Patent Description:
Laser bond inspection (LBI) is a process that is used to evaluate an adhesive bond in a bonded structure. LBI uses a laser pulse to create a plasma, which generates stress waves in the bonded structure. In an example, the bonded structure includes carbon fiber reinforced polymer (CFRP)-to-CFRP or CFRP-to-metal. The stress waves mechanically create a tension load on the adhesive bond. During exposure to this load, a weak joint will fail, and a strong joint will not. Bonded structures with weak joints are thus be identified and repaired or discarded. However, current LBI systems are large and expensive. Therefore, what is needed is an improved system and method for evaluating a bond.

<CIT> describes a plasma actuator including an electrode member, an application electrode, a ground electrode, and a supporting member. The electrode member has a first surface facing a processing object and a second surface of an opposite side of the first surface. The application electrode is provided in the first surface. The ground electrode is provided in the second surface or an inner portion of the electrode member. The supporting member is provided in at least one of the electrode member and the application electrode to form a processing space between the processing object and the electrode member. The supporting member is capable of abutting on the processing object.

<CIT> describes a flow control system including a movable wing attachable to a wing of an aircraft, and a plasma actuator mountable on a surface of the movable wing. The flow control system is configured to control air flow around the wing by having the changing of the steering angle of the movable wing work in conjunction with the operation of the plasma actuator.

<CIT> describes a nondestructive bond strength testing method, including: coupling an expendable device to a structure under test, the expendable device including a patterned planar array of exploding bridge wires; simultaneously vaporizing the patterned planar array of exploding bridge wires by applying a pulse of electrical energy to the patterned planar array of exploding bridge wires; and sensing an initial disbonding signature of the structure under test.

<CIT> describes methods, systems, and apparatuses for creating bond delaminations in a controlled fashion within adhesively bonded structures. In one embodiment, a system for inducing a defect in a bond of a bonded article includes a laser and a laser processor head. The laser processor head includes a housing, a lens disposed within the housing, at least one magnet disposed within the housing, and at least one sensor disposed within the housing. The system is capable of applying a laser pulse of sufficient energy fluence to cause localized weaknesses in the bond.

<CIT> describes a method of prestressing a component including the use of an electrical discharge or current to produce a plasma within a medium located adjacent the component. The plasma generates a shock wave which impacts a surface of the component to produce a region of compressive residual stress within the component.

<NPL>) describes assessment of bond defects in adhesive joints before and after the treatment with laser generated shock waves.

According to an aspect of the claimed invention, there is provided a system for evaluating a bond as defined in claim <NUM>.

According to another aspect of the claimed invention, there is provided a method for evaluating a bond as defined in claim <NUM>.

A system for evaluating a bond is disclosed. The system includes a first electrode and a second electrode. A dielectric material layer is positioned at least partially between the first and second electrodes. A power source is connected to the first and second electrodes. The power source is configured to cause the first and second electrodes to generate an electrical arc. The electrical arc is configured to at least partially ablate a sacrificial material layer to generate a plasma.

In another implementation, a system includes a support. The system also includes a first electrode in contact with the support. The system also includes a second electrode spaced apart from the support and the first electrode. The system also includes a dielectric material layer in contact with the support. The dielectric material layer is positioned at least partially between the support and the second electrode and at least partially between the first electrode and the second electrode, such that the second electrode is not in contact with the support or the first electrode. The system also includes a power source connected to the first and second electrodes. The power source is configured to transmit an alternating current pulse to the first and second electrodes, which causes the first and second electrodes to generate an electrical arc. The electrical arc at least partially ablates a sacrificial material layer on a bonded structure to generate a plasma. The generation of the plasma generates a compression wave that is directed into the bonded structure. The compression wave reflects off of the bond in the bonded structure as a tension wave.

A method for evaluating a bond is also disclosed. The method includes placing a sacrificial material layer on a surface of a bonded structure. The method also includes transmitting an electrical pulse to a first electrode and a second electrode, which causes the first and second electrodes to generate an electrical arc. The electrical arc at least partially ablates the sacrificial material layer to generate a plasma. The generation of the plasma generates a compression wave that is directed into the bonded structure. The compression wave reflects off of the bond in the bonded structure as a tension wave.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings, as claimed.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate aspects of the present teachings and together with the description, serve to explain the principles of the present teachings.

It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding rather than to maintain strict structural accuracy, detail, and scale.

Reference will now be made in detail to the present teachings, examples of which are illustrated in the accompanying drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific examples of practicing the present teachings. The following description is, therefore, merely exemplary.

The present disclosure is directed to a plasma actuator that represents a smaller, less expensive alternative to LBI systems. The plasma actuator includes a support, first and second electrodes, and a dielectric material layer. The plasma actuator is configured to generate an electrical arc that at least partially ablates a sacrificial material layer to create a plasma, which generates the waves that travel into the bonded structure to evaluate a quality of the bond, as described in greater detail below.

