Friction force models play a fundamental\ud role for simulation ofmechanical systems. Their choice\ud affects the matching of numerical results with physically\ud observed behavior. Friction is a complex phenomenon\ud depending on many physical parameters and\ud working conditions, and none of the available models\ud can claim general validity. This paper focuses the\ud attention on well-known friction models and offers a\ud review and comparison based on numerical efficiency.\ud However, it should be acknowledged that each model\ud has its own distinctive pros and cons. Suitability of\ud the model depends on physical and operating conditions.\ud Features such as the capability to replicate stiction,\ud Stribeck effect, and pre-sliding displacement are\ud taken into account when selecting a friction formulation.\ud For mechanical systems, the computational efficiency\ud of the algorithm is a critical issue when a fast\ud and responsive dynamic computation is required. This\ud paper reports and compares eight widespread engineering\ud friction force models. These are divided into two\ud main categories: those based on the Coulomb approach and those established on the bristle analogy.The numerical\ud performances and differences of each model have\ud been monitored and compared. Three test cases are discussed:\ud theRabinowicz test and other two test problems\ud casted for this occurrence

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The present paper deals with the problem of numerical estimation of fatigue life in spot welded structures. It is evidenced that the use of a particular suited analytical solution inside the finite element calculation is possible and provides gains in both accuracy and computer time saving. The main point discussed in the paper regards the approach to discretize the analytical solution of the region surrounding the spot weld to the mesh of the rest of the structure. Independence to mesh refinement is achieved very early as discussed through examples. Chance is given to account of progressive damaging of spot welds. Comparison with traditional mesh techniques is also performed