# Chapter1-What Is Mechanical Design¶

## Ex2-pg13¶

In [1]:
import math

print('MACHINE DESIGN \n Timothy H. Wentzell, P.E. \n EXAMPLE-1.2   Page 13 ')
##Example 1.2

Sy=61000.                   ##[psi] Tensile strength of AISI 1020 cold drawn steel from Appendix 4 Page no 470
SF=2.;                      ##[] safety factor
F=300.;                     ##[lb] Weight of the ball
L=36.;                      ##[in] Length of round bar
Sy=61000.;                  ##[psi] Tensile strength from Appendix 4
M=F*L;                     ##[in*lb] Bending moment Appendix 2

Sall=Sy/SF;                ##[psi] Allowable stress
Z=M/Sall;                  ##[in^3] Section modulus for bending Sall=M/Z
D=(32.*Z/math.pi)**(1./3.);        ##[in] Diameter of bar

##Use 13/8 in bar
D1=1.625;

print'%s %.2f %s '%('\n\n Diameter of Bar is ',D1,' in');

##Checking Deflection
I=math.pi*D1**4/64.;              ##[in^4] Moment of inertia Appendix 3
E=30.*10**6.;                  ##[lb/in^2] Modulus of elasticity
Delta=F*L**3./(3.*E*I);        ##[in] Deflection

##Note- In the book I=0.342 in^4 is used instead of I=0.3422814 in^4

print'%s %.2f %s '%('\n The deflection of bar is',Delta,' in');

##Note: The deviation of answer from the answer given in the book is due to round off error.(In the book values are rounded while in scilab actual values are taken)

MACHINE DESIGN
Timothy H. Wentzell, P.E.
EXAMPLE-1.2   Page 13

Diameter of Bar is  1.62  in

The deflection of bar is 0.45  in