Final answer:
The three main features of a stress-strain graph are the elastic region where materials return to their original shape; the plastic region where permanent deformation occurs; and the fracture point, where the material ultimately breaks.
Step-by-step explanation:
The three main features of a stress-strain graph which represent the behavior of materials under load include the elastic region, the plastic region, and the fracture point.
Elastic Region
In the elastic region, the material will return to its original shape when the load is removed. This portion of the graph is typically linear and obeys Hooke's Law, where the stress is proportional to the strain.
Plastic Region
Following the elastic region is the plastic region, where the material undergoes permanent deformation. The stress and strain are no longer proportional, and the graph curve becomes nonlinear.
Fracture Point
Finally, the graph culminates at the fracture point, where the material breaks. This occurs after the ultimate tensile strength is reached, and no further stress can be sustained by the material.