Three Mechanical Engineering Lessons on a Bolt head

myminifactory

This entry is for the MAMSS x McGill competition, and I'm proud to represent McGill University! Three monumental engineering failures are etched into the memories of every mechanical engineer. Textbooks and professors consistently highlight these incidents as pivotal lessons that every mechanical engineer must grasp. The de Havilland Comet disasters resulted in catastrophic tears in the plane's fuselage during flight on 26 occasions. A staggering 13 of those instances were fatal, claiming 426 lives. As a pioneering jet propulsion technology, the comet flew at unprecedented heights, but its square windows ultimately sealed its fate. The sharp corners of these windows created stress concentrations in the fuselage, and when paired with the repeated pressurization and de-pressurization of the cabin, they led to an earlier-than-expected fatigue failure. These incidents underscored the importance of recognizing stress concentrations and fatigue failure. The Liberty Ships were a class of cargo vessels built in the US during World War II. Many were constructed using a novel welding fabrication technique instead of traditional riveted plate fabrication. The North Atlantic's frigid temperatures caused the steel in the hull to transition from ductile to brittle, an oversight that went unaccounted for. In brittle materials, cracks propagate with alarming ease, much like in glass or porcelain. Small cracks in the ships' hulls grew unchecked since they were welded, not riveted. If the hulls had been made of riveted plates, most of these cracks would have stopped at the plate edges. The result was nearly 1500 instances of significant brittle fractures in the Liberty Ships' hulls. In fact, many cracks originated at the square edge of a hatch, once again highlighting the significance of stress concentrations. Even more astonishingly, three ships split cleanly in half without warning! This was an invaluable lesson for mechanical engineers on brittle fracture, crack propagation, and temperature effects on metal ductility. If I had a dime for every time I saw the Tacoma Narrows bridge video in class... I'd have a small fortune! The Tacoma Narrows bridge experienced a complete failure due to wind-induced oscillations that caused the bridge to vibrate violently and uncontrollably. This phenomenon is known as resonant vibration. Every object has a frequency at which it naturally wants to vibrate, and on that fateful day, the winds were perfectly aligned to push the bridge to the point of resonance. The bridge twisted back and forth at angles up to 45 degrees and bent upward and downward. Eventually, the suspension bridge collapsed completely, and the roadway fell into the water. This disaster serves as a poignant reminder of the importance of considering vibrations and harmonic oscillation. This 3D print showcases three representations of these disasters extending from the head of a bolt. The three radial lines on the bolt indicate a grading of 5 as defined by the SAE (Society of Automotive Engineers), which is an indicator of the bolt's strength. The head of the bolt is designed to be flat, minimizing material usage in printing. It measures 150mm wide and 15mm deep.