Allowable stress

Definition

Allowable stress is the maximum stress that a material can safely withstand without failing or yielding under specified conditions. It is an essential factor in design and analysis, ensuring that structures and components can support loads without risking structural integrity, which is closely related to the concept of factor of safety.

5 Must Know Facts For Your Next Test

1. Allowable stress is typically calculated by dividing the yield strength or ultimate strength of a material by a chosen factor of safety.
2. Different materials have different allowable stress values, which are influenced by factors such as temperature, loading conditions, and duration of load.
3. In engineering design, it is crucial to select an appropriate factor of safety to determine allowable stress, as it directly affects the safety and reliability of structures.
4. Allowable stress ensures that components operate well within their limits during normal conditions and can accommodate unexpected overloads or impacts.
5. Codes and standards often dictate specific allowable stress values for various applications to ensure consistent safety practices across engineering fields.

Review Questions

• How does the concept of allowable stress relate to the factor of safety in engineering design?
  • Allowable stress is directly influenced by the factor of safety, which is a critical aspect of engineering design. The factor of safety provides a margin for error by ensuring that the actual stresses experienced by a material during use are well below its allowable stress. This relationship helps prevent failure due to unforeseen loads or material defects, allowing engineers to create safer and more reliable structures.
• Discuss the importance of considering environmental factors when determining allowable stress for a material.
  • When determining allowable stress for a material, it is essential to consider environmental factors such as temperature, humidity, and exposure to chemicals. These conditions can affect a material's strength and performance. For instance, elevated temperatures might reduce yield strength, thereby necessitating a lower allowable stress. By taking these factors into account, engineers ensure that designs remain safe and functional under varying real-world conditions.
• Evaluate the impact of improper selection of allowable stress on structural integrity and safety in engineering applications.
  • Improper selection of allowable stress can lead to catastrophic failures in engineering applications, resulting in significant safety hazards. If allowable stresses are set too high, structures may experience unexpected loads or fatigue beyond their capacity, leading to collapse or severe damage. Conversely, setting them too low can result in over-engineered designs that are unnecessarily costly and resource-intensive. Therefore, accurately determining allowable stress based on material properties and expected conditions is crucial for balancing safety and efficiency in engineering design.

Related terms

Ultimate Stress: The maximum stress that a material can withstand when subjected to a load before failure occurs.

Factor of Safety:

A design principle that provides a safety margin by comparing the allowable stress to the actual stress experienced by a material.

Yield Strength:

The stress level at which a material begins to deform plastically, marking the transition from elastic deformation to permanent deformation.