Shock attenuation characteristics of methylcellulose hydrogels: Phenomenological modeling

The shock attenuation characteristics of aqueous methylcellulose (MC) gels were characterized experimentally and modeled towards their application in bodily protection systems against traumatic injury. The attenuation of MC gel with 4 different thicknesses (4, 7, 10 and 20 mm) and 3 concentrations (5, 10 and 15%Wt) was measured, using an instrumented (Hopkinson) bar and piezoresistive sensors for direct force sensing on the gel. First, the impulse attenuation was systematically characterized for all combinations of thickness and composition, and the results were analyzed statistically. The impulse attenuation increases with both thickness and MC concentration. A non-linear function was then fitted to the experimental results. The fitted functions increase monotonically with both the thickness and the concentration of the gel layer. However, the slope of each function decreases gradually with the thickness of the layer, thereby indicating an effective thickness beyond which shock attenuation efficiency does not increase significantly. The frequency dependence of the attenuation was determined next and found to be relatively independent of both thickness and gel concentration up to 100 kHz. A phenomenological expression was developed and validated for the shock attenuation of MC gels as a function of their composition, thickness and spectral content of the shock.