Rib Bending Research Articles

Fatigue performance of root-to-throat cracks repaired by bonding steel: experimental and numerical investigations

Root-to-throat cracks are one of typical fatigue cracking modes in rib-to-deck welded joints of orthotropic steel bridge decks (OSDs). An efficient technique of non-destructive bonding steel plates (BSP) was proposed to address the cracking issue. A series of local full-scale test specimens with and without strengthening were performed under different loading cases. Meanwhile, the typical failure modes and fatigue performance of welded joints were evaluated. Subsequently, fracture mechanical models were developed to deepen the understanding on crack propagation behavior and strengthening effectiveness. Finally, a parametric study was carried out to explore the effects of various parameters on stress intensity factors (SIFs) at the crack tips. The results showed that fatigue cracks dominated the crack propagation of the welded throats in the case of rib bending. External BSP on rib-to-deck welded joints contributed greatly to the extended in-service life of existing cracked structures. To be more specific, the fatigue stress range response at the cracked region was reduced by an average of 90.6% by means of the BSP method. By comparing SIFs, it was found that the BSP retrofit method led to a reduction of at least 78%. The predicted directions of crack propagation agreed well with the observations from fatigue tests. Moreover, the thickness of bonded plates exerted more significant effects on fatigue improvement.

Study of Rib Bending at Installation of Insertion into Rib

Study of Rib Bending at Installation of Insertion into Rib

The influence of some geometric parameters on heat transfer in axial cooling systems of electronic equipment made on the basis of split fins

The active development of advanced digital technologies over the past 10 years has led to the formation of a new set of tasks related to ensuring the uninterrupted and predictable operation of electronic and electric power equipment. Thus, modern telecommunication and computer systems during their normal operation are characterized by significant heat release. One of the main problems of such systems, along with the observance of weight and size characteristics, is the provision of certain operating thermal conditions of the components in a wide range of external conditions. In such situations, passive and active systems with axial fins are very often used. As a result of the work, experimental studies of heat transfer intensification under conditions of forced convection using split ribs were carried out and presented. The effectiveness of the use of split fins has been shown, during the experiment the most optimal geometric parameters of the working section and the corresponding operating characteristics have been identified. Based on the processing and analysis of experimental data, it was found that this method of intensification makes it possible to increase the intensity of heat transfer up to 64%, since the cutting of the ribs makes it possible to actively prevent the formation of a boundary layer and additionally turbulize the flow, which in turn favorably affects the thermal parameters of the entire system. The visualization of the heat transfer process was performed, which illustrates the active vortex flows formed during the flow around and separation from the edges of the rib of the oncoming coolant flow. The calculation of the thickness of the boundary layer near the split rib was made, in which it was found that for all investigated angles of rib bending γ, an increase in the Re number is characterized by a decrease in the thickness of the boundary layer in the entire range of thermal loads. In conclusion, a general assessment of the influence of geometric and regime parameters on the intensity of heat transfer with forced air supply was carried out.

Understanding nonlinear behaviors of auxetic foams using X-ray tomography and pore structure analysis

With a thermo-mechanical compression process, regular polyurethane (PU) foams can transform into auxetic foams showing a negative Poisson's ratio. Using tensile tests and X-ray tomography, we investigate the structure-property relation of a series of PU foams prepared with different amount of compression treatment. We find that the Poisson's ratio decreases with the amount of compression but reaches a plateau while the maximum strain with auxetic effects keeps increasing. With pore structure analysis on the 3D tomography of those foams, the structure origin of the nonlinear mechanical behaviors is found to be closely related to the bending of ribs in the auxetic foams. We found that the Poisson's ratio is correlated with the fraction of bent ribs while the maximum auxetic strain is determined by the degree of rib bending. Our results provide insights in designing better foam-based auxetic materials for large deformation applications.

