22
en
1.
Stabilise the sample bolt at approximately 9°C (48°F). If the water bath method is used this is
accomplished in a stirred bath of ice and water. Measure and record this minimum temperature as
.
2.
Apply the transducer and couplant to the bolt and record the Ultrasonic Length at Zero Load
.
3.
Repeat steps 1 and 2 at the target temperatures (
to
) 9°C (48°F), 20°C (68°F), 31°C (88°F), and
42°C (108°F) (or some other similar range with 5 temperatures), measuring the ultrasonic lengths (
to
) respectively. This process must be done for each of the sample bolts in the experiment.
4.
Use the following equation to calculate a linear regression, using the temperatures and lengths
recorded for all the sample bolts to determine the temperature factor:
where:
x = temperature
y = change in reference length
n = number of sample points per bolt
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 0.01 mm in metric units (0.001” in English 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:
where:
= Load Factor
= Cross Sectional Area of the Bolt
= Modulus of Elasticity
= Clamp Length of the Bolt
= Diameter of the Bolt
Note: If no load factor has been entered, the gauge 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:
where:
= Load
= Average length under stress
= Change in length (elongation)
T
0
L
U
0
T
1
T
5
L
1
L
5
TemperatureFactor
xy
∑
x
∑
⎝
⎠
⎛
⎞
y
∑
⎝
⎠
⎛
⎞
n
--------------------------------
–
x
2
∑
x
( )
2
∑
n
------------------
–
-----------------------------------------------------
6
×
10
=
L
F
A
σ
E
C
L
D
+
(
)
----------------------
3
–
×
10
=
L
F
A
σ
E
C
L
D
P
Δ
L
AE
×
L
E
---------------------
=
P
L
E
Δ
L
