Scaling Effects in the Manufacture and Testing of Advanced Sandwich Structures

Abstract

This thesis investigates the properties of novel sandwich structures based on both grid-stiffened composite structures and tube-reinforced honeycomb structures. Both of these structures offer attractive properties and can potentially be used in load-bearing and energy-absorbing structures. The work is linked through an investigation of size effects and scaling behavior. In the first part of the thesis, scaling effects in the manufacture and testing of glass fiber reinforced epoxy grid-stiffened structures have been investigated. Four nominally-identical scaled sizes of mold have been manufactured, in which the length, width, height and internal channel sizes were varied to achieve ¼, ½, ¾ and full-scale stiffened structures. Grid-stiffened beams were removed from the cured panels and tested in flexure on scaled bending fixtures. The VARTM manufacturing study on the four scaled sizes indicated that resin infusion incurred more rapidly in the smallest mold, possibly due to difficulties in accurately cutting the glass fabric, which in turn reduced the effective areal density of the fabric, thereby modifying its effective permeability. The flow rates and velocities of the resin fronts in the larger mold sizes were similar, suggesting that an appropriately scaled mold can be used to successfully predict the infusion process in more representative structures. Flexural tests on the grid-stiffened samples highlighted a similar response in the three largest samples, with the smallest sample again offering a modified response. Similar failure mechanisms, including fracture of the grid structure, debonding at the skin-grid interface and flexural failure in the center of the sample, were observed in all of the samples. In the second part of the thesis, the energy-absorbing response of novel composite tube-reinforced honeycomb are investigated. Here, woven and unidirectional tubes are inserted into a honeycomb structure to develop lightweight energy-absorbing structures. Tests under quasi-static and dynamic conditions have shown that these materials are capable of absorbing very high levels of energy, with values of specific energy absorption (SEA) as high as 100 kJ/kg being recorded. Tests to assess the effect of sample size have shown that these materials do not exhibit any clear scaling effect, with values of SEA being similar in the ¼, ½, ¾ and n = 1 samples. It is believed that these materials can be used in the design of new lightweight energy-absorbing structures.

Date of Award	Dec 2017
Original language	American English
Supervisor	Wesley Cantwell (Supervisor)