Checkline TI-MINIMAX - Manual (Page 102)

Dakota Ultrasonics
96
Chapter 11 Load Measurement
11.1 Calculating a load factor
The load factor is an empirically determined value for the geometry of the bolt. It
is the amount of load required to elongate the bolt 0.001” in English Units or
0.01mm in Metric Units. The accurate load factor for the bolts being measured is
determined by the Calibrate Bolt function.
An approximate value of this geometry dependent factor can be calculated as
follows:
( )
3
10
− ×
+
=
D C
E A
L
L
F
σ
Load Factor
=
σ
A Cross Sectional Area of the Bolt
E
= Modulus of Elasticity
=
L
C Clamp Length of the Bolt
=
D Diameter of the Bolt
Note: If no load factor has been entered the MINI-MAX defaults to zero.
The relationship between load and elongation is a function of the elasticity of the
bolt material, and the geometry of the bolt in the application being measured.
Hooke’s Law expresses this relationship:
E
L
AE l
P
× ∆
=
Hooke’s Law
P = Load
L
E
= Average length under stress
∆
L = CHANGE IN LENGTH
(ELONGATION)
A = CROSS SECTIONAL AREA OF
THE BOLT
E = Modulus of elasticity
The cross sectional area of the bolt is defined as the average area of a fastener
under stress. This factor is only used in the MINI-MAX’s calculation of load. It
has no effect on stress or elongation, time, or strain, and is directly proportional
to the load measured ultrasonically. If the cross sectional area is off by 5%, the