Microstructure-induced giant elastic nonlinearity of threshold origin: Mechanism and experimental demonstration

There are known numerous examples of strong physical nonlinearity of elastic microinhomogeneous materials caused by the presence of a small amount of a “soft” component (cracks, intergrain contacts, bubbles, etc.). The dimensionless parameter $B/A$ of quadratic nonlinearity for such materials can be on the order of 102–103 in contrast to values on the order of unity typical of ideal crystals, homogeneous amorphous solids or liquids. The sign of this nonlinearity is such that all those materials become stiffer as pressure increases. We consider an extension of this “soft-rigid paradigm” of the nonlinearity increase by accounting for threshold-type properties intrinsic to some inclusions. We show that the nonlinearity in this case can additionally be orders of magnitude higher. We present an example of such a material which unlike “normal” media becomes softer with increasing pressure. Its quasistatic negative parameter $B/A$ reaches ~ (0.5–1)$\cdot$ 105, which to our knowledge is a record value.