Full-Vector Analysis of Bending Waveguides by Using Meshless Finite Cloud Method in a Local Cylindrical Coordinate System

By using a meshless finite cloud method, a full-vector mode solver in terms of transverse-magnetic-field components for optical dielectric waveguide bends is developed in a local cylindrical coordinate system. To construct the interpolation function, both the point collocation and the fixed reproducing kernel technique are utilized, and then with the help of the continuity conditions of the longitudinal field components and the perfectly matched layer absorbing boundary conditions, a standard matrix eigenvalue is obtained. Compared with the conventional meshed numerical techniques, the distributions of solution points of the present meshless method can be applied to the area of complexity in a completely free manner. Consequently, excellent convergence with high accuracy can be realized. Moreover, the present method can be applied to both the uniform and non-uniform nodal distributions, thus the computational procedure is relatively flexible. To validate the proposed method, both fundamental and high-order leaky modes for a typical rib bending waveguide are analyzed and their modal field distributions and corresponding effective refractive indexes are presented. Results are in good agreement with those published earlier, showing the effectiveness of the present method.

Numerical Investigation of an Unsteady and Anisotropic Turbulent Flow Downstream a 90° Bend Pipe with and without Ribs

In this work, a numerical study of the dynamical behavior of unsteady and anisotropic turbulent flow downstream a 90° bended pipe was presented. For this purpose, comparative computations are carried out employing two flow configurations, bend pipe with ribs and bend pipe without ribs with a curvature radius ratio Rc/D=2.0. In the bend pipe with ribs, the pitch ratios Pt/e=40 and the rib height to pipe diameter e/D is 0.1. This model has been utilized to assess the effect of ribs on flow where the presence of the ribs leads to a complex velocity field with regions of flow separation upstream and downstream of the ribs. The Reynolds-Averaged Navier–Stokes (RANS) approach is employed and the computational model is validated by comparisons with the existing experimental data. The simulations are conducted with the commercials CFD software FLUENT for Dean number varying from 5000 to 40000. The result analysis shows that the higher resistance generated by the ribs produced relatively larger velocity gradient (∂U/∂y) compared to the case of bend pipe without ribs where a more uniform mean velocity profile is observed. The turbulence intensities are higher in the ribbed bend pipe compared to those in the non-ribbed case and depend faintly on the Dean number. The levels of the Reynolds shear stresses are significantly enhanced by the ribs compared to the case without ribs. This increasing is explained by significantly higher levels of turbulence production over those ribs produced by large values of ∂U/∂y.

CFD analysis of unsteady and anisotropic turbulent flow in a circular-sectioned 90° bend pipe with and without ribs: A comparative computational study

The Reynolds–averaged Navier–Stokes (RANS) equations were solved along with Reynolds stress model (RSM), to study the fully-developed unsteady and anisotropic single-phase turbulent flow in 90° bend pipe with circular cross-section. Two flow configurations are considered the first is without ribs and the second is with ribs attached to solid walls. The number of ribs is 14 ribs regularly placed along the straight pipe. The pitch ratios is 40 and the rib height e (mm) is 10% of the pipe diameter. Both bends have a curvature radius ratio, of 2.0. The solutions of these flows were obtained using the commercial CFD software Fluent at a Dean number range from 5000 to 40000. In order to validate the turbulence model, numerical simulations were compared with the existing experimental data. The results are found in good agreement with the literature data. After validation of the numerical strategy, the axial velocity distribution and the anisotropy of the Reynolds stresses at several downstream longitudinal locations were obtained in order to investigate the hydrodynamic developments of the analyzed flow. The results show that in the ribbed bend pipe, the maximum velocity value is approximately 47% higher than the corresponding upstream value but it is 9% higher in the case of the bend pipe without ribs. It was also found for both cases that the distribution of the mean axial velocity depends faintly on the Dean number. Finally, it can be seen that the analyzed flow in the bend pipe without ribs appears more anisotropic than in bend pipe with ribs.

