Bending Region Research Articles

Effect of crack location on buckling and dynamic stability in plate frame structures

It is well known that damages affect the dynamic characteristics of the structures in such a way that they may lead those structures to fail. Therefore, it is essential to construct a reliable mathematical model for estimating the effect of the damage in these structures. In this study, the effect of the straight, through-thickness crack and its location on the thin single-bay one-storey, two-bay-one-storey, and single-bay two-storey plate frames is investigated. For this purpose, a four-node quadrilateral plate bending and membrane elements are combined to perform finite element free vibration analysis of the healthy and cracked thin plate frame structures. The Classical Plate Theory is employed to satisfy the strain and stress conditions of these thin structures. A computer code is written using MATLAB to obtain the first three natural frequencies, critical buckling loads, and the first unstable regions of the healthy and cracked thin structures. To ensure the validity of the employed mathematical model, a convergence analysis is performed via ANSYS. The effect of crack location in plate frame structures is investigated by measuring the differences between the healthy and cracked structures’ first three buckling modes and the first unstable region. It is seen that the bending regions of the buckling modes are more affected by the crack than the other zones. Besides, crack occurrence within these regions has more impact on the first unstable regions. Accordingly, it has been revealed that the bending regions are the weakest locations of the frame structures. Therefore, potential cracks occurred within these regions may affect the structural integrity more than those of emerged in other regions.

Three-roller continuous setting round process for longitudinally submerged arc welding pipes

In order to solve the problems of excess ovality and cross-section distortion of longitudinally submerged arc welding pipes after forming, a new three-roller continuous setting round process was proposed. This process can be divided into three stages: loading stage, roll bending stage and unloading stage. Based on the discretization idea, the mechanical model of the primary statically indeterminate problem of the longitudinally submerged arc welding pipes at the roll bending stage was established, and the deformation response was obtained. The simulation and theoretical results show that there are three positive bending regions and three reverse bending regions along the circumference of the pipe. The loading force of each roller shows growth, stability and downward trend with time. The error between the theoretical fitting curve and the simulated data point is very small, and the simulation results verify the reliability of the theoretical calculation. The experimental results show that the residual ovality decreases with the increase of the reduction, and the reduction of the turning point is the optimum reduction. In addition, the residual ovality of the pipe is less than 0.7% without cross-section distortion, which verifies the feasibility of this process.

EXPERIMENTAL INVESTIGATION OF SPRINGBACK OF LOCALLY HEATED ADVANCED-HIGH STRENGTH STEELS

Sheet metal bending is one of the important metals forming processes at ambient temperature. The usage of high-strength steel is one of the stronger materials for the construction of components in the automotive industries. However, for complex shapes, cold forming is not always sufficient, and heating the workpiece plays a major role in manufacturing these shapes. Bendability may increase with increasing forming temperature and currently, hot forming of advanced high strength steels (AHSS) is becoming more attractive. While hot forming of AHSS is beneficial for high formability, subsequent quenching is required to maintain final strength. This procedure extends the production time. In this study, temperature gradients, bending loads, and springback after V-bending were investigated. The experimental study was carried out on a 2 mm thick Docol 1500M steel at various temperatures by using a speed-controlled servo press machine. The bending regions of the specimens were locally heated to 200, 300, 400, 500, and 600oC by using a high-frequency induction heating device. The results show that; punch loads were significantly lowered with increasing the local heating temperature during bending. There were no cracks observed on the specimens. The amount of spring back is decreasing with the bending temperature and around 500oC almost no springback was measured. Negative spring back was observed for the bending temperatures higher than 500oC

Numerical and Experimental Investigation of the Bending Zone in Free U-Bending

Abstract With the increasing application of the advanced high strength steel material in the automobile industry, the thickness reduction of the bending area has attracted more and more attention since the product strength is highly influenced by the quality of the bending region. In this paper, three major factors, the thickness reduction, the variation of the local bending radius within the bending zone, and the tooling mark on the product’s surface, are investigated through three different loading patterns for a free U-bending profile numerically and experimentally. The results demonstrate a thinning pattern consists of three peaks over the bending region for large bending ratio (R/t = 2.14) and only one peak for small bending ratio (R/t = 0.5). Corresponding valleys for the local radius are found to match the thinning pattern. Further, the use of finite element simulation can successfully predict the location and the severity of the wear on the product. From the experiment results, even if the metal blank only experienced one stroke, the tooling mark contains both adhesive and abrasive wear. A better understanding of the characteristics of the bending zone is achieved, and the findings can help in improving the design process for forming strategies.

