Smooth Transition Zone Research Articles

Experimental assessment of the flexural/shear strengthening effectiveness of new CFRP bars

The potential of a new carbon fibre reinforced polymer (CFRP) bar (CutInov) is explored for the simultaneous flexural and shear strengthening of reinforced concrete (RC) beams. This bar has a stick geometric configuration, with one part applied according to the near surface mounted (NSM) technique and the other according to the embedded through section (ETS) technique, both connected with a smooth transition zone. The NSM part aims to increase the flexural capacity of the RC element, whereas the ETS part, inclined at 45° relative to the RC beam’s axis, aims to provide shear strengthening and to avoid premature end debonding and rip-off failure modes to the NSM part. To avoid premature rupture at the transition zone of this bar, CFRP fan-type anchors are applied in the critical regions of the beam. An experimental programme with almost real-scale RC beams was executed, composed of a reference beam (Ref) and two beams strengthened with CutInov bars, one with (3CI_A) and the other without CFRP anchors (3CI). Compared to the Ref beam, the 3CI beam presented an increase of 55%, 71%, and 79% in terms of load at a deflection corresponding to serviceability limit state conditions, load at yield initiation of the flexural steel reinforcement, and maximum load, while 3CI_A have even developed better indicators, 61%, 95%, and 117%, demonstrating the efficiency of the CFRP anchors.

Phase field modeling and simulation of the evolution of twelve crystallographic martensite variants in austenitic parent grains – three‐dimensional simulations

AbstractDue to its outstanding strength martensitic microstructures are of great importance in steels. Accordingly, this work deals with a simulation model capable of simulating the evolution of the martensitic microstructure. The focus is on the consideration of twelve crystallographic martensite variants corresponding to the Nishiyama‐Wassermann orientation relationship. For this, the phase field method, which regularizes sharp interfaces as smooth transition zone on basis of order parameters is used. The order parameters are used to interpolate between the initial parent phase austenite and the final product phase martensite. The evolution of a martensitic microstructure initiated by a supercooling under isothermal conditions is considered. In order to define the displacive characteristics of the martensite variants, the well‐known phenomenological theory of martensite crystallography is deployed. Three‐dimensional simulations using the finite element method in the small strain context show the applicability of the model to polycrystalline structures.

Multi-Material Wire Arc Additive Manufacturing of low and high alloyed aluminium alloys with in-situ material analysis

In recent years, the interest in the improved functionalisation of Additive Manufacturing components through multi-material solutions has increased because of the new possibilities in product design. In this work, an advanced Wire Arc Additive Manufacturing process for fabrication of multi-material structures of different aluminium alloys was investigated. Mechanical properties such as tensile strength, yield strength, fracture elongation, and hardness were analysed for multi-material parts and compared with the mechanical properties of mono-material parts. It was found that the strength of multi-material components was limited by the properties of the individual aluminium alloys and not by those of the material transition zones. Microsections and EDX line scans revealed a smooth transition zone without any significant defects. Furthermore, process monitoring approaches for quality assurance of the correct material composition in such multi-material structures were investigated. Different sensor data were captured during multi-material Wire Arc Additive Manufacturing to identify and observe various characteristics of the process. It was shown that the voltage, current, acoustic, and spectral emission data can be used for in-situ monitoring to detect the chemical differences between the two aluminium alloys 6060 and 5087. Characteristic patterns in the frequency range were found, which can be attributed to a frequency shift that occurred due to the different material properties. Spectral analysis revealed changes in the ratios of green and blue light emission to red light emission, which was also due to the different magnesium contents.

The improvement of the dynamic behavior of railway bridge transition zone using furnace slag reinforcement: A numerical and experimental study

Transition zones between railway tracks and bridge decks can cause higher dynamic impacts. A solution is smoothly changing the track stiffness by gradually mixing steel furnace slag into the stone ballast. A nominated bridge transition zone is divided into 5 blocks of 7 meters long, with the mixing percentages of 0%, 25%, 50%, 75% and 100%. The mechanical behaviors of furnace slag-ballast combinations (FS-BCs) were studied using experiments of shear strength test, Los Angles abrasion index and plate load test. Furthermore, the dynamic behavior of bridge transition zone with FS-BCs blocks was investigated using a field validated FEM model. Results show that the 100%, 75%, 50% and 25% furnace slag by weight of ballast can increase the shear strength and ballast layer bending modulus by 13%, 12%, 9% and 7% at speed of 300 km/h compared with those of the stone ballast. The FEM study shows that rail deflections are reduced about 20%, 14%, 21% and 16% at speed of 300 km/h corresponding to 100%, 75%, 50% and 25% FS-BCs and accelerations are significantly reduced as well as increasing FS content of each block in bridge transition zone so that a smooth bridge transition zone can be achieved.

