CA2623305C - Electrochemical fatigue sensor system and methods - Google Patents
Electrochemical fatigue sensor system and methods Download PDFInfo
- Publication number
- CA2623305C CA2623305C CA2623305A CA2623305A CA2623305C CA 2623305 C CA2623305 C CA 2623305C CA 2623305 A CA2623305 A CA 2623305A CA 2623305 A CA2623305 A CA 2623305A CA 2623305 C CA2623305 C CA 2623305C
- Authority
- CA
- Canada
- Prior art keywords
- substrate
- fatigue
- sensor assembly
- crack
- sensor
- 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.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
-
- 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
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
- G01F1/64—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by measuring electrical currents passing through the fluid flow; measuring electrical potential generated by the fluid flow, e.g. by electrochemical, contact or friction effects
-
- 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
- G01N17/02—Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement
-
- 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
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0062—Crack or flaws
- G01N2203/0066—Propagation of crack
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0073—Fatigue
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/0617—Electrical or magnetic indicating, recording or sensing means
- G01N2203/0629—Electrical or magnetic indicating, recording or sensing means using thin films, paintings
Abstract
A method and an electrochemical sensor device for determining a fatigue status of a growing crack in a substrate. The device includes an electrode formed from a stainless steel mesh and having a bottom surface that is coated with an adhesive layer and has a release paper attached to the adhesive layer. The adhesive layer is exposed through separation of the release paper from the adhesive layer. Contacting the adhesive layer to the substrate secures the device to the substrate and forms a cavity that contains an electrolyte and is partially bound by the substrate. The adhesive seals the bottom surface of the device to the substrate in order to prevent leakage of electrolyte from the cavity. When the substrate is subjected to cyclic loading, the fatigue status of the growing crack in the substrate is determined in accordance with a measured current between the reference electrode and the substrate.
Description
-- ~
Electrochemical Fatigue Sensor System and Methods Field of the Invention The present invention relates generally to electrochemical fatigue sensor devices, and systems and methods for using such devices.
Backjzxound of the Invention Referring now to Figure 1, there is shown a schematic diagram of an electrochemical fatigue sensor (EFS) device 10, in accordance with the prior art. EFS
device 10 can be used to implement a non destructive fatigue crack inspection method for determining if inspected fatigue cracks are actively growing. For example, EFS
device 10 may be applied to a fatigue critical location on a laboratory specimen or structure to be inspected. EFS device 10 consists of an electrolyte 12, sensor 14, and a potentiostat 20 for applying a constant polarizing voltage between the structure (substrate 16) and the sensor 14.
EFS device 10 works on electrochemical principles. The structure is anodically polarized to create a protective, passive film on the surface to be tested. A
polarizing voltage between the structure and the electrode produces a DC base current in the cell. If the structure being interrogated by the EFS undergoes a cyclic stress, then the current flowing in the cell fluctuates in a complex relation to the variation of the mechanical stress state. Thus, an AC current is superimposed on the DC base current.
Depending on the material of the structure and the loading conditions as well as the state of the fatigue damage in the structure, the transient current of the cell provides information on the status of the fatigue damage.
The electrochemical conditions imposed during EFS interrogation of a structure are designed to induce a stable passive oxide film on the surface of the material.
During cyclic loading, the fatigue process causes micro plasticity and strain localization on a very fine scale. The interaction of the cyclic slip and the passivating process causes temporary and repeated alterations of the passive films. These alterations, including dissolution and repassivating processes, give rise to transient currents.
The EFS transient currents are complex, involving cyclic changes in the electrical double layer at the interface of the metal and the EFS electrolyte, generally possessing the same frequency as that of the mechanical stress, but having a complex phase relationship depending on the specific metal interrogated. In addition, the disruption of the oxide films on the metallic surface by the cyclic slip causes an additional component of the transient current which has double the frequency of the elastic current because plasticity effects occur during both the tensile and compressive parts of the cycle. As fatigue dainage develops with accumulated cycles and cracks form, the cracks induce localized plasticity at different parts of the fatigue cycle from those in which the background micro plasticity occurs and in which cracks have not yet formed. The crack-induced plasticity thus introduces higher harmonic components into the transient EFS current. Analysis and calibration of these various current components allow the fatigue crack growth to be determined.
Existing EFS devices, such as that shown in Figure 1, suffer from numerous drawbacks. For example, known EFS devices are cumbersome to attach to a substrate and fill with electrolyte. Known EFS devices also suffer from poor sensitivity, and the signal processing techniques for analyzing EFS signals generated by such devices also appear to be inadequate. The present invention addresses such shortcomings in the prior art.
