The Importance of Access to Validated Data
- 1. Chris Middleton Engineering Librarian, University of Nottingham c.middleton@nottingham.ac.uk, 0115 8467463 The Importance of Access to Validated Data
- 2. The context Supporting engineering research Standard texts Research articles Technical information Also Supporting engineering design Student projects Academic consultancy Industrial R & D
- 3. Sources of design data Based on standard components Supplier’s catalogues From first principles Standards from legislative bodies British Standards, ASTM, IEC Reference works handbooks, data books Using validated data….. W=S t (0.55d 2 - 0.25d) W=working strength S t = allowable working stress d=nominal outside diameter
- 4. Validated data What? Proven data derived by empirical means Why? Informs complex situations not easily analysed theoretically Reliable quality Defence against negligence Where? ESDU - Engineering Science Data Units
- 5. ESDU - www.esdu.com View abstracts at: AERADE (http://aerade.cranfield.ac.uk/esdu_index.html) TechXtra ( http://www.techextra.ac.uk/esdu/index.php) Validated engineering design data, methods, equations and software based on 66 years' experience Choose from 23 series covering aerospace, chemical, process, structural and mechanical engineering topics. Performance Physical Data, Chemical Engineering Physical Data, Mechanical Engineering Process Engineering Technology Sound Propagation Stress and Strength Structures Transonic Aerodynamics Tribology Vibration and Acoustic Fatigue Wind Engineering Aerodynamics Aircraft Noise Composites Construction Engineering Dynamics Engineering Structures Fatigue – Endurance Data Fatigue – Fracture Mechanics Fluid Mechanics – Internal Flow Fluid Mechanics, Internal Flow (Aerospace) Heat Transfer Mechanisms
- 6. Example Design a tension bolt to support a known load (F) Factors to consider: Strength of bolt material Bolt diameter and thread design Tightening torque Pre-load (P) Applying torque to increase the pre-load minimises the effect of the load forces and so increases fatigue life. Source: Parmley, R.O.,ed., 2000. Illustrated sourcebook of Mechanical Components. New York: McGraw-Hill. pp19 -12.
- 7. Standards relating to bolt design Standard grade specifications give the minimum mechanical properties for the bolt. Source: Oberg, E., et al., eds. Machinery's handbook 26th ed. New York : Industrial Press, 2000. pp. 1488
- 8. British Standards British Standards Institution, 1964. BS. 3580: 1964. Guide to design considerations on the strength of screw threads. Gives formulae and details the relationships between material strength and features of bolt design and manufacture Lists variables such as lubrication used, types of washers, coarse or fine threads States “it is recommended that torque-tension relations be established experimentally for the conditions of the particular application.” British Standards Institution, 2005. BS EN 14399-2:2005. High-strength structural bolting assemblies for preloading. Suitability test for preloading. The principle of the test is to tighten the assembly and to measure, during tightening, the following parameters: the bolt force; the relative rotation between the nut and the bolt; the torque, if required; the bolt elongation, if required.
- 9. Cobb, B.J. Preloading of bolts. In: Parmley, R.O.,ed., 2000. Illustrated sourcebook of Mechanical Components. New York: McGraw-Hill. pp 19-12 to 19-16 But practical variations are listed: applied torque, thread design, friction forces between touching surfaces. So safety margins and tests are required. Design curves are produced based on the stress-torque equation and the preload-torque equation: For a given bolt diameter read up to the desired load for the tightening torque and read down for the material strength requirement.
- 10. ESDU 86014: Applying, measuring and maintaining pretension in steel bolts Abstract: ESDU 86014 discusses factors affecting the tension in a bolt, and indicates the methods by which a desired tension may be obtained, with a comparison of their relative accuracy and cost. Methods of measuring the bolt loads are also discussed. To determine the bolt pretension achieved by application of a known torque, the results of 1900 tests were analysed to yield curves for both lubricated and unlubricated threads of BSF(BA) and Unified or ISO metric forms . The test data related to nuts of mild and high strength steel seated on mild or high strength steel or aluminium alloy washers , and lubricants ranged from light oil to extreme pressure greases . No significant trend with material or lubricant could be isolated. Techniques for applying a known torque are considered, and their accuracy reviewed . Methods of locking the nut are described , together with their advantages and disadvantages, and include mechanical, frictional, adhesive or deformation techniques.
- 11. All elements and variable subjected to test and analysis Detailed graphs produced leading to design guidelines with indications of accuracy
- 12. Summary Designers need good quality data to ensure safety. They need to: Either use theoretical methods to design a product design test methods to prove the capabilities of the product conduct tests to prove that critical elements meet all the required standards Or use validated data proved by extensive evaluation and accepted as reliable