EP1725859A2 - Procede et appareil de controle de la sante de materiaux composites - Google Patents

Procede et appareil de controle de la sante de materiaux composites

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Publication number
EP1725859A2
EP1725859A2 EP05723488A EP05723488A EP1725859A2 EP 1725859 A2 EP1725859 A2 EP 1725859A2 EP 05723488 A EP05723488 A EP 05723488A EP 05723488 A EP05723488 A EP 05723488A EP 1725859 A2 EP1725859 A2 EP 1725859A2
Authority
EP
European Patent Office
Prior art keywords
composite
sensor
matrix
resistivity
conductive
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05723488A
Other languages
German (de)
English (en)
Other versions
EP1725859A4 (fr
Inventor
Kenneth S. Watkins, Jr.
Shelby J. Morris
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Polymer Aging Concepts Inc
Original Assignee
Polymer Aging Concepts Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Polymer Aging Concepts Inc filed Critical Polymer Aging Concepts Inc
Publication of EP1725859A2 publication Critical patent/EP1725859A2/fr
Publication of EP1725859A4 publication Critical patent/EP1725859A4/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/44—Resins; Plastics; Rubber; Leather
    • G01N33/442—Resins; Plastics
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light

Definitions

  • the present invention relates to health monitoring of composite materials, and, more particularly, to health monitoring of polymeric composite materials by use of conductive composite age sensors.
  • Polymeric materials degrade with age, especially in severe environmental conditions. Degradation may be (1) chemical, such as chain scission and cross-linking, (2) physical, such as loss of volatile fractions and environmentally induced macroscopic changes such as crystallinity, and physical changes due to a tendency for thermodynamic equilibrium, and (3) mechanical degradation such as cracking and delamination. Due to the increasing use of polymers in consumer products, transportation industries, military applications and commercial and industrial processes, there is a growing need for monitoring of the condition and remaining age of these materials before unsafe conditions or degraded performance occurs.
  • Non-destructive health monitoring of composite materials includes visual inspections, radiography, and acoustic methods. While these methods are effective for some applications, they suffer several serious disadvantages. For example, visual inspections are useful only on components with full visual access, and are not effective for flaws below the surface of the component. Radiography requires access to the components and it is time consuming and requires special training for evaluation of the results. The equipment is very expensive and subject to considerable controls to prevent radiation damage to personnel and equipment. Acoustic methods such as ultrasonic inspections require specialized equipment, considerable operator training, and good access to the component. All of these methods are effective only in detecting actual mechanical flaws such as cracks, and are not effective in predicting deterioration of the composite prior to development of the mechanical flaws.
  • an object of the present invention is to provide a sensor and method for monitoring the condition of composite materials.
  • Another object is to provide a heath monitoring method for composites which provides indication of deterioration of the composite before mechanical degradation such as cracks or delamination occurs.
  • Another object is to provide a heath monitoring method for composites which is capable of detecting chemical and physical aging early in life.
  • Another object is to provide a heath monitoring method for composites which utilizes simple, inexpensive equipment.
  • Another object is to provide a heath monitoring method for composites which does not require extensive training for field use.
  • Another object is to provide a heath monitoring method for composites which does not require visual or physical access to the component being monitored.
  • Still another object is to provide a heath monitoring method for composites which is compatible with wireless monitoring.
  • the method of the present invention determines the condition of a composite component by measurement of the resistivity of a conductive composite sensor formed from a polymeric matrix and conductive particles and comparing the resistivity of the sensor with the resistivity of aged sensors and component specimens to (1) correlate indirectly the resistivity measurement with mechanical properties of the component and (2) determine the remaining life of the component.
  • the resistance of the sensor may be easily measured in the field over the life of the component.
  • the calculated resistivity of sensor is compared to the resistivity of aged specimens to correlated condition of the sensor and, indirectly the component.
  • the aged specimens may be naturally or acceleration aged and resistivity and mechanical properties measured for correlation with sensor data.
  • the polymeric matrix of a composite component ages by chemical and physical aging and by mechanical degradation.
