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### MEC211: Câu hỏi trắc nghiệm 1 (tiếng Anh)

• Đăng bởi: lethithanhbinh
• Sinh viên
• 18/05/2019

1. Two identical circular rods of same diameter and same length are subjected to same magnitude of axial tensile force. One of the rods is made out of mild steel having the modulus of elasticity of 206 GPa. The other rod is made out of cast iron having the modulus of elasticity of 100 GPa. Assume both the materials to be homogeneous and isotropic and the axial force causes the same amount of uniform stress in both the rods. The stresses developed are within the proportional limit of the respective materials. Which of the following observations is correct?

(a) Both rods elongate by the same amount

(b) Mild steel rod elongates more than the cast iron rod

(c) Cast iron rod elongates more than the mild steel rod

(d) As the stresses are equal strains are also equal in both the rods

Đáp án: C

2. A steel bar of 40 mm × 40 mm square cross-section is subjected to an axial compressive load of 200 kN. If the length of the bar is 2 m and E = 200 GPa, the elongation of the bar will be:

(a) 1.25 mm
(b) 2.70 mm
(c) 4.05 mm
(d) 5.40 mm

Đáp án A

3. An axial residual compressive stress due to a manufacturing process is present on the outer surface of a rotating shaft subjected to bending. Under a given bending load, the fatigue life of the shaft in the presence of the residual compressive stress is:

(a) Decreased

(b) Increased or decreased, depending on the external bending load

(c) Neither decreased nor increased

(d) Increased

Đáp án D

4. A static load is mounted at the centre of a shaft rotating at uniform angular velocity. This shaft will be designed for

(a) The maximum compressive stress (static)
(b) The maximum tensile stress (static)

(c) The maximum bending moment (static)

Đáp án D

5. Fatigue strength of a rod subjected to cyclic axial force is less than that of a rotating beam of the same dimensions subjected to steady lateral force because

(a) Axial stiffness is less than bending stiffness

(b) Of absence of centrifugal effects in the rod

(c) The number of discontinuities vulnerable to fatigue are more in the rod

(d) At a particular time the rod has only one type of stress whereas the beam has both the tensile and compressive stresses.

Đáp án D    