Longitudinal Compression Research Articles

Stiffness tailoring in sinusoidal lattice structures through passive topology morphing using contact connections

Structures with adaptive stiffness characteristics present an opportunity to meet competing design requirements, thus achieving greater efficiency by the reconfiguration of their topology. Here, the potential of using changes in the topology of planar lattice structures is explored to achieve this desired adaptivity and observe that lattice structures with rectangle-like unit-cells may undergo elastic buckling or bending of cell walls when subject to longitudinal compression. Under sufficient load intensity, cell walls can deform and contact neighbouring cells. This self-contact is harnessed to change the topology of the structure to that of a kagome-like lattice, thereby establishing new load paths, thus enabling enhancement, in a tailored manner, of the effective compressive and shear stiffness of the lattice. Whilst this phenomenon is independent of characteristic length scale, we focus on macroscopic behaviour (lattices of scale ≈ 200 mm). Experimentally observed responses of 3D-printed lattices correlate excellently with finite element analysis and analytical stiffness predictions for pre- and post-contact topologies. The role of key geometric and stiffness parameters in critical regions of the design space is explored through a parametric study. The non-linear responses demonstrated by this topology morphing lattice structure may offer designers a new route to tailor elastic characteristics.

LONGITUDINAL COMPRESSION THERAPY FOR SMALL BOWEL STRICTURE CROHN'S DISEASE: DURABLE RESOLUTION IN SWINE MODEL

Abstract INTRODUCTION Small bowel stricture is common in Crohn’s disease (CD), both de novo and after resection. With all standard treatments having high recurrence rates, CD patients would benefit greatly from a novel and highly durable non-surgical intervention. We report the first long-term study of longitudinal compression therapy (LCT) for the treatment of anastomotic strictures in an animal CD stricture model. LCT entails progressive endoluminal compression of stricture tissue between two flange-like device components. The goal is to gradually bring about necrosis of fibrotic tissue interposed between the two flanges while allowing remodeling with minimal iatrogenic inflammation around the periphery. METHODS Stable anastomotic strictures with hallmarks of CD small bowel strictures were created in 6 pigs, using an established method entailing ileocolonic anastomosis creation with a bypassed ileal segment to maintain patency of the gastrointestinal tract followed by serial injections of phenol/trinitrobenzenesulfonic acid at the anastomosis site. Instead of using LCT devices deployed wholly endoscopically, to best study stricture response to LCT in this model, we used devices with magnetic elements for compressive force generation and integrated ultraminiature sensor arrays for monitoring treatment progression; one 23 mm diameter device component was placed via a surgical enterotomy and a second was deployed endoscopically. Animals were followed for 9 weeks after LCT to gauge post-treatment stricture response. RESULTS LCT device placement was successful in all animals. Five animals reached the 9-week timepoint. One animal was sacrificed on day 12 due to urinary tract complications unrelated to the device. The initial therapeutic response took place over a 3-hour period after device placement, with LCT devices applying increasing force from 3 to 10 Newtons. In endoscopic assessments, widened lumens were noted, with openings 3.3-fold larger at 2 weeks and 3.7-fold larger at 9 weeks. In comparison, for endoscopic balloon dilation in the same animal stricture model, the openings were 2.3-fold larger at 2 weeks, declining to 1.9-fold at 9 weeks. Endoscopic and macroscopic evaluation after euthanasia demonstrated newly patent lumens after excision of stricture tissue, with healthy-appearing mucosa and no macroscopic findings of stricture. CONCLUSION Prior work by our group and others--in animal models and in a small number of treated patients--has provided favorable indications of efficacy of LCT for treating refractory strictures. To the best of our knowledge, this is the first study to include long-term follow-up of LCT in a validated animal model of Crohn’s stricture. This work provides strong preliminary support that LCT’s combination of resection and neo-epithelialization can durably resolve CD stricture. LCT clinical studies are planned as a next step. Design and operation of device systems for longitudinal compression therapy for small bowel stricture in Crohn’s. (a) Longitudinal compression therapy device systems incorporate a dual-flange design, with a mechanism for drawing the flanges together to longitudinally compress the stricture. For single-sided access, expanding flange designs can be used (inset, top left). The LCT device systems used in this study are pairs of discrete non-expanding flange components, with one flange component placed proximal to the strictured region via laparotomy; magnetic elements in the flange components supply the compressive force. This design facilitates incorporation of ultraminiature sensor arrays into the flange components for monitoring stricture response to treatment (inset bottom right). (b)-(d) Steps in longitudinal compressive therapy: (b) advancing the LCT device through the stricture; (c) stricture compression between distal flange and expanded proximal flanges; (d) completion of therapy. Representative result for LCT in the porcine model of Crohn’s small bowel stricture. (a) Before treatment, a length of bowel 15 mm long is badly strictured, with the lumen less than 10 mm at its narrowest point. (b) At 2 weeks after LCT treatment, the narrowest point is markedly larger. (c) At 9 weeks post LCT treatment—a time after which balloon dilated strictures tend to have recurred—the LCT treated stricture is even more open than at 2 weeks post, consistent with the LCT intervention having spurred healing instead of exacerbating fibrosis. Three-dimensional anatomy of strictured segments determined by impedance-based measurement (Endoflip, Medtronic).

