Large Static Loads Research Articles

Transient Response of a Short-Length (L/D = 0.2) Open-Ends Elastically Supported Squeeze Film Damper: Centered and Largely Off-Centered Whirl Motions

Commonly employed in air breathing (gas turbine) engines, squeeze film dampers (SFDs) reduce the amplitude of rotor vibration while traversing system critical speeds or in transient events such as during a maneuver load, a hard landing, a blade loss, or an engine startup/shutdown sequence that could instantaneously shift a damper journal eccentricity (es) to near its clearance (c). Experiments investigate the dynamic force performance of an open ends, short-length (L/D = 0.2) SFD test rig with radial clearance c = 267 μm and undergoing centered (es/c = 0) to largely off-centered (es/c → 1) whirl orbit motions induced by both a large static load plus a dynamic load. Four rods, symmetrically arranged to resemble a squirrel cage, elastically support the SFD test rig. A hydraulic load system displaces the test damper structure into static eccentricity (es/c). One of two types of dynamic load with amplitude FX = FY excite the SFD: a single-frequency, stepping from low frequency to high frequency discretely; or a sine-sweep frequency growing linearly with time at 6 Hz/s, 33 Hz/s, 40 Hz/s, or 55 Hz/s. For motions departing from es/c = 0.0, 0.95, and 0.99, the dynamic load uses a sine-sweep frequency varying from 5 Hz to 245 Hz and evolving rapidly at ∼33 Hz/s. Measurements of SFD displacements characterize the behavior of the SFD rig during its transient response which crosses two system natural frequencies. For motions departing from a largely off-centered condition (es → c), the dynamic load forces the damper to whirl with highly elliptical orbits, in particular while crossing a resonance (damped natural frequency). Moreover, the dynamic motions departing from es ∼ c are smaller in amplitude than those arising from a centered condition (es/c = 0). The larger damping produced by a very small squeeze film thickness explains the difference in response amplitude. At a largely off-centered condition (es/c = 0.99) and a low excitation frequency (f < 40 Hz), intermittent contact between the damper journal and its housing occurs as evidenced by a large magnitude recorded dynamic pressure (on the order of MPa). For whirl motions around various static eccentricity positions, es/c = 0.0–0.75, the dynamic load covers a frequency range from 10 Hz to 100 Hz using either a single-frequency excitation or a sine-sweep frequency excitation with a slow growth rate ∼6.5 Hz/s to induce a quasi-steady-state response. The experimental procedure builds complex stiffness in the frequency domain for identification of SFD stiffness, damping, and added mass force coefficients, (K, C, M)SFD. For motions centered around small to large static eccentricities, es/c = 0–0.75, the identified (K, C, M)SFD coefficients from sine-sweep frequency dynamic loads coincide with those extracted from single-frequency dynamic load tests over the same frequency range. Short-length SFD theory predictions for damping coefficients agree with the experimental results. Predicted added mass or inertia coefficients, like the model, fall short of the target experimental magnitudes. The test results give practitioners the credence to certify the ability of a SFD to control rotor response amplitude during typical transient events.

Thermomechanical characterisation of commercial Gas Diffusion Layers of a Proton Exchange Membrane Fuel Cell for high compressive pre-loads under dynamic excitation

A Proton Exchange Membrane Fuel Cell (PEMFC) is a mechanically constrained stack composed of several heterogeneous elements. The internal mechanical stress and the mechanical heterogeneity strongly influence the overall PEMFC performances and have to be known and mastered. One of the core components of the PEMFCs is the Gas Diffusion Layer (GDL). In general, this element is composed of non-woven carbon fibre paper or woven carbon cloth. Consequently, the mechanical properties necessary to develop an optimal fuel cell are complicated to extract. Moreover, the mechanical properties of the GDL, and in particular the compression modulus, have to be accurately characterised with respect to various excitation types related to the transportation applications. Consequently, it is essential to investigate, from experiments, the compression modulus of the GDL with respect to large static loads, dynamic loads, different excitation frequencies and temperature. The objective of this paper is to provide the results measured for three widely used commercial GDLs (SGL 24 AA, SGL 24 BA and SGL 24 BC) using an experimental characterisation method with high compressive pre-loads under dynamic excitation over a large temperature range. The experiments show that the stabilisation of the non-linear mechanical behaviour occurs after five loading/unloading cycles. The static pre-loads highly influence the dynamic compression modulus. However, the level of the excitation frequency does not appear to modify the mechanical behaviour. Temperature seems to linearly influence the dynamic compression modulus in two different temperature domains.