Mechanical Behavior of Triaxial Geogrid Used for Reinforced Soil Structures

Geosynthetics-reinforced soil (GRS) structures have been widely used for the prevention of geological hazards. As a recently introduced product, the triaxial geogrid has been confirmed to provide improved performance due to the more stable grid structure. This paper presents an evaluation of the mechanical behavior based on a series of laboratory tests. The unconfined tensile strength of biaxial geogrid and triaxial geogrid in different loading directions relative to the orientation of ribs was investigated. Then, more than 8 pullout tests were conducted on the triaxial geogrid specimens embedded in the compacted sand. The internal displacements along the geogrid length were monitored. The results show that the triaxial geogrid has been shown to provide nearly uniform tensile strength in all loading directions as compared with the biaxial geogrid. The triaxial geogrid deformation is mainly characterized by rib bending and nodal distortion along with an inward squeeze perpendicular to the pullout direction. The interface friction between the soil and the geogrid develops in a progressive mode, and an elasto-plastic-softening characteristic is detected experimentally due to the extensibility of geogrid.

Dynamic Response and Robustness Evaluation of Cable-Supported Arch Bridges Subjected to Cable Breaking

Cable-supported arch bridges have had many cable break accidents, which led to dramatic deck damage and even progressive collapse. To investigate the dynamic response and robustness of cable-supported arch bridges subjected to cable breaking, numerical simulation methods were developed, compared, and analyzed, and an effective and accurate simulation method was presented. Then, the cable fracture of a prototype bridge was simulated, and the dynamic response of the cable system, deck, and arch rib was illustrated. Finally, the robustness evaluation indexes of the cable system, deck, and arch rib were constructed, and their robustness was evaluated. The results show that the dynamic response of the adjacent cables is proportional to the length of the broken cable, while the dynamic response of the deck is inversely proportional to the length of the broken cable. The dynamic amplification factor of the cable tension and deck displacement is within 2.0, while that of the arch rib bending moment exceeds 2.0. The break of a single cable will not trigger progressive collapse. When subjected to cable breaking, the deck system has the least robustness. The proposed cable break simulation procedure and the robustness evaluation method are applicable to both existing and new cable-supported bridges.

Detailed subject-specific FE rib modeling for fracture prediction

Objective: The current state of the art human body models (HBMs) underpredict the number of fractured ribs. Also, it has not been shown that the models can predict the fracture locations. Efforts have been made to create subject specific rib models for fracture prediction, with mixed results. The aim of this study is to evaluate if subject-specific finite element (FE) rib models, based on state-of-the-art clinical CT data combined with subject-specific material data, can predict rib stiffness and fracture location in anterior-posterior rib bending.Method: High resolution clinical CT data was used to generate detailed subject-specific geometry for twelve FE models of the sixth rib. The cortical bone periosteal and endosteal surfaces were estimated based on a previously calibrated cortical bone mapping algorithm. The cortical and the trabecular bone were modeled using a hexa-block algorithm. The isotropic material model for the cortical bone in each rib model was assigned subject-specific material data based on tension coupon tests. Two different modeling strategies were used for the trabecular bone.The capability of the FE model to predict fracture location was carried out by modeling physical dynamic anterior-posterior rib bending tests. The rib model predictions were directly compared to the results from the tests. The predicted force-displacement time history, strain measurements at four locations, and rotation of the rib ends were compared to the results from the physical tests by means of CORA analysis. Rib fracture location in the FE model was estimated as the position for the element with the highest first principle strain at the time corresponding to rib fracture in the physical test.Results: Seven out of the twelve rib models predicted the fracture locations (at least for one of the trabecular modeling strategies) and had a force-displacement CORA score above 0.65. The other five rib models, had either a poor force-displacement CORA response or a poor fracture location prediction. It was observed that the stress-strain response for the coupon test for these five ribs showed significantly lower Young’s modulus, yield stress, and elongation at fracture compared to the other seven ribs.Conclusion: This study indicates that rib fracture location can be predicted for subject specific rib models based on high resolution CT, when loaded in anterior-posterior bending, as long as the rib’s cortical cortex is of sufficient thickness and has limited porosity. This study provides guidelines for further enhancements of rib modeling for fracture location prediction with HBMs.

