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+// exa 4.9 Pg 113
+clc;clear;close;
+
+// Given Data
+Sut=860;//MPa
+Syt=690;//MPa
+Pmin=60;// N
+Pmax=120;// N
+R=50/100;// reliability
+l=500;//mm
+d=10;//mm
+Se_dash = 0.5*Sut;// MPa
+// for machines surface
+ka=0.70;// surface finish factor
+kb=0.85;// size factor (assuming t<50 mm)
+kc=1;// reliability factor
+kd=1;// temperature factor
+ke=1;// load factor
+
+Se=ka*kb*kc*kd*ke*Se_dash;// MPa( Endurance limit)
+Mmax=Pmax*l;// N.mm
+Mmin=Pmin*l;// N.mm
+Mm=(Mmax+Mmin)/2;// N.mm
+Ma=(Mmax-Mmin)/2;// N.mm
+Sm=32*Mm/%pi/d**3;//MPa
+sigma_m=Sm;//MPa
+Sa=32*Ma/%pi/d**3;//MPa
+sigma_a=Sa;//MPa
+Sf=Sa*Sut/(Sut-Sm);//MPa
+
+//calculating section
+OB=6;//unit ref. o at 3
+BE=OB-3;//unit
+OC=Sf;// MPa
+AE=log10(0.9*Sut)-log10(Se);//MPa
+AC=log10(0.9*Sut)-log10(Sf);//MPa
+CD=BE*AC/AE;//
+//log10(N)=3+CD
+N=10**(3+CD);// cycle
+printf('\n life of the spring, N = %.f cycles',N)
+//Note : answer in the textbook is wrong.