Material Science - short answer questions from AMIE exams

If we test a cast-iron sample in tensile mode, will there be any appreciable plastic deformation? Why?
Very small plastic deformation is associated with the tensile test of C.I. because it is brittle.

For which type of fracture, the direction of crack motion is very nearly perpendicular to the direction of the applied tensile stress?
The direction of crack propagation is nearly perpendicular to applied tensile stress in Brittle fracture. 

Which alloying element is most important to make steel corrosion-resistant and what is the minimum percentage of this element required?
To shape steel corrosion-resistant chromium is added with a minimum of 0.7%.

Every plastic is polymer but every polymer may not be plastic. Is it true? Justify.
  • The statement is true. 
  • All polymers are not plastics, but all plastics are polymers. For instance, cellulose is a polymer; but, it cannot be processed in the same way as a plastic material unless it is modified.
  • Polymers can exist organically or be created synthetically, and consist of chains of joined individual molecules or monomers. Plastics are a type of polymer composed of chains of polymers that can be partially organic or fully synthetic. Simply put, all plastics are polymers, but not all polymers are plastics.
What is the SI unit of modulus of elasticity?
The S.I. unit of modulus of elasticity is PASCAL (N/m2). Young’s Modulus is the initial part of a stress/strain curve and describes the ability of a wire to resist elastic deformation under load. 

How would one increase the corrosion resistance of a cold-rolled steel plate without painting or electroplating?
The corrosion resistance of a cold-rolled steel plate can be increased by heat treatment or by making its cathode.

What are the chemical names of any two of the following plastics?
Teflon ; Perspex ; Terylene ; Bakelite 
  • Teflon is polytetrafluoroethylene (PTFE)
  • polymethyl methacrylate
  • Terylene is polyethene terephthalate
  • bakelite is phenyl formaldehyde.
What is ductility and in what terms, is it measured?
Ductility is the ability to be drawn into small sections from large sections. This is measured by percentage elongation or percentage reduction.

A test piece is 100 mm long. It is subjected to 0.2 % strain. What would be its length at this strain level?
Use formula, strain = Δl/l 

Which of the following materials would result in a cup-and-cone type fracture?
Alumina; Cast-iron; Mild Steel; Perspex
Steel is on the higher side of the Galvanic series as compared to brass, so it will corrode faster.

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