Axial Stiffeners Research Articles

Numerical study on steel plate girders ‐ Intermediate transverse stiffeners axial force

AbstractTransverse stiffeners are used in steel plate girders with slender webs to provide lateral support to the web along the span and thus increase the plate girder shear resistance. Furthermore, transverse stiffeners anchor the tension field, resulting in axial compression in the stiffener. Despite this, it is widely assumed that the design axial force provided by the FprEN 1993‐1‐5 [1] for the transverse stiffeners is significantly greater than that observed in experimental testing and numerical simulations.The results of 550 nonlinear numerical simulations of plate girders loaded in shear up to failure are presented. Shear resistance and axial stiffener forces are evaluated while the effects of a wide parameter range as web aspect ratio and thickness, flange‐to‐web area ratio, and steel grade are investigated. The numerical results are compared to the European standard design values. Finally, a statistical analysis of the set of results is presented.The numerical analyses show that the axial forces installed in the intermediate transverse stiffeners are significantly lower than those specified by FprEN 1993‐1‐5 [1].

Design and Performance Analysis of Wavy Nonrotating Pneumatic Soft Actuator

Abstract Soft robots can accomplish hand rehabilitation training to ensure better safety and compliance for hand rehabilitation. In this study, a wavy nonrotating soft actuator structure was proposed for hand rehabilitation, and an axial stiffener was added to the main structure of the actuator according to the function of the bamboo fiber. A physical model of the actuator was fabricated using a multistep casting molding method, and the performance of the designed soft actuator was tested experimentally. The results showed that the bending angle and contact force gradually increased with increasing pressure. The average maximum bending angle and contact force can reach 286 ± 14.3 deg and 1.04 ± 0.051 N, with a pressure of 72 kPa. Meanwhile, the bending torques of the soft actuator at each joint of the finger were tested, to verify that it can meet the needs of soft actuators for hand applications. Furthermore, the load lifting of the soft actuator with axial stiffeners can increase by 6 mm on average compared with a soft actuator without axial stiffeners under negative pressure. In conclusion, the pneumatic soft actuator can produce two different motion functions under the action of one cavity. In addition, a soft actuator with an axial stiffener can improve the load capacity under negative pressure. By assembling the actuators, a three-finger gripper was manufactured. The gripper could grasp and lift objects. Therefore, this work provides a new route for the development of pneumatic soft actuators and soft robots, which has efficient driving.

Pitting corrosion identification approach based on inverse finite element method for marine structure applications

This paper presents a state-of-the art inverse finite element method (iFEM) for full-field, real-time structural health monitoring (SHM) of corroding structures. The study focuses on detecting the location and identifying the extent of pitting corrosion, which is one of the most hazardous forms of corrosion due to the difficulties regarding its prediction and detection. For this purpose, high-fidelity finite element (FE) models of corroded samples with complex-shaped, semi-ellipsoidal, and cylindroconical defects are developed to replicate the strain field of pitting corroded structures. The strain fields produced by the FE models, verified against experimental data, are reconstructed by the iFEM model using a robust and practical four-node quadrilateral inverse-shell element, iQS4. A strain-based damage criterion is defined to obtain the damage distribution and the location of corrosion pits on dog-bone tensile test samples with full sensor iFEM and coupled iFEM-GA reduced sensor technique. Finally, in a practical example of a structure with complex geometry, the proposed method's performance is assessed through detecting the location of corrosion damage on a cylindrical marine structure with axial stiffeners.

Оценка технической возможности достижения одинакового хода поршней в кривошипно-шатунном механизме с прицепными шатунами

