On the load dependence of friction: Role of the long-range elastic coupling

When an elastic block is squeezed in contact with a substrate the contact will in general consist of many asperity contact regions. During sliding the long-range elastic coupling between the contact regions have a big influence on the sliding dynamics: when the loading force increases the density of contact regions increases, which affects the lateral coupling between the contact region, and introduces a dependence of the friction force on the loading force. Here we present a full three-dimensional model study of the role of the elastic coupling on the friction force. The theory is applied to rubber friction, but the mechanism for the dependence of the friction coefficient on the load is relevant for non-rubber materials as well.