  • Chemical aging affects the polymeric chains, for example by chain scission and crosslinking.
  • Physical aging changes the macroscopic nature of the polymeric structure such as packing density (crystallinity or the tendency to reach the lowest energy level) of the structure, and physical changes such as loss of volatile fractions at elevated temperatures.
  • Mechanical degradation is the occurrence of mechanical defects such as cracks or delamination of the composite structure, for example from cyclic mechanical or thermal stresses. These mechanical defects become more likely after chemical aging effects that result in reduced elongation at break (EAB) of the matrix.
  • a conductive composite sensor incorporating conductive particles will show a decrease in resistivity due to the shrinkage of the matrix as shown in US Provisional Application 60/362,157, (currently PCT/US03/06844) hereby incorporated as reference.
  • the matrix of the sensor utilizes the same or similar polymer as the composite component.
  • the sensor may be bonded to a surface of the composite component, or it may be integrated as a region such as a strip interior to the component.
  • a "standard” sensor capable of indicating integrated time-temperature aged conditions by measurement of resistivity is used as a "standard" age-measurement device.
  • the integrated time-temperature age condition is measured against aged composite component specimens to indirectly correlate mechanical properties and remaining age of the component.
  • the resistance of the sensor may be measured by a simple resistance-measuring device such a high range ohmmeter.
  • the resistance may be measure by direct contact with the sensor, or it may be read by electrodes bonded or embedded in the sensor. Wired or wireless methods may be used to communicate resistance readings to other equipment for storage and processing.
  • the composite component is made into a sensor itself by addition of conductive particles to the component matrix and the resistivity of the component itself is monitored.
  • Condition of the component may be determined by measurement of the resistivity of the component and correlated with aged specimens of the component material. Electrode pairs, either bonded to the component, or manually or automatically located provides resistance measurements for analysis. Initial measurements of the component measured at several locations and through several axes of the component provide a baseline measurement for comparison with later measurements.
  • conductive particles are selected to be chemically inert for the matrix under the expected environmental conditions of the component.
  • Carbon particles such as those in the form of carbon black provide a low-cost conductive filler for many applications.
  • other carbon forms such as carbon nanotubes provide advantages such as lower volume requirements for the desired initial resistivity, and strength improvements in a composite.
  • metallic particles such as silver, aluminum, nickel and copper may be used.
  • Metallic oxides and semi-conductor materials may also be used.
  • the conductive filler is adjusted to obtain the desired initial resistivity without unacceptable degradation of mechanical properties.
  • the resistivity range between the intrinsic resistivity of the matrix and conductive particles may be enormous, in some cases more than 16 decades.
  • the greatest sensitivity for detecting age-related shrinkage of the polymeric matrix is in the steepest portion of the resistivity- volume fraction curve of the conductive composite. Typically this occurs over several decades approximately in the midpoint of the log-resistivity vs. volume fraction curve of the sensor composite curve.
  • Sensitivity is typically low within one or two decades of either the intrinsic resistivity of the matrix and the conductive particles.
  • the initial resistivity is adjusted by addition of conductive particles to be in a range between two decades below the intrinsic resistivity of the sensor matrix and two decades greater than the intrinsic resistivity of the conductive particles.
  • the initial resistivity is adjusted to be in a range between three decades below the intrinsic resistivity of the sensor matrix and three decades greater than the intrinsic resistivity of the conductive particles.
  • the initial resistivity is adjusted to be in a range between four decades below the intrinsic resistivity of the sensor matrix and four decades greater than the intrinsic resistivity of the conductive particles.
  • the initial resistivity is adjusted to be in a range between five decades below the intrinsic resistivity of the sensor matrix and five decades greater than the intrinsic resistivity of the conductive particles.
