I have this example:
- $M_k$ = 80 Nm
- $d_1$ = 30 mm
- $d_2$ = 20 mm
- $a$ = 600 mm
- $b$ = 500 mm
- $G$ = 8,5e4 MPa
I want to know the twist at free end of this shaft. I am using the formula:
$$\phi = \dfrac{M_k \cdot a}{G \cdot \dfrac{\pi d_1^4}{32}} + \dfrac{M_k \cdot b}{G \cdot \dfrac{\pi d_2^4}{32}}$$
It gives me 0,037 rad.
But the result in the book is 0,013 rad. Where is the error?