Tip Loading Research Articles

Vertical vibration capacity of a single pile in dry sand

ABSTRACTIn this study, the dynamic response of pile foundation in dry sandy soil excited by two opposite rotary machines was considered experimentally. A small scale physical model was manufactured to accomplish the experimental work in the laboratory. The physical model consists of two small motors supplied with eccentric mass (0.012 kg) and eccentric distance (20 mm) representing the two opposite rotary machines, an aluminum shaft as the pile, and a steel plate a pile cap. The experimental work was achieved taking the following parameters into considerations: pile embedment depth ratio (L/d, where L is the pile length and d is its diameter) and operating frequency of the rotary machines. All tests were conducted in medium dense fine sandy soil with 60% relative density. Twelve tests were performed to measure the change in load transferred through the pile’s tip to the underlying soil. To predict precisely the dynamic load that will be induced from the rotary machines, a mini load cell with a capacity of 100 kg was mounted between the aluminum plate (the machine base) and the steel plate (pile cap). The results revealed that, before machine operation, the pile tip load was approximately equal to the static load (machine and pile cap), whereas during machines’ operation, the pile tip load decreased for all embedment depth ratios and operating frequencies. This reduction was due to the action of skin friction that was mobilized along the pile during operation, and as a result the factor of safety against pile bearing failure increases. For all operating frequencies and pile lengths, the factor of safety against bearing failure increased during machines’ operation, where the pile tip load became less than its value before starting operation. During operation, the skin friction resistance mobilized along pile length led to decrease the bearing load.

An extended interpretation of the free-fall piezocone test in clay

Seabed strength may be determined rapidly using free-fall penetrometers as the tool is simply released from above the sea-floor and penetrates under gravity into the seabed. The speed and ease of deployment relative to conventional ‘push-in’ penetrometers is attractive, with the trade-off of more complex interpretation. This paper considers two approaches for deducing the undrained shear strength from a slender conical tipped penetrometer. The first requires as input only the vertical acceleration of the penetrometer, where the soil strength is determined indirectly by considering the various forces acting on the penetrometer and solving the equation of motion. The second determines the undrained shear strength more directly by combining tip load cell and u2 pore pressure measurements. In both cases, adjustments for drag resistance and strain-rate effects are necessary to deduce a strength compatible with that determined from the equivalent push-in penetrometer test. Application of both methods to a serie...

Coronary Angioplasty Guidewires: Differential Characteristics and Technology

Coronary angioplasty guidewires (CAG) are one of the elements considered essential for percutaneous coronary intervention (PCI). However, in scientific literature there are not as many publications about them as exist for other devices. In this review, we will analyse the technology, characteristics and classification of the CAGs, paying special attention to their structure and tip load.

The influence of tip shape on bending force during needle insertion

Steering of needles involves the planning and timely modifying of instrument-tissue force interactions to allow for controlled deflections during the insertion in tissue. In this work, the effect of tip shape on these forces was studied using 10 mm diameter needle tips. Six different tips were selected, including beveled and conical versions, with or without pre-bend or pre-curve. A six-degree-of-freedom force/torque sensor measured the loads during indentations in tissue simulants. The increased insertion (axial) and bending (radial) forces with insertion depth — the force-displacement slopes — were analyzed. Results showed that the ratio between radial and axial forces was not always proportional. This means that the tip load does not have a constant orientation, as is often assumed in mechanics-based steering models. For all tip types, the tip-load assumed a more radial orientation with increased axial load. This effect was larger for straight tips than for pre-bent or pre-curved tips. In addition, the force-displacement slopes were consistently higher for (1) increased tip angles, and for (2) beveled tips compared to conical tips. Needles with a bent or curved tip allow for an increased bending force and a decreased variability of the tip load vector orientation.

