About Us

When the model lies, check your boundary conditions

Recently chased a high-cycle fatigue crack in a simple bracket. FEM predicted 30% margin, shaker replication said otherwise. Root cause: test article had realistic stack-up, paint, sealant, aged isolators, and torque scatter, which changed joint stiffness and damping. Our model used ideal bolts and uniform contact. Strain gauges lit up at a lug we barely meshed.

Updating joint modeling (surface contact with micro slip, preload scatter, frequency-dependent damping) closed the gap. The life went from infinity to a number that matched the crack. Not glamorous, but getting the boundary right beat tweaking S-N curves.

How are you treating joints in vibration fatigue these days? Do you calibrate damping and preload from coupon tests, or lean on handbooks until flight test forces a correction? What small non-idealities have most moved your margins?

trevorfea

Jun 11 at 4:00 PM

We pull preload scatter and hysteretic damping from a small joint coupon: torque - tension tests with ultrasonic bolts, then sine sweeps to fit a backbone and micro slip contact, with handbook values only as priors. The things that have moved margins most for me are paint/sealant in the faying surface cutting clamp, hole clearance and countersink burrs shifting strain hotspots, and isolator aging shifting modes; do you model torque relaxation and clamp loss over thermal cycling explicitly or fold it into the preload distribution?

When the model lies, check your boundary conditions

Related Conversations

Stop polishing meshes when your loads are guesses

When a 5% modal match is not enough

When PSDs Lie: Non-Gaussian Vibration and Fatigue Damage

When ML Meets Fatigue Data: Useful, But Only With Guardrails

Short, repeatable abuse tests beat long FATs on packaging lines

Recent Conversations

Day 814 – This was Long Overdue

Explosion-proof enclosures are now available for this series of gas analyzers

Coriolis vs weigh-scale on flammable drum lines

When PSDs Lie: Non-Gaussian Vibration and Fatigue Damage

Fluor Joint Venture Reaches Substantial Completion on Chicago Transit Authority’s Red and Purple Line Project

Your Conversations

Day 814 – This was Long Overdue

Explosion-proof enclosures are now available for this series of gas analyzers

Fluor Joint Venture Reaches Substantial Completion on Chicago Transit Authority’s Red and Purple Line Project

Nova Minerals completes engineering and design for antimony processing plant in Alaska

Former Middle School Reimagined as Multi-Use Community Hub Opens in White Bear Lake