Material Assignment
MCD4270: Material Project Page 1 MCD4270–LIGHTER, FASTER, STRONGER PROJECT: MATERIALS TESTING, SELECTION AND DESIGN Team Assignment (6% of semester marks) Coversheet must be attached to your assignment, signed by all group members. Make sure that the team number and member’s names are clearly displayed. You must either tick the box to say that all students have contributed equally, or assign percentage contributions to each student in the appropriate boxes. The assignment (hard copy) must be submitted in your lab week 9. Submissions should be typed in Times New Roman 12 point font, and be single spaced; use 2cm margins. Figures and tables should all be numbered and referred to in the text. In both parts of the assignment, marks will be awarded for clarity and succinctness of answers. Marks will be awarded for short, clear answers. You will lose marks for answers that include wrong or irrelevant information, or for answers that are considered too long. All references to other work (text books, internet sites etc) should be acknowledged using the IEEE convention. DO NOT “copy and paste” answers from other teams, the internet, books or other sources! Doing so is considered as plagiarism. For further details see the library resources on citing and referencing at http://monash.edu/library/skills/resources/tutorials/citing/index.html and the plagiarism policy at http://www.policy.monash.edu/policy-bank/academic/education/conduct/plagiarism- policy.html http://monash.edu/library/skills/resources/tutorials/citing/index.html http://www.policy.monash.edu/policy-bank/academic/education/conduct/plagiarism-policy.html http://www.policy.monash.edu/policy-bank/academic/education/conduct/plagiarism-policy.html MCD4270: Material Project Page 2 Part 1: Answer all the following questions: Question 1 (5 marks) (a) Present the engineering stress-strain curves obtained by tensile testing the as- rolled and annealed aluminium specimens. These should be presented together on a single graph. Hint: if using Excel, be sure to select a “XY scatter” rather than a “line” graph, as in some cases a “line” graph does not correctly plot the x values. (b) Using appropriate equations to transform your data, add plots of True Stress vs True Strain for both your samples to your graph from part (a). Make sure that you only plot the region where these equations are valid. For any other region, indicate approximately where you would expect the curve to lie (this part should be drawn over the original graph). Question 2 (10 marks) By generating a line of best fit for the elastic region of the graphs, determine the elastic modulus of the as-rolled and annealed aluminium samples that were tested. On an atomic scale, what determines the modulus of a material? According to theory would you expect the modulus of the annealed sample to be higher, lower or the same as the as-rolled aluminium? Do your measurements match up with this prediction? Explain your answers. Question 3 (4 marks) Using the engineering stress-strain curve that you obtained by tensile testing the annealed aluminium specimen, determine the 0.2% proof stress, ultimate tensile strength, uniform elongation and ductility for the material. Show how you found these values on a new graph. Question 4 (9 marks) The yield stress, Young’s modulus, UTS and ductility (elongation) for Aluminium 1050 H19 and Aluminium 1050 O can be found in Table 1. These correspond to fully work- hardened and annealed aluminium respectively. Table 1: Literature values for Al 1050 H19 and Al 1050 O (CES Edupack database) Grade E (GPa) σy (MPa) UTS (MPa) Ductility (%) H19 70.5 165 175 3 O 70.5 35 80 38 MCD4270: Material Project Page 3 Prepare tables that compare the yield stress, UTS and ductility of your cold rolled sample with Al1050 H19. Discuss the similarities and differences between the theoretical values and the ones you measured. Repeat for your annealed sample compared with Al1050 O. Discuss what this might imply about the amount of work hardening in the specimens that you tested. Question 5 (12 marks) - Qualitatively, describe how the ductility and yield stress of the annealed specimen compare to the as-rolled specimen. - What is a dislocation? - How can dislocations be introduced into a metal? - What effect do dislocations have on material behaviour in the elastic region? - What effect do dislocations have on material behaviour in the plastic region? - Why does the number of dislocations change a material’s properties? MCD4270: Material Project Page 4 Part 2: Design project: Your engineering firm has won a contract to design and build a new truss footbridge across the Yarra River. The design team in your engineering firm has generated an initial truss design, based