The article presents the technical capabilities for achieving the specified operating characteristics of engine components and parts taking into account the geometric characteristics of the crank mechanism (crank mechanism). It also presents the assessment and achievements of the required level of strength parameters of some structural elements of the main connecting rod and the entire mechanism as a whole. Making changes to a proven design and established production is a complex and multifactorial task. It is necessary to make changes that would minimize production and technological losses. Besides, they must fit harmoniously into existing technology and production capabilities ensuring the fulfillment of new technical requirements and characteristics. When solving the problem of ensuring the same piston stroke for a V-2 engine, the analysis of the design documentation showed that in addition to making changes to the design of the crank mechanism, it is necessary to make changes to other engine parts. The need for these changes was determined by the method of “scrolling” the assembly of crankshaft parts in the volume of the engine crankcase using 3D modeling programs for parts and checking their performance. The results of assessing the kinematics of the crankshaft engine of V-2 type engines proved that in addition to changing the design of the main connecting rod, it is necessary to perform additional processing of the axial stiffener rib of the upper half of the crankcase, as well as to make changes to the design of the trailing connecting rod in order to eliminate contact with the cylinder liner and, possibly, the liner itself. However, changes in the engine design will entail significant changes in the technological process of its manufacture. Obviously, these changes should be minimal. In order to preserve the engine design, it is necessary to make some significant changes. They can affect significant production and technological changes, which in conditions of mass production require fairly strong theoretical and practical justification. Therefore, when implementing these technical solutions, it was necessary to perform calculation and kinematic analysis based on 3D modeling and logical analysis, excluding disruption of engine operation. In addition, to assess the load on the lower head of the connecting rod, a hydrodynamic calculation was performed. The results also include the hydromechanical characteristics of a complexly loaded bearing and a diagram of the hydrodynamic pressures acting in a thin lubricant layer

Effects of circular plates on forced vibration of orthogonally stiffened cylindrical shell in wavenumber-frequency domain

A modified variational method for orthogonally stiffened cylindrical shell coupled with multiple circular plates is proposed in this paper. A unified variational modelling procedure is developed to accommodate three dimensional deformation restrains between the shell and substructures, including circular plates, ring and axial stiffeners. The vibration displacements are analytically expanded with Fourier series in the circumferential direction. The input energies due to external loads and the responses of the shell in circumferential wavenumber domain can be naturally obtained, which significantly facilitate the effect analysis of substructures. Close orthogonal independent polynomials are employed for the displacements in the axial direction to achieve satisfactory solutions. The convergence and accuracy of the present method are validated by comparing the analytical and numerical results. The effects of circular plates on vibration responses under different external forces are investigated. The contributions of different circumferential modes to the forced responses are analyzed, and reasons for the effects of the circular plates are then revealed in the circumferential wavenumber-frequency domain. The results indicate that the circular plates not only lead to frequency shift, but also coupling of the circumferential modes of the shell, which will respectively account for frequency shifts and increase of the resonance peaks.

Evaluation of mechanical properties of poly(L‐lactic acid) braided stents with axial stiffeners

AbstractPoly(l‐lactic acid) (PLLA) has been widely used in constructing biodegradable braided stents due to high biocompatibility and biodegradability. However, poor mechanical properties of this stent are main weaknesses. In this paper, the mechanical properties of PLLA braided stents containing axial stiffeners were evaluated. The stents with stiffener diameters of 0.11, 0.19 and 0.28 mm are named SS11, SS19 and SS28, respectively, and the stent without stiffener is named SS00 as control. The results show that compared with SS00, the bending stiffness of SS11, SS19 and SS28 is increased by 0.77, 1.76, and 2.70 times, respectively. Meanwhile, chronic outward force at an indicated use diameter of 5 mm is increased by 0.83, 0.50, and 0.21 times, but elastic recovery rate is decreased by 5.6%, 14.6%, 22.5%. In addition, radial stiffness of SS11, SS19, and SS28 are increased by 2.81, 2.08 and 1.62 times, respectively. Therefore, the radial support performance is improved and the bending flexibility is weakened by adding stiffeners. Taken together, SS11 can provide sufficient radial support force and low axial force in clinical applications. This study may provide a reference for optimizing the mechanical properties of the biodegradable braided stents.

Simulation of the eigenvalue problem for tapered rotating beams by the modified decomposition method

The modified decomposition method is applied to analyze the transverse vibrations of tapered rotating beams incorporating both axial centrifugal stiffening and flexible end constraints. Unlike prior analyses relying upon a power series expansion about the left end constraint, we instead expand the solution for the transverse deflection about the interval midpoint, which has significant advantages including an increased rate of convergence and readily adaptation to the Robin-type boundary conditions. The modified decomposition method facilitates systematic solution of the mathematical model including parametric simulations where the boundary conditions can be varied without resolving the original equation.

