Claims:1. A method for manufacturing a modular wind blade for a wind turbine, the method comprising:
heating a metal component (140) sandwiched between a first section (120) and a second section (130) of the modular wind blade, to form a thermoplastic weld (110);
transmitting a microwave signal (62) to the metal component (140) through an external surface (124) of the modular wind blade and receiving a reflected microwave signal (64);
identifying a defect in the thermoplastic weld (110); and
repairing the defect.

2. The method as claimed in claim 1, wherein transmitting the microwave signal (62) and receiving the reflected microwave signal (64) is through a same external surface (124) of the modular wind blade.

3. The method as claimed in claim 1, wherein a section (120) of the modular wind blade through which the microwave signal (62) passes to the metal component (140) comprises a composite comprising a thermoplastic polymer matrix and reinforcing fibers.

4. The method as claimed in claim 3, wherein the composite is transparent to the microwave signal (62).

5. The method as claimed in claim 1, wherein identifying a defect in the thermoplastic weld comprises measuring a reflection coefficient of the reflected microwave signal (64).

6. The method as claimed in claim 1, wherein identifying a defect in the thermoplastic weld comprises comparing the reflected microwave signal (64) with a dynamic threshold value on the reflected microwave signal (64).

7. The method as claimed in claim 1, further comprising functionally integrating heating the metal component (140) and transmitting the microwave signal (62), for identifying the defect in the thermoplastic weld (110) during or immediately after forming the thermoplastic weld (110).

8. The method as claimed in claim 1, wherein the metal component (140) is a metal mesh.

9. A method for externally inspecting a thermoplastic weld (110) in a modular wind blade for a wind turbine, wherein the thermoplastic weld (110) is formed by joining a first section (120) and a second section (130) of the modular wind blade by heating a metal component (140) sandwiched therebetween, the method comprising:
transmitting a microwave signal (62) to the metal component (140) through an external surface (124) of the modular wind blade and receiving a reflected microwave signal (64);
measuring a reflection coefficient of the reflected microwave signal (64); and
ascertaining a defect-free thermoplastic weld (110) or identifying a defect in the thermoplastic weld (110).

10. The method as claimed in claim 9, wherein ascertaining the defect-free thermoplastic weld (110) comprises comparing the reflected microwave signal (64) with a dynamic threshold value on the reflected microwave signal (64).

11. The method as claimed in claim 9, wherein the metal component (140) is a metal mesh.

12. A method for externally inspecting a thermoplastic weld (210) formed by joining a first polymer component (220) and a second polymer component (230) by heating a metal component (240) sandwiched therebetween, the method comprising:
transmitting a microwave signal (62) to the metal component (240) through an external surface (222) of the polymer components (220, 230) and receiving a reflected microwave signal (64);
measuring a reflection coefficient of the reflected microwave signal (64); and
ascertaining a defect-free thermoplastic weld (210) or identifying a defect (216) in the thermoplastic weld (210).

13. The method as claimed in claim 12, wherein transmitting the microwave signal (62) and receiving the reflected microwave signal (64) is through a same external surface (222) of the polymer components (220, 230).

14. The method as claimed in claim 12, wherein identifying a defect in the thermoplastic weld (210) comprises measuring a reflection coefficient of the reflected microwave signal (64).

15. The method as claimed in claim 12, wherein identifying a defect (216) in the thermoplastic weld comprises comparing the reflected microwave signal (64) with a dynamic threshold value on the reflected microwave signal (64).