Hybrid Robust Control Law with Disturbance Observer for High-Frequency Response Electro-Hydraulic Servo Loading System

Addressing the simulating issue of the helicopter-manipulating booster aerodynamic load with high-frequency dynamic load superimposed on a large static load, this paper studies the design of the robust controller for the electro-hydraulic loading system to realize the simulation of this kind of load. Firstly, the equivalent linear model of the electro-hydraulic loading system under assumed parameter uncertainty is established. Then, a hybrid control scheme is proposed for the loading system. This control scheme consists of a constant velocity feed-forward compensator, a robust inner loop compensator based on disturbance observer and a robust outer loop feedback controller. The constant velocity compensator eliminates most of the extraneous force at first, and then the double-loop cascade composition control strategy is employed to design the compensated system. The disturbance observer–based inner loop compensator further restrains the disturbances including the remaining extraneous force, and makes the actual plant tracking a nominal model approximately in a certain frequency range. The robust outer loop controller achieves the desired force-tracking performance, and guarantees system robustness in the high frequency region. The optimized low-pass filter Q(s) is designed by using the H∞ mixed sensitivity optimization method. The simulation results show that the proposed hybrid control scheme and controller can effectively suppress the extraneous force and improve the robustness of the electro-hydraulic loading system.

로커-백 피벗을 갖는 틸팅 패드 저널 베어링의 회전체동역학적 성능 예측 및 기존 결과와의 비교

In this paper, we predict the rotordynamic force coefficients of tilting pad journal bearings (TPJBs)with rocker-back pivots, and we compare the predictions to recently published predictions and test data. Thepresent TPJB model considers the rocker-back pivot stiffness calculated based on the Hertzian contact-stress the-ory, which is nonlinear with the application of a force . For the five-pad TPJB in load-between-pad and load-on-pad configurations, the predictions show the pressure- and film-thickness distributions, the deflection andstiffness of the individual pivots, and bearing stiffness and damping coefficients. The minimum film thicknessand peak pressure occur at the bottom pad on which the applied load is directed. Because of the preload, the pres-sure is positive even at the upper pad in the opposite direction to the applied load. The pivot deflection and stiff-ness are maximum at the bottom pad that receives the heaviest pressure load. The predicted stiffness coefficientsincrease as the static load and rotor speed increase, while the damping coefficients decrease as the rotor speedincreases, but increase as the static load increases. In general, the predicted stiffness coefficients agree well withthe test data. The predicted damping coefficients overestimate the test data, particularly for large static loads. Ingeneral, the current predictive model considering the pivot stiffness improves the accuracy of the rotordynamicperformance compared to previously reported models.Keywords: damping(감쇠), pivot stiffness(피벗 강성), rocker-back pivot (로커-백 피벗), stiffness( 강성), tiltingpad journal bearing(틸팅 패드 저널 베어링)

