Faculty of Mechanical Engineering, Technion, Israel
Shock Attenuation Characteristics of Methylcellulose Hydrogels: Experimentation and Phenomenological Modeling
Liquid methylcellulose hydrogels have a definite potential to mitigate strong shocks, of the kind responsible for traumatic brain injury. As such, they can complement the usual armor layers aimed at destroying the threat while transmitting the shock elastic energy without disturbance.
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 20mm) 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.
In the next step, (kinetic) energy mitigation was experimentally characterized using a momentum trap setup, thereby completing the picture of the shock energy attenuation by liquid MC hydrogels.
Prof. Daniel Rittel holds the Zandman Chair in Experimental Mechanics and heads the Materials Mechanics Center at Technion. D. Rittel was the Clark B. Millikan Visiting Professor in Aeronautics (2007) at Caltech where he holds a Visiting Associate position. He is the incumbent of a Catedra de Excellencia at UC3M (Madrid) in 2012 and 2019, where he is now an Honorary Professor. Throughout the years, D. Rittel has developed expertise in many aspects of dynamic failure, including fracture mechanics, constitutive behavior, dynamic failure mechanisms and numerical modeling, and more recently dental biomechanics and soft matter. D. Rittel’s interest is in thermomechanics and physics of dynamic failure, specifically dynamic fragmentation, fracture, adiabatic shear banding, and hysteretic heating. In 2015, D. Rittel was awarded the prestigious Gili Agostinelli Prize (Torino Academy of Sciences, Italy) for his work on adiabatic shear localization, and in 2018, he was awarded the BJ. Lazan award from the SEM.