Analysis of TRIP Steel HCT690 Deformation Behaviour for Prediction of the Deformation Process and Spring-Back of the Material via Numerical Simulation.

This paper deals with the analysis of TRIP steel HCT690 deformation behaviour. The mechanical properties and deformation characteristics of the tested material are determined using selected material tests and tests that consider the required stress states used to define the yield criterion boundary condition and subsequent deformation behaviour in the region of severe plastic deformation. The measured data are subsequently implemented in the numerical simulation of sheet metal forming, where they are used as input data for the computational process in the form of a selected material model defining the yield criterion boundary and, furthermore, the material hardening law during deformation of the material. The chosen numerical simulation process corresponds to the sheet metal forming process, including the subsequent spring-back of the material, when the force does not affect the material. Furthermore, the influence of the chosen computational model and selected process parameters on the deformation and spring-back process of the material is evaluated. In addition to that, at the end of the paper, the results from the numerical simulation are compared with experimentally produced sheet stamping.

Failure of sternal wires depends on the number of turns and plastic deformation: combined experimental and computational approach.

OBJECTIVES: The number of turns at the end of a wire closure is not described or discussed in any cardiosurgical guidelines. The hands-on experience of the surgeon plays a significant role. The aim of this work was to clarify the relationship between the number of turns of the suture and the resulting strength of the sternal fixation. METHODS: The study was performed in 2 independent steps. The first step was a finite element simulation, where the stress and strain distribution of the sternal fixation was observed. The second step included the experimental set-up and the statistical evaluation of the results. RESULTS: Our study showed that the failure force rose linearly as the number of turns increased. The lowest average measured force was 370 N (3 turns); the highest was 430 N (7 turns). The failure modes were either untwisting of the wires or rupture of the closure, which is controlled by the number of turns. As the number of turns increases, superficial cracks can occur. CONCLUSIONS: Based on our results, the 5-turn option is the best solution for the closure. The failure force is still double the value reported in the literature, so there is a high safety margin for failure. The failure mode is untwisting; hence, no unexpected fracture can occur, and there is still an elastic core in the cross-section of the wire.