Deformation Step Research Articles

Quasi-static compression response of a novel multi-step auxetic honeycomb with tunable transition strain

Auxetic honeycombs with multi-step deformation have received widespread attention due to their multifunctionality and superior mechanical properties. To improve the tunability of the auxetic honeycomb, a novel multi-step auxetic honeycomb (MSAH) is proposed by combining star-rhombic parts with crossed thin walls. MASH is characterized by multi-step deformation, and its stress-strain curve has three significant plateau stages. The strain during the transition between different deformation steps can be adjusted by designing unit cells with different geometrical parameters. In the compression process, the ordered contact of the cell walls of MASH is the critical reason for realizing the multi-step deformation. The quasi-static compression finite element model of MASH is established and verified by experiments. Quasi-static compression response and deformation mechanism of MASH are studied. Then, the effects of geometrical parameters on the compression response of MASH are investigated. The results show that the wall thickness has a greater effect on the compressive stress, and the cell-wall angle determines the deformation mode of MASH. Furthermore, the transition strain of MASH is theoretically analyzed and verified by numerical simulations. This study provides a reference for designing multi-step deformation honeycombs and applying multi-stage energy absorbers.

Symmetric Piecewise Developable Approximations

AbstractWe propose a novel method for generating symmetric piecewise developable approximations for shapes in approximately global reflectional or rotational symmetry. Given a shape and its symmetry constraint, the algorithm contains two crucial steps: (i) a symmetric deformation to achieve a nearly developable model and (ii) a symmetric segmentation aided by the deformed shape. The key to the deformation step is the use of the symmetric implicit neural representations of the shape and the deformation field. A new mesh extraction from the implicit function is introduced to construct a strictly symmetric mesh for the subsequent segmentation. The symmetry constraint is carefully integrated into the partition to achieve the symmetric piecewise developable approximation. We demonstrate the effectiveness of our algorithm over various meshes.

Interaction between inclusions and the TRIP effect during tensile loading of an L-PBF 18Ni-300 maraging steel and effect on ductility

The influence of non-metallic inclusions on the tensile ductility of a direct aged 18Ni300 maraging steel produced by L-BBF was investigated on two materials having the same microstructure and a different content of non-metallic inclusions. The strain-induced transformation of austenite promotes the TRIP effect enhancing ductility. In the presence of a high amount of inclusions, the minimum strain needed to trigger strain-induced transformation is reached after necking, and the transformation cannot contribute to ductility. The effect of inclusions is to promote stress rising and strain accumulation, but mostly to make TRIP uneffective. To recover the effectiveness of TRIP and, in turn, increase ductility, the stability of reverted austenite should be reduced, in order to anticipate its transformation in martensite that is able to extend the uniform deformation step.

Exploring potential energy surfaces to reach saddle points above convex regions.

Saddle points on high-dimensional potential energy surfaces (PES) play a determining role in the activated dynamics of molecules and materials. Building on approaches dating back more than 50 years, many open-ended transition-state search methods have been developed to follow the direction of negative curvature from a local minimum to an adjacent first-order saddle point. Despite the mathematical justification, these methods can display a high failure rate: using small deformation steps, up to 80% of the explorations can end up in a convex region of the PES, where all directions of negative curvature vanish, while if the deformation is aggressive, a similar fraction of attempts lead to saddle points that are not directly connected to the initial minimum. In high-dimension PES, these reproducible failures were thought to only increase the overall computational cost, without having any effect on the methods' capacity to find all saddle points surrounding a minimum. Using activation-relaxation technique nouveau (ARTn), we characterize the nature of the PES around minima, considerably expanding on previous knowledge. We show that convex regions can lie on activation pathways and that not exploring beyond them can introduce significant bias in the saddle-point search. We introduce an efficient approach for traversing the convex regions, almost eliminating exploration failures, while multiplying by almost 10 the number of identified unique and connected saddle points as compared to the standard ARTn, thus underlining the importance of correctly handling convex regions for completeness of saddle point explorations.