  • the initial resistivity is selected to be within five decades of the steepest portion (most sensitive) of the log-resistivity vs. volume fraction curve of the selected sensor composite. In the more preferred embodiments, the initial resistivity is selected to be within four decades of the steepest portion (most sensitive) of the log- resistivity vs. volume fraction curve of the selected sensor composite. In the still more preferred embodiments, the initial resistivity is selected to be within three decades of the steepest portion (most sensitive) of the log-resistivity vs. volume fraction curve of the selected sensor composite. In the still more preferred embodiments, the initial resistivity is selected to be within two decades of the steepest portion (most sensitive) of the log- resistivity vs. volume fraction curve of the selected sensor composite. In the most preferred embodiments, the initial resistivity is selected to be within one decade of the steepest portion (most sensitive) of the log-resistivity vs. volume fraction curve of the selected sensor composite.
  • FIG. 1 is a cross section drawing of a conductive composite condition sensor disposed on the surface of a composite material
  • FIG. 1A is a detail cross section drawing of the condition sensor of FIG. 1 bonded to the matrix portion of a composite component
  • FIG. 2 is a log-resistivity vs. volume percent conductive filler curve for a typical conductive composite condition sensor
  • FIG. 3 is a Ln resistivity vs. Ln elongation-at-break curve for ethylene propylene rubber taken at two temperatures, showing correlation of resistivity of a sensor and mechanical properties ;
  • FIG. 4 is a cross section of a condition sensor bonded to a composite component utilizing a bonding/interface layer between the condition sensor and the matrix of the composite component;
  • FIG. 5 is a cross section of a condition sensor bonded to a composite material which utilizes strength fibers dispersed in the composite matrix;
  • FIG. 5A is a detail cross section of the composite material of FIG. 5;
  • FIG. 6 is a perspective cut-away drawing showing contact of the electrodes of a resistance measuring device to measure the resistance of a condition sensor disposed on the surface of a composite material;
  • FIG. 7 is a perspective cut-away drawing of a multi-conductor tape with electrodes bonded to the condition sensor of a composite material, the tape used to communicate resistance reading of the condition sensor to a resistance measuring instrument;
  • FIG. 8 is a perspective drawing of a communications method utilizing multiple radio frequency identification devices(RFIDs) with electrodes attached to a tape bonded to a sensor strip, and a reader for interrogating and communicating resistivity data from the RFIDs;
  • FIG. 9 is a schematic and block diagram of a RFTD and reader used to communicate a threshold pass/fail resistivity reading to a RFID reader;
  • FIG. 10 is a perspective cutaway drawing of an embodiment of the present invention where conductive particles are added to a composite component to create a condition sensor of the component itself by using electrodes to measure the resistance through one or more axis or planes of the component;
  • FIG. 10A is a detail cross section of the composite component of FIG. 10 showing dispersion of the conductive particles in the matrix of the component;
  • FIG. 11 is a graph showing possible resistance readings for several electrode pairs of the conductive composite component of FIG. 10, showing decrease in resistance of the electrode pairs over time due to chemical and physical aging and increases in resistance due to mechanical flaws;
  • FIG. 12 is a resistance-time graph of a short time period of a condition sensor over a short time interval showing the response to short-time stress/strain effects in the component.
  • condition sensor for composite materials and a method for determining the condition of the composite material by measurement of the resistance of the condition sensor.
  • FIG. 1 is a cross section drawing of a preferred embodiment of a conductive composite condition sensor 101 for a composite material 103.
  • Composite material 103 is made of a reinforcement fiber such as reinforcement fabric 105 dispersed in a thermoplastic or thermoset polymer matrix 107.
  • Reinforcement fabrics include fibers made of metallic, carbon, glass, boron, ceramic and polymeric fibers. The reinforcement fibers may be in woven or non-woven mats, or they may be dispersed in the matrix.
  • Matrix material 107 includes thermoplastic materials such as polyamides, polyolefins and fluoropolymers, and thermosets such as epoxies and polyesters.
  • condition sensor 101 consists of conductive particles 109 such as carbon black particles dispersed in a polymeric sensor matrix 111.
  • conductive particles 109 such as carbon black particles dispersed in a polymeric sensor matrix 111.
  • the addition of conductive particles 109 to sensor matrix 111 results in a conductive composite having an electrical resistivity vs. conductive particle volume fraction response similar to that shown in the curve of FIG. 2.
  • Condition sensor 101 provides an indirect measurement of composite material 103 condition including degradation due to chemical aging, physical aging, and mechanical degradation.
  • Chemical aging results in volumetric shrinkage and densification of the polymer matrix due chemical aging mechanisms such as chain cross-linking and chain scission.
