Aluminum bicycle frames

When given a choice among materials, determining the most energy-wise material seldom easy. Consider the energy needed to build an alnminnm bicycle frame versus a steel tubular frame. The aluminum bicycle frame takes considerably more energy to build, and needs replacement more often. 

Aluminum (Al), a metal with a high strength-to-weight ratio and a high resistance to corrosion, is often used for structures such as high-quality bicycle frames. Compufe both the number of moles of atoms and the number of atoms in a 10.0-g sample of aluminum. 

Figure 7.13 Bicycle frames are sometimes made of 3/2.5 titanium alloy, an alloy of titanium containing 3% aluminum and 2.5% vanadium. 

Mass density is more than a convenient way to define a ratio for calculations. It is also an important characteristic of materials. Among the reasons that aluminum is a popular structural material is that its relatively low density is often important. When a design calls for a strong but lightweight material, aluminum is a good candidate. We ll look at this aspect further in the closing insight in Section 1.6 when we look at various materials used in bicycle frames. 

The three most common materials for bicycle frames are aluminum, steel, and titanium. Table 1.3 shows typical values for the elastic modulus, yield strength, and density of these materials. 

Suppose that a new material has been devised for a bicycle frame with an elastic modulus of 22.0 x 10 psi. Is this bike fiame hkely to be more or less stiff than an aluminum fiame ... 

How many moles of aluminum are in the bicycle frame Exact... 

For example, consider bicycle frames constructed from steel, aluminum, or carbon flber/epoxy. Since the modulus of elasticity of aluminum is less than that of both steel and carbon liber, one might expect that the increased flexibility of the frame would result in less transmission of road inputs. Furthermore, one might also expect based on stiffness that the steel frame would be less harsh than the carbon fiber frame. However, rankings of the harshness by a bicycle rider in order of decreasing harshness would be aluminum, steel, and finally carbon fiber. This order occurs because of decreased damping follows the order of increased perceived harshness. While carbon fiber will impart more transmitted force from a large impact, much of the impression of ride harshness occurs due to the sustained vibration of either an impact event or continual vibration input from the road surface. Additionally, fatigue of cyclists is often partially attributed to sustained vibration of the bicycle. 

However, if the bicycle is meant to be a substitute for the automobile, the lighter aluminum frame material can dramatically lower the human power output needed to climb hills. The energy saved during the use of the aluminum frame will more than compensate for the greater energy needed to manufacture it. 

Alloys are solid metallic mixtures designed to meet specific needs (see Section 5.15). For example, the frames of racing bicycles can be made of a steel that contains manganese, molybdenum, and carbon to give them the stiffness needed to resist mechanical shock. Titanium frames are used, but not the pure metal. Titanium metal stretches easily, so much so that it becomes deformed under stress. However, when alloyed with metals such as tin and aluminum, titanium maintains its flexibility but keeps its shape. 

Use the web to research the differences in the design of steel-framed bicycles versus aluminum-framed bicycles. Write a report that details the similarities and differences you discover. 

Use the web to research the relative cost of aluminum, steel, and titanium frames for bicycles. Speculate about how much of the relative cost is due to the costs of the materials themselves. 

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