An Interface-Preserving Moving Mesh in Multiple Space Dimensions

An interface-preserving moving mesh algorithm in two or higher dimensions is presented. It resolves a moving ( d -1)-dimensional manifold directly within the d -dimensional mesh, which means that the interface is represented by a subset of moving mesh cell-surfaces. The underlying mesh is a conforming simplicial partition that fulfills the Delaunay property. The local remeshing algorithms allow for strong interface deformations. We give a proof that the given algorithms preserve the interface after interface deformation and remeshing steps. Originating from various numerical methods, data is attached cell-wise to the mesh. After each remeshing operation, the interface-preserving moving mesh retains valid data by projecting the data to the new mesh cells. An open source implementation of the moving mesh algorithm is available at Reference [ 1 ].

Rheology of Ti-6Al-4V alloy under non equilibrium conditions during β forging

During the “β-forging” of Ti-6Al-4V structural aircraft components that follows pre-heating above the β-transus, the skin zone of the blank actually cools down to below the β-transus whilst being deformed, as a result of heat losses towards the atmosphere or the dies. The core areas of the bulkiest sections of the blank, however, can be deformed above the β-transus during the whole processing time. This paper focuses on the development of an innovative rheological model to support the numerical modelling of the forging process, suitable for both the equilibrium conditions above the β-transus and the non-equilibrium conditions below. For that purpose, small-scale hot compression tests were performed with the thermomechanical simulator Gleeble 3500, after pre-heating in the β-field of Ti-6Al-4V at 1100 °C and rapid cooling to the compression temperature under the β-transus, which was varied between 750 °C and 950 °C. In some cases, a lag time -or stabilization time- at constant temperature was introduced between the cooling step and the deformation step. Effects of lag time and deformation temperature on microstructural evolutions and rheological properties of Ti-6Al-4V were investigated. Results show that the lack of stabilization time leads to a significant reduction of the flow stress at low strain. Such a behavior is associated with non-equilibrium thermodynamic conditions at the beginning of deformation and the progress of phase transformation during deformation. Based on that observation, an analytical formulation for the targeted rheological model is proposed. It includes a sub-model for the kinetics of phase transformation derived from the literature.

Evolution of Through-Thickness Texture and Microstructure of an ARB-Processed Nb1-Zr Alloy

AbstractThis study investigates the effects of accumulative roll bonding processing on a commercial Nb1Zr alloy. The sheets were subjected to preheating, followed by five reduction cycles. Microstructural evolution was examined through metallography, revealing increasing homogenization of the morphology across the laminate thickness. Microhardness increased from 109 HV to 187 HV in the final laminate due to grain refinement. Electron back-scattered diffraction analysis showed removal of shear strain effects with each deformation step, highlighting microstructural heterogeneity and texture variation. The Goss texture was intensified at the surface during the third cycle, attributed to surface recrystallization. Low-angle grain boundaries were prevalent initially, shifting to a bimodal distribution favoring high-angle grain boundaries with increased deformation, linked to dynamic recovery and recrystallization.

Отклик химических связей никеля на растягивающие деформации кристалла Ni-пиридиндикарбоксамида

We have carried out a theoretic research of plasticity for the coordination and noncovalent bonds modelling uniaxial mechanical deformation of the crystal cell of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide)-nickel (II) dichloride. For this purpose, we have modeled stretching deformation of the crystal structure along its crystallographic axes using the 3-corrected Hartree-Fock method with the following semi-empirical corrections for the weak interactions (the Grimme correction of dispersion interactions, D3, basis set superposition error removal by the atom-pair wise geomet-rical counterpoise correction, gCP, and correction of short-ranged basis set incompleteness effects, SRB) with the use of periodic boundary conditions. We have concluded that the geometry of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide complex has high stability to the increased defor-mations. We have carried out the analysis of the bond lengths and dihedral angels within the metal complex, which has shown insignificant changes of bond lengths, in particular, the bond length change is equal to 4.3 % for N…Ni…N and 5.4 % for Ni…O. The conformation straightening ef-fects of one of the N-butylamine chain has been found under the high stretching deformation of the crystal cell (7–8 Å) due to analysis of dihedral angles and the distance between specific atoms of N-butylamine chain that proves the hypothesis about a forced and twisted conformation state of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide. In addition, we have found the appearance of a cavity and a crack at the last deformation steps (8–10 Å), which is caused by shifts of neighbour-ing metal complexes in relation to each other; it influences the location of chloride ions. It is noteworthy that cavities and cracks are formed regardless of the axis choice along which the ten-sile deformation is modeled. This fact indicates that the crystal should not exhibit elasticity, but rather brittleness.