Incorporation of Smart Concrete in Large-Scale RC Beams for Evaluating Self-Sensing and structural Properties

Only using a small number of samples in the absence of reinforcement, the concrete self-monitoring behaviour is tested, which is inaccurate for real-world structures. The behaviour of concrete is primarily tested, which can be inaccurate for structures in real time. This study examined the self-sensing ability of large-scale reinforced concrete beams that are 1500 mm long and 125 mm wide embedded with smart concrete at top and bottom surfaces for a length of 350 mm. As shear failure is catastrophic, the present study focused on evaluating RC beams' self-sensing property failing under shear, and shear reinforcement was not given for the same reason. A total of six RC beams, 3 of are 250 mm deep and 3 are 350 mm deep with variable reinforcement ratios, were tested in a four-point bending test to study the self-sensing properties such as strain and crack/damage sensing. Mechanical/structural properties of all the beams have been documented, along with self-sensing properties. The results obtained showed that partially placed smart concrete in the RC beam's pure bending region successfully sensed all strain and damage/cracks without any impact due to beam depth and reinforcement ratio. During testing, it was observed that 250-mm-deep beams failed due to flexure/concrete crushing, and 350-mm-deep beams failed due to shear. In particular, smart concrete's self-sensing property showed promising results for the beams that failed due to flexure by representing all the cracks developed in the pure bending region. Fraction change in resistance (FCR) has also been obtained for all the beams during self-sensing testing, and this FCR has been successfully co-related with concrete strain in compression and steel strain in tension. An empirical equation was also derived separately for beams that failed in shear and flexure, which provides a co-relation between FCR and concrete or steel strain.

Optical emission enhancement of bent InSe thin films

In contrast to the majority of two-dimensional semiconductors such as transition metal dichalcogenides, indium selenide (InSe) possesses an intrinsic large out-of-plane oriented band-edge luminescent dipole. This unique anisotropic feature of band-edge optical emissions can be exploited to achieve enhanced optical signal in bent regions of materials created by geometrical modification. We herein investigate based on first-principle calculations the mechanism of this optical emission enhancement by modelling the photoluminescence processes in bent and flat regions of the InSe thin film. We propose in our model that the shorter-wavelength interband transition, labelled as transition B′, between the second-highest valence band and the bottom of conduction band plays an important role in the enhancing process. Our model robustly describes the dependence of optical emission enhancement in the bent InSe thin films on thickness, incident light orientation, and excitation photon energy. In particular, we found that when excitation photon energy is lower than the energy of transition B′, strong enhancement up to hundreds of times can be obtained by applying an incident light at an angle less than 70° to the InSe layers. Our results provide useful references for modulating luminescent properties of InSe films toward flexible optoelectronic device applications.

Photodriven Transient Picosecond Top-Layer Semiconductor to Metal Phase-Transition in p-Doped Molybdenum Disulfide.

Visible light is shown to create a transient metallic S-Mo-S surface layer on bulk semiconducting p-doped indirect-bandgap 2H-MoS2 . Optically created electron-hole pairs separate in the surface band bending region of the p-doped semiconducting crystal causing a transient accumulation of electrons in the surface region. This triggers a reversible 2H-semiconductor to 1T-metal phase-transition of the surface layer. Electron-phonon coupling of the indirect-bandgap p-doped 2H-MoS2 enables this efficient pathway even at a low density of excited electrons with a distinct optical excitation threshold and saturation behavior. This mechanism needs to be taken into consideration when describing the surface properties of illuminated p-doped 2H-MoS2 . In particular, light-induced increased charge mobility and surface activation can cause and enhance the photocatalytic and photoassisted electrochemical hydrogen evolution reaction of water on 2H-MoS2 . Generally, it opens up for a way to control not only the surface of p-doped 2H-MoS2 but also related dichalcogenides and layered systems. The findings are based on the sensitivity of time-resolved electron spectroscopy for chemical analysis with photon-energy-tuneable synchrotronradiation.