Electrochemical Fatigue Sensor System and Methods Field of the Invention The present invention relates generally to electrochemical fatigue sensor devices, and systems and methods for using such devices.
Backjzxound of the Invention Referring now to Figure 1, there is shown a schematic diagram of an electrochemical fatigue sensor (EFS) device 10, in accordance with the prior art. EFS
device 10 can be used to implement a non destructive fatigue crack inspection method for determining if inspected fatigue cracks are actively growing. For example, EFS
device 10 may be applied to a fatigue critical location on a laboratory specimen or structure to be inspected. EFS device 10 consists of an electrolyte 12, sensor 14, and a potentiostat 20 for applying a constant polarizing voltage between the structure (substrate 16) and the sensor 14.
EFS device 10 works on electrochemical principles. The structure is anodically polarized to create a protective, passive film on the surface to be tested. A
polarizing voltage between the structure and the electrode produces a DC base current in the cell. If the structure being interrogated by the EFS undergoes a cyclic stress, then the current flowing in the cell fluctuates in a complex relation to the variation of the mechanical stress state. Thus, an AC current is superimposed on the DC base current.
Depending on the material of the structure and the loading conditions as well as the state of the fatigue damage in the structure, the transient current of the cell provides information on the status of the fatigue damage.
The electrochemical conditions imposed during EFS interrogation of a structure are designed to induce a stable passive oxide film on the surface of the material.
During cyclic loading, the fatigue process causes micro plasticity and strain localization on a very fine scale. The interaction of the cyclic slip and the passivating process causes temporary and repeated alterations of the passive films. These alterations, including dissolution and repassivating processes, give rise to transient currents.
The EFS transient currents are complex, involving cyclic changes in the electrical double layer at the interface of the metal and the EFS electrolyte, generally possessing the same frequency as that of the mechanical stress, but having a complex phase relationship depending on the specific metal interrogated. In addition, the disruption of the oxide films on the metallic surface by the cyclic slip causes an additional component of the transient current which has double the frequency of the elastic current because plasticity effects occur during both the tensile and compressive parts of the cycle. As fatigue dainage develops with accumulated cycles and cracks form, the cracks induce localized plasticity at different parts of the fatigue cycle from those in which the background micro plasticity occurs and in which cracks have not yet formed. The crack-induced plasticity thus introduces higher harmonic components into the transient EFS current. Analysis and calibration of these various current components allow the fatigue crack growth to be determined.
Existing EFS devices, such as that shown in Figure 1, suffer from numerous drawbacks. For example, known EFS devices are cumbersome to attach to a substrate and fill with electrolyte. Known EFS devices also suffer from poor sensitivity, and the signal processing techniques for analyzing EFS signals generated by such devices also appear to be inadequate. The present invention addresses such shortcomings in the prior art.
Summary of the Invention The present invention is directed to a method for determining a fatigue status of a growing crack in a substrate. An electrochemical sensor device is provided and includes an electrode formed from a stainless steel mesh. The electrochemical device has a bottom surface that contacts the substrate. The bottom surface is coated with an adhesive layer, and a release paper is attached to the adhesive layer. The release paper is separated from the adllesive layer, thereby exposing the adhesive layer. The electrochemical sensor device is secured to the substrate by bringing the adhesive layer in contact with the substrate and thereby forming an electrolyte cavity bounded in part by the substrate. The adhesive seals the bottom surface of the device to the substrate in order to prevent leakage of electrolyte from the cavity. The cavity is filled with the electrolyte.
When the substrate is subjected to cyclic loading, the fatigue status of the growing crack in the substrate is determined in accordance with a measured current between the reference electrode and the substrate.
In accordance with a further aspect, the present invention is directed to an electrochemical sensor device for determining a fatigue status of a growing crack in a substrate. The system includes a reference electrode formed from a stainless steel mesh material that is substantially impermeable to an electrolyte. The reference electrode has a bottom side that faces the substrate and a top side that faces away from the substrate. At least one opening is provided in the mesh material, said at least one opening being sufficient in size to permit electrolyte to flow through the reference electrode. A first electrolyte cavity is formed between the substrate and the bottom side of the reference electrode. A second electrolyte cavity is formed between the top side of the reference electrode and a cover of the device. An electrolyte inlet port is formed in a wall of the first electrolyte cavity. A bleeder output port is formed in a wall of the second electrolyte cavity. A sensor measures a current between the reference electrode and the substrate when the substrate is subjected to cyclic loading.
