1.1 Your reporting manager RM is convinced that the best possible way to prevent the bracket from failure is to ensure that it is enough rigid thereby ensuring absolute zero deflection at all points of the bracket.

Faculty of Engineering, Environment and Computing

7041MAA Finite Element Analysis

Notes: Design of new bracket

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Mark allocation guidelines to students

Aim

The aim of this coursework (CW) is to demonstrate your ability to receive and interpret data to create and evaluate the credibility of an FEA model as well as critically assess the results thereof; including dissemination using technical arguments. In other words, pre-process, solve and post-process the results of FEA. You will also be required to optimise the structure in terms of maintaining or improving structural performance whilst minimising or maximising given attributes.

Introduction

Finite Element Analysis (FEA) is an invaluable tool to modern day engineers, enabling the capability to make design decisions based on a components simulated performance under different loading and environmental conditions as well as validation of load case and load path calculations.

You have just landed a job at an exciting new company specialising in design and production. Your new reporting manager, the Chief Executive Officer (CEO) is very excited about you joining the company as an FE expert. As the only engineer with any background knowledge of structural mechanics and FEA the expectations of you are sky-high!

Although your reporting manager, RM, is very friendly and extremely enthusiastic (s)he has no knowledge of structural mechanics what-so-ever – but RM is convinced that you are an FE guru! The future of the company rests on your shoulders as any significant warranty issues (such as poor structural performance; for example a cracked frame) will severely cripple if not bankrupt the company; you need to tread carefully…

Notes

N1 Your company can only afford 1 FE license – they use Altair HyperWorks; consequently no other FE software can be used for the impending tasks, i.e. this CW.

N2 There is only 1 geometry model for all brackets; a HyperMesh (*.hm) model is available on Moodle.

N3 Your company is developing a number of new brackets of various sizes and shapes. In this CW, they do however only want you to work on one version, which is decided by your Student ID (SID). A bracket consists of a frame as illustrated below.

Figure 1 Schematic view of a bracket

1. a.   The material that make up your bracket is defined by the last digit of your SID using the below key:

0-2: Aluminium

3-6: Steel

7-9: Titanium

The material properties can be found in Table 1.

Table 1 Material properties

As an example, if your SID is 1234567 your bracket will be made from Titanium.

b. The applied perpendicular force (along the Z-axis) on bracket’s base holes (A to F) is defined by the 2nd last digit of your SID using the below key:

0-2: 50 [N]

3-6: 100 [N]

7-9: 150 [N]

c. The applied perpendicular force (along the Z-axis) on bracket’s top holes (H to K) is defined by the 3rd last digit of your SID using the below key:

0-2: 250 [N]

3-6: 300 [N]

7-9: 350 [N]

d. The applied moment (around the Z-axis) on bracket’s top hole G is defined by the 3rd last digit of your SID using the below key:

0-2: 1 [Nm]

3-6: 2 [Nm]

7-9: 3 [Nm]

e. Your value of the bracket thickness is defined by the fourth last digit of your SID using the below key:

0-2: 3 [mm]

3-6: 4 [mm]

7-9: 5 [mm]

Figure 2 Bracket’s holes under loading - Design of new bracket

N4 Your reporting manager (RM) is very busy – (s)he does not like reading long-winded reports; hence (s)he has created a template for all reporting which you will find in a separate document entitled: “333MAE_1920SEPDEC_CW_report_template.docx”

You must use this document for your CW; no other formats will be accepted. Pay close attention to the instructions in this document. If you do not follow these, you will be deducted marks.

N5 You may assume that all loading is linear static and that all material behaviour is isotropic. N6 You should be as succinct and concise as possible in your responses.

N7 Remember that statements without justifications are not credible.

Task 1 – Pre-processing, solving and post-processing

1.1 Your reporting manager RM is convinced that the best possible way to prevent the bracket from failure is to ensure that it is enough rigid thereby ensuring absolute zero deflection at all points of the bracket. RM wants your view on the real world feasibility of this; please comment and discuss.

1.2 RM wants the bracket to be as light as possible without failing (yielding) during operation based on two worst loading scenarios. RM therefore asks you to perform a structural assessment of the bracket. RM provides you with the following notes and points out that the below descriptions including the global coordinate system defined therein:

• The frame thickness of the bracket must be constant.
• The supports in holes A and F are constrained in the translation and rotation in the X, Y and Z-directions.
• Load Case 1 (LC1) should represent the “normal force” on the base holes A to F. The normal force should be applied (in the Z-direction) on the

“base holes”.

• Load Case 2 (LC2) should represent the “normal force” on the base holes A to F and the top holes H to K. They should be applied (in the Z- direction) on the holes.
• “Both cases should include the moment effects” around the hole G. This moment is applied (around the Z-direction).

RM asks you to:

1. Complete a mesh convergence study and define which mesh size has been used (and why).
2. Demonstrate how the mesh has been refined.
3. Determine what the smallest thickness of the bracket can be (without failing) and the final mass of the bracket.
4. Evidence that the bracket will not fail.

1. Based on your findings define and justify a mesh protocol with the most important mesh quality parameters so that future FEA can be completed quicker. You should note that listing “irrelevant” parameters or not justifying parameter choices will be seen as failing solve this part of the task.

1.3 Following your structural analysis in 1.2, RM now wants you to determine the lowest natural frequency of the bracket. The Noise Vibration and Harshness (NVH) engineers based at the manufacturing plant have asked you to clearly (and uniquely) identify the location of the largest excitation magnitude for the first (lowest) natural frequency. Mysteriously the Isla Sorna plant employees have recently stopped answering their phones so you have no alternative but to make sure your documentation is not open to interpretation.

1.4 A short while after you have sent your report containing the vibration analysis results from 1.3 you receive an email from the NVH engineers. They have determined that the vibration from the bracket is 1% lower than the value you have determined in 1.3. They have therefore decided that there is no need for concern, as there is a 1% margin: surely, results obtained via FEA are correct. RM concurs with the NVH engineers; after all time is of the essence and there are many other issues to resolve. As the structural engineer what is your view?

Task 2 – Optimisation

RM has been very pleased with your work so far. Company has ordered metal sheet with certain thickness for bracket manufacturing.

Innovation is however a core ambition of bracket and RM therefore wants you to “improve” the bracket design in terms of enhancing structural performance whilst minimising mass. You suggest that applying (FE based) optimisation tools will enable you to drastically improve the entire bracket. Following several discussions between yourself and RM you mutually agree on the following targets:

• Bracket design improvements:
  • The bracket supports must not fail (yield) subject to LC1 and LC2 (as applied in 1.2).
  • The cost of manufacturing must not rise significantly; i.e. your design must be as simple as possible

• Bracket improvements:
  • Maximise the first natural frequency of the bracket (min. 10% higher than the value determined in 1.3).
  • The material of the bracket cannot be changed.
  • The thickness of bracket cannot be changed.
  • The bracket must not fail (yield) or break subject to LC1 and LC2 (as applied in 1.2).

2.1 Based on your discussions with RM you decide to conduct a topology optimisation of the Bracket. Remember to validate your new design before you present it to RM - (s)he will be very critical of your proposal unless the “predicted performance” is backed up (and thoroughly discussed) by appropriate FEA. Design of new bracket

1.1 Your reporting manager RM is convinced that the best possible way to prevent the bracket from failure is to ensure that it is enough rigid thereby ensuring absolute zero deflection at all points of the bracket. RM wants your view on the real world feasibility of this; please comment and discuss.