Datasheet

59
Material Failure Testing
Property decay can lead to three different modes of failure: loss of strength, loss of toughness or change in
appearance. The critical mode for any given application would depend upon the application and the
requirements it places upon the material itself.
Loss of strength is monitored by tensile testing samples of the material before and after it has been
weathered. This test will reveal the decreasing strength accompanied by extended weathering.
Loss of toughness can be monitored by measuring changes in elongation and impact strength. As
ultraviolet light exposure time increases and the material becomes brittle, its elongation and impact strength
are greatly reduced. It is important to note that brittle failures can occur even when the tensile strength
shows no change.
Although change in appearance is normally not a failure mode for cable ties, the plastic does tend to discolor
and lose its surface gloss as exposure increases. These changes can be measured by color difference using
Adams units which are similar to National Bureau of Standard units.
Panduit has its own weathering test program to determine estimated life of various cable tie materials.This
includes examining many previously aged samples obtained throughout the world.
In all cases, the amount of property decay increased with increasing exposure to ultraviolet light. The
principal signs of degradation were found to be brittleness, cracking and loss of surface gloss. It was also
determined that the time for failure to occur was shorter than indicated from industry tests performed on
material samples. This discrepancy is in part due to the fact that cable ties were tested in an end use,
stressed condition, while most plastic resin suppliers conduct weathering tests using unstressed test bars.
Three cable tie materials (TEFZEL

, HALAR
▲
and stainless steel) have superior ultraviolet light resistance.
In tests conducted to date, both have shown no significant signs of degradation.
Determining the outdoor life expectancy of any material is difficult since there are other factors, besides
ultraviolet light stability, which have to be considered. These factors are listed below and should be
considered before specifying a cable tie material.
FACTORS DECREASED LIFE
Chemicals Applications which have chemicals present can reduce the life.
This is
the most detrimental factor to the life of a tie.
Bundle
Diameter
As the bundle diameter is reduced, the tie has more bending stress.
A thick strap on small diameter has more stress.
Loading If the tie is under high loading, this will add additional stress on the tie
body.
Thickness A thinner tie will have a decreased life since surface cracks will
penetrate the thickness of the tie faster.
Vibration Applications with high vibrations will cause impact which will propa-
gate any surface cracks.
Degree of
Exposure
No shield or shade, southern exposure, higher altitudes and high
temperatures decrease the life of the cable tie.
Moisture Dry environments cause nylon 6.6 ties to become more brittle. High
humidity plus high temperatures can result in degradation due to
hydrolysis in nylon.
Galvanized
Metals
Acid rain and acid moisture acting on galvanized metals release
chemicals known to attack nylon 6.6.
*Based on assumption of minimum loading, no chemical al attack and
impact-free conditions.
WEATHERING LIFE EXPECTANCY
Materials
(P/N Suffix)
Years*
Natural Polypropylene (-109) 1
Natural 6.6 Nylon 1-2
Flame Retardant Black 6.6 Nylon (-60) 1-2
Flame Retardant 6.6 Nylon (-69) 1-2
Heat Stabilized 6.6 Nylon (-30) 4-5
Heat Stabilized Natural 6.6 Nylon (-39) 1-2
Weather Resistant 6.6 Nylon (-0 & -00) 7-9
Heat Stabilized Weather Resistant 6.6 Nylon (-300) 7-9
Weather Resistant Polypropylene (-100) 7-9
Weather Resistant Nylon 12 (-120) 12-15
TEFZEL (-76) >15
HALAR (-702) >15
Stainless Steel (MLT prefix) >30
▲
HALAR is the Registered Trademark for Ausimont Inc. fluoropolymer

TEFZEL is the Registered Trademark of E. I. DuPont Co., fluoropolymer
Weathering
Table A - External Factors Which Affect the Life of a Cable Tie