Tip Loading Research Articles

Civil turbofan engine exhaust aerodynamics: Impact of fan exit flow characteristics

It is envisaged that future civil aero-engines will operate with greater bypass ratios compared to contemporary configurations to lower specific thrust and improve propulsive efficiency. This trend is likely to be accompanied with the implementation of a shorter nacelle and bypass duct for larger engines. However, a short bypass duct may result in an aerodynamic coupling between the exit flow conditions of the fan Outlet Guide Vanes (OGVs) and the exhaust system. Thus, it is imperative that the design of the exhaust is carried out in combination with the fan exit profile. A parabolic definition is used to parameterise and control the circumferentially-averaged radial profiles of stagnation pressure and temperature at the fan OGV exit. The developed formulation is coupled with a parametric exhaust design approach, an automatic computational mesh generator, and a compressible flow solution method. A global optimisation strategy is devised comprising methods for Design of Experiment (DOE), Response Surface Modelling (RSM), and genetic optimisation.A combined Design Space Exploration (DSE) comprising both geometric, as well as fan exit profile variables, is performed to optimise the exhaust geometry in conjunction with the fan exit profile. The developed approach is used to derive optimum exhaust geometries for a tip, mid, and hub-biased fan blade loading distribution. It is shown that the proposed formulation can ameliorate adverse transonic flow characteristics on the core after-body due to a non-uniform bypass inflow. The hub-loaded profile was found to be most penalising in terms of exhaust performance compared to the mid and tip-loaded variants. It is demonstrated that the combined fan exit profile and exhaust geometry optimisation offers significant performance improvement compared to the fixed inflow cases. The predicted performance benefits can reach up to 0.19% in terms of exhaust velocity coefficient, depending on fan loading characteristics. A notable improvement is also noted in terms of bypass nozzle discharge coefficient. This suggests that the combined optimisation can lead to an exhaust design that can satisfy the engine mass-flow rate demand with a reduced geometric throat area, thus potentially offering further exhaust size and weight benefits.

A Microscopic Experimental Method Transversely Loading on Single High-Performance Fibers

We developed a microscopic experimental method that transversely loads and images single high-performance fibers. The experimental set-up was inside the chamber of a scanning electron microscope (SEM). Force and displacement histories were recorded by the loading device. The SEM enabled in-situ observation of the fiber’s initial contact with the transverse indenter and subsequent deformation, crack initiation and propagation until the final failure. Within the loading device, fiber gauge length, indenter tip radius and loading direction can be varied as desired. To demonstrate the new experimental capability, initial results for a razor blade transversely cutting a Dyneema® SK76 fiber are presented in this paper. To avoid the effect from the conductive coating on the mechanical behavior of the fiber, a low vacuum detector was adopted to capture the deformation and failure of an uncoated fiber. These experiments revealed the damage and failure processes of single fibers with high-resolution micrographs.

Bipolar radiofrequency ablation: The impact of tip load, application duration, power, and indifferent electrode size on the transmurality of a lesion

Bipolar radiofrequency ablation: The impact of tip load, application duration, power, and indifferent electrode size on the transmurality of a lesion

Modified semi-circular bend test to determine the fracture toughness of anisotropic rocks

The conventional semi-circular bend (SCB) test of anisotropic rocks, with symmetric loading, generates a Mixed-Mode I/II crack tip loading when the crack is not aligned with one of the principal material directions. This paper presents a modified SCB test for anisotropic rocks to ensure a pure Mode I crack tip loading. It is demonstrated that the stress intensity factor (SIF) solution of an anisotropic SCB specimen depends on two dimensionless parameters, the anisotropy ratios of the Young’s modulus and apparent shear modulus, as well as the anisotropy orientation. These two dimensionless parameters are selected since they have physical meaning, and are generally bounded for rock materials. Based on these anisotropy parameters, the semi-circular test is modified to configure pure Mode I, or tensile stress at the crack tip, by using an asymmetric three-point bend configuration. Extensive finite element analyses are performed to obtain the span ratio and normalized SIF of the SCB specimen with different anisotropy ratios and orientations.

