Trapped fluid in contact interface

Abstract

We study the mechanical contact between a deformable body with a wavy surface and a rigid flat taking into account pressurized fluid trapped in the interface. A finite element model is formulated for a general problem of trapped fluid for frictionless and frictional contact. Using this model we investigate the evolution of the real contact area, maximal frictional traction and global coefficient of friction under increasing external pressure. Elastic and elasto-plastic material models, compressible and incompressible fluid models and different geometrical characteristics of the wavy surface are used. We show that in case of incompressible fluid, due to its pressurization, the real contact area and the global coefficient of friction decrease monotonically with the increasing external pressure. Ultimately the contact opens and the fluid occupies the entire interface resulting in vanishing of static friction. In case of compressible fluids with pressure-dependent bulk modulus, we demonstrate a non-monotonous behaviour of the global coefficient of friction due to a competition between non-linear evolution of the contact area and of the fluid pressure. However, for realistic compressibility of solids and fluids, contact-opening cannot be reached at realistic pressures. An asymptotic analytical result for the trap-opening pressure is found and shown to be independent of the surface slope if it is small. On the other hand, in case of elasticperfectly plastic materials, we again observe fluid permeation into the contact interface. Finally, we study the distribution of frictional tractions during the depletion of the contact area under increasing pressure. This process leads to emergence of singularity-like peaks in the tangential tractions (bounded by the Coulomb's limit) near the contact edges. We point out the similarity between the processes of trap opening and interfacial crack propagation, and estimate the complex stress intensity factor in the framework of linear elastic fracture mechanics.

Hydraulic Transport Through Calcite Bearing Faults With Customized Roughness: Effects of Normal and Shear Loading

“…The fully mated transmissivity results are in strong compatibility with experimental results. This highlights the strong influence of flow channeling on fracture hydraulic transport capacity which cannot be neglected in the analysis (Shvarts, 2019; Shvarts & Yastrebov, 2018a; Watanabe et al, 2009). Note that in the experiments, the surface mating was difficult to control when setting up the half fractures in the triaxial cell.…”

“…To examine the exact contribution of shear stress applied on the fracture, more complex elastic–plastic models are required. First attempts going in this direction are the models of Yastrebov et al (2017) and those of Shvarts and Yastrebov (2018a, 2018b) where the problem is approached through spectral boundary element methods and full monolithic coupling of the mechanical deformation and hydraulic transport in the fractures. These methods should allow the extension to shear stress and plasticity (Frérot et al, 2019) with the geometries used in this study (grooves suborthogonal to fluid flow and shear sense as well as parallel ones).…”

Fluid flow across a wavy channel brought in contact

“…In[42], this assumption was shown to be too prohibitive for certain applications even if the surface slope is assumed infinitesimal.…”

Computational framework for monolithic coupling for thin fluid flow in contact interfaces

“…We have recently studied the behaviour of hydrostatically pressurized fluid trapped in a contact interface without considering the fluid flow (Shvarts and Yastrebov, 2018b). We used the augmented Lagrangian method for the contact constraints, and the classic Lagrange multiplier method permitted us to take into account the additional constraint in case of incompressible fluid, while the penalty method was applied if the fluid was assumed compressible.…”

“…We introduced a novel trapped fluid super-element based on all out-of-contact segments (faces in 3D), surrounded by a contact patch, so that displacements of all nodes associated with this element were included into its degrees of freedom (DOF) vector. Moreover, we proposed a technique of extension of the trapped fluid element on the surrounding contact zone by superposing locally the contact and fluid pressure fields, which simplified considerably computations in certain cases (see Appendix B in (Shvarts and Yastrebov, 2018b)). Therefore, an additional objective of the current study is to incorporate the formulation of the trapped fluid element into the computational framework, permitting to quantify the effect of trapped fluid zones on the coupled problem.…”