Dakota MAX II, Operation Manual

Page: 117 / 216

109
CHAPTER ELEVEN
LOAD MEASURMENT
11.1 Calculating 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

Load Factor


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 MAX II 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
MAX II’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 load
measurement will also be off by 5% proportionally. For a cylindrical bolt with the
same geometry, the area may be approximated as follows:
2
2







D
A

D = minor diameter of the bolt, allowing for
threads.