Deformation of an electron bunch caused by free-electron lasers

This study reported the longitudinal compression and extension of an electron bunch by free electron laser (FEL) interaction. By observing coherent edge radiation generated by an FEL facility at Kyoto University, which has the highest extraction efficiency of an FEL oscillation, we found that an electron bunch interacting with a cavity-type linac FEL elongated when a detuning length of an optical cavity was positive. The transition from compression to extension of the electron bunch was bounded by a perfect synchronism condition between the electron bunch and the FEL pulse, and the change rate of the root-mean-square bunch length was as high as 14%. Therefore, it was experimentally demonstrated that a slight temporal difference between the electron bunch and the optical pulse dramatically changed not only the FEL power but also the outline of electron distribution in the bunch.

TRIAXIAL STRESS STATE OF CONCRETE UNDER LONGITUDINAL DEFORMATION OF TUBE-CONCRETE SAMPLES

The effects that occur during the transition of concrete to a complex stress state, resulting from the limitation of transverse deformations due to the steel shell, are considered using experimental modeling. The studies were carried out on CFST samples of three standard sizes, as well as on differentiated samples of pure concrete and steel tube. Diagrams of work of samples under longitudinal compression and their comparison are given. The use of CFST structures turns out to be very effective not only as a result of saturation of the supporting structure with material, but due to the mutual influence of the components of the structure on each other. A quantitative assessment and a qualitative justification for increasing the efficiency of the concrete core as part of a CFST element are given. It is shown that the increase in the bearing capacity of the sample due to the reinforcement of a simple tube with concrete is several times higher than the differentiated bearing capacity of the concrete core. This fact makes it possible to consider CFST structures as composite ones with a non-linear increase in strength due to the joint work of the system components. The transition of specimens to the plastic state of tube-concrete specimens occurs at the same values of longitudinal deformation as for hollow steel tubes, but at high load values. The effects that occur in concrete under the influence of a steel shell create a triaxial stress state, which makes it possible to multiply the bearing capacity of any brittle material. It is shown that concrete under conditions of such a stressed state behaves rather like an amorphous material, does not collapse at all stages of deformation, and there are practically no processes of crack initiation and its propagation in concrete.