Analysis of Microstructure Evolution of Co-Cr-Mo Alloy during Isothermal Forging

The article analyzes the microstructure evolution of Co-Cr-Mo alloy during isothermal forging. The process of isothermal forging can be a technological solution to produce a semi-finished product for subsequent deformation processing and obtain a high-quality microstructure that excludes casting defects. Based on analysis of microstructure and phase composition and calculations, the required modes of ingot homogenization are determined. Finite element method simulation of the forging has shown that temperature and deformation conditions make deformation in the single-phase γ-region possible. However, at lower temperatures, σ-phase particles may precipitate at the last steps of deformation. After isothermal forging and water quenching, a mixture of recrystallized and polygonized structures with an average grain size of 5–10 μm and precipitation of ultra-fine dispersed particles of σ-phase (~0.13 μm) at grain boundaries are formed. Isothermal forging in the temperature range of 1100–1200 °C and at low strain rates of up to 1 s−1 allows obtaining a microstructure without pores, cracks, and large inclusions. Thus, it makes it possible to use the forging billet for further deformation by different metal forming methods.

Structure and Properties of High-Strength Cu-7.7Nb Composite Wires under Various Steps of Strain and Annealing Modes

Microstructure and mechanical properties of in situ Cu-7.7Nb microcomposite (MC) wires manufactured by cold drawing with intermediate heat treatment (HT) have been studied. The evolution of Nb filaments morphology under various steps of deformation and modes of intermediate HT have been studied by the SEM and TEM methods. According to X-ray analysis, internal microstresses accumulate in the niobium filaments of the drawn MC, leading to a decrease in ductility. After heat treatment, the ductility of the wire increases significantly, since the microstresses in the niobium decrease even at the lowest HT temperature. The strength of the composite decreases under the HT because of negative changes in morphology and interface density of Nb filaments. The <110>Nb texture is stable under the HT up to 800 °C. The Nb filaments morphology and semi-coherent boundaries at Cu/Nb interfaces are restored under the post-HT cold drawing, leading to a sharp increase in the strength of the MC wire. Reducing the niobium concentration to 7.7%Nb relative to the traditional MC with 16–20%Nb and the recovery of the wire ductility under the HT makes it possible to obtain long-scale high-strength microwires with an extremely small diameter of 0.05 mm and high ultimate tensile strength of 1227 MPa.

Impact of soft magnetic α‐Fe in hard Nd2Fe14B magnetic materials: A micromagnetic study

AbstractThe striving for the independence of fossil energy sources by further development of renewable energies as well as the change in mobility act as a driving force on technological innovations. Magnetic materials with improved magnetic efficiency help to push the limits for optimized, low‐loss power conversion applications and electrification. Besides improving the chemical composition, that is, gaining better performance using alloys reduced or free of heavy rare earth elements, microstructure optimization has proven to be a crucial field of research. In order to better control the grain size, phase distribution and texture of the polycrystalline material, new process routes, such as severe plastic deformation, need to be investigated and explored in addition to the state‐of‐the‐art method – sintering. Here, attention must be paid to the possible formation of soft magnetic α‐Fe after the casting process prior to the actual deformation step, as these secondary phases negatively affect the hysteretic behavior of the magnet. Assistance in the analysis of the underlying magnetic mechanisms is provided by micromagnetic theory. Besides the reliable prediction of the magnetization distribution on micron‐scale, especially in a multi‐phase microstructure, it also allows for the analysis of the magnetic hysteresis behavior. This work provides a micromagnetic simulation frame work based on a finite element scheme. Relying on this framework the effective hysteresis behavior of two different heterogeneous microstructures (Nd2Fe14B and Nd2Fe14B/α‐Fe) are analyzed and compared.