<FIG> illustrates a schematic view of a system <NUM> for evaluating a bond in a bonded structure <NUM>, according to an implementation. The system <NUM> includes a plasma actuator that provides an alternative to LBI systems. Thus, the system <NUM> evaluates the bond (e.g., assists in determining a quality of the bond) in the bonded structure <NUM> without use of a laser. Evaluation of the bond may be performed in accordance with ASTM STP1455-Mechanism of adhesive in secondary bonding of fiberglass composites with peel ply surface preparation. More particularly, the system <NUM> applies a predetermined force to the bond. The predetermined force is from about <NUM>% to about <NUM>% (e.g., about <NUM>%) of the force required to break an ideal bond (or from <NUM>% to <NUM>% (e.g., <NUM>%) of the force required to break an ideal bond). The bond is then inspected. If the bond is not fractured or broken, the bond is passing/satisfactory. If the bond is fractured or broken, the bond is not passing/not satisfactory.

According to the invention, the bonded structure <NUM> includes a first component <NUM> and a second component <NUM> that are bonded together by a bond material <NUM> (e.g., the bond). As will be appreciated, there may be more components that are bonded together, but for simplicity, only two components are illustrated. In some examples, the first and second components <NUM>, <NUM> are made at least partially from CFRP. In other examples, the first component <NUM> is made at least partially from CFRP, and the second component <NUM> is made at least partially from metal. The bond material <NUM> can be a resin, an adhesive, or an epoxy (e.g., boron epoxy or carbon epoxy).

The system <NUM> includes a support <NUM>. The support <NUM> may also be referred to as a support surface or a substrate. The support <NUM> can be or include a polyimide material, a polyamide material, or both. In some examples, the support <NUM> is made at least partially from a polyamide tape such as KAPTON® tape. The support <NUM> provides high heat-resistance and high dielectric strength. The support <NUM> also prevents unintended dielectric arcs.

The system <NUM> also includes a first electrode 130A and a second electrode 130B. The first and second electrodes 130A, 130B are configured to generate an electrical arc, as described in greater detail below.

The first and second electrodes 130A, 130B are made at least partially from copper or other metals. The electrical arc at least partially depends upon the material(s) in the first and second electrodes 130A, 130B. For example, the material(s) can affect the magnitude, direction, and/or temperature of the electrical arc.

In some implementations, the first and second electrodes 130A, 130B are the same size (e.g., length, width, and/or height). However, in some implementations, like that shown in <FIG>, the first electrode 130A has a different size (e.g., a different length) than the second electrode 130B. For example, the first electrode 130A can have a length from about <NUM> to about <NUM>, e.g., about <NUM> (or from <NUM> to <NUM>, e.g., <NUM>), and the second electrode 130B can have a length from about <NUM> to about <NUM>, e.g., about <NUM> (or from <NUM> to <NUM>, e.g., <NUM>). The electrical arc at least partially depends upon the sizes (e.g., lengths) of the first and second electrodes 130A, 130B. The sizes (e.g., lengths) affect the magnitude, direction, and/or temperature of the electrical arc. As the size(s) of the electrodes(s) 130A, 130B increase(s), the amount of electrical current required to generate the electrical arc also increases. Larger electrical arcs have higher temperatures.

The first and second electrodes 130A, 130B are spaced apart from one another. As shown, the first and second electrodes 130A, 130B can be spaced apart from one another by a first distance <NUM> in a first direction that is parallel or substantially parallel to a surface <NUM> of the bonded structure <NUM>. The first and second electrodes 130A, 130B can also be spaced apart from one another by a second distance <NUM> in a second direction that is perpendicular or substantially perpendicular to the surface <NUM> of the bonded structure <NUM>. The first distance <NUM> can be from about <NUM> to about <NUM>, e.g., about <NUM> (or from <NUM> to <NUM>, e.g., <NUM>), and the second distance <NUM> can be from about <NUM> to about <NUM>, e.g., about <NUM> (or from <NUM> to <NUM>, e.g., <NUM>). Thus, as shown, the first electrode 130A is positioned farther from the bonded structure <NUM> than the second electrode 130B. The electrical arc at least partially depends upon the spacing/positioning of the first and second electrodes 130A, 130B with respect to one another. For example, the spacing/positioning affects the magnitude, direction, and/or temperature of the electrical arc. Moving the first and second electrodes 130A, 130B closer together reduces the size of the electrical arc, which reduces the temperature of the electrical arc. Conversely, moving the first and second electrodes 130A, 130B farther apart increases the size of the electrical arc, which increases the temperature of the electrical arc.

