Case study · May – Jul 2026
Wind turbine blade-root bolt failure investigation
Led a root-cause investigation into blade-root bolts failing after three to four years on an operating utility-scale wind turbine designed for twenty — analysis, a parametric load model, and a test and inspection plan.
- Time to bolt failure in service
- 3–4 yr
- Design life of the blade-root joint
- 20 yr
Objective
Blade-root bolts on an operating utility-scale wind turbine were failing after three to four years in service, against a design life of twenty. The goal was to find the most likely cause and set out how to confirm it.
My role
I led the investigation and delivered the technical report, which the client adopted for its failure review.
Approach
I started from first principles. I quantified the bolt preload stress, the fatigue cycles accumulated in service and the cyclic load carried by each bolt in the group. Together these describe the environment the joint actually sees.
To make the analysis easy to question, I built a parametric Excel model covering bolt preload stress, fatigue-cycle accumulation and load distribution across the bolt group. Assumed thread pitch, bolt grade and geometry can each be changed to see how sensitive the result is.
Findings
The analysis pointed to loss of preload and joint flexibility as the highest-probability root causes. These are conclusions from analysis; the test program below was designed to confirm or rule them out physically.
Test and inspection plan
- Laboratory program: SEM fractography, metallography, hardness testing and residual preload measurement, scoped to a fixed budget.
- Field inspection: a risk-based plan using stratified sampling, with quantified criteria for escalating from sampling to wider inspection.
Outcome
The technical report was adopted for the client’s failure review.