Reach of an inclined cantilever with a tip load

We investigate the problem of determining the reach of an inclined cantilever for a given point load suspended from its tip. Two situations are considered. Firstly, we find the maximum reach of the cantilever by varying its angle of inclination. Secondly, we find the reach of the cantilever subject to the condition that its tip is at some specified height, above or below, the level of the clamped end. In the second case, the reach of the cantilever is maximised by shortening its physical length whilst keeping the physical load and physical height of load deployment constant. All of our solutions representing various reaches of an inclined cantilever for a given point load suspended from its tip are shown to be stable to the snap-back instability.

Size Effect in Single Crystal Copper Examined with Spherical Indenters

The increasing hardness with decreasing penetration depth, referred to as indentation size effect (ISE) was previously investigated experimentally and theoretically by many researchers, however the mechanisms responsible for ISE are still being discussed. Generally, ISE is related to the density of geometrically necessary dislocation stored within a small volume beneath the indenter tip. In this study ISE is investigated experimentally in a single crystal copper using spherical indenter tips of different radii. Some new aspects of ISE are shown: a qualitative change of shape of residual impression (pile-up/sink-in pattern) when tip radius or load is modified, an increase of maximum pop-in load with decrease of tip radius as well as the well-known increase of hardness when tip radius decreases are analyzed. As we observe a difference of the residual imprint morphology which depends on tip radius and load, we apply two methods of hardness estimation: true hardness and nominal hardness. The former is determined on the basis of direct measurement of the contact area while accounting for a specific pile-up pattern, while the latter is determined by measuring the contact area using residual penetration depth. We show that hardness–tip radius relationship has a linear form for the nominal hardness and bilinear form for the true hardness.

Boundary stabilization of a hybrid Euler–Bernoulli beam

ABSTRACT We consider the uniform stabilization of a hybrid model consisting of an Euler–Bernoulli beam with a tip load at the free end of the beam. Our main result proves that the semigroup associated with this model is not exponentially stable. Additionally, we prove that the semigroup decays polynomially to zero as as time goes to infinity.

Fracture Mechanics Solutions for Interfacial Cracks between Compressible Thin Layers and Substrates

The decohesion of coatings, thin films, or layers used to protect or strengthen technological and structural components causes the loss of their functions. In this paper, analytical, computational, and semi-analytical 2D solutions are derived for the energy release rate and mode-mixity phase angle of an edge-delamination crack between a thin layer and an infinitely deep substrate. The thin layer is subjected to general edge loading: axial and shear forces and bending moment. The solutions are presented in terms of elementary crack tip loads and apply to a wide range of material combinations, with a large mismatch of the elastic constants (isotropic materials with Dundurs’ parameters − 1 ≤ α ≤ 1 and − 0.4 ≤ β ≤ 0.4 ). Results show that for stiff layers over soft substrates ( α → 1 ), the effects of material compressibility are weak, and the assumption of substrate incompressibility is accurate; for other combinations, including soft layers over stiff substrates ( α → − 1 ), the effects may be relevant and problem specific. The solutions are applicable to edge- and buckling-delamination of thin layers bonded to thick substrates, to mixed-mode fracture characterization test methods, and as benchmark cases.

Stall Inception in Low-Pressure Ratio Fans

A combined experimental and computational test program, with two low-pressure ratio aero-engine fans, has been used to identify the flow mechanisms at stall inception and the subsequent stall cell growth. The two fans have the same rotor tip clearance, annulus design, and downstream stators, but different levels of tip loading. The measurement data show that both the fans stall via spike-type inception, but that the growth of the stall cell and the final cell size is different in each fan. The computations, reproducing both the qualitative and quantitative behavior of the steady-state and transient measurements, are used to identify the flow mechanisms at the origin of stall inception. In one fan, spillage of tip leakage flow upstream of the leading edge plane is responsible. In the other, sudden growth of casing corner separation blockage leads to stall. These two mechanisms are in accord with the findings from core compressors. However, the transonic aerodynamics and the low hub-to-tip radius ratio of the fans lead to the following two findings: first, the casing corner separation is driven by shock-boundary layer interaction and second, the spanwise loading distribution of the fan determines whether the spike develops into full-span or part-span stall and both types of behavior are represented in the present work. Finally, the axial momentum flux of the tip clearance flow is shown to be a useful indicator of the leakage jet spillage mechanism. A simple model is provided that links the tip loading, stagger, and solidity with the tip clearance axial momentum flux, thereby allowing the aerodynamicist to connect, qualitatively, design parameters with the stall behavior of the fan.

