Subsequent Bending Research Articles

Disappearing and reappearing of structure order in colloidal photonic crystals.

Mechanoresponsive colloidal photonic crystals embedded in elastic solid matrices exhibit tunable optical properties under mechanical force, showing great potential for various applications. However, the response of colloidal crystals embedded in a liquid matrix remains largely unexplored. In this study, we investigate the structural and optical transitions of colloidal crystals composed of particles suspended in a liquid oligomer under pressing and shear forces. We observe that pressing induces a transition from an ordered to a disordered particle arrangement, while subsequent bending shear, such as simple hand-flipping, restores the ordered structure. This reversible transition produces press-induced optical traces that can be erased by subsequent shear, making this material a promising candidate for applications in reversible direct-writing photonic paper and anti-counterfeiting technologies. Our work provides new insights into the structural dynamics of liquid colloidal photonic crystals under mechanical force and highlights their potential for mechanoresponsive applications.

Anisotropy and Temperature Dependence of Annealing During Mechanical Bending in Ni-Mn-Ga-Based Melt-Spun Ribbons

AbstractMechanical response during bending experiments of Ni-Mn-Ga-Co-Cu melt-spun ribbons with the L21 austenite structure was studied. This material exhibited anisotropy in mechanical properties depending on the side to which the applied bending force was directed. When force was applied to the “free side,” a substantial load drop was observed in the initial stage of bending. On the other hand, no load drop anomalies were observed when force was applied to the “wheel side.” Additionally, mechanical training effects were assessed by applying up to 10 bending cycles. It was demonstrated that with an increase in the number of bending cycles, there was no significant decrease in bending force, and the load–displacement curve remained unaltered. The temperature dependence of annealing of the ribbons' mechanical properties was also examined. The Ni-Mn-Ga-Co-Cu melt-spun ribbons were annealed at 373 K, 573 K, 773 K, 973 K, and 1173 K for 30 min, followed by subsequent bending tests. Annealing influenced bending response through two major phenomena detected. The first was associated with crystal structure ordering and recovery; while, the second was attributed to grain growth. Changes in mechanical properties influenced by different annealing temperatures were correlated with alterations in the microstructure of the studied ribbons.

RSM applied to lattice patterns for stiffness optimization

PurposeIn this study, response surface methodology (RSM) is applied to a three-point bending stiffness analysis of low-cost material (PLA) specimens printed using FDM technology to analyze the performance of different internal lattice structures (Octet and IsoTruss principally). The purpose of this study is to extend the definition from a discrete (lattice) model to an analytical one for its use in subsequent design phases, capable of optimizing the type of cell to be used and its defining parameters to find the best stiffness-to-weight ratio.Design/methodology/approachThe representative function of their mechanical behavior is extrapolated through a two-variable polynomial model based on the cell size and the thickness of the beam elements characterizing it. The polynomial is obtained thanks to several tests performed according to the scheme of RSM. An analysis on the estimation errors due to discontinuities in the physical specimens is also conducted. Physical tests applied to the specimens showed some divergences from the virtual (ideal) behavior of the specimens.FindingsThe study allowed to validate the RSM models proposed to predict the behavior of the system as the size, thickness and type of cells vary. Changes in stiffness and weight of specimens follow linear and quadratic models, respectively. This generally allows to find optimal design points where the stiffness-to-weight ratio is at its highest.Originality/valueAlthough the literature provides numerous references to studies characterizing and parameterizing lattice structures, the industrial/practical applications concerning lattice structures are often still detached from theoretical research and limited to achieving functioning models rather than optimal ones. The approach here described is also aimed at overcoming this limitation. The software used for the design is nTop. Subsequent three-point bending tests have validated the reliability of the model derived from the method’s application.

