String/Cable Creep?

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  • August 17, 2006 at 10:32 pm #495141 Back to Top REPORT
    symo
    Symo


    Joined: 6/29/2004
    Creep ?[/size:ehg39hc0]

    The “creep” should be done in 50-100 shots. I haven’t had the string move since the initial breaking in period……and I had over 3000 shots through it

    _________________

    The comment above is typical of the comments that we see posted on forums about string “Creep”.

    Strictly speaking “Creep” is a property associated with particular materials (both metallic and non-metallic) and is a material property. It is the non-recoverable elongation of the material and is generally considered to occur over longer periods of time when a material is subjected to a relatively constant load and in many cases, the material may be at elevated temperature as well as a constant load. Further the degree of elongation tends to be time, temperature and load dependent. This means that an increase in any one of these factors tends to increase the amount of elongation that occurs.

    In the case of the HMPE materials “Spectra ™” and “Dyneama ™” the present molecular structure of this material is such that it exhibits Creep (Non-Recoverable elongation) under load and temperatures that can exist under conditions of normal usage. However actual Creep elongation is not a factor during the normal bowstring “break in period” unless the bow is exposed to rather elevated temperatures of over 100 °F (37.8 °C).

    The bow string stretch that occurs during the normal bowstring break in period tends to be independent of the material that the bow string is made of. This elongation can be attributed to two sources that occur in the process of making a bow string. One part of this elongation comes from the process of turning the desired raw material into the string material. Filaments or ends of the base material are combined to form the basic bowstring material and in the process, the various filaments may be commingled with other filaments and lubricants and coloring agents. This process tends to bulk the finished product to some extent. Another part of the elongation can come from the actual bowstring or cable making process. Things like how the string is laid up(with or without tension or the amount of tension), how the string is served, where in the process it is served, and the serving material used. There can also be other proprietary steps in the process from one manufacturer to another that effects elongation.

    It is the factors involved in the production of the bow string material and actual string or cable that results in the stretch that occurs during the break in period after changing out or putting on a new string and/or cable.

    The result is “mechanical elongation,” it is non-recoverable elongation of the string and cables resulting from the mechanical processes used to produce them. Under initial tension and shooting the individual string filaments lay together, excess wax or lubricant is squeezed out from in between the fibers, any differences in individual strand tensions are equalized and generally speaking the string or cable lays into its working condition and the system becomes more predictably consistent.

    Note: This mechanical elongation that occurs during the string “Break in” period is non- recoverable but it is not to be confused with “Creep” which is a material property.

    An example would be a bow string made with the material “Vectran ™”(Vectra LCP). This bowstring material exhibits virtually no creep characteristics under normal usage conditions, but will exhibit about the same mechanical elongation that occurs during the string break in period as strings/cables made from other materials.

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