Detection and Characterization of Damage in Quasi-Static Loaded Composite Structures Using Passive Thermography

Abstract

Real-time nondestructive evaluation is critical during composites load testing. Of particular importance is the real time measurement of damage onset, growth, and ultimate failure. When newly formed damage is detected, the loading is stopped for further detailed characterization using ultrasound inspections or X-ray computed tomography. This detailed inspection data are used to document failure modes and ultimately validate damage prediction models. Passive thermography is used to monitor heating from damage formation in a hat-stiffened woven graphite epoxy composite panel during quasi-static seven-point load testing. Data processing techniques are presented that enable detection of the small transient thermographic signals resulting from damage formation in real time. It has been observed that the temperature rise due to damage formation at the surface is composed of two thermal responses. The first response is instantaneous and conforms to the shape of the damage. This heating is most likely due to irreversible thermoelastic, plastic deformation, and microstructural heating. The second response is a transient increase in temperature due to mechanical heating at the interface of failure. Two-dimensional multi-layered thermal simulations based on quadrupole method are used to investigate the thermal responses. In particular, the instantaneous response is used as the transient response start time to determine damage depth. The passive thermography measurement results are compared to ultrasonic measurements for validation.

A Novel Infrared Thermography Sensing Approach for Rapid, Quantitative Assessment of Damage in Aircraft Composites

“…Overall, the synergy of PPT and LT leads to the fast and accurate characterization of damage at all subsurface depths penetrable by IRT. It must be noted that no limitation is imposed on the type of excitation source, which can include lamps, microwaves, ultrasounds, or Eddy currents, provided the source is powerful enough for the clear thermographic representation of the defects [ 34 , 49 ].…”

“…In passive IRT, the structure or section under investigation is physically at a higher temperature than the ambient one; hence no external thermal excitation is needed for defect inspection. In active IRT, external thermal stimulation is applied in a uniform way to induce thermal contrasts to a material so that minute temperature changes can be captured [32][33][34]. The main difference between available active IRT methodologies is the modulation of the heat source; based on the type of the thermal excitation, approaches such as step heating (SH), pulsed phase thermography (PPT), vibro-thermography (VT) and LT, have been developed [35].…”

A Methodology to Investigate Skin-Stringer Separation in Postbuckled Composite Stiffened Panels

“…Bertolini et al [7][8] showed that this can be used both for symmetrical and skewed buckling. Recently, NASA performed seven-point bending tests as part of the Advanced Composite Consortium (ACC) program [9][10][11][12].…”

Composite Thermal Nondestructive Evaluation Research at NASA Langley

“…In the area of accurate strength and life prediction, composites testing required real time inspections of composites during loading to detect and control damage growth. Passive thermography has been successfully used to detect and control damage onset and growth and has fundamentally changed how composite structures are tested at NASA Langley [1,2]. When damage is detected, the loading is stopped and another inspection technique such as ultrasound or X-ray CT provides a detailed assessment of the panel damage as a function of depth.…”