Failure Modes | Kaelan

Henry Petroski argued that engineering advances through failure. Success teaches less than collapse. The Tacoma Narrows Bridge revealed aeroelastic flutter. The Challenger disaster exposed O-ring cold sensitivity. The Hyatt Regency walkway collapse showed how a minor design change transformed a safe connection into a fatal one. Each failure added to collective knowledge.

A failure mode is a specific way something can go wrong. A rope can fail by breaking (exceeding tensile strength) or by coming untied (knot failure). A bridge can fail by buckling (compression), yielding (bending), fatigue (cyclic loading), or corrosion (material degradation). Different modes require different prevention strategies.

Good design anticipates failure modes and addresses the most dangerous ones. Fail-safe design ensures that when failure occurs, it happens safely — a fuse blows before the house catches fire, a pressure relief valve opens before the tank explodes. Fail-soft design degrades gracefully — the system loses capability but keeps working. Fail-secure design defaults to a secure state — the lock stays locked when power fails.

The principle of damage tolerance accepts that flaws exist and designs around them. Aircraft structures are designed to carry full load even with cracks up to a certain size. Inspections catch cracks before they reach critical length. The system accounts for imperfection rather than demanding perfection.

Failure analysis is detective work. The fracture surface tells a story: brittle failure looks different from fatigue failure. The rust pattern indicates where water collected. The deformation shows the direction of force. Experienced analysts read these signs like tracking animals — the evidence reveals what happened.

What failure teaches: every system has a weakest link. Find it before it finds you. Test to destruction in controlled conditions. Learn from near-misses, not just catastrophes. And when you change something — even a small thing — trace the implications through the whole system. The Hyatt walkway failed because someone moved a nut to make fabrication easier.