Final answer:
Values above the heavy line on a load chart indicate the failure points for materials, correlating to when a metal will fail under stress. This is essential in engineering for assessing structural stability.
Step-by-step explanation:
Above the heavy line crossing the load chart are values for failure in material strength. Specifically, these values indicate when a material, such as metal, will fail or fracture under a given load. It pertains to data often found in a stress-strain graph, which is a fundamental concept in materials engineering and structural analysis. Such charts are critical for ensuring the safety and reliability of structures or components subjected to various forces and stresses.
The provided figures, such as Figures 21.49 and 21.54, discuss electrical aspects like high-voltage transmission lines and insulator resistance, which although tangentially related to engineering, do not directly pertain to load charts and material failure. However, Figure 12.25 clearly describes a typical stress-strain plot for a metal under a load, indicating how the material behaves all the way up to its fracture point, which is indeed demarcated by a heavy line on a load chart.