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

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4. Results and discussion The stress distribution in the femoral part of the total hip prosthesis due to human walking was determined for assumed different depths of debonded area between femoral shaft and bone. For the first studied case, with completely fixed femoral shaft, without debonded area, maximum stresses appeared under the collar of the femoral component of the prosthesis, as depicted by the rectangle in Fig. 5a. In case of loosened femoral shaft models shown in Figs. 5b, c and d, maximum stresses appeared above the fixed area of the femoral shaft. In particular, in the model described in Fig. 5b, tensile stresses appear on the lateral side, and compressive stresses appear on the medial side of the prosthesis shaft. This is in good agreement with observations reported by Griza et al. (2008), that fatigue cracks occur at the location with tensile stresses. In the model described in Fig. 5c, slightly lower tensile and compressive stresses appear at similar locations as in the case of model shown in Fig. 5b, while in this case additional higher tensile and compressive stresses appear slightly above the fixed area. The model described in Fig. 5d showed a similar tendency as the model shown in Fig. 5c, with slightly higher stress level above the fixed area and slightly lower stresses in the upper part of the model. It should be noted here that, as a result of 3D scanning, some imperfections occurred in the transition parts and sites of geometry discontinuity of the specimen, which caused additional stress concentrations as can be seen in Fig. 6a.

Tensile stress 106 MPa

Tensile stress 105 MPa

Maximum tensile stress 108 MPa

Compressive stress

Maximum compressive stress

Compressive stress

Maximum compressive stress

Maximum tensile stress

Maximum tensile stress

Maximum tensile stress

Maximum compressive stress

Maximum compressive stress

(a) (d) Fig. 5. Stress distribution of maximum principal stress (absolute). (a) The first case; (b) the second case; (c) the third case; (d) the fourth case. (b) (c)

(a) (d) Fig. 6. Tensile stress concentration areas. (a) The first case; (b) the second case; (c) the third case; (d) the fourth case. (b) (c)