19
en
1.
Select MENU/GEOM/QUANTITY and scroll the value to ELONG
2.
Press MENU/MATL/TYPE and press ENTER
3.
Use UP and DOWN to select the correct material type from the list and press ENTER
4.
The new bolt type material selected is displayed to the right of the sub menu item.
Note: If the material type is not in the list of types, select a similar type. This step is only to get the velocity
value close to the true value. Write down the velocity of the material type selected. This will be considered
the Current Velocity.
5.
Press OK to set the material type and return to the menu screen, or ESC to cancel.
6.
Set the value of ALEN / APPROX. LEN. to the correct length of the fastener and then conduct an
AUTO SET with the transducer attached to one end of the fastener - see “Auto Set” on page 29.
The ultrasonic length of the fastener is displayed.
7.
Calculate the correct velocity using the following equation:
8.
Select MENU/MATL/VELOCITY and press ENTER
9.
Adjust to the correct value
10.3 STRESS FACTOR CALIBRATION
The sonic stress factor is an empirically determined value for the bolt material or type of bolt being
measured. It expresses the ratio of the elongation, or stretch, of the bolt, to the apparent ultrasonic change
in length. Since the change in ultrasonic length is approximately 3 times the change in physical length, due
to the change in velocity, a stress factor must be applied to correct the ultrasonic length in the gauge.
The Sonic Stress Factor is calculated using the following equation:
where:
The procedure in this section describes how to determine the Sonic Stress Factor for bolts of a specific bolt
material and specific geometry by measurement of the change in bolt length.
To complete this procedure you will need the following equipment:
•
A laboratory or room in which the temperature can be maintained at 19°C to 21°C (66°F to 70°F).
•
A means of applying load to the bolt. Ideally this would be a tensile load machine, capable of
measuring the applied load to within 450 N (100 lbs). However, since the actual value of the applied
load is not used in calculating the stress factor, any means of applying an approximate load to the bolt
will suffice. This includes tightening the bolt against a fixture that simulates the actual joint.
•
A mechanical means of traceable measurement of the physical length of the sample fasteners at
various tensile loads to an accuracy of plus or minus 2.5 µm (0.0001”).
Examples of such devices include the following
•
The length measurement function of a sophisticated tensile test machine
•
Mechanical or electronic height gauges
•
Averaged values of length measurement with mechanical and electronic micrometers.
•
A minimum of three sample bolts which are representative of the bolt type and geometry for which the
Sonic Stress Factor is to be determined.
PhysicalLength
UltrasonicLength
-------------------------------------------------
CurrentVelocity
×
CorrectVelocity
=
SonicStressFactor
Δ
L
MECHANICAL
Δ
L
ULTRASONIC
---------------------------------------
L
M
1
L
M
0
–
L
U
1
L
U
0
–
--------------------------
=
=
L
U
0
UltrasonicLengthAtZeroLoad
=
L
M
0
MechanicalLengthAtZeroLoad
=
L
U
1
UltrasonicLengthAtLoad
=
L
M
1
MechanicalLengthAtLoad
=
