SSRAO

Explanation:
Engineering stress at fracture is the fracture load divided by the original cross-sectional area, whereas true stress at fracture is the same load divided by the smaller instantaneous area at the fracture section. For a ductile specimen that necks, the instantaneous area is smaller, so the true fracture stress is generally greater than the engineering fracture stress. The precise value depends on the measurement and stress state in the necked region.

Explanation:
For a material obeying the Hollomon relation σ = Kεⁿ, using true plastic strain and assuming the usual tensile-instability conditions, the Considère criterion gives ε = n at the onset of necking. Here K = 500 MPa and n = 0.5, so the true stress at necking is 500√0.5 = 353.55 MPa. At this point the engineering stress is σ/(1 + ε) = 353.55/1.5 ≈ 235.7 MPa. Therefore, option B is correct. This result assumes the stated power law applies over the relevant plastic-strain range.

Explanation:
Fatigue loading or cyclic loading refers to fluctuating loads over time. The maximum stress amplitude that a material can withstand for an infinite number of cycles without failing is defined as the endurance limit or fatigue limit. Elastic, proportional, and yield strengths are determined under static or monotonic loading conditions.

Explanation:
Percentage reduction in area = [(A₀ − A_f)/A₀] × 100. For a circular specimen, A is proportional to d², so %RA = [1 − (d_f/d₀)²] × 100 = [1 − (10.5/12.8)²] × 100 ≈ 32.7%. The closest option is 32.6%.

Explanation:
BCC metals commonly show a ductile-to-brittle transition. As temperature decreases through the transition range, impact energy can fall sharply over a relatively narrow temperature interval. The exact transition behavior depends on composition, microstructure, and test conditions.

Explanation:
At elevated temperatures, creep is thermally activated. In many metals, higher temperature increases vacancy diffusion and can accelerate dislocation climb, thereby increasing the steady-state creep rate. The dominant mechanism depends on temperature, stress, grain size, and material.

Explanation:
The Vickers hardness test uses a square-based diamond pyramid indenter with an angle of 136° between opposite faces. Brinell uses a spherical steel or tungsten carbide ball. Rockwell uses a diamond cone or ball indenter with different preload configurations. Knoop uses an elongated rhombohedral diamond indenter.

Explanation:
An ideal perfectly plastic material has a constant flow stress after yielding, with no strain hardening. Therefore, increasing the true plastic strain does not change the true flow stress in this model.