micro-measurements@vishay.com
Crack Propagation Patterns
Vishay Micro-Measurements
Document Number: 11521
Revision 09-May-03
www.vishaymg.com
98
Special Purpose Sensors - Crack Propagation Patterns
Crack Propagation Gages provide a convenient method for
indicating rate of crack propagation in a test part or structure.
The CPA, CPB, and CPC patterns consist of a number of
resistor strands connected in parallel. When bonded to a
structure, progression of a surface crack through the gage
pattern causes successive open-circuiting of the strands,
resulting in an increase in total resistance. The CPA pattern
incorporates 20 resistor strands; the CPB, with the same
basic configuration, incorporates ten. Both series produce
stepped increases in resistance with successive open-
circuiting as indicated in the charts below. In applications
where space permits, the CPC pattern may be preferred
because of greater uniformity of increases in total resistance
with successive strand fractures.
The resistor strands of the CPD pattern operate
independently, each producing an open circuit when fractured.
This type of gage allows the user to electrically predetermine a
specific point in the fracturing process at which the
instrumentation will perform some type of altering function.
GAGE CHARACTERISTICS
Crack Propagation Gages have a nominal gage thickness of
only 0.0017 in (0.043 mm). The high-endurance K-alloy foil
grid has a single cycle strain range of up to ±1.5% with a
fatigue life of greater than 10
7
cycles at ±2000 microstrain.
GAGE RESISTANCE CHARTS
See Circuitry on Page 99
The standard backing is a glass-fiber-reinforced epoxy
matrix. These gages are useful through the temperature
range of –452°F (–269°C) to over +450°F (+230°C).
Since exact self-temperature compensation is unnecessary
in crack propagation studies, all of these gages are supplied
in 09 S-T-C.
Crack Propagation Gages feature small copper pads on the
tabs for ease of soldering.
ADHESIVES AND PROTECTIVE COATINGS
Crack Propagation Gages should be installed with a solvent-
thinned adhesive incorporating a cure temperature of at least
+300°F (+150°C). M-Bond 600 or 610 adhesives are
recommended for use over the widest temperature range.
Handling tape should not be applied over the grid or
soldering tabs during installation. Room-temperature-curing
adhesives are not recommended for use with Crack
Propagation Gages.
Protective coating selection considerations are similar to those
for CD-Series Crack Detection Gages. Refer to appropriate
datasheet for protective coating recommendations.
50
45
40
35
30
25
20
15
10
5
0
50
45
40
35
30
25
20
15
10
5
0
50
45
40
35
30
25
20
15
10
5
0
0 5 10 15 20 0 5 10 15 200510
RESISTANCE - OHMS
(WITH 50Ω SHUNT)
RESISTANCE - OHMS
(WITH 50Ω SHUNT)
RESISTANCE - OHMS
Direction of
Propogation
P PP
CPCO3
(1/2 Size)
CPA01
CPA02
CPB02
STRANDS FRACTURED
CPA01 & CPA02
STRANDS FRACTURED
CPB02 STRANDS FRACTURED
CPC03
micro-measurements@vishay.com
Crack Propagation Patterns
Vishay Micro-Measurements
Document Number: 11521
Revision 09-May-03
www.vishaymg.com
99
Special Purpose Sensors - Crack Propagation Patterns
CPA, CPB, AND CPC PATTERNS
An ohmmeter with milliohm sensitivity is a suitable readout instrument.
Alternately, a strip chart recorder, connected in the manner shown at right,
can be used to obtain a step curve of strands broken versus time.
CPD Pattern
Low voltage instrumentation can be employed to shut off a motor, sound
an alarm, or trigger some other type of alerting function.
Conventional strain gage instrumentation is not readily adaptable for use with Crack Propagation Gages.
NOMINAL DIMENSIONS
GAGE PATTERN RESISTANCE
AND DESIGNATION IN
Actual size shown OHMS a b c Length Width
TK-09-CPB02-005/DP 5
0.25 0.50 0.10 0.56 0.16
6.4 12.7 2.5 14.2 4.1
TK-09-CPA01-005/DP 5
0.50 1.00 0.20 1.08 0.28
12.7 25.4 5.1 27.4 7.1
TK-09-CPA02-005/DP 5
1.00 2.00 0.40 2.08 0.48
25.4 50.8 10.2 52.8 12.2
TK-09-CPC03-003/DP 3
0.70 0.75 1.57 0.80 1.62
17.8 19.1 39.9 20.3 41.1
TK-09-CPD01-NRA/DP 110
0.75 1.00 1.00 1.11 1.11
19.1 25.4 25.4 28.1 28.1
MATRIX
Ten Grid Lines — 0.010 in (0.25 mm) between centerlines.
Twenty Grid Lines — 0.010 in (0.25 mm) between centerlines.
Twenty Grid Lines — 0.020 in (0.51 mm) between centerlines.
Twenty Grid Lines — 0.080 in (2.03 mm) between centerlines
Twenty Grid Lines — 0.050 in (1.27 mm) between centerlines.
a
b
c
c
ba
c
ba
CPA, CPB CPC CPD
50Ω
–
STRIP
CHART
RECORDER
10 mV
RANGE
15 Vdc
POWER
SUPPLY
Crack
Propagation
Gage
+
–
+
100KΩ
1% WW
CIRCUITRY