  • Physical aging includes loss of matrix volatile components, resulting in an increase in volume fraction of the conductive particles 109. Physical aging also results in a reduction of free-volume of polymeric material below the glass transition temperature with time.
  • Mechanical degradation includes cracking such as micro cracks, and delamination. Mechanical degradation may be caused by mechanical stresses such as thermally-induced stress and cyclic stresses such as fatigue and vibration.
  • a sufficient quantity of conductive particles 109 are added to matrix 111 to adjust the electrical resistivity of conduction sensor 101 in a sensitive range 209 of the electrical percolation curve shown in FIG. 2.
  • FIG. 2 is an electrical percolation curve 201 showing the log of the electrical volume resistivity R as a function of volume fraction V FC of the conductive particles:
  • V c is the volume of the conductive particles
  • V M is the volume of the matrix
  • N T is the total volume of the conductive particles and the matrix.
  • R 10 10 to 10 18 ohm-cm.
  • N F c Further increases in N F c result in a rapid decrease of resistivity as the volume fraction of the conductive particles is increased by a small amount.
  • This region of high sensitivity to V F c shown in region 209 of curve 201, includes the steepest (inflection) portion 210 of curve 201 and includes portions of the curve above and below deflection point 210 where the steepness of curve 201 is less than the inflection point, but greater than the threshold values.
  • Further increases in V F c produce the upper percolation threshold (region of point 212) where there exist substantial conductive paths as a result of the conductive filler so that further increases in V FC produce only small changes in the resistivity of the composite.
  • the upper 212 and lower 207 percolation thresholds are not distinct points observable on the resistivity vs. V F c curve.
  • the lower percolation threshold for V F c (point 207) is the value corresponding to a resistivity (point 204 of FIG. 2) one order of magnitude less than the resistivity of the matrix alone.
  • the upper percolation value for V F c (point 212) is the value corresponding to a resistivity (value 214 of FIG. 2) one order of magnitude greater than the inherent resistivity of the conductive particles.
  • Typical conductive fillers are carbon black, carbon nanotubes and metallic particles such as silver, nickel and aluminum, although other conductive and semi-conductive particles such as metallic oxides can be used.
  • the conductive particles are highly structured particles such as highly structured carbon black particles or nanotubes to reduce the volume fraction of conductive particles required. In other embodiments, less-structured particles are used to increase the steepness of curve portion 209.
  • sensor matrix 111 is a high-resistivity (insulative) thermoplastic or thermoset polymer. In the most preferred embodiments, sensor matrix 111 is the same matrix as used in composite matrix 107.
  • the type of conductive particles and volume fraction of the conductive particles V F c are selected to provide the desired level of sensitivity of condition sensor 101 and provide a range of resistivity that can be measured by the selected instrumentation.
  • the sensitivity of the sensor is determined by the steepness or slope of curve 201, the most sensitive portion being the portion of the curve 209 including, and adjacent to, the point of steepest slope (210).
  • the value of resistivity is chosen so that the desired dimensions of the sensor and resistivity provide a range of resistance that can be read by the selected resistance-measuring instrument.
  • the resistivity R of lower percolation value 204 is not in a high sensitive measurement portion of the curve since the slope of curve is low at point 207. Also, since resistivity at point 204 is typically one order of magnitude less than the resistivity of the matrix, an insulator, sensors of a practical size would result in sensor resistances far higher than field instrumentation would allow. On the other hand, the upper percolation value 214 would also provide poor sensitivity since the slope of curve 201 is low in this region.
  • the filler type and content is adjusted so that V F c is approximately at the steepest point 210 of curve 201 at the beginning of aging. In this manner, sensitivity of the decrease in volume fraction N F c due to aging and measured by the resistance of the sensor is greatest at the beginning of life.
  • a higher value of V F c may be chosen for practical reasons, for example to make electrical measurement of the sensor resistance easier at the expense of some sensitivity of the measurement.
  • a practical target sensor utilizes a filler type and quantity for the starting resistivity R to be from one-tenth to nine tenths (on a log scale) of the total range of resistivity from the intrinsic resistivity of the filler to the intrinsic resistivity of the matrix.
