🔧 Mechanical Design Fundamentals – Types of Stress
In mechanical design, every component experiences forces. How these forces act determines the type of stress inside the material. A good designer must understand these before creating CAD/CAE models.
1️⃣ Stress (σ)
📌 Definition → Internal resistance offered by a material per unit area when an external force is applied.
📌 Formula → σ = F / A
📌 Units → N/m² (Pascal or MPa)
✔ Why it matters? Stress analysis ensures that parts don’t fail under real-world loads.
2️⃣ Tensile Stress (Tension)
Occurs when forces try to stretch or pull apart a material.
👉 Example → A rope in a crane lifting a load, or a bolt under axial pulling force.
✔ Designers must ensure the ultimate tensile strength (UTS) of the material is higher than working stress.
3️⃣ Compressive Stress (Compression)
When forces push or squeeze a material, reducing its length.
👉 Example → Columns, pistons, or press-fit joints.
⚠ Risk → Buckling (sudden sideways failure in long slender members).
4️⃣ Shear Stress (τ)
When forces act parallel to the surface, causing layers to slide over each other.
📌 Formula → τ = F / A (parallel force / shear area)
👉 Example → Rivets, bolts under shear, scissors cutting paper.
✔ Important in fastener and joint design.
5️⃣ Torsional Stress (Twisting)
When torque (rotational force) is applied, causing shear stress around the axis.
👉 Example → Shafts in engines, gearboxes, propellers.
📌 Formula → τ = T·r / J
T = Torque
r = Radius
J = Polar moment of inertia
✔ Key design factor → Angle of twist must be within limits to avoid misalignment.
6️⃣ Bending Stress (Flexural)
When a beam or shaft is subjected to a load that causes it to bend.
👉 Combination of tension (at one side) and compression (at the other).
📌 Formula → σ = M·y / I
M = Bending moment
y = Distance from neutral axis
I = Moment of inertia
👉 Example → Bridges, cantilever beams, levers.
✅ Why This Matters in CAD/CAE?
Every CAD design will eventually be checked in CAE. Knowing these stress types allows engineers to:
Select the right material
Apply the correct load conditions in FEA
Ensure safety & reliability of designs
source : Technocraft Academy