Compressive behavior of large rupture strain (LRS) FRP-confined square concrete columns: experimental study and model evaluation

A large rupture strain (LRS) fiber reinforced polymer (FRP), with a rupture strain value of more than 5%, is a promising alternative to traditional FRPs with a 1–3% rupture strain for seismic retrofitting of reinforced concrete (RC) structures. The LRS FRPs provide a bilinear stiffness around concrete columns while this feature is linear for traditional FRPs (e.g., carbon FRP). This paper presents a careful analysis of the compressive behavior of LRS FRP wrapped square column, especially since their confining stress is nonuniformly distributed. A total of 66 square concrete columns, measuring 150 × 150 × 300 mm with varied corner radii from 0 to 75 mm were tested under monotonic axial compression. The experimental results, in terms of full stress–strain behavior, compressive strength, hoop strain distribution, and dilation behavior were systematically investigated. As the corner radius increases, the strength enhancement after LRS FRP confinement also increases, and the hoop strain is more uniformly distributed. The stress–train curves exhibit a triple-section pattern with a smooth transition zone. The peak dilation rate of LRS FRP-confined concrete is higher than that of traditional FRP-confined concrete, and the curve of dilation rate versus axial strain exhibits a remarkably long stable response. Moreover, results show that most existing models of FRP-confined concrete can provide conservative predictions for an improved compressive strength of LRS FRP-confined square concrete columns.

Perfil de velocidad promedio entre una capa de fluido y un medio poroso: La capa límite de Brinkman

It has been mentioned that, the existence of some terms in Darcy's law are the result of the up-scaling method applied to the Stokes flow problem at the pore scale. To address this debate, in this work we perform, at the pore-scale, flow simulations in a free fluid/porous medium system using different models of granular porous media. The local velocity obtained from the Stokes equation allows to obtain the Darcy-scale velocity profiles by a direct averaging instead of using the up-scaled model. The results show the existence of a smooth transition zone in the average velocity profiles near the free fluid/porous medium inter-region. The size and shape of such transition zone depend on the size of the averaging domain and they are a result of averaging local quantities and not a result of solving average equations. In this way, we confirm the existence of an average velocity boundary layer (i.e. Brinkman boundary layer); thus the pertinence of considering other terms in Darcy's law can be certainly justified. We have also determined the extension of the influence of the flow in the free fluid inside the porous medium and the perturbation of the flow in porous medium on the flow in the free fluid.

Transepithelial Topography-Guided Ablation Assisted by Epithelial Thickness Mapping for Treatment of Regression After Myopic Refractive Surgery

To evaluate the outcomes of transepithelial, topography-guided, epithelial mapping-assisted ablation in the treatment of regression after myopic refractive surgery. A retrospective consecutive case series of 70 eyes of 52 patients with regression after previous corneal refractive surgery for treatment of myopic and compound myopic astigmatism underwent re-treatment using transepithelial topography-guided and epithelial mapping-assisted custom ablation with a wide and smooth transition zone design. The ablation profile was based on data from corneal topography, whereas the epithelial ablation depth was decided by corneal epithelial mapping obtained by optical coherence tomography. The mean follow-up time after re-treatment was 13.6 ± 9.4 months (range: 6 to 51 months). At the patients' last follow-up visit, 98.5% and 76.5% had uncorrected distance visual acuity of 20/40 and 20/20 or better. Safety and efficacy indexes were 1.05 and 0.92, respectively. The mean spherical equivalent was reduced from -1.10 ± 0.65 to -0.16 ± 0.34 diopters. Both total root mean square, odd-order, and even-order higher order aberrations improved significantly (P = .021, .040, and .030, respectively), whereas corneal asphericity remained unchanged (P = .662). Epithelial thickness profile showed significant smoothing between the central 2-mm and 2- to 5-mm paracentral areas. Transepithelial topography-guided and epithelial mapping-assisted custom re-treatment with a wide and smooth transition zone design is safe and effective for addressing myopic regression in patients who have previously undergone myopic refractive surgery. [J Refract Surg. 2019;35(8):525-533.].