  • the senor utilizes a filler type and quantity for the starting resistivity R to be from one-fourth to three fourths (on a log scale) of the total range of resistivity from the intrinsic resistivity of the filler to the intrinsic resistivity of the matrix. In the still more preferred embodiments, the sensor utilizes a filler type and quantity for the starting resistivity R to be from one-third to two thirds (on a log scale) of the total range of resistivity from the intrinsic resistivity of the filler to the intrinsic resistivity of the matrix.
  • the senor utilizes a filler type and quantity for the starting resistivity R to be from two fifths to three fifths (on a log scale) of the total range of resistivity from the intrinsic resistivity of the filler to the intrinsic resistivity of the matrix.
  • V F c increases as the polymeric fraction densities due to crosslinking, chain scission, and loss of volatile fractions. Due to the steepness of the percolation curve, a small increase of V F c due to aging is sensed by a decrease in resistivity R.
  • Data such as resistivity and mechanical property measurements from accelerated aging, such as that disclosed in PCT application 60/362,157 (currently PCT/US03/06844, hereby incorporated by reference) provides data for empirical correlation of material properties by measurement of sensor resistivity.
  • FIG. 3 is a chart showing correlation of elongation-at-break (EAB) as a function of resistivity for ethylene propylene rubber (EPR) composite samples.
  • the conductive filler is carbon black and the loading is 26.5% by weight.
  • the resistivity and EAB data was collected from EPR composite samples oven aged at 125C and 150C and data plotted on log scales. Mechanical properties such as EAB of the base polymer (without fillers) may be measured and co ⁇ elated with the composite sample.
  • FIG. 4 is an alternative embodiment of the invention showing bonding or interface layer 401 disposed between condition sensor 101 of FIG. 1 and the upper layer of matrix 107.
  • Bonding layer 401 may be the same matrix material as matrix 107, or it may be an adhesive layer such as a pressure-sensitive bonding agent, hot-melt or other adhesive material. In applications where matrix 107 is a poor insulator, layer 401 may be an insulative layer having a resistivity sufficiently high to prevent detrimental response of sensor 101.
  • Fig. 5 is a cross section of an embodiment of the invention showing condition sensor 101 disposed on composite material 503.
  • Composite material 503 comprises fibers 505 dispersed in resin or matrix 507 as best shown in detail FIG 5A.
  • sensor composite matrix 111 (FIG. 1A) is the same polymeric composition as matrix 507.
  • condition sensor 101 In an alternative positioning of condition sensor 101, the conductive particles of the condition sensor may be mixed and deposited below the surface of composite material 503 as shown in phantom lines 509.
  • the matrix of sensor 101 is the same as the matrix of the composite material.
  • FIG. 6 is a perspective drawing of a resistance measuring instrument 621 being used to measure the resistance of a portion of a condition sensor strip 601 disposed on a composite material 603. Electrodes 621A, 621B allow measurement of resistance of the portion of condition sensor 601 between electrodes 621 A, 621B. Instrument 621, such as a high range ohmmeter measures resistance r between electrodes 621A, 621B.
  • the resultant value of R may be used to determine the mechanical properties of the polymer composite as a function of R, for example from data such as that shown in FIG. 3. Lower R threshold limits, based on minimum acceptable mechanical properties may be established for the desired material.
  • FIG. 7 is a perspective drawing of an alternative embodiment of a communications method utilizing a multi-conductor ribbon tape 731 bonded to condition sensor strip 701 of composite material portion 703.
  • Tape 731 may be a polymeric tape such as a polyethyleneterephthalate (PET) tape having ribbon conductors 733 embedded in conductor portion 731A.
  • Electrodes 735, bonded to electrode support portion 73 IB make mechanical and electrical contact with upper surface 701 A of sensor strip 701.
  • Contact surface 731C of tape 731 may be bonded to surface 701A, or alternatively, embedded in sensor surface 701 A before curing of sensor strip 701.
  • Conductors 733 may be electrically connected to a connector (not shown) on an end of tape 731, or alternatively connected to other wired or wireless means of communicating resistance measured between electrodes 735.
  • the spacing of electrodes 735, and the width and thickness of sensor strip 701 determine conversion of measured resistance between electrodes and resistivity of the sensor.
  • FIG. 8 is a perspective drawing of a wireless communications strip 800 communicating resistance measurements of a conductive composite condition sensor 801 to a reader 841.
  • Communications strip 800 comprises a plurality of passive radio frequency identification devices (RFIDs) 834 embedded in a polymeric tape such as a polyester tape 803.
  • RFIDs passive radio frequency identification devices
  • Electrodes 835, disposed on tape portion 803A and connected to RFID 834 makes electrical contact with condition sensor 801.
