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Preload the load string
Product Support: www.instron.com
Figure 20. Typical grip installation
Preload the load string
This procedure eliminates backlash and deflections within the load string which can
degrade the integrity of test results, especially when testing at high loads. The
procedure involves preloading the entire load string and then hand-tightening all the
lock nuts on all the grips and couplings. Even when using self-aligning couplings on the
upper grip, it is good practice to preload the lower grip.
You will need a rigid specimen that is strong enough to sustain the preload value without
breaking. This means a specimen that can sustain a load that is:
• 10% above the expected test load, or
• the maximum load rating of the weakest component of the load string (grips or load
cell)
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