Characterization of resistance welded hybrid sandwich sheets with additively manufactured core structure

Abstract Production of additively manufactured sandwich sheets is limited to small sizes. In the new introduced process route, additively manufactured core structures are joined with rolled face sheets by resistance welding, and the formability of the hybrid sandwich sheets is investigated. The necessity of developing the humps to improve the quality of resistance welding is initially investigated. Two different core structures, namely honeycomb and hollow sphere, are selected, and electrical-thermal coupled simulations with the ABAQUS software are performed to study the temperature distribution during resistance welding without and with hump. The strength of the joints for the fabricated sandwich sheets is verified by a quasi-static shear test. It is experimentally proven that the sandwich sheets without a hump in the core structure are not fully joined, and desired temperature localization is possible only by applying the hump. This is because the hump reduces the contact area, which leads to an increase in current density at the point where the resistance ratios are changed. This leads to higher temperatures in the intended joining zone. Different hump geometries for the core structure are designed, fabricated, and joined to the face sheets under different process parameters. The spot contact yields up to 50% higher shear strength than the linear or area contact. The free air bending results show that the double weld is essential for successful subsequent bending. It is also concluded that increasing the resistance welding time by more than 120 ms does not affect the joining strength of hybrid sheets.

Silicon carbide ceramics formed by binder jetting: A study focusing on the printing layer thickness and the PIP densification process

Binder jetting (BJ) additive manufacturing has the advantages of high precision, fast forming speed, and no need for supporting structure, which is especially suitable for the forming of metallic and ceramic components with complex structures. In this paper, SiC ceramic parts were obtained by BJ additive manufacturing and precursor impregnation pyrolysis (PIP) cycles. It has been observed that the thickness of the printing layer significantly affects the strength of the SiC green body. The SiC green body exhibited the highest bending strength (3.1 ± 0.2 MPa) and lower dimensional deviation (0.47–1.64 %) when printed with a layer thickness of 50 μm. However, the bending strength of the SiC ceramics (after densification) had little variations when different printing layer thicknesses were utilized. In the subsequent densification process, the density, hardness, and bending strength of SiC ceramics increase as the number of PIP cycles increases obviously, and the flexural strength reached 228.7 ± 14.2 MPa after 9 PIP cycles, while the shrinkage rates in the X, Y, and Z direction were 1.9 %, 2.8 %, and 1.2 %, respectively. In addition, the influence mechanism of printing parameters on the strengths of the green bodies and SiC ceramics was also discussed. Specifically, it was found that with the layer thickness increase, the strengths of SiC ceramics also increase.

Moderate magnitude clockwise rotation of the Yunlong Basin: Implications for synchronous Eocene rotation of the southeastern Tibetan Plateau

Abstract The clockwise rotation and southeastward extrusion of the southeastern Tibetan Plateau have played important roles in accommodating the uplift and deformation of the plateau. Numerous paleomagnetic studies have suggested post–late Eocene clockwise rotation of the southeastern Tibetan Plateau along the eastern Himalaya syntaxis, whereas few researchers have addressed the specific Eocene deformation, leading to ambiguous interpretations of the tectonic evolution in the region. Herein, we conducted a paleomagnetic study of the Yunlong Formation in the Yunlong Basin, which is Late Cretaceous to early Paleocene in age. In total, 386 oriented samples were collected. Rock magnetic, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analyses revealed detrital carriers, such as hematite and some magnetite. In thermal demagnetization processes, 332 characteristic remanent magnetizations were isolated, which yielded positive reversals and tilt tests, providing a site-mean direction of declination (Ds) = 56.0° ± 2.6°, inclination (Is) = 34.3° ± 3.8°, α95 = 2.7°, k = 91.0, and N = 31 after tilt correction. Magnetostratigraphic analysis was performed, and a depositional age of 79–61 Ma for the section was obtained, which is consistent with the previous paleontological and detrital zircon ages. Compared with the Eurasia reference pole of the period, the data revealed a 45.2° ± 5.1° clockwise rotation of the Yunlong area since 79–61 Ma. The integrated regional paleomagnetic results suggest the occurrence of ~20° of clockwise rotation of the Lanping-Simao terrane during the Eocene, which is similar (in terms of magnitude and time of occurrence) to that of the Gonjo Basin in the eastern Qiangtang terrane. Integrated with other lines of geologic evidence, we propose a new deformation model in which the entire southeastern Tibetan Plateau experienced ~20° of rigid clockwise rotation during the Eocene, followed by subsequent oroclinal bending.

