Composite Flanges Research Articles

A bistable helical structure based on composite tape-springs

Conventional twistable structures use discrete parts articulated around a number of linkages. These allow only a limited degree of twisting angle, are low in storage ratio, heavy and complex in morphing mechanisms. Double-helix structures are commonly applied to induce twistable shape-changing capability for deployable structures, these being capable of large axial deformations where prestressed thin-shell composite flanges or strips are employed; however, their structural stabilities are susceptible to thermal effects, and suffer from non-zero Gaussian curvature deformation induced by prestressing of the precured flat strips. Here, we propose a novel bistable helical structure, where zero Gaussian curvature deformation applies, and shows more stable and reliable morphing mechanics for a twistable structure to be engineered. This is achieved by exploiting bistable composite tape-spring (CTS) structures, where two CTS samples are pin-joined through spokes to formulate a helical structure. It is capable of large axial morphing, and stable in both the fully extended and twisted configurations, with adjustable storage ratio. A theoretical model was established to predict its bistability and a bespoke axial displacement rig was developed to investigate its non-linear morphing mechanisms in order to reveal the underlying fundamentals. These will facilitate torsional structural design for aerospace deployable structures.

Stress Analysis of ASME Section X Flanges Using Classical Lamination Theory

AbstractThe increased usage of fiber reinforced plastic (FRP) composite pressure vessels and piping components in the past decades in the residential and industrial sectors is attributed to the FRP material resistance to corrosion and chemical attacks. FRP composite flanges are, however, known for their anisotropic behavior. In the ASME code section X, FRP composite flanges are treated using an analytical approach derived from that metallic flanges in addition to the fact that the geometries are made to fit them as much as possible and not designed independently. This is known to have caused structural flaws for certain FRP flange classes and sizes. Using a recently developed anisotropic FRP flange approach, it is proposed to identify the most critical flanges by analyzing the flange parameters such as flange ring rotation and stresses in their different parts; gasket, flange ring, hub, and shell subjected to pressure loading. The study on the strength of flanges described in ASME section X RD-620.1 table, will reveal the most critical size and class flanges and their highly stressed locations. To conduct such a study, the selected flange material is an E glass/Vinyl Ester laminate composite. The study shows that FRP flanges of classes 25 and 50 are most vulnerable and should comparatively be less loaded. The stresses are found to reach 50 MPa in the shell and 58 MPa in the flange ring while the maximum flange rotation is 0.83 deg.

Experimental investigation on progressive collapse resistance of precast concrete frame structures with different beam-column connections

In this paper, twelve 1/4-scale precast concrete (PC) substructural specimens with different beam-column connections under progressive collapse scenario were tested and the results were compared with that of the corresponding conventional reinforced concrete (RC) subassemblies. For assembled monolithic concrete (AMC) specimens, the top longitudinal reinforcement bars of beam passed though the beam-column joint continuously. However, the bottom longitudinal reinforcement bars of beam were either anchored as a 90° bend or lap spliced in the cast-in-place joints. Moreover, the flange effects as well as the effects of transverse beam and slab were also investigated according to spatial subassemblies with or without precast composite slabs. For fully assembled concrete (FAC) specimens, dowel bars and corbel connections, as well as steel plates and hidden corbel connections were used in the beam-column joints. Test results showed that the AMC specimens with or without precast composite flanges (slabs) exhibited almost the same progressive collapse resistance as RC specimens in the literatures, except for the peak value of the vertical load at the compressive arch action (CAA) stage for the AMC specimen with lap-splice of bottom rebars in the joints. Significant CAA at small deformation stage and subsequent tensile catenary action (TCA) at large deformation stage developed in the laminated beams under column removal scenarios. Furthermore, the transverse beam and composite slab effects could obviously increase the capacity of an AMC two-span beam. However, unlike RC specimens, CAA and TCA were not completely developed in the FAC specimens due to pull-out failure of the rebars in the beam-column joints or premature failure of the welding points between steel plates and rebars.

Composite and Metal Structural Elements Joint Strength

The paper reveals the hybrid structure strength studies results, which consists of composite and metal parts. The object of the study was an experimental transmission shaft of an aircraft high-lift system. It consisted of a composite tube and metal flanges. New high-strength composites, modern metal powders and additive technology were used for its manufacture. This is the feature that differ the shaft from the typical metal structures used at present. The shaft strength investigation included static tests and calculations. During the tests, the maximum torque and the corresponding shaft twist angle were determined. Based on the computational analysis results, the critical stresses and reserve factors of its structural elements were calculated. The assessment of the effectiveness of the new technologies application for joining structural elements using discrete pins was carried out.

