Research On Impact Mechanical Properties Of Aluminum Foam Sandwich Plate At Elevated Temperatures

The aluminum foam is a new kind of light-weight and low-cost material with highspecific stiffness, high specific strength and efficient energy absorption, which also has heatinsulation, sound insulation, vibration reduction and electromagnetic shield advantages.Aluminum foam composite could be used as important parts of in air-crafts and spacecrafts. Todate, researches on the mechanical properties of aluminum foam and its sandwich structures havebeen conducted mostly at room temperature, but the tough application environment of near-spacepresents a number of challenges to aluminum foams and its structures in temperature, so it is veryimportant to study the mechanic properties of aluminum foams and its sandwich structures atelevated temperature.The paper measures straight the mechanic properties at elevated temperature,through quasi-static uni-axial compression of aluminum foams and Drop test of aluminum foamsandwich plates at elevated temperature. And then a reasonable simulation model of aluminumfoam sandwich plates is established considered temperature and damage, the impact energyabsorption of sandwiches with different core mass ratio are researched. The paper doesn’t onlystudy the mechanic properties of aluminum foam sandwiches at elevated temperature, but alsodevelops impact test and simulation model considered damage at elevated temperature. Theseare very significant to other related studies.(1) The paper presents an experimental study on mechanical behaviors of quasi-staticuni-axial compression of aluminum foams at different temperature(-50℃～300℃)。It wasshowed that the environmental temperature affected the mechanical properties of aluminumfoams significantly. The elastic modulus, the yield strength and the plateau stress woulddecreased with temperature increasing. Based on the six-parameter constitutive model offoam materials by Liu and Subhash, the simplified five-parameter constitutive model wasproposed by the analysis of parameters. A uni-axial compression constitutive modelconsidering temperature effects of closed-cell aluminum foam with specific porosity wasestablished through experimental data. The constitutive model could depict stress and strainrelationships of aluminum foams at different temperatures well, and the relationships wouldbe used in numerical simulation of structural optimization. Based on the simplifiedfive-parameter constitutive model, the mechanical properties at higher temperatures wereobtained: when the temperature exceeds300℃， with the temperature increasing, thealuminum experiences three states of “non-compaction”,“full flow” and “softening” afteryielding at different high temperatures. At the same time, to the numerical simulation ofsandwich structure, the tensile mechanical properties of alloy skin were obtained by tests. (2) A furnace, attached to an Instron Dynatup9250HV drop hammer system, wasdesigned to accomplish the penetration tests at elevated temperatures up to500℃. The systemsuccessfully completed the Drop tests of aluminum foam sandwich plates at elevatedtemperature and obtained the low velocity penetration mechanical behaviors of sandwichplates which provided an experimental basis for the optimal design of sandwich structures. Inorder to process the experimental data well, the numerical vibration analysis of sandwich andthe single skin were carried to help to determine threshold frequencies of the FFT (FastFourier Transform）filter for the initial impact data. The load-displacement curve presented“four stages” significantly, and the four stages were closely linked with the failure modes.The temperatures had a significant impact on the failure mechanism and energy absorption ofsandwich plates. The double peak loads and the energy absorption would gradually reducewith temperatures increasing and the material presented significant plastic deformation.(3) Aimed at the characteristic of the failure parameters of aluminum foams, related tothe hydro-static pressure and hard to determine, we developed a numerical method todetermine the failed parameter combined with the impact experiment of aluminum panel, anda reliable penetration finite element model of sandwich plates was built with the failureparameters of aluminum foam at different temperatures. The sensitivities of damageparameters on the load-displacement curves were studied and the revising process ofparameters was given.(4) Using the finite element model of sandwich panel, impact-resistant behavior wasstudied among the different mass ratio of foam core under the condition of the total mass as aconstant. A simple modeling method of using script language was developed in the paper.Simulation results indicate that the amount of the absorbed energy and the maximum reactionforce of aluminum foams under impact increase as the mass ratio of aluminum foam increases.Comparing to the single aluminum panel, the aluminum foam sandwich may reduce themaximum load nearly to the half, and the mount of absorbed energy changes little, whichmeans that the aluminum foam core has important protective effect. The above results mayprovide a guide for the politicization design of other similar sandwich structures.