PSI - Issue 13

Milena Babić et al. / Procedia Structural Integrity 13 (2018) 438 – 443 E. D. Pasiou, S. K. Kourkoulis , M. G. Tsousi, Ch. F. Markides/ Structural Integrity Procedia 00 (2018) 000 – 000

440

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and scans were taken for each position. After the scanning was completed, the subsequent scans were aligned by using reference points. The result of the aligned scans was a point cloud in STL format, as shown in Fig. 2b. The obtained STL file was imported to Geomagic Design X software. In this software, CAD model, depicted in Fig. 4b, was built based on the obtained point cloud. It was not possible to remove the polyethylene acetabular cup from the femoral component head. The head geometry was reconstructed from the scanned surface visible and accessible in the point cloud, as shown in Fig. 2b.

(a) (c) Fig. 2. (a) Scanning process; (b) point cloud obtained by scanning process; (c) CAD model built based on the point cloud. (b)

3. Finite element model and analyses

The CAD model obtained by the scanning process and Geomagic Design X software was imported to FEM software Abaqus, where it was used as a base to create a FEM model. In the FEM modelling and analysis, the second order tetrahedral elements C3D10 were used. The prosthesis material was austenitic stainless steel for cast ASTM F-745. The mechanical properties of the considered material according to Griza et al. (2008) are shown in Table 1.

Table 1. Mechanical properties of stainless steel. Mechanical properties

ASTM F-745

Elastic modulus (GPa)

205

Poisson’s ratio

0.3

Initial yield stress (MPa)

235 502

Intermediate yield stress (MPa) Maximum yield stress (MPa)

666.82

The aim of this study was to identify the influence of debonding of the prosthesis femoral component shaft and femoral bone on stress and strain distribution in the femoral component, and consequently its influence on the fatigue life. Four different cases were studied assuming different debonded areas. The first case assumed a newly implanted prosthesis without debonding, which was modelled with completely fixed femoral shaft of the total hip prosthesis. The next three cases assumed loosened femoral component of the same prosthesis with different depth of debonded area. The debonded area was modelled through implementing boundary conditions, where the nodal displacements of the debonded area are allowed and nodes of the intact area are fixed, as depicted in Fig. 3. By numerical simulations, stress and strain distribution for a typical human walking load case were calculated for the considered FEM models.