On the Modeling of Anisotropic Fiber-Reinforced Polymer Flange Joints

Abstract Fiber-reinforced plastic composite flanges have recently experienced a spectacular development in the area of pressure vessels and piping. The current procedures used for the design of these flanges are a major concern because of their inappropriateness to address the anisotropic behavior of composite materials. The current ASME code section X related to the design procedure of composite flanges uses the same analytical method as that of section VIII division 2, which treats the flanges as isotropic materials such as metallic flanges. This study deals with Fiber-reinforced plastic (FRP) bolted flange joints integrity and bolt tightness. A new developed analytical FRP model that treats anisotropic flanges with and without a hub is presented. The model is based on the anisotropy and a flexibility analysis of all joint elements including the gasket, bolts, and flanges. It is supported experimentally with tests conducted on a real NPS 3 class 150 WN FRP bolted flange. Furthermore, three different numerical models based on three-dimensional anisotropic layered shell and solid element models were conducted to further compare and verify the results obtained from the new developed analytical approach. The results show that the new model has potential to be used as an alternative tool to FEM to analyze the stresses and deformation of problematic FRP bolted joints.

Failure analysis of GFRP columns subjected to axial compression manufactured under various curing-process conditions

Fibre reinforced polymers are one of the most used materials in the manufacturing of thin-walled structures due to their favourable mechanical properties in terms of strength-to-weight ratios. The curing-process conditions of polymer-based composites can be a source of the residual stresses which can play the main role in failure mechanisms of a composite. The work presents a comparative failure analysis following the post-buckling state of thin-walled composite columns made by autoclave methods with various curing parameters and geometrical concepts. The study inspected the compression of thin-walled composite profiles with C-shaped sections and square cross-sections made of unidirectional preimpregnated tapes of glass/epoxy. It was presented that the boundaries of the halfwaves of the composite flanges are the initiation point of local but catastrophic damage (out-of-plane buckling and plies split) of the composite. These regions are stress concentration points in columns. However, the dominant form of damage is delamination. Delamination is the propagation stage of failure of composite, which propagates from initiation points. The progress of delamination occurs because of increasing load, halfwave deformation and column stiffness reduction. Depending on the curing parameters and geometrical concepts some additional, important failure initiation mechanisms, such as stepped cracks and fibre rupture, were noticed.

Raman thermometry based thermal resistance analysis of GaN high electron mobility transistors with copper-based composite flanges

The electrical performance and the long-term reliability of GaN-based high electron mobility transistors (HEMTs) are greatly affected by the Joule self-heating effect under high power density operation condition. Measurement of the junction temperature and analysis of the thermal resistance of the constituent layers including the packaging material are critically important for thermal design and reliability assessment of GaN-based HEMTs. In this paper, Raman thermometry combined with the finite element thermal simulation is used to compare the junction temperature and the thermal resistance of a GaN HEMT mounted on a novel Cu/graphite composite flange with those of a conventional CuMo flanged device. The results show that the junction temperature of the Cu/graphite flanged device is 15% lower than that of the CuMo flanged device at a power dissipation of 1.43 W/mm, while the overall device thermal resistance is 18.7% lower in the Cu/graphite flanged device. In addition, the temperature distributions of each layer along the cross-plane direction are analyzed for the two devices; the thermal resistance ratio of the Cu/graphite flange is 40% of the overall device thermal resistance, while the CuMo flange account for 53% of the overall thermal resistance of the device. This proves the effectiveness and benefit of using the Cu/graphite composite material package of high thermal conductivity to improve the heat dissipation of GaN HEMTs. By tuning the mass fraction of the graphite, it is possible to further increase the thermal conductivity of the Cu/graphite composite flange and to further reduce the device thermal resistance. It is observed in the Raman thermal measurement that the highest thermal resistance after flanging is the interfacial thermal resistance between the GaN epitaxial layer and the SiC substrate (~50 m<sup>2</sup>·K/GW). For obtaining the better thermal characteristics of the GaN HEMT, it is crucial to reduce the GaN/SiC interfacial thermal resistance through interface engineering during the epitaxial growth. In the meantime, Raman thermometry combined with the finite element thermal simulation is demonstrated to be an effective method for implementing the thermal characterization of the GaN-based devices and the constituent material layers, and the principle and procedure of the method are described in detail in the paper.

Моделирование технологических дефектов и оценка их влияния на статическую прочность композитных фланцев

This work presents an approximate methodology based on the numerical simulation aimed at assessing how defects affect static strength of polymer composite flanges in load bearing elements used in aeronautical engineering. Various defects may occur in the process of flange forming in the areas of bending, e.g. curvature of the layers, resin pockets, voids, delamination and others. Thus, there is an actual problem of assessing how technological defects affect the strength of this part. The main defects in composite laminates are defined and a review of literature related to strength problems for such structures are presented in this work. The numerical stress-strain analysis of composite flange with main types of defects under force loading condition was carried out with ANSYS software. A two - dimensional axisymmetric finite element model was used. For the development of the structural model a parametric modelling approach was applied, including defect size, configuration and location parameters. The problem was solved in a general statement for an anisotropic elastic body. In order to keep the original part profile, we reduced the overall thickness of the layers in the local area near the defect by the size of the defect, so the overstated value of structural strength was obtained in simulation. The safety factor of the flange was estimated by stress components using the maximum stress criterion. The stresses in the material principal directions and interlaminar shear and normal stresses were determined for analysis. A comparison of the obtained data with the results for a defect-free flange allows estimating the impact of each defect or its combination on the static strength of flange.

