The properties of environmentally-friendly sandwich structures



Mohamed Yusoff, Mohd Zuhri
(2015) The properties of environmentally-friendly sandwich structures. Doctor of Philosophy thesis, University of Liverpool.

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Abstract

This research study aims to manufacture and characterise the properties of sandwich structures based on natural fibre composites. Bamboo tubes and flax-based composite (reinforced polypropylene and polylactide) were selected as the main materials to be investigated. Initial testing was focused on investigating the sensitivity of the tensile properties of the composites from various processing conditions and understanding the energy-absorbing characteristics of the individual bamboo tubes. Following this, bamboo honeycomb, bamboo-reinforced foam, corrugated flax-based composites, square and triangular interlocking flax-based composites and corrugated paperboard with flax-based composite skins were manufactured.The flax-based honeycomb and corrugated structures were manufactured using compression moulding techniques and subsequently bonded to skins based on the same material using an epoxy resin. These structures were tested in compression at quasi-static and dynamic rates of strain in order to determine their mechanical strength and specific energy absorption characteristics. It has been shown that the energy-absorbing capacity of the bamboo tubes tends to increase with decreasing inner diameter to the thickness (D/t) ratio. In addition, a chamfered profile was employed to successfully trigger the tubes to fail in a progressive manner. Bamboo tubing has been observed to offer excellent energy absorption characteristics and has potential for use inenergy-absorbing engineering applications. Tests on the flax-based composite structures have shown that the wall thickness and the number of unit cells have an effect on the strength and energy-absorbing capability of the core. The flax reinforcedpolypropylene (flax/PP) composite structures failed in buckling and fibre fracture, whereasthe flax reinforced polylactide (flax/PLA) systemfailed in buckling with delamination. Of the structures investigated here, the flax/PP cores offer superior mechanical properties to their flax/PLA counterparts. Further investigations on the effect of bonding flax/PP and flax/PLA skins to a corrugated paperboard have show that there is no significant difference in the properties between those two flax-based materials. Finally, the compression response of the square and triangular honeycomb structures has been modelled using finite element (FE) techniques. The FE model succesfully predicted the strength, energy-absorbing characteristics, buckling behaviour and failure modes observed in these natural fibre based core materials.

Item Type: Thesis (Doctor of Philosophy)
Subjects: T Technology > TJ Mechanical engineering and machinery
Divisions: Fac of Science & Engineering > School of Engineering
Depositing User: Symplectic Admin
Date Deposited: 22 Aug 2016 07:43
Last Modified: 22 Aug 2016 07:43
URI: http://livrepository.liverpool.ac.uk/id/eprint/2028839
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