16. The method as claimed in claim 12, wherein the metal component (240) is a metal mesh.

17. The method as claimed in claim 12, wherein the first polymer component (220) is a first section (120) of a modular wind blade and the second polymer component (230) is a second section (130) of the modular wind blade.
, Description:BACKGROUND
[0001] Embodiments of the disclosure generally relate to microwave inspection of thermoplastic welds. More particularly, embodiments of the disclosure relate to a method for externally inspecting a thermoplastic weld using a microwave probe and evaluating the results therefrom.
[0002] In recent years, sizes of the wind turbines for wind power generation have increased to improve power generation efficiency and the absolute power generated. One of the key contributors to increased energy production is the blade length. For example, an average blade length of a newer generation wind turbine may be 40 meters or more. When the wind blade is increased in length as described above, various challenges occur. For example, difficulties may arise in integral manufacturing and transportation both from cost and logistics perspective. Therefore, it is desirable to construct wind blades in segments to enable manufacture of a wind blade in a modular manner. For example, longitudinal segments of a wind blade may be manufactured separately for ease of handling and transportation and then assembled into full length wind blades at a wind farm site.
[0003] Different designs and methods have been investigated in the past to join two blade segments to build the blade to full length at site and to inspect the joints formed thereby. Sections of modular wind blades are typically made of thermoplastic materials and are joined together by welding, on-site, thereby forming thermoplastic welds. Therefore, it is desirable to devise a simple method to detect a defect, if present, in the thermoplastic weld. An ability to detect defects in a thermoplastic weld is a function of the nature of the input energy, physical properties of the material, thickness and shape of the joining materials, and size and type of the defects to be detected. Ultrasound, infrared, and microwave-based inspection techniques using difference in material properties between defective and non-defective areas are generally known. For ultrasound-based detection techniques, the detection capabilities depend on ultrasound attenuation in the material. Infrared detection techniques generally depend on changes in thermal diffusivity. Microwave inspection techniques generally depend on the changes in dielectric properties of the thermoplastic material and the thermoplastic weld formed.
[0004] Thermoplastic welds may be of two types. In a first type of thermoplastic weld, two thermoplastic materials (e.g., of two segments of the modular wind blades) may be directly heated to form the weld. In a second type of thermoplastic weld, a metal component placed between the two thermoplastic materials is heated, typically through resistive or inductive means and the heat generated in the metal component is used to create the thermoplastic weld. Traditional thermoplastic weld inspection techniques are generally applied to thermoplastic welds that are formed by directly heating the thermoplastic materials.
[0005] Currently, there are not many techniques available for specific inspection of the thermoplastic welds that have been created using metal components. US5902935A discusses a system that evaluates the quality of thermoplastic welds with an embedded copper mesh by inputting an electromagnetic pulse to the embedded susceptor and listening to the acoustic response from the vibrations that the pulse generates, to determine weld quality. However, this method uses two different types of transducers: an electromagnetic one for excitation and an acoustic one for received signals. Further, for ultrasound-based techniques, generally an ultrasound probe needs to be in contact with the material being inspected. In addition, ultrasound inspection typically needs a couplant that leads to additional processes. An ICONE17-75746 research paper, “Microwave based NDE inspection of HDPE pipe welds” by Robert Stakenborghs and Jack Little, discusses microwave inspection of HDPE pipe welds. In this paper, microwave inspection is carried out by creating a map of the weld based on various factors such as angle of incidence, dielectric constant of the materials, and surface geometry. However, this paper does not discuss microwave inspection of thermoplastic welds having metal components as a part of the thermoplastic weld.
BRIEF DESCRIPTION
[0006] In one aspect, the disclosure relates to a method for manufacturing a modular wind blade for a wind turbine. The method includes heating a metal component sandwiched between a first section and a second section of the modular wind blade to form a thermoplastic weld, transmitting a microwave signal to the metal component through an external surface of the modular wind blade and receiving a reflected microwave signal, identifying a defect in the thermoplastic weld, and repairing the defect.
[0007] In another aspect, the disclosure relates to a method for externally inspecting a thermoplastic weld in a modular wind blade for a wind turbine. The thermoplastic weld is formed by joining a first section and a second section of the modular wind blade by heating a metal component sandwiched between the first section and the second section. The method for externally inspecting includes transmitting a microwave signal to the metal component through an external surface of the modular wind blade and receiving a reflected microwave signal, measuring a reflection coefficient of the reflected microwave signal, and ascertaining a defect-free thermoplastic weld or identifying a defect in the thermoplastic weld.
[0008] In yet another aspect, the disclosure relates to a method of externally inspecting a thermoplastic weld formed by joining a first polymer component and a second polymer component by heating a metal component sandwiched therebetween. The method includes transmitting a microwave signal to the metal component through an external surface of the polymer components and receiving a reflected microwave signal, measuring a reflection coefficient of the reflected microwave signal, and ascertaining a defect-free thermoplastic weld or identifying a defect in the thermoplastic weld.
BRIEF DESCRITPION OF THE DRAWINGS
[0009] These and other features and aspects of embodiments of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings.
[0010] FIG. 1 illustrates a schematic of a portion of a modular wind blade including a thermoplastic weld and a system for externally inspecting the thermoplastic weld, in accordance with some aspects of the present disclosure;
[0011] FIG. 2 illustrates a schematic of a system for externally inspecting a thermoplastic weld, in accordance with some aspects of the present disclosure;
[0012] FIG. 3A shows a photograph of a hole in a metal mesh;
[0013] FIG. 3B illustrates an ultrasound inspection image of a hole in a metal mesh embedded in a thermoplastic weld;
[0014] FIG. 3C illustrates a microwave reflection image of a hole in a metal mesh embedded in a thermoplastic weld, in accordance with some aspects of the present disclosure;