The system <NUM> also includes a dielectric material layer <NUM> positioned at least partially between the first and second electrodes 130A, 130B. The first direction (referenced above) may be parallel or substantially parallel to a plane <NUM> through the dielectric material layer <NUM>, and the second direction may be perpendicular or substantially perpendicular to the plane <NUM>. The plane <NUM> may also be parallel or substantially parallel to the surface <NUM> of the bonded structure <NUM>. The dielectric material layer <NUM> can have a thickness from about <NUM> to about <NUM>, e.g., about <NUM> (or from <NUM> to <NUM>, e.g., <NUM>). The dielectric material layer <NUM> can be or include a polyimide film with a silicone adhesive, such as KAPTON® tape. In other implementations, the dielectric material layer <NUM> is made at least partially from polytetrafluoroethylene (PTFE). For example, the dielectric material layer <NUM> can be made from TEFLON®. The dielectric material layer <NUM> is configured to provide an electrical barrier between the first and second electrodes 130A, 130B. As the thickness and/or resistance of the dielectric barrier increases, more electrical current is needed to generate the electrical arc. Conversely, as the thickness and/or resistivity of the dielectric barrier decreases, less electrical current is needed to generate the electrical arc.

As shown, the first electrode 130A is in contact with and/or coupled to the support <NUM> and/or the dielectric material layer <NUM>. The second electrode 130B is in contact with and/or coupled to the dielectric material layer <NUM>, but not in contact with and/or coupled to the support <NUM>. The dielectric material layer <NUM> is in contact with and/or coupled to the support <NUM>, the first electrode 130A, the second electrode 130B, or a combination thereof.

The system <NUM> includes a power source <NUM> that is connected to the first and second electrodes 130A, 130B. The power source <NUM> can have a voltage from about <NUM> kilovolts (kV) to about <NUM> kV (or from <NUM> kV to <NUM> kV). The power source <NUM> generates an alternating current (AC) pulse having a duration from about <NUM> nanoseconds (ns) to about <NUM> millisecond (ms), about <NUM> ns to about <NUM> ns, or about <NUM> ns to about <NUM> ns (or from <NUM> ns to <NUM>, <NUM> ns to <NUM> ns, or <NUM> ns to <NUM> ns). For example, the pulse can have a duration of <NUM> ns or about <NUM> ns. The pulse causes the first and second electrodes 130A, 130B to generate the electrical arc.

According to the invention, a sacrificial material layer <NUM> is coupleable to and/or contactable with the surface <NUM> of the bonded structure <NUM>. The sacrificial material layer <NUM> is made from a material that is configured to be at least partially ablated by the electrical arc to generate a plasma. For example, the sacrificial material layer <NUM> can be made at least partially from a polyvinyl chloride tape.

A liquid (e.g., water or FLUORINERT®) <NUM> is positioned at least partially between the surface <NUM> of the bonded structure <NUM> and the dielectric material layer <NUM>. As shown, the liquid <NUM> is positioned on the sacrificial material layer <NUM>. As described in greater detail below, the ablation of the sacrificial material layer <NUM> generates a compression wave, and the liquid <NUM> directs at least a portion of the compression wave into the bonded structure <NUM> (e.g., toward the bond material <NUM>).

<FIG> illustrates a flowchart of a method <NUM> for evaluating the bond in the bonded structure <NUM>, according to an implementation. The method <NUM> may be performed using the system <NUM>. An illustrative order of the method <NUM> is described below; however, it will be appreciated that one or more steps of the method <NUM> may be performed in a different order and/or omitted.

The method <NUM> includes placing the sacrificial material layer <NUM> on the surface <NUM> of the bonded structure <NUM>, as at <NUM>. In some examples, the sacrificial material layer <NUM> is adhered to the surface <NUM>. The method <NUM> also includes placing the liquid <NUM> between the system <NUM> and the sacrificial material layer <NUM>, as at <NUM>. In some examples, the liquid is placed on the sacrificial material layer <NUM>.

The method <NUM> includes generating an electrical pulse using the system <NUM>, as at <NUM>. More particularly, the power source <NUM> is connected to the electrodes 130A, 130B and transmits an electrical (e.g., AC) pulse to the electrodes 130A, 130B, which causes the electrodes 130A, 130B to generate the electrical arc. The electrical arc least partially ablates at least a portion of the sacrificial material layer <NUM> to generate a plasma <NUM> (see <FIG>). Thus, the plasma <NUM> can be generated without the user of a laser, which allows the system <NUM> to have a smaller footprint and be less expensive than conventional LBI systems.

