Nonlinear explicit analysis and study of the behaviour of a new ring-type brake energy dissipator by FEM and experimental comparison

The aim of this paper is to comprehensively analyse the performance of a new ring-type brake energy dissipator through the finite element method (FEM) (formulation and finite element approximation of contact in nonlinear mechanics) and experimental comparison. This new structural device is used as a system component in rockfall barriers and fences and it is composed of steel bearing ropes, bent pipes and aluminium compression sleeves. The bearing ropes are guided through pipes bent into double-loops and held by compression sleeves. These elements work as brake rings. In important events the brake rings contract and so dissipate residual energy out of the ring net, without damaging the ropes. The rope's breaking load is not diminished by activation of the brake. The full understanding of this problem implies the simultaneous study of three nonlinearities: material nonlinearity (plastic behaviour) and failure criteria, large displacements (geometric nonlinearity) and friction-contact phenomena among brake ring components. The explicit dynamic analysis procedure is carried out by means of the implementation of an explicit integration rule together with the use of diagonal element mass matrices. The equations of motion for the brake ring are integrated using the explicit central difference integration rule. The presence of the contact phenomenon implies the existence of inequality constraints. The conditions for normal contact are @l>=0,g>=0 and g@l=0, where @l is the normal traction component and g is the gap function for the contact surface pair. To include frictional conditions, let us assume that Coulomb's law of friction holds pointwise on the different contact surfaces, @m being the dynamic coefficient of friction. Next, we define the non-dimensional variable @t by means of the expression @t=t/@m@l, where @m@l is the frictional resistance and t is the tangential traction component. In order to find the best brake performance, different dynamic friction coefficients corresponding to the pressures of the compression sleeves have been adopted and simulated numerically by FEM and then we have compared them with the results from full-scale experimental tests. Finally, the most important conclusions of this study are given.