Regional disparity in the axial skeleton of Saurichthyidae and implications for axial regionalization in non‐teleostean actinopterygians

AbstractThe postcranial axial skeleton of actinopterygian fishes is typically divided into three regions: (1) an anterior abdominal region, (2) a posterior caudal region and (3) those vertebrae supporting the caudal fin. However, in some actinopterygians, the axial skeleton is more finely subdivided, with up to six morphologically distinct sub‐regions recognized. Phylogenetic continuity and homology of structures across these sub‐regions have not been investigated in detail, either between or among groups. We examine variation in axial regionalization in saurichthyid fishes, a clade of extinct non‐teleostean actinopterygians with highly variable axial skeletal morphology but an otherwise conservative body plan, and compare these findings to other non‐teleostean actinopterygians to assess conservation of a regionalized axial skeleton within bony fishes. We document up to eight distinct regions in the vertebral column of Triassic Saurichthys: (1) a postoccipital region, (2) an anterior and (3) a posterior abdominal region, (4) a transitional region spanning the abdominal–caudal boundary, (5) an anterior and (6) a posterior caudal region and (7) preural and (8) ural regions. Based on taphonomical and morphological evidence, the transitional region appears to function in axial stiffening in the area of the median fins, whereas the abdominal region is highly flexible. The degree to which these axial regions are osteologically differentiated is highly variable across Saurichthyidae, implying iterative evolution of differentiation and de‐differentiation over relatively short geological timescales. Such variably expressed regionalization was also identified in the outgroup non‐teleostean actinopterygians Birgeria and Australosomus. Despite variation in morphological disparity, the regions identified in saurichthyids correlate well with those documented in some teleosts and Paleozoic actinopterygians, suggesting potential deep patterning homology but independent evolution of specific regionalized axial morphologies in response to changing functional demands.

Fatigue Life Assessment of the Shell Structure of Purified Terephthalic Acid Filter Press.

The filter press is one of the most important devices in purified terephthalic acid (PTA) refinement, and it is of great significance to ensure the fatigue strength of the structure in operation. In this study, the fatigue life prediction of the shell structure of the PTA filter press was investigated through numerical and experimental methods. Firstly, the accurate stress at the critical area of the stiffener was obtained based on the thermomechanical model and submodel approach proposed. Subsequently, the fatigue life was evaluated by the fatigue strength reduction method and hot spot stress method. Finally, the shell structure is optimized by increasing the size of the axial stiffener and continuous hoop stiffener. The results unveil that both thermal load and outer structure constraints have little effect on the radial displacement and stress amplitude of the shell structure. Through modifying the fatigue design curve of the fatigue strength reduction method, the shell structure of the PTA filter press has 42.0% and 0.3% failure probabilities in the previous and present cyclic pressure conditions. Furthermore, the hoop stiffener plays an important role in reducing radial displacement and stress amplitude, among which three hoop stiffeners exhibit the most satisfactory optimization.

On the Effect of Functionally Graded Materials on Resonances of Rotating Beams

Radially rotating beams attached to a rigid stem occur in several important engineering applications. Some examples include helicopter blades, turbine blades and certain aerospace applications. In most studies the beams have been treated as homogeneous. Here, with a goal of system improvement, non-homogeneous beams made of functionally graded materials are explored. The effects on the natural frequencies of the system are investigated. Euler-Bernoulli theory, including an axial stiffening effect and variations of both Young's modulus and density, is employed. An assumed mode approach is utilized, with the modes taken to be beam characteristic orthogonal polynomials. Results are obtained via Rayleigh-Ritz method and are compared for both the homogeneous and non-homogeneous cases. It was found, for example, that allowing Young's modulus and density to vary by approximately 2.15 and 1.15 times, respectively, leads to an increase of 23% in the lowest bending rotating natural frequency of the beam.

MMP12 Deletion Preferentially Attenuates Axial Stiffening of Aging Arteries.

