Browsing by Author "Darlington, M. W."
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Item Open Access An apparatus for the measurement of tensile creep and contraction ratios in small non-rigid specimens(College of Aeronautics, 19) Darlington, M. W.; Saunders, D. W.An apparatus is described for precise measurement of creep properties in specimens with gauge lengths down to 1.2 cm. An extensometer has been developed which is supported independently of the specimen and exerts a load on the specimen of less than 5 grams. It can thus be used with small non-rigid specimens. The extensometer will detect strains down to 2 x 10-6. The stability is excellent. An adaptation of the system which allows simultaneous measurement of tensile strain and lateral strain during creep is also described. The apparatus was designed for the measurement of anisotropy of creep properties in oriented thermoplastics and reference to such measurements is given. It is however entirely suitable for general application to small specimens.Item Open Access Creep studies on oriented thermoplastics(College of Aeronautics, 1969) Darlington, M. W.; Saunders, D. W.The enhancement of many of the mechanical properties of thermoplastics which may be achieved by orienting the molecules has been known for some time. It has been exploited in the production of textile fibres end oriented films. Molecular orientation also occurs during processes such as extrusion, moulding or forming. Here, unless carefully controlled, it may well cause a deterioration in the properties of the finished article. In view of this a systematic study on the anisotropy of the mechanical properties of thermoplastics, resulting from molecular orientation, is being carried out at present in these laboratories … [cont.].Item Open Access Mechanical properties and structure of extruded short glass fibre-filled polyethylene(Cranfield University, 1990-01) Jollands, M. C.; Darlington, M. W.The work described in this thesis concerns the mechanical properties and structure of extruded short glass Fibre-Filled polyethylene. High density polyethylene was compounded with E-glass and coupling agent, and extruded into 110 m diameter pipe, using a normal production extruder, by Stewarts & Lloyds Plastics, Huntington. A normal die and a novel die, based on the Monsanto expanding mandrel die, were used to produce pipes with varying fibre orientation distributions (FED). The structure of the pipe was analysed in terms of density, crystallinity, glass weight Fraction, and Fibre length and orientation distributions. Various mechanical properties were measured, to confirm the structure results, namely tensile creep and compression modulus, and tensile strength. 3-point bending tests of pipe were undertaken. The measured deflections under load were compared with simple bending theory and finite element analysis predictions. Kc, a Jc,-testing of samples was undertaken. JC-testing was not successful, so Kc testing was adopted. The Kc results are analysed in terms of FOD and test seed, and it is shown that alignment in the direction of load does not allays produce the most resistance to crack growth. Fatigue testing of impact tension and slant-edge cracked specimens was undertaken, with crack growth at several angles to extrusion. Results are very different for samples produced with the different dies, and also depend on fibre length, glass volume fraction, angle to extrusion, and test stress amplitude.Item Open Access The mechanical properties of anisotropic polymers: progress report no. 3(College of Aeronautics, 1967-03) Darlington, M. W.Item Open Access The mechanical properties of anisotropic polymers: progress report no. 5(College of Aeronautics, 1968-03) Darlington, M. W.A report of work carried out during the period 1st October, 1967, to 31st March, 1963.Item Open Access The mechanical properties of anisotropic polymers: Progress report no. 6(College of Aeronautics, 1968-09) Darlington, M. W.Part 1 General Developments The basic development work on the tensile creep apparatus was completed by March, 1968. A description of the latest 'heavy-duty' creep rig and two types of contraction extensometer, together with the relevant creep trials, was given in Progress Report No. 5. Since then two further 'heavy-duty' creep rigs have been assembled and tested and are now ready for use with rigid plastics. In addition, further trials of the double transducer contraction extensometer described in Report No. 5 have been carried out. These trials are described in part 2 of this report The trials were considered reasonably satisfactory and each of the three heavy-duty creep rigs has now been fitted with a device of this type in addition to the normal tensile extensometer. The polythene creep rig described in Progress Report No. 3 has been working satisfactorily for over a year and no further modifications have been made in the period under review. At the conclusion of the above-mentioned trials it was considered that the creep apparatus was unlikely to require any further major changes. A detailed report of all the apparatus has therefore been prepared with the intention of submitting it for publication to the Journal of Scientific Instruments. It is at present being examined at the Ministry of Technology. (CoA Memo. No. 158).Item Open Access The mechanical properties of anisotropic polymers: progress report no. 7(College of Aeronautics, 1969-03) Darlington, M. W.Part I General Developments The major part of the period under review was devoted to a study of the tensile creep properties of isotropic and uniaxially oriented Perspex sheets (standard grade) using the three heavy-duty creep rigs mentioned in the previous Progress Report (No. 6. September, 1968). Measurements of lateral contraction were made simultaneously with the tensile strain measurements during most of the creep tests. The creep rupture behaviour and optical anisotropy of the oriented sheets were also studied in an attempt to present a more complete picture of the behaviour of the material. Some of the early results of this work have already been published and copies sent to the Ministry. (Darlington and Saunders; 1969). Details of the complete work will be found in part II of this report. The two types of contraction extensometer described in Progress Report No. 5 were used during the Perspex studies and reasonable agreement was obtained between the results. The techniques required with the contraction devices were considerably improved during the period under review and the absolute validity of the contraction measurements is now more certain. Some comments on the general performance of the apparatus are given in section 2.8.4.Item Open Access xtrusion of short fibre reinforced polyethylene pipes(Cranfield University, 1990-02) Wilson, K. A.; Darlington, M. W.Short fibre reinforced thermoplastic pipe was produced by an extrusion process which oriented the fibre reinforcement predominantly into the pipe hoop direction. The fibre reinforcement was thereby used to maximise the internal pressure resistance and resistance to crack propagation of the pipe in the axial direction. Careful selection of materials and development of a suitable compounding method enabled polyethylene, glass fibres and a coupling agent to be combined such that fibre length retention and effective coupling gave worthwhile improvements in the physical properties over the polyethylene matrix polymer. Extrusion configurations developed were based upon the use of motionless dies having a diverging mandrel, and other methods, to bring about melt hoop expansion. Die geometry was varied to assess the influence of such factors as melt expansion ratio, divergence angle and die land length. _ Study of the complex fibre orientation distribution produced during extrusion and the die geometry variables has led, with the application of the classical particle rotation theory proposed by Jeffrey, to the development of predictive computer software for different die configurations. Predictions have been found to agree qualitatively with measured fibre orientation ' distributions in pipes. Physical testing has enabled characterisation of a range of pipes produced under different conditions having different levels of fibre reinforcement and with different fibre orientation distributions.