3. You are comparing two different processing methods used for forming Ti6A14V i

Question

3. You are comparing two different processing methods used for forming Ti6A14V into a femoral stem of a hip joint prosthesis. The following diagram shows the structures that result from the two methods: (a)Which of the two processing methods results in a material with a higher ultimate tensile strength? Why? (5) (b) Stress shielding effect is a common complication after orthopedic implantation especilly for total hip and knee arthroplasty. Briefly describe it How do we avoid it! (5) e PMHA Stress

Explanation / Answer

a) Method A results in a material with a higher tensile strength, as it has a higher number of grain boundaries, which are barriers to slip. Therefore it will take a greater stress to initiate slip, which is the cause of plastic deformation.

b)Stress shielding effect refers to the reduction in bone density (osteopenia) as a result of the removal of typical stress from the bone by an implant (for instance, the femoral component of a hip prosthesis).This is because, by Wolff's law, bone in a healthy person or animal will remodel in response to the loads it is placed under. Therefore, if the loading on a bone decreases, the bone will become less dense and weaker because there is no stimulus for continued remodeling that is required to maintain bone mass.

To avoid stress shielding effect: use radial functionally graded biomaterials, Titanium-Based Biomaterials.

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