[0015] FIG. 3D illustrates a microwave reflection image of a hole in a metal mesh embedded in a thermoplastic weld at a certain depth, in accordance with some aspects of the present disclosure;
[0016] FIG. 4A shows a photograph of a tear in a metal mesh;
[0017] FIG. 4B illustrates an ultrasound inspection image of a tear in a metal mesh embedded in a thermoplastic weld; and
[0018] FIG. 4C illustrates a microwave reflection image of a tear in a metal mesh embedded in a thermoplastic weld, in accordance with some aspects of the present disclosure.
DETAILED DESCRIPTION
[0019] In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings. The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. As used herein, the term “or” is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise.
[0020] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
[0021] According to some aspects of the disclosure, a method for manufacturing a modular wind blade for a wind turbine is disclosed. The method includes forming a thermoplastic weld by heating a metal component sandwiched between a first section and a second section of the modular wind blade, transmitting a microwave signal to the metal component through an external surface of the modular wind blade and receiving a reflected microwave signal, identifying a defect in the thermoplastic weld, and repairing the defect. The term "thermoplastic" refers to a polymer material that softens upon heating and hardens upon cooling. A thermoplastic material may be bonded to another material by heating and softening the thermoplastic material and optionally applying pressure in order to fuse the thermoplastic material to the other material. As used herein, a “thermoplastic weld” refers to a joint formed between two components by softening thermoplastic materials of the components with heat.
[0022] Methods for manufacturing, inspecting, and repairing modular wind blades are often tailored to suit their large structures. One approach to weld different sections of the modular wind blade is to indirectly heat the thermoplastic materials of the two sections of the modular wind blade and press them together. The thermoplastic weld described herein is formed by joining a first section and a second section of the modular wind blade by heating a metal component sandwiched between the first polymer component and the second polymer component. Resistive or inductive heating may be used for the welding process. High integrity of the formed thermoplastic welds is desirable for the integrity of the modular wind blade. Any defect in the metal component may result in insufficient bonding and a poor thermoplastic weld at that location. Hence a microwave reflection-based external inspection technique is employed for inspecting thermoplastic welds formed between the thermoplastic sections of modular wind blades.
[0023] Externally inspecting a thermoplastic weld is a non-destructive technique of evaluating the thermoplastic weld, without the need for a physical access to any internal portions of the components that are joined or the thermoplastic weld that is formed. According to the embodiments of the present disclosure, externally inspecting the thermoplastic weld includes transmitting a microwave signal from a microwave probe through an external surface of the modular wind blade to the metal component present in the thermoplastic weld and receiving the reflected signal. In some embodiments, the reflected microwave signal is received in the same microwave probe from which the microwave signal was transmitted. The reflected microwave signal may be evaluated and analyzed to identify a defect in the thermoplastic weld. Based on the identification of a defect in the thermoplastic weld, the identified defect may be repaired.
[0024] A schematic of a portion 100 of a modular wind blade that can be manufactured, inspected, and repaired-if needed, by the disclosed method is illustrated in FIG. 1. The portion 100 of the modular wind blade includes a first section 120 and a second section 130 joined through a thermoplastic weld 110. The thermoplastic weld 110 present between the first section 120 and the second section 130 is formed by heating a metal component 140 sandwiched between the first section 120 and the second section 130. Once the thermoplastic weld 110 is formed, the thermoplastic weld 110 includes the metal component 140.
[0025] The metal component 140 present in the thermoplastic weld 110 may be composed of any metal, alloy, or any other electrically conducting material that is able to effectively heat up and create the weld. In some embodiments, the metal component 140 includes openings facilitating contact of the first section 120 and the second section 130 through the metal component 140. In some embodiments, the metal component is a metal mesh that allows contact between the softened first section 120 and the softened second section 130. For example, the metal component 140 in the form of a metal mesh may be placed between the first section 120 and the second section 130, and the first section 120 and the second section 130 may be indirectly heated by heating the metal mesh. The heat dissipated from the metal mesh to the first section 120 and the second section 130 softens or melts joining surface of at least one of the first section 120 and the second section 130 and forms the thermoplastic weld 110 between the first section 120 and the second section 130.
[0026] The thermoplastic weld 110 present between the first section 120 and the second section 130, may be formed at more than one location in the modular wind blade. In the embodiment illustrated in FIG. 1, the thermoplastic weld 110 is formed between the first section 120 and the second section 130 at two locations. The first section 120 of the modular wind blade has an internal surface 122 and an external surface 124. The second section 130 of the modular wind blade has an internal surface 132 and an external surface 134. The internal surface 122 of the first section 120 and the internal surface 132 of the second section 130 join at a first location 125 and further at a second location 135. In the first location 125, a thick portion of the first section 120 is joined to a thin portion of the second section 130. In a second location 135, a thin portion of the first section 120 is joined to a thick portion of the second section 130. A microwave probe 60 is employed for the external inspection of the thermoplastic weld 110. The microwave probe 60 transmits microwave signal 62 and collects the reflected microwave signal 64 as the probe is scanned over the surface. The transmitted microwave signal 62 passes through an external surface of the modular wind blade. In the illustrated embodiment of FIG. 1, the transmitted microwave signal 62 passes through an external surface 124 of the first section 120 of the modular wind blade. Alternately or additionally, the microwave probe 60 may be positioned on the side of the second section 130 of the modular wind blade and the microwave signal 62 may be transmitted through an external surface 134 of the second section 130.
