Which property is defined as the slope of the straight line portion of the stress-strain curve within the elastic range?

The property that is defined as the slope of the straight line portion of the stress-strain curve within the elastic range is Young's Modulus. This modulus is a fundamental material property that quantifies the relationship between stress (force per unit area) and strain (deformation) in the elastic region of the material's behavior.

In the elastic range, materials deform proportionally to the applied stress, and the slope of this linear portion of the stress-strain curve is what defines Young's Modulus. This value provides insight into the material's stiffness: a higher Young's Modulus indicates a stiffer material that deforms less under load, while a lower value signifies a more flexible material that readily deforms.

Understanding this concept is critical in civil engineering, as it helps engineers select the appropriate materials for structures based on their expected loads and deformation characteristics.