Finite element estimates of interface stress in the trans-tibial prosthesis using gap elements are different from those using automated contact

When compared with automated contact methods of finite element (FE) analyse s, gap elements have certain inherent disadvantages in simulating large sli p of compliant materials on stiff surfaces. However, automated contact has found limited use in the biomechanical literature. A non-linear, three-dime nsional, geometrically accurate, FE analysis of the trans-tibial limb-socke t prosthetic system was used to compare an automated contact interface mode l with a gap element model, and to evaluate the sensitivity of automated co ntact to interfacial coefficient of friction (COF). Peak normal stresses an d resultant shear stresses were higher in the gap element model than in the automated contact model, while the maximum axial slip was less. Under prox imally directed load, compared with automated contact, gap elements predict ed larger areas of stress concentration that were located more distally. Ga p elements did not predict any relative slip at the distal end, and also tr ansmitted a larger proportion of axial load as shear stress. Both models de monstrated non -linear sensitivity to COF, with larger variation at lower m agnitudes of COF. By imposing physical connections between interface surfac es, gap elements distort the interface stress distributions under large sli p. Automated contact methods offer an attractive alternative in application s such as prosthetic FE modeling, where the initial position of the limb in the socket is not known, where local geometric features have high design s ignificance, and where large slip occurs under load, (C) 2000 Elsevier Scie nce Ltd. All rights reserved.