Debonding at the core–skin interphase region is one of the primary failure modes
in core sandwich composites under shear loads. As a result, the ability to characterize
the mechanical properties at the interphase region between the composite skin and core is critical for design analysis. This work intends to use nanoindentation to characterize the viscoelastic properties at the interphase region, which can potentially have mechanical properties changing from the composite skin to the core. A sandwich composite using a polyvinyl chloride foam core covered with glass fiber/resin composite skins was prepared by vacuum-assisted resin transfer molding. Nanoindentation at an array of sites was made by a Berkovich nanoindenter tip. The recorded nanoindentation load and depth as a function of time were analyzed using viscoelastic analysis. Results are reported for the shear creep compliance and Young’s relaxation modulus at various locations of the interphase region. The change of viscoelastic properties from higher values close to the fiber composite skin
region to the smaller values close to the foam core was captured. The Young’s modulus at a given strain rate, which is also equal to the time-averaged Young’s modulus across the interphase region was obtained. The interphase Young’s modulus at a loading rate of 1 mN/s was determined to change from 1.4 GPa close to composite skin to 0.8 GPa close to the core. This work demonstrated the feasibility and effectiveness of nanoindentation-based interphase characterizations to be used as an input for the interphase stress distribution calculations, which can eventually enrich the design process of such sandwich composites.
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‘Green’ composites based on liquid crystalline cellulose fibers and avocado seed starch
Fully biodegradable unidirectional green composites with excellent tensile
properties were fabricated by combining one of the highest specific strength
liquid crystalline cellulose (LCC) fibers as the reinforcement and microfibrillated
cellulose (MFC) strengthened nonedible avocado seed starch (AVS)-based resin.
MFC/AVS resin was crosslinked using 1,2,3,4-butane tetracarboxylic acid as
well as plasticized using sorbitol or glycerol. Combination of alkali, mechanical
and thermal treatments improved LCC fiber fracture stress from 1.5 GPa to over
1.9 GPa and Young’s modulus from 49 to 64 GPa. While the type and amount of
plasticizer used changed the fracture strain of MFC/AVS resin, they also
showed significant influence on the mechanical properties of the unidirectional
composites. These composites prepared by hand lay-up, based on modified LCC
fibers resulted in fracture stress of over 380 MPa and Young’s modulus of
19.5 GPa with less than 40% fiber content. Results suggest that there is scope to
improve the properties further by using higher fiber content and automated
manufacturing. These ‘green’ composites with excellent strength and stiffness
may be used in many applications such as construction, automobile and others.
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- Award ID(s):
- 1735971
- NSF-PAR ID:
- 10257107
- Date Published:
- Journal Name:
- Journal of materials science
- Volume:
- 56
- Issue:
- 56
- ISSN:
- 1573-482X
- Page Range / eLocation ID:
- 6204 - 6216
- 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/s10853-020-05676-2JMSC-D-20-06608R2
