Mechanical Metallurgy Questions and Answers – Fracture – Notch Effect

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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
View Answer

Answer: c
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.
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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
View Answer

Answer: b
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.

3. The fracture strain in the following diagram will be equal to ______
mechanical-metallurgy-questions-answers-fracture-notch-effect-q3
a) A
b) B
c) C
d) Zero
View Answer

Answer: c
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
b) Temperature
c) Strain rate
d) Shape of specimen
View Answer

Answer: d
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.
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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.
a) True
b) False
View Answer

Answer: b
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.
a) increases
b) decreases
c) does not alter
d) no relationship
View Answer

Answer: a
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
View Answer

Answer: a
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.
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8. The Hydrostatic stress __________________ the dislocation pileup in the material.
a) increases
b) decreases
c) does not increase
d) sometimes increases and then decreases
View Answer

Answer: c
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.
a) True
b) False
View Answer

Answer: a
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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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn