Fracture properties of fibre and nano reinforced composite structures
MetadataShow full item record
Interlaminar cracking or delamination is an inherent disadvantage of composite materials. In this study the fracture properties of nano and fibre-reinforced polypropylene and epoxy composite structures are examined. These structures were subjected to various tests including Single Edge Notched Bend (SENB) and Mixed Mode Bending (MMB) tests. Polypropylene nanocomposites infused with 0.5, 1, 2, 3 and 5 weight % nanoclays showed correspondingly increasing fracture properties. The 5 weight % specimen exhibited 161 % improvement in critical stress intensity factor (KIC) over virgin polypropylene. XRD and TEM studies show an increase in the intercalated morphology and the presence of agglomerated clay sites with an increase in clay loading. The improvement in KIC values may be attributed to the change in structure. Tests on the fibre-reinforced polypropylene composites reveal that the woven fibre structure carries 100 % greater load and exhibits 275 % lower crack propagation rate than the chopped fibre specimen. Under MMB conditions, the woven fibre structure exhibited a delamination propagation rate of 1.5 mm/min which suggests delamination growth propagates slower under Mode I dominant conditions. The woven fibre / epoxy structure shows 147 % greater tensile modulus, 63 % greater critical stress intensity factor (KIC), and 184 % lower crack propagation rate than the chopped fibre-reinforced epoxy composite. MMB tests reveal that the load carrying capability of the specimens increased as the mode-mix ratio decreased, corresponding to an increase in the Mode II component. Delamination was through fibre–matrix interface with no penetration of fibre layers. A failure envelope was developed and tested and may be used to determine the critical applied load for any mode-mix ratio. The 5 weight % nanocomposite specimen exhibited a greater load carrying capability and attained a critical stress intensity factor that was 10 % less than that of the fibre-reinforced polypropylene structure, which had three times the reinforcement weight. Further, the nanocomposite exhibited superior strain energy release rates to a material with ten times the reinforcement weight. The hybrid structure exhibited 27 % increase in tensile modulus over the conventional fibre-reinforced structure. Under MMB conditions, no significant increase in load carrying capability or strain energy release rate over the conventional composite was observed. However, the hybrid structure was able to resist delamination initiation for a longer period, and it also exhibited lower delamination propagation rates.
Showing items related by title, author, creator and subject.
A technique for the multiobjective optimisation of laminated composite structures using genetic algorithms and finite element analysis Walker, Mark; Smith, Ryan E. (Elsevierhttp://dx.doi.org/10.1016/S0263-8223(03)00098-9, 2003)A methodology for using genetic algorithms with the finite element method to minimise a weighted sum of the mass and deflection of fibre reinforced structures with several design variables is described. The design constraint ...
Kekana, Marino (Elsevierhttp://dx.doi.org/10.1016/S0263-8223(02)00184-8, 2003)This study examines an active control model in which the open circuit mode is assumed. A finite element model in which only the displacement field is approximated is developed. The charge–potential relationship is incorporated ...
A procedure to select the best material combinations and optimally design composite sandwich cylindrical shells for minimum mass Walker, Mark; Smith, Ryan E. (Elsevierhttp://dx.doi.org/10.1016/j.matdes.2004.10.003, 2006)A methodology to select the best material combination and optimally design composite sandwich cylinders having fibre reinforced skins and low density cores for minimum mass is described. Sandwich constructions generally ...