  • Antenna 834A allows communication of sensor portion 801 A resistance between sets of electrodes 835 to RFID reader 841.
  • the RFIDs are covered by an auxiliary tape portion 803B.
  • RFID 834 is embedded in the matrix of the composite.
  • FIG. 9 is a block and schematic diagram of a passive RFID such as RFID 834 of FIG. 8 communicating with a RFID inte ⁇ ogator or reader 841.
  • RFID 834 is passive (powered by radio frequency energy coupled from reader 841) having an degradation sensor 903 input to provide a "pass/fail" age threshold to reader 841.
  • RFID chip 905 is a passive RFID chip with an "on- off ' sensor input 904 such as a MCRF202 RFID manufactured by Microchip, Inc.
  • RFID chip 905 receives input from threshold comparators 907A, 907B through NOR gate 909 at sensor input 904 and provides the programmed digital identification code upon normal aging condition of sensor 903.
  • RFID chip 905 Upon a failure mode, RFID chip 905 provides an inverted identification code to reader 841.
  • a failure mode signal is generated by NOR gate 909 if age sensor 903 is aged sufficiently for the resistance of sensor 903 to be less than a threshold value determined by reference resistors 913, 915, 917, 919.
  • a failure mode (inverted code) is also generated if sensor 903 opens.
  • Antenna 834A provides power to the device and communication with reader 841.
  • the unique code programmed into the non-volitile memory of RFID chip 905 is associated with application data such as assembly, component and component location in which RFID 834 is installed.
  • application data such as assembly, component and component location in which RFID 834 is installed.
  • related assembly, component manufacturing, and location data may be related by a digital database accessible by reader 841.
  • Reader 841 utilizes an oscillator/demodulator 921 controlled by a microprocessor 923 to produce the radio frequency energy 925 communicating with, and providing power for, RFID 834.
  • Modulation produced by RFID chip 905 (corresponding with programmed identification code and the state of sensor 903) is demodulated by oscillator/demodulator 921 and microprocessor 923 provides RFID identification and pass/fail criteria to respective indicators 927, 929.
  • Battery 931 provides power for reader 841.
  • Antenna 911 provides communication with antenna 834A of RFID 834.
  • a separate computer may provide the database association and indication functions for reader 841.
  • RFID 905 may be an active RFID with internal volatile memory and a clock.
  • Battery 941, shown in phantom lines provides power for an active RFID.
  • Sensor 903 output at 943 may be connected directly to the sensor input 904.
  • Active RFID 905 would provide the means to periodically store voltage readings corresponding to sensor 903 resistance values. The resistance values would be downloaded upon interrogation by reader 841 and correlated with resistivity values to determine the condition and remaining life of sensor 903.
  • FIG. 10 is a cutaway perspective drawing showing an alternative embodiment of the present invention showing condition monitoring of a conductive composite component 1001.
  • Component 1001 may be a structural component such as a beam, column, spar, truss or it may be a portion of a body panel, wall panel or other structural components. In still other applications, component 1001 may be a tank, vessel, or piping portion or it may be a decorative component.
  • component 1001 is a conductive composite component made of a conductive particle or fiber 1003 dispersed in polymeric matrix 1005, as best shown in FIG. 10A.
  • Polymeric matrix 1005 may be a thermoplastic or thermosetting resin or it may be a commodity or engineered plastic material or blend.
  • Conductive fibers 1003 may be any conductive metal, metal oxide, or semi-metallic particle or fiber.
  • conductive fiber 1003 is a carbon black particle or fiber and in the most preferred embodiments, fiber 1003 is a carbon nanotube. Highly structured carbon blacks or nanotubes allow the composite to be made conductive with a low volume fraction of the conductive fiber.
  • the volume fraction of the conductive fiber is adjusted so that the volume resistivity of the bulk portion of conductive composite component 1001 is in the range 209 of FIG. 2.
  • the volume fraction of the conductive fiber is adjusted so that the volume resistivity of the bulk portion of conductive composite component 1001 is between 10E2 and 10E12 ohm-cm.
  • the volume fraction of the conductive fiber is adjusted so that the volume resistivity of the bulk portion of conductive composite component 1001 is between 10E4 to 10E10 ohm-cm. Selection of resistivities in these ranges allows reasonable sensitivity to aging mechanisms and reasonable ease of measurement with field instrumentation. Selection of the desired bulk material resistivity may also be made based on considerations such as static dissipative properties, lightening susceptibility, electrical grounding specifications of the component.
