Mechanical properties of aluminum/polypropylene/aluminum sandwich sheets

The aluminum/polypropylene/aluminum (A1/PP/A1) sandwich sheets have been developed for potential application of these materials for automotive body panels in future high performance automobiles with significant weight reduction. The tensile properties of the A1/PP/A1 sandwich sheets were examined in the present study as well as those of the aluminum skin and the polypropylene core at room and elevated temperatures. It was found that the sandwich sheet with hard skin and low volume fraction of the polypropylene core showed the highest tensile strength, whereas that with soft skin and high volume fraction of the polypropylene core showed the lowest strength. The sandwich sheet with hard skin showed much smaller work hardening rate than that with soft skin. All sandwich sheets showed serration phenomena on their flow curves. However, the magnitude of serration was significantly diminished in the sandwich sheet with high volume fraction of polypropylene core. The tensile strength of the sandwich sheet was compared with that calculated from the rule of mixture based on the tensile strengths of the aluminum skin and the polypropylene core. The results showed that there were good agreements between the experimentally obtained values and the calculated values. From the tensile tests at elevated temperatures, it was found that the tensile strength of the sandwich sheet with high volume fraction of polypropylene core was more sensitive to temperature than that with low volume fraction of polypropylene core. During tensile deformation of the sandwich sheet, it was found that fracture first took place in the aluminum skin and then in the polypropylene core and at the interface. The interface strength was found to be strong enough to avoid premature debonding at the interface before fracture took place in the entire sandwich sheet.