In accordance with a still further aspect, the present invention is directed to a method for determining a fatigue status of a growing crack at a suspected fatigue location on a substrate. A first electrochemical sensor device that includes a first reference electrode is provided. A second electrochemical sensor device that includes a second reference electrode is also provided. The first electrochemical sensor device is positioned over the suspected fatigue location on the substrate, and a first current signal between the first reference electrode and the substrate is measured when the substrate is subjected to cyclic loading. The second electrochemical sensor device is positioned at a location on the substrate where fatigue cracking is not probable, and a second current signal between the second reference electrode and the substrate is measured when the substrate is subjected to cyclic loading. The fatigue status of the growing crack at the suspected fatigue location is assessed by comparing information from the first and second current signals.
Brief Description of the Drawings Figure 1 is a schematic diagram of an electrochemical fatigue sensor device, in accordance with the prior art.
Figure 2A is an isometric view of an EFS device in accordance with the present invention.
Figure 2B is an exploded view of the EFS device shown in Figure 2A.
Figure 2C is a top view of the EFS device shown in Figure 2B.
When the substrate is subjected to cyclic loading, the fatigue status of the growing crack in the substrate is determined in accordance with a measured current between the reference electrode and the substrate.
In accordance with a further aspect, the present invention is directed to an electrochemical sensor device for determining a fatigue status of a growing crack in a substrate. The system includes a reference electrode formed from a stainless steel mesh material that is substantially impermeable to an electrolyte. The reference electrode has a bottom side that faces the substrate and a top side that faces away from the substrate. At least one opening is provided in the mesh material, said at least one opening being sufficient in size to permit electrolyte to flow through the reference electrode. A first electrolyte cavity is formed between the substrate and the bottom side of the reference electrode. A second electrolyte cavity is formed between the top side of the reference electrode and a cover of the device. An electrolyte inlet port is formed in a wall of the first electrolyte cavity. A bleeder output port is formed in a wall of the second electrolyte cavity. A sensor measures a current between the reference electrode and the substrate when the substrate is subjected to cyclic loading.
In accordance with a still further aspect, the present invention is directed to a method for determining a fatigue status of a growing crack at a suspected fatigue location on a substrate. A first electrochemical sensor device that includes a first reference electrode is provided. A second electrochemical sensor device that includes a second reference electrode is also provided. The first electrochemical sensor device is positioned over the suspected fatigue location on the substrate, and a first current signal between the first reference electrode and the substrate is measured when the substrate is subjected to cyclic loading. The second electrochemical sensor device is positioned at a location on the substrate where fatigue cracking is not probable, and a second current signal between the second reference electrode and the substrate is measured when the substrate is subjected to cyclic loading. The fatigue status of the growing crack at the suspected fatigue location is assessed by comparing information from the first and second current signals.
Brief Description of the Drawings Figure 1 is a schematic diagram of an electrochemical fatigue sensor device, in accordance with the prior art.
Figure 2A is an isometric view of an EFS device in accordance with the present invention.
Figure 2B is an exploded view of the EFS device shown in Figure 2A.
Figure 2C is a top view of the EFS device shown in Figure 2B.
Figure 3 is a diagram illustrating the early stages of the crack initiation process.
Figure 4 illustrates a FFT of EFS data for a 0.01 inch growing crack, in accordance with the present invention.
Figure 5 illustrates a comparison between EFS signals from a reference EFS device and a crack monitoring EFS device, in accordance with the differential EFS
techniques of the present invention.
Detailed Description of the Preferred Embodiments Referring now to Figures 2A-2C, an EFS device 100 in accordance with the present invention is shown. The sensor includes reference electrode 110 which, in one embodiment, is a mesh made from stainless steel 304. The sensor also includes sections 120, 130 which, in one einbodiment, are each made from foam that has been coated on both sides with a pressure sensitive adhesive. In one embodiment, each of sections 120, 130 has a surface area that corresponds to a 2" x 2" square, or smaller. A
release paper (not shown) is attached to the adhesive on the bottom side 122 of section 120.
An electrolyte inlet port 150 is formed in a wall of the section 120. The electrolyte inlet port 150 is coupled to filler tube 160 (e.g., a plastic straw). A bleeder output port 170 is formed in a wall of the section 130. The bleeder output port 170 is coupled to bleeder tube 180 (e.g., a plastic straw). EFS device 100 also include a clear cover plate 190. EFS
device 100 is assembled by contacting the adhesive on the top surface 134 of section 130 with the cover plate 190; contacting the adhesive on the bottom surface 132 of section 130 with the top surface 114 of the electrode 110; and contacting the adhesive on the top surface of 124 of section 120 with the bottom surface 112 of electrode 110.
