A sharp internal corner looks simple in CAD.
From a mechanical design point of view, it can be one of the most important features on the entire part.
The reason is stress concentration.
## What happens at a sharp corner?
When a load passes through a component, stress is not always distributed evenly.
A sudden change in geometry can concentrate stress around a small region.
Common examples include:
– Sharp internal corners – Holes – Keyways – Grooves – Threads – Notches – Abrupt section changes
## The simple fix: a fillet
A radius can smooth the load path and reduce local stress concentration.
But the radius should not be chosen blindly.
It must also consider:
– Manufacturing process – Tool diameter – Mating parts – Clearance – Material – Fatigue requirements
## Why fatigue makes it more important
A component under repeated loading can be much more sensitive to local stress concentration than one under a single static load.
A part may survive one high load and still fail after many cycles.
That is why small geometry details can have a large effect on fatigue life.
## What FEA can and cannot tell you
FEA is useful for identifying high-stress regions and comparing design changes.
But a perfectly sharp theoretical corner can also create a very high or mathematically problematic local result.
The model should represent the real manufactured geometry.
Do not simply stare at the maximum colour on a stress plot.
Ask whether the geometry, mesh, loads and boundary conditions represent the real part.
## A practical design habit
Whenever you create an internal corner, ask:
“Does this corner need to be sharp?”
If not, add a realistic radius.
Then check whether the radius can actually be manufactured.
## Design is about load paths
A strong mechanical design often looks simple because the geometry has been arranged so that forces flow smoothly through the component.
That is one of the biggest differences between “I can model it” and “I can design it.”
2026 Engineering Update
Mechanical engineering is moving toward more connected design-to-manufacturing workflows. Three developments are especially useful for engineers:
- AI-assisted engineering: AI is increasingly being used alongside CAD, simulation and engineering data to explore designs and reduce repetitive work.
- Digital twins and digital threads: connected product and manufacturing data can help teams validate changes earlier and maintain better traceability from design through production.
- Design-for-manufacturing skills: engineers are increasingly expected to combine 3D CAD, simulation, GD&T, DFM/DFA, automation and data skills rather than work in isolated disciplines.
The practical takeaway: learn the fundamentals first, then use new digital tools to make engineering decisions faster, clearer and easier to validate.