Arterial stiffening is a hallmark of aging, but how aging affects the arterial response to pressure is still not completely understood, especially with regard to specific matrix metalloproteinases (MMPs). Here, we performed biaxial inflation-extension tests on C57BL/6 mice to study the effects of age and MMP12, a major arterial elastase, on arterial biomechanics. Aging from 2 to 24 months leads to both circumferential and axial stiffening with stretch, and these changes are associated with an increased wall thickness, a decreased inner radius-wall thickness ratio, and a decreased in vivo axial stretch. Analysis of in vivo stretch and stress-stretch curves with arteries from age- and sex-matched wild-type (WT) and MMP12-null arteries demonstrates that MMP12 deletion attenuates age-dependent arterial stiffening, mostly in the axial direction. MMP12 deletion also prevents the aging-associated decrease in the in vivo stretch and, in general, leads to an axial mechanics phenotype characteristic of much younger mice. Circumferential arterial mechanics were much less affected by deletion of MMP12. We conclude that the induction of MMP12 during aging preferentially promotes axial arterial stiffening.

Analytical investigation of fiber-orientation dependent stresses in a thick stiffened fiber-reinforced composite beam on simple supports

Fiber orientation dependent stresses in a thick, stiffened composite beam on simple supports are investigated analytically using a scalar potential field expressed in terms of displacement components of plane elasticity. The potential field of the present mixed-boundary-value problem is obtained by solving a single partial differential equation of equilibrium, which is then used to derive the expressions of relevant displacement and stress components in terms of Fourier series. Investigations are carried out for both the cases of lateral and axial stiffeners at the opposing ends of the beam. Two limiting cases of fiber orientation are considered for a number of fiber reinforced composite materials with a wide range of beam aspect ratio. The present analysis verifies the fiber orientation to be one of the important design variables not only for thick beams but also for moderately long beams, especially when the ends of the beam are stiffened.

New Insight to Improve Energy Absorption Characteristics of Long Circular Tubes with Stiffeners as Controllable Energy-dissipating Devices

Long cylindrical tubes exhibit poor energy absorption due to Euler's buckling mode when they are used as energy-dissipating devices. This paper addresses a new structural design solution with the aim to improve crashworthiness characteristics of long cylindrical aluminium tubes. In this connection, axial stiffeners are introduced into the tube to force the plastic deformation which helps to control the buckling mode. A generic static experimental procedure has been performed in the tubes with stiffeners and the load-displacement curves have been analyzed. The results have been compared with the geometrically identical bare tubes. The results revealed that the tubes with stiffeners would offer energy absorption superior to bare tubes under compressive loading situations. Non-linear finite element analyses have also been carried out to explore the static and axial impact response of stiffened tubes (with axial stiffeners) and bare tubes (without stiffeners) using ABAQUS/Explicit©. The numerically predicted crushing force and fold formation are found to be in good agreement with the experimental results. The results revealed that axial stiffeners can stabilize the deformation behaviour and thus the proposed stiffeners could be a good candidate for enhancing the crashworthiness characteristics of the long cylindrical tubes as a controllable energy absorption element.

In Vivo Quantification of the Deformations of the Femoropopliteal Segment

Purpose: To quantify the deformations of the femoropopliteal (FP) segment in patients undergoing endovascular revascularization and to compare the posttreatment deformations caused by primary nitinol stent implantation to those produced by percutaneous transluminal angioplasty (PTA). Methods: Thirty-five patients (mean age 69±10 years; 20 men) scheduled for endovascular therapy were recruited for the study. During endovascular interventions, angiographic images were acquired with the legs straight and with a hip/knee flexion of 20°/70°. Image acquisition was performed before PTA for all patients, after PTA in 17 patients receiving this treatment only, and after primary stent implantation in the remaining 18 patients. A semiautomatic approach was used to reconstruct the 3-dimensional patient-specific artery models from 2-dimensional radiographs. Axial shortening and curvature changes in the arteries in vivo were calculated for the calcified, dilated, and stented regions, as well as the regions that were distal and proximal to the diseased and treated segments. Results: Leg flexion resulted in shortening of the artery in all investigated FP segments. The dilated arteries exhibited greater shortening compared with their stented counterparts (post-PTA 7.6%±4.9%, poststent 3.2%±2.9%; p=0.004). Leg flexion also led to an increase in the curvatures of all the sections of the FP segment. While stented arteries had significantly higher curvature values than PTA within the regions proximal to the treated sections, the choice of the treatment method did not affect the curvature of the other segments. Despite this, 40% of the stented arteries exhibited kinking during leg flexion. Conclusion: The choice of the treatment method affects the postinterventional axial deformations of the FP segment but does not influence the curvature behavior. While PTA results in a more flexible artery, stents restrict the arteries’ shortening capabilities. Depending on the anatomical position of the stents, this axial stiffening of the arteries may lead to chronic kinking, which may cause occlusions and, consequently, affect the long-term success of the procedure.