  • Placement of electrode pairs in locations such as those of electrode pairs 1007A, 1007B, 1009A, 1009B, and 1011 A, 101 IB allows measurement of electrical resistance between the known locations of the electrode pairs.
  • electrode pair 1007A, 1007B measures the resistance of component 1001 in the thickness direction as shown in the figure.
  • a reference (base case) database is established by making at least one, and preferably a number of resistance measurements at established electrode locations.
  • the electrodes may be portable and placed manually, or they may be moved to predetermined locations by a robotic mechanism (not shown).
  • electrode pairs may be bonded or otherwise attached to component 1001 by an adhesive or mechanical fasteners.
  • the electrodes may be small discrete electrodes as shown, strip or electrodes covering entire surface portions of the component.
  • a surface electrode may be permanently bonded to the back surface 1031 of component 1001, and one or more small electrodes may be placed at pre-determined locations on other surfaces of component 1001 to measure degradation.
  • Conductive composite component 1001 may comprise reinforcement fibers in the form of strips, mats or woven sheets 1033.
  • FIG. 11 is a resistance-time graph showing possible resistance curves 1101, 1103, 1105 of several electrode pairs such as the electrode pairs of FIG. 10.
  • the initial resistance between the pairs of electrodes is represented by the initial resistance at time 0 for each curve.
  • the resistivity of the composite material may be calculated with numerical means or approximated by measurement of a standard specimen in order to co ⁇ elate mechanical properties or aging effects.
  • the resistance curves measured across baseline locations will decrease with time due to reduction of volume fraction of the conductive particles as discussed previously. Abnormal decreases would be investigated. Significant reduction at some locations with respect to others may indicate abnormally high aging rates, for example due to localized heating. Resistance readings over time should be taken at the same temperature to reduce the effects of resistance changes due to thermal expansion and contraction of the components.
  • Increases in resistivity such as the increases 1105A, 1103A in curves 1103 and 1105 at time Tl may be indications of mechanical flaws such as cracks. Cracks may appear suddenly, or over time, depending on the composite, stresses, and environment. The effect on resistance readings will depend on the size, location and orientation of the crack. For example, large cracks in a plane perpendicular and directly between electrodes will result in a large increase in resistivity. Other electrode pairs where the crack is small or more distant to the electrodes, or the plane is not perpendicular to the field lines of the electrode pair will result in smaller changes. Should the mechanical flaw remain stable the resistance curves will continue to decrease as shown in 1105B, 1103B. Increases in crack size with time will result in further increases in resistance of the affected electrode pairs. Investigation of the electrode location and magnitude of change will provide a means for further investigation, such as by radiography or ultrasonic examination techniques known in the art.
  • FIG. 12 is a resistance-time plot for curve 1101 A taken over a very short time interval 1201 of FIG. 11.
  • the short time scale variations of resistance of electrode pairs such as the electrode pairs of FIG. 10 provide a resistance response to stress-strain conditions of composite component 1001.
  • a cyclic stress on component 1001 produces a co ⁇ esponding cyclic strain and results in a cyclic resistance response of an electrode pair positioned on component 1001.
  • Comparison of the resistance values of the electrode pairs using known stresses on component 1001 provides a means to co ⁇ elate sensor output with applied stresses on the component.
  • Analytical and modeling approaches may also be used to co ⁇ elate sensor output with stress-strain conditions of the component.
  • Heath Monitoring Method and Sensor Apparatus for Composite Materials provides an in-situ, non-destructive method for indirect measurement of mechanical properties and indication of remaining age of composite materials.
  • the method and materials of the presents invention provides the following additional advantages: • The method may be used on virtually any polymeric material when combined with a conductive filler material; • Simple, low-cost instrumentation may be used; • The method is compatible with other NDT methods; and • The method is simple, requires minimal operator training, and is low in cost.
  • the age sensor of this invention may be applied to other materials and products besides composite materials.
  • the resistivity of this "universal" sensor may be co ⁇ elated to the condition of the material or product by natural or acceleration aging of the material or product and comparing with the resistivity of the sensor.
  • Numerical techniques such as A ⁇ henius methodology or empirical comparisons may be made to co ⁇ elate sensor resistivity with mechanical properties and remaining age of the material or product monitored.