Fatigue properties of parts printed by PolyJet material jetting

Purpose – This paper aims to seek to fill a gap in the literature by characterizing the fatigue life and microstructure of a printed elastomer material, the TangoBlackPlus material. Design/methodology/approach – Because the TangoBlackPlus material is marketed as “rubber-like”, the printed elastomer specimens were tested according to the ASTM D4482-11 “Test Method for Rubber Property Extension Cycling Fatigue”. The microstructure of the printed material and multi-material interface was examined by slicing specimens and examining them under an optical microscope. Findings – Findings are developed to show the relationship between elongation and expected fatigue life. Findings also indicate that the smoother, non-support encased “glossy” surface finish option for PolyJet parts improve the fatigue life of components and that there are a number of microscopic voids in the TangoBlackPlus material that seem to be concentrated at layer and print head boundaries. Research limitations/implications – This paper provides a glimpse into the fatigue properties and microstructure of printed elastomeric parts, a previously unstudied area. This work is limited in that it only looks at specimens created in a single orientation, on a single machine, with a single material. More work is needed to understand the general fatigue properties of printed elastomers and the factors that influence fatigue life in these materials. Practical implications – The authors provide several design guidelines based on the findings and previous work that can be used to increase the fatigue life of printed elastomer components. Originality/value – As additive manufacturing (AM) technology moves from a prototyping tool to a tool used to create end use products, it is important to examine the expected lifespan of AM components. This work adds to the understanding of the expected product lifecycle of printed elastomer components that will likely be expected to withstand large repeated loading conditions.

Influence of pin corrosion on mechanical characteristic of UHVDC disc suspension insulators and solutions

Hardware corrosion has occurred upon lots of suspension-type porcelain and glass insulators of ±800 kV Chusui and Xiangshang UHVDC transmission lines in China since October 2011. The cause of pin corrosion and its influence on the mechanical property of insulators are researched in this paper. The mechanical load that insulator bears under the circumstance of conductor icing and galloping is calculated by means of ANSYS software. Also, the failure forms of insulators under large mechanical load condition are analyzed. On the basis of this, the method that installing organic material sleeve onto the zinc sleeve to vary its corrosion area is proposed. The problem of mechanical strength decreasing of the insulators caused by expansion of corroded by-products is solved. Insulator samples with organic material sleeves of three structures including zinc sleeve half package type, flush type, and whole package type are made, and pin electrolytic corrosion simulation tests are carried out upon the three kinds of samples respectively by means of the spray water method. It turns out that half package type organic material sleeve alters the corrosion part of zinc sleeve effectively and the pins of insulators with two other kinds of organic material sleeves were corroded seriously. The electric field intensity of insulators is calculated by means of ANSOFT software. Calculation results indicate that the semi-conductive rubber sleeve provides the insulator with better electric field intensity characteristic.

Creep lifing methodologies applied to a single crystal superalloy by use of small scale test techniques

In recent years, advances in creep data interpretation have been achieved either by modified Monkman–Grant relationships or through the more contemporary Wilshire equations, which offer the opportunity of predicting long term behaviour extrapolated from short term results. Long term lifing techniques prove extremely useful in creep dominated applications, such as in the power generation industry and in particular nuclear where large static loads are applied, equally a reduction in lead time for new alloy implementation within the industry is critical. The latter requirement brings about the utilisation of the small punch (SP) creep test, a widely recognised approach for obtaining useful mechanical property information from limited material volumes, as is typically the case with novel alloy development and for any in-situ mechanical testing that may be required. The ability to correlate SP creep results with uniaxial data is vital when considering the benefits of the technique. As such an equation has been developed, known as the kSP method, which has been proven to be an effective tool across several material systems. The current work now explores the application of the aforementioned empirical approaches to correlate small punch creep data obtained on a single crystal superalloy over a range of elevated temperatures. Finite element modelling through ABAQUS software based on the uniaxial creep data has also been implemented to characterise the SP deformation and help corroborate the experimental results.

Fracture Analysis of the Orthopedic Plates used in Joining of the Lower-Limb Bones

Abstract. Breakage of the orthopedic plates that join the fractured bones of the lower-limb can cause major problems in healing treatment of the patients. Augmentation of the necessary medical treatment, prolongation of the healing duration and medical cost enhancement are a few problems caused. An investigation on the root of such failures is beneficial to prevent such disasters. Consideration was given therefore to 100 patients hospitalized in Imam Reza Hospital, Kermanshah, I.R. Iran. Lower limb examinations showed 6 broken plates, 1 broken rod and 1 broken nail. All broken samples were characterized by atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. Cyclic loading was revealed as the main source of the undesirable problem. Marginal incentives were also identifiable; some of them were: (a) large static and dynamic loads, (b) patient's premature movements, (c) presence of inclusions in the plates and (d) porous plates made by rare incompetent manufacturers.

