to repeated loads during normal vehicle operation. Road irregularities, braking,
acceleration, and cornering forces create cyclic stresses in structural components.
Over time, these repeated stress cycles may cause fatigue cracks and eventual failure
if the component is not properly designed for fatigue life.
1. Engineering Question
If a suspension control arm experiences fluctuating loads while the vehicle
travels over rough roads, how much fatigue damage accumulates over millions
of loading cycles and will the component survive its intended service life?
2. Stress Calculation Formula
In many automotive suspension components, loads create bending stresses.
The bending stress in a component can be estimated using the formula:
σ = (M × c) / I
- σ = bending stress (MPa)
- M = bending moment caused by road loads (N·m)
- c = distance from neutral axis to outer surface (m)
- I = second moment of area of the cross section (m⁴)
As a vehicle moves over bumps and uneven surfaces, the bending moment acting
on the suspension component changes continuously. Using the formula above,
engineers calculate the resulting stress values and record them over time.
These stress values form a stress history dataset that can be exported as a CSV file.
3. Example Stress History (CSV Data)
A simplified example of stress values measured in a suspension arm may appear
as the following stress history sequence:
80 120 140 110 130 150 125 95 140 110
Each value represents the stress level in MPa at a specific moment in time
as the vehicle encounters road loads.
This stress sequence can be exported from vehicle simulation software
or strain gauge sensors installed during testing.
4. Fatigue Analysis Workflow
Engineers can evaluate fatigue damage in automotive components using
a typical fatigue analysis workflow:
- Export stress history data from simulation software or sensor measurements.
- Upload the stress sequence CSV into a fatigue analysis tool.
- Apply rainflow cycle counting to identify stress cycles.
- Use the material S–N curve to estimate fatigue life for each cycle.
- Calculate cumulative fatigue damage using Miner’s Rule.
5. Analyze This Data
You can upload similar stress history data and estimate fatigue damage using the
FatigueLab Fatigue Damage Calculator
This allows engineers and students to evaluate how cyclic loads affect the
fatigue life of automotive components such as suspension arms,
axles, and chassis structures.