When deformed beyond their elastic limits, crystalline solids flow plastically via particle rearrangements localized around structural defects. Disordered solids also flow, but without obvious structural defects. We link structure to plasticity in disordered solids via a microscopic structural quantity, “softness,” designed by machine learning to be maximally predictive of rearrangements. Experimental results and computations enabled us to measure the spatial correlations and strain response of softness, as well as two measures of plasticity: the size of rearrangements and the yield strain. All four quantities maintained remarkable commonality in their values for disordered packings of objects ranging from atoms to grains, spanning seven orders of magnitude in diameter and 13 orders of magnitude in elastic modulus. These commonalities link the spatial correlations and strain response of softness to rearrangement size and yield strain, respectively.

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Atomic force microscopy-based nanoindentation is used to image and probe the local mechanical properties of thin disordered nanoparticle packings. The probed region is limited to the size of a few particles, and an individual particle can be loaded and displaced to a fraction of a single particle radius. The results demonstrate heterogeneous mechanical response that is location-dependent. The weak locations may be analogous to the "soft spots" previously predicted in glasses and other disordered packings.

the interaction (characterized by the range of adhesion z 0 ).The intrinsic work of adhesion W adh is the energy per unit area required to separate two planar surfaces from equilibrium contact to infi nite separation. In terms of surface energy (γ i of surface i ) and interfacial energy (γ ij between surfaces i and j ), the work of adhesion is calculated as follows:In accordance with prior literature on adhesion and roughness, [ 9 ] the intrinsic work of adhesion W adh,int is defi ned as the work of adhesion between two perfectly fl at, planar surfaces. While W adh,int is a continuum concept, it can be robustly mapped onto an atomistic description of two atomically fl at, single-crystal surfaces in contact. The effective work of adhesion, W adh,eff , is defi ned as the work of adhesion for the same material pair and the same global geometry (planar), but with the addition of local surface roughness on one or both surfaces. The distinction between W adh,int and W adh,eff is shown schematically in Figure 1 . The W adh,int is determined by the identity of the materials in contact, and the environment, whereas W adh,eff is a function of W adh,int and the local surface topography. For hard, non-conforming materials, W adh,eff is typically much smaller than W adh,int . The primary reason for this is that the roughness increases the effective separation between the two materials, and therefore signifi cantly increases γ ij between the materials as they can no longer make intimate contact. Roughness can also increase the surface energies γ i and γ j , but this effect is typically overwhelmed by the change in γ ij . This distinction is drawn because many experimental techniques exist to measure W adh,eff (for example, using microfabricated beam tests [ 10 ] ), but generally applicable techniques to deduce from this the W adh,int are not well established.Physically, z 0 describes the equilibrium separation distance between perfectly fl at surfaces, i.e., the separation distance at which their interaction force is zero. However, in many mathematical descriptions of adhesion (for instance, refs. [ 5,7,8,11 ] ) z 0 also scales the distance over which adhesion acts for a particular material. Therefore, the parameter z 0 is referred to in this paper as the "range of adhesion," (in accordance with Greenwood, [ 5 ] who calls it the "range of action of the surface forces").The adhesive interactions between nanoscale silicon atomic force microscope (AFM) probes and a diamond substrate are characterized using in situ adhesion tests inside of a transmission electron microscope (TEM). In particular, measurements are presented both for the strength of the adhesion acting between the two materials (characterized by the intrinsic work of adhesion W adh,int ) and for the length scale of the interaction (described by the range of adhesion z 0 ). These values are calculated using a novel analysis technique that requires measurement of the AFM probe geometry, the adhesive force, and the position where the snap-in instability occurs. Values ...

To describe adhesion between bodies of known arbitrary shape and known elastic properties, contact mechanics models require knowledge or assumptions of a minimum of two parameters, the strength of the adhesive interaction (characterized by the intrinsic work of adhesion W adh,int ) and the length scale of the interaction (described by the range of adhesion z 0 ). One parameter can easily be measured if the other is estimated or assumed, but experimental techniques for determining both simultaneously are lacking. Here, we demonstrate a novel techniquecalled the Snap-in/pull-off Numerical Adhesion Parameter method-for experimentally determining both parameters simultaneously using adhesion measurements performed with an atomic force microscope probe whose geometry has been characterized. The method applies to materials that approach the rigid limit (high elastic moduli). The technique is explained and validated analytically for simple shapes (flat punch, paraboloid, and right cone), and trends in results are compared against prior literature. This approach allows calculation of the adhesion parameters to enable prediction of adhesion behavior, including for advanced technology applications.