Stress-Strain Curve Plotter — Python GUI App for Engineering Analysis

Project Description

A standalone Python desktop application that reads material data from CSV or Excel files and generates a stress-strain curve. It computes key mechanical properties such as Young’s Modulus, Yield Strength (using 0.2% offset method), and Ultimate Strength. Built using Tkinter, Matplotlib, Pandas, and NumPy, this tool is intended for engineers, researchers, or students analyzing material behavior.

1. Young’s Modulus (Elastic Modulus)

Definition:
Young’s Modulus is the slope of the initial, linear portion of the stress-strain curve. It quantifies stiffness — how much a material resists deformation under stress.

How the app calculates it:

• Takes the linear region of the data (commonly up to 0.2% strain)
• Applies linear regression to compute the slope
• Formula used: E=Δσ/Δε

Engineering Insight:
High Young’s Modulus → Stiff material (e.g., steel)
Low Young’s Modulus → Flexible material (e.g., rubber)

Code Location:

linear_region = strain <= 0.002
youngs_modulus = np.polyfit(strain[linear_region], stress[linear_region], 1)[0]

Explanation:

• strain <= 0.002: selects the linear (elastic) region.
• np.polyfit(..., 1)[0]: performs linear regression and returns the slope, which is Young’s Modulus.

Where it is used in the app:
Used later to draw the offset line for computing yield strength.

2. Yield Strength (Using 0.2% Offset Method)

Definition:
Yield Strength is the stress at which permanent (plastic) deformation begins. It marks the transition from elastic to plastic behavior.

Why the 0.2% Offset Method?

• Some materials (like metals) do not have a clear “yield point”
• The 0.2% offset method is a standard engineering practice:
  Draw a line parallel to the elastic slope, offset by 0.002 strain (0.2%)

How the app calculates it:

• Computes the offset line using Young’s Modulus
• Finds the intersection point between the curve and offset line
• That intersection point gives:
  • Yield Stress
  • Corresponding Strain

Engineering Insight:
This value is crucial in designing components that should not undergo permanent deformation under regular use.

Code Location:

offset_strain = strain + 0.002
offset_line = youngs_modulus * offset_strain
diff = np.abs(stress - offset_line)
yield_index = np.argmin(diff)
yield_stress = stress[yield_index]
yield_strain = strain[yield_index]

Explanation:

• offset_strain = strain + 0.002: creates a new strain line, offset by 0.2%
• offset_line = youngs_modulus * offset_strain: calculates the offset line using the elastic slope
• np.abs(stress - offset_line): calculates how far each point is from that line
• np.argmin(diff): finds the index where the stress curve is closest to the offset line
• yield_stress and yield_strain: give the yield point

Where it is used in the app:

• Plotted on the graph as a red dot
• Displayed in the result message:

f"Yield Strength: {yield_stress:.2f} MPa at Strain: {yield_strain:.4f}"

Ultimate Tensile Strength (UTS)

Definition:
The maximum stress that the material can withstand before necking or failure.

How the app calculates it:

• Simply finds the maximum value in the stress array

Engineering Insight:
A measure of the material’s peak strength. Design for UTS is common in failure analysis, but in safety-critical applications, engineers design well below this value.

Code Location:

ultimate_strength = np.max(stress)

Explanation:

• Finds the maximum stress value in the dataset.
• This is the peak of the stress-strain curve before fracture or necking.

Where it is used in the app:
Displayed in the result pop-up message:

f"Ultimate Strength: {ultimate_strength:.2f} MPa"

Summary Table

Property	What It Measures	How It’s Calculated	Importance
Young’s Modulus	Stiffness (elastic slope)	Slope of initial curve	Structural rigidity
Yield Strength	Onset of permanent deformation	0.2% offset method	Design limit for elastic behavior
UTS	Max stress before failure	Max value of stress	Peak strength before necking

Graphical Plot Code (Where the Properties Are Visualized)

fig, ax = plt.subplots(figsize=(6, 4))
ax.plot(strain, stress, label='Stress-Strain Curve')  # Full curve
ax.plot(offset_strain, offset_line, '--', label='0.2% Offset Line')  # For yield
ax.plot(yield_strain, yield_stress, 'ro', label=f'Yield Point\n({yield_strain:.4f}, {yield_stress:.2f})')

In Summary – Key Code Lines

Property	Key Line(s)
Young’s Modulus	youngs_modulus = np.polyfit(strain[linear_region], stress[linear_region], 1)[0]
Ultimate Strength	ultimate_strength = np.max(stress)
Yield Strength	Series of lines using offset line logic and np.argmin(diff)

Key Features of the App

Tools and Technologies

Tool	Purpose
Python	Main language
Tkinter	GUI development
Matplotlib	Plotting charts
Pandas	Data loading and manipulation
NumPy	Numerical calculations
OpenPyXL	Excel file support
PyInstaller	Packaging as .exe

My Reflection

This project helped me improve my understanding of file handling, GUI layout management, and numerical methods in mechanical engineering. I also learned how to bundle applications with PyInstaller and troubleshoot real-world deployment issues like missing dependencies.