Compound Velocity Synchronizing Control Strategy for Electro-Hydraulic Load Simulator and Its Engineering Application.

An electro-hydraulic load simulator (EHLS) is a typical case of torque systems with strong external disturbances from hydraulic motion systems. A new velocity synchronizing compensation strategy is proposed in this paper to eliminate motion disturbances, based on theoretical and experimental analysis of a structure invariance method and traditional velocity synchronizing compensation controller (TVSM). This strategy only uses the servo-valve's control signal of motion system and torque feedback of torque system, which could avoid the requirement on the velocity and acceleration signal in the structure invariance method, and effectively achieve a more accurate velocity synchronizing compensation in large loading conditions than a TVSM. In order to facilitate the implementation of this strategy in engineering cases, the selection rules for compensation parameters are proposed. It does not rely on any accurate information of structure parameters. This paper presents the comparison data of an EHLS with various typical operating conditions using three controllers, i.e., closed loop proportional integral derivative (PID) controller, TVSM, and the proposed improved velocity synchronizing controller. Experiments are conducted to confirm that the new strategy performs well against motion disturbances. It is more effective to improve the tracking accuracy and is a more appropriate choice for engineering applications.

Electrical fatigue behaviour in lead zirconate titanate: an experimental and theoretical study

A systematic investigation on electrical fatigue in lead zirconate titanate (PZT) is carried out for different loading frequencies. Experiments are conducted up to 106 cycles to measure the electrical displacement and longitudinal strain on bulk ceramics in the bipolar mode with large electrical loading conditions. A simplified macroscopic model based on physical mechanisms of domain switching is developed to predict the non-linear behaviour. In this model, the volume fraction of a domain is used as the internal variable by considering the mechanisms of domain nucleation and propagation (domain wall movement). The measured material properties at different fatigue cycles are incorporated into the switching model as damage parameters and the classical strain versus electric field and electric displacement versus electric field curves are simulated. Comparison between the experiments and simulations shows that the proposed model can reproduce the characteristics of non-linear as well as fatigue responses.

Statistical shape analysis of clavicular cortical bone with applications to the development of mean and boundary shape models

During car collisions, the shoulder belt exposes the occupant's clavicle to large loading conditions which often leads to a bone fracture. To better understand the geometric variability of clavicular cortical bone which may influence its injury tolerance, twenty human clavicles were evaluated using statistical shape analysis. The interior and exterior clavicular cortical bone surfaces were reconstructed from CT-scan images. Registration between one selected template and the remaining 19 clavicle models was conducted to remove translation and rotation differences. The correspondences of landmarks between the models were then established using coordinates and surface normals. Three registration methods were compared: the LM-ICP method; the global method; and the SHREC method. The LM-ICP registration method showed better performance than the global and SHREC registration methods, in terms of compactness, generalization, and specificity. The first four principal components obtained by using the LM-ICP registration method account for 61% and 67% of the overall anatomical variation for the exterior and interior cortical bone shapes, respectively. The length was found to be the most significant variation mode of the human clavicle. The mean and two boundary shape models were created using the four most significant principal components to investigate the size and shape variation of clavicular cortical bone. In the future, boundary shape models could be used to develop probabilistic finite element models which may help to better understand the variability in biomechanical responses and injuries to the clavicle.

