How do you determine the 0.1% proof stress from a force-extension graph?

To determine the 0.1% proof stress from a force-extension graph, the correct approach is to locate a distance equal to 0.1% of the total gauge length from the origin of the graph. This involves drawing a line parallel to the initial linear portion of the stress-strain curve starting at this 0.1% strain point. The intersection of this line with the stress-strain curve indicates the stress value corresponding to the 0.1% proof stress.

By focusing on the 0.1% offset, you provide a practical approach to assess material yield, acknowledging that this measure accounts for a slight plastic deformation that can provide insights into material behavior under load. This method is commonly used in material testing to establish a consistent criterion for determining when a material begins to behave plastically, which is crucial for applications in engineering where material reliability and performance are critical.