[0027] The microwave probe 60 may be moved in the direction of 80 and transverse to the direction 80, to inspect maximum area of the thermoplastic weld 110. The probe may be used to run a line scan or a two-dimensional raster scan to provide images of the scanned area. A microwave power used for the external inspection of the thermoplastic weld 110 may vary depending on the microwave loss of the material of the wind blade, thickness of the material and the operating frequency. In some embodiments, the microwave power used for the external inspection of the thermoplastic weld 110 is in range of few milliwatts. In some embodiments, the microwave power used for external inspection of the thermoplastic weld 110 is less than 50 milliwatts. In a non-limiting example, the range of microwave power needed for the external inspection of a 42 mm thick section of a modular wind turbine blade is less than 5mW.
[0028] In some embodiments, both transmitting the microwave signal and receiving the reflected microwave signal is through a same external surface of the modular wind blade. For example, in the embodiments illustrated in FIG. 1, the reflected microwave signal 64 at both the locations 125 and 135 can be measured by the microwave probe 60, by transmitting microwave signal through the external surface 124 of the first section 120 and receiving the reflected microwave signal 64 through the external surface 124. In these embodiments, the microwave signal is transmitted from the microwave probe 60 through the first section 120 and the reflected microwave signal 64 is received through the same first section 120 of the modular wind blade.
[0029] In some embodiments, modular wind blades are formed of polymer composites having reinforced fibers. Thus, in some embodiments of the disclosed method, a section of the modular wind blade through which the microwave signal passes to the metal component 140 includes a composite having a thermoplastic polymer matrix and reinforcing fibers. In some embodiments, at least one of the first section 120 and the second section 130 includes a fiber reinforced microwave-transparent thermoplastic material matrix (not shown in figures). In some embodiments, glass fibers are used as the reinforcement material. The composite materials discussed herein are transparent to microwaves or have low loss for microwaves.
[0030] As used herein, a material is considered to be “microwave transparent”, if the material has a low loss for the incident microwave signal such that the transmitted microwave signal 62 can reach the metal component 140, get reflected from the metal component 140, and the reflected microwave signal can be detected and analyzed. In some embodiments, the method may be used to find a defect in a thermoplastic weld as long as the signal loss (determined by tan ?) of the incident microwave in the thermoplastic material is low enough that microwave can penetrate through the thickness of the thermoplastic material to the thermoplastic weld 110, get reflected, and detected.
[0031] Since the thermoplastic weld 110 present between the first section 120 and the second section 130 is formed by indirect heating of the thermoplastic materials by heating the metal component 140, an uneven heating of the metal component 140 would result in an uneven heating of the thermoplastic materials of the wind blade sections around the metal component 140 and thereby result in an uneven formation of the thermoplastic weld 110. A defect (not shown in FIG. 1) of the metal component 140 would result in a variation in heating around the defect, compared to the heating around rest of the metal component 140. This variation in heating would result in a defect in the thermoplastic weld 110. Therefore, if a defect of the metal component 140 at a local region is identified, the resultant defect in the thermoplastic weld 110 at that local region can also be identified.
[0032] A defect of the metal component 140 may be a presence, size, shape, type or number of occurrences of a defect in the metal component 140, an inclusion present on the metal component 140, or a combination thereof. As used herein, an “inclusion” refers to an obstruction that affects heat-transfer from the heated metal component 140 to the at least one of the first section 120 and the second section 130.
[0033] In some embodiments, identifying the defect of the metal component 140 includes determining presence of a defect in the metal component 140, determining a size, shape, type, or number of occurrences of the defect present in the metal component 140, determining an inclusion present on the metal component 140, or any combinations thereof. In some embodiments, identifying a defect in the thermoplastic weld 110 includes determining presence of a defect in the thermoplastic weld 110, determining a size, shape, type, or number of occurrences of the defect present in the thermoplastic weld 110, or a combination thereof. The reflected microwave signal 64 is analyzed with respect to the transmitted microwave signal 62 to identify the defect in the metal component 140 and thereby identify a defect in thermoplastic weld 110.
[0034] In some embodiments, identifying a defect in the thermoplastic weld 110 includes measuring a reflection coefficient of the reflected microwave signal 64. As used herein, a “reflection coefficient” of the reflected microwave signal 64 is the ratio of the amplitude of the reflected microwave signal to the amplitude of the incident microwave signal 62. In some embodiments, the reflection coefficient is a complex reflection coefficient that includes both amplitude and phase information of the reflected microwave signal 64 with respect to the incident signal 62. A reflection coefficient of the reflected microwave signal that includes reflection from the metal component 140 in the thermoplastic weld 110 is typically higher than the reflection coefficient of the reflected microwave signal that does not include a reflection from the metal component 140 in the thermoplastic weld 110. In some embodiments, identifying a defect in the thermoplastic weld includes comparing the reflected microwave signal 64 with a dynamic threshold value on the reflected microwave signal 64.
[0035] It is to be noted that for the first location 125 of the defect, in some embodiments, the transmitted microwave signal 62 travels through almost the entire thickness of the first section 120, gets reflected from the metal component 140, and the reflected microwave signal is received by the microwave probe 60. In some embodiments, a thickness of the first section 120 may be in a range from about 12 mm to about 43 mm. In some embodiments, depending on the energy of the incident microwave signal and microwave signal loss in the material of the first section 120, a thickness of the first section 120 may be in a range from about 30 mm to about 100 mm. The penetration of microwaves through this thickness and reflection of the microwave signal from the metal component aids microwave inspection at such a depth, still providing valuable information of the defect in the thermoplastic weld 110 at the first location 125. Achieving this depth of inspection with thermoplastic materials is challenging for conventional techniques such as ultrasound inspection.