The impact of post-cutoff bend curvature on channel kinematics in meandering rivers: an example from the Trinity River, Texas, USA

Abstract Neck and chute cutoffs along meandering rivers are near-instantaneous morphodynamic perturbations that drive modification of planform channel geometry and kinematics at the cutoff site and in adjacent bends. Despite their ubiquity, quantitative and predictive linkages between post-cutoff planform bend geometry and subsequent bend kinematics remain limited. Here, using a 37-year record of Landsat-derived river channel centrelines from a meandering reach of the Trinity River in Texas (USA) and a newly developed directed graph-based approach for high-resolution channel tracking, we identify a linkage between post-cutoff bend curvature and the magnitude, spatial extent, and temporal duration of cutoff influence on local and non-local channel bend kinematics. We further explore this relationship using a kinematic model of meandering applied to synthetically generated river reaches and the Landsat-derived Trinity River centrelines. While the model captures the observed linkages between post-cutoff bend curvature and resultant bend kinematics, it underpredicts the magnitude of cutoff influence observed in the real centreline data – particularly at the cutoff site – by up to one order of magnitude. Our results provide a promising advance in the characterization and prediction of the spatiotemporal impact of cutoffs on local and non-local post-cutoff channel bend kinematics.

ВСТАНОВЛЕННЯ ВПЛИВУ ПАРАМЕТРІВ ПРЕСУВАННЯ НА ПРОЦЕС ГНУТТЯ БУКОВИХ МЕБЛЕВИХ ЗАГОТОВОК

It is substantiated that the technology of cold bending of pre-pressed blanks has a perspective. It was established that the minimum bending radius depends on the direction of pressing and the degree of pressing. It was determined that pressing in the radial and tangential directions does not give the desired effect during bending, which is evidenced by a large number of defects (respectively 47-67% and 34-61%) associated with the specific structure of the wood. In particular, during pressing, the wood cells are deformed along the pressing line, and during subsequent bending, the elongation of the wood in the peripheral part passes across the pressing line and is only partially compensated by the pressed cell walls. It was experimentally established that the results are significantly different when the workpieces are axially pressed. When the degree of pressing is increased from 15 to 25%, the number of high-quality blanks increases and amounts to 83-97%, respectively. This can be explained by the fact that during axial pressing, wood cells are deformed along the line of pressing. During subsequent bending, the elongation of the wood in the peripheral part also takes place along the line of pressing and is compensated to a much greater extent by the pressed cell walls. It was found that when the workpieces are pressed along the axis, uneven pressing along the length occurs, that is, only approximately half of the length of the workpiece is pressed. This is probably the main reason for the defect. Additional research and possibly new technological solutions are needed to solve the problem of uneven pressing during axial pressing. Prospective directions of research into bending processes of beech furniture blanks have been formed, in particular from the development of new bending technologies; optimization of pressing parameters; modeling of bending processes; study of the influence of humidity and temperature; study of the strength and durability of bent blanks.

Flexural rigidity of pressurized model notochords in regular packing patterns

The biomechanics of embryonic notochords are studied using an elastic membrane model. An initial study varying internal pressure and stiffness ratio determines tension and geometric ratios as a function of internal pressure, membrane stiffness ratio, and cell packing pattern. A subsequent three-point bending study determines flexural rigidity as a function of internal pressure, configuration, and orientation. Flexural rigidity is found to be independent of membrane stiffness ratio. Controlling for number and volume of cells and their internal pressure, the eccentric staircase pattern of cell packing has more than double the flexural rigidity of the radially symmetric bamboo pattern. Moreover, the eccentric staircase pattern is found to be more than twice as stiff in lateral bending than in dorsoventral bending. This suggests a mechanical advantage to the eccentric WT staircase pattern of the embryonic notochord, over patterns with round cross-section.

