This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Types of Fracture”.
1. How is fracture stress defined?
a) MN m-2
b) J m-2
d) GN m-1
Explanation: Fracture is defined as the breaking of a material into multiple parts. The fracture stress is defined as meganewton per square meter or MN m-2 and is denoted by σf.
2. What is the SI unit of fracture toughness?
a) N m-2
b) J m-2
c) J m-1
d) N m-1
Explanation: Fracture toughness is regarded as the rate of strain energy released. Its SI unit is joule per meter square (J m-2) and is denoted as Gc.
3. The tensile strength required to break interatomic bonds across two adjacent planes is ________
Explanation: Calculations for shear strength of perfect crystal has been found to be similar to that of two adjacent planes. It was determined that the tensile strength necessary to rupture interatomic bonds of two adjacent atomic planes is of the order of Y/6.
4. What is the breaking stress of brittle materials?
Explanation: It was found that the tensile strength of two adjacent atomic planes was Y/6. However, brittle materials may break at a stress of the order of Y/1000. Here, Y is Young’s modulus.
5. In crystalline materials, fracture occurs normal to crystallographic planes called ___________
a) Fracture point
b) Cleavage plane
c) Brittle plane
d) Crystallographic point
Explanation: In crystalline materials, fracture usually occurs after some deformation. In these materials, the fracture occurs normal to crystallographic planes called cleavage planes.
6. What is the surface energy of a crack?
b) 2 ϒ c
c) 4 ϒ c
d) 12 ϒ c
Explanation: Griffith suggested the norm for the formation and spreading of cracks in brittle materials. He found that the surface energy of the crack is 4 ϒ c. Here, ϒ is the surface energy per unit area of the material.
7. The maximum stress at the tip of the crack is defined by _________
Explanation: When tensile stress is applied to a material, the maximum stress occurs at the tips. This maximum stress is denoted as σmax and is given by .
8. Griffith theory is applicable for ______ materials.
a) All brittle
b) Perfect brittle
c) All ductile
d) Perfect ductile
Explanation: The stress required to cause brittle fracture varies inversely as the square root of crack length. From observation, we understand that Griffith theory is applicable only to perfect brittle materials like glass.
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