Design of custom cranial prostheses combining manufacturing and drop test finite element simulations

G Palumbo,A Piccininni,E Sgambitterra,G Ambrogio

doi:10.1007/s00170-020-06213-w

Abstract

In this work, impact puncture tests (drop tests) have been used to both tune numerical models and correlate the performance of customised titanium cranial prostheses to the manufacturing process. In fact, experimental drop tests were carried out either on flat disk-shaped samples or on prototypes of titanium cranial prostheses (Ti-Gr5 and Ti-Gr23 were used) fabricated via two innovative sheet metal forming processes (the super plastic forming (SPF) and the single point incremental forming (SPIF)). Results from drop tests on flat disk-shaped samples were used to define the material behaviour of the two investigated alloys in the finite element (FE) model, whereas drop tests on cranial prostheses for validation purposes. Two different approaches were applied and compared for the FE simulation of the drop test: (i) assuming a constant thickness (equal to the one of the undeformed blank) or (ii) importing the thickness distribution determined by the sheet forming processes. The FE model of the drop test was used to numerically evaluate the effect of the manufacturing process parameters on the impact performance of the prostheses: SPF simulations were run changing the strain rate and the tool configuration, whereas SPIF simulations were run changing the initial thickness of the sheet and the forming strategy. The comparison between numerical and experimental data revealed that the performance in terms of impact response of the prostheses strongly depends on its thickness distribution, being strain hardening phenomena absent due to the working conditions adopted for the SPF process or to the annealing treatment conducted after the SPIF process. The manufacturing parameters/routes, able to affect the thickness distribution, can be thus effectively related to the mechanical performance of the prosthesis determined through impact puncture tests.Graphical abstract

Highlights

The continuous research for a new category of prosthetic implants capable of improving the life expectancy of patients, reducing the risk of an additional surgery or prolonged hospitalisation, is still an open question [1]
In order to test the effect of the thickness distribution on the final part in the single point incremental forming (SPIF) process, both the two forming strategies described in Section 2.3.2 were simulated
Drop tests on disk-shaped samples represent a valid alternative to the widespread characterisation technique based on tensile tests: even if tensile tests are simple and robust, drop test data could rapidly provide information which, being directly extracted from the same test to be simulated, revealed to be effective in the proposed inverse characterisation methodology

Summary

Introduction

The continuous research for a new category of prosthetic implants capable of improving the life expectancy of patients, reducing the risk of an additional surgery or prolonged hospitalisation, is still an open question [1]. Ensuring the proper mechanical anchoring while matching, at the same time, the aesthetic requirements represents the starting point for the design of superior implantable devices In such a scenario, one of the most critical aspects remains the optimal combination of the best material [4]—to ensure the prescribed biocompatibility [5] and the corrosion resistance [6] once implanted—with the most suitable manufacturing process to achieve the required shape complexity. One of the most critical aspects remains the optimal combination of the best material [4]—to ensure the prescribed biocompatibility [5] and the corrosion resistance [6] once implanted—with the most suitable manufacturing process to achieve the required shape complexity In this field, several studies have demonstrated the effectiveness of sheet metal forming processes in the manufacturing of complex biomedical implants.

Methods

Results

Conclusion