Characterization of the phase transition mechanism of P(NiPAAm-co-AAc) copolymer hydrogel using 2D correlation IR spectroscopy

A thermo-responsive polymer, poly(N-isopropylacrylamide) (PNiPAAm), was copolymerized with acrylic acid (AAc) in this study. Its phase transitions during the heating and cooling processes were investigated using IR spectroscopy, principal component analysis (PCA), and two-dimensional correlation spectroscopy (2D-COS). During the heating process, the hydrogen bonding between side chain in P(NiPAAm-co-AAc) copolymer hydrogel and H2O was broken first, and then the formation of the intramolecular interaction in P(NiPAAm-co-AAc) copolymer hydrogel occurred. However, unlike the heating process, intensities of bands in the CH stretching region were changed before those in the CO stretching including the NH bending region during the cooling process. The results indicate that the phase transition of P(NiPAAm-co-AAc) copolymer hydrogel is an irreversible process at the molecular levels.

Molecular Dynamics Simulation of Cellulose Synthase Subunit D Octamer with Cellulose Chains from Acetic Acid Bacteria: Insight into Dynamic Behaviors and Thermodynamics on Substrate Recognition.

The present study reports the building of a computerized model and molecular dynamics (MD) simulation of cellulose synthase subunit D octamer (CesD) from Komagataeibacter hansenii. CesD was complexed with four cellulose chains having DP = 12 (G12) by model building, which revealed unexpected S-shaped pathways with bending regions. Combined conventional and accelerated MD simulations of CesD complex models were carried out, while the pyranose ring conformations of the glucose residues were restrained to avoid undesirable deviations of the ring conformation from the 4C1 form. The N-terminal regions and parts of the secondary structures of CesD established appreciable contacts with the G12 chains. Hybrid quantum mechanical (QM) and molecular mechanical (MM) simulations of the CesD complex model were performed. Glucose residues located at the pathway bends exhibited reversible changes to the ring conformation into either skewed or boat forms, which might be related to the function of CesD in regulating microfibril production.

Investigation on cavitation erosion of diamond-like carbon films with heterogeneous multilayer structure

Cavitation tests of three heterogeneous multilayer diamond-like carbon (DLC) films (Ti/DLC, TiCx/DLC and Ti-TiCx/DLC) were performed using a vibratory test rig to evaluate their cavitation erosion resistance. Results indicated that the cavitation erosion of multilayer DLC films resulted from flexural cracks in the bending regions, then fatigue failures were developed along the uplifted regions of the films. Comparing to TiCx/DLC film and Ti-TiCx/DLC film, Ti/DLC film had the lowest average erosion area. It was concluded that multilayer structure with titanium as adhesion layer improved the adhesion strength and reduced the plastic deformations of the DLC films in the incubation phase; these Ti layers also decreased the residual stress of the DLC films and reduced the cracks within the films in the attenuation phase; lower ID/IG ratio could improve the fatigue resistance of the multilayer films in the steady phase.

Local heat clamp bending of carbon fiber-reinforced thermoplastic sheet

Local heat clamp bending equipment for carbon fiber-reinforced thermoplastic (CFRTP) sheets has been developed. The equipment holds a CFRTP sheet with thin metal foils to heat the bending region to the resign melting temperature and then bends the sheet keeping the hold by the foils under continuous pressure application during cooling. Using this equipment, it has been revealed that even a unidirectional continuous carbon fiber sheet can be locally bent by the in-plane wavy deformation of the fiber in the inner plies, while keeping the same profile length of the outside ply. In contrast, in the bending of unidirectional carbon fiber sheets with cutting at constant length, a combination of the wavy deformation of the inside ply and expansion of the outside ply has been observed. The developed bending equipment will be useful for the bending of CFRTP sheets similar to how a press brake is used for sheet metal forming. The development of the local heat clamp bending equipment will expand a field of bending for mass production using CFRTP sheets.

