Compressive Deformation Behavior And Energy Absorption Property Of Cenosphere/Al Syntactic Foams

Energy absorbing materials are able to protect these components subjected to dynamic impact loading in the transportation, machinery, engineering structures, weapons and aerospace industry. Based on the application of the impact protection and previous investigations on energy absorbing materials, one advanced cenosphere/Al syntactic foam, which is an aluminum microporous composites, are designed and fabricated.Cenosphere/Al syntactic foam are fabricated using pressure infiltration technique. Two kinds of aluminum matrix of cenosphere/Al syntactic foam are selected1199Al alloys and6061Al alloys, besides the fly ash cenosphere as a reinforced particle is selected different diameter of70μm,120μm,200μm. Cenosphere/Al syntactic foam are systematically investigated the microstructure, compression behavior and impact energy absorption properties by using optical microscope (OM), transmission electron microscope (TEM), scanning electron microscope (SEM), split Hopkinson pressure bars (SHPBs). Moreover, the deformation mechanism of compression and effects from the size of cenosphere on properties of cenosphere/Al syntactic foam are discussed, respectively.Properties of the cenospheres are characterized by XRD and TEM. The results show that the main chemical composition of the cenosphere is SiO2and Al2O3, the density is in the range of0.66g/cm3, the porosity content is70%. Analysis of TEM indicates that cenospheres-Al matrix interfaces are in good bond. In addition, interfacial reactions occurs between cenospheres and6061Al matrix, whose products are MgAl2O4and Si. However, interfacial reactions don’t happen between cenospheres and1199Al matrix.Based on the metallographic photos from OM and SEM, the volume fraction of cenospheres and the uniformity of distribution in the cenosphere/Al syntactic foam are analyzed using the ImageTool and ImageJ software. The volume fraction of cenospheres in the microporous composites including average diameter of70μm and200μm cenospheres are49.1%and49.8%, respectively. However, a lower volume fraction of cenospheres in the microporous composites including average diameter of120μm cenospheres is45.4%, which is related to the space stacking manner of cenospheres. Additionally, the distribution of these hollow sphere is uniform, no significant segregation, in three kinds of composites including three sizes of cenospheres.The stress-strain curve of cenosphere/Al syntactic foam exhibits the typical “three-stages” in the quasi-static compression, like other porous materials. Peak stress of the three sizes of cenosphere/1199Al syntactic foam are84.8MPa,73.4MPa,48.7MPa, respectively, which suggests that a trend of the higher intensity caused by the smaller cenospheres. Compared with the quasi-static compression, in the dynamic compression, the peak stress of cenosphere/1199Al syntactic foam increased into124.7MPa,119.8MPa,59.4MPa, which exhibits a significant strain rate effect. But, the strain rate effect doesn’t depend on the size of cenospheres.The process of cenosphere/Al syntactic foam quasi-static compression are observed using the in-situ compression in the SEM. The hollow spheres exhibit obvious deformation, broken and collapse, and one “fracture zone” presents in the deformed composites. The composites are crushed with the development of “fracture zone” layer by layer. The roundness of hollow spheres calculated through ImageJ software shows that the roundness of the hollow spheres is gradually reduced during the compression process, which indicates that the hollow spheres is gradually compressed into ellipsoid. The finite element unit cell model of cenosphere/Al syntactic foam is established according to unit cell model of Gibson-Ashby. Furthermore, the stress analysis suggests that there is a reciprocal relationship in yield strength and cenosphere size in the compression process.One designed “sandwich” multilayer structure including the cenosphere/Al syntactic foam can obviously hinder the propagation of stress waves through the laminated structure in the dynamic compression test. The obstruction of stress wave is related to the properties of matrix. The results from finite element simulation shows that the composites in the “sandwich” structure occurs a large deformation during the dynamic compression process, and the composites bear most of the stress. Therefore, the “sandwich” structure plays an excellent protection in impact.