Tectonics of the Western Internal Jura fold-and-thrust belt: 2D kinematic forward modelling

The balancing technique, called 2D kinematic forward modelling, is a powerful tool to understand the kinematic evolution of fold-and-thrust belts. This study presents a new 2D kinematic forward model for the westernmost Internal Jura fold-and-thrust belt (FTB), situated immediately adjacent to the Geneva Basin. The technique used not only provides a new valid balanced cross-section but also offers new insights regarding the kinematic evolution of the Western Internal Jura FTB. Our model proposes a pure thin-skinned style dominated by forward stepping deformation accompanied by minor back-stepping thrust sequences. A first deformation step is attributed to the thrusting of the Crêt de la Neige Anticline, followed by the Crêt Chalam Thrust and its imbrications. This is followed by thrusting along the Tacon and the Bienne thrusts. Imbricate fault-bend folding explains the steep southern limb of the Crêt de la Neige and the Bellecombe anticlines. 2D kinematic forward modelling yields a total amount of shortening by 23.6 km for the Western Internal Jura FTB. In addition to the primary décollement located at the base of the Keuper Group evaporites, three other décollements are found within the marly layers of the Aalenian “faciès de transition” units, the Oxfordian “Couches d’Effingen-Geissberg” members and the Berriasian Goldberg formation. The multiple thrust horizon approach is supported by new precise seismic interpretations. Our model provides a valid alternative to previous models that either propose local thickening of the Triassic evaporites or inversion of normal faults in the basement. This fully explains the elevated position of the Mesozoic cover in the Jura FTB.

Left atrium surface mesh reconstruction from cardiac MRI

Abstract Funding Acknowledgements Type of funding sources: None. Background The strive towards personalised medicine is universal across all aspects of healthcare. In the management of atrial fibrillation (AF), this can take the form of shape analysis tools to predict an individual’s outcome from catheter ablation (1–3), or electrophysiological simulations to plan an ablation strategy (4–6). Fundamental to their application is our ability to derive accurate three-dimensional (3D) anatomical models of a patient’s left atrial geometry from cross-sectional imaging. MRI is widely utilised in this regard due to its excellent tissue characterisation. However, constructing surface meshes can be challenging given its relatively sparse two-dimensional (2D) image planes. A particular challenge exists in producing a mesh that balances concordance with left atrium segmentation and smoothing terms to eliminate sharp edges and artifact from the contouring process. Objective Here, we describe a novel method for left atrium surface mesh reconstruction from MRI contours. Methods Cardiac MRI was performed on ten patients with paroxysmal or persistent AF, on a 3T clinical MR scanner using phased-array receiver coils. Image sequences included respiratory and ECG-gated 15-minute post contrast late gadolinium enhancement, with a 1.3mm slice thickness and in-plane resolution of 0.66×0.66mm2. Seven individuals were in sinus rhythm, and three in AF at the time of MRI. A single, custom, graphical interface tool implemented in Matlab R2014a enabled 3D mesh reconstruction from 2D MRI slices (7,8). Endocardial surfaces of the left atrium were manually segmented by an experienced clinician, with the pulmonary veins and left atrial appendage excluded at their ostia (Figure 1A). Our tool produced an initial sparse representation with vertices equally spaced along the contours (Figure 1B). Attractor points were defined along the contours, with subdivision and Laplacian smoothing applied to the mesh. This was balanced with a deformation step, which iteratively pulled the mesh towards the attractor points (Figure 1C), resulting in its final shape (Figure 1D). Results Reconstruction performance was evaluated by measuring the distance between heart contours and the reconstructed 3D surface for each case, producing the value for average misalignment 0.71 ± 0.58mm, which compares favourably to the in-plane resolution. Conclusions Our approach offers a highly accurate method for producing 3D anatomical models of the left atrium from MRI, which is fully automated following segmentation through an interactive graphical interface. The iterative optimisation between attractor-based deformation towards the original contours and the Laplacian smoothing enables us to create smooth geometries which remain true to their segmentations. Furthermore, our approach does not require the use of a template mesh, which can result in final geometries being biased towards the template.