Improvement in the anisotropic mechanical properties and formability of Al–Si–Mg–Cu-based alloy sheets

The anisotropic mechanical properties and formability of Al–Si–Mg–Cu-based alloy sheets were investigated by varying their recrystallized grain sizes. By adding Cr and Mn and controlling the homogenization heat treatment, the recrystallized sheets with average grain sizes of 85, 61, 54, and 26 μm were prepared. As the average grain sizes of the recrystallized sheets decreased from 85 to 26 μm, the yield strength (YS) increased from 69.5 to 86.4 MPa due to grain boundary and particle strengthening. At the same time, the elongation was improved because the reduction in the stress concentration delayed the formation of the large-scale necking. The anisotropy in YS and elongation significantly decreased because a large number of fine grains with various orientations operated similar slip systems in all directions. Furthermore, grain refinement can increase and decrease the plastic strain ratio (r‾) and planar anisotropy (Δr), respectively, due to the formation of random textures. A bending formability map was proposed, which showed the acceptable and non-acceptable bending regions based on the grain size and flanging radius. This study provided valuable insight regarding the effects of refining recrystallized grains on anisotropic mechanical properties and formability.

Microstructure and Texture Evolutions During Deep Drawing of Mg-Al-Mn Sheets at Elevated Temperatures.

Texture and microstructure evolution of ingot and twin-roll casted Mg–Al–Mn magnesium sheets were examined during deep drawing at elevated temperatures. The twin-roll casted sheets possessed smaller grain sizes and weaker basal intensity levels than the ingot-casted sheets. The strength and elongation at room temperature for the twin-roll casted sheets were greater than those of the ingot-casted sheets. At elevated temperatures, the ingot-casted sheets showed better elongation than the twin-roll casted sheets. Different size and density of precipitates were examined using transmission electron microscopy (TEM) for both ingot-casted and twin-roll-casted sheets. The deep drawing process was also carried out at various working temperatures and deformation rates, and 30 mm/min to 50 mm/min, respectively. The middle wall part of cups were mainly tensile deformation, and the lower bent regions of drawn cups were most thinned region. Overall, the ingot-casted sheets revealed better deep drawability than the twin-roll casted sheets. Microstructure and texture evolution of the top, middle and lower parts of drawn cups were investigated using electron backscatter diffraction. Increased deformation rate is important to activate tensile twins both near the bent and flange areas. Ingot casted sheets revealed more tensile twins than twin-roll casted sheets. Increased working temperature is important to activate non-basal slips and produce the DRXed grain structure in the flange. Dynamic recrystallization were frequently found in the top flanges of the cups. Both tensile twins and non-basal slips contributed to occurrence of the dynamic recrystallization in the flange.

Towards understanding of different solid forms of formoterol fumarate: Combined computational and experimental approach

In this study, specimens of Formetrol fumerate were investigated using IR and Raman vibrational spectroscopy as well as quantum chemical calculations. The structure of formetrol fumerate was optimised using density functional theory calculations and the geometry optimization has been carried out on three different solvate crystal forms; di-hydrate, di-ethanolate, and di-isopropanolate in addition to the anhydrate form with and without intramolecular hydrogen bonding. Molecular assignments are proposed on the basis of ab initioB3LYP DFT calculations with a 6–31 G∗ basis set and vibrational wavenumbers. Crystallographic investigation has been carried out to formetrol anions and protonated anions arising from crystal structures of the studied conformers and it was evidenced that the di-hydrate form has the highest energy probably due to the greater possibility of intramolecular hydrogen bonding. Infrared and Raman spectra were calculated from the optimised structures. Many modes in the calculated spectra were matched with the experimental spectra and a description of the modes was given. By analysis of the theoretical vibrational modes, it was proved that formetrol fumerate specimens are likely to be dihydrate form with and without intramolecular hydrogen bonding. Additionally, several spectral features and band intensities in the stretching and bending regions were explained. Quantum mechanical calculations allowed improved understanding of formetrol fumerate and its vibrational spectra as an important β2 antagonistic compound in various pharmaceutical formulations. The obtained data could provide useful information about its interactions with excipients and other components.

