The Southern Research Nondestructive Evaluation (NDE) group specializes in materials characterization and precision testing of materials and structures. Our experienced engineers and technicians have extensive expertise in physics, materials engineering, software development, and mathematics; we apply these specialized skills to provide diverse capabilities ranging from the application and development of NDE techniques to the characterization of advanced composite materials. We specialize in developing novel approaches and solutions for our clients’ most challenging projects.
Material Property Measurement
Tests are used to determine basic material properties that are compared to our extensive database of similar materials. Our measurement capabilities include:
- Density (by dimension and/or by immersion)
- Ultrasonic velocity (at room temperature and down to 100 K)
- Ultrasonic attenuation
- Open porosity
- Electrical resistivity (cryogenic and at room temperature; elevated temperatures can also be performed)
- Moisture diffusivity
This evaluation incorporates techniques to determine if defects exist in a material and to measure the size, type, and location of any located defects. For example, various tools are available to inspect pieces of materials for voids, delaminations, cracks, reinforcement orientation, and other defects. This allows for acceptance testing, intentional avoidance of nonstandard material, and/or intentional selection of odd material to better understand the material performance. SR utilizes the following material inspection techniques:
- C-scan (pulse echo and through transmission)
- Ultraspec – SR has developed and patented this unique ultrasonic evaluation tool using spectroscopy techniques. Ultrasonic spectroscopy is a quick and effective method to inspect materials for porosity, microcracking, defects, thickness, velocity, etc. Using a continuous swept-frequency input signal, the system can cover a wide range of frequencies without compromising energy. The higher energy results in an output signal with a robust signal-to-noise ratio in the frequency domain. Using a wide range of frequencies allows the user to pinpoint attenuation characteristics in real time.
SR performs in-house radiographic inspections using low-to medium-energy X-ray equipment; the resulting images are digitally enhanced to provide optimum viewing of material conditions such as voids, inclusions, and porosity. Special techniques are also employed to identify fiber orientation in composite materials.
- Medical CT
- “Micro” CT
- Digital enhancement
- Collimated Scanning Radiography (CSR)
- Capable of handling large parts in lead-lined room
- Microencapsulated – To supplement typical dye penetrant techniques, SR has developed a proprietary technique using fluorescent microcapsules tailored to specific size ranges with distinctive colors associated with the chosen range of particle size. The penetrant is an alcohol-based system in which 0.5 to 3 micron, 1 to 6 micron, and 5 to 15 micron diameter fluorescent microcapsules are suspended. Other size ranges and dyes can be produced on special order.
SR has developed a nondestructive method to characterize ply characteristics in carbon-based, composite materials. Eddy current is a measure of the electrical properties of a material; as such, its use for determining ply properties is also dependent on base material electrical properties. SR has developed a technique that is self-calibrating or self-adjusting to the composite electrical properties. The primary focus of our efforts to date have been to develop the most advanced eddy current probes, set up, and analysis techniques. The newly developed eddy current technique uses a custom-made probe that has significant orientation bias. The relative resistivity between the “across ply” and “with ply” directions allow calculation of ply angle and estimation of base conductivity.
- Ply angle
Based on our clients’ needs, we have expanded our instrumentation and metrology expertise to increase our understanding of how materials respond to load temperature. In some cases, we have created very specific systems to meet the needed performance. Our advanced capabilities include:
- Precision thermal expansion (PTE)
- Modal acoustic emission – SR has acquired a four-channel Acoustic Emission system from Digital Wave Corporation. Modal AE provides the ability to determine the type of failure (e.g., fiber bundle breakage, delamination or matrix cracking) occurring in composite material, based on frequency content and wave mode shape detected. This equipment is used to detect and locate cracking in small test specimens loaded in tension, compression, shear, or fatigue. In addition, this system is capable of determining the types of acoustic emission sources in plates, rods, shells, and other thin-walled (up to about 2 inches thick) materials using the shape of the wave mode rather than counting events as with traditional technology.
- Strain Field Visualization
- Ultrasonic velocity at cryogenic temperatures
As an advanced analytical capability available to our clients, SR offers optical and scanning electron microscopy (SEM) for evaluations of material structure and behavior. The SEM is an integral tool in providing analyses such as the determination of failure mode, analysis of material defects or contaminants, and analysis of microstructures and material characterization.