on pedestrian live loading from the Australian codes of practice. Self-weight will be included once the material choice has been made – this is beyond the scope of this assignment. Using the method of joints, the forces in members AB and BC were determined and are shown in Figure 1. Figure 1: Footbridge truss design showing members A-B in tension (T) and A-C in compression (C). Your task is to select appropriate candidate materials and dimensions for members AB and AC according to the design brief outlined below. Due to material supply considerations with your company, you must construct the members using materials listed in Table 2. Note that different materials and final cross-sectional areas/shapes may be used for Members AB and AC, as outlined in the design briefs. Ignore the self-weight of the bridge for all calculations. Both yielding and buckling are to be considered as failures. Assume the members AB and AC have pin ends, thus ensure the appropriate effective length buckle coefficients are used. MCD4270: Material Project Page 5 MEMBER AB Length 2000 mm Loading 22 kN axial load in tension with no yielding. Design envelope: The beam must fit into a space with a cross section no greater than 100 mm wide by 30 mm high (see Figure 2a). Ductility: The material chosen must undergo some level of plastic deformation before failure (non-zero ductility) Cost: Minimum Required precision: Your final design must be given to the nearest millimetre. MEMBER AC Length 2000 mm Loading 21 kN axial load in compression with no yielding and buckling. (Hint: buckling can potentially occur in more than one direction). Design envelope: The beam must fit into a space with a cross section no greater than 40 mm deep by 40 mm wide (see Figure 2b). Ductility: The material chosen must undergo some level of plastic deformation before failure (non-zero ductility) Cost: Minimum Mass: Minimum Required precision: Your final design must be given to the nearest millimetre. Figure 2: Schematic of maximum beam dimensions (mm) for members AB (a) and AC (b) MCD4270: Material Project Page 6 Question 1 (10 marks) Identify and eliminate materials that do not meet the design criteria for each member. Take into account the mode of failure as well as non-zero ductility in your process. Show all working and briefly outline your methodology. Question 2 (12 marks) The following are possible materials indices that can be considered for each member, where ρ = material density and Cm = material cost per unit mass. The mass or cost of the final beam will be minimised when a material is chosen that maximises the value of the corresponding material index: 1. Stiffness limited design (buckling): Minimum mass ? 1 2⁄ ? Minimum cost ? 1 2⁄ ?? × ? 2. Strength limited design (yielding): Minimum mass ? 2 3⁄ ? Minimum cost ? 2 3⁄ ?? × ? [Please read ALEXANDRIA reading materials for Week 3-4: Materials Selection for an explanation of Material Indices if desired] Determine an appropriate material index or set of indices for each member and rank the 6 most efficient materials for members AB and AC from Table 2. Present your results in a Table. Briefly discuss your rationale for selecting the material index for each member. Question 3 (8 marks) Design an appropriate member (for both AB and AC) using the top three materials, choosing an appropriate cross-sectional shape and dimensions, and justify all your results with calculations or discussion. Question 4 (4 marks) Apart from cost and mass, name 4 additional considerations that might be important in choosing materials for the bridge. Provide a short explanation for each of your responses. MCD4270: Material Project Page 7 Table 2: Materials to be investigated for use in design of the beam (average values taken from CES Edupack, level 2 database) Material Yield stress (MPa) Modulus (GPa) Elongation (%) Density (tonne/m3) Cost ($/kg) Softwood (clear wood) 40 9.35 2.21 0.52 1.07 CFRP (Carbon fibre reinforced polymer) 800 109.5 0.335 1.55 42.3 Wrought magnesium alloys 262.5 44.5 10.75 1.725 3.51 Age-hardening wrought aluminium alloys 352.5 74 10.5 2.7 2.38 Polycarbonate 64.5 2.22 110 1.175 5.16 High carbon steel 780 207.5 18.5 7.85 0.59 Concrete 2 20 0 2.45 0.0535 Silicon carbide 505 430 0 3.155 18.85 GFRP (fibreglass) 151 21.5 0.9 1.86 31.4 Hardwood (clear wood) 47.5 22.9 1.9 0.94 0.74 Brick 9.5 22.5 0 1.85 1.22 Cast iron (ductile) 465 172.5 10.5 7.15 0.61 Low carbon (mild) steel 322.5 207.5 36.5 7.85 0.59 Polyamides (e.g. nylon) 72.4 2.91 65 1.13 4.58 Titanium alloys 975 115 7.5 4.6 25 Tin 11 43 65 7.26 25.35 Team Assignment (8% of semester marks) Part 1: Answer all the following questions: Question 1 (5 marks) Question 2 (10 marks) Question 3 (4 marks) Question 4 (9 marks) Question 5 (12 marks)