Synchrotron X-Ray Topography Study on the Relationship between Local Basal Plane Bending and Basal Plane Dislocations in PVT-Grown 4H-SiC Substrate Wafers

Synchrotron monochromatic beam X-ray topography (SMBXT) in grazing incidence geometry shows black and white contrast for basal plane dislocations (BPDs) with Burgers vectors of opposite signs as demonstrated using ray tracing simulations. The inhomogeneous distribution of these dislocations is associated with the concave/convex shape of the basal plane. Therefore, the distribution of these two BPD types were examined for several 6-inch diameter 4H-SiC substrates and the net BPD density distribution was used for evaluating the nature and magnitude of basal plane bending in these wafers. Results show different bending behaviors along the two radial directions - [110] and [100] directions, indicating the existence of non-isotropic bending. Linear mapping of the peak shift of the 0008 reflection along the two directions was carried out using HRXRD to correlate with the results from the SMBXT measurements. Basal-plane-tilt angle calculated using the net BPD density derived from SMBXT shows a good correlation with those obtained from HRXRD measurements, which further confirmed that bending in basal plane is caused by the non-uniform distribution of BPDs. Regions of severe bending were found to be associated with both large tilt angles (95% black contrast BPDs to 5% white contrast BPDs) and abrupt changes in a and c lattice parameters i.e. local strain.

Springback behaviors of extruded 6063 aluminum profile in subsequent multi-stage manufacturing processes

The process for manufacturing automotive aluminum profiles is a multi-stage process, which includes porthole die extrusion, aging treatment, bending, and electrophoretic painting. Prediction and reduction of springback are essential in quality control of bent profiles. However, existing researches related to springback issues were mainly focused on bending process stage. This study aimed to investigate the springback behaviors of extruded aluminum profile during the whole manufacturing process by numerical simulations with experimental validations. Formation mechanism and rule of springback for aluminum profile at different process stages were revealed. The optimum process route for manufacturing bent aluminum profiles was proposed. The research results reveal that compared with the transient bending region, the springback of aluminum profile during bending process induced by the finished bending region and two straight regions is relatively small. Springback angle increases with increasing bending angle and aging time. After bending tools unloading, the stresses of the two straight zones are almost completely relaxed. However, large residual tensile and compressive stresses exist in the material adjacent to the neutral layer of aluminum profile in transient and finished bending regions. Consequently, residual stress relaxation causes additional springback of bent profiles during subsequent heat treatment processes. The additional springback angle shows linear correlation with bending angle and parabola correlation with aging time. The total springback angle is minimum for process route 3 that extruded profile is firstly bent to required shape, then treated by artificial aging and finally treated by electrophoretic painting.

Deep slab seismicity limited by rate of deformation in the transition zone.

Deep earthquakes within subducting tectonic plates (slabs) are enigmatic because they appear similar to shallow earthquakes but must occur by a different mechanism. Previous attempts to explain the depth distribution of deep earthquakes in terms of the temperature at which possible triggering mechanisms are viable, fail to explain the spatial variability in seismicity. In addition to thermal constraints, proposed failure mechanisms for deep earthquakes all require that sufficient strain accumulates in the slab at a relatively high stress. Here, I show that simulations of subduction with nonlinear rheology and compositionally dependent phase transitions exhibit strongly variable strain rates in space and time, which is similar to observed seismicity. Therefore, in addition to temperature, variations in strain rate may explain why there are large gaps in deep seismicity (low strain rate), and variable peaks in seismicity (bending regions), and, possibly, why there is an abrupt cessation of seismicity below 660 km.

