FEA assignment 2019 PDF

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Department of Mechanical Engineering Mechanics and Materials Semester 1, 2019 Unit 3: Finite element analysis Assignment: Computer based stress and strain analysis NOTE: Your report should be typed in font size 12 pts. Objective This assignment will expose students to a commercial Finite Element Analysis (FEA) package. It is not expected that students will gain a mastery of this or any specific package, but rather, it is hoped that students will gain a deeper insight to the issues that underlie computer based analysis, irrespective of the specific software being used. Students will use SolidWorks computer software to complete this assignment. Assessment This assignment is worth 25% of the final mark. The report is to be completed by each student individually and submitted online by 5 pm on Friday 24th of May. The report should not exceed 15 pages, including figures and appendices. Introduction One of the leading furniture manufacturing companies has decided to design a new steel chair for the people who suffers from the severe obesity (see figure 1). This chair is going to build for the people who has up to 200 kg weight. 20% of the weight can be applied to the back of the chair and remaining force can be applied to the seat. Please note that all the dimensions are in mm.

Back of the chair

Fillet Radius Seat

Beam Thickness

Figure 1: Chair

1

Part 1 Format your report such that each numbered item below is repeated in the report, followed by your answer. 1- Perform an analytical analysis the chair (see Fig. 2), considering it as a 2D truss structure. The individual beams can be assumed to be a square section (40x50 mm) along its length, and the fillets can be ignored. a. Construct the stiffness matrix for the whole structure (10 marks) b. Write a matrix form of the equations, relating applied forces to nodal displacements (5 marks) c. Calculate reaction forces, nodal displacements and stress in all members (10 marks)

Figure 2: 2D truss structure 2- Construct a model for the chair in SolidWorks, and provide a figure showing the final mesh, loads and constraints. Please present your model as a third angle projection (see attached drawing). (5 marks) 3- State and justify how you have modelled the loads and constraints, along with any assumptions you have made regarding this. (10 marks) 4- Perform a mesh sensitivity analysis to find an appropriate global or local mesh size. Present a figure showing average stress v. mesh size, as well as a figure showing computation time vs. mesh size. (10 marks) 5- Provide a von-Mises stress contour plot of the chair. Identify the location and magnitude of the region of highest stress. (5 marks) 6- Compare the results obtained from SolidWorks and those calculated analytically and discuss potential reasons for the observed difference. (5 marks) 7- Propose methods for checking your FEA results. (10 marks) 2

Part 2 A second design is required for the chair withstand a load which is 100% higher than that used in the initial design. The goal is to minimise the mass, keeping the maximum von-Mises stress less than its yield stress, and the maximum resultant displacement (URES) less than 2 mm. 8- How does an independent increase in fillet radius or beam thickness change the maximum stress and displacement in the body? Which parameter has a greater effect? (10 marks) 9- Find the optimal geometry by changing both the beam thickness (for all beams) and the fillet radius (for all fillets) according to the information in the table below. Plot the results on a URES displacement vs. beam thickness graph, with separate lines for each fillet radius value. Present the optimal geometry in a table, including the maximum stress and displacement. (15 marks)

Beam Thickness Fillet Radius

Minimum 10mm 5mm

Step Size 5mm 5mm

Maximum 50mm 40mm

10- Provide a von-Mises stress contour plot of the optimised chair. Identify the location and magnitude of the region of highest stress. (5 marks)

3

Geometry: Isometric view:

4

3rd angle projection:

5...