Transcatheter pulmonary valve perforation using chronic total occlusion wire in pulmonary atresia with intact ventricular septum

Background:Perforation of pulmonary valve using radiofrequency ablation in pulmonary atresia with intact ventricular septum (PA IVS) is a treatment of choice. However, significant cost of the equipment limits its utility, especially in the developing economies.Objective:To assess the feasibility, safety, and efficacy of perforation of pulmonary valve using chronic total occlusion (CTO) wires in patients with PA IVS as an alternative to radiofrequency ablation.Methods:This is a single-center, nonrandomized, retrospective study conducted during June 2008 to September 2015. Twenty-four patients with PA IVS were selected for the procedure during the study period. The median age and weight of the study population were 8. days and 2.65 kg, respectively. Four patients were excluded after right ventricular angiogram as they showed right ventricular-dependent coronary circulation. The pulmonary valve perforation was attempted using various types of CTO wires based on the tip load with variable penetrating characteristics.Results:The procedure was successful in 16 of twenty patients using CTO wires: Shinobi in nine, Miracle in four, CROSS-IT in two, and Conquest Pro in one. Two patients had perforation of right ventricular outflow tract (RVOT). Pericardiocentesis was required in one patient to relieve cardiac tamponade. Later, the same patient underwent successful hybrid pulmonary valvotomy. The other patient underwent ductus arteriosus (DA) stenting. Balloon atrial septostomy was needed in three cases with systemic venous congestion. Desaturation was persistent in five cases necessitating DA or RVOT stenting to augment pulmonary blood flow. There were two early and two late deaths. The mean follow-up was 22.66 ± 16 months. Three patients underwent one and half ventricle repair and one Blalock–Taussig shunt during follow-up.Conclusion:Perforation of the pulmonary valve can be done successfully using CTO wires in selected cases of pulmonary atresia with intact ventricular septum.

混合整数2次錐計画法による3次元骨組構造物のトポロジー最適化

Recently, methods to obtain truss or frame with high stiffness by the topology optimization problem of minimizing compliance has been studied actively. In general, cross-sectional areas or shapes of each member are defined as design variables in such a topology optimization problem. Practically, since the member cross-sections are to be selected from predetermined candidates, the design variables are treated as discrete variables. Therefore, heuristics or mixed-integer programming (MIP) is selected as the algorithm for solving truss or frame topology optimization problems. In particular, MIP has an advantage that the global optimality of the solution is guaranteed mathematically. However, it is difficult for MIP to treat large scale problems because of the high computational cost. In previous studies, the topology optimization using MIP is limited to small-scale problems, such as trusses or 2D-frames. In recent years, second-order cone programming (SOCP) has attracted attention since it can be solved efficiently by using the interior-point method. It is reported in the latest study that mixed-integer second-order cone programming (MISOCP), i.e., the problem obtained by adding the integrity to some of the variables of SOCP, can deal with the large scale problem compared with MIP. In this paper, the topology optimization of 3D-frame, which is difficult to treat by using MIP, is solved by using MISOCP. First, the 3D-frame topology optimization problem of minimizing compliance is formulated as MISCOP by using the dual problem of total potential energy minimization problem. From this formula, various 3D-frame topology optimization problems of minimizing compliance in which various sets of cross-sectional shapes are defined as design variables are considered. In this paper, 3D-cantilever with tip load, latticed dome with central concentrated load, and simple building with vertical and horizontal loads are optimized by SOCP in various design value cases. In almost all of the optimization cases, the solver has terminated with finding the global optimal solution. In only a few optimization cases which could not find the global optimal solutions, the MISOCP solver was run with time limit and the best feasible solutions found by the solver are reported. These solutions are not necesarily global optimal solutions, but these are good solutions in the cases of this paper. As numerical experiments for comparison, topology optimization problems treated in this paper were tried to be solved by using MIP as well, but the optimal solutions could not be found at all within realistic computational time. The obtained main results are as follows: •The 3D-frame topology optimization problem of minimizing compliance can be formulated as MISOCP by using the dual problem of total potential energy minimization problem. •MISOCP can solve various large scale 3D-frame topology optimization problems which are difficult for MIP to treat because of the high computational cost. •For a larger problem which is beyond the capability of MISOCP, MISOCP cannot find the global optimal solution but can find solution good enough. The commercial solvers which treat MISOCP have been developed extensively, and calculation speed is improved year after year. Against this background, there exists a possibility that the MISOCP will become a powerful topology optimization tool for building structures.

