Browsing by Author "Loughlan, Joseph"

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    The compressive post-buckling behaviour of thin plates with cutouts
    (Cranfield Institute of Technology, 1987-02) Paracha, N. B.; Loughlan, Joseph
    This thesis presents an investigation of the buckling and post-buckling behaviour of plates with cutouts under uniform compression. The theoretical analysis developed for this purpose is based on a combined finite element/-spline procedure which formulates a mathematical representation of the membrane stresses within the plate according to its flat and unbuckled state. These mathematical representations are then utilised in the subsequent energy analysis to determine the point of initial buckling and in a semi-energy post-buckling analysis to determine behaviour of plate after initial instability. A comprehensive study is made with regard to buckling loads, in-plane displacements, out-of-plane deflections and the internal stress variations of simply supported square plates with centrally located circular and square cutouts. The analysis caters for the nonlinearity due to changes in the buckled shape in the post-buckling region. The results have, however, been presented for both single term and multiterm solutions. An experimental investigation has also been conducted to obtain information on displacements and stresses. Plates with circular and square cutouts have been tested on a rig designed and manufactured at the College of Aeronautics. The present theoretical results have been compared with the theoretical and experimental results of other investigators. The theoretical results are shown to be in fairly good agreement with the experimental results of plates with circular and square cutouts of various sizes.
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    The constrained torsional analysis of thin-walled variable cross-section multi-cell laminated composite beams
    (Cranfield University, 1999-08) Ahmed, Malik Nazir; Loughlan, Joseph
    A Constrained Torsional Analysis of Thin-Walled Variable Cross-Section Multi-Cell Laminated Composite Beams has been undertaken . The existing Isotopic theory has been modified using the effective engineering elastic constants to cater for the Composite structures under torsional loads. The relevant computer programs for the Composite structure analysis have also been developed. The results are discussed in detail for single-cell and multi-cell prismatic/tapered beams for all [0/45/-45/90], lay up in flanges and webs, all [45/-45]2], lay-up in flanges and webs, and for flanges [0/45/-45/90], & webs [45/-45]2], lay-up. The theoretical results obtained are then compared with those obtained from a finite element method analysis carried out by the author employing MSC commercial package PATRAN/NASTRAN. This has provided confidence in the validity and capability of the developed Composite theory in handling the Torsional Analysis of Variable Cross-section Single-Cell & Multi-Cell Laminated Composite Beams.
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    Enhancing the post-buckling response of composite plate/panel structures utilizing shape memory alloy actuators - a smart structural concept.
    (Cranfield University, 1999-02) Thompson, S. P.; Loughlan, Joseph
    The feasibility of enhancing the post-buckling load bearing capability of carbon/epoxy----- - composite plate/panel structures' utilizing embedded activated near equiatomic nickeltitanium, Ni-Ti, shape memory alloy, SMA, wire actuators has been investigated. Enhanced post-buckling is achieved through utilization of the unique shape memory phenomenon inherent within the Ni-Ti material. The unique phenomenon requiring a thermal stimulus. Within this investigation, such a thermal stimulus is provided for by an electrical current. Several host laminates, varying in lay-up architecture, have been considered. Two control strategies have been employed that utilize the unique SMA response at an elevated temperature. Control strategy 1 features embedded SMA actuators located within tubes that run along the specimens neutral plane. Here, the SMA's are constrained to external boundaries. Control strategy 2 also features embedded SMA actuators. For this control strategy, however, the actuators are partially constrained to the host laminate. For each strategy, upon SMA energization, shape memory constraint results with the formation of a recovery force within the SMA material. It is this recovery force that is employed to control the post-buckling response of the selected laminated specimens. A requirement for control strategy 2 is that the SMA/host interface must be of sufficient quality to sustain an elevated temperature as well as the imposed recovery force. Pertaining to control strategy 1, for the associated specimens, activation of constrained pre-strained SMA wire actuators can result with a significant specimen post-buckled deflection alleviation while under the influence of an external compressive load that is approximately three times the critical buckling value. While not as effective as control strategy 1, the concept behind control strategy 2 has been shown to work. Its efficient, or optimal, utilization, however, has yet to be demonstrated. For all the specimen configurations, the constrained SMA response act's to pull the specimens back to their flat configuration. This is true even when employing a low SMA volume fraction. Depending on the magnitude of the in-plane compressive load, however, this can result with post-buckled instability. SMA restoration recovery forces not only reduce the peak displacement amplitude, they also alleviate high stress levels, local to the boundary supports, that are typical to postbuckled plate/panel configurations. The tendency of adaptation is to redistribute the loading back towards the plates central region, such that, a more uniform stressed state exists. The stability of the adapted shape is dependent upon the laminate stacking sequence. Due to the elevated temperature required for SMA energization, the stacking sequence chosen should be such that temperature effects have minimal influence on the structural performance. SMA utilization would certainly be of benefit when such components are subjected a thermal environment by a means other than electrical energization. As an example, heating, associated with skin friction, may be sufficient to drive the actuators through their phase transition such that they exert stabilising recovery forces on the skin sections of high speed aircraft. The performance benefits of the SMA/carbon/epoxy composites materials, however, must carefully be assesseda gainst issueso f technical risk, producability, maintainability, reliability, and, of course, cost. The improved performance must be at an affordable price.