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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Medicinal Chemistry (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)

Abstract

L'invention concerne un procédé in-situ de contrôle de la santé d'un composé composite (103) utilisant un détecteur de condition (101) constitué de particules électro-conductrices (109) réparties dans une matrice polymérique (111). Ce détecteur est relié à la surface de matrice du matériau composite ou formé sur celle-ci. Un retrait lié à l'âge de la matrice du détecteur aboutit à une baisse de la résistance du détecteur de condition. La mise en corrélation de la mesure de la résistance du détecteur avec des données issues de spécimens âgés permet une détermination indirecte des propriétés mécaniques et de l'âge restant du composé composite.
EP05723488A 2004-02-24 2005-02-23 Procede et appareil de controle de la sante de materiaux composites Withdrawn EP1725859A4 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US54732704P 2004-02-24 2004-02-24
PCT/US2005/005604 WO2005081930A2 (fr) 2004-02-24 2005-02-23 Procede et appareil de controle de la sante de materiaux composites

Publications (2)

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EP1725859A2 true EP1725859A2 (fr) 2006-11-29
EP1725859A4 EP1725859A4 (fr) 2007-10-17

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EP05723488A Withdrawn EP1725859A4 (fr) 2004-02-24 2005-02-23 Procede et appareil de controle de la sante de materiaux composites

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EP (1) EP1725859A4 (fr)
WO (1) WO2005081930A2 (fr)

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US7659728B1 (en) 2006-08-23 2010-02-09 Watkins Jr Kenneth S Method and apparatus for measuring degradation of insulation of electrical power system devices
US7612325B1 (en) 2007-08-22 2009-11-03 Watkins Jr Kenneth S Electrical sensor for monitoring degradation of products from environmental stressors
DE102011115812B4 (de) * 2011-10-13 2016-08-11 Bayern-Chemie Gesellschaft Für Flugchemische Antriebe Mbh Verfahren zur Lebensdauerüberwachung von Raketen und Begleitprobe zur Durchführung desselben
FR3038710B1 (fr) * 2015-07-10 2021-05-28 Cpc Tech Capteur d'une caracteristique physique, comportant de preference une structure multicouches
WO2017100258A1 (fr) 2015-12-07 2017-06-15 Dana Heavy Vehicle Systems Group, Llc Architectures de chaîne cinématique distribuée pour véhicules utilitaires avec groupe motopropulseur électrique hybride et essieux de désaccouplement à double gamme
CN108883699B (zh) 2016-03-28 2022-02-11 德纳重型车辆系统集团有限责任公司 具有多个比率的单电动机驱动车轴
IL247408B (en) 2016-08-21 2018-03-29 Elbit Systems Ltd A system and method for identifying weaknesses in the adhesion between structural elements

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US5111025A (en) * 1990-02-09 1992-05-05 Raychem Corporation Seat heater
US5554679A (en) * 1994-05-13 1996-09-10 Cheng; Tai C. PTC conductive polymer compositions containing high molecular weight polymer materials
US6063486A (en) * 1996-12-10 2000-05-16 Tdk Corporation Moisture sensor comprising conductive particles and a hygroscopic polymer of polyvinyl alcohol
US6491849B1 (en) * 2001-01-22 2002-12-10 General Cable Technologies Corp. High performance power cable shield

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US5111025A (en) * 1990-02-09 1992-05-05 Raychem Corporation Seat heater
US5554679A (en) * 1994-05-13 1996-09-10 Cheng; Tai C. PTC conductive polymer compositions containing high molecular weight polymer materials
US6063486A (en) * 1996-12-10 2000-05-16 Tdk Corporation Moisture sensor comprising conductive particles and a hygroscopic polymer of polyvinyl alcohol
US6491849B1 (en) * 2001-01-22 2002-12-10 General Cable Technologies Corp. High performance power cable shield

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Title
See also references of WO2005081930A2 *

Also Published As

Publication number Publication date
WO2005081930A2 (fr) 2005-09-09
WO2005081930A3 (fr) 2006-03-09
EP1725859A4 (fr) 2007-10-17

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