Once assembled, EFS device 100 is ready to be applied to a substrate in order to monitor a fatigue status of a growing crack in the substrate. As mentioned above, the bottom surface 122 of section 120 is coated with an adhesive layer, and a release paper is attached to the adhesive layer. In order to apply EFS device 100 to the substrate, the release paper is separated from the adhesive layer on the bottom surface 122 of section 120, thereby exposing the adhesive layer on the bottom surface 122 of section 120. EFS
device 100 is next secured to the substrate by bringing the adhesive layer in contact with the substrate and thereby forming a lower electrolyte cavity bounded on the bottom by the substrate, on the sides by the walls of section 120, and on the top by electrode 110. The adhesive seals the bottom surface 122 of section 120 to the substrate in order to prevent leakage of electrolyte from the lower electrolyte cavity. EFS device 100 also includes an upper electrolyte cavity bounded on the bottom by electrode 110, on the sides by the walls of section 130, and on the top by clear cover 190. In one embodiment, the stainless steel mesh used for forming electrode 110 is substantially impermeable to the electrolyte. At least one opening 116 (shown in Figure 2C) is provided in the mesh material, the opening 116 being sufficient in size to permit electrolyte to flow through the reference electrode 110.
After EFS device 100 is affixed to the substrate as set forth above, electrolyte is supplied (e.g., pumped) into the device via filler tube 160. The electrolyte initially fills the lower electrolyte cavity. After the lower electrolyte cavity is filled, electrolyte continues to be supplied via filler tube 160, thereby causing electrolyte to flow via opening 116 from the lower electrolyte cavity into the upper electrolyte cavity. The process continues until the upper electrolyte cavity is also filled (e.g., when the electrolyte begins to flow out of bleeder tube 180). Once the fill process is complete, tubes 160, 180 are pinched off and both sides 112, 114 of electrode 110 are covered with electrolyte.
During the fill process, the interior of EFS device 100 may be visually monitored through clear cover 190 in order to assure that the device is full of electrolyte and that no bubbles are present. In one embodiment, the electrolyte used for filling the EFS
device 100 is:
1.2M H3BO3 + 0.3M NaZB4O7= 10H2O + 0.24M Na2MoO4=2 H20 It will be understood by those skilled in the art that otller electrolyte formulations could also be used.
After EFS device 100 is installed and filled, as described above, a potentiostat (not shown) is coupled to the reference electrode 110 and the substrate, in order to measure current flow between electrode 110 and the substrate. When the substrate is subjected to cyclic loading, the fatigue status of a growing crack in the substrate can be determined in accordance with the measured current between the reference electrode 110 and the substrate (the EFS signal).
The EFS techniques of the present invention offer several advantages over other methods of non-destructive evaluation in that it offers the potential to detect fatigue crack growth as well as having the ability to detect very small cracks (0.005 inches). Figure 3 illustrates the process of dislocations piling up to form intrusions and extrusions. Such intrusions and extrusions and the formation of a crack at early stages of crack growth may be detected with electro-chemical fatigue sensors in accordance with the present invention.
In the laboratory, it was found that when pure sinusoidal loading is used to fatigue samples, two dominate frequencies are contained in the EFS signal. A fast Fourier transform (FFT) of EFS data for a specimen with a 0.01 inch growing crack revealed both a 1 hz and a 2 hz frequency component, as shown in Figure 4. The 1 hz component is due to the elastic deformations and the 2 hz component is due to the localized plastic deformations. As the crack grows and the crack growth rate increases the magnitude of the second harmonic at 2 hz increases. Under high loading and prior to fatigue cracking local plasticity caused by the high applied load produces similar secondary harmonics. In order to differentiate between the plasticity caused by cracking and loading, a secondary reference sensor is used. The use of a primary and a secondary sensor together is referred to as differential EFS.
Differential EFS in accordance with the present invention uses two EFS sensors 100, one as the reference (R) and one as the crack nleasureinent (M) sensor, in order to determine a fatigue status of a growing crack at a suspected fatigue location on a substrate. A first EFS device 100 (e.g., the M sensor device) is positioned over the suspected fatigue location on the substrate, and a first current signal between the reference electrode in the C sensor device and the substrate is measured when the substrate is subjected to cyclic loading. A second EFS device 100 (e.g., the R sensor device) is positioned at a location on the substrate where fatigue cracking is not probable, and a second current signal between the reference electrode in the Reference sensor device and the substrate is measured when the substrate is subjected to cyclic loading.