[0036] In some embodiments described above, the method includes identifying the defect in the thermoplastic weld 110 at the time of formation of the thermoplastic weld 110 or immediately after the weld formation. The thermoplastic weld 110 is formed by heating the metal component 140 sandwiched between the first section 120 and the second section 130, as disclosed earlier. A method of externally inspecting the thermoplastic weld 110 during formation or immediately after the formation includes transmitting a microwave signal 62 from the microwave probe 60 through at least one of the first section 120 and the second section 130 to the metal component 140 during formation of the thermoplastic weld 110 or immediately thereafter, and receiving a reflected microwave signal 64. The method may be used at the time of joining two section 120, 130 to form the thermoplastic weld 110, by continuously monitoring for defects during formation of the thermoplastic weld 110 itself.
[0037] As used herein, inspecting “immediately after formation of the thermoplastic weld” refers to inspecting the just-joined thermoplastic weld 110, before cooling of the entire thermoplastic weld 110 to the room temperature. In an example embodiment, robotic arms may be equipped with resistive or induction heating coils and the microwave probe 60 so that the metal component 140 may be heated to indirectly heat the first section 120 and/or the second section 130 for joining, while also measuring the defect in the just formed thermoplastic weld 110 by inspecting using the microwave probe 60. In some embodiments, a temperature of the thermoplastic weld 110 during formation of the thermoplastic weld 110 may be greater than 100 degrees Celsius, and the method includes externally inspecting and evaluating the results, when the thermoplastic weld 110 is heated to such temperatures. In some embodiments, inspecting the reflected microwave signal during or immediately after the joint formation includes automatically detecting the defect of the metal component 140 through a thresholding scheme. Identifying defects during formation or immediately after formation of the thermoplastic weld 110 may be advantageous to repair the defects in the thermoplastic weld 110 of large structures, such as, for example, modular wind blades, as and when they are getting formed, and before the welds are subjected to actual use. Defect, if detected in the thermoplastic weld 110, may be repaired using one or more of several methods for local treatment of the thermoplastic materials near the defect, including, but not limited to, local heating the metal component 140 to a higher temperature.
[0038] In some embodiments, the above-mentioned method may be used to ascertain an absence of defect in the thermoplastic weld 110 so that the modular wind blade having the joined first section 120 and the second section 130 is ascertained to be defect-free, before putting the modular wind blade to use. As used herein a formed thermoplastic weld 110 is referred to be defect-free, if the identified defect in the thermoplastic weld 110 may not hinder operation of the modular wind blade in its expected operation duration.
[0039] In some embodiments, the disclosed method is used for externally inspecting the thermoplastic weld in previously manufactured modular wind blades. Continuing to refer to FIG. 1, in some specific embodiments, the method of externally inspecting the thermoplastic weld 110 using a microwave probe 60 may be used to inspect the thermoplastic weld 110 that is previously formed by joining the first section 120 and the second section 130 of the modular wind blade by heating the metal component 140 sandwiched therebetween. The method for externally inspecting includes transmitting a microwave signal 62 to the metal component 140 through an external surface 124 of the modular wind blade and receiving a reflected microwave signal 64, measuring a reflection coefficient of the reflected microwave signal 64, and ascertaining a defect-free thermoplastic weld 110 or identifying a defect in the thermoplastic weld 110.
[0040] While the above-described embodiments are specific to the external inspection of the thermoplastic welds in large structures such as in modular wind blades, the above-described method of external inspection may be used in any thermoplastic weld formed by heating a metal component sandwiched between two polymer components. According to some embodiments of the present disclosure, a method for externally inspecting a thermoplastic weld is described. The method includes externally inspecting the thermoplastic weld by using a microwave probe and evaluating the results obtained by the microwave inspection. The thermoplastic weld, under inspection, is formed by joining two polymer components, by heating the metal component disposed therebetween. The polymer components include a thermoplastic material at their joining surfaces. The thermoplastic material present at the joining surface of a first polymer component may be same as, or different from, a thermoplastic material present at the joining surface of a second polymer component. The metal component may be heated and the heat from the metal component is used to soften the thermoplastic material for joining the first polymer component and the second polymer component. The thermoplastic weld under external inspection may be a previously manufactured thermoplastic weld or may be the thermoplastic weld under inspection during the manufacturing of the thermoplastic weld.
[0041] The method of externally inspecting includes transmitting a microwave signal to the thermoplastic weld, receiving a reflected microwave signal and analyzing the reflected microwave signal. The reflected microwave signal from the thermoplastic weld includes reflected microwave signal from the metal component that is heated to form the thermoplastic weld. In some embodiments, the method includes transmitting the microwave signal to the metal component through an external surface of the polymer components and receiving a reflected microwave signal, measuring a reflection coefficient of the reflected microwave signal, and ascertaining a defect-free thermoplastic weld or identifying a defect in the thermoplastic weld.
[0042] According to some embodiments of the present disclosure, externally inspecting the thermoplastic weld includes transmitting a microwave signal through at least one of the first polymer component and the second polymer component to the metal component. In some embodiments, the method includes externally inspecting from one side of the thermoplastic weld, thus essentially conducting a one-sided inspection of the thermoplastic weld. In these embodiments, the externally inspecting includes transmitting the microwave signal from the microwave probe through one of the first polymer component and the second polymer component and receiving the reflected microwave signal at the same microwave probe, via the same polymer component through which the microwave signal was transmitted. In some embodiments, the microwave signal is transmitted only through the first polymer component to the metal component and the reflected microwave signal is evaluated. In some other embodiments, the microwave signal is transmitted only through the second polymer component to the metal component and the reflected microwave signal is evaluated. In certain embodiments, one microwave probe may transmit a microwave signal through the first polymer component to the metal component and another microwave probe may transmit another microwave signal through the second polymer component to the same metal component. The reflected microwave signals from both sides may be collected individually and compared to get better clarity on the defects associated with the metal component.
