DEFORMABILITY OF CONTACT LAYERS

Machine and structural components have volume and surfaces. The last does not have an ideal shape, and they are rough. When two components have mechanical contact (like one foot of a desk and the floor), this contact has a common contact surface. It is well known that real contact surface is much smaller than the nominal cross-section of the smaller component. Furthermore, the volume that is near the contact surface is not dense. It contains asperities and empty space between them. This article answers the question “What happens with this contact volume and could we measure its size when the load changes?”  The theory starts with an acceptance that this volume (contact layer) is filled non-homogeneously with solid material and therefore its mechanical behaviour is non-linear.   This paper suggests a semi-empiric model that describes this phenomenon and also a method for interpretation and presentation of nonlinear force-displacement diagrams. This semi-empiric relationship is , where P is the load,  is the uniaxial deformation of the system with base length L, containing one contact layer and both a, b are regression coefficients. The paper presents results for deformability of the contact layer between a specimen, made of light silicate concrete, and the steel support.