**5.2.3 Loads**

158 Recent Advances in Arthroplasty

Fig. 1. Fatigue testing. The 3D finite element model developed in the analysis

Fig. 2. Implant attached to bone. Finite element model developed in the analysis

Abaqus 6.4.5.

All the models were created, analyzed and afterwards the results were processed using

In all cases for fatigue testing, the applied load was the load specified in the standard, of 2300 N. The load was applied on the upper surface of the piece that applys the load. For implant attached to bone the applied load was an arbitrary load of 1000 N in the

acetabular component of the prosthesis. Besides the pre-tensioning bolt load was simulated.

### **5.2.4 Results**

### **a. Fatigue testing:**

Due to the assembly load between the stem components, high levels of compressive contact stress were obtained. Therefore, and to wean the study of the influence of these stresses, we considered in the analysis the stress components S33, which would be responsible for a possible material fatigue. The simulation results obtained for the three models using different materials are given in Table 7.

Figure 3 shows the S33 stress distribution in the implant made of beta titanium alloy.


(\*) The indicated compression component was mainly due to the contact stresses.

Table 7. Simulation results for the three models

Fig. 3. S33 stress distribution (MPa)

Whereas the applied load varies between zero and 2300 N, the minimum stresses are related to those produced by the preload of the bolt connecting both parts of the implant, and the maximum stresses are due to the load of 2300 N.

Titanium as a Biomaterial for Implants 161

the loads. Comparing the stemmed models, from the point of view of stress and displacements that were produced in the bone, with the titanium Ti35Nb7Zr5Ta implant, the behaviour of the whole bone-implant is nearer to the natural bone, and the effect of

Fig. 6. S33 Stress in the bone, stemmed Ti35Nb7Zr5Ta implant model

It is well known that porosity decreases the Young's modulus of a material, thus it could be thought as a means to reduce stress shielding. It is difficult to get the properties for FEA analysis but it could be used some approach to represent the Young's modulus of a material with a given fraction of porosity. However, the effect the porosity on fatigue strength discourage using fully porous material in joint arthroplasty implants because porous metal alone does not provide sufficient mechanical strength to sustain the physiological loads

Acero, J.; Calderón, J.; Salmeron, J.; Verdaguer, J. & Consejo, C. (1999). The behaviour of

Cameron, H.; Pilliar, R. & Macnab, I. (1976). The rate of bone ingrowth into porous metal.

Currey, J. (1998). Mechanical properties of vertebrate hard tissues. *Proceedings of the* 

titanium as a biomaterial: microscopy study of plates and surrounding tissues in facial osteosynthesis. *Journal of Cranio-maxillofacial Surgery,* Vol.27, No.2, (April

*Journal of Biomedical Materials Research,* Vol.10, No.2, (March 1976), pp. 295-302,

*Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine,* Vol.212,

**5.3 Fully porous material in hip implants** 

1999), pp. 117-123

ISSN 00219304

No.6, (1998), pp. 399-411, ISSN 09544119

(Ryan et al., 2006).

**6. References** 

stress shielding was the smaller.

Using the mechanical properties of the materials, were drawn Goodman diagrams and plotted the points corresponding to the applied loading (Figures 4 and 5). From them, it could be seen that the implants have unlimited duration of life with the geometry, loads and properties considered. However, it can be seen in the diagram for the stainless steel implant that the point representing working conditions is located near the boundary of the safe zone.

### Fig. 4. Goodman's diagram. Ti6Al4V

It should be noted that the environment in which the implant should work would influence the final fatigue behaviour.

#### **b. Implant fixed to bone:**

In Figure 6 the S33 stress is shown for the bone, from the analysis of the stemmed Ti35Nb7Zr5Ta implant. Comparing whit the model without the implant, in the stemmed ones it was observed a change in the stress pattern, because the stem shielded the bone from

Fig. 5. Goodman's diagram. 316L and Ti35Nb7Zr5Ta

Using the mechanical properties of the materials, were drawn Goodman diagrams and plotted the points corresponding to the applied loading (Figures 4 and 5). From them, it could be seen that the implants have unlimited duration of life with the geometry, loads and properties considered. However, it can be seen in the diagram for the stainless steel implant that the point representing working conditions is located near the boundary of the safe zone.

It should be noted that the environment in which the implant should work would influence

In Figure 6 the S33 stress is shown for the bone, from the analysis of the stemmed Ti35Nb7Zr5Ta implant. Comparing whit the model without the implant, in the stemmed ones it was observed a change in the stress pattern, because the stem shielded the bone from

316 L

Fig. 4. Goodman's diagram. Ti6Al4V

Fig. 5. Goodman's diagram. 316L and Ti35Nb7Zr5Ta

Ti35Nb7Zr5

the final fatigue behaviour. **b. Implant fixed to bone:**  the loads. Comparing the stemmed models, from the point of view of stress and displacements that were produced in the bone, with the titanium Ti35Nb7Zr5Ta implant, the behaviour of the whole bone-implant is nearer to the natural bone, and the effect of stress shielding was the smaller.

Fig. 6. S33 Stress in the bone, stemmed Ti35Nb7Zr5Ta implant model
