ANSWER SCHEME UNIVERSITI MALAYSIA PERLIS Peperiksaan Pertengahan Semester Pertama Sidang Akademik 2014/2015 31 October 2014 ENT 145 Material Engineering [Kejuruteraan Bahan] Masa: 2 jam Please make sure that this question paper has FOUR (4) printed pages including this front page before you start the examination. [Sila pastikan kertas soalan ini mengandungi EMPAT (4) muka surat yang bercetak termasuk muka hadapan sebelum anda memulakan peperiksaan ini.] This question paper has THREE (3) questions. Answer all questions and each question contributes 20 marks. [Kertas soalan ini mengandungi TIGA (3) soalan. Jawab semua soalan dan setiap soalan menyumbang 20 markah.]
Question 1 [Soalan 1] - 2 - (a) (b) What are the main classes of engineering materials? [Apakah kelas-kelas utama bahan-bahan kejuruteraan.] (2 Marks / Markah) Answer1.1: Metallic, polymeric, ceramic, composite, and electronic materials are the five main classes. Why should Mechanical Engineers be knowledgeable about composition, properties, and processing of materials? [Mengapa Jurutera Mekanikal perlu berpengetahuan tentang komposisi, ciri-ciri, dan pemprosesan bahanbahan?] (4 Marks / Markah) Answer1.18: All branches of mechanical engineering will require selection of materials for a variety of applications in automobiles, power plants, and machines (to name a few) based on a variety of requirements including weight, strength, stiffness, deformability, corrosion, conductivity, magnetism, etc. Knowledge of composition, properties, and processing is critical to select, modify, and apply materials to various applications. (you can highlight many more reasons for the importance of materials knowledge in your field) (c) Describe the properties (mechanical, electrical, etc.) of materials and name a material for each type that are exclusively made up of: [Terangkan sifat-sifat (mekanikal, elektrik, dan lain-lain) bahan-bahan dan namakan satu bahan bagi setiap jenis yang secara eksklusif terdiri daripada:] (i) ionic bonds, [ikatan ionik] (ii) covalent bonds, and [ikatan kovalen, dan] (iii) metallic bonds. [ikatan metal] (9 Marks / Markah)
- 3 - (d) Sterling silver contains 92.5 wt% silver and 7.5 wt% copper. Copper is added to silver to make the metal stronger and more durable. A small silver spoon has a mass of 100 grams. Calculate the number of copper and silver atoms in the spoon. Given atomic weight of copper and silver is 107.9 g/mole and 63.55 g/mole, respectively. [Sterling perak mengandungi 92.5 wt% perak dan 7.5 wt% tembaga. Tembaga ditambah kepada perak untuk membuat logam yang lebih kuat dan lebih tahan lama. Satu sudu perak kecil mempunyai jisim 100 gram. Kira bilangan atom bagi tembaga dan perak dalam sudu.] (5 Marks / Markah)
Question 2 [Soalan 2] - 4 - (a) Give the electron configurations for the following ions by using spdf notion: Fe 2+, Al 3+, Cu +, O 2. [Berikan konfigurasi elektron bagi ion-ion berikut dengan menggunakan tanggapan spdf: Fe 2+, Al 3+, Cu +, O 2.] (4 Marks / Markah)
- 5 - (b) An iridium atom, Ir has FCC crystal structure. Compute the radius of iridium atom, Ir. Consider a density of 22.4 g/cm 3, an atomic weight of 192.2 g/mol and n = 4 atoms/unit cell. [Suatu atom Iridium, Ir mempunyai struktur kristal FCC. Kirakan jejari atom Iridium, Ir. Pertimbangkan ketumpatan 22.4 g/cm 3, berat atom 192.2 g/mol dan n = 4 atom/unit sel.] (7 Marks / Markah)
- 6 - (c) Calculate the atomic packing factor for face centered cubic (FCC). [Kira faktor pembungkusan atom untuk kubik wajah berpusat (FCC).] (3 Marks / Markah)
- 7 - (d) Draw direction vectors in unit cells for the following cubic directions: [Lukiskan arah vektor dalam sel unit untuk arahan padu berikut:] (i) (ii) (iii) [11 1 ] [11 0] [1 21 ] (3 Marks / Markah)
- 8 - (e) A cubic plane has the following axial intercepts: a = 1/3, b = -2/3, c = 1/2. What are the Miller indices of this plane? [Sesatah padu mempunyai pintasan paksi berikut : a = 1/3, b = -2/3, c = 1/2. Apakah indeks Miller sesatah ini?] (3 Marks / Markah)
Question 3 (From FE 2013/2014) - 9 - (a) Answer: Discuss the differences between brittle and ductile metals with respect to its tensile stressstrain behaviour. [Bincangkan perbezaan antara logam rapuh dan logam mulur berdasarkan kepada sifat tegangan tegasanterikan.] (4 Marks / Markah) Ductile Metal experience plastic deformation upon fracture Brittle Metal very little or no plastic deformation (b) Answer: A cylindrical specimen of hypothetical metal alloy has a diameter of 8.0 mm. A tensile force of 1000 N produces an elastic reduction in diameter of 2.8 x 10-4 mm. Compute the modulus of elasticity for this alloy, given that the Poisson s ratio is 0.30. [Satu spesimen bagi logam aloi hipotesis berbentuk silinder mempunyai garis pusat 8.0 mm. Daya tegangan sebanyak 1000 N menghasilkan pengurangan anjal bagi garis pusat sebanyak 2.8 x 10-4 mm. Kira modulus anjal bagi aloi ini, diberi nisbah Poisson ialah 0.30.] (6 Marks / Markah)
- 10 - (c) Table 1 shows a list of materials and their mechanical properties. Each of the material will be tested as a cylindrical rod specimen with 100 mm long and having a diameter of 10 mm. If the tensile load is 27.5 kn, answer the following questions. [Jadual 1 menunjukkan senarai bagi bahan dan sifat mekanikalnya. Setiap bahan tersebut akan diuji sebagai satu specimen rod silinder dengan panjang 100 mm dan diameter 10 mm. jika beban tegangan ialah 27.5 kn, jawab soalan-soalan berikut.] Table 1 [Jadual 1] Material Modulus of Yield Strength Elasticity (GPa) (MPa) Poisson s Ratio Aluminum alloy 70 200 0.33 Brass alloy 101 300 0.34 Steel alloy 207 400 0.30 Titanium alloy 107 650 0.34 Answer: (i) From Table 1, choose the material(s) that will not experience plastic deformation. Justify your choice(s). [Daripada Jadual 1, pilih bahan yang tidak akan mengalami ubah bentuk plastik. Justifikasi pilihan anda.] (6 Marks / Markah)
- 11 - Answer: (ii) By referring your answer in (i), select the material(s) that will not experience a diameter reduction of more than 7.5 x 10-3 mm. [Dengan merujuk kepada jawapan di (i), pilih bahan yang tidak akan mengalami pengurangan garis pusat tidak lebih daripada 7.5 x 10-3 mm.] (4 Marks / Markah) -ooooo-