[0043] FIG. 2 schematically illustrates a thermoplastic weld 210 between a first polymer component 220 and a second polymer component 230. FIG. 2 further illustrates a microwave inspection system 50 configured to externally inspect the thermoplastic weld 210, according to some methods described in this disclosure. The thermoplastic weld 210 is a joined region of the first polymer component 220 and the second polymer component 230, further including the metal component 240.
[0044] The microwave inspection system 50 is designed to detect a defect in the thermoplastic weld 210. The microwave inspection system 50 includes a microwave probe 60 and an analyzer 70. In FIG. 2, the microwave probe 60 is configured to transmit a microwave signal 62 through the first polymer component 220 to the metal component 240 and receive a reflected microwave signal 64 in the microwave probe 60.
[0045] The first polymer component 220 and the second polymer component 230 may be any polymer components that can be joined to form the thermoplastic weld 210. In some embodiments, at least one of the first polymer component 220 and the second polymer component 230 includes a microwave transparent thermoplastic material.
[0046] In some embodiments, the first polymer component 220, the second polymer component 230, or both may include a composite material. In some embodiments, at least one of the first polymer component 220 and the second polymer component 230 is a polymer composite including reinforcement fibers. The reinforcement fibers may be present in a matrix of the microwave transparent thermoplastic material. In some embodiments, the at least one of the first polymer component 220 and the second polymer component 230 includes a reinforcement that has low incident microwave signal loss such that the polymer component including the reinforcement fibers is microwave transparent. In some embodiments, the first polymer component 220, the second polymer component 230, or both the first and the second polymer components are sections of a modular wind blade that are joined together to form a modular wind blade, as previously described.
[0047] The metal component 240 present in the thermoplastic weld 210 may be composed of any metal or alloy. In some embodiments, the metal component 240 is a metal mesh. The metal component 240 in the form of a metal mesh may be placed between the first polymer component 220 and the second polymer component 230, and the first polymer component 220 and the second polymer component 230 may be indirectly heated by heating the metal mesh. The heat from the metal mesh to the first polymer component 220 and the second polymer component 230 softens or melts joining surface of at least one of the first polymer component 220 and the second polymer component 230 and forms the thermoplastic weld 210 between the first polymer component 220 and the second polymer component 230.
[0048] A defect of the metal component 240 may be a presence, size, shape, type or number of occurrences of a defect 246 in the metal component 240, an inclusion present on the metal component 240, or a combination thereof. A method of identifying a defect of the metal component 240 includes determining the presence of a defect 246 in the metal component, determining a size, shape, type or number of occurrences of the defect 246 present in the metal component 240, determining an inclusion present on the metal component 240, or any combinations thereof.
[0049] The defect 246 in the metal component 240 is a discontinuity present in the structure of the metal component 240. Since the metal component 240 is used for joining the first polymer component 220 and the second polymer component 230 to form the thermoplastic weld 210, a defect 246 in the metal component 240 may directly translate to irregular heating of the first polymer component 220, the second polymer component 230, or both, in the vicinity of the defect 246; and thus, create a defect 216 in the thermoplastic weld 210. Non-limiting examples for a defect 246 in the metal component include a hole or a tear, in the metal component 240.
[0050] A defect 248 of the metal component 240 may be an inclusion of an external material that is present in the proximity of the metal component 240. As used herein, an external material is a material that is not part of the metal component 240 or an intended material of the first polymer component 220, the second polymer component 230, or the thermoplastic weld 210. The intended material of the first polymer component 220, the second polymer component 230, or the thermoplastic weld 210 is the material that is intentionally added while forming these parts. A presence of an inclusion, depending on its thermal conductivity characteristics, may impede joining of the first polymer component 220 and the second polymer component 230 during the formation of the thermoplastic weld 210. Examples for a defect 248 include, but are not limited to, unintended inclusions during manufacturing process like piece of a glove or a tape, or any combination thereof.
[0051] A defect of the thermoplastic weld 210 is different from the defect 246, 248 of the metallic component 240, yet have a direct relationship with the defect 246, 248 of the metal component 240. The defect in the thermoplastic weld 210 may be any inconsistency in the formed thermoplastic weld 210. For example, a gap in the thermoplastic weld 210, a thermoplastic weld 210 of lower strength as compared to an average expected strength of the thermoplastic weld 210, or a combination thereof may be considered as a defect in the thermoplastic weld 210. A defect 216 of the thermoplastic weld 210 may be formed as a result of the defect 246 associated with the metal component 240 and may be a lack of joining or formation of a weak joint between the first polymer component 220 and the second polymer component 230. For example, a defect 246 in the metal component 240 would reduce the local heat transferred to the first polymer component 220 and the second polymer component 230. This reduced heat may, in effect, result in a weak thermoplastic weld 210, at that localized region. Thus, a defect 246 in the metal component 240 has a direct relationship with the defect 216 in the thermoplastic weld 210. Defect 248 in the form of an external inclusion on the metal component 240 may also impede the transfer of heat from the metal component 240 to the first polymer component 220 or the second polymer component 230, depending on the location of the external inclusion in the thermoplastic weld 210, and thereby result in formation of a potentially weak thermoplastic weld 210. A defect 249 may be formed in the thermoplastic weld 210 as a result of the defect 248 of the metal component 240 and may include an external material, along with the lack of joining or the formation of a weak joint. In the present disclosure, these relationships between the defects 246, 248 of the metal component 240 and the defect 216, 249 of the thermoplastic weld 210 respectively, are effectively used in identifying the defect in the thermoplastic weld 210.
