Characteristic Strength of a Material

Introduction:
The characteristic strength of a material refers to the strength value that is associated with a certain level of confidence. It is an important parameter used in engineering design to ensure the safety and reliability of structures or components. The characteristic strength is determined through extensive testing and analysis of the material's properties.

Explanation:
The correct answer for the characteristic strength of a material is option 'B', which is the safe strength. This means that the characteristic strength is the strength value at which the material is expected to perform reliably under normal working conditions without failure. It is also commonly referred to as the design strength.

Here are the reasons why the characteristic strength is considered as the safe strength:

1. Ultimate Strength: The ultimate strength (option 'A') of a material refers to the maximum stress that a material can withstand before it fails. However, using this value for design purposes would not provide a sufficient factor of safety, as it does not account for uncertainties in material properties, manufacturing processes, and other external factors.

2. Maximum Strength: The maximum strength (option 'C') of a material represents the highest strength value that can be achieved under ideal laboratory conditions. This value is not suitable for design purposes as it does not consider the variability and uncertainties that exist in real-world applications.

3. Working Strength: The working strength (option 'D') of a material is the strength value that is used during the normal operation of a structure or component. However, this strength value is typically lower than the characteristic strength to provide an additional safety margin.

4. Safety and Reliability: The characteristic strength is determined based on statistical analysis, considering the distribution of strength values obtained from a large number of tests. It takes into account the variations in material properties, manufacturing processes, and other factors to ensure a high level of safety and reliability in design.

5. Factor of Safety: The characteristic strength is typically used in conjunction with a factor of safety, which is a multiplier applied to the characteristic strength to provide an additional margin for uncertainties. The factor of safety accounts for uncertainties in material properties, loading conditions, and other factors to ensure that the structure or component can withstand unexpected events or variations.

In conclusion, the characteristic strength of a material is the safe strength that is used in engineering design to ensure the reliability and safety of structures or components. It accounts for uncertainties and is typically used in conjunction with a factor of safety to provide an additional margin of safety.