Browsing by Author "Rothwell, A."

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    The analysis of reinforced circular and elliptical cutouts under various loading conditions
    (College of Aeronautics, 1961-07) Houghton, D. S.; Rothwell, A.
    The effect of reinforced cutouts in a plane sheet under various loading conditions is considered, and a number of experimental results are given for circular and elliptical cutouts with a uniform plate reinforcement, subjected to various systems of biaxial tension and pure shear. These experiments were conducted using a plane loading frame, and the results are compared with the theoretical plane stress solution. For the circular cutout the effect of neglecting the bending stiffness of the reinforcement is considered. Some additional experiments were carried oUt on a 60 in. diameter pressurised cylinder containing an elliptical hole reinforced according •to Mansfield's neutral hole theory. The strains in the sheet in the region of the neutral hole are .compared with the corresponding strains in the uncut sheet. The experimental results obtained generally show a good agreement with the theory.
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    Application of finite element methods to the post-buckling behaviour of thin plates containing imperfections
    (Cranfield University, 1978-02) Allahyari, H.; Rothwell, A.
    A finite element program, applicable to the pre- and post-buckling behaviour of plates with imperfections, is developed. Suitable incremental stiffness matrices are generated for a plate element with four nodes and twenty degrees of freedom. Preliminary work, together with a prototype pro- gram, is carried out on a simple strut in order to compare various nonlinear solution techniques, both incremental and iterative. Th6 plate program is veri- fied by large deflection calculations for a square plate under lateral pressure, and by comparison with theoretical buckling loads for a perfect plate, closely agreeing with previous theoretical work. Experimental results in compression, both with and without an artificially introduced imperfection, are used to demonstrate real plate behaviour, and they enable a comparison to be made with computed results. Measure- ments of deflection are made by the Moire fringe tech- nique, as well as by dial gauges. The program is used to investigate the effect of buckling on the compressive and shear stiffness of plates with various degrees of imperfection, including the compressive stiffness of a square plate after buckling in shear.
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    The effect of curvature on the stress concentrations around holes in shells
    (College of Aeronautics, 1962-05) Houghton, D. S.; Rothwell, A.
    An experimental investigation has been carried out to investigate the effect of curvature on the stress concentrations around holes in shell structures. Two methods have been employed: - (I) Araldite cylinders, containing holes of various shapes, subjected to axial tension, internal pressure and torsion were examined by the photoelastic frozen stress technique. (2) Aluminium alloy curved panels and hemispheres were used in conjunction with miniature electrical strain gauges. The results are compared with the theoretical solutions and suggest that the curvature effect can be significant, particularly for the case of shear or biaxial loading.
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    The stresses around some unreinforced cutouts under various loading conditions
    (College of Aeronautics, 1961-03) Houghton, D. S.; Rothwell, A.
    A number of experimental results are given for unreinforced circular; elliptical and square cut-outs with rounded corners, under a variety of loading conditions. These results are then compared with the infinite flat plate solution, using the complex stress function and the method of conformal transformation. It is generally considered sufficiently accurate for a plane stress solution to be applied to problems of cut-outs in cylindrical shells, provided that the cut-out dimensions are small compared with the radius of curvature of the shell. In order to investigate this effect of shell curvature, a number of experiments were carried out on cutouts in two pressurised cylinders, and to obtain a wider range of loading conditions, a further series of experiments was conducted using a plane loading frame. Two aluminium alloy cylinders, of 44 in. and 60 in. diameter, were pressurised using air, and the stress conditions around the cutouts examined using electrical resistance strain gauge techniques. The plane loading frame enabled any combination of bi-axial tension and shear to be applied to a plane sheet containing the cut-out under examination. In this way the effects of body forces, which might arise in such applications as aircraft and nuclear reactors, could be simulated. The experimental results which are given generally show a close agreement with the theoretical plane stress solution.