Design optimization of Sandwich Structures.
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The document outlines a research project focused on design optimization of aerospace sandwich composites to enhance flexural strength and stiffness while minimizing weight and cost. It discusses theoretical foundations, current experimental approaches, and future plans for further research, including simulations and tests on various core densities and skin materials. Acknowledgments were made for financial support and laboratory resources utilized in the project.
Design optimization of Sandwich Structures.
- 1. Design Optimization of Aerospace Sandwich Composites for Strength and Stiffness K. Padmanabhan AR and DB Project No: 1650 SMBS, VIT University-Vellore. May 2013
- 2. Objectives • To design optimize aerospace sandwich composites for maximum flexural strength and stiffness ( current) • To design optimize aerospace sandwich composites for minimum weight and cost ( future)
- 3. Theoretical Background • GR Froud’s publication : Maximum strength occurs when skin weight equals core weight and maximum stiffness occurs when skin weight equals half of core weight. (General ) • LJ Gibson’s publication: Maximum stiffness occurs when skin weight is one fourth of core weight ( Metal skin rigid polymeric foam core) • Available literature is scanty in general on design optimization. G. R. Froud, “Your Sandwich Order, Sir?”, Composites, July (1980) p 133 . L. J. Gibson, Materials Science and Engineering, 67 (1984) 125-135.
- 4. Current Approach • Semi-empirical approach. • To experimentally determine the strength and the stiffness optimization rules for sandwich composites fabricated out of glass and/or carbon fabric skins and cores made of rigid cellular solids with closed pores. • Different core densities and thicknesses to be experimented. • To refine the FEA models in accordance with the design optimization rules. For example employ layer effect in flexure to sandwich composites. • Correlation of the shape factors with the observed stiffness and strength.
- 6. Experimental Approach • Hand Wet Lay Up and Hand Wet Lay Up followed by Vacuum Bagging fabrication of sandwich composites. • Conventional machining of test specimens • Flexural testing in Instron 8801 and Structural UTM • Failure analyses and feedback
- 8. Testing and Failure Analyses An Instron 8801 flexure set up. ASTM D 790 M & ASTM D 7250 M Compressive face skin failure & core crushing
- 9. FEA Results and Discussion Shear Strain Shear Stress
- 10. Results and Discussion PUF Sandwich Composites 125 kg/cu. m density and 10 mm thick rigid foam. G/E skin with 100 GSM and 280 GSM weave.
- 11. Results and Discussion PUF sandwich Composites 125 kg/ cu. m density and 50 mm thick rigid PUF foam . G/E Skin with 260 GSM weave.
- 12. Results and Discussion PIR Sandwich Composites 125 kg/cu. m density and 10 mm thick rigid foam. G/E skin with 100 GSM and 280 GSM weave.
- 13. ` Polyisocyanurate foams are more fire resistant than polyurethane foams. Otherwise the mechanical properties of the respective sandwich composites are in the same range for similar densities and thicknesses.’ Ref: Lloyd insulations brochure on rigid foams, 2012.
- 14. Future Plan • To continue with different rigid foam densities and thicknesses for simulation and experiments. • To conduct more simulation and experiments to find thumb rules on strength and stiffness optimization in rigid foam core and fibre/matrix skin sandwich composites. • To include resin bond tests between core and skin ( Shear and peel tests). • To endeavour to achieve accomodative behaviour between core and skin for design optimization through choice of resin. • To include layer effect in skin in design optimization • To include flexural parameters in design optimization ( like bending modulus and span to depth ratio).
- 15. Acknowledgement • AR and DB for the financial support and advice. • VIT management for the equipment purchase and support. • CAMPT DST-FIST facility and Structures lab, VIT, for mechanical testing. • My project associate and students.