SHOCK RESPONSE OF SOFT MATERIALS FOR STRUCTURAL APPLICATIONS

Abstract

Soft materials have been used extensively as energy absorbers in different industries such as marine, protective equipment, automotive, aerospace and transportation due to their light weight, low impedance, low mechanical stiffness and low strength. Foams, rubbers, polymers, hydrogels, and biological tissues are some examples of soft materials. Low density closed cell foams are widely used in marine and transportation industry as energy absorbers due to their light weight and low impedance. Mechanical responses of these materials are very sensitive to loading medium, rate and direction. Fundamental investigation into the mechanical response of these materials is paramount before they can be incorporated into the design of future structural applications that would be exposed to low and high loading rates. For this purpose, a comprehensive study was conducted to investigate the underwater mechanical response of low density (35 – 100 kg/m3) closed cell polymer foams under hydrostatic and underwater shock loadings. Moreover, shear thickening fluids have received significant attention for various applications such as traction control, smart structures and body armors. AMCS hydrogel as a shear thickening fluid is widely used in energy mitigation application due to its load or temperature induced gelation. Structural shock mitigation of AMCS hydrogel under different loading rates was investigated, and its mitigation performance was compared with water. The underwater constitutive behavior of PVC foams with varying densities was investigated experimentally. The experiments were conducted in an optically clear acrylic tube, which allowed for visualization of the specimen and the application of 3D Digital Image Correlation. A series of calibration experiments was conducted to investigate the applicability of the Digital Image Correlation technique for measuring the deformation of underwater objects inside of a curved acrylic tube of considerable thickness. The results of the calibration experiments demonstrated that a submerged object located in the middle of the acrylic tube appears magnified in the radial direction. This apparent magnification was taken into account during the analysis of the deformation for all underwater experiments. The hydrostatic loading was achieved by fitting the acrylic tube with a nylon piston and compressing the piston with an Intron testing machine. Hydrostatic load of up to 5 MPa was achieved during quasi-static compression of the piston. The load applied by the Instron machine was coupled with the Digital Image Correlation data to analyze the constitutive behavior of the PVC foams. The hydraulic crush pressure, bulk modulus, and energy stored up to densification strain were