Crack path predictions in fiber reinforced composites

Composite materials exhibit beneficial features compared to conventional engineering material, e.g. a comparable strength and a reduced weight at the same time. To fully exploit these beneficial properties within technical structures, fracture mechanical concepts must be taken into account. The global fracture behavior in composite materials is related to the local delamination at interfaces between matrix and inclusion as well as the local fracture behaviors of the constituents. Because of their structure, the global elastic and fracture mechanical properties of composites are in general anisotropic. In this work, the directional crack resistance of polypropylene (PP) containing a certain amount of glass fibers (GF) or regenerated cellulose fibers (RCF) is measured. A crack deflection criterion based on the J-integral vector is introduced and implemented into a crack growth model. The J-integral is applied to calculate crack tip loading quantities on a global level, excluding all numerically inaccurate values at the crack tip. With this approach crack paths in anisotropic aluminum alloys have recently been precisely predicted. Crack growth simulations at compact tension (CT)-specimens of PP with GF and RCF are carried out, showing good agreement with the experiments. Several effects resulting from the directional crack resistance are investigated and explained, e.g. a crack deflection at mode-I loaded specimens.

Weak and strong bi-material interfaces and their influence on propagating cracks in plane elastic structures

The developing crack paths in heterogeneous structures are the result of the inhomogeneous state of stress. The latter stems from e.g. voids or inclusions in an elastic matrix, which are bonded either by strong or weak interfaces. Besides the stiffness of an inclusion, the kind of interface has a decisive influence on the state of stress and therefore on propagating cracks. It is experimentally proven that cracks tend to grow towards regions with lower stiffness (Tilbrook et al., 2006; Judt et al., 2015), therefore matrix cracks might be attracted by interface delamination cracks. In this research the matrix crack growth in bi-material structures is simulated, incorporating dissipative processes arising at weak interfaces and a reference is provided by simulating the crack propagation in the same bi-material but with a strong (perfect) interface. Incremental crack extensions constitute the matrix crack growth, requiring a continuous modification of the geometry. An intelligent re-meshing procedure is applied, where the loading history cannot be neglected due to the presence of dissipative processes (Judt and Ricoeur, 2013b). The crack deflection and crack tip loading are determined by the J-integral criterion and the energy release rate, respectively. The resulting crack paths confirm that the matrix crack tends to grow into the direction of regions with lower stiffness. If weak interfaces are considered, an extremely attracting effect on propagating matrix cracks caused by the delamination is observed, which is stronger than the influence of divergent stiffnesses.

Erratum to: Mixed-mode crack tip loading and crack deflection in 1D quasicrystals

Erratum to: Mixed-mode crack tip loading and crack deflection in 1D quasicrystals

Bi-BCM: A Closed-Form Solution for Fixed-Guided Beams in Compliant Mechanisms

A fixed-guided beam, with one end is fixed while the other is guided in that the angle of that end does not change, is one of the most commonly used flexible segments in compliant mechanisms such as bistable mechanisms, compliant parallelogram mechanisms, compound compliant parallelogram mechanisms, and thermomechanical in-plane microactuators. In this paper, we split a fixed-guided beam into two elements, formulate each element using the beam constraint model (BCM) equations, and then assemble the two elements' equations to obtain the final solution for the load–deflection relations. Interestingly, the resulting load–deflection solution (referred to as Bi-BCM) is closed-form, in which the tip loads are expressed as functions of the tip deflections. The maximum allowable axial force of Bi-BCM is the quadruple of that of BCM. Bi-BCM also extends the capability of BCM for predicting the second mode bending of fixed-guided beams. Besides, the boundary line between the first and the second modes bending of fixed-guided beams can be easily obtained using a closed-form equation. Bi-BCM can be immediately used for quick design calculations of compliant mechanisms utilizing fixed-guided beams as their flexible segments (generally no iteration is required). Different examples are analyzed to illustrate the usage of Bi-BCM, and the results show the effectiveness of the closed-form solution.

Mixed-mode crack tip loading and crack deflection in 1D quasicrystals

Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between $$J_{1}$$ , $$J_{2}$$ and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon–phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

Methodology to Determine a Tip-Loss Factor for Highly Loaded Wind Turbines

The commonly observed overprediction of tip loads on wind-turbine blades by classical blade-element momentum theory is investigated by means of an analytical method that determines the exact tip-loss factor for a given blade flow angle. The analytical method is general and can be applied to any higher-fidelity computational method such as free-wake methods or computational fluid dynamics analyses. In this work, the higher-order free-wake method WindDVE is used to compute tip-vortex rollup and wake expansion in the near wake of a highly loaded wind-turbine rotor. The resulting spanwise distributions of the blade flow angle serve as input to the analytical method that is subsequently tested for the National Renewable Energy Laboratory phase 6 rotor by implementing a corrected tip-loss factor into the blade-element code XTurb. It is found that a simple modification can be added to the classical tip-loss factor in blade-element momentum theory that leads to improved prediction of blade tip loads at no additional computational expense.