Design and mechanical properties of hierarchical isogrid structures validated by 3D printing technique

Based on general lattice structure, a hierarchical isogrid (isotropic grid) structure with T-ribs was designed to enhance the buckling resistance and plastic performance, and manufactured by three-dimensional (3D) printing technique. It is proposed that under edgewise compression, the latticed panel has three structural failure modes, including material failure, global buckling and local buckling. Hierarchical topology simultaneously improves the out-of-plane and in-plane rigidity of the lattice ribs, as T-ribs balance the global bending rigidity and the local rib bending rigidity, endowing the panel higher buckling resistance. In the stage of post-failure plastic bending, the T-rib lattice shows good load-carrying ability and deforming ductility. Based on three failure modes, a multi-failure theory was built and verified by experiments and finite element method (FEM). A plastic model for the hierarchical isogrid panels was built to predict the post-failure deformation. The failure mode map method was proposed, providing reference for further optimal design.

Natural characteristics analysis of aircraft wing box based on finite element method and measured data

Compared with other mechanical products, aircraft structures have more rigorous requirements on flying performance, safety, reliability and service life. Based on the finite element method (FEM), the key component of the wing box model is explored in this paper, which provides a reference for the structure design and manufacture of aircraft wing box. The three-dimensional point cloud data of components are obtained by optical measurement systems, the deviation analysis between the point cloud model and the nominal model is carried out as a prerequisite, and then the natural characteristics of the model is analyzed. The results show that 99.15 % of the measured points have deviations within 0.38 mm, which verifies the accuracy of the nominal model. The first six modes are all bending modal shape, and the larger amplitude region mainly occurs in the wing ribs, which means its bending strength should be improved for structure design. Besides, the sixth-mode simultaneously result in front spar, stringer and rib bending vibration.

Thoracic response targets for a computational model: A hierarchical approach to assess the biofidelity of a 50th-percentile occupant male finite element model

Current finite element human thoracic models are typically evaluated against a limited set of loading conditions; this is believed to limit their capability to predict accurate responses. In this study, a 50th-percentile male finite element model (GHBMC v4.1) was assessed under various loading environments (antero-posterior rib bending, point loading of the denuded ribcage, omnidirectional pendulum impact and table top) through a correlation metric tool (CORA) based on linearly independent signals. The load cases were simulated with the GHBMC model and response corridors were developed from published experimental data. The model was found to be in close agreement with the experimental data both qualitatively and quantitatively (CORA ratings above 0.75) and the response of the thorax was overall deemed biofidelic. This study also provides relevant corridors and an objective rating framework that can be used for future evaluation of thoracic models.

Vector analysis of bending waveguides by using a modified finite-difference method in a local cylindrical coordinate system

A vector mode solver for bending waveguides by using a modified finite-difference (FD) method is developed in a local cylindrical coordinate system, where the perfectly matched layer absorbing boundary conditions are incorporated. Utilizing Taylor series expansion technique and continuity condition of the longitudinal field components, a standard matrix eigenvalue equation without the averaged index approximation approach for dealing with the discrete points neighboring the dielectric interfaces is obtained. Complex effective indexes and field distributions of leaky modes for a typical rib bending waveguide and a silicon wire bend are presented, and solutions accord well with those from the film mode matching method, which shows the validity and utility of the established method.

Antierosion in a 90° bend by particle impaction

AbstractRibbed bend protection, a new method to protect duct bends against erosion in gas–solid flows, was studied theoretically. In this method, ribs are evenly welded on the outer wall of the inside bend at 20°–80°, and the material of the bend is medium carbon steel. An experimental system is set up to perform 3‐D numerical work simultaneously. Experimental and numerical results agree well and confirm that the method is simple and efficient for erosion protection. Numerical simulation is used to study the axial gas‐flow characteristics along the bend and the secondary flow at the cross section. Detailed analyses involving the impact of velocity and the incidence angle of particle–metal (particle‐rib or particle‐duct) impact show the mechanism of the antierosion effect. As a result, both experimental and theoretical predications demonstrate that the average erosion rate of ribbed bends is only one‐third of the bare bend under test conditions, and that rectangular ribs possess greater antierosion ability than square ribs do. Besides, the predictions suggest that the erosion of the wall is more serious than that of the ribs on a ribbed bend, while the wear distribution pattern remains unchanged after adding ribs at the bend.

