Question 4 (5+5+5=15 marks): Composite beams
The figure shows intervertebral bones, a healthy disc, and its simplified model. Assuming the idealized geometry with given parameters and composite beam response under axial loads, answer the questions below (Elastic modulus of cortical bone = 10 GPa. Elastic modulus of trabecular bone = 2 GPa, r = 20 mm, and r = 15 mm).
a) Calculate the elastic modulus of the composite beam.
b) Calculate the stresses acting on cortical and trabecular bone under a compressive force of 100 N on the disc.
c) If the disc becomes diseased over time such that the Young's modulus of trabecular bone decreases by 50%, what is the effect of the change in the short term on stress distribution, and in the long term on disc response.