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(a) Typical case of the relationship between load (1) and unload (2) and the penetration depth for GF material; (b) the elastic modulus of GF in relation to their density and fractional composition; (c) relationship between the compression depth and the applied load for GF, with the density being 1.0 g/cm3 by the fraction 40–80 μm (the black curve), 160–200 μm (the red curve), >500 μm (the green curve).
