Attached is a pdf file indicating a discrepancy in the governing eq for radial displacements in a sphere.  I am + Dr. Bower's text is correct but I cannot reconcile my derivation with his so I am assuming there must be some underlying assumption or approximation I am not aware of.

 Can anyone provide me with greater insight?

my email: jberg3@unl.edu

I am working on my PhD in Biomedical Engineering at the University of Neb. and have enrolled inES 242r because failure modes of many orthopedic implants can be attributed to initial flaws & fractures of material coatings.  This course, albeit, focuses on ductile materials, the principles seem relevant.