Mechanical Behaviors Of Closed-cell Aluminum Foams And Sandwich Panels At Elevated Temperatures

Metallic foams, as ultra-light materials, exhibit many unique characteristics in mechanical, thermal, electromagnetic, and acoustic properties and have been widely used in many areas, such as aerospace industry, marine shipping industry and automotive engineering. However, by considering an overall analysis of resistance, energy absorption and maintenance in real applications, the bare metallic foams would not be used but some kind of composite structures along with compact metals are desired. In most cases, metallic foams serve as the cores of sandwich structures. To date, researches on the mechanical behavior of metallic foams and their sandwich structures are limited mainly at room temperature. However, the mechanical properties of metallic foams and metallic foam cored sandwich structures at high temperatures have been much less documented. The large potential and demands of metallic foams to be used in applications of lightweight bearing carrier in aircrafts and spacecrafts is the main reason and motivation to investigate their high temperature mechanical properties and their thermo-mechanical coupling effects urgently.It was aimed in the present thesis to study the mechanical properties and energy absorptions of aluminum foams and aluminum foam cored sandwich panels at different temperatures. This was done mainly by carrying out experiments, together with theoretical analysis and numerical simulations. Four different case studies, to determine the high temperature performance of aluminum foams and aluminum foam cored sandwich structures were conducted, which are (1) Quasi-static and dynamic properties, impact behavior and plastic indentation behavior of closed-cell aluminum foams at different temperatures,(2) Indentation and three-point bending behavior of aluminum foam cored sandwich beams at different temperatures,(3) Indentation and perforation behaviors of sandwich panels at different temperatures, and (4) Multi-function design of aluminum foam cored hybrid sandwich panels with interlayer. The main achievements are as follows.The quasi-static and dynamic properties of closed-cell aluminum foams at different temperatures were studied experimentally, and the dependent relationship of aluminum foams to temperatures was obtained. Recent interest in metallic foams for the sacrificial cladding applications has generated the need for the studies of graded metallic foams. Thus, the propagation of compaction wave in closed-cell aluminum foams with a temperature gradient under high velocity impact was investigated. An analytical solution was proposed and numerical simulations were carried out to verify the proposed theoretical model of foam compaction. The relations of critical length, critical impact velocity and impact force of the aluminum foam rod with temperature gradient to the temperature distribution and the relation of critical impact velocity of an aluminum foam rod with a given length to the temperature contrast at its two ends were evaluated to guide the application designs.Deep indentation response of closed-cell aluminum foam under different temperatures was experimentally investigated by using a flat-ended punch and a hemispherical-ended punch. The indentation deformation behavior and mechanism of aluminum foams at different temperatures were compared and analyzed, and the dependent relationships of the plastic collapse strength, energy absorption to temperatures were obtained. An empirical formula incorporating indentation depth effect and temperature effect was presented for tear energy. Based on dimensional analysis and finite element simulations, several scaling relationships in the indentation of metallic foams with a spherical indenter were obtained and the dependence of the spherical indentation force of closed-cell aluminum foam on temperature, relative density of foam and dimensionless indentation depth were examined.The deformation/failure behavior, load carrying capacity and energy absorption capability of aluminum foam cored sandwich beams under quasi-static indentation and three-point bending at different temperatures were investigated experimentally. The effects of several parameters on the structural responses of sandwich beams were examined, such as the diameter of the punch, face sheet thickness, core thickness and relative density. Failure mode maps of sandwich beams at elevated temperatures were achieved and the change trends of failure modes with the temperature were analyzed. This study provides the foundation for predicting the low velocity impact responses of sandwich beams and can be regarded as the theoretical basis of optimization design and engineering application of sandwich beams.Indentation and perforation response of sandwich panels with composite face sheets and aluminum foam core were investigated experimentally. Effects of some key parameters on the overall energy absorption behavior of the panels were explored, such as impact energy, face sheets and core thickness, core density and indenter nose shape. The dependency of the load-displacement responses of sandwich panels on boundary conditions was also discussed and drop hammer tests were carried out to compare the quasi-static and low velocity impact responses. The effects of temperature on the deformation/failure modes, load carrying capacity and energy absorption capability of sandwich panels are studied through carrying out quasi-static and low velocity impact perforation and indentation experiments under different temperatures.Based on an overall analysis of load carrying, energy absorption and thermal insulation of metallic foam cored sandwich structures, a new hybrid sandwich structure has been developed by inserting lightweight, efficient thermal insulating interlayers between the face sheet and the foam core. Optimum selection was made by studying and comparing the thermal insulation performance, load carrying capacity and energy absorption capability of different designs of the sandwich panels. The structural responses of the traditional sandwich panel and a hybrid sandwich panel under different temperatures were studied experimentally.