This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Fracture – Notch Effect”.
1. In which way, the notch decreases the tendency of brittle failure?
a) By producing high local stresses
b) By introducing triaxial tensile state of stress
c) By providing low local strain hardening and cracking
d) By creating a local magnification to the strain rate
Explanation: The local strain in the high stress concentration region is the main cause of brittle failure. So by producing low local strain, hardening and cracking can suppress the brittle fracture tendency.
2. The fracture of material occurs when the flow curve _______________
a) is under the fracture curve
b) intersects the fracture curve
c) is parallel to fracture curve
d) is perpendicular to fracture curve
Explanation: The fracture of material occurs when the flow curve intersects the fracture curve. The flow curve gives the true stress-strain values, and when intersecting with flow curve, it gives the values of stress to cause failure in the material.
Explanation: The fracture will be the strain value corresponding to the point where the fracture curve intersects the flow curve. So, in this case, it is equal to length C.
4. Which of the following does not influence the ductile to the brittle transition of a material?
a) Stress state
c) Strain rate
d) Shape of specimen
Explanation: The ductile to brittle transition is the material property of a metal which is influenced by metallurgical factors, and the shape of the sample has no significant impact in converting a ductile material into a brittle material.
5. In the case of 3-dimension state of stress, if one of the stress values, say, principal stress direction becomes compressive, the fracture stress reduces significantly.
Explanation: If one of the primary stress becomes compressive, the fracture stress will increase. Because the compressive stress compensates for the cracking of the material.
6. The hydrostatic compressive state of stress __________ the fracture strength of the material.
c) does not alter
d) no relationship
Explanation: The hydrostatic compressive stress (hydrostatic pressure) resists fracture and increases the ductility. The triaxial pressure is utilized in many metalworking operations, like wiredrawing and extrusion.
7. The hydrostatic component of stress exerts no __________
a) shear stress
b) tensile stress
c) compressive stress
d) triaxial stress
Explanation: The hydrostatic component of stress does not produce shear stress. Because the stress in all the principal direction is equal, so the difference in stress in any two directions is zero, causing the shear stress also to be zero.
8. The Hydrostatic stress __________________ the dislocation pileup in the material.
c) does not increase
d) sometimes increases and then decreases
Explanation: There is no shear stress act in a hydrostatic stress state, so there is no change in dislocation density or pile up of dislocation.
9. The hydrostatic stress influence the crack propagation but not the crack initiation.
Explanation: Compressive stress act to close the dislocation pile up and help in propagation but there is shear stress, so the new cracks never generate in such condition.
Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.
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