A Force-Sensing Bipolar Forceps to Quantify Tool–Tissue Interaction Forces in Microsurgery

The ability to exert an appropriate amount of force on brain tissue during surgery is an important component of instrument handling. It allows surgeons to achieve the surgical objective effectively while maintaining a safe level of force in tool–tissue interaction. At the present time, this knowledge, and hence skill, is acquired through experience and is qualitatively conveyed from an expert surgeon to trainees. These forces can be assessed quantitatively by retrofitting surgical tools with sensors, thus providing a mechanism for improved performance and safety of surgery, and enhanced surgical training. This paper presents the development of a force-sensing bipolar forceps, with installation of a sensory system, that is able to measure and record interaction forces between the forceps tips and brain tissue in real time. This research is an extension of a previous research where a bipolar forceps was instrumented to measure dissection and coagulation forces applied in a single direction. Here, a planar forceps with two sets of strain gauges in two orthogonal directions was developed to enable measuring the forces with a higher accuracy. Implementation of two strain gauges allowed compensation of strain values due to deformations of the forceps in other directions (axial stiffening) and provided more accurate forces during microsurgery. An experienced neurosurgeon performed five neurosurgical tasks using the axial setup and repeated the same tasks using the planar device. The experiments were performed on cadaveric brains. Both setups were shown to be capable of measuring real-time interaction forces. Comparing the two setups, under the same experimental condition, indicated that the peak and mean forces quantified by planar forceps were at least 7% and 10% less than those of axial tool, respectively; therefore, utilizing readings of all strain gauges in planar forceps provides more accurate values of both peak and mean forces than axial forceps. Cross-correlation analysis between the two force signals obtained, one from each cadaveric practice, showed a high similarity between the two force signals.

Effect of stiffeners on nonlinear buckling of cylindrical shells with functionally graded coatings under torsional load

Stiffened cylindrical shells are widely used in modern engineering structures, especially in aircraft, oil-transmitting pipeline, spacecraft industry and ocean engineering. Due to the increasing demands for high structures performances, this paper presents the effect of stiffeners on the nonlinear buckling of cylindrical shells with functionally graded (FG) coatings under torsional load. The cylindrical shell is reinforced with external axial stiffeners. The material properties are assumed to vary continuously through the thickness direction. Equilibrium and stability equations for cylindrical shells are derived by using the classical shell theory (CST) with von-Karman nonlinear kinematic relations. Using analytical approach, Galerkin procedure, and the Airy stress function, the resulting equations are employed to obtain the closed-form expression for the critical buckling loads and load–deflection relation. The influences of the number of stiffeners, volume fraction exponent, the thickness of the metal layer, and geometric parameters on the nonlinear buckling behavior of the cylindrical shell with FG coatings are examined in details.