In Vitro Mimetic Models for the Bone-Cartilage Interface Regeneration.

In embryonic development, pure cartilage structures are in the basis of bone-cartilage interfaces. Despite this fact, the mature bone and cartilage structures can vary greatly in composition and function. Nevertheless, they collaborate in the osteochondral region to create a smooth transition zone that supports the movements and forces resulting from the daily activities. In this sense, all the hierarchical organization is involved in the maintenance and reestablishment of the equilibrium in case of damage. Therefore, this interface has attracted a great deal of interest in order to understand the mechanisms of regeneration or disease progression in osteoarthritis. With that purpose, in vitro tissue models (either static or dynamic) have been studied. Static in vitro tissue models include monocultures, co-cultures, 3D cultures, and ex vivo cultures, mostly cultivated in flat surfaces, while dynamic models involve the use of bioreactors and microfluidic systems. The latter have emerged as alternatives to study the cellular interactions in a more authentic manner over some disadvantages of the static models. The current alternatives of in vitro mimetic models for bone-cartilage interface regeneration are overviewed and discussed herein.

Modeling the evolution of microstructures in finite plasticity

AbstractKochmann and Hackl introduced in [1] a micromechanical model for finite single crystal plasticity. Based on thermodynamic variational principles this model leads to a non‐convex variational problem. Employing the Lagrange functional, an incremental strategy was outlined to model the time‐continuous evolution of a first order laminate microstructure. Although this model provides interesting results on the material point level, due to the global minimization in the evolution equations, the calculation time and numerical instabilities may cause problems when applying this model to macroscopic specimens.In order to avoid these problems, a smooth transition zone between the laminates is introduced to avoid global minimization, which makes the numerical calculations cumbersome compared to the model in [1]. By introducing a smooth viscous transition zone, the dissipation potential and its numerical treatment have to be adapted. We obtain rate‐dependent time‐evolution equations for the internal variables based on variational techniques and show as an example single slip shear. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A variational viscosity-limit approach to the evolution of microstructures in finite crystal plasticity

A micromechanical model for finite single crystal plasticity was introduced by Kochmann & Hackl (2011 Contin. Mech. Thermodyn. 23, 63–85 ( doi:10.1007/s00161-010-0714-5 )). This model is based on thermodynamic variational principles and leads to a non-convex variational problem. Based on the Lagrange functional, an incremental strategy was outlined to model the time-continuous evolution of a first-order laminate microstructure. Although this model provides interesting results on the material point level, owing to the global minimization in the evolution equations, the calculation time and numerical instabilities may cause problems when applying this model to macroscopic specimens. In this paper, a smooth transition zone between the laminates is introduced to avoid global minimization, which makes the numerical calculations cumbersome compared with the model in Kochmann & Hackl. By introducing a smooth viscous transition zone, the dissipation potential and its numerical treatment have to be adapted. We outline rate-dependent time-evolution equations for the internal variables based on variational techniques and show as first examples single-slip shear and tension/compression tests.

Limit shaping formed sections on grading machines

A mathematical model of a smooth transition zone extent, which allows to determine the limit angles hem, to establish continuity technology and perform calculations when designing interstand distance nomenklatura-based grading equipment.

Ultramorphological assessment of dentin-resin interface after use of simplified adhesives.

