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Course B5.9SC1: Mechanics of Materials B

Assignment 3

Investigating the mechanical properties of composites

Important information about this assignment:

1. This assignment is worth 25% of the total for the Course B5.9SC1.

2. The deadline for submission is 12 noon in your local time zone on the Friday of Week 10. If the assignment is submitted late (even by a minute) it will be subject to a 30% deduction in marks. If the assignment is submitted more than five working days late it will not be marked.

3. Students who have mitigating circumstances which result in late or incomplete submission MUST make an application for mitigating circumstances.

4. You MUST include the standard University Declaration in your submission (see “Important Course Information” on Canvas). Reports not containing such a declaration will not be marked.

5. The assignment is “open book”, meaning that you are assumed to have access to any notes, tutorial questions, examples and solutions that have been issued to you. Any other material that you use MUST be referenced.

6. You MUST use your own words. Do not copy passages from the notes as this will not attract any marks.

7. Your submission MUST NOT contain any hand-written material. Any graphs, tables, or results MUST have been produced by you. You are strongly advised to keep an evidence folder of spreadsheets, MATLAB code or other means you used to produce your results. This file may be asked for by the marker and you MUST be able to produce it at short notice.

8. Do not clog your submission with detailed calculations. Any algebra or arithmetic that you feel you need to record should be put in your evidence folder

9. If you think that any information is missing in any question, make an assumption, and state clearly what assumption you have made. The questions are deliberately chosen to be open-ended.

Advice 

This question is aimed at assessing your understanding of Topic 4 of the Course. You are required to combine various ingredients (fibres and matrix) and investigate the resulting mechanical properties that can be obtained. Avoid combinations that have already been worked through in the tutorial examples, although you may use the answers to the tutorial questions for comparison with your own results. You should aim to investigate the effect of one or more variable on laminate and ply properties and to demonstrate your understanding of as many of the methods as you can.

You should spend around 10 hours (productive time) working on this assignment. Write a single, integrated report (around 1200 words) on your findings, supported by graphs and tables, as appropriate. Keep detailed calculations along with any secondary files (e.g. spreadsheets, Matlab worksheets) as an evidence folder, which you can refer to from your report. Do not submit your evidence file but retain it in case it is asked for during the marking process.

Your answer will be assessed against the following 5 criteria:

Competence (30% of total): For showing that you are able to use each of the techniques covered in the Topic

Scope (20% of total): For the range of variables that you have examined.

Analysis (30% of total): For having a focus for your investigation and forming some conclusions

Adventure (10% of total): For applying the techniques beyond the specific ways in which they are demonstrated in the examples

Presentation (10% of total): For getting across your ideas in a clear and concise way

Questions

Using data from Tables 1 and 2 (or similar data that you have found from your own research), answer the two following questions, illustrating your answers with calculated values of the relevant properties.

a) Fibre reinforced composites (FRCs) are mixtures of (usually) two isotropic materials, the fibre having a modulus one or two orders of magnitude higher than the matrix. Summarise how the direction and proportion of fibres can influence the elastic properties of FRCs. You should refer to unidirectional continuous and short fibre reinforcement and to laminates that are in plane stress and your summary should refer to equations from the notes.

b) Explain the factors which affect the strength of unidirectional FRCs when stretched along the direction of the fibres. (The strength is defined as the stress at which the composite breaks). You should refer to equations for both continuous and discontinuous fibre reinforcement.

Table 1: Elastic properties and strengths of matrix and fibre materials

Table 2: Shear strengths of fibre-matrix interface (MPa) for materials in Table 1