A new type of flat-bar specimen for non-proportional mixed-mode crack tip loading under uniaxial tension

Non-proportional cyclic loading is a challenging issue for numerical crack path predictions. Principal stress axes and the vector of the J-integral rotate during loading and the mixed-mode ratio of stress intensity factors changes within a load period. Reliable criteria for crack deflection, accounting for arbitrary loading and boundary conditions under non-proportional loading, have not yet been found. Experimental research in this field nowadays requires expensive set-ups and multiaxial testing equipment such as hydraulic biaxial or tension-torsion testing machines. In this paper, a specimen is presented, suitable for uniaxial testing, however providing conditions of non-proportional loading. Finite element simulations show that the variance of mixed-mode parameters is sufficiently large to cover the range of KII/KI-ratios required for investigating crack deflection criteria.

Effect of corrosion damage on a pipeline burst pressure and repairing methods

On the basis of the calculation of the stress field around the corrosion-damaged areas on the external part of a pipeline used for the transport of hydrocarbons, an analysis of the effect of the level of post-repair burst pressure by composite patches is proposed. This work examines some points of views on the burst pressure standards calculation on real test on pipeline with external corrosion defects. This study divided to three parts. In the first, an inspection is given for a real pipe exhibiting a surface corrosion defect. The corrosion defects were collected and divided into six important defects. The internal pressure has increased to the burst of pipeline. The second part illustrated a numerical study of the defects interaction effect on the safety of pipeline. The third part of this study is showing a finite element analysis of repaired pipe using the composite repair; we will study the effect of the composite sleeve number on the structural integrity of the pipe. The principle of failure assessment (FAD) diagram is described, and particularly, the definition of the non- dimensional applied crack tip loading $${k}_{\mathrm{r}}$$ , the non- dimensional net applied stress (or load) $${S}_{\mathrm{r}}$$ or $${L}_{\mathrm{r}}$$ is given. The interest lays in the fact that many pipes defects are scratch or gouge types. In the FAD, results demonstrated that the composite repair method does not affect the interpolation curve and, at the same time, had a slightly effect on the function point.

Anisotropic nanoscale and sub-nanoscale friction behaviors between phosphorene and silicon tip

Understanding the frictional properties of phosphorene is essential for reliable fabrication and sustainable operation of phosphorene-based nanotechnology devices. Although recent studies have revealed that phosphorene exhibits anisotropic frictional characteristics, the detailed mechanisms are not well analyzed, and the influence of some experimental parameters (e.g., spring stiffness, tip load force, and tip size), which are very sensitive to atomic frictional forces, were not considered. This study was carried out to address the above shortcomings. The anisotropic frictional behavior of phosphorene and its detailed mechanism were analyzed using potential energy profiles. Also, the effects of spring stiffness and tip load force on the stick-slip behaviors were investigated. Furthermore, we studied the sub-nanoscale stick-slip behavior during the nanoscale slip motion. The nanoscale and sub-nanoscale stick-slip phenomena were originated from the tip's behavior of passing over the bond between the phosphorus atoms and over the puckered honeycomb structure along the zigzag and armchair directions. We utilized a simple one-dimensional model to explain the energy profiles. The influence of tip size on the stick-slip behavior was also examined and found related to the initial nanoscale slip velocity. As the tip diameter decreased, a high-frequency sub-nanoscale stick-slip phenomenon and shorter nanoscale slip duration were identified.

