Page 6 - 诺霸英文2022

INTRODUCTION

INTRODUCTION TO TORQUE

Tightening to Yield
Bolts tightened to yield provide consistently higher preloads from smaller diameter bolts. The reduced fastener stiffness reduces
the fatigue loading to which the bolt is subjected under repeated external load reversals, e.g. cylinder heads and connecting rods.
In theory, a bolt tightened to its yield point will provide the strongest and most fatigue-resistant joint possible, within the physical
limitations of the bolt material and manufacturing process.
The downside of this method is the cost of the sophisticated equipment necessary to determine when the bolt goes into yield.

Torque Tension Calculator
For further information and guidance on
establishing the correct tightening torque for a
fastener, see Norbar’s web based calculator,
www.norbar.com/Support/Calculators/Torque-
Tension-Calculator

When Torque Doesn’t Equal
Tight
Ultrasonic Transducer
As we have established, it is the
tension in a fastener rather than
the torque that is the critical
factor. Torque is an indirect means
of establishing tension and in a
correctly engineered joint and with
a controlled tightening process, it
is a satisfactory method under the Time of Flight
majority of circumstances. UNTIGHTENED Pulse Echo

However, in joints that are highly Pulse Echo Time of Flight
critical due to safety or the cost TIGHTENED
and implications of machine
down-time, a more direct means
of establishing tension is needed.
Various methods exist including
several types of load indicating
bolts or washers. However, one of
the most versatile methods is to
measure the extension of the bolt Measured
Time Change
due to the tightening process using
ultrasound�

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