Casting and installation of segmental precast quadratic concrete driven geothermal energy piles

Geothermal energy pile foundations are used both for structural purposes and to provide sustainable, clean, and cost-effective ground energy for heating and cooling buildings [1]. The majority of energy piles are cast-in-place concrete piles, which require extensive and expensive drilling during construction. A better alternative is to use precast concrete segmental driven energy piles, which can be cast in large quantities with high-quality assurance at a concrete factory, after which they are transported and installed into the ground [2]. This study aims to present a novel method of casting and installing segmental energy piles that utilize an innovative steel joint [3] for connecting the precast concrete segments on-site. In addition to structural integrity, the steel joint provides the possibility of a leak-proof coupling and continuity for heat-exchanging pipes embedded in concrete segments. The precast-driven pile foundations are made of high-strength concrete with a 14-day compressive strength of almost 80 MPa and have a quadratic shape with a maximum length of 12 m and a square width of 270 mm or 350 mm. In the 270-mm piles, a single U-loop can be used, while in the 350-mm piles, two U-loops can be used as presented in Figure 1. The heat-exchanging pipes are coupled inside the sidewall channels of the steel joint which are shielded using a steel cover plate, riveted to the joint. At the tip of the bottom segment of the piles, there is a strong steel rock shoe with a hardened steel point that allows the piles to penetrate the bedrock [4]. At a construction site, the joint and pipes can be connected quickly without any welding or electric equipment that expedites the installation work and obsoletes the health and safety risk associated with electricity. Utilizing the precast energy piles presented in this study increases the quality, and speed of installation while decreasing the overall cost of the project compared to cast-in-place energy piles. To prove the proper performance of the piles under real construction conditions, structural integrity tests and hydraulic pressure tests were performed according to BS EN 12794:2005 [5] and ASTM F2164–21 [6], and the results are briefly presented and discussed in the present study. Structural integrity tests consisted of impact tests in which 1000 blows imposing a minimum stress level of 28 MPa were applied on the pile segments connected using the new driven energy pile joint. During the impact tests, the pile structure and the joints remained undamaged. After the impact tests, the pipes were pressurized up to 100 psi (690 kPa) and no leakage or pressure drop was observed. Then the pile segments were cut according to the standard into shorter segments and subsequent bending tests were performed to measure the bending capacity. The bending tests show that the driven energy pile joints have a similar bending capacity as conventional normal joints. The results of this study show that segmental precast concrete energy piles using the new steel driven energy pile joints, are a perfect alternative for cast-in-place energy piles, which can provide sufficient structural and bearing capacity and can be used both for heating and cooling buildings.

Experimental investigation on the fracture properties of concrete under different exposure conditions

The fracture properties of concrete subjected to sulphate attack are investigated. First, concrete beams were subjected to different exposure conditions, i.e., full immersion, partial immersion and dry-wet cycling, for 90, 180 and 270 days, and a subsequent three-point bending test was conducted. A softening constitutive relationship of concrete was then derived and a simplified bilinear model was proposed for different exposure conditions. Finally, a chemical titration test was conducted to obtain the profiles of sulphate ion contents along the depth of concrete. The results indicate that, when concrete is subjected to different exposure conditions, the initial fracture toughness increases but the unstable fracture toughness decreases with the exposure duration. The stress-free crack opening displacement in the simplified bilinear model decreases significantly, indicating that concrete attacked by sulphate becomes more brittle. In addition, the sulphate ion content decreases rapidly along the depth and the sulphate ion content in concrete under dry-wet cycling is obviously higher than those under the other exposure conditions, demonstrating that dry-wet cycling results in the most serious sulphate attack on concrete.

Bo-LSTM based cross-sectional profile sequence progressive prediction method for metal tube rotate draw bending

Predicting the cross-sectional profile of the whole bending segment for metal tube bending is essential to achieve high-precision bending, yet still remains challenging. The existing prediction methods mainly base on theoretical derivation under certain assumptions and approximations, which do not fully characterize the whole bending segment profile neither do they fully utilize the information in the bending process. In this study, a Bo-LSTM-based progressive prediction method for the cross-sectional profile sequence is proposed, which comprehensively utilizes the profile information during the bending process and achieves an accurate prediction of the cross-sectional profile of the whole bending segment in the subsequent bending process. Firstly, the method of describing the cross-sectional profile in polar radial vector and the cross-sections of the bending segment in discrete sequences are proposed, which cover the information of cross-sectional distortion and wall thickness variation (viz. cross-sectional defects) for the whole bending segment. Secondly, an LSTM network is constructed integrating Bayesian-optimization-based hyper-parameters selection approach to progressively predict the tube cross-sectional profile sequence. Finally, the proposed methods are verified on simulated datasets as well as experimental data, and the accuracy is compared with networks of different structures. The results show that Bo-LSTM has better prediction accuracy. Meanwhile, the progressive prediction pattern has better robustness compared to chain prediction pattern.

