Method and Means to Analyze Thermographic Data Acquired During Automated Fiber Placement

NASA's new calibration system is a proprietary method to quickly design and make predictable and repeatable gap-and-overlap defects when employing AFP. The system creates defects within the course of layup with known sizes, geometries, and locations. Using this defect-creation technique, one can now accurately quantify the ability to detect defects on inspection systems, perform accurate risk assessments, and calibrate in-situ inspection equipment to specific materials. The equipment that makes the defects can be efficiently and inexpensively 3D printed. This technique is currently being used to successfully calibrate NASA's in situ inspection system for their AFP equipment. AFP is experiencing increasing adoption in aerospace, automotive, and other industries that leverage large-scale advanced composite components. NASA's new AFP calibration system could be very useful to companies that develop and manufacture AFP machines or AFP machine inspection equipment to improve the quality of their products in a provable manner. Furthermore, users of AFP machines may find value in the tool for creating their own calibration standards.

This NASA invention enables several benefits that mitigate limitations associated with conventional ATP systems, including the following: (1) avoids obtuse head rotation or cross-tool translation when laying adjunct tape plies, (2) simultaneously places tape on both sides of a part via two robots, (3) eliminates external anchoring frame requirements, and (4) translates parts during build while also translating the applicator head. The ability to perform simultaneous layup on opposite sides of the component, as well as reduction of head rotation reversal during bidirectional tape layup, offers increased layup speed. The invention offers increased placement accuracy as a result of reduced movement between tape layup operations and the eliminated need for an anchoring frame (facilitated by simultaneous pressure extrusion of prepreg by the two robots). NASAs automated tow/tape placement system has two key unique features: the use of two opposed ATP cars to enable a tool-less process, and an on-the-fly reversal tape/tow laydown tooling head. The system uses two opposing (i.e., underside-to-underside) ATP cars, and can build parts vertically, horizontally, or at any other angle, depending on the workspace available. The ATP die wheels can be reversed or turned to draw the composite back and forth at different angles to create a layer-by-layer composite structure. Both cars can dispense TPC tape thus, either car can function as an opposing tool surface while the other performs prepreg lay-up. For structures that do not vary in thickness, both cars can lay tape at the same time doubling layup speed. Current ATP robots must rotate the large tooling head, or traverse panels without layering tape to achieve bidirectional layup, where each additional movement introduces alignment error. To increase layup rate while simultaneously minimizing misalignment, NASAs system incorporates an on-the-fly reversal tape/tow laydown tooling head to enable efficient bidirectional layup.

This system connects the properties of the guided waves to the phase changes of a composite part. The system measures temperature, strain, and guided waves during cure almost simultaneously. During life-cycle monitoring, it is feasible to use embedded fiber optic sensors for both load monitoring because of the ability to measure strain and damage detection because of the ability to record ultrasonic guided waves. The guided wave system is incorporated directly into standard curing equipment and technique. It has also been tested and works with flat panels as well as complex structures. The technology would be valuable to manufacturers of aircraft parts (fuselage, wing and other sections), marine hull sections, high speed rail sections, automotive parts and perhaps even building parts. One major application that exists presently, is the fabrication of fuselage and wing sections for aircraft where carbon fiber composite sections are used such as Boeing's 787 Dreamliner.

NASA's novel method was developed to more accurately measure the position and shape of optical fibers. Multi-core optical fibers contain multiple light-guiding cores arranged symmetrically. Sensors, such as FBGs, are embedded into each of the cores (Figure 1). Such an arrangement allows for the measurement of strain in each core of the fiber at specific axial locations along the fiber. When a multi-core fiber is subjected to bending, the strain imposed in each core relative to one another is used to provide position information (Figure 2). In the past, shape-sensing measurements using optical fibers estimated bending at sequential points along the fiber, and the resulting measurement had many discontinuities and errors. The combination of these errors resulted in a very poor indication of actual fiber position in three-dimensional space. NASA's patent-pending algorithms and apparatus incorporate not only fiber bending measurements, but fiber twisting measurements as well, to eliminate previous sources of error. The uniqueness of the algorithm is in how the curvature, bend-direction, and twisting information of the fiber are all brought together to obtain a highly accurate 3-D location and shape characterization. The new methods have been demonstrated to significantly improve the accuracy of multi-core fiber optic shape sensors.

The FOSS technology revolutionizes fiber optic sensing by using its innovative algorithms to calculate a range of useful parameters—any and all of which can be monitored simultaneously and in real time. FOSS also couples these cutting-edge algorithms with a high-speed, low-cost processing platform and interrogator to create a single, robust, stand-alone instrumentation system. The system distributes thousands of sensors in a vast network—much like the human body's nervous system—that provides valuable information. How It Works Fiber Bragg grating (FBG) sensors are embedded in an optical fiber at intervals as small as 0.25 inches, which is then attached to or integrated into the structure. An innovative, low-cost, temperature-tuned distributed feedback (DFB) laser with no moving parts interrogates the FBG sensors as they respond to changes in optical wavelength resulting from stress or pressure on the structure, sending the data to a processing system. Unique algorithms correlate optical response to displacement data, calculating the shape and movement of the optical fiber (and, by extension, the structure) in real time, without affecting the structure's intrinsic properties. The system uses these data to calculate additional parameters, displaying parameters such as 2D and 3D shape/position, temperature, liquid level, stiffness, strength, pressure, stress, and operational loads. Why It Is Better FOSS monitors strain, stresses, structural instabilities, temperature distributions, and a plethora of other engineering measurements in real time with a single instrumentation system weighing less than 10 pounds. FOSS can also discern between liquid and gas states in a tank or other container, providing accurate measurements at 0.25-inch intervals. Adaptive spatial resolution features enable faster signal processing and precision measurement only when and where it is needed, saving time and resources. As a result, FOSS lends itself well to long-term bandwidth-limited monitoring of structures that experience few variations but could be vulnerable as anomalies occur (e.g., a bridge stressed by strong wind gusts or an earthquake). As a single example of the value FOSS can provide, consider oil and gas drilling applications. The FOSS technology could be incorporated into specialized drill heads to sense drill direction as well as temperature and pressure. Because FOSS accurately determines the drill shape, users can position the drill head exactly as needed. Temperature and pressure indicate the health of the drill. This type of strain and temperature monitoring could also be applied to sophisticated industrial bore scope usage in drilling and exploration. For more information about the full portfolio of FOSS technologies, see visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing