Final answer:
The tensile strain stress behavior of a steel alloy includes a linear region where elongation is proportional to stress, followed by plastic deformation, and finally fracture at the breaking stress. This is represented on a stress-strain diagram, with the linear portion corresponding to Young's modulus for steel, and the breaking stress indicating the material's ultimate strength.
Step-by-step explanation:
The behavior of tensile strain stress for a steel alloy can be understood by examining how the material reacts to forces that cause elongation. When a steel rod, such as a 2.0-m-long steel rod with a cross-sectional area of 0.30 cm² holding a heavy 550-kg platform, experiences tensile stress, it undergoes an elongation. This elongation is proportional to the applied stress up to a certain point, as described by Young's modulus, which is a measure of the steel's stiffness and is given for steel as Y = 2.0 × 10¹¹ Pa. When the stress increases further, it reaches a breaking stress or ultimate stress; for steel, this can be as high as 20.0 × 10¹¹ Pa depending on the alloy composition. A stress-strain diagram can be used to graphically represent this relationship, showing a characteristic curve for steel that initially rises linearly (the elastic region) before reaching a point where permanent deformation occurs (the plastic region), and finally, reaching the fracture point where the material breaks.