A first wave is generated in response to the ablation of the sacrificial material layer <NUM> and/or the generation of the plasma <NUM>. The first wave is a compression wave. The first wave is directed toward the surface <NUM> of the bonded structure <NUM> (e.g., toward the bond material <NUM>) at least partially by the liquid <NUM>. The first wave can also or instead be directed toward the surface <NUM> of the bonded structure <NUM> (e.g., toward the bond material <NUM>) at least partially in response to the material of the electrodes 130A, 130B, the size of the electrodes 130A, 130B, the positioning of the electrodes 130A, 130B, the positioning of the dielectric material layer <NUM>, or a combination thereof. The first wave reflects off of the bonded structure <NUM>. More particularly, the first wave reflects off of the bond material <NUM> and/or the surface <NUM> as a second wave. The second wave is a tension wave.

The first wave and/or the second wave may apply a predetermined force to the bond (e.g., bond material <NUM>). The predetermined force is from about <NUM>% to about <NUM>%, e.g., about <NUM>% (or from <NUM>% to <NUM>%, e.g., <NUM>%) of the force required to break an ideal bond.

According to the invention, the method <NUM> also includes inspecting the bonded structure <NUM>, as at <NUM>. For example, the bond (e.g., bond material <NUM>) can be inspected with a non-destructive inspection (NDI) system <NUM> (see <FIG>) such as an ultrasound imaging system or an ultrasonic inspection system after the first wave reflects off of the bond material <NUM> to form the second wave. The inspection detects inconsistencies and/or damage to the bond that occur(s) in response to the contact with the first wave and/or the second wave. If the inspection reveals that the bond (e.g., bond material <NUM>) is fractured or broken, then the quality of the bond is determined to be bad (i.e., the bond did not pass inspection). If the inspection reveals that the bond (e.g., bond material <NUM>) is not fractured or broken, then the quality of the bond is determined to be good (i.e., the bond passes inspection). Such an inspection of the bond is enough to meet the requirements of ASTM D5528-<NUM> - Standard Test Method for Mode <NUM> Interlaminar Fracture Toughness of Unidirectional Fiber-reinforced Polymer matrix composites. Alternative or additional steps may also be performed.

In other implementations, one or more portions of the system <NUM> can be replaced or modified to generate different pulse widths, electrical arcs with different properties, waves with different properties, or a combination thereof. For example, one or both of the electrodes 130A, 130B can be replaced with different electrode(s) that are made of a different material and/or have a different size/shape. In addition, the positioning of the electrodes 130A, 130B (e.g., the spacing between the electrodes 130A, 130B) can be varied. In other examples, the dielectric material layer <NUM> can be replaced with a different dielectric material layer that is made of a different material and/or has a different shape/size. In addition, the positioning of the dielectric material layer <NUM> can be varied. Replacing or modifying the electrodes 130A, 130B and/or the dielectric material layer <NUM> as described above affects the magnitude, direction, and/or temperature of the electrical arc. For example, the dielectric material layer <NUM> can be replaced with a second dielectric material layer having a different thickness and/or resistivity, which affects the amount of electrical current needed to generate the electrical arc and/or the temperature of the electrical arc.

In at least one implementation, the system <NUM> may not include/use inspection tape with copper traces, as is oftentimes used by LBI systems, because the system <NUM> does not include an electromagnetic transducer (EMAT) to translate the compression wave and/or the tension wave. Indeed, the system does not receive the compression wave.

The foregoing system <NUM> and method <NUM> can replace peel ply tests, which use mechanically applied stress to pull a bond apart. The foregoing system <NUM> and method <NUM> can also replace LBI tests, which use a laser to generate the plasma and the compression wave.

The tensile force needed to damage or break a bond with a satisfactory/passing quality may be known prior to performing the method <NUM>. Thus, the waves generated during the testing can have a force that is less than the force needed to break the bond (e.g., between <NUM>% and <NUM>% of the force, or between about <NUM>% and about <NUM>% of the force). If the inspection shows that the bond is still intact after the wave(s) contact the bond, then the bond is considered to have the desired quality (the bond passes the test). If the inspection shows that the bond is damaged or broken after the wave(s) contact the bond, then the bond is not considered to have the desired quality (the bond fails the test).

Claim 1:
A system (<NUM>) for evaluating a bond in a bonded structure (<NUM>) comprising a first component (<NUM>) and a second component (<NUM>) that are bonded together by a bond material (<NUM>), the system comprising a sacrificial material layer (<NUM>) coupleable to and/or contactable with a surface (<NUM>) of the bonded structure, the system comprising:
a first electrode (130A);
a second electrode (130B);
a dielectric material layer (<NUM>) positioned at least partially between the first and second electrodes;
a power source (<NUM>) connected to the first and second electrodes, wherein the power source is configured to cause the first and second electrodes to generate an electrical arc, wherein the electrical arc is configured to at least partially ablate a sacrificial material layer (<NUM>) to generate a plasma, optionally wherein the first electrode, the second electrode, or both are made from copper; and
a non-destructive inspection system (<NUM>).