” measuring equipment must be designed to be user friendly and manufactured in such a way that a structural failure will not occur while being used by any skill level technician or employee.

            This brings us to the second design benefit of the TBARtm algorithm to define and implement “Zone Flextm characterization.

            As stated in the first article of this series “TBARtm vs. Kick (Bend) Point” it is stated that when you are working with a player and you build for him the perfect club and he asks you for a ‘back up club’. You purchase the same shaft, flex, kick point, weight and manufacturer and build him a club with the very same specifications, physical and mechanical properties and he takes it out to his next event and reports back to you that it does not feel or play the same at all ; as depicted in “TBARtm, Measurement and Method of, Part 3

            The major problem is that the standard industry flex range is dynamically much larger and in reality in many cases overlaps corresponding flexes (‘S’ flex may overlap the ‘R’ flex and or the ‘X’ flex). Although a flex measured statically or dynamically appears to be a narrow range when in fact it is actually proportionally wider and more complicated when you compound the flex dynamic with the players attributes of swing speed, tempo, muscular and mental input.

            So now you are left with the realization of “what happened” and “why”, “what did I do wrong”, when in fact you may have had little or no control of the unfavorable outcome. The first club (the one the player preferred) that you built may have been with a shaft that was on the high side of the recommended flex range and the second shaft you received was vice-versa or cross-versa? Now do you tip it only or butt cut only or both or do you install off center? The fact is you have little or no idea of what to do and most likely your golf shaft supplier will be of little or no help either! But ‘PENLEY’ can and will help!

See “TBARtm with Zone Flextm Characterization” Part 6 of 6

Copyright © 2008, 2015 Carter Penley. All Rights Reserved
(all theories and analysis are still pertinent)

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