Nanoscale 3D characterisation of soft organic material using conductive scanning probe tomography

The 3D nanostructure of organic materials plays a key role in their performance in a broad range of fields, from life sciences to electronics. However, characterising the functionality of their morphologies presents a critical challenge requiring nanometre resolution in 3 dimensions and methods that do not excessively distort the soft matter during measurement. Here we present scanning probe tomography using a commercial Pt-Ir coated tip and controlling the tip loading force to sequentially characterise and remove layers from the surface of a sample. We demonstrate this process on a sample exhibiting a polymer nanowire morphology, which is typically used for organic electronic applications, and present a tomographic reconstruction of the nanoscale charge transport network of the semi-crystalline polymer. Good electrical connectivity in 3D is demonstrated by directly probing the electrical properties of the inter-nanowire charge conduction.

A comprehensive interpretation of the J-integral for cohesive interface cracks and interactions with matrix cracks

In linear elastic fracture mechanics various loading quantities exist to describe the crack tip loading, like stress intensity factors, the energy release rate or the J-integral. The J-integral is calculated along an arbitrary integration path and is related to the other loading quantities. In non-standard problems including e.g. temperature gradients, material inhomogeneities or interfaces, the path independence of the J-integral is only ensured considering additional terms. Material interfaces can be strong (perfect) or weak (imperfect), whereas dissipative processes only arise in weak interfaces. In this paper a matrix crack with a classical crack tip stress singularity is investigated, interacting with an interface crack, in the latter case modelling the fracture process zone in front of the physical crack tip by cohesive zone theory. The dissipation in the interface due to delamination has an influence on the loading of the matrix crack in terms of the J-integral and thus on its deflection and path. In order to identify this influence, the matrix crack tip loading is calculated accurately applying the J-integral in connection with a large integration contour enclosing the interface. Additional terms on the one hand ensure path independence, on the other their physical interpretation is desirable. In particular the contribution of the cohesive zone is considered closely, revealing a generalized mixed-mode relation of the J-integral and crack tip opening displacements, depending on the cohesive law, as in the classical mode I case, and on the boundary value problem. With multiple dissipative processes, the global energy release rate of the multi-crack system is not trivially calculated either. Numerical examples reveal e.g. that the matrix crack tip loading in the presence of an imperfect interface may be increased, even though energy is dissipated. Crack growth simulations show the preference of a matrix crack to grow into the direction of lower stiffness giving rise to an extremely attracting effect of damaged interfaces.

An Experiment of Sequential Data Assimilation in Cantilevered Beam Model Based on the Ensemble Kalman Filter

An experiment of sequential data assimilation in a cantilevered beam model is presented. The sequential data assimilation is based on the Ensemble Kalman filter (EnKF), which can be easily incorporated in nonlinear finite element analysis. A simple system noise setting scheme is presented, which can set a variance of the system noise in accordance with the residual error in the EnKF. In the experiment, a tip load of the beam is considered as a model parameter to be estimated. The experimental results indicate that the model parameter is accurately estimated by using the EnKF even when the tip load is rapidly changed.

Cohesive Zones and Interactions of Mixed-Mode Interface and Matrix Cracks

The heterogeneous state of stress in composite materials and the possible damage in interfaces, lead to a complicated problem concerning matrix crack tip loading analysis and crack path prediction. A powerful and accurate tool for calculating crack tip loadings is the J-integral, which was independently introduced by Rice and Cherepanov. The calculation of crack deflection angles using the J-integral criterion is enabled by the J-integral vector formulation, whereupon the calculation of matrix crack tip loadings and also interface crack tip loadings is possible. The J-integral and the crack tip opening displacement, as crack tip loading quantity of cohesive zone models, were related by Rice for the pure mode I loading case. In this work mixed mode loading conditions are considered, resulting in a generalization of the single mode I relation. The generalized relation is verified considering a Dugdale type crack under mixed mode loading. The formulation of a criterion for the transition of an interface crack to a matrix crack is also enabled by the generalized relation, resulting in a modification of the J-integral vector criterion of crack deflection. Numerical implementation of this criterion holds its own challenges concerning crack tip inaccuracy, where examples will be evaluated.<br/> The interaction between a matrix and an interface crack is investigated too. On the one hand analytically by calculating the matrix crack tip loading in the presence of an interface crack using remote integration contours, revealing that the interface crack tip loading is included therein, on the other hand numerically by simulating growing matrix and interface cracks.