Applicability of a laser pre-treatment for a robust subsequent bending of thin sheet metal

In conventional bending, locally varying residual stress states are one of the main causes for dispersion of bending angle. In this paper, a novel approach is investigated to reduce the dispersion of bending angle by modifying the residual stress state of thin sheets prior to the forming process. For this purpose, steel sheets were pre-treated with a nanosecond-pulsed fiber laser in confined ablation. The deflections were compared to sheets processed with thermal laser bending. It is revealed that the thermal mechanism dominates with respect to the deflection of the sheet because the deflection is in the same direction as that of laser-bent sheets. However, the induced deflection is smaller compared to the laser-bent ones. Moreover, it can be demonstrated that the robustness of subsequent bending operations is increased by the laser pre-treatment. The increase in robustness allows to achieve narrower tolerance windows for thin sheet metal without using cost-intensive tools and high punch forces.

Cyclical dermal micro-niche switching governs the morphological infradian rhythm of mouse zigzag hair

Biological rhythms are involved in almost all types of biological processes, not only physiological processes but also morphogenesis. Currently, how periodic morphological patterns of tissues/organs in multicellular organisms form is not fully understood. Here, using mouse zigzag hair, which has 3 bends, we found that a change in the combination of hair progenitors and their micro-niche and subsequent bend formation occur every three days. Chimeric loss-of-function and gain-of-function of Ptn and Aff3, which are upregulated immediately before bend formation, resulted in defects in the downward movement of the micro-niche and the rhythm of bend formation in an in vivo hair reconstitution assay. Our study demonstrates the periodic change in the combination between progenitors and micro-niche, which is vital for the unique infradian rhythm.

Bending behavior of the cysteinyl bolaamphiphile nanobelt assembly induced by the anisotropic disulfide bond formation

In this study, we explore how the covalent bonds linking individual building block molecules can substantially alter the suprastructure of molecular self-assembly. We focus on the role of covalent bonding within the self-assembled structures of a cysteinyl bolaamphiphile which consists of two cysteinyl motifs connected by a central hydrophobic heptyl chain spacer. The cysteinyl bolaamphiphile molecules self-assemble into a nanobelt structure with the creation of disulfide bonds during assembly, which prompts anisotropic molecular ordering and subsequent bending of the nanobelts. A series of control experiments revealed the twofold contribution of disulfide bonds: they facilitate the bending of the nanobelt assembly and the formation of longer assembled structures. Molecular dynamics simulation study confirms that the anisotropic distribution of disulfide bonds causes the bending of a nanobelt assembly. Moreover, the simulation and experimental studies demonstrated an increase in the nanobelt curvature as more disulfide bonds are generated. These results highlight the previously unappreciated influence of covalent bonds in causing macroscopic deformation of self-assembled structures.

Buckling in columns. Solution of the indeterminations of Euler's theory and derivation of an equation for inelastic buckling

Buckling in columns under central load has always been a complex problem and until now remains unclear. This work consists of two parts. In the first, a theory is presented to solve the indeterminations of Euler's theory, such as: Moment, slope, deflection, moment and shear reactions. In this sense, the column is analyzed as if it were a prismatic member under pure bending, due to the application of a bending moment and consequently the elastic curve of the column is calculated by the traditional method. Using a second hypothesis, it is established that elastic buckling occurs when the compressive and bending energies become equal; and solving it the Euler's Formula for the critical load is obtained exactly. In the second part, and with the indeterminations already resolved, the maximum-strain-energy failure criterion is raised, in the critic section, where the maximum moment occurs, due to the compressive load and subsequent bending. This allows us to obtain an extraordinary equation for inelastic flexural buckling that predicts highly accurate results consistent with laboratory tests. In the stress diagram versus slenderness, we can see the flat zone of the short columns, and the critical slenderness ratio, that in the case of ASTM-A36 structural steel, points directly to one hundred and twenty (120). And, of course, we can calculate the critical stress according to the type of cross-section and buckling axis and direction. An ideal column is considered, i.e., without initial deflection, with the application point of load on the centroid, and without residual stresses. A lineal stress-strain diagram is used until the yield point.

