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Composites MSc NDT Assignment 2011-12

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  Imperial College London Department of Mechanical Engineering MSc Module in Non-Destructive Testing, 2011/2012 NDT Coursework Exercise Peter Cawley, Room 564, Mech Eng, e-mail p.cawley@imperial.ac.uk Background If composite materials are to be used in safety-critical areas such as aircraft primary structure, it is essential that they are inspected both before service and at intervals during their life. It is therefore necessary to specify non-destructive testing (NDT) procedures which will detect any defect which would cause premature failure. The first step in selecting an inspection technique is to determine what type and size of defect must be detected. This is done by assessing the significance of each possible type of defect on the performance and life of the structure. The NDT course deals with the different possible inspection techniques and having completed it, you should be able to select an inspection technique for the detection of any specified defect. Your other courses will deal with the significance of defects, and hence with the decision on which defects it is essential to detect. Course Objective  At the end of the course you should be able to select an appropriate technique for any given inspection problem in composite materials. In order to achieve this overall objective, you must be able to: 1. state all the possible inspection methods; 2. describe the principles of operation of each method; 3. state the sensitivity of each method; 4. list the major advantages and disadvantages of each method. Coursework Outline The coursework exercise is an investigation into an NDT task. An inspection problem is explained in the section below. You are to work in groups of 2 or 3, to develop and present a proposal for the solution of the inspection problem. The material of the NDT course should be sufficient to cover the possible NDT methods, but you may wish to supplement this with information from elsewhere, such as the library. Some references are given below.  A single report should be prepared by each group. Please ensure that all members contribute equally, and please include a statement that this is so, at the start of the report. The reports should be submitted by Friday 17th February 2012. Please submit one PDF copy via Blackboard and one hard copy via your Year Box outside the Teaching Office. The Problem Your manager has asked you to propose an inspection system for the drive shaft for a high performance car shown in the attached sketch. The shaft is essentially a 400 mm long filament wound CFRP tube with internal diameter 25 mm and wall thickness 3 mm. It is wound at ±450 and has a 68% volume fraction.  Aluminium end fittings are bonded into the tube at each end, the bond being over a 25 mm length; the tube is chamfered in order to ensure a good fit. Since the machining of the chamfer and subsequent bonding is expensive it is proposed to carry out the inspection in two stages. After production of the tubes, their volume fraction and winding angle is to be checked and any delaminations larger than 10 mm in diameter are to be found. The volume fraction is to    2   be determined to ±4% and the winding angle to ±30. After the end fittings are bonded, it is necessary to detect any disbonds larger than 5 mm in diameter and also to detect any areas where the porosity in the bondline exceeds about 10%. The production rate is expected to be 500 per week. You are to prepare a report for your manager outlining the possible inspection techniques and justifying the system which you propose. If different options are possible, you should state clearly their relative advantages and disadvantages. You must provide your manager with sufficient information (not including exact costings) to enable him/her to make an outline investment case to the board. You must therefore make clear what system(s) you recommend and give approximate costs (i.e. will it be £1k, £5k, £10k, £50k, £100k …). This is more important than great detail about the background to different NDT techniques – you only need include sufficient background information to justify your choice of technique. There is no need to regurgitate lecture notes, and only a very few words are required to eliminate methods that are clearly unsuitable. You should discuss in detail how the tests will be carried out - what equipment is needed, how it will be set up, what measurements are involved etc.   Bibliography 1. Halmshaw, R. 'Non-Destructive Testing', Edward Arnold, 1987. 2. Summerscales, J. (ed) 'Non-Destructive Testing of Composite Materials', Vol 1 (1987), Vol 2 (1990), Elsevier Applied Science. 3. NDT course notes. 4. Adams, R.D. and Cawley, P. 'A survey of defect types and non-destructive testing techniques for composite materials and bonded joints', NDT International, Vol 21, pp208-222, 1988. CFRP (wall thickness approx 3 mm)Aluminium end fittingadhesive (thickness approx 100 µm)400 mm25 mm Not to scale60 mm Schematic Diagram of Drive Shaft Assembly  
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