Реконструкция развития соляных структур Верхнекамского месторождения солей

The article highlights some issues of geology and genesis of structural forms of the Verkhnekamskoye Salt Deposit (Perm krai). On the example of the Popovskiy salt dome location, the results of detailed studies and analysis of data on the geological structure of sedimentary strata and their morphology are presented. The reconstruction of the evolution of salt structures, the uplifts and depressions was carried out. The main factors and mechanisms, which controlled the development of a modern tectonic structure of this territory, were determined. Significant role in formation of the modern tectonic features of the upper part of the sedimentary cover played the accumulation in the Kungurian age of the Permian the ductile salt rocks, which, at the Late Paleozoic - Early Mesozoic subsequent stages of the territory evolution, determined the increased tectonic mobility of salt and supra-salt deposits, and the formation of high-amplitude uplifts and basins. Differences in tectonogenesis of the upper part of the sedimentary cover, comprising the ductile salt-bearing strata and the underlying rigid rocks, led to the division of the sedimentary cover of the Solikamskaya depression of the Cis-Ural trough into two tectonic stages. The lower level includes uplifts representing the draping structures of the Fransian-Tournaisian reef massifs and brachianticline folds of longitudinal compression, and the upper level comptises the structures formed as a result of the halokinesis of plastic rocks.

Rheological properties magnetically elastic material samples under extreme compression modes

The magnetoelastic material samples in compression tests are investigated. The studied materials rheological properties are carried out on an automated testing machine. Compressive moduli changes diagrams depending on deformation values up to limiting extreme values are plotted. Transition ranges from linear to nonlinear, longitudinal compression moduli, depending on the specimen compression degree, were fixed. Repeated tests on specimens showed a decrease in the compression moduli by several times. In revealing rheological properties the investigated materials shape memory effect is demonstrated.

Exploring the structure-property relations of thin-walled, 2D extruded lattices using neural networks

This paper investigates the structure–property relations of thin-walled lattices, characterized by their cross-sections and heights, under dynamic longitudinal compression. These relations elucidate the interactions of different geometric features of a design on mechanical response, including energy absorption. We proposed a combinatorial, key-based design system to generate different lattice designs and used the finite element method to simulate their response with the Johnson–Cook material model. Using an autoencoder, we encoded the cross-sectional images of the lattices into latent design feature vectors, which were supplied to the neural network model to generate predictions. The trained models can accurately predict lattice energy absorption curves in the key-based design system and can be extended to new designs outside of the system via transfer learning.

Mechanism of short pitch rail corrugation: initial excitation and frequency selection for consistent initiation and growth

ABSTRACT This paper proposes a new hypothesis for the formation process of short pitch rail corrugation. An FE wheel-track dynamic model is utilized to verify the hypothesis by reproducing corrugation initiation and consistent growth. It is found longitudinal compression modes are responsible for corrugation initiation with necessary initial excitation that allows flexibility for longitudinal vibration. Consistency between longitudinal compression and vertical bending eigenfrequencies of the wheel-track system is required for consistent corrugation growth, which also determines maximum corrugation amplitude. Corrugation initiates by frequency selection instead of wavelength fixing. The proposed mechanism can explain field observations including the wavelength and periodicity of corrugation in the Netherlands, why corrugation forms on continuously-supported tracks where pinned-pinned resonance does not exist, and the small variation between the corrugation wavelength and train speed.

Collision characteristics of the intermediate coupler of a rail vehicle

Suppose the intermediate coupler of a rail vehicle is unstable during the collision process and loses its connection and energy dissipation functions. In that case, it will significantly reduce the performance of the train crashworthiness function and increase the risk of train derailment. This paper aims to establish a refined finite element model (RFEM) that can simulate the buckling behaviour and investigate the bending resistance and buckling instability characteristics of the intermediate coupler, and the accuracy of the RFEM was verified by quoting the results of an existing intermediate coupler impact test. The results demonstrated that the proposed coupler modelling method could better simulate the energy absorption characteristics and unstable behaviour. Compared to the test results, the differences in the initial crushing force, maximum longitudinal compression displacement, minimum crushing force, and maximum crushing force were 6.5%, 1.3%, 3.6%, and 6.5%, respectively. Within the allowable range of parameters, the maximum bending force linearly increased with an increase in the initial longitudinal compression displacement. As the pitch or yaw angle increased, the longitudinal buckling load of the coupler linearly decreased and became more sensitive to the pitch angle. When pitch and yaw angles existed simultaneously, the longitudinal buckling load was further reduced.

