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.
Highlights
The development of progressive damage analysis (PDA) models allows for predicting damage in composite structures and determines the residual strength and the remaining life
Nondestructive evaluation is used as a tool to validate PDA models to enable comparisons between measured damage vs. predicted damage [1,2]
Work being performed at NASA Langley involves the development of PDA models [3,4,5,6,7,8] and building an nondestructive evaluation (NDE) database of measured damage under both fatigue and quasi-static testing of composite structures
Summary
The development of progressive damage analysis (PDA) models allows for predicting damage in composite structures and determines the residual strength and the remaining life.PDA models can potentially help to eliminate testing requirements and decrease certification times for new composite materials and designs [1]. The development of progressive damage analysis (PDA) models allows for predicting damage in composite structures and determines the residual strength and the remaining life. PDA models can be used as a tool to assess the safety of as built structures which might have manufacturing imperfections or service damage. PDA models, require validation [2]. Nondestructive evaluation is used as a tool to validate PDA models to enable comparisons between measured damage vs predicted damage [1,2]. Work being performed at NASA Langley involves the development of PDA models [3,4,5,6,7,8] and building an nondestructive evaluation (NDE) database of measured damage under both fatigue and quasi-static testing of composite structures. The challenge is to incrementally control the grow of the damage during loading and document the damage growth using ultrasound or X-ray CT (computed tomography)
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