Reference no: EM132968672

Materials for Engineers

Problem 1

1) "Airbus utilizes advanced composites in its jetliner product line that have been at the forefront of materials science".
Select suitable engineering composite material/s for aerospace engineering applications that satisfies the following requirements:
i. Tensile strength approximately 1000 MPa
ii. Modulus of elasticity more than 100 GPa
iii. Density less than 2000 kg/m3

2)

A) Use the first two Ashby charts (below) to select a set of materials that satisfy these requirements.

B) Use the third Ashby chart, standard textbook and/or any other resource to refine your selection to present three best materials if the following additional requirements are also to be fulfilled.

i. Light weight
ii. Good corrosion resistance
iii. Sustainability

Explain the selection process in each case quoting any references used.

Problem 2

Strengthening of Metals

"Cold working is the plastic deformation of metals below the recrystallization temperature. In most cases of manufacturing, such cold forming is done at room temperature. Sometimes, however, the working may be done at elevated temperatures that will provide increased ductility and reduced strength, but will be below the recrystallization temperature".

The figure on the left below demonstrates how steel, brass, and copper increase Tensile Strength with increasing the degree of cold work. The price for this enhancement of strength is in the ductility of the metal. The reduction in ductility with the percentage of cold work is shown in the figure on the right.

Once a cold worked material is heat treated, the recrystallization process resets the cold work properties to zero cold work case. Therefore, when excessive cold work is required without sacrificing the ductility of a material, a component is partially cold worked which is followed by heat treatment to reset the properties before the next stage of cold work. This process may be repeated for number of times as required.
Use the above explanation and the graphs to answer the following question.

A cylindrical rod of brass originally 12.1 mm in diameter is to be cold worked by drawing. The circular cross section will be maintained during deformation. A cold-worked tensile strength more than 380 MPa and a ductility of at least 15% EL are desired. Furthermore, the final diameter must be 9.0 mm.

A) Calculate the percentage cold work expected during the drawing which reduces the diameter from 12.1 mm to 9 mm. Use the given diagrams to justify that the required tensile strength and/or the ductility cannot be matched with the proposed amount of cold work.

B) As an alternative, consider the required values of tensile strength and the ductility, separately to determine the target values of percentage of cold work and hence propose a suitable range for the percentage of cold work. Considering the range, decide on a suitable amount of cold work.

C) It is suggested that to reduce the diameter of the rod to an intermediate value to satisfy the proposed percentage of cold work in b) above. Apply the cold work formula to determine the final diameter of the rod after this first stage of the cold work.

D) Explain the rest of the process of reducing the cross-section to 9.0 mm diameter whilst achieving the required ductility and tensile strength. What is the percentage of cold work retained in the rod?

Attachment:- Materials for Engineers.rar