Thermomechanical treatments for a dual phase cast high entropy alloy

Thermomechanical treatments modify the cast microstructure of a dual phase hypoeutectic high entropy alloy. The as-cast microstructure consists of an FCC matrix and a BCC eutectic phase forming a semi-continuous network. The as-cast material is subjected to various thermomechanical treatments: I) hot compression; II) hot compression with strain rate jumps; III) multi-stage hot compression with intermediate stages of isothermal soaking; IV) hot compression followed by annealing. The material recovers rapidly after the strain rate jump and no dependence of the yield stress on the previous deformation step is observed. Much of the stress relaxation occurs within seconds during the hold for the multi-stage tests. A steady-state stress is reached for the first holding cycle, while progressively slower softening is observed for later holding cycles. The eutectic BCC phase fragments during hot deformation, while discontinuous dynamic recrystallisation associated with the formation of Σ3 occurs in the FCC phase. Precipitates are formed at high temperatures and pin the high-angle grain boundary motion. The rotation of the eutectic BCC phase and the precipitates during plastic deformation also promotes local lattice rotation of the FCC phase. As a result, a fine and intricate substructure is formed in the interdendritic spaces. Complete recrystallisation is not achieved during either hot deformation or annealing, suggesting that practical grain refinement of the investigated alloy would only be achieved at larger strains or a combination of larger deformations and intermediate annealing treatments.

Microstructure refinement of a cast high entropy alloy by thermomechanical treatments

This work investigates the hot compressive behaviour of a cast high entropy alloy. The alloy is subjected to four different thermomechanical treatments to refine the as-cast microstructure: hot compression tests at constant strain rates (0.001s−1 and 1s−1), hot compression tests with strain rate jumps (between 0.001s−1 and 1s−1), multi-stage hot deformation with holding intervals of 1 and 5 min, and hot compression at 0.1s−1 followed by annealing. The three first tests were carried out at 1100 °C and the deformation step of the last type was carried out at 1050 °C followed by annealing at 1150 °C. The deformation at 0.001s−1 promotes dynamic recrystallisation. Dynamic recrystallisation occurs when jumping from 1s−1 to 0.001s−1 and does not occur if the jump is from 0.001s−1 to 1s−1. Multi-stage interrupted tests show that 1 min holding between the stages promote dynamic recrystallisation, while static recrystallisation occurs more pronouncedly for 5 min inter-stage holding. Due to the large initial grain size, deformation does not occur homogeneously within the grains, and heterogeneous static recrystallisation occurs within the deformed specimen. Whether the alloy is solution heat treated or deformed in the as-cast condition does not affect the recrystallisation behaviour. Overall, refining the coarse cast microstructure of the investigated alloy is possible, although more deformation steps are needed to produce a homogeneous microstructure.

Impact strength and fracture behavior of Halloysite nanotube (HNT)-modified carbon fiber-reinforced polymers (CFRPs) based on the electrophoretic dispersion (EPD) process

Because particles that accumulate without movement can lead to a deposition gradient, the formation of a stable suspension is essential for the electrophoretic dispersion (EPD) process. The hydrophobic properties of Halloysite nanotubes (HNTs) were easily dispersed in many nonpolar polymers without further deformation steps. However, the uniform dispersion of HNTs in aqueous solutions is a pre-EPD process task. The zeta potential controls the main parameters of EPD processes, such as the density of deposits, particle orientation and velocity, and repulsive interactions between particles, which determine the stability of the suspension. In this study, the solution stability range for the addition of nanoparticles was measured and the optimal dispersion range was determined. In addition, an HNT-reinforced composite material was created by determining the optimal dispersion stability range of HNT, and the impact strength and fracture mechanism of the interface were analyzed. The solution stability and dispersion were the best between pH 6.6 and 6.8, and the highest impact strength was confirmed at 0.7 wt%. The HNT confirmed the interfacial dispersion of the EPD-fibers using scanning electron microscopy and dispersive X-ray spectroscopy (SEM-EDS).