This study assessed dentin-resin interface integration in Class I cavities restored with simplified adhesives by using a focused ion-beam milling (FIB) and transmission electron microscope (TEM). Class I cavities (1.5-mm depth with dentin thickness of ∼0.5 mm, 4-mm length, and 2-mm width) were prepared on freshly extracted, sound human molars. Two all-in-one adhesive systems (Scotchbond/Single Bond Universal [SUD] and Xeno-V(+) [X5D]) were used and compared with a two-step etch-and-rinse system (Prime&Bond NT [NTD]). The adhesives were applied according to the manufacturers' guidelines. A universal resin composite (Filtek Z350 XT Universal) was used to restore the cavities in one bulk filling and was irradiated at 550 mW/cm(2) for 40 seconds by a quartz-tungsten-halogen light (Optilux 501). After exposure to liquid nitrogen coolant, the specimens were milled to nanoscale thickness by FIB to view and then assess the area of dentin-resin interface by TEM. Unlike the unfilled X5D, a noticeably smooth transition zone at the dentin-resin interface was shown for the SUD and NTD adhesives. The SUD demonstrated an uneven hybrid layer with clearly demineralized collagen bundles. Ultramorphologically, dispersed needlelike apatite crystals were detected within the partially demineralized dentin or the hybrid layer of both compositionally different all-in-one simplified adhesives. Conversely, these crystals were entirely absent from the hybrid layer of the etch-and-rinse NTD adhesive. In the X5D group, a bright band was noted beneath the hybrid layer. The methacryloxydecyl dihydrogen phosphate monomer containing ultramild self-etch adhesive (SUD) was still validated in terms of its capability in dentin adhesion.

The rooting system of Leptophloeum Dawson: New material from the Upper Devonian, Famennian Witpoort Formation of South Africa

The rhizomorphs of Early (Devonian and Early Carboniferous) arborescent lycopsids are known from only a handful of taxa. That of Leptophloeum is previously described from a single fragmentary specimen from China that, in our opinion, has been incorrectly interpreted. Here we describe several relatively well-preserved examples of Leptophloeum rhizomorphs from the Famennian aged Waterloo Farm Lägerstatte of South Africa. We demonstrate an unlobed cormose morphology separated from the microphyll bearing axis by a smooth transition zone. This provides one of the few known examples of a cormose lycopsid rhizomorph dating back to the Devonian. We assign this material and all previously published South African Leptophloeum material to Leptophloeum rhombicum.

Fracture Surface Analysis in Thixojoined Tool Steels

Thixojoining has been developed for D2 and M2 tool steels. The suitable globular microstructure and excellent bonding quality are obtained through this work. Scanning electron microscopy (SEM) observation along the joint interfaces showed a smooth transition zone with no cracks. In addition, fracture surface of the shear test samples showed that the fracture mode was transgranular. Finally, based on obtained results, this method presented high quality joint with nonequilibrium diffusion interface.

A vanishing viscosity approach to the evolution of microstructures in finite plasticity

AbstractMaterial microstructures in finite single‐slip crystal plasticity occur and evolve due to deformation. Their formation is not arbitrary, they tend to form structured spatial patterns. This hints at a universal underlying process. As in the approach of D. Kochmann and K. Hackl, we use a variational framework, focusing on the Lagrange functional to describe the evolving mircrostructure. We modify this approach by introducing a small smooth transition zone between the domains in order to improve the numerical treatment. We present explicit time‐evolution equations for the volume fractions and the internal variables. We outline a numerical scheme. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A New Extension of the Rank Transform for Stereo Matching

Stereo matching methods often use rank transform to deal with image distortions and brightness differences prior to matching but a pixel in the rank transformed image may look more similar to its neighbor, which would cause matching ambiguity. We tackle this problem with two proposals. Firstly, instead of using two values 0 and 1,we increase the discriminative power of the rank transform by using a linear, smooth transition zone between 0 and 1 for intensities that are close together. Secondly, we propose a new Bayesian stereo matching model by not only considering the similarity between left and right image pixels but also considering the ambiguity level of them in their own image independently. We test our algorithm on both intensity and color images with brightnesss differences. Corresponding 2D disparity maps and 3D reconstruction results verify the effectiveness of our method.