Short pitch corrugation mitigation by rail constraint design

Short pitch corrugation is a quasi-periodic rail defect that induces a high level of noise and accelerates track degradation. This paper proposes a methodology to mitigate short pitch corrugation by rail constraint design, including four steps. In Step 1, corrugation is numerically reproduced by employing a three-dimensional (3D) finite element (FE) vehicle-track model with degraded fastenings. In Step 2, the corrugation initiation mechanism is identified by the operating deflection shapes (ODSs) approach. In Step 3, different types of rail constraints are designed and their effects on rail vibration modes are analysed. Then FE models of these rail constraints are built up and validated. In Step 4, rail constraint models from Step 3 are applied to the 3D FE vehicle-track interaction model and their effectiveness on corrugation mitigation is evaluated. The results indicate rail longitudinal compression modes and the induced longitudinal dynamic contact force dominate the initial differential wear and corrugation initiation. Based on this mechanism, a new rail constraint is designed in this work that can completely suppress longitudinal compression modes and significantly reduce the fluctuation amplitude of the longitudinal contact force so that corrugation can hardly initiate. This paper first points out a direction for field corrugation mitigation by strengthening the rail longitudinal constraint.

Efficiency of cavity dissolution in rock salt by water submerged jets

To create cavities when dissolving rock salt, it is most expedient to supply the solvent through the nozzles of a perforated pipe in the form of submerged jets. This article examines the physical dissolution of a cavity with water from a stationary nozzle with a diameter of 0.004 m at two constant velocities at the nozzle cross-section. The efficiency of cavity dissolution, which has an almost cylindrical shape with a semi-cylindrical bottom, was analyzed at a nozzle cross-section speed of 8.85 m/s. The obtained results are explained on the basis of the fact that the formed cavity is a short dead-end channel where longitudinal compression acts. The flow in such a channel is caused by the back pressure exerted by its end. And the back pressure, in turn, hinders the development of the jet that flows out of the stationary nozzle, limiting its range. The cessation of significant expansion of the jet is indirectly confirmed by the use of an empirical formula for the distribution of the maximum water velocity along the axis of the jet. Its value at the end of the section of the most intense dissolution of the cavity becomes 8.85 times smaller compared to the speed at the nozzle cross-section. The boundaries of the area of the most intense dissolution of the cavity are determined by the relationship between the depth of the cavity, the diameter of the nozzle, the velocity at its cross-section, and the time of dissolution, which can be used to model the dissolution of cavities at different values of the velocity at the cross-section of the nozzle at its constant diameter. It was found that the relationship between the radius and depth of the cavity is linear. The angle between the boundary of the cavity size change and the axis of the nozzle is 20°23'. These results show that the dissolution of cavities is effective in a limited range of their dissolution time, the limits of which depend on the velocity of the solvent at the nozzle section. To confirm the obtained results, it is necessary to investigate the geometric characteristics of the cavities for other values of the nozzle diameters.

Splitting failure of a composite under longitudinal tension

AbstractSignificant variation can be found in measurements for the longitudinal tensile strength of the same unidirectional (UD) composite. A splitting failure is one of the main reasons. It is shown in this paper that the shear stress component resulted from a longitudinal tension and a fiber misalignment can cause the matrix to fail before fiber break. The misalignment angle consists of an initial off‐axial angle and a further fiber rotation during the loading. Based on the micromechanics Bridging Model and the matrix true stress theory established by the author, splitting failure has been analyzed and predicted rigorously in this paper, only using the fiber and matrix properties together with the fiber misalignment angle. The fiber initial misalignment angle of a unidirectional plate can be obtained from testing statistics, or deducing from measured longitudinal compression strength. Our research indicates that the longitudinal tensile strength and the relevant failure mode can be significantly affected by the fiber initial misalignment.