Experimental and numerical investigation of a new method for protecting bends from erosion in gas-particle flows

In the present paper, both experimental and numerical results confirm that the method of fixed ribs on the outer wall of inside bend is a simple and efficient erosion protection method for protecting bends from erosion in gas-particle flows. Ribs are fixed on the bend in 20–80° and the material used (ribs and bend) is medium carbon steel. The numerical results show satisfactory agreement with the experimental data. From the numerical results, detailed analyses involving the impact velocity and incidence angle of particle–bend impact (including particle–rib and particle–wall) unveil the reason of the ribbed bend anti-erosion effect.

An experimental investigation of a new method for protecting bends from erosion in gas-particle flows

Bend erosion is a fairly serious problem in conveyer pipe system. This paper intends to introduce a new anti-erosion method for bend: ribbed anti-erosion method. Experimental research has been done by fixing ribs in the range of 10° – 70° on the outer-wall of inside 90°-bend. As a result, the experiment got anti-erosion efficiency: 93.02%. It shows that ribbed bend technology is a simple and efficient anti-erosion method. Besides, the experiments indicate that rectangle ribs tend to do more obvious anti-erosion effect than square ribs do when they have equal height.

An experimental investigation of a new method for protecting bends from erosion in gas-particle flows

This paper intends to introduce a new way of bend erosion protection: the ribbed bend erosion protection method. Experimental research has come out fixing ribs on the outer-wall of the inside bend as well as on the wall of the straight pipe extending behind the bend in order to decrease the erosion damage caused by the “bend effect”. The experiment shows that ribbed bend technology is a simple and efficient erosion protection method, which can greatly enhance bend erosion protection ability. It also shows that the rib relative height and the rib gap between two adjacent ribs are two important parameters in the ribbed bend erosion protection ability. The same result can be reached on the straight pipe extending from the bend.

Effect of rib bending on Bloch wave structure of a rib-stiffened plate

It is well known that flexural vibration on a flat plate stiffened by periodically placed line supports shows stop/passband behavior in frequency, associated with Bloch waves. For a one-dimensional situation, with plate vibration incident normally on the ribs, a simple model in which the ribs exert forces normal to the plate by virtue of their mass often suffices to explain stop bands that occur when the rib spacing d accommodates an integer number of the half-wavelengths of plate vibration. This paper presents results for cases where the ribs present normal forces as well as moments to the plate. Particular attention is paid to the case where the rotary impedance offered by the rib is limited by the rib’s own flexibility in bending. At special antiresonance frequencies associated with the rib’s own bending motion, the rib rotary impedance is seen to rise sharply and to give rise to stop bands additional to those generated by the rib normal forces.

Effects of porcine somatotropin and dietary phosphorus on growth performance and bone properties of gilts

One hundred eight gilts (initial weight = 58.5 kg) were used to determine the effects of porcine somatotropin (pST) and dietary P on growth performance and bone mechanical properties and mineralization during the finishing phase (58 to 105 kg) and a 35-d postfinishing phase. Gilts were injected daily with placebo (control) or 4 mg of pST and fed diets containing .4, .8, or 1.2% P in a 2 x 3 factorial arrangement. From 58 to 105 kg, administration of pST increased (P < .01) ADG and G/F and decreased (P < .01) ADFI. When mean weight of the gilts in a pen reached 105 kg, half the gilts were slaughtered and first rib, femur, and third and fourth metacarpals were collected for determination of mechanical properties and bone ash. A pST x P interaction was observed (P < .05) for rib bending moment and modulus of elasticity; maximum rib bending moment was attained by control gilts at .8% P and rib modulus of elasticity values remained constant across P levels, whereas rib bending moment and modulus of elasticity increased as dietary P increased from .4 to 1.2% in pST-treated gilts. Administration of pST decreased (P < .05) stress of the rib, femur, and metacarpals compared with control gilts. Increasing dietary P resulted in a linear (P < .10) increase in bending moment, stress, and ash content for rib, femur, and metacarpal bones. The remaining 54 gilts were individually fed 1.8 kg/d of a common diet for 35 d postfinishing.(ABSTRACT TRUNCATED AT 250 WORDS)