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    Parametric analysis for structural design and weight estimation of cantilever and strut-braced wing-boxes
    (AIAA, 2023-01-19) Taflan, Murat; Smith, Howard; Loughlan, Joseph
    Computationally cheap and accurate enough weight estimation tools are needed for the multidisciplinary design optimization and the design exploration studies of novel aircraft at the conceptual design stage. In this study, a new wing-box structural design and weight estimation method for conceptual or early preliminary design of novel aircraft configurations is introduced. The wing-box weight estimation is achieved through structural sizing using standard structural theoretical procedures. To achieve this, a new wing geometric description with a new wing-box idealization model is introduced. Realistic symmetric maneuver, rolling, and combined loading cases are generated following CS.25 requirements. The structure is sized considering bending, shear, and buckling constraints, and the total weight is estimated from the sized components. The tool is validated against data from nine cantilever and one strut-braced aircraft with aluminum and composite wing- boxes, and a standard error of 1.7% and an average error of -0.2% are achieved. The effect of the strut addition on the total wing-box weight of high aspect-ratio wings is studied. It was shown that the strut helped reduce the wing-box weight of aluminum and composite wing-boxes by 11.9% and 16.2%, respectively. The capabilities and sensitivity of the new wing-box weight estimation method are also successfully presented through an in-depth parametric study. The effects of fourteen aircraft design parameters on the total wing-box weight of moderate and high aspect-ratio cantilever and strut-braced wings are investigated. It was shown that some design parameters have a significant effect on the wing-box weight of cantilever and SBW aircraft, and any wing-box weight estimation model not covering these effects is likely to have limited accuracy or sensitivity.
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    The stability and post-buckling behaviour of stiffened plates in compression
    (1990-02) Jhita, P. S.; Loughlan, Joseph
    The investigation reported in this thesis was carried out to examine the behaviour of stiffened plates subjected to uniform end compression using energy methods. The thesis begins with a short introduction, followed by a review of the relevant literature. The basic differential equations and energy expressions, using plate theory are then derived. The theoretical analysis of the mechanics of local, lateral and overall instability of asymmetrically and symmetrically edge stiffened plates is then presented. The analysis is then extended to investigate the behaviour of infinitely wide panels with stiffeners of deformable cross section. The results obtained from this analysis are used to highlight the shortcomings of using an infinitely wide panel model to predict the behaviour of a panel of a finite size through comparison with existing work. This is then followed by the analysis of a simply supported panel of finite size stiffened by stiffeners of rigid cross section. Plate theory was used to model the skin and beam theory to model the stiffeners. The results obtained from the analysis compared favourably with those already existing. The method is then extended to investigate the post buckling behaviour of simply supported plates and stiffened panels. The post-buckling behaviour of plates has received a considerable amount of attention since plates can carry loads beyond the critical load. The use of this additional strength.is of great importance to the design of aerospace, naval and civil engineering structures since considerable weight savings can be achieved. In comparison the post-buckling of light gauge integrally stiffened panels has received far less attention. Most of the published literature concentrates on the interaction between the local and overall buckling modes and the sensitivity of panels to geometrical imperfections when the local and overall buckling loads are nearly coincident. In all the above investigations, the overall buckling load for the panel is assumed to be equal to the Euler load for a pin-ended strut with the cross-section equal to the repeated panel cross- section. This implies that the transverse edges of the panels are assumed to be free. In general, stiffened panels are supported by a system of crossframes. A consequence of this layout is that lateral support is provided on all boundaries of the panel and therefore the wide strut model is invalid. In the present work the panels are assumed.to be simply supported along all four edges. It is shown that the post-buckling behaviour of these panels is substantially different to that of the wide strut model. The thesis finishes with a summary of the findings and a list of the main conclusions.
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    Structural sizing and mass estimation of transport aircraft wings with distributed, hydrogen, and electric propulsions
    (Cambridge University Press (CUP), 2024) Taflan, Murat; Smith, Howard; Loughlan, Joseph
    Current literature offers limited mass estimation methodologies and their application in the conceptual or preliminary design stages of moderate to high aspect ratio wings with electric, hydrogen or distributed propulsions. This study presents the development and application of a quasi-analytical wing mass estimation method to address this limitation. The proposed method is distinguished from the existing mass estimation methods by its expanded realistic load cases, sensitivity to several design parameters, improved accuracy with short computational time and capabilities for future applications. To achieve these features, new geometric models are introduced; 483 load cases including symmetric manoeuvre, rolling, and combined cases are covered following airworthiness requirements; the structural elements are idealised and sized with strength and buckling criteria; existing methods are evaluated and integrated cautiously for secondary structures and non-optimum masses. A computation time of 0.1s is accomplished for one load case. The developed method achieved the highest accuracy with an average error of -2.2% and a standard error of 1.8% for wing mass estimates compared with six existing methods, benchmarked against thirteen wings of different aircraft categories. The effects of engine numbers with dual- to 16-engine setups and the dry wing concepts on the wing mass are investigated. The optimised number of engines and their locations decreased the wing mass of the high aspect ratio wing significantly. In contrast, the dry wing design increased the wing masses of all baseline aircraft. The future applications and improvements of the presented method in novel configurations and multidisciplinary designed optimisation studies are explained.