66 research outputs found
Analytical Prediction of Failure Strength of Co-cured Composite Skin-Stiffener Joints
No full textComposite materials are widely appreciated by the engineers for aerospace applications because of their property tailorability, high specific strength, high specific stiffness, less weight and many other advantages. Various technologies are used worldwide for fabrication of these composite structures. One of such state of the art technologies is co-curing, where the primary structure is co-cured along with the secondary structure by eliminating the fasteners and allowing many other benefits of co-curing. The integral structure realized through co-curing approach will result in cost benefits by reducing the part count, fasteners and assembly time. Such type of fabrication is adopted in transport aircraft wing and
empennage structures where the substructure members like spars, ribs etc are co-cured with the skin forming co-cured joints. When such joints are present in wing structures
they are subjected to direct or in-direct out-of-plane loads caused by pressure generated due to the presence of fuel. The behavior and the strength of these joints under out-of- plane loads are of concern and has been the topic of many analytical and experimental studies. However, only limited information is available in the open literature. For the present study a typical transport aircraft wing, which is made of composites and fabricated using co-curing technology, is considered. The co-cured wing structure with internal fuel pressure imparting out-of-plane loads on joints are addressed in this paper. The joint strength assessment through feature level test by introducing the same level of defect concentration on such joints would be time consuming and expensive. On the other hand Finite Element (FE) analysis using suitable commercial software with appropriate model of the joint would provide a substantial understanding on the strength of the joint. In
the present paper attempts are made to understand the structural behavior of typical co-cured composite joints subjected to pull-off load, in presence and absence of a typical manufacturing defect. The authors demonstrate here the approach to predict the failure strength of co-cured joints under contemplation analytically using a polynomial invariant based three dimensional failure theory. The paper explains the methodology established for predicting failure strength under pull-off load which is a first step towards certification of co-cured joints with and without manufacturing defects
Estimation of failure load of composite bonded joints using 1D and 2D FE analysis and the mathematical equation of strain and bond energy in the adhesive layer
No full textAdhesively bonded composite (ABC) joints used in the composite structures are modeled using 1D and 2D elements to generate the finite-element mesh. The present modeling technique has captured the overall structural behavior of ABC joints precisely. The analytical study proposed a novel failure criterion of ABC joints after understanding the structural behavior of joints through the modeling approach. A failure criterion developed based on the principle of conservation of energy stored within the adhesive layer by virtue of its allowable strength properties and consumed by applying stress per a unit load. The ultimate failure load of joints of popular configurations is estimated based on the principle of conservation of energy. The 1D–2D finite-element modeling approach has revealed the presence of a new form of mechanical energy named as the Bond energy concealed within the adhesive layer. A new failure mechanism and their modes are explained through the novel failure criterion. The numerical value of Bond energy is calculated by using a peculiar mathematical relationship between the allowable shear strength property and the Young’s modulus of the adhesive layer. The ultimate failure load estimated by the novel failure criterion is compared with that of third-party experimental results and found fair agreement of 1–11% difference, which is acceptable with appreciation
Modeling the behaviour of an advanced material based smart landing gear system for aerospace vehicles
No full textStress Analysis of Ailerons-control bracket attachment to front-spar in SARAS composite wing
No full textThis report presents the FE stress analysis of Aileron-control bracket attachment to front-spar in SARAS composite wing. The wing is having eight aileron control brackets attached to fiont-spar between sta#4 to sta#21. During the actuation of the aileron. the force is transferred to the bracket by metallic tubes which are connected trough bracket. These forces are reacted by the front-spar and front-spar gussets to which the brackets are attached through fasteners. Each bracket should be able to transfer the actuator load efficiently and it is necessary to ensure the strength and stiffness of the surrounding parts for the smooth operation of the aileron. Brackets and attachment are modeled in detail and the brackets are integrated with global wing model. FE stress analysis is carried out for all
three design ultimate load conditions. Failure-index of composite part is extracted on the basis of Yamada-Sun failure criteria. It is found that failure-index of front-spar which is connected with aileron-bracket to front-spar and front-spar gusset, the fastner forces are also extracted. Margin of safety for shear-strenth of fasteners and bearing-stress of CFC and metal connections are also positive
Analytical Studies on Auxiliary Box in Composite Fin of Civil Aircraft and Validation of Structural Design by Optimization
No full textA need is aroused in recent days for a separate space to house the actuators of control surface of wing and empennage structures of civil aircraft. The creation of an independent space outside main structural box is understood as auxiliary box structure. The space for auxiliary box is created by providing an auxiliary spar member between front and rear spars. This auxiliary spar is provided based on technical evidence that mere provision of spar should not make main structural box to reduce its bending stiffness and torsional rigidity. Various analytical studies have been carried out to find the optimum location of spars that resulted in least displacement with least possible mass of the fin structure. The present studies have been carried out on a composite fin structure of civil aircraft which had been previously designed for a given loading and geometry through classical approach. The structural optimization also carried out on a few fin models to see the difference in the mass obtained from structural optimization with that of mass of initial design. It is seen that there is good agreement between optimized mass and that mass of initial design through classical method.