The fatigue status of the growing crack at the suspected fatigue location is then assessed by comparing information from the first and second current signals. More specifically, using signal processing the two signals can be compared to determine if a crack is present.
Examining Figure 5 one can see that M measurement sensor provides a larger magnitude than the reference signal thus indicating a crack.
Finally, it will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present invention as defined in the appended claims.
Figure 4 illustrates a FFT of EFS data for a 0.01 inch growing crack, in accordance with the present invention.
Figure 5 illustrates a comparison between EFS signals from a reference EFS device and a crack monitoring EFS device, in accordance with the differential EFS
techniques of the present invention.
Detailed Description of the Preferred Embodiments Referring now to Figures 2A-2C, an EFS device 100 in accordance with the present invention is shown. The sensor includes reference electrode 110 which, in one embodiment, is a mesh made from stainless steel 304. The sensor also includes sections 120, 130 which, in one einbodiment, are each made from foam that has been coated on both sides with a pressure sensitive adhesive. In one embodiment, each of sections 120, 130 has a surface area that corresponds to a 2" x 2" square, or smaller. A
release paper (not shown) is attached to the adhesive on the bottom side 122 of section 120.
An electrolyte inlet port 150 is formed in a wall of the section 120. The electrolyte inlet port 150 is coupled to filler tube 160 (e.g., a plastic straw). A bleeder output port 170 is formed in a wall of the section 130. The bleeder output port 170 is coupled to bleeder tube 180 (e.g., a plastic straw). EFS device 100 also include a clear cover plate 190. EFS
device 100 is assembled by contacting the adhesive on the top surface 134 of section 130 with the cover plate 190; contacting the adhesive on the bottom surface 132 of section 130 with the top surface 114 of the electrode 110; and contacting the adhesive on the top surface of 124 of section 120 with the bottom surface 112 of electrode 110.
Once assembled, EFS device 100 is ready to be applied to a substrate in order to monitor a fatigue status of a growing crack in the substrate. As mentioned above, the bottom surface 122 of section 120 is coated with an adhesive layer, and a release paper is attached to the adhesive layer. In order to apply EFS device 100 to the substrate, the release paper is separated from the adhesive layer on the bottom surface 122 of section 120, thereby exposing the adhesive layer on the bottom surface 122 of section 120. EFS
device 100 is next secured to the substrate by bringing the adhesive layer in contact with the substrate and thereby forming a lower electrolyte cavity bounded on the bottom by the substrate, on the sides by the walls of section 120, and on the top by electrode 110. The adhesive seals the bottom surface 122 of section 120 to the substrate in order to prevent leakage of electrolyte from the lower electrolyte cavity. EFS device 100 also includes an upper electrolyte cavity bounded on the bottom by electrode 110, on the sides by the walls of section 130, and on the top by clear cover 190. In one embodiment, the stainless steel mesh used for forming electrode 110 is substantially impermeable to the electrolyte. At least one opening 116 (shown in Figure 2C) is provided in the mesh material, the opening 116 being sufficient in size to permit electrolyte to flow through the reference electrode 110.
After EFS device 100 is affixed to the substrate as set forth above, electrolyte is supplied (e.g., pumped) into the device via filler tube 160. The electrolyte initially fills the lower electrolyte cavity. After the lower electrolyte cavity is filled, electrolyte continues to be supplied via filler tube 160, thereby causing electrolyte to flow via opening 116 from the lower electrolyte cavity into the upper electrolyte cavity. The process continues until the upper electrolyte cavity is also filled (e.g., when the electrolyte begins to flow out of bleeder tube 180). Once the fill process is complete, tubes 160, 180 are pinched off and both sides 112, 114 of electrode 110 are covered with electrolyte.
During the fill process, the interior of EFS device 100 may be visually monitored through clear cover 190 in order to assure that the device is full of electrolyte and that no bubbles are present. In one embodiment, the electrolyte used for filling the EFS
device 100 is:
1.2M H3BO3 + 0.3M NaZB4O7= 10H2O + 0.24M Na2MoO4=2 H20 It will be understood by those skilled in the art that otller electrolyte formulations could also be used.
After EFS device 100 is installed and filled, as described above, a potentiostat (not shown) is coupled to the reference electrode 110 and the substrate, in order to measure current flow between electrode 110 and the substrate. When the substrate is subjected to cyclic loading, the fatigue status of a growing crack in the substrate can be determined in accordance with the measured current between the reference electrode 110 and the substrate (the EFS signal).
