Document Type

Thesis

Date of Degree

Spring 2015

Degree Name

MS (Master of Science)

Degree In

Mechanical Engineering

First Advisor

Olesya I. Zhupanska

Abstract

Low-velocity impact damage in IM7/977-3 carbon fiber reinforced polymer (CFRP) composites was investigated using 3D computed tomography (CT). 32-ply IM7/977-3 symmetric cross-ply composites were impacted at different impact energy levels and with different impactors (DELRIN® resin flat-ended cylindrical and tool steel hemispherical strikers) using an Instron 8200 Dynatup drop-weight impact machine. The impact energies were chosen to produce slightly visible damage, characterized by short cracks on the impacted surface and little delamination on the non-impacted surface (29.27 J), and barely visible damage, characterized by indentation on the impacted surface but no visible delamination on the back surface of the specimens (20.77 J). Internal damage was assessed using the Zeiss METROTOM 1500 industrial CT scanning system, and CT images were reconstructed using VGStudio MAX and the MyVGL 2.2 viewer. To determine the extent of the damage zone, impacted 152.4 mm square composite plates were initially scanned. As the relatively large specimen size did not allow for evaluation of internal cracks and isolation of delamination at ply interfaces, smaller specimens that enclosed the damaged region (45 mm square plates) were cut out and imaged. The CT scan results showed that volume of the impact damage zone had a generally positive correlation with impact energy, maximum load, and maximum deflection, but that the relationship was generally weak. Absence of a definite correlation between damage volume and impact energy was unexpected, as the difference in the impact energy was up to 30%.

Public Abstract

As composite materials become more common in sporting goods, automotive applications, and aerospace structures, reliable methods of damage assessment will become increasingly important. Composite structures, unlike metals, tend to develop internal damage and fail in different ways. In the present work low-velocity impact damage, like that which could be produced from a dropped tool, was investigated for aerospace-grade carbon fiber reinforced polymer composite plates. Each plate was composed of 32 alternating-direction layers (plies) and was symmetric about the center plies. Each plate was impacted using a drop-weight test machine, and the impact force, deflection, and energy were measured. Two impact energies were investigated: One that produced slightly visible damage (in the form of cracks and back surface damage) and one that produced barely visible damage (in the form of a small front surface indent). To determine the extent of the internal damage the plates were scanned using an industrial CT imaging system, which produced a 3D x-ray image. As the scan of the original specimens (152.4 mm square plates) had too low of a resolution to uniquely identify all internal damage features, the plates were cut to a smaller size (45 mm square plates) and scanned again. The images produced from the smaller plates had a resolution approximately 2.5 times smaller than the thickness of the individual plies, which allowed for a more accurate internal damage assessment. Results showed that the amount of internal damage increased as the impact energy increased, but that the relationship was generally weak.

Keywords

publicabstract, composites, computed tomography, low velocity impact

Pages

xiv, 167

Bibliography

165-167

Copyright

Copyright 2015 Brandon Michael Demerath

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