E10190-000816
FOS
Page 15
1
=
Current strain, in
strains
0
=
Initial strain, in
strains
This total strain includes the mechanical strains and thermal strains in the investigated
structure. The method detailed below explain how to obtain the mechanical strain due to
applied effective stress.
The real strain
r
(due to applied effective stress) can be computed with the following
formula:
r
T
T
1
0
(3)
Where:
r
=
Real strain, in
strains
=
Total strain reading, in
strains
T
1
=
Temperature reading of structure, in °C
T
0
=
Initial temperature reading of structure, in °C
=
Expansion factor of structure in
m/m/°C on which the
gauge is fixed, generally in the range of 10
m/m/°C
16
m/m/°C for steel. The
expansion factor can be
known from laboratory test.
Numerical example:
0
=
2200.2 units, initial reading of FOS with the ROCTEST's fiber-optic
readout unit
1
=
2407.8 units, current reading of FOS with ROCTEST's fiber-optic
readout unit
T
0
=
20.2°C, initial temperature reading
T
1
=
26.2°C, current temperature reading
=
12.0
m/m/°C, structure expansion factor
First the total strain (
) must be found:
1
0
2407 8
2200 2
207 6
.
.
.
microstrains
Therefore the real strain
r
is:
r
T
T
1
0
