plot is going to zero

I am doing a plot, but I don't know why the curve is going to (0,0).

c = 0.66*10^-8;
m = 2.25; 
K_IC= 65; 

R=-1; 
a_0 = 0.1; 

delta_K_TH = 5; 

s=[4];
n=[1.7813e+06];

sigma_maximum = 2; 
while sigma_maximum<=40 

a_f = (1/pi)*(K_IC/(1.1215*sigma_maximum))^2 intensity factor

sigma_minimum =sigma_maximum*R;
delta_sigma=sigma_maximum-sigma_minimum 

delta_K = 1.1215*delta_sigma*sqrt(pi*a_0)

if(delta_K >= delta_K_TH)

syms a;

number_cycles = int((c.*(1.1215.*delta_sigma.*sqrt(pi*a)).^ m).^-1,a_0,a_f); % necessary number of cycles to make the material fail

single(number_cycles) 
 n(sigma_maximum)= number_cycles;
s(sigma_maximum)=sigma_maximum;  
end 
sigma_maximum=sigma_maximum+1
end
plot(n,s)

[bym]

please format your code using {}code button

What are you trying to do? It looks like some sort of fracture mechanics, but the code is a hot mess... best I could clean it up is following... but still am lost

c = 0.66*10^-8; 
m = 2.25; 
K_IC= 65;

R=-1; 
a_0 = 0.1;

delta_K_TH = 5;

s=4; 
n=1.7813e+06;

sigma_maximum = 2; 
while sigma_maximum<=40

a_f = (1/pi)*(K_IC/(1.1215*sigma_maximum))^2; %?intensity factor

sigma_minimum =sigma_maximum*R; 
delta_sigma=sigma_maximum-sigma_minimum;

delta_K = 1.1215*delta_sigma*sqrt(pi*a_0);

if(delta_K >= delta_K_TH)

syms a;

number_cycles = int((c.*(1.1215.*delta_sigma.*sqrt(pi*a)).^ m).^-1,a_0,a_f); % necessary number of cycles to make the material fail

single(number_cycles) ;
n(sigma_maximum)= number_cycles; 
s(sigma_maximum)=sigma_maximum;
end
sigma_maximum=sigma_maximum+1
end
plot(n,s)

Answer 1

[Roger Stafford]

The test you make at:

   if(delta_K >= delta_K_TH)

is not satisfied for 'sigma_maximum' equal to 2 and 3. Consequently the 2nd and 3rd positions in the arrays 'n' and 's' are skipped and left at a default value of 0. That would give you a (0,0) value in your plot.

If you don't want that to happen, you should change the lines

   n(sigma_maximum) = number_cycles;
   s(sigma_maximum) = sigma_maximum;

to

   n = [n,number_cycles];
   s = [s,sigma_maximum];

This would avoid leaving the two default zero values in 'n' and 's'. However they would then possess only 38 elements each.

[Matheus]

Thank you. definitely, help me

[Matt J]

If it helped you, you should click Accept on Roger's answer.