海底占有面積が狭小な沖合浮体係留方式に関する基礎研究

In this study, the concept of "vertically movable tension leg mooring system" is proposed for the purpose that an offshore floating body subject to comparatively large static horizontal loads for its scale, which is represented by floating wind power generator, ocean current power generator, etc., is moored so that the occupied plane area of the mooring system may become as small as possible. In the system, a gravity type template is hung from the floating body with vertical lines and the template is moored with relatively short catenary chains to seabed anchors. The advantages of the proposed system are discussed comparing mainly with the tension leg mooring, and the fundamental mooring characteristics are shown with model calculations.

On the parametric large deflection study of Euler–Bernoulli cantilever beams subjected to combined tip point loading

The problem of determining the parametric large deflection components of Euler–Bernoulli cantilever beams subjected to combined tip point loading is studied in this paper. We introduce the characteristic equation of the beam's deflection and, with employing the recently developed automatic Taylor expansion technique (ATET), present deflection solutions in terms of the loading parameters to the Euler–Bernoulli boundary value problem. The obtained ATET deflection solutions, verified by comparison with the numerical solutions, are valid for the entire beam length, and independently and efficiently adaptable for the very large loading conditions, and easily implementable for engineering analyses and syntheses. Exploiting these solutions as theoretical tools we study the beam's angular and axial deflections behavior for several tip point loading conditions. Besides the widely known beam's axial inflection points, we also recognize beam's angular inflection points for the mixed loading condition and show that the parametric solutions are intelligent in recognizing the right deflection branch for both inflection types.

Dynamic crack nucleation and propagation in polycrystalline aluminum aggregates subjected to large inelastic deformations

The major objective of this work has been to apply a new compatibility-based fracture theory to the investigation of dynamic failure of polycrystalline metals and alloys. To model the nucleation and propagation of failure surfaces at the microstructural scale, under large deformations and dynamic loading conditions, a general fracture criterion based on the integral law of compatibility is used. This new fracture criterion, was coupled with rate-dependent dislocation-density based crystalline plasticity formulations to elucidate the microstructural mechanisms related to the evolution of intergranular and transgranular failure and to understand how grain sizes and strain-rate sensitivity affect aggregate strength, ductility, and dynamic damage tolerance. It is shown that cracks commonly nucleate at triple junctions and at grain boundaries as intergranular cracks, and that slip bands through grains result in transgranular cracks.

Modelling of equal channel angular pressing using a mesh-free method

Severe plastic deformation (SPD) processes are widely recognised as efficient techniques to produce bulk ultrafine-grained materials. As a complement to experiments, computational modelling is extensively used to understand the deformation mechanisms of grain refinement induced by large strain loading conditions. Although considerable research has been undertaken in the modelling of SPD processes, most of the studies have been accomplished using mesh-based methods, such as the finite element method (FEM). Mesh-based methods have inherent difficulties in modelling high-deformation processes because of the distortions in the mesh and the resultant inaccuracies and instabilities. As an alternative, a mesh-free method called smoothed particle hydrodynamics (SPH) is used. The effectiveness of this technique is highlighted for modelling of one of the most popular SPD techniques, equal channel angular pressing. A benchmark between SPH and FE calculation is performed. Furthermore, a number of simulations under different processing conditions are compared to existing literature data. A satisfactory agreement is found, which indicates that SPD processes can be approached by mesh-free methods, such as SPH.

Study on Steel Strand’s Reasonable Tension Order of Reaction Wall

Pre-stressed reaction wall is an important test facility in structure laboratory．Reaction wall will bear large static and dynamic loads when working, so pre-stressed concrete structure is often used. A model of micro-concrete pre-stressed reaction wall is made in the test in order to insure tension quality of steel strand of reaction wall. Proposed 4 different tension schemes of reaction wall pre-stress rebar, and a comparative study on the variety trend and distribution of strain on reaction wall in the 4 different schemes．The experimental results show that the best schemes of tension pre-stress rebar is：use the wall cross-section center of gravity as the symmetric point, tension symmetrical up and down from central to outside．And we suggest that two times or supplement tension methods be use to stretching steel strand of reaction wall.