Efficient distal tip size of primary guidewire for antegrade percutaneous coronary intervention in chronic total occlusion: The G-FORCE study

BackgroundAlthough several new techniques have been introduced for CTO such as the retrograde approach, the fundamental question of what type of guidewire is the most appropriate as a primary guidewire in the antegrade approach has not been answered. MethodsThe G-FORCE study was designed as a prospective multicenter randomized controlled trial to determine the efficient primary guidewire in antegrade approach for chronic total occlusion (CTO). The first guidewire was randomly assigned to a regular size distal tip group (0.014in. size) or tapered tip group (0.010in. or less). The primary endpoint was defined as successful lesion penetration by the first guidewire into distal true lumen. This study was registered at ClinicalTrials.gov with identifier NCT00987610. ResultsA total of 260 patients were enrolled, with an average age of 66±11years and 16% were female. The average J-CTO score was 1.8±1.1. The primary endpoint was achieved in 38% and 32% of patients using tapered and regular distal tip guidewires, respectively (P=0.80). The final PCI success rate was 81% vs. 85%, respectively (P=0.57). Easy CTO lesions with a J-CTO score=0 exhibited a primary endpoint significantly different between tapered and regular distal tip primary guidewires (79% vs. 40%; P=0.046). Guidewire distal coating or distal tip load did not relate with primary guidewire success rate. ConclusionTapered and regular distal tip guidewires are equivalent as a first choice for CTO. Tapered guidewires are superior for CTO lesions with a J-CTO score=0.

Static analysis of bi-directional functionally graded curved beams

Flexure of bi-directional functionally graded (FG) circular beams is analyzed using the kinematical assumptions of the Euler–Bernoulli theory. The material properties are varied along the axis (tangential direction) and thickness (radial direction) of the beam simultaneously. Analytical results are presented for statically-determinate circular cantilever beams under the action of various tip loads. Finally, parametric studies are conducted to investigate the variation of critical stresses and displacements with the gradation parameters. These indicate the possibility of tailoring the response of bi-directional FG beams to fit a wide range of structural constraints.

Experimental study of self-recirculating casing treatment in a subsonic axial flow compressor

Parametric studies of recirculating casing treatment were experimentally performed in a subsonic axial flow compressor. The recirculating casing treatment was parameterized with injector throat height, injection position, and circumferential coverage percentage. Eighteen recirculating casing treatments were tested to study the effects on compressor stability and on the compressor overall performance at three blade speeds. The profiles of recirculating casing treatment were optimized to minimize the losses generated by air recirculation. In the experiment, the stalling mass flow rate, total pressure ratio, and adiabatic efficiency of the compressor were measured to study the steady-state effects on the compressor performance of recirculating casing treatments, and static pressure disturbances on the casing wall were monitored to study the influence on stall dynamics. Results indicate that both the compressor stability and overall performance can be improved through recirculating casing treatment with appropriate geometrical parameters for all the test speeds. The influence on stall margin of one geometric parameter often depends on the choice of others, i.e. the interaction effects exist. In general, the recirculating casing treatment with a moderate injector throat and a large circumferential coverage is the optimal choice to enhance compressor stability. The injector of recirculating casing treatment should be placed upstream of the blade tip leading edge and the injector throat height should be lower than four times the rotor tip gap for the benefits of compressor efficiency. At 71% speed, the blade tip loading is decreased through recirculating casing treatment at the operating condition of near peak efficiency and increased near stall. Moreover, the outlet absolute flow angle is reduced in the tip region and enhanced at lower blade spans for both operating conditions. The stall inceptions are not changed with the implementation of recirculating casing treatment for all the test speeds, but the stall patterns are altered at 33% and 53% speeds, i.e. the stall with two cells is detected in the recirculating casing treatment compared with the solid casing with only one stall cell.