Kinematic indicators in Riphean carbonate rocks of the Siberian Platform Western framing (on the example of the Alad’inskaya Formation)

Introduction. New data on the structure of sections of the Middle Riphean Alad’inskaya Formation at the Kamenskaya subzone of the Yenisei Range (r. Irkineeva) were obtained. These sections indicate the tectonic nature of brecciated and banded dolomite varieties with the associated areas of cavern development, representing promising objects of oil and gas exploration works.Aim. To substantiate the tectonic nature and structural confinement of cavern development areas in dolomites of the Alad’inskaya Formation.Materials and methods. The sections of Alad’inskaya Formation carbonates, located along the Irkineeva river, were studied, including determination of the sample phase composition by the X-ray diffraction method (ARL X’TRA) and examination of samples in sections (Leica DMLR) and by a scanning electron microscope (TESCAN VEGA 3 LMH). Kinematic indicators were studied and classified; a model of structural formation in carbonate rocks was substantiated.Results. A detailed layer-wise description of the studied section, illustrated by various-scale images, was carried out. The kinematic indicators of specified rocks with a reference to a particular section were revealed, described and systematized. A conclusion is made about the genetic association of dolomite breccia, banded dolomites, and cavern development areas with a local thrust, observed at the base of the studied section.Conclusion. The tectonic nature of brecciated and banded dolomites of the Alad’inskaya Formation and the structural control of cavern development areas are substantiated. As a result, the model of structural formation in lamellar carbonates under longitudinal compression is verified.

Creep and post-creep mechanical properties of reinforced concrete columns

In this study, 32 groups of reinforced concrete axial compression columns were examined using creep tests and axial compression failure tests after creep. The reinforced concrete columns were of strength grade C30–C60, load level 0.09–0.38, and total reinforcement ratio 0.79–2.01%. This study investigated the effects of the axial compressive strength of concrete under loading, the load level, and the total reinforcement ratio of longitudinal compression steel bars on the creep and post-creep mechanical properties of reinforced concrete short columns under axial compression. A formula for calculating the creep of reinforced concrete short columns under axial compression is proposed. A formula for calculating the peak compressive strain of reinforced concrete short columns under axial compression considering the effect of creep is established.

Formation and propagation of buckles in coilable cylindrical thin shells with a thickness discontinuity

This paper studies the snap-through buckling that occurs ahead of the coiled region in thin, linear-elastic, isotropic coilable cylindrical shells with a sudden change in the thickness of the shell cross section. The study is focused on Triangular Rollable And Collapsible (TRAC) booms. It is shown that coiling of these shells leads to longitudinal compression of the inner flange mid-surface, which in turn leads to the formation of a buckle in the transition region between the fully coiled and fully deployed parts of the inner flange. This buckle grows to reach a steady-state configuration and is then pushed along the shell without changing its shape when the shell is coiled.

Build orientation optimization of additive manufactured parts for better mechanical performance by utilizing the principal stress directions

As Additive Manufacturing technology is excellent for the production of function-based optimized parts. By choosing the right printing orientation, the dimensional accuracy and surface quality of the parts can be improved. But also possible to achieve improvement of the mechanical properties by the proper orientation. An algorithm has been developed, which can determine the optimal build orientation based on a numerical simulation for a given load case. The adverse and favourable load directions can be defined according to the layer's position by knowing the anisotropic behavior of the printed parts. The optimal print orientation has been found for four investigated geometries, according to the No-Preference and Weighted Sum multiple-objective optimization methods, and therefore the expected mechanical performance was increased. The algorithm was able to reduce the amount of unfavourable stresses by 100 % for simple beam geometries with longitudinal tensile and compression loads, while the more complex geometries were improved to the best possible extent.

Fiber arrangement endow compression resistance of the mantis shrimp hammer-like appendage

For engineering materials, it is important to search for strategies to enhance certain combinations of mechanical properties, because many performances, such as strength and toughness, are mutually exclusive. Effective strategies have evolved in the biological tissues of many plants and animals to construct composite materials with unique combinations of mechanical properties. One impressive example is found in the hammer-like appendages of mantis shrimp, which are exceptionally resistant to crushing because they must withstand the reaction forces created when attacking prey. In this paper, quasi-static compression tests, advanced microscopic observation, and spectroscopic analysis were employed to identify a series of characteristic changes, including changes in mineral composition and arrangement of chitin fibers, and the resulting toughening mechanisms are also examined. The combination of experiments and finite element analysis revealed that by combining different fiber arrangements and components in adjacent macroscopic layers, longitudinal stress could be shifted to the lateral direction, hence efficiently enhancing longitudinal compression resistance while avoiding catastrophic failure. Overall, these findings further the understanding of the fiber structure and toughening mechanism of appendages, which may serve as a foundation for the development of tough bioinspired composites.