Numerical modelling of the process chain for aluminium Tailored Heat-Treated Profiles

Lightweight construction in modern car design leads to an increased usage of various aluminium semi-finished products. Besides sheet material, aluminium extrusion profiles are frequently used due to their high stiffness and variety of possible cross-sections. However, similar to sheet material, aluminium profiles exhibit limited formability in comparison to mild steel materials. One possibility to increase the forming limits of precipitation hardened aluminium alloys is the so-called Tailored Heat Treatment technology. By a local short-term heat treatment, the material is softened and the material flow can be controlled to reduce stresses in critical forming zones. The purposeful definition of the heat treatment zones is mandatory to improve the forming results. Therefore, numerical methods are necessary. In this investigation, a numerical process chain is presented. It combines the thermo-mechanical simulation of a local laser heat treatment with a subsequent bending process of the heat-treated profile using the alloy EN AW-6082. The temperature distribution, mechanical properties, and finally, the bending result of the numerical model are validated by experimental tests.

Initiation and growth of edge cracks after shear cutting of dual-phase steel

Dual-phase steels suffer from low edge ductility, which limits their formability. In this study, an in-plane bending test is used to investigate the initiation and evolution of edge cracks. The edges of samples were prepared by shear cutting and afterwards further deformed by the in-plane bending test. Void distribution and non-uniform plastic deformation were explored with the help of scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) analysis and microhardness measurement in different regions of the material edge. The extent of micro-cracks was revealed by microcomputed tomography (µCT) scan. The result shows that the blanking process creates inhomogeneous void distribution in the thickness direction. As the deformation increases during the subsequent in-plane bending test, the micro-cracks initiate at the burr region and grow towards the rollover region. Once they entirely pass the thickness of the material, they grow further, away from the edge. High roughness, plastic deformation, and void volume fraction were observed at the burr region, triggering crack initiation. The in-plane bending test successfully distinguished the dominant mechanism behind edge cracking.

Characterization of the Mechanical Properties of Selectively Embossed Sheet Metal Materials Under Multi-Axial Loads

The application of embossed structures close to the sheet surface allows for work hardening to be introduced into sheet metal materials, leading to an improvement in their mechanical properties. So far, this was demonstrated in previous research work via tensile tests with differently embossed dual-phase steel specimens. Since tensile tests only reproduce uniaxial loading of the sheet metal material, no conclusions can yet be drawn about the property modification that can be achieved by near-surface embossing concerning real-life, multi-axial loading scenarios. To get deeper knowledge about the deformation behaviour of embossed components, it is important to consider multi-axial load cases. In the investigations reported in this paper, a multi-axial load case was realized by testing embossed bending specimens of DP600 and DP800 using a three-point bending device. The tests showed an overall improvement in the maximum bending force needed for the three-point bending test due to embossing of the materials investigated. Further, the tests indicated that lower-strength materials get more influenced by embossing than higher-strength materials. By simulating the process of embossing the bending specimens and the subsequent three-point bending test, an even deeper understanding of the material property modification could be generated.

Partial resistance tempering of hot-stamped components made of 22MnB5 for subsequent bending

The manganese-boron alloy 22MnB5 is particularly used for structural and safety-relevant parts in the automotive industry. Parts made from this alloy are usually produced using the hot forming process. Here, the sheet is heated to over 950 °C using an industrial roller hearth furnace. The heated sheet is then simultaneously formed and quenched in a cooled tool with a temperature gradient of more than 27 K/s. This leads to the formation of a martensitic microstructure with a hardness value of over 450 HV10 and an elongation at break of less than 6%. The small strain potential of such components makes them difficult to form after hot-stamping. Due to the high temperature gradients of resistance heating, a sheet can be heat-treated locally without a large temperature transition zone. This can be used to locally soften already hot-stamped components for subsequent operations such as bending. Within the scope of this paper, resistance heating is used to soften a hot-stamped 22MnB5+AlSi sheet stripe of 3 mm width. The sheet could consequently be bent over an angle of 90° without cracking the substrate.