Getting wrong plot for stress vs strain curve

%Artur Chuvik
%MAE 315 Intro Lab
%Fall 2020

%Preparing the script
clc
close all
clear all

%For the fall 2020 intro lab, we are given a displacement data and recorded
%axial force from a tensile test performed on a carbon steel specimen.
%Using this data, we calculate the stress and strain and plot a stress vs
%strain curve. From this, we calculate the ultimate and rupture stresses
%and strains, value of Young's Modulus, yield point, and the zeroth-order
%uncertainty in the ultimate stress, ultimate strain, and Young's modulus.

%Create L, t, w, F, and d as symbols to manipulate
syms L t w F d %length, thickness, and width of specimen, axial force, and 
%displacement from tensile test respectively

L = 6.5 %inches
t = 0.085 %inches
w = 0.465 %inches

%Import data
raw_data = importdata('Intro_specimen.txt','\t');
info = raw_data.data; %Extract useful data

d = info(:,1) %First column of data is axial displacement

F = info(:,2) %Second column of data is axial ford

strain = info(:,3) %Third column of data is axial strain

%Will be plotting stress vs strain curve, so need equations for stress

stress = F/(w*t)

figure(1)
plot(strain,stress)
hold on
title('Stress vs Strain')
xlabel('Strain(in/in)')
ylabel('Stress(in/in^2)')
hold all
legend('Stress')

So I'm trying to make a stress vs strain curve, but when I run this, it comes out weird... what am I doing wrong?

Also I need to determine the ultimate stress, rupture stress, and yield point.. how do I do that?

[VBBV]

attach your data file