Buckling resistance of longitudinally stiffened panels with closed stiffeners under direct longitudinal stresses

AbstractThe buckling behaviour of panels may be determined according to EN 1993‐1‐5 [1]. Most of the design rules relating to stiffened panels in EN 1993‐1‐5 were derived on the basis of open‐section stiffeners. Several recent investigations have shown that the application of the design rules according to EN 1993‐1‐5 considering the torsional stiffness of the stiffeners may overestimate the resistance of the panels. Therefore, the recent Amendment A2 to EN 1993‐1‐5 states that the torsional stiffness of stiffeners should generally be neglected in determining critical plate buckling stresses. In addition, prEN 1993‐1‐5 [2] provides rules for considering the torsional stiffness of stiffeners. However, in this article it is shown that even the rules of prEN 1993‐1‐5 are not sufficient to overcome the safety deficiencies. The article focuses on the investigation of the buckling behaviour of stiffened panels with closed‐section stiffeners subjected to constant longitudinal compression stresses. Improved rules have been developed that allow to consider the torsional stiffness of the stiffeners. Based on an extensive numerical parametric study, a new interpolation equation between column‐ and plate‐like behaviour is proposed. In comparison to [3], the investigations have been extended to the effective width method. They show that the proposal provides a safe and economic solution for the reduced stress method and the effective width method when considering the torsional stiffness of stiffeners by calculating the critical plate buckling stresses.

Dynamic deformability of oblique sections of compressed reinforced concrete beams on yielding supports

Due to the growing possibility of the likelihood of dynamic loads on buildings from natural and man-made emergency situations, it is necessary to design reinforced concrete structures resistant to such impacts. The aim of this work is to study effective methods of the structure protection such as yielding supports and longitudinal compression, deformability of oblique sections of reinforced concrete structures under compression and bending. The paper proposes the experimental methodology. It is shown that time of the structural resistance significantly increases with decreasing stiffness of yielding supports. When the longitudinal compression grows, deformation of transverse reinforcement reduces in the structure. It is demonstrated that the use of elastoplastic yielding supports reduces deformation of transverse reinforcement as compared to rigid supports.

A facile 3D bio-fabrication of customized tubular scaffolds using solvent-based extrusion printing for tissue-engineered tracheal grafts.

Tracheal implantation remains a major therapeutic challenge due to the unavailability of donors and the lack of biomimetic tubular grafts. Fabrication of biomimetic tracheal scaffolds of suitable materials with matched rigidity, enhanced flexibility and biocompatibility has been a major challenge in the field of tracheal reconstruction. In this study, customized tubular grafts made up of FDA-approved polycaprolactone ( ) and polyurethane ( ) were fabricated using a novel solvent-based extrusion 3D printing. The printed scaffolds were investigated by various physical, thermal, and mechanical characterizations such as contact angle measurement, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), radial compression, longitudinal compression, and cyclic radial compression. In this study, the native goat trachea was used as a reference for the fabrication of different types of scaffolds (cylindrical, bellow-shaped, and spiral-shaped). The mechanical properties of the goat trachea were also compared to find suitable formulations of . Spiral-shaped scaffolds were found to be an ideal shape based on longitudinal compression and torsion load maintaining clear patency. To check the long-term implantation, in vitro degradation test was performed for all the 3D printed scaffolds and it was found that blending of with reduced the degradation behavior. The printed scaffolds were further evaluated for biocompatibility assay, live/dead assay, and cell adhesion assay using bone marrow-derived human mesenchymal stem cells (hMSCs). From biomechanical and biological assessments, of spiral-shaped scaffolds could be a suitable candidate for the development of tracheal regenerative applications.