Polymer matrix composites are popular in the aerospace industry due to their high strength to weight ratio. While they have become popular, understanding and predicting their specific damage evolution mechanisms remains a challenge especially in designing with damage tolerance criteria. One challenge often faced is the presence of surface damage either induced during manufacturing, machining, or service of a composite part. While many studies have investigated how quasi-static, low-velocity, and ballistic impact results in damage in the material, there remains a need to further understand the reduction in performance that results from such surface damage. In this work, micro-indentation was conducted on a unidirectional IM7/8552 laminate composite specimen to induce quasi-static impact damage that results in surface damage. The specimen was then loaded in tension to 33% of its expected failure load and imaged using synchrotron X-ray micro-computed tomography to qualitatively investigate the progression of surface damage into sub-surface damage. This work shows that at 33% of tensile failure load, surface damage propagates into delamination and fiber breakage of plies directly sub-surface. This work sheds light on the progression of surface damage at loads less than 50% of the ultimate strength of a unidirectional laminate composite.
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Evaluation of the Effect of Thermal Oxidation and Moisture on the Interfacial Shear Strength of Unidirectional IM7/BMI Composite by Fiber Push-in Nanoindentation
Fiber push-in nanoindentation is conducted on a
unidirectional carbon fiber reinforced bismaleimide resin
composite (IM7/BMI) after thermal oxidation to determine
the interfacial shear strength. A unidirectional IM7/BMI laminated
plate is isothermally oxidized under various conditions:
in air for 2 months at 195 °C and 245 °C, and immersed in
water for 2 years at room temperature to reach a moisturesaturated
state. The water-immersed specimens are subsequently
placed in a preheated environment at 260 °C to receive
sudden heating, or are gradually heated at a rate of approximately
6 °C/min. A flat punch tip of 3 μm in diameter is
used to push the fiber into the matrix while the resulting loaddisplacement
data is recorded. From the load-displacement
data, the interfacial shear strength is determined using a
shear-lag model, which is verified by finite element method
simulations. It is found that thermal oxidation at 245 °C in air
leads to a significant reduction in interfacial shear strength of
the IM7/BMI unidirectional composite, while thermal oxidation
at 195 °C and moisture concentration have a negligible
effect on the interfacial shear strength. For moisture-saturated
specimens under a slow heating rate, there is no detectable
reduction in the interfacial shear strength. In contrast, the
moisture-saturated specimens under sudden heating show a
significant reduction in interfacial shear strength. Scanning
electron micrographs of IM7/BMI composite reveal that both
thermal oxidation at 245 °C in air and sudden heating induced microcracks and debonding along the fiber/matrix interface,
thereby weakening the interface, which is the origin of failure
mechanism.
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- Award ID(s):
- 1636306
- NSF-PAR ID:
- 10048020
- Date Published:
- Journal Name:
- Experimental Mechanics
- ISSN:
- 0014-4851
- Page Range / eLocation ID:
- 1-13
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s11340-017-0335-6
