E08-korrigert - Exercise 8 PDF

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TMM4100 Materials Technology 2017 E08

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Exercise 08 Topic: Metals, ceramics and polymers References: Callister Chapter 13, 14 and 15 + lecture notes/presentations Problem-1 The density of graphite is approximately 2200 kg/m3 and the density of pure alpha iron at room temperature is 7874 kg/m3. Compute the volume fraction of graphite in a cast iron having 3.0 wt% Carbon. Assume that all the carbon exists as graphite. Problem-2 Compute the resulting density of the cast iron presented in the previous problem (use the same assumptions as found in that problem). Problem-3 3 different materials with essential features (density, modulus of elasticity, yield strength and price) are found in the table: Material Low carbon steel alloy (A36) Stainless steel (316) An aluminum alloy (6061)

ρ [kg/m3] E [GPa] σy [MPa] Price [NOK/kg] 7850 207 230 3.50 7950 193 310 32.00 2700 69 275 13.00

A 1 m long rod shall carry a tensile force equal to 5 kN. The elongation shall not be more than 1 mm. You are free to choose the diameter of the rod.

a) Compute the minimum material cost for a solution using the Low carbon steel alloy b) Compute the minimum material cost for a solution using the Stainless steel c) Compute the minimum material cost for a solution using the Aluminum alloy Problem-4 A 1 m long rod shall carry a tensile force equal to 5 kN without plastic yielding. You are free to choose the diameter of the rod. Now, based on the materials from the previous problem: a) Compute the minimum material cost for a solution using the Low carbon steel alloy b) Compute the minimum material cost for a solution using the Stainless steel c) Compute the minimum material cost for a solution using the Aluminum alloy

TMM4100 Materials Technology 2017 E08

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Problem-5 The flexural strength of Aluminum oxide (Al2O3) has been measured by 3-point flexural testing.

The cross section of the test specimen had dimensions b = 10 mm and h = 5 mm. The span length L between the supports was 100 mm. The failure load F obtained from 10 parallel tests was: 710 , 780 , 685 , 705 , 815 , 730 , 745 , 790 , 715 , 725 N. a) What was the mean flexural strength? (Note: this quantity is expressed by unit MPa) b) In some specific fictive guide/standard the mean strength of 10 samples minus 3 standard deviations (see equation 8.22) is considered as a design strength having sufficiently low probability of failure for a specific application. Compute this value for the aluminum oxide. Problem-6 Compute the density of graphite based on the dimensions found in the illustrations:

TMM4100 Materials Technology 2017 E08

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Problem-7 The relaxation modulus Er  t  for a polymer is found to fit well to the relation Er (t )  A   B  A e t/

A relaxation experiment has been conducted with an instantaneous strain at t = 0 equal to 0.005 and where the instantaneous stress was 9.0 MPa. The strain was then kept constant and the stress was measured as given in the figure:

a) Find the numerical values of the constants A and B b) Estimate the value for the time constant τ.

TMM4100 Materials Technology 2017 E08

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Questions 1) What is the mechanism behind the relatively high mechanical damping of cast irons compared to steels? 2) Describe the micro-structure of gray cast iron from a fracture mechanical point of view: Could the low tensile strength be easily explained? 3) The density of carbon fibers is significantly lower than the density of graphite. Why? 4) ... and by the way: what is a typical density of carbon fibers? 5) How is creep of metals fundamentally different than creep of polymers? 6) Why is Tg for PP greater than Tg for PE? 7) Will all crystalline polymers have a glass transition temperature? 8) Could the glass transition temperature be greater than the melting temperature? 9) Name 3 types of polymers that are commonly used between the glass transition temperature and the melting temperature 10) What happens to an elastomer (rubber) when the temperature goes below Tg? Concepts check (not to be submitted) 11) What is a polymer fiber? 12) What is a polymer film? 13) What is a polymer foam? 14) What is a thermoplastic elastomer? 15) What is the difference between a thermoset and a thermoplastic 16) Some very common polymers contain only carbon and hydrogen. Name at least 3 Numerical answers P1: 0.0997 (= 9.97 vol%) P2: 7309 P3: a) 0.66 NOK, b) 6.60 NOK, c) 2.54 NOK P4: a) 0.60 NOK, b) 4.10 NOK, c) 0.64 NOK P5: a) 444 MPa, b) 368 MPa P6: 2280 kg/m3...