Preparation Of Foam Core Sandwich Composites And Life Prediction

Foam core composite sandwich structures offer many advantages, such ashigh stiffness to weight ratio and corrosion resistance, which make foam corecomposite structures get a great deal of attention and application in the aerospace,aircraft, transportation and energy, especially in marine field. The reasonablecore/skin thickness ratio was designed,in order to give full play to thecharacteristics of high stiffness. However, in the marine vessels service life,sandwich structures are frequently exposed into marine environment, affected byalternating wet and dry, sunshine, temperature factors, which affected theperformance of the sandwich structures. Only a scant amount of such informationhas thus far been attained for foam-cored composites.When core/skin thickness ratio was more than5.77according to the relevantformulas, it could play the greater degree of advantage. Firstly, the sandwichstructures which met ratio were prepared by Vacuum-Bag Process. Secondly, thespecimens aging was carried out, including UV aging and alternating high and lowtemperature damp heat aging. Furthermore, to analyze mechanical properties offoam-cored sandwich composites, we conducted flatwise tension, plane shear andbending test, respectively, meanwhile, aging life prediction of foam-coredsandwich composites was made by using experimental data. The main conclusionswere:1. When core/skin thickness ratio was more than5.77, sandwich structureswould have higher stiffness;2. The weight gain of specimens was negative under UV aging, however, thevalue was less than0.2%; The weight gain of specimens under alternating highand low temperature damp heat aging demonstrated trends akin to those predictedby Fick’s law, its maximum moisture uptake, at equilibrium state was about0.4%;3. In the test of mechanical properties of specimens aged, Flatwise tension:there were four kinds of failure modes, At the beginning of the period, failure wasin the form of foam failure, then it was in the skin/core interface and skin in the latter part, and the value decreased in turn. shear strength was reduction in theaging time. Bending stiffness: its downward trend was similar in the differentaging conditions and maximum falling range was in first week of aging. shearstiffness: its downward trend was similar in the different aging conditions andafter56days it rised slightly. There was a bigger impact on bending stiffness thanshear stiffness under aging environment;4. In the test of bending strength, failure mode was compressive failure inupper skin in the earlier stage of the test and there was core shear failure later. Thebending strength was chosen to predict life based on resident strength model.