Fig. 4
From: Locally-curved geometry generates bending cracks in the African elephant skin
Stratum corneum cracking by growth versus shrinkage. a, b Under the model of growth and deficient desquamation, addition of keratinous sheets at the curved stratum basale makes the outer sheets experience strong bending stresses perpendicular (blue double arrow in inset of a) to the direction of troughs (T), causing cracks (red lines in b) to propagate in-between papillae (P). c, d Conversely, simulation of stratum corneum desiccation results in a cracking pattern (red lines in d) incompatible with those observed on elephants: simulated shrinkage makes the outer sheets experience stresses parallel (blue double arrow in inset of c) to the direction of troughs (T), causing cracks (red lines in d) to nucleate perpendicular to (rather than along) the trough directions, propagate over papillae (P) and not intersect at trough junctions. Mesh edges in a, c are coloured by the intensity of strain, from zero (white) to the critical strain (εc, saturated red) at which edges are broken. Results shown are for εc = 0.3 and h/<d> = 1/6 ( <d> = average trough spacing), at a stage when ~3% of the mesh edges are cracked