Localized amorphism after high-strain-rate deformation in TWIP steel

The microstructural features of shear localization, generated by a high-strain-rate deformation (∼105s−1), of a twinning-induced plasticity (TWIP) steel containing about 17.5wt.% Mn were well characterized by means of optical microscopy, transmission electron microscopy and electron backscatter diffraction. The high deformation rate was obtained by a ballistic impact penetration test on the TWIP steel sheet. In addition to the deformation twins observed as the main microstructural characterization in the matrix, some shear bands consisting of complex microstructures were also evidenced in the highly deformed area. Inside the shear band, there exist a large region of amorphous phase and a smooth transition zone that also contains nanocrystalline phases. The grain size decreases gradually in the transition zone, changing from a coarse scale (>100nm) to a fine scale (<10nm) adjacent to the amorphous region. The coexistence of the amorphous state and the fine-scaled nanocrystalline phase clearly suggests that melting inside the shear bands occurred, which is corroborated by calculations showing a very high rise in temperature due to localized plastic deformation and extremely rapid cooling by heat dissipation into the specimen.

Investigation of the Performance of the Menifocal Z Gas-Permeable Bifocal Contact Lens During Continuous Wear

The Menifocal Z is an alternating vision, concentric, bifocal gas-permeable (GP) contact lens; center distance is connected to near periphery by a smooth transition zone. The lens is produced using tisilfocon A (Menicon Z material), which is approved for up to 30 days of continuous wear (CW). The aim of this study was to evaluate the clinical performance of the Menifocal Z when worn for up to 30 days of CW for 6 months. Thirty-five existing GP lens wearers were enrolled in the study. Subjects were fitted with Menifocal Z lenses and follow-up visits were conducted after 2 weeks of daily wear and 1 day, 1 week, 6 weeks, 3 and 6 months of CW. A range of objective and subjective clinical performance measures were assessed, including distance and near visual acuity, the physiological response to CW, and subjective evaluation of vision and comfort. Twenty-seven subjects (77%) completed the study and eight (23%) discontinued: five (14%) as a result of lens-related problems (four vision, one comfort) and three (9%) as a result of non-lens related reasons. Average CW time achieved by the subjects was 22 +/- 2 days. Mean binocular logarithm of the minimum angle of resolution (logMAR) acuities at 6 months were: high contrast distance 0.03 (20/20-), low contrast distance 0.63 (20/80-), and high contrast near 0.26 (20/25, N4). Adverse responses and lens binding were minimal, and there were no significant increases in corneal staining, corneal vascularization, or superior palpebral conjunctival papillae over time (p > 0.05). Problems with night vision (distance and near) with the lenses were the most common difficulties reported by the subjects. The Menifocal Z appears to be a promising option for presbyopic vision correction, providing successful correction of distance and near vision in a group of experienced GP lens wearers. The hyper Dk tisilfocon A (Menicon Z) material allowed for safe wear of the lenses on a CW basis.

Multiphase computations using sharp and continuous interface techniques for micro-gravity applications

The Eulerian–Lagrangian method is a popular and effective approach for handling multi-fluid problems involving substantial shape variations. Specifically, one can consider the interface either as a sharp discontinuity, consistent with the fundamental continuum theory, or as a smooth transition zone, reducing numerical difficulties in tracking distinct regions. In this article, we highlight the performance characteristics of both techniques. Computationally, both approaches can be devised using similar concepts, namely, the interface is represented by marker points and advected in a Lagrangian framework, and the mass, momentum, and energy conservation equations are solved on a fixed (Eulerian) Cartesian grid using a second-order projection method. The main difference lies in the way of accounting for the interfacial conditions and communication across the interface. The sharp interface method is more demanding computationally because the field equations in each zone need to be coupled with those in other materials/phases, by explicitly tracking the interfacial conditions via matching procedures. In return, second-order accuracy can be attained as compared to the first-order accuracy in the continuous interface method. Nevertheless, in physical applications, both approaches can be highly effective in handling a variety of multi-fluid problems involving moving boundaries. Several examples are presented to highlight the various performance characteristics of the two techniques. To cite this article: W. Shyy, C. R. Mecanique 332 (2004).

Choke-Free Flow in Ovoidal Sewers with Increase in Bed Elevations

The condition of choke-free flow in ovoidal sewers subject to a rise in bed elevation is considered. For a subcritical approach flow with a smooth and gradual transition zone, the maximum limiting rise in bed elevation for ovoidal sewers is determined. Based on a condition of critical flow downstream of the transition zone, the energy and continuity equations are solved numerically to obtain the maximum permissible limits of bed elevation rises and allowable ranges for upstream flow depths. Design graphs are presented for practical use.