Multidimensional Damage Detection System

Guided wavefield techniques require excitation of guided waves in a specimen via contact or noncontact methods (such as attached piezoelectric transducers or laser generation). The resulting wavefield is recorded via noncontact methods such as laser Doppler vibrometry or air-coupled ultrasound. If the specimen contains damage, the waves will interact with that damage, resulting in an altered wavefield (compared to the pristine case). When guided wave modes enter into a delaminated region of a composite the energy is split above/below delaminations and travels through the material between delaminations. Some of the energy propagates beyond the delamination and re-emerges as the original guided wave modes. However, a portion of the wave energy is trapped as standing waves between delaminations. The trapped waves slowly leak from the delaminated region, but energy remains trapped for some time after the incident waves have propagated beyond the damage region. Simulation results show changes in the trapped energy at the composite surface when additional delaminations exist through the composite thickness. The results are a preliminary proof-of-concept for utilizing trapped energy measurements to identify the presence of hidden delaminations when only single-sided access is available to a component/vehicle. Currently, no other single-sided field-applicable NDT techniques exist for identifying hidden delamination damage.

NASA's System for In-situ Defect (e.g., porosity, fiber waviness) Detection in Composites During Cure consists of an ultrasonic portable automated C-Scan system with an attached ultrasonic contact probe. This scanner is placed inside of an insulated vessel that protects the temperature-sensitive components of the scanner. A liquid nitrogen cooling systems keeps the interior of the vessel below 38°C. A motorized X-Y raster scanner is mounted inside an unsealed cooling container made of porous insulation boards with a cantilever scanning arm protruding out of the cooling container through a slot. The cooling container that houses the X-Y raster scanner is periodically cooled using a liquid nitrogen (LN2) delivery system. Flexible bellows in the slot opening of the box minimize heat transfer between the box and the external autoclave environment. The box and scanning arm are located on a precision cast tool plate. A thin layer of ultrasonic couplant is placed between the transducer and the tool plate. The composite parts are vacuum bagged on the other side of the tool plate and inspected. The scanning system inside of the vessel is connected to the controller outside of the autoclave. The system can provide A-scan, B-scan, and C-scan images of the composite panel at multiple times during the cure process. The in-situ system provides higher resolution data to find, characterize, and track defects during cure better than other cure monitoring techniques. In addition, this system also shows the through-thickness location of any composite manufacturing defects during cure with real-time localization and tracking. This has been demonstrated for both intentionally introduced porosity (i.e., trapped during layup) as well processing induced porosity (e.g., resulting from uneven pressure distribution on a part). The technology can be used as a non-destructive evaluation system when making composite parts in in an oven or an autoclave, including thermosets, thermoplastics, composite laminates, high-temperature resins, and ceramics.

Glenn's breakthrough technology introduces batch-fabricated, miniature sensors embedded and distributed over a large surface area of a material or product during the manufacturing process. The sensors can be utilized for test instrumentation or as an integrated in-situ monitoring system. This integrated manufacturing approach preserves the structural and mechanical system integrity by eliminating the antiquated plug-in approach, invasive machining, manual insertion, and gluing processes currently required to implant sensors into a material. The sensor ladder network of resistors and capacitors breaks down as result of the thermo-physical effects caused by temperature, shock, radiation, corrosion, or other reactions, causing a change in the electrical properties. A processor interprets these changes in the electrical properties and generates a high-resolution, large-area surface profile. The profile demonstrates the amount or rate of material deterioration and temperature change, and is used to optimize geometric structural design, develop materials, predict performance, and make decisions. These sensors play an important role as industries work to realize material performance and product design. This type of monitoring is ideal for infrastructures, nuclear enclosures, or any system susceptible to surface deterioration.

The tester was designed to monitor electrical faults in either online or offline modes of operation. In the online mode, wires are monitored without disturbing their normal operation. A cable can be monitored several times per second in the offline mode, and once per second in the online mode. The online cable fault locator not only detects the occurrence of a fault, but also determines the type of fault (short/open/intermittent) and the location of the fault. This enables the detection of intermittent faults that can be repaired before they become serious problems. Since intermittent faults occur mainly during operations, a built-in memory device stores all relevant fault data. This data can be displayed in real time or retrieved later so maintenance and repairs can be completed without spending countless hours attempting to pinpoint the source of the problem. Hardware and algorithms have also been developed to safely, efficiently, and autonomously transfer electrical power and data connectivity from an identified damaged/defective wire in a cable to an alternate wire path. This portion of the system consists of master and slave units that provide the diagnostic and rerouting capabilities. A test pulse generated by the master unit is sent down an active wire being monitored by the slave unit. When the slave unit detects the test pulse, it routes the pulse back to the master unit through a communication wire. When the master unit determines that a test pulse is not being returned, it designates that wire as faulty and reroutes the circuit to a spare wire.

The NASA impactor is a fully portable device that propels an instrumented projectile so that it impacts a vehicle, structural component, or test specimen. The device includes a projectile inside an exterior tube. The projectile itself contains a commercial load cell designed to obtain the dynamic force response during the impact event. Furthermore, a digital oscilloscope and optical sensor are combined to measure the velocity just prior to impact so that the impact energy of the projectile onto the test surface can be calculated. In the current configuration, impacts with energies between 4 and 40 J (between about 3 and 30 ft-lbs) are obtainable, and could be adjusted by changing the spring to one with a different spring constant. The tube can be handheld or rigidly mounted at any angle such that the impact response can be evaluated at specified positions throughout the test article. The impactor device is primarily designed for use on composite structures to investigate the structural response from a low-velocity impact, as composite materials are highly susceptible to damage from low-velocity impacts where the damage may not be visible but results in great loss of strength. If the damage cannot be detected visually, it can be seen through nondestructive testing (ultrasonic, flash thermography or X-ray). However, the device may also be used on structures to evaluate and tune structural health monitoring systems. The technology has been designed, prototyped, and implemented in four military or government programs for impact testing on metallic and composite structures, including a helicopter roof in 2013. The cost of the parts for the prototype was approximately $9,000. Production costs are expected to be lower.