The EFS techniques of the present invention offer several advantages over other methods of non-destructive evaluation in that it offers the potential to detect fatigue crack growth as well as having the ability to detect very small cracks (0.005 inches). Figure 3 illustrates the process of dislocations piling up to form intrusions and extrusions. Such intrusions and extrusions and the formation of a crack at early stages of crack growth may be detected with electro-chemical fatigue sensors in accordance with the present invention.
In the laboratory, it was found that when pure sinusoidal loading is used to fatigue samples, two dominate frequencies are contained in the EFS signal. A fast Fourier transform (FFT) of EFS data for a specimen with a 0.01 inch growing crack revealed both a 1 hz and a 2 hz frequency component, as shown in Figure 4. The 1 hz component is due to the elastic deformations and the 2 hz component is due to the localized plastic deformations. As the crack grows and the crack growth rate increases the magnitude of the second harmonic at 2 hz increases. Under high loading and prior to fatigue cracking local plasticity caused by the high applied load produces similar secondary harmonics. In order to differentiate between the plasticity caused by cracking and loading, a secondary reference sensor is used. The use of a primary and a secondary sensor together is referred to as differential EFS.
Differential EFS in accordance with the present invention uses two EFS sensors 100, one as the reference (R) and one as the crack nleasureinent (M) sensor, in order to determine a fatigue status of a growing crack at a suspected fatigue location on a substrate. A first EFS device 100 (e.g., the M sensor device) is positioned over the suspected fatigue location on the substrate, and a first current signal between the reference electrode in the C sensor device and the substrate is measured when the substrate is subjected to cyclic loading. A second EFS device 100 (e.g., the R sensor device) is positioned at a location on the substrate where fatigue cracking is not probable, and a second current signal between the reference electrode in the Reference sensor device and the substrate is measured when the substrate is subjected to cyclic loading.
The fatigue status of the growing crack at the suspected fatigue location is then assessed by comparing information from the first and second current signals. More specifically, using signal processing the two signals can be compared to determine if a crack is present.
Examining Figure 5 one can see that M measurement sensor provides a larger magnitude than the reference signal thus indicating a crack.
Finally, it will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present invention as defined in the appended claims.
Claims (9)
1. A sensor assembly for an electrochemical fatigue sensor system for determining the fatigue status of a crack in an electroconductive substrate, comprising:
a body with interior and exterior faces;
a cavity within the body confining an electrolytic fluid;
an electrode positioned within the cavity, configured so that the electrolyte is on both sides of the electrode;
an adhesive that affixes the interior face of the body to the substrate and a second adhesive that affixes a cover plate to the exterior face of the body; and a means for adding the electrolyte to the cavity after the sensor assembly is affixed to a substrate.
a body with interior and exterior faces;
a cavity within the body confining an electrolytic fluid;
an electrode positioned within the cavity, configured so that the electrolyte is on both sides of the electrode;
an adhesive that affixes the interior face of the body to the substrate and a second adhesive that affixes a cover plate to the exterior face of the body; and a means for adding the electrolyte to the cavity after the sensor assembly is affixed to a substrate.
2. The sensor assembly of claim 1, wherein the body further comprises a plurality of layers that may be assembled on the surface of the substrate.
3. The sensor assembly of claim 1, wherein the electrode is selected from a mesh or sheet of a conductive metal.
4. The sensor assembly of claim 1, wherein the electrode is stainless steel.
5. A method for determining the fatigue status of a crack in a substrate, comprising a set of two sensor assemblies according to claim 1, and the fatigue status of a crack is determined by comparing a measured electric current from the two sensor assemblies.
6. The method of claim 5, wherein each sensor assembly is coupled to a potentiostat that measures current passing through the sensor assembly when a constant voltage is applied to the substrate during cyclic loading of the substrate.
7. The method of claim 5, wherein one sensor assembly is positioned over a suspected fatigue location on the substrate, and the other sensor assembly is positioned where a fatigue crack is unlikely, and the fatigue status of the substrate is assessed by measuring the difference between the electrical signals between the two sensor assemblies.
8. The method of claim 5, wherein data from the potentiostat measurements of current from the sensor assemblies during cyclic loading is transferred to a computer for signal processing to determine the fatigue status of the substrate.
9. A method for determining the fatigue status of a crack in a substrate, comprising a set of two sensor assemblies according to claim 1, wherein one sensor assembly is positioned over a suspected fatigue location on the substrate, and the other sensor assembly is positioned where a fatigue crack is unlikely; and the fatigue status of a crack is determined by measuring an electric current from each sensor assembly, wherein each measurement is from a potentiostat that measures current passing through the sensor assembly when a constant voltage is applied to the substrate during cyclic loading of the substrate; and performing a signal analysis of the potentiostat current measurements to determine the fatigue status of the substrate.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US11/240,677 | 2005-09-30 | ||
| US11/240,677 US7572360B2 (en) | 2005-09-30 | 2005-09-30 | Electrochemical fatigue sensor systems and methods |
| PCT/US2006/018833 WO2007040651A2 (en) | 2005-09-30 | 2006-05-16 | Electrochemical fatigue sensor system and methods |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2623305A1 CA2623305A1 (en) | 2007-04-12 |
| CA2623305C true CA2623305C (en) | 2010-05-11 |
Family
ID=37900856
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2623305A Expired - Fee Related CA2623305C (en) | 2005-09-30 | 2006-05-16 | Electrochemical fatigue sensor system and methods |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US7572360B2 (en) |
| EP (1) | EP1943506A4 (en) |
| JP (1) | JP4364932B2 (en) |
| KR (1) | KR101279210B1 (en) |
| CN (1) | CN101278193B (en) |
| AU (1) | AU2006297854B2 (en) |
| BR (1) | BRPI0616617B1 (en) |
| CA (1) | CA2623305C (en) |
| HK (1) | HK1125453A1 (en) |
| WO (1) | WO2007040651A2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU2009282053B2 (en) * | 2008-08-12 | 2015-05-14 | Efs International S.A. | Potentiostat data link |
| CN102095596A (en) * | 2011-01-11 | 2011-06-15 | 中南大学 | Real-time temperature compensation method of bridge fatigue life gauge |
| CN102095597A (en) * | 2011-01-11 | 2011-06-15 | 中南大学 | Method for measuring temperature correction factor of bridge fatigue life gage |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4065373A (en) * | 1976-04-26 | 1977-12-27 | Petrolite Corporation | Hydrogen patch cell |
| US4435252A (en) * | 1980-04-25 | 1984-03-06 | Olin Corporation | Method for producing a reticulate electrode for electrolytic cells |
| JPS57101741A (en) * | 1980-12-16 | 1982-06-24 | Mitsubishi Heavy Ind Ltd | Method for attaching measuring cell |
| CN2043757U (en) * | 1989-01-25 | 1989-08-30 | 沈阳飞机制造公司 | Crack detector |
| GB2244810B (en) * | 1990-06-02 | 1994-01-26 | Sycopel Scient Ltd | Test cell |
| FR2676807A1 (en) * | 1991-05-22 | 1992-11-27 | Tech Milieu Ionisant | Apparatus and method for measuring the surface area of a surface |
| JP3121953B2 (en) | 1993-02-24 | 2001-01-09 | 東北電力株式会社 | Method for detecting carbide in low alloy steel by electrochemical polarization method |
| US5771890A (en) * | 1994-06-24 | 1998-06-30 | Cygnus, Inc. | Device and method for sampling of substances using alternating polarity |
| US6026691A (en) | 1995-06-30 | 2000-02-22 | University Of Pennsylvania | Methods and devices for electrochemically determining metal fatigue status |
| US6151969A (en) * | 1998-07-14 | 2000-11-28 | Southwest Research Institute | Electromechanical and electrochemical impedance spectroscopy for measuring and imaging fatigue damage |
| US6328878B1 (en) | 1999-08-11 | 2001-12-11 | Dacco Sci, Inc. | Adhesive tape sensor for detecting and evaluating coating and substrate degradation utilizing electrochemical processes |
| JP3342467B2 (en) * | 2000-03-30 | 2002-11-11 | 川崎重工業株式会社 | Crack-type fatigue detecting element, method of manufacturing the same, and damage estimation method using crack-type fatigue detecting element |
| US6611151B1 (en) * | 2000-09-21 | 2003-08-26 | The United States Of America As Represented By The Secretary Of The Navy | Coating assessment system based on electrochemical noise |
| CN1182390C (en) * | 2003-01-17 | 2004-12-29 | 清华大学 | Detection method for movable flaw produced by stress or fatigue |
| CN1282876C (en) * | 2004-10-27 | 2006-11-01 | 东华大学 | Multifunctional measuring method and device for flexible material bending fatigue |
-
