Section 1.3 1.4 As an engineer, you work for a company that makes mountain bicyc

Question

Section 1.3 1.4 As an engineer, you work for a company that makes mountain bicycles. Some bicycles that have been in use for several years have had handlebars that failed by completely breaking off where the handlebar is clamped into the stem that connects it to the rest of the bicycle. What is the most likely cause of these failures? Describe some of the steps that you might take to redesign this part and to verify that your new design will solve this problem. Repeat Prob. 1.4 for failures in the cast aluminum bracket used to attach the rudder of a small recreational sailboat. 1.5

Explanation / Answer

Ans1.4: The components that make up a bicycle have a useful service life. Bicycle frames, forks, handlebars, wheels, brakes and other parts may fail due to a design or manufacturing defect, overloading, or simply wear out over the life of a bicycle. Design factors such as function, light weight, durability and cost dictate the material used for a component. All of these considerations can play a role in the likelihood and nature of a component’s failure.

Different types of failures occur in the different parts of the bicycle components, for handlebars it is mentioned below:

The handlebars are connected to the bicycle fork by the stem. The bars and stem support some of the rider’s weight and also receive the steering inputs from the rider. When the integrity of this assembly is compromised then rider loses its ability to steer the handlebars and may lose the ability to stay in upright position on the bicycle.

Ans1.5: After hull integrity, rudder integrity is the most vital component of a seaworthy vessel, yet most sailors pay more attention to LED lighting or smartphone apps than they do to their boat’s rudder. Before you shrug off rudder failure as a remote concern, consider that the incidence of mid-ocean rudder failures is close to 1 percent—and that’s on sturdy boats that presumably have received a truck-to-keel going over before setting off.

Stock failure: Most rudders are constructed around a solid or hollow stainless steel or aluminum stock. This tube or bar connects the rudder to the boat’s steering mechanism. In the case of a spade rudder, it also attaches the rudder to the boat.

Stocks can fail in several ways, all related to inadequate strength. However, a rudder stock should not be so strong that it pries open the bottom of a boat rather than bending in a collision or grounding. This makes spade rudders on lightly built boats unavoidably more vulnerable to a bent stock—the rudder is sacrificed to save the hull.

A bent metal stock can result in a rudder being jammed off-center, which will thwart any efforts to steer a boat with sails, drogues, a jury rudder or by towing lines. Composite rudder stocks, meanwhile, will break rather than bend.

Under normal operating conditions, a rudder stock is subject to repeated and reversing torsional stress, which it can easily handle if it is sized correctly. However, as everyone who has twisted the head off an old screw knows, corrosion changes everything. Stainless steel, in particular, suffers when deprived of oxygen, which is exactly what happens up inside a rudder tube full of stagnant seawater. This effect is exacerbated where the shaft comes in contact with a solid bearing surface, which rubs away the oxide film that protects the steel. Hidden from view, the stock begins to corrode.Over time, its strength is compromised enough that an impact or strong twist snaps it like a pretzel, and the rudder falls away.

Framework failure: A rudder blade is not simply cast onto its stock like a lollipop on a stick, but is held in place by an internal metal framework. In the weakest configuration, the stock extends only just below the top of the rudder where its end is welded to a mild-steel plate, looking something like a bad oar. It doesn’t take a materials engineer to predict what is going to happen as a 4-foot rudder blade flexes this plate back and forth. The more common practice of spot-welding metal bars—like reverse tillers—onto a stock that extends deep into the blade is better in that there are multiple welds to resist the twisting stresses and the continuous stock absorbs the bending stress. Also, the rudder will not necessarily fall away when these welds fail.

A well-engineered interior framework is made out of stainless steel or aluminium, rather than mild steel, and is firmly attached to the stock with long, strong welds. However, even if the interior frame is a single stainless plate that is welded to the stock for almost its entire interior length, it is almost impossible to maintain a perfect seal between the composite blade and the metal stock. Water eventually penetrates into the blade and fosters corrosion, especially where welding has altered the molecular structure of the metal. As the water inside the rudder is trapped, this type of deterioration continues unabated even in a boat stored on land. If corrosion weakens the framework to its breaking point, rotating the stock will fail to turn the rudder blade.

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.