Crack Propagation Patterns Vishay Micro-Measurements 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 opencircuiting 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 standard backing is a glass-fiber-reinforced epoxy matrix. These gages are useful through the temperature range of -452F (-269C) to over +450F (+230C). 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 solventthinned adhesive incorporating a cure temperature of at least +300F (+150C). 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. 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 Protective coating selection considerations are similar to those for CD-Series Crack Detection Gages. Refer to appropriate datasheet for protective coating recommendations. 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 107 cycles at 2000 microstrain. GAGE RESISTANCE CHARTS See Circuitry on Page 99 50 Direction of Propogation P 45 40 P P 35 30 25 CPA01 CPA02 20 45 40 RESISTANCE - OHMS (WITH 50 SHUNT) RESISTANCE - OHMS (WITH 50 SHUNT) 40 50 15 35 RESISTANCE - OHMS 45 50 CPB02 30 25 20 15 35 25 20 15 10 10 10 5 5 5 0 0 0 0 5 10 15 STRANDS FRACTURED CPA01 & CPA02 www.vishaymg.com 98 20 CPCO3 (1/2 Size) 30 0 5 10 STRANDS FRACTURED CPB02 micro-measurements@vishay.com 0 5 10 15 20 STRANDS FRACTURED CPC03 Document Number: 11521 Revision 09-May-03 Crack Propagation Patterns Vishay Micro-Measurements Special Purpose Sensors - Crack Propagation Patterns c c a c b a b a b CPA, CPB GAGE PATTERN AND DESIGNATION Actual size shown TK-09-CPB02-005/DP CPC NOMINAL RESISTANCE IN OHMS 5 CPD DIMENSIONS MATRIX a b c Length Width 0.25 6.4 0.50 12.7 0.10 2.5 0.56 14.2 0.16 4.1 Ten Grid Lines -- 0.010 in (0.25 mm) between centerlines. TK-09-CPA01-005/DP 5 0.50 12.7 1.00 25.4 0.20 5.1 1.08 27.4 0.28 7.1 Twenty Grid Lines -- 0.010 in (0.25 mm) between centerlines. TK-09-CPA02-005/DP 5 1.00 25.4 2.00 50.8 0.40 10.2 2.08 52.8 0.48 12.2 Twenty Grid Lines -- 0.020 in (0.51 mm) between centerlines. TK-09-CPC03-003/DP 3 0.70 17.8 0.75 19.1 1.57 39.9 0.80 20.3 1.62 41.1 Twenty Grid Lines -- 0.080 in (2.03 mm) between centerlines TK-09-CPD01-NRA/DP 110 0.75 19.1 1.00 25.4 1.00 25.4 1.11 28.1 1.11 28.1 Twenty Grid Lines -- 0.050 in (1.27 mm) between centerlines. CIRCUITRY 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. + 15 Vdc POWER SUPPLY - 100K 1% WW Crack Propagation Gage STRIP CHART RECORDER 10 mV - RANGE + 50 Conventional strain gage instrumentation is not readily adaptable for use with Crack Propagation Gages. Document Number: 11521 Revision 09-May-03 micro-measurements@vishay.com www.vishaymg.com 99