Polyelectrolyte in Electric Field: Disparate Conformational Behavior along an Aminopolysaccharide Chain.

Electrical signals are increasingly used in fabrication of hydrogels (e.g., based on aminopolysaccharide chitosan) to guide the emergence of complex and anisotropic structure; however, how an imposed electric field affects the polymer chain conformation and orientation during the self-assembly process is not understood. Here, we applied nonequilibrium all-atom molecular dynamics simulations to explore the response of a charged chitosan chain comprising 5- or 20-monomer units to a constant uniform electric field in water and salt solution. While no conformational or orientational response was observed for the polyelectrolyte (PE) chains under the small electric fields within the simulation time, a field strength of 400 mV/nm induced significant changes. In water, a 5-mer chain is found to be slightly bent and oriented parallel to the field; however, surprisingly, a 20-mer chain displays candy-cane-like conformations whereby one half of the chain is collapsed and flexible, while the other half of the chain is stretched along the electric field. In salt solution, the disparity remains between the two halves of the 20-mer chain, although the backbone is extremely flexible with multiple bent regions and non-native conformations occur near the chain center in one of the three trajectories. The disparate conformational response along the polyelectrolyte chain may be attributed to the balancing forces between chain dynamics, electric polarization, counterion binding, and hydrodynamic pressure as well as friction. These findings reconcile existing experiments and theoretical studies and represent an important step toward understanding the complex roles of electric field and salt in controlling the structure and properties of soft matter.

Research on Cs/O activation process of near-infrared In0.53Ga0.47As photocathodes

Abstract We report a systematic theoretical investigation on the activation mechanism of near-infrared In0.53Ga0.47As photocathodes. Adsorption energies, dipole moments, work functions, density of states, band structures and electron affinity of Cs/O co-adsorption on (001) surface of In0.53Ga0.47As photocathodes are investigated. First-principles calculation results indicate that the structural stability is greatly enhanced when oxygen atoms adsorb on the Cs-covered surface. The incorporation of oxygen atom helps lower the work function further to achieve the true NEA state. Moreover, two adatom-induced surface dipoles, namely [Csn+-In0.53Ga0.47Asn−] and [Cs+-O2--Cs+], are also adopted to explain the relationship between the adatoms and the substrate. The HOMO and LUMO levels can further move downward and the band bending region is enlarged after Cs/O co-activation. Meanwhile, new energy bands appear in the deep valence band due to the joint effect of Cs 5s, Cs 5p, O 2s and O 2p state electrons. Finally, Cs/O activation experiments are carried out and the photocurrent curves during activation procedure are recorded. The change of photocurrent is closely related to the work function variation, which affects the photoemission of the photocathodes. In order to clearly show the electron affinity, the variation of surface barrier height of InGaAs photocathodes with Cs/O adlayer is also given.

High-pressure behavior of a linear chain alkane, tricosane

Exploring the behavior of hydrocarbon under pressure is important for understanding its role in planetary sciences and also for exploring novel organic chemistry. In this study, we explored the high-pressure behavior of a linear-chain hydrocarbon, tricosane (C23H48), using Raman spectroscopy. We compressed tricosane up to 23 GPa and did not find any evidence for pressure-induced amorphization within the conditions explored in this study. Upon compression, we observe new modes in the low energy region 100–300 cm−1. In order to understand the appearance of these new modes at high pressures, we used complementary ab initio calculations and explored the effect of chain configurations (linear and bent) on the predicted Raman spectra. We find that these new modes observed at higher pressures are better explained by bent configuration of tricosane chains. Thus, based on high-pressure Raman spectra, it is very likely that a linear chain of tricosane is bent under pressure, i.e., it undergoes a pressure-induced trans-gauche transformation. It is also likely that such bent regions (i.e., kinks) will act as sites along which large chain hydrocarbons could dissociate into smaller chain lengths at extreme conditions relevant to the interiors of Jovian planets.