Conf Name: International Conference On Trends in Product Life Cycle, Modeling, Simulation and Synthesis PLMSS-201
Stress Analysis of a Stepped-Lap Bonded Repair Joint in Composite Laminate under Compressive Loading
No full textWith increasing the usage of advanced composite materials in aircraft structures, it is required to have a suitable repair technology for composite airframe. One of the primary requisites of the repair in such structures is that the repaired surface should not affect the aerodynamic contour. Adhesively bonded repair joints are generally preferred over mechanically fastened repair joints to avoid the stress concentration and achieve smooth aerodynamic surface. Significant numbers of research works have been carried on interface stress distributions for lap, butt and scarf adhesive repaired joints under the static tensile loading. However, the behavior of stepped-lap adhesive joints under compressive loading has not been fully understood and there are not many literatures available on this subject. The present work focuses on stress analysis of a laminate that is repaired through a stepped-lap joint repair scheme. The stress analysis has been carried out and stress distributions in the laminate, patch and adhesive were studied. In order to establish and validate the FE approach for analysis of stepped-lap repair joint subjected to compression, an experimental study also has been carried out. The strains from the analysis have been compared with the strains obtained from the test at important locations. Both the results have shown good agreement
Influence of Fuselage Bulkhead Stiffness on Composite Wing Weight of a Civil Aircraft
No full textWeight estimation of aircraft components is extremely important in the initial phase of aircraft design process as it will be a crucial input to estimate aircraft performance parameters. Generally, the sizing of aircraft components has to be performed individually by simulating the stiffness of the adjoining structure. Thus a conceptual design of how the components are integrated is of paramount importance. In the case of wing design, having done a conceptual design of integration of wing to fuselage, for weight estimation of the wing structure, it is appropriate to include the fuselage bulkheads in the wing model to simulate close to real boundary conditions though not actual. However, it is important to provide proper stiffness to the bulkheads as it will have a major impact on the outcome of the results. Hence numerical optimization studies are carried out on the composite wing structure of a civil aircraft along with the fuselage bulkheads of varied stiffness using NASTRAN solver. The optimization problem is formulated with minimum mass as the objective with strength and buckling constraints. The stiffness of the bulkhead is varied by varying the thickness with a constant cross section. Only the inter-spar box of the wing is considered for the study as it is the main load carrying portion of the wing. It is observed that the bulkhead stiffness plays a major role on the final results
Stress Analysis of Composite wing of SARAS Aircraft at extreme operating temperatures
No full textThis report presents the FE stress analysis of SARAS Composite wing due to thermal load and structural loads (flight and landing loads). This structure is expected to operate at extreme temperature (-54OC and 71°C). The stress analysis of composite wing with these thermal loads along with structural loads assumes more importance in view of the
directional dependence of co-efficient of thermal expansion between various members. The joints between metallic landing beams and surrounding composite structure are
investigated. These joints are subjected to shear transfer at the fastener locations due to difference in co-efficient of thermal expansion between composite and metallic materials. FE analysis of wing is carried out with combination of thermal and critical flight and landing load cases. FE analysis shows that the structure is safe from strength point of view. Failure-indies are less than 1.0. Also, the fasteners forces and corresponding bearing stresses are calculated at the landing gear beam joint to composite structure. The margin of safety for fasteners shear and bearing are positive showing that the joints are
safe
Integrity Evaluation of Feature Level Test Specimen of an Aircraft Primary Composite Structure
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