SBIR-STTR Award

Advanced aircraft designs require technology improvements that incorporate the use of advanced materials and material systems for high specific stiffness and temperature capabilities. Improved crack detection and material property measurement techniques are required to support the development and verification of material systems. A development program is proposed that will improve for high-temperature application two thermography techniques to enable the quantification of flaws both in terms of geometry and stress intensity factors. Forced Diffusion Thermography(FDT)is an NDE method that uses projected, dynamic patterns of light to thermally excite a specimen structure with an oscillating thermal pattern that is synchronously imaged and processed for the detection of flaws. Thermoelastic Stress Analysis(TSA)is a differential thermography technique capable of nearly real-time measurement of mixed-mode stress intensity factors. Both FDT and TSA use the same dynamic thermography equipment to measure the small temperature fluctuations upon which these techniques are based. FDT and TSA have several attributes that will make them superior to other methods for assessing structural integrity in extreme environments. FDT and TSA are non-contacting full-field techniques, not significantly impaired by convection currents or other anomalies in a high-temperature environment, able to work on a wide range of materials and composites, and able to produce standard(DC)thermal images as well as differential(AC)thermal images.

Keywords:
NDE Thermoelasticity Thermography High-Temperature

The recent development of a new high speed differential thermography camera by Stress Photonics for NASA opens new opportunities to develop highly useful tools to aid in life prediction and characterize damage in monolithic materials subjected to extreme environments. In the case of monolithic materials, the fracture mechanics parameters KI, KII, KIII, crack length, and crack orientation can be measured. For composites, stiffness, microcrack density, and other indications of material damage can be measured by using thermoelastic and thermal diffusivity measurements. Additionally, differential thermography can be used to characterize the redistribution of stresses at critical design features such as fastener holes and notches. Concepts proven in Phase I and elsewhere can now be combined to provide a set of tools in the form of hardware and software that will allow engineers to assess the criticality of damage in a wide range of materials and thermal environments.