Patent Application
20070118313
The present disclosure relates to systems and methods for inspecting composite laminates, and more specifically, to improved systems and methods for detecting discontinuous fibers in composite laminates.
Composite laminates with discontinuous fibers (i.e. wrinkles) may adversely impact the strength of the laminate. Wrinkles that cause physical indentations on the surface of a laminate may be easily detected using visual methods. Wrinkles that occur internal to the composite laminate, however, may not be easy to detect due to the normal surface appearance produced during the manufacturing and cure cycle. In this case, there may be typically no indication that the structure has discontinuous fibers which may reduce the strength of the laminate.
A variety of systems and methods are known for inspecting composite materials using ultrasound. Such systems include, for example those pulse-echo systems generally disclosed in U.S. Pat. No. 6,874,365 B2 issued to Deveney et al., U.S. Pat. No. 6,041,020 issued to Caron et al., and U.S. Pat. No. 5,118,464 issued to Richardson et al., as well as those through-transmission systems generally disclosed in U.S. Pat. No. 6,484,583 B1 issued to Chennell et al. and U.S. Pat. No. 5,372,043 issued to Speight et al. Although desirable results have been achieved using such prior art systems, improved systems for detecting discontinuous fibers in composite laminates would have utility.
The present invention is directed to systems and methods for detecting discontinuous fibers in composite laminates. In one embodiment, a method of performing an ultrasonic inspection of a composite laminate includes transmitting an incident ultrasonic signal onto a front surface of the composite laminate at a plurality of locations over an area of interest, receiving a full waveform at each of the plurality of locations over the area of interest, storing the full waveform at each of the plurality of locations over the area of interest, and analyzing the full waveform at each of the plurality of locations over the area of interest for an amplitude distortion indicative of a fiber discontinuity within the composite laminate, including selecting a gate value corresponding to a depth location within the composite laminate and displaying a C-scan image of an amplitude value from the full waveform at the plurality of locations over the area of interest.
Embodiments of the present invention are described in detail below with reference to the following drawings.
The present invention relates to systems and methods for detecting discontinuous fibers in composite laminates. Many specific details of certain embodiments of the invention are set forth in the following description and in
In general, embodiments of the present invention may detect discontinuous fibers in composite laminates using ultrasonic signals and a software gating process that enables interrogation of the laminate at discrete depths. More specifically, embodiments of the invention may start with by collecting a full RF ultrasonic waveform for the composite laminate under inspection. The RF waveform may then be post-processed to produce a series of images that evaluates the RF signal amplitude at each layer within the composite laminate. An amplitude of the signal response at each layer indicates whether the signal is from the fibers within the laminate or from the thin layer of resin between plies within the laminate. At any given depth within the laminate where fiber distortion exists, the signal response may produce high and low amplitude values. In one particular embodiment, the high and low amplitude values of the signal response produce a Moray pattern in the C-scan data, as described more fully below.
The ultrasonic sensor 104 (and auxiliary ultrasonic sensor 105) may be coupled to a position control device 110 and to a data acquisition and control system 120. The position control device 110 is adapted to provide position control of the ultrasonic sensor 104 (and the auxiliary ultrasonic sensor 105) along the x, y, and z axes, and may be used to perform point measurements or x-y scanning measurements over the composite laminate 102. In one particular embodiment, the ultrasonic system 100 may include one or more hardware components commercially-available from UTEX Scientific Instruments, Inc. of Mississagua, Ontario, Canada.
As shown in
As further shown in
More specifically,
In general, in samples without wrinkles (or other defects, such as foreign material or delaminations), the amplitude response between the front and back surfaces 138, 140 typically appears as low-level noise, as depicted in the first C-scan image 406 shown in
In one particular embodiment, the incident ultrasonic signal 106 has a frequency of approximately 1.0 MHz, however, in alternate embodiments, the incident ultrasonic signal 106 may have a frequency within the range of approximately 0.1 MHz to 10 MHz, depending upon a variety of factors, including the material characteristics of the composite laminate 102. Of course, any other suitable frequencies of the incident ultrasonic signal 106 may be used. In addition, in some embodiments, the frequency bandwidth of the incident ultrasonic signal 106 may be adjusted to be a relatively broadband frequency bandwidth (e.g. approximately ±5%), however, in alternate embodiments, larger or smaller frequency bandwidths may be used.
Referring again to
It will be appreciated that the amplitudes of the RF waveform 300 at depths within the laminate may be relatively low compared to the amplitude perturbations 302, 306 caused by the front wall 138 and back wall 140 of the composite laminate 102. These low amplitudes may need to be enhanced in order to produce the sensitivity necessary to detect wrinkles in the composite laminate 102. In one particular embodiment, this enhancement is accomplished by adjusting (e.g. reducing) a color palette range 512 over a baseline RF signal 308 (
Similarly, at the third and fourth gate values 602, 702, the third and fourth C-scan images 606, 706 also show amplitude distortions indicative of the fiber wrinkle 510 within the composite laminate 102. In this way, the amplitude signals may be mapped along the z axis through the composite laminate 102. In a particular embodiment, one or more portions of the method 200 may be automated to enable the C-scan images to be displayed in succession (e.g. as a movie) starting at the front surface 138 and continuing through the composite laminate 102 to the back surface 140. After the analysis of the area of interest is complete (block 214), the method 200 is terminated at a block 206.
Referring again to
In operation, the data acquisition and control system 120 is adapted to perform a method of performing ultrasonic inspections of a composite laminate in accordance with the invention. For example, the operator 142 may input one or more control signals that cause the system 100 to scan the area of interest 144 and store the full RF waveform data from the area of interest 144 into the memory component 124. The operator 142 may then transmit a command which causes the CPU 122 to invoke the software product to automatically perform one or more of the acts described above without further action or intervention by the operator 142. More specifically, the data acquisition and control system 120 may invoke a set of software instructions (e.g. stored in the memory component 126) that causes the CPU 122 to perform one or more aspects of a method of performing ultrasonic inspections. Alternately, one or more aspects of the various processes described above may be implemented in the data acquisition and control system 120 using any suitable programmable or semi-programmable hardware components (e.g. EPROM components).
Embodiments of methods and systems for detecting wrinkles within composite laminates in accordance with the present invention may provide advantages over the prior art. Using Planer Peak Amplitude Mapping (described above) and a gating method which enables an operator to step through the RF waveform data through the depth of the composite laminate 102, embodiments of the present invention enable improved analysis, detection, and characterization of fiber discontinuities (or wrinkles) in comparison with the prior art. More specifically, prior art systems typically monitor a backwall signal via a gate which produces a C-scan image that measures the total energy loss of the incident ultrasonic signals 106 after it passes through the composite laminate 102. Embodiments of the present invention, however, enable the operator to efficiently analyze the amplitude response at specific or predefined depths within the composite laminate.
While preferred and alternate embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.
