In-situ Characterization and Inspection of Additive Manufacturing Deposits using Transient Infrared Thermography

This technology provides comprehensive, detailed, and accurate NDE detection and characterization of subsurface defects in composites and some metallic hardware. This complete software suite normalizes and calibrates the data, which provides more stable measurements and reduces the occurrence of errors due to the operator and to camera variability. When using flash IR thermography to evaluate materials, variations in the thermal diffusivity of the material manifest themselves as anomalies in the IR image of the test surface. Post-processing of this raw IR camera data provides highly detailed analysis of the size and characterization of anomalies. The newly incorporated Transient and Lock-In Thermography methods allow the analysis of thicker material and with better flaw resolution than Flash Thermography alone. The peak contrast and peak contrast time profiles generated through this analysis provide quantitative interpretation of the images, including detailed information about the size and shape of the anomalies. The persistence energy and persistence time profiles provide highly sensitive data for detected anomalies. Peak contrast, peak time, persistence time, and persistence energy measurements also enable monitoring for flaw growth and signal response to flaw size analysis. This technology is at a technology readiness level (TRL) of 7 (system prototype demonstration in an operational environment), and the innovation is now available for your company to license. Please note that NASA does not manufacture products itself for commercial sale.

The in situ inspection technology for additive manufacturing combines different types of cameras strategically placed around the part to monitor its properties during construction. The IR cameras collect accurate temperature data to validate thermal math models, while the visual cameras obtain highly detailed data at the exact location of the laser to build accurate, as-built geometric models. Furthermore, certain adopted techniques (e.g., single to grouped pixels comparison to avoid bad/biased pixels) reduce false positive readings. NASA has developed and tested prototypes in both laser-sintered plastic and metal processes. The technology detected errors due to stray powder sparking and material layer lifts. Furthermore, the technology has the potential to detect anomalies in the property profile that are caused by errors due to stress, power density issues, incomplete melting, voids, incomplete fill, and layer lift-up. Three-dimensional models of the printed parts were reconstructed using only the collected data, which demonstrates the success and potential of the technology to provide a deeper understanding of the laser-metal interactions. By monitoring the print, layer by layer, in real-time, users can pause the process and make corrections to the build as needed, reducing material, energy, and time wasted in nonconforming parts.

Modeling additive manufacturing processes can be difficult due to the scale difference between the active processing point (e.g., a sub-millimeter melt pool) and the part itself. Typically, the tools used to model these processes are either too computationally intensive (due to high physical fidelity or inefficient computations) or are focused solely on either the microscale (e.g., microstructure) or macroscale (e.g., cracks). These pitfalls make the tools unsuitable for fast and efficient evaluations of additive manufacturing build files and parts. Failures in parts made by laser powder bed fusion (L-PBF) often come when there is a lack of fusion or overheating of the metal powder that causes areas of high porosity. AM-PM uses a point field-based method to model L-PBF process conditions from either the build instructions (pre-build) or in situ measurements (during the build). The AM-PM modeling technique has been tested in several builds including a Ti-6Al-4V test article that was divided into 16 parts, each with different build conditions. With AM-PM, calculations are performed faster than similar methods and the technique can be generalized to other additive manufacturing processes. The AM-PM method is at technology readiness level (TRL) 6 (system/subsystem model or prototype demonstration in a relevant environment) and is available for patent licensing.

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.

This technology provides a methodology to measure damage onset and grow at multiple locations in a composite structure during fatigue loading. The thermography inspection is non-contact and can cover very large areas. The acoustic emission sensors require contact at only the sensor attachment points and can cover large areas. The acoustic emission measurement is very sensitive to damage formation events such as matrix cracking, fiber breaks, and delamination, however the event location is approximate. An infrared camera is able to detect damage growth and location at areas of heating (due to fiber breaks, rubbing of disbond areas and matrix cracks) and thus confirm the acoustic emission measurements. If the loading is cyclic the infrared camera is also able to detect the relative depth of the damage. Combining both technologies helps to reduce false indications, confirm damage growth areas and where ultimate failure will occur. This provides a measurement capability to detect growing damage (location and size) for improved structures testing or during in-service applications. Multiple infrared (IR) cameras and multiple acoustic emission sensors can be employed internally or externally for full coverage of the structure. When significant damage growth is detected, the structure can be taken out of service for repair or for further inspections. This technology has been demonstrated for structures testing. In-situ NDE inspections are necessary to provide structural engineers a tool to incrementally control and document damage growth as a function of fatigue cycles before failure. This allows for the comparison of NDE results to develop and validate progressive damage analysis (PDA) models. The ultimate goal is to use the validated PDA models to decrease the time required to certify composite structures and therefore save development costs. Real time NDE can document the progression of damage and provide the documentation of ultimate failure mechanisms.