HYBRID SHEARWALL SYSTEM — SHEAR STRENGTH AT THE INTERFACE CONNECTION

Based on a series of alternating, displacement-controlled load tests on ten one-third scale models, to study the behaviour of the interface of a hybrid shear wall system, it was proved that the concept of hybrid construction in earthquake prone regions is feasible. The hybrid shear-wall system consists of typical reinforced concrete shear walls with composite edge members or flanges. Ten different anchorage bar arrangements were developed and tested to evaluate the column-shearwall interface behaviour under cyclic shear forces acting along the interface between column and wall panel. Finite element models of the test specimens were developed that were capable of capturing the integrated concrete and reinforcing steel behaviour in the wall panels. Special models were developed to capture the interface behaviour between the edge columns and the shear wall. A comparison between the experimental results and the numerical results shows excellent agreement, and clearly supports the validity of the model developed for predicting the non-linear response of the hybrid wall system under various load conditions.

Buckling and debond growth of partial debonds in adhesively bonded composite splice joints

The strains at which buckling and debond growth occur in adhesively bonded composite flanges containing an initial debond were experimentally measured. Test parameters including initial debond geometry, flange material stiffness, and the adhesive critical strain energy release rate (Gc) were investigated. Debond growth was found to be strongly dependent on initial debond length but weakly dependent on flange width; i.e., debonding resistance did not increase in direct proportion with the bonded overlap dimension. Flanges having higher bending stiffness exhibited significantly lower debonding strain. Finally, the effect of Gc was evaluated at three levels by controlling the adhesive cure temperature and bondline thickness. Lower values of Gc (207 and 552 J/m2) allowed debond growth to occur while at the highest value of Gc (1500 J/m2), alternate failure modes occurred prior to debond growth. Ultrasonic C-scans revealed that debond growth occurred along a curved front, as dictated by the post-buckling deformation of the flanges.

Buckling of Composite Flanges in Partially Disbonded Adhesive Joints

This paper contributes newly developed closed-form buckling solutions for generic one-edge-free problems common to partially disbonded composite structures. These solutions are shown to be accurate by comparison with experimentally measured buckling loads which are also reported in this paper. The buckling of partially disbonded regions in adhesive joints is a safety concern due to the potential for ensuing buckling-driven disbond growth. In order to design structures to be tolerant to these flaws, closed-form expressions that predict buckling load have been developed based on a one-edge-free buckling model. Comparison of the closed-form predictions with the finite element results verifies the accuracy of the solutions. Validation of these analyses was achieved by comparison with the experimentally determined buckling loads. These were measured to fall within a range of predicted values, as defined by the choice of boundary condition opposite the disbonded flange-free-edge: either clamped or simply-supported. Assumption of either boundary condition provides upper- and lower-bound predictions of buckling in partially disbonded joint flange configurations.

Local buckling of thin-walled fibre composite beams under transverse loading

Plate structures are often subjected to differential compression due to nonuniform bending during their service life. In practice, most beams are subjected to transverse loads that create moment gradient; the resulting loading system for such beams is a combination of longitudinal stress gradient with associated shearing and transverse stresses. This paper presents a theoretical view of elastic local instability of anisotropic composite beams which are treated as assemblies of symmetric angle-ply composite plates buckling under nonlinear varying, uniaxial compressive forces. Uniformly distributed load and central concentrated load are two common loading systems acting on simply supported, wide-flange I-section beams. The Galerkin method is applied to the resulting plate equilibrium equations. The present study shows that the buckling load obtained from the proposed approach for composite flanges is greater than that obtained by existing solutions. Results also show that for beams subjected to the uniformly distributed load loading system, local buckling may be initiated in the web, especially for short-span deep beams. However, under the central concentrated load loading system, the compressive flange limits buckling strength.Key words: local buckling, stress gradient, fibre composite, pultruded beam.

Nonsteady-state damage accumulation processes in composite flanges under cyclic loads

We consider two typical flanges: for a powerplant casing and for the casing of suspensions with a sound-absorbing duct. We model the behavior of flanges under the action of cyclic external loads based on solution of the nonlinear axisymmetric problem of elasticity theory. In order to take into account fatigue fracture of the layers of the structure, we use maximum stress criteria, a tensor damage function, the rule of linear summation of damage, and reduction schemes for the deformation characteristics of the layers, describing different fracture mechanisms. We indicate the possible nature of the development of fracture zones in composite flanges. We have established the spare load-bearing capacity of the flanges after fracture begins.

Prediction of the bearing capacity of composite flanges for aircraft-engine casing parts

Computed results of the stress-strain state of four different composite flanges for aircraft engines are presented for assigned external-load parameters, and their most heavily loaded regions are defined. The static strength of the structures is found from the stresses in the layers using the maximum-stress criterion and Hill's modified criterion. It is established that transverse tensile stresses are most critical. The service life of the flanges is estimated on the basis of the fatigue-failure criterion of the weakest link.