Nonlinear Finite Element Analysis Of Frictional Contact Problems Using Variational Inequalities Microform

Dynamic contact problems play an important role in dictating the integrity, performance and safety of many engineering systems/components involved in vehicle design, armament and ballistics, metal forming/cutting, and surface treatments, just to name a few. Despite their importance to the mechanical integrity of the systems examined, dynamic contact effects are frequently treated using oversimplifying assumptions, which neglect the main feature of the problem. This is because of the complexity of the governing system of equations. In this work, dynamic frictional contact problems are formulated using the more reliable and consistent variational inequalities (VI) approach. Three aspects of the problem are accordingly examined. The first is concerned with the development of the appropriate variational inequality formulations and solution strategies for dynamic frictional contact problems involving material and geometrical nonlinearity. Two models of surfaces are taken into account: (i) perfectly smooth surfaces, and (ii) more realistic surfaces, which take into account the change in compliance due to surface roughness. A new technique for representing the kinematic contact conditions is developed. Two newly devised numerical procedures are devised to solve the general dynamic frictional contact problem for elastic and elasto-plastic media. The first solution strategy, which regularises friction, is based upon the iterative use of mathematical programming and Lagrange multipliers. The second approach is accomplished using a nondifferentiable optimisation algorithm, through a sequence of mathematical programming sub-problems. The second aspect of the work is concerned with the selection of a suitable time integration scheme for contact problems. The values of the time integration parameters are so chosen to ensure that the solution is second order accurate, unconditionally stable, preserves energy and momentum during rigid impact, thus minimising numerical oscillations and ensuring optimal numerical dissipation. Finally, the developed algorithms are validated and applied to the analysis of several interesting engineering problems. The numerical predictions are compared to existing experiments as well as a commercial finite element code. The results reveal that the new dynamic friction contact formulations are more accurate than the traditional variational methods. These newly developed algorithms should provide designers with a powerful tool for treating dynamic elasto-plastic problems involving frictional contact.

This book presents the mathematics behind the formulation, approximation, and numerical analysis of contact and friction problems. It also provides a survey of recent developments in the numerical approximation of such problems as well as several remaining unsolved issues. Particular focus is placed on the Signorini problem and on frictionless unilateral contact in small strain. The final chapters cover more complex, applications-oriented problems, such as frictional contact, multi-body contact, and large strain. Finite Element Approximation of Contact and Friction in Elasticity will be a valuable resource for researchers in the area. It may also be of interest to those studying scientific computing and computational mechanics.

A perturbed Lagrangian-based variational formulation is proposed for the finite element solution of fully nonlinear frictional contact problems. In the spirit of an operator splitting methodology, an analogy exists between the proposed treatment for the stick-slip motion and the corresponding treatment in elastoplasticity. Within the context of discrete formulations arising from a finite element approximation, explicit expressions for the frictional consistent contact tangent stiffness and residual are derived from variational equations by using a consistent linearization procedure for both the sliding and adhesion phases. The consistent tangent operator is always non-symmetric for the case of frictional sliding owing to the nature of the Coulomb's friction law employed. For two-dimensional applications, a three-node contact element is employed in the finite element discretization. Numerical examples are also presented that illustrate the performance of the proposed formulation. Keywords: structural mechanics.

This volume builds on the ideas of geometric non-linearity explained in Volume One. Continuum mechanics, plasticity and stability theory are covered in greater depth as it explores the research on non-linear finite elements. A supplementary set of programmes is available on the.