[0052] Generally, microwaves are reflected from any interface where two materials, having different dielectric permittivity, meet. Therefore, continuing to refer to FIG. 2, depending on the material of the first polymer component 220, the reflected microwave signal 64 may include a reflected signal from one or more of: an interface within the first polymer component 220, an interface between the first polymer component 220 and the thermoplastic weld 210, or interfaces between the polymer materials of the thermoplastic weld 210 and the metal component 240 of the thermoplastic weld 210. Thus, the reflected microwave signal 64 includes the reflection of the transmitted microwave signal 62 from a first surface 242 of the metal component 240 in the thermoplastic weld 210. The reflected microwave signal 64 may further include signals reflected from any fiber reinforcements in the first polymer component 220, if present, and any signals reflected from the polymer materials of the thermoplastic weld 210, in addition to the reflection from the first surface 242 of the metal component 240. However, the signal reflected from the first surface 242 of the metal component 240 is stronger, in comparison with the other, above-mentioned reflected signals included in the reflected microwave signal 64. Therefore, the defects associated with the metal component 240 can be clearly distinguished. In some embodiments, depending on the dielectric characteristics of any inclusion, if present, the reflected microwave signal 64 may further include additional signals reflected by the inclusion. The inclusions may further reduce the microwave signals reaching the first surface 242 of the metal component 240, thereby altering the net reflected microwave signal. This change in signal may further be used for analyzing the inclusions present over the metal component 240.
[0053] In some embodiments, the microwave probe 60 may be located at a distance “d” from a surface 222 of the first polymer component 220. In some embodiments, the distance d is greater than 10 millimeters. A microwave probe located at a distance d from the surface allows an inspection of the thermoplastic weld 210, even when the thermoplastic weld 210 is at a higher temperature than room temperature, without damaging the microwave probe 60. This can be particularly advantageous in an inspection of the thermoplastic weld 210 during formation or immediately after formation. For example, the first polymer component 220 may be at a temperature higher than the room temperature, when the thermoplastic weld 210 is being formed. Contacting a high temperature surface may damage the microwave probe 60. The capability of inspecting from a distance “d” from the surface 222 of the first polymer component is an added advantage of the currently disclosed inspection method. In some embodiments, the current method of inspection may be used when a temperature of the thermoplastic weld 210 during its formation, is greater than 100 degrees Celsius. In some other embodiments, the microwave probe is located adjacent to the surface 222 of the first polymer component.
[0054] The analyzer 70 is communicatively coupled to the microwave probe 60 and is configured to analyze the reflected microwave signal 64 and identify a defect of the metal component 240 based on a characteristic of the reflected microwave signal 64. In some embodiments, the analyzer 70 includes a vector network analyzer connected to the microwave probe 60 and measures the reflected signal. The analyzer 70 may further include electronic components such as a computer, for example.
[0055] The microwave signal 64 that is reflected from the thermoplastic weld is collected by the microwave probe 60 and is used for evaluating the results of external inspection. In accordance with embodiments of the present method of externally inspecting, evaluating the results of external inspection includes analyzing the reflected microwave signal 64 to identify the defect of the metal component 240 and identifying the defect in the thermoplastic weld 210 based on the identified defect of the metal component 240.
[0056] Analyzing the reflected microwave signal 64 assists in identifying the defects in the thermoplastic weld 210. Analyzing the defects 246, 248 of the metal component 240 aids in qualitatively and quantitatively identifying the corresponding defect 216, 249 in the thermoplastic weld 210. A defect in the thermoplastic weld 10 may be a presence, size, shape, type or number of occurrences of a defect 216, 249 in the thermoplastic weld 210. A method of identifying a defect in the thermoplastic weld 210 includes determining a presence of a defect 216, 249 in the thermoplastic weld 210, determining a size, shape, type or number of occurrences of the defect 216, 249 present in the thermoplastic weld 210, or a combination thereof.
[0057] Reflection characteristics of the defects 246, 248 associated with the metal component 240 may also vary. For example, a defect 246 in a metal mesh, such as a hole or tear may result in reduced reflection from that portion of the metal mesh, and thus provide a direct indication of absence of a metallic material in that portion. This, in turn, may provide an indication of improperly joined portions in the thermoplastic weld 210 or weaker thermoplastic welds at the corresponding location in the thermoplastic weld 210. A defect 248, such as, for example, external material inclusion on the metal component 240, may result in a reflected signal 64 that includes an additional signal that is reflected from the boundary of thermoplastic material and the external material inclusion, as noted earlier. Further, in some embodiments, an undulation generated in the thermoplastic weld 210, due to an inclusion of external material on the metal component 240, may also provide a variation in the reflected signal 64, thereby indicating a change in the quality of the thermoplastic weld at that location.
[0058] Various methods may be used to analyze the reflected microwave signal 64 from the metal component 240 to detect the defect of the metal component 240. In some embodiments, an energy transmitted via the reflected microwave signal may be converted into an output voltage signal. The resulting voltage may be sampled at discrete locations of the thermoplastic weld or may be collected continuously across the weld. In some embodiments, the method of analyzing includes visual inspection. The visual inspection may be a visual characterization of the output voltage signals of the reflected signals on a screen and taking a decision on the presence, type, or number of defects associated with the metal component 240. In some embodiments, the method of analyzing is through an automatic detection. In certain embodiments, identifying the defect in the thermoplastic weld 210 is through a thresholding scheme, by comparing the reflected microwave signal 64 with a dynamic threshold value on the reflected microwave signal 64. In a thresholding scheme, a threshold value of a reflection coefficient for a local region, with respect to a mean value of the reflection coefficient of the local region, may be identified such that a reflection coefficient less than the threshold value for the microwave signal reflected from that local region indicates a presence of a defect associated with that local region of the metal component. Using thresholds with respect to local means can be helpful in dealing with background signal variations in the thermoplastic sample.