Model tests comparing the behavior of pre-bored grouted planted piles and a wished-in-place concrete pile in dense sand

The compressive bearing capacity of wished-in-place (WIP) concrete piles and pre-bored grouted planted (PGP) piles in dense sand was investigated by means of model tests. In total, three model piles were tested. The load–displacement response, axial force and tip resistance of each model pile were measured in the static load test process. Several conclusions can be drawn from the model test results: the pre-bored grouted planted nodular (PGPN) pile and the pre-bored grouted planted pipe (PGPP) pile have ultimate skin friction 1.23–1.36 times and 1.34–1.46 times greater than the ultimate skin friction of the wished-in-place (WIP) pile, respectively. The tip bearing capacity of the PGP pile is similar to the tip bearing capacity of the WIP pile, and the hyperbolic model of normalized tip resistance (qb/qc) and normalized tip displacement (Sb/D) can represent the tip load–displacement response of the WIP and PGP piles well.

Exterior reinforced concrete beam column joint subjected to monotonic loading

The joints between beams and columns are crucial zones in a reinforced concrete moment resisting frame. The behaviour of such joints greatly influences the strength and ductility of the overall frame. In this research, analysis of three-dimensional numerical models of exterior reinforced concrete beam-column joints under monotonic loading was performed using the finite element ABAQUS package. Concrete and reinforcing steel material nonlinearities, as well as bond characteristics between reinforcing bars and surrounding concrete were considered in the analysis. A parametric study involving thirty joint models was conducted to examine the influence of concrete strength, column axial load, joint stirrups and shape of the beam top reinforcement on the beam tip load and displacement capacities. The concrete dimensions and reinforcement of the studied models were chosen to ensure the occurrence of joint failure. The study showed that the beam tip ultimate load significantly increased as the concrete strength, column axial load and joint stirrups were increased. Joints with L-shaped beam top reinforcing bars exhibited similar performance to those with U-shaped bars. The use of straight bars for beam top reinforcement significantly reduced the beam tip ultimate load.

Prediction of hydrodynamic performance of pump propeller considering the effect of tip vortex

There is a strong gap flow in the pump jet propulsor, in order to predict the hydrodynamic performance of the pump jet propulsor, the steady-state hydrodynamic disturbance model was established by the panel method. The pump jet propulsor was divided into two systems, rotor-hub and stator-duct, and inter-system interference was considered by induced velocity. Aiming at the geometric shape of stator, a method of leaf meshes based on circular cone was proposed. Based on the actual situation of the internal flow of the pump, a tip leakage vortex model suitable for the flat-topped blade was proposed. Comparing the results of pressure, circulation, and propulsion performance, it was found that when the influence of tip vortex is considered, the overall annular distribution of rotor blade and tip load are closer to the actual situation, and the performance curve is in good agreement with the viscous flow, which shows that this method can effectively predict the steady hydrodynamic performance of the pump jet propulsor.

An experimental investigation on the fatigue crack growth behaviour of AISI/SAE 1045 under load sequences containing underloads

AbstractThe estimation of load interaction effects is essential for residual lifetime calculations of components with cracks. Whereas overloads are widely investigated, there is still no consensus about the effects and mechanisms of underloads. For this reason, load sequences containing underloads are experimentally examined within this paper. Because Kmax and R are not appropriate for describing the cyclic crack tip loading at tension/compression loading, the σtip concept is used to quantify the crack driving force at compressive loads. Among others, the tests also include load sequences that have not been reported in the literature yet like underloads that are applied at a certain distance after an overload. The influence of underloads on crack arrest is also investigated. The experimental tests are performed with the tool steel AISI/SAE 1045.