Study on Steel Strand’s Reasonable Tension Order of Reaction Wall

Pre-stressed reaction wall is an important test facility in structure laboratory．Reaction wall will bear large static and dynamic loads when working, so pre-stressed concrete structure is often used. A model of micro-concrete pre-stressed reaction wall is made in the test in order to insure tension quality of steel strand of reaction wall. Proposed 4 different tension schemes of reaction wall pre-stress rebar, and a comparative study on the variety trend and distribution of strain on reaction wall in the 4 different schemes．The experimental results show that the best schemes of tension pre-stress rebar is：use the wall cross-section center of gravity as the symmetric point, tension symmetrical up and down from central to outside．And we suggest that two times or supplement tension methods be use to stretching steel strand of reaction wall.

Red-Green-Blue wavelength interferometry and TV holography for surface metrology

Surface discontinuities greater than half a wavelength can not be measured unambiguously using single wavelength interferometry. In TV holography, it is difficult to quantify the data under relatively large loading conditions due to the overcrowding of fringes with a single wavelength. Further, single wavelength does not reveal the contour of rough surfaces with TV holography. Multiple wavelengths measurements using red, green, and blue wavelengths can overcome these problems. In this paper a multiple wavelength interferometric system with colour CCD is demonstrated for such measurements. The interference patterns are recorded by a single chip colour CCD camera which makes the data acquisition as simple as in single wavelength case. The interference pattern is decomposed into its R G B components to evaluate the phase at individual wavelengths. An eight step phase shifting algorithm is used to simplify the application of phase shifting technique in the multiple wavelength system. Experimental results on an etched silicon sample for the measurement of large discontinuities and on a MEMS pressure sensor for the measurement of shape and relatively large deflection are presented.

A fracture criterion for finitely deforming crystalline solids—The dynamic fracture of single crystals

The major objective of this work has been to develop, within a continuum framework, a microstructurally-based computational theory to investigate dynamic failure in metals. To model the nucleation and propagation of failure surfaces at the microstructural scale, under large deformations and dynamic loading conditions, general finite-deformation theory, as relating to the decomposition of the deformation gradient, was tailored to monitor displacement incompatibilities and fracture in crystalline solids subjected to large deformations. Based on this proposed decomposition, a general fracture criterion for finitely deforming crystals, using the integral law of incompatibility, was developed. The analyses indicate that this newly proposed fracture formulation and criterion can be validated with experimental results, and can be used to accurately predict brittle and ductile failure modes for the large deformation of single crystals. As part of the newly proposed decomposition of the deformation gradient, sub-problems can also be solved for lattice distortions, such as twinning and geometrically necessary dislocation (GND) densities. Accordingly, the interactions of GND densities with cracks were investigated for single crystals. GND densities were shown to form as loops for stationary crack tips, but no loops formed for propagating cracks.

Effects of sodium and zinc neutralization on large deformation hysteresis of an ethylene methacrylic acid butyl acrylate copolymer

The mechanical hysteresis and recovery behaviors of an elastomeric ethylene methacrylic acid butyl acrylate (EMAABA) copolymer, its sodium-neutralized (EMAABANa) and zinc-neutralized (EMAABAZn) counterparts are evaluated and compared under large strain loading conditions. Experiments at different rates, under cyclic loading conditions and in relaxation indicate two major hysteresis mechanisms: a characteristic viscoelastic mechanism operative at all strains and a microstructural evolution/breakdown mechanism incurred during large strains. Loading-unloading cycles show large rate-dependent hysteresis loops with significant recovery of strain upon unloading, revealing a highly dissipative yet resilient behavior. The microstructure breakdown mechanism occurs during the initial strain excursion as revealed by subsequent loading cycles showing a significantly more compliant behavior and dramatically reduced hysteresis loops. The neutralized materials are found to be significantly stiffer, stronger and more dissipative compared to the neat material while still retaining the same level of recovery. Therefore the neutralization of this material provides an excellent means to tune stiffness and dissipation while retaining resilience, providing mechanical performance properties attractive for abrasion, impact and puncture resistant applications.