[0059] As discussed earlier, the defect in the thermoplastic weld 210 may be identified based on the defect of the metal component 240. This may be carried out through various methods. In some embodiments, identifying the defect in the thermoplastic weld 210 based on the identified defect of the metal component 240 includes visual inspection of the reflected signal, ascribing that to a defect of the metal component 240 and taking a decision regarding the defect present in the thermoplastic weld 210. As discussed earlier, the disclosed method may be used to identify various defects in the thermoplastic weld 210. In some embodiments, the method includes determining presence of a defect in the thermoplastic weld 210, a size, a shape, type or number of occurrences of the defect present in the thermoplastic weld 210, or any combinations thereof.
[0060] Embodiments of the present disclosure are directed to a method for identifying a defect in a thermoplastic weld by identifying a defect of the metal component present in the thermoplastic weld. The discussed method is clearly different from the current, conventionally known methods of external inspection of thermoplastic welds. The currently known conventional techniques of external inspection of the thermoplastic welds are typically based on the ultrasound, infrared, or microwave signals attenuated, transmitted, or reflected from the thermoplastic materials of the weld. In contrast, the disclosed method includes assessing reflected microwave signal from the metal component that is used for forming the thermoplastic weld. The presence of the metal component in the thermoplastic weld gives strong reflection signals that get altered by the presence of associated defects and enables easier detection of defects associated with the metal component. Other advantages of the disclosed method include, but are not limited to, possibility of non-contact inspection, one sided inspection, use of non-harmful radiation for the inspection, possibility of in situ inspection at high temperatures, capability to obtain image of the defect, possible large area coverage through the usage of array of sensors, and possibility of complete automation of the inspection.
EXAMPLES
[0061] The following examples are presented to further illustrate non-limiting embodiments of the present disclosure.
[0062] Two thermoplastic weld samples were prepared. Thermoplastic components that were welded together had a thickness varying from about 12 mm to 43mm. Metal meshes were used for joining the thermoplastic materials. A metal mesh having a defect in the form of a hole was used for forming of a first thermoplastic weld and another metal mesh having a defect in the form of a tear was used for forming a second thermoplastic weld. The thermoplastic welds were inspected by ultrasound inspection techniques and by microwave reflection methods. FIG. 3A shows a photograph of the mesh that is used for forming the first thermoplastic weld sample. FIG. 3B illustrates the results of an ultrasound inspection carried out on the first thermoplastic weld sample at 10 MHz, at a location equivalent to the second location 135, shown in FIG. 1. Higher and lower frequencies were also used for ultrasound inspection; however, the hole defect was not clearly distinguishable using those frequencies as well.
[0063] Microwave inspection of the first thermoplastic weld sample was carried out by using a Ku band (12-18 GHz) waveguide adapter. The waveguide was attached to a scanner and connected to a vector network analyzer. The probe was excited over a range of frequencies. Experiments were carried out in the reflection mode enabling one-sided inspection. Sensors were kept at different distances (stand-offs) from the metal mesh and the effect of stand-off and frequency were studied. Optimal frequencies for various stand-offs giving best contrast between defective and non-defective areas were determined.
[0064] FIG. 3C illustrates an image obtained by the external inspection of the first thermoplastic weld sample by using the microwave probe at 17.37 GHz, at a location equivalent to the second location 135 shown in FIG. 1. In the image 3B obtained by the ultrasound inspection, it was very difficult to ascertain the position of the hole in the metal mesh, while the hole was readily recognizable in Fig. 3C obtained by the microwave inspection. FIG. 3D is an image obtained by the external inspection of the first thermoplastic weld sample by using the microwave probe at 17.37 GHz, at a location equivalent to the first location 125, shown in FIG. 1. Thus, in the image obtained by one-sided inspection of the thermoplastic weld, the transmitted microwave had to travel through the thickness of the one of the thermoplastic component for the collection of the reflected signal. However, even the image obtained at such a depth clearly showed the defect (hole) in the metal mesh that is embedded in the first thermoplastic weld.
[0065] FIG. 4A shows a photograph of the tear in the metal mesh used for forming the second thermoplastic weld. FIG. 4B illustrates the results of an ultrasound inspection carried out at 20 MHz on the metal mesh containing the tear, at a location equivalent to the second location 135, shown in FIG. 1. Higher and lower frequencies were also used for ultrasound inspection, however the tear in the metal mesh was not clearly distinguishable using those frequencies as well. Microwave inspection of the second thermoplastic weld sample was carried out by using a Ku band (12-18 GHz) waveguide adapter by exciting the probe over a range of frequencies. Experiments were carried out in the reflection mode and the sensors were kept at different stand-offs from the metal mesh. Optimal frequencies for various stand-offs giving best contrast between defective and non-defective areas were determined.
[0066] FIG. 4C illustrates an image obtained by the external inspection of the second thermoplastic weld sample by using the microwave probe at 17.37 GHz, at a location equivalent to the second location 135, shown in FIG. 1. In the image in FIG.4B obtained by the ultrasound inspection, it was very difficult to ascertain the position of the tear in the metal mesh, while the tear was readily recognizable in the image in FIG.4C obtained by the microwave inspection. Therefore, a defect in the metal part could be more clearly identified by the microwave reflection method as compared to the results obtained by the ultrasound inspection method. This advantage of the microwave inspection can be readily utilized in identifying defects in the thermoplastic welds.
[0067] This written description uses some examples to disclose the claimed disclosure, including the best mode, to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The scope of the claimed disclosure may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the appended claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.