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Biological cells sense and respond to mechanical forces, but how such a mechanosensing process takes place in a nonlinear inhomogeneous fibrous matrix remains unknown. We show that cells in a fibrous matrix induce deformation fields that propagate over a longer range than predicted by linear elasticity. Synthetic, linear elastic hydrogels used in many mechanotransduction studies fail to capture this effect. We develop a nonlinear microstructural finite-element model for a fibre network to simulate localized deformations induced by cells. The model captures measured cell-induced matrix displacements from experiments and identifies an important mechanism for long-range cell mechanosensing: loss of compression stiffness owing to microbuckling of individual fibres. We show evidence that cells sense each other through the formation of localized intercellular bands of tensile deformations caused by this mechanism.

ABSTRACT--This study investigates heat generation in metals during plastic deformation. Experiments were designedto measure the partition of plastic work into heat and stored energy during dynamic deformations under adiabatic conditions. A servohydraulic load frame was used to measure mechanical properties at lower strain rates, 10 -3 s -1 to 1 s -1. A Kolsky pressure bar was used to determine mechanical properties at strain rates between 103 s -1 and 104 s -1. For dynamic loading, in situ temperature changes were measured using a high-speed HgCdTe photoconductive detector. An aluminum 2024-T3 alloy and c~-titanium were used to determine the dependence of the fraction of plastic work converted to heat on strain and strain rate. The flow stress and 13 for 2024-T3 aluminum alloy were found to be a function of strain but not strain rate, whereas they were found to be strongly dependent on strain rate for c~-titanium.

The controversial issue of whether dislocations can travel faster than shear or longitudinal waves is investigated. The Peierls model, modified to account for drag and gradient effects, furnishes a kinetic relation between the applied shear stress and speed of uniformly moving dislocations. This relation predicts intersonic and supersonic speeds at high enough stress, but also regimes of unstable motion, in agreement with recent atomistic simulations.

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