2005
- 2005-09-30 US US11/240,677 patent/US7572360B2/en active Active - Reinstated
-
2006
- 2006-05-16 CN CN2006800364232A patent/CN101278193B/en not_active Expired - Fee Related
- 2006-05-16 WO PCT/US2006/018833 patent/WO2007040651A2/en active Application Filing
- 2006-05-16 AU AU2006297854A patent/AU2006297854B2/en not_active Ceased
- 2006-05-16 JP JP2008533327A patent/JP4364932B2/en not_active Expired - Fee Related
- 2006-05-16 CA CA2623305A patent/CA2623305C/en not_active Expired - Fee Related
- 2006-05-16 BR BRPI0616617-2A patent/BRPI0616617B1/en not_active IP Right Cessation
- 2006-05-16 EP EP06759893.8A patent/EP1943506A4/en not_active Withdrawn
- 2006-05-16 KR KR1020087008735A patent/KR101279210B1/en active IP Right Grant
-
2009
- 2009-04-01 HK HK09103097.7A patent/HK1125453A1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| WO2007040651A2 (en) | 2007-04-12 |
| CN101278193B (en) | 2012-08-22 |
| BRPI0616617B1 (en) | 2017-10-10 |
| EP1943506A4 (en) | 2016-04-20 |
| BRPI0616617A2 (en) | 2011-06-28 |
| KR20080053499A (en) | 2008-06-13 |
| EP1943506A2 (en) | 2008-07-16 |
| CA2623305A1 (en) | 2007-04-12 |
| AU2006297854B2 (en) | 2011-03-31 |
| CN101278193A (en) | 2008-10-01 |
| US20070074976A1 (en) | 2007-04-05 |
| AU2006297854A1 (en) | 2007-04-12 |
| JP4364932B2 (en) | 2009-11-18 |
| JP2009510431A (en) | 2009-03-12 |
| US7572360B2 (en) | 2009-08-11 |
| WO2007040651A3 (en) | 2007-10-11 |
| HK1125453A1 (en) | 2009-08-07 |
| KR101279210B1 (en) | 2013-06-26 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US6015484A (en) | Detection of pitting corrosion | |
| CN103926146B (en) | A kind of small sample constant load stress corrosion test device and method of testing thereof | |
| US7508223B1 (en) | Multihole and multiwire sensors for localized and general corrosion monitoring | |
| CN201635064U (en) | Resistivity static sounding probe | |
| CN110208114B (en) | Interface vibration single shear test device and method for simulating power contact problem | |
| CA2623305C (en) | Electrochemical fatigue sensor system and methods | |
| Santo Zarnik et al. | Estimation of the long-term stability of piezoresistive LTCC pressure sensors by means of low-frequency noise measurements | |
| CN111788478B (en) | Corrosion measuring device | |
| CN105698664A (en) | Detecting device and detecting method suitable for strain of concrete | |
| Hou et al. | Crack monitoring method based on Cu coating sensor and electrical potential technique for metal structure | |
| KR101477962B1 (en) | Apparatus and method for detecting pitting corrosion of metal using acoustic emission method | |
| Ogunniyi et al. | Investigation of electrically isolated capacitive sensing skins on concrete to reduce structure/sensor capacitive coupling | |
| CN106092401B (en) | A kind of ferromagnetics conductor material stress measuring method and system based on Kelvin effect | |
| KR101210472B1 (en) | Apparatus and method for detecting the micro-scale crack using nonlinear characteristics of ultrasonic resonance | |
| MX2008004270A (en) | Electrochemical fatigue sensor system and methods | |
| Varela et al. | Monitoring cathodic shielding and corrosion under disbonded coatings | |
| CN109164143A (en) | Drag-line corrosion monitor and its method for prestressed cable corrosion monitoring | |
| CN104048633B (en) | A kind of device and method of the micro hole hole wall re cast layer thickness detecting thermal source molding | |
| Dragan et al. | Health Monitoring of the helicopter main rotor blades with the structure integrated sensors | |
| CN115855788A (en) | Metal material corrosion monitoring device and monitoring method | |
| RU152943U1 (en) | DEVICE FOR DIAGNOSTIC OF HUMIDITY OF INSULATING MATERIAL OF HEAT AND SOUND INSULATION OF VEHICLE | |
| JPH0666877A (en) | Measuring device for insulating characteristic of insulator | |
| CN115753585A (en) | In-situ detection system and detection method based on stress and gap coupling effect | |
| Aloui et al. | Measurement of thin liquid film thickness between two mechanical surfaces in relative movement using the conductimetry technique: Application for hydrodynamic lubrication | |
| CN114778673A (en) | Power-based glass elastic modulus measuring device and method |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20210517 |