Numerical investigations in structures with imperfect material interfaces and cracks

AbstractNatural fiber reinforced bio‐polymers are in the focus of many research projects to understand and improve the mechanical behavior subjected to different process parameters during production. To provide safe and reliable light weight constructions, special interest is directed towards the damage and fracture behavior of such composite materials. Here, the material's behavior at the imperfect material interface between fiber and matrix plays an essential role and governs inelastic effects at the interfaces on the one hand, and the behavior of growing cracks on the other. The reduction of the elastic potential is related to both energy consuming processes in the system and in general is going along with a reduction of the crack tip loading and a shift of the crack growth direction. In this paper, the crack tip loading analysis in structures with perfect and imperfect material interfaces is presented and applied to different specimens. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

On Frequency Sensitivity and Mode Orthogonality of Flexible Robotic Manipulators

This paper presents sensitivity analysis of vibration frequencies of flexible manipulators with respect to variations of systems parameters such as rotational inertia of hub, and mass, moment, and side of tip load. Both Euler-Bernoulli and Timoshenko dynamical models of flexible manipulators are discussed. By using variational method, sensitivity indices are obtained with explicit expressions for measuring the sensitivity of frequencies. Based on variational formulations, a novel method for deriving the orthogonal relations among vibration modal shape functions of flexible manipulators is introduced. With this method, the orthogonal relations can be derived easily without invoking the tedious process of differentiation and integration by part, as commonly used in their derivation.

Pseudo-rigid-body models for circular beams under combined tip loads

Circular beams can offer potential advantages to designers of compliant mechanisms and provide useful alternatives to other types of compliant elements. However, they pose unique challenges due to lack of effective models for predicting deformation upon loading. In this work, the kinematic and stiffness properties of circular beams with uniform cross sections subjected to combined force and moment loads are represented using pseudo-rigid-body models. The pseudo-rigid-body models serve as numerical approximations for easy derivation of mechanism equations, and also enable quick solutions using multi-body software packages. The models are derived by comparisons against beam theory, and the values of the parameters are presented in the form of fitting functions for a large range of arc angles. The validity and applicability of these models in analysis are demonstrated with the example of a micro-force sensor. Their use in design is demonstrated with the case of developing flexure mechanisms for microspines in grasping applications, with comparisons against Finite Element Analysis to prove their accuracy and speed. The PRB models can serve as tools facilitating design of compliant mechanisms with circular beams.

Extended Glauert Tip Correction to Include Vortex Rollup Effects

Wind turbine loads predictions by blade-element momentum theory using the standard tip-loss correction have been shown to over-predict loading near the blade tip in comparison to experimental data. This over-prediction is theorized to be due to the assumption of light rotor loading, inherent in the standard tip-loss correction model of Glauert. A higher- order free-wake method, WindDVE, is used to compute the rollup process of the trailing vortex sheets downstream of wind turbine blades. Results obtained serve an exact correction function to the Glauert tip correction used in blade-element momentum methods. It is found that accounting for the effects of tip vortex rollup within the Glauert tip correction indeed results in improved prediction of blade tip loads computed by blade-element momentum methods.

Antegrade wire escalation for chronic total occlusions in coronary arteries

Antegrade wire escalation (AWE) remains the method of choice for tackling chronic total occlusions (CTOs), especially for lesions with low J-CTO score. To increase the number of operators which treat CTOs and increase AWE success rates, there is a need for a clear, algorithmic approach. We report the results of a simple AWE algorithm with new guidewire technology in coronary CTOs. Hundred consecutive CTO lesions selected for AWE as the primary strategy were included in five Benelux centers. The algorithm follows a step-wise increase in guidewire tip load. Lesions were categorized according to the J-CTO score. Primary endpoint was successful guidewire crossing. No differences in baseline demographics were present between successful and unsuccessful procedures. Overall, in 75% of the lesions AWE resulted in successful crossing. AWE success rates in easy, intermediate, difficult and very difficult CTOs were 83, 86, 71 and 43%, respectively. 46% could be crossed using a soft guidewire only. An additional success of 34 and 60% could be reached with an intermediate and stiff guidewire, respectively. Adding additional techniques resulted in 88% overall success. Procedure and fluoroscopy times, radiation doses and use of contrast were within highly acceptable ranges (67 ± 39 min, 27 ± 19 min, 1.7 ± 1.3 Gy, 264 ± 123 ml). The algorithm and new wire technologies led to high success rates. AWE as a standalone procedure is highly successful in J-CTO 0-1. Low- and intermediate-volume CTO operators should try to implement a systematic approach in their CTO procedures, especially for lesions with low J-CTO scores. Adding additional techniques further increases these success rates.