Can a continuous mineral foam explain the stiffening of aged bone tissue? A micromechanical approach to mineral fusion in musculoskeletal tissues

Recent experimental data revealed a stiffening of aged cortical bone tissue, which could not be explained by common multiscale elastic material models. We explain this data by incorporating the role of mineral fusion via a new hierarchical modeling approach exploiting the asymptotic (periodic) homogenization (AH) technique for three-dimensional linear elastic composites. We quantify for the first time the stiffening that is obtained by considering a fused mineral structure in a softer matrix in comparison with a composite having non-fused cubic mineral inclusions. We integrate the AH approach in the Eshelby-based hierarchical mineralized turkey leg tendon model (Tiburtius et al 2014 Biomech. Model. Mechanobiol. 13 1003–23), which can be considered as a base for musculoskeletal mineralized tissue modeling. We model the finest scale compartments, i.e. the extrafibrillar space and the mineralized collagen fibril, by replacing the self-consistent scheme with our AH approach. This way, we perform a parametric analysis at increasing mineral volume fraction, by varying the amount of mineral that is fusing in the axial and transverse tissue directions in both compartments. Our effective stiffness results are in good agreement with those reported for aged human radius and support the argument that the axial stiffening in aged bone tissue is caused by the formation of a continuous mineral foam. Moreover, the proposed theoretical and computational approach supports the design of biomimetic materials which require an overall composite stiffening without increasing the amount of the reinforcing material.

A fully consistent linearized model for vibration analysis of rotating beams in the framework of geometrically exact theory

The equations of motions governing the free vibrations of prismatic slender beams rotating in a plane at constant angular velocity are derived according to a geometrically exact approach. Compared to other modeling methods, additional stiffening terms induced by pre-stress are found in the dynamic equations after fully consistent linearization about the deformed equilibrium configuration. These terms include axial, bending and torsional stiffening effects which arise when second-order generalized strains are retained. It is shown that their contribution becomes relevant at moderate to high angular speeds, where high means that the equilibrium state is subject to strains close to the limit where a physically linear constitutive law still applies. In particular, the importance of the axial stiffening is specifically investigated. The natural frequencies as a function of the angular velocity and other system parameters are computed and compared with benchmark cases available in the literature. Finally, the error on the modal characteristics of the rotating beam is evaluated when the linearization is carried out about the undeformed configuration.

Differential effects of relaxin deficiency on vascular aging in arteries of male mice.

Exogenous treatment with the naturally occurring peptide relaxin increases arterial compliance and reduces vascular stiffness. In contrast, relaxin deficiency reduces the passive compliance of small renal arteries through geometric and compositional vascular remodeling. The role of endogenous relaxin on passive mechanical wall properties in other vascular beds is unknown. Importantly, no studies have investigated the effects of aging in arteries of relaxin-deficient mice. Therefore, we tested the hypothesis that mesenteric and femoral arteries stiffen with aging, and this is exacerbated with relaxin deficiency. Male wild-type (Rln (+/+)) and relaxin knockout (Rln (-/-)) mice were aged to 3, 6, 12, 18, and 23 months. Passive mechanical wall properties were assessed by pressure myography. In both genotypes, there was a significant increase in circumferential stiffening in mesenteric arteries with aging, whereas in the femoral artery, aging reduced volume compliance. This was associated with a reduced ability of the artery to lengthen with aging. The predominant phenotype observed in Rln (-/-) mice was reduced volume compliance in young mice in both mesenteric and femoral arteries. In summary, aging induces circumferential stiffening in mesenteric arteries and axial stiffening in femoral arteries. Passive mechanical wall properties of Rln (-/-) mouse arteries predominantly differ at younger ages compared with Rln (+/+) mice, suggesting that a lack of endogenous relaxin only has a minor effect on vascular aging.

Application of third order shear deformation theory in buckling analysis of 2D-functionally graded cylindrical shell reinforced by axial stiffeners

This paper presents buckling analysis of a two-dimensional functionally graded cylindrical shell reinforced by axial stiffeners (stringer) under combined compressive axial and transverse uniform distributive load. The shell material properties are graded in the direction of thickness and length according to a simple power law distribution in terms of the volume fractions of the constituents. Primarily, the third order shear deformation theory (TSDT) is used to derive the equilibrium and stability equations. Since there is no closed form solution, the numerical differential quadrature method, (DQM), is applied for solving the stability equations. Initially, the obtained results for an isotropic shell using DQM were verified against those given in the literature for simply supported boundary conditions. The effects of load, geometrical and stringer parameters along with FG power index in the various boundary conditions on the critical buckling load have been studied. The study of results confirms that, stringers have significant effects on critical buckling load.