Reviewing the effect of pyrolysis temperature on the fourier-transform infrared spectra of biochars

Abstract Pyrolysis of feedstocks to produce biochar for soil remediation employed to be a convenient method regarding improvement of soil fertility, increasing carbon stability and decreasing greenhouse gas emissions. Biochar properties and its effect after incorporation into the soils vary depending on the characteristics of feedstocks and pyrolysis process. This paper aims to compare the effect of pyrolysis temperature on the frequency of functional groups in different biochars made from plant feedstocks over the temperature range from 300 °C to 700 °C. An increase in pyrolysis temperature positively affects biochar surface properties until the deformation step in C = O, –COOH, and OH groups and as a result, the surface area of biochar decreases at high temperature (more than 600 °C). The breakdown of hemicellulose, cellulose, and lignin also occurs at temperatures more than 600 °C. Consequently, the biochar quality is reduced with increasing pyrolysis temperature although such biochar may be suitable for rising the content of stable carbon in the soils. Over the long-term, the stability of biochar can contribute to carbon sequestration, retention of water and ions in the soil.

Influence of Processing Route on the Fracture Resistance of Equal Channel Angular Pressing Deformed Iron

The mechanical behavior of pure iron (Armco‐iron) deformed at 200 °C by equal angular channel pressing using processing route BC is investigated with a focus on the fracture properties. In particular, the fracture toughness in terms of elastic–plastic fracture mechanics is evaluated for different specimen orientations with respect to the last deformation step. In addition, the results are comprehensively compared with material processed by route A. The microstructural features of both deformation routes are presented and the underlying microstructure–property relationships are discussed. Both deformation routes (A and BC) lead to a comparable strength even though the microstructural features differ. Route A contains a banded and well‐aligned structure almost parallel to the extrusion direction. For route BC, the microstructural alignment is rotated with respect to the pre‐crack orientation and the grain structure is more heterogeneous. For both deformation routes, the crack plane orientation plays a significant role in the fracture characteristics. The fracture toughness along the extrusion direction, with substantially low fracture toughness for route A, is markedly enhanced for route BC. Consequently, route BC offers a pathway to obtaining severe plastic deformation (SPD) materials with high damage tolerance and a considerably lower extent of anisotropy.

Yield point phenomenon in low-alloyed TRIP-aided steel: role of retained austenite

Multiphase TRIP-aided steels are generally characterised by a continuous yielding behaviour. The processing route involving a deformation step in the intercritical (ferrite + austenite) region showed an undesirable discontinuous yielding. This is attributed to the formation of fresh dislocations in the soft ferrite matrix that trap the diffusing carbon and form Cottrell atmospheres. The discontinuous yielding disappears when fresh mobile dislocations are introduced through transformation of the retained austenite to martensite.

4D-printed bilayer hydrogel with adjustable bending degree for enteroatmospheric fistula closure.

Recently, four-dimensional (4D) shape-morphing structures, which can dynamically change shape over time, have attracted much attention in biomedical manufacturing. The 4D printing has the capacity to fabricate dynamic construction conforming to the natural bending of biological tissues, superior to other manufacturing techniques. In this study, we presented a multi-responsive, flexible, and biocompatible 4D-printed bilayer hydrogel based on acrylamide-acrylic acid/cellulose nanocrystal (AAm-AAc/CNC) network. The first layer was first stretched and then formed reversible coordination with Fe3+ to maintain this pre-stretched length; it was later combined with a second layer. The deformation process was actuated by the reduction of Fe3+ to Fe2+ in the first layer which restored it to its initial length. The deformation condition was to immerse the 4D construct in sodium lactate (LA-Na) and then expose it to ultraviolet (UV) light until maximal deformation was realized. The bending degree of this 4D construct can be programmed by modifying the pre-stretched lengths of the first layer. We explored various deformation steps in simple and complex constructs to verify that the 4D bilayer hydrogel can mimic the curved morphology of the intestines. The bilayer hydrogel can also curve in deionized water due to anisotropic volume change yet the response time and maximum bending degree was inferior to deformation in LA-Na and UV light. Finally, we made a 4D-printed bilayer hydrogel stent to test its closure effect for enteroatmospheric fistulas (EAFs) in vitro and in vivo. The results illustrate that the hydrogel plays a role in the temporary closure of EAFs. This study offers an effective method to produce curved structures and expands the potential applications of 4D printing in biomedical fields.