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Difficulty: MediumMaterial Properties

Why are highly hardened steel bolts typically avoided in mechanical applications subjected to heavy shock loads and constant vibrations, such as automotive suspension systems?

  1. A
    Highly hard materials are extremely flexible and are likely to vibrate loose from the assembly over time.
  2. Extremely hard materials tend to be brittle and can suddenly fracture when subjected to high-impact forces.Answer
  3. C
    Increasing the hardness of steel proportionally increases its ductility, causing the bolt to stretch permanently.
  4. D
    The high hardness causes the bolt to undergo rapid thermal expansion when exposed to friction from vibrations.

Answer

Extremely hard materials tend to be brittle and can suddenly fracture when subjected to high-impact forces.
The correct answer accurately identifies the trade-off between hardness and brittleness. While hardened steel resists wear and static loads very well, it lacks the toughness required to absorb sudden kinetic energy. Instead of yielding slightly under a severe shock, a fully hardened bolt will snap, which is a catastrophic failure in an automotive suspension.

Step-by-Step Solution

1
Analyze the mechanical requirements of the scenario.
Automotive suspension systems experience heavy shock loads and constant vibrations.
Identifying the applied forces helps determine which material properties are most critical for the component to survive.
2
Evaluate the material property in question (Hardness).
Hardness is a material's resistance to localized deformation, such as scratching or indentation. However, as steel is hardened, it typically loses its toughness and ductility.
Understanding the trade-offs of material treatments is essential for engineering component selection.
3
Relate the material property trade-offs to the required application.
Because hardened steel is brittle, a sudden shock from the suspension could exceed its ultimate tensile strength without any prior stretching, causing the bolt to snap catastrophically. Therefore, a moderately hard but tougher bolt is preferred.
Components in shock-loading environments must be able to absorb energy (toughness) rather than strictly resisting deformation.

Key Concept

Material Toughness vs. Brittleness
Estimated Time:1m 0s
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Topics

Material Properties

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