Sheet Bending Research Articles

Preparation, Characterization, and In Vitro Testing of Nanoclay Antimicrobial Activities and Elicitor Capacity.

Clay-based nanocomposites (nanoclays) are interesting systems to hold a wide type of active substances with a wide field of industrial applications. Bentonite-chitosan nanoclay was obtained via cationic exchange of natural bentonite (Bent) with an aqueous solution of chitosan (CS). Their physicochemical and morphological properties were discussed under the light of Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Bent-CS characterization indicated that CS was intercalated in 10% (w/w). This polycationic polymer was oriented mostly in a monolayer arrangement, interacting by electrostatic forces between Bent sheets. The antimicrobial action of Bent-CS nanoclay was assayed onto phytopathogens, the bacterium model Pseudomonas syringe pv. tomato DC3000 ( Psy) and the necrotrophic fungus Fusarium solani f. sp. eumartii ( F. eumartii). In addition to demonstrating cell death on both microorganisms, Bent-CS exerted elicitor property on tomato plantlets. The biological actions of this natural nanomaterial might make it proper to be used in crops.

Ripply3 is required for the maintenance of epithelial sheets in the morphogenesis of pharyngeal pouches.

During tissue development, the morphogenesis of epithelial sheets is regulated by many factors, including mechanical force, although the underlying mechanisms remain largely unknown. In the pharyngeal region of the vertebrate embryo, endodermal epithelium is reiteratively folded outward to form pharyngeal pouches, making partitions between the pharyngeal arches. Ripply3, encoding a member of the Ripply family of adaptor proteins, is required for the pouch formation posterior to the 2nd pharyngeal pouch. In this study, we found that the expression of mouse Ripply3 was specifically activated in accordance with the bending of the endodermal epithelium during the pouch formation. In Ripply3-deficient embryos, a continuous monolayer of the endodermal epithelium was not maintained posterior to the 2nd pharyngeal pouch. Corresponding to the endodermal region of the deformed epithelium, the activated form of Integrin β1, which was localized at the basal side of the epithelial cells in the wild-type embryos, was not persistently observed in the mutants. On the other hand, cell proliferation and apoptotic cell death in the endoderm were not obviously affected by the Ripply3 deficiency. Significantly, Ripply3 expressed in cultured cells was found to be preferentially accumulated in the focal adhesions, which are Integrin-mediated adhesive contact sites transmitting mechanical force between the extracellular matrix and attached cells. Furthermore, Ripply3 promoted the maturation of focal adhesions in these cells. Thus, Ripply3 appears to have been activated to enhance the connection between the extracellular matrix and endodermal epithelial cells, as a mechanism to resist the mechanical stress generated during the bending of the epithelial sheets.

Molecular dynamics simulation of nickel‐coated graphene bending

The work presents a force field molecular dynamics study of nickel-coated graphene sheet bending at temperatures 300 and 1300 K. Nickel film is represented by nickel atoms located above the centres of carbon hexagons. Parameters for carbon–nickel interaction are fitted with regard to the accurate density functional calculations. Unstrained or flat configuration of the nickel–graphene system is found to be energetically unfavourable for the considered temperatures. Two types of curvatures are taken into account. Positive curvature is characterised by the nickel atoms located closer to the bending axis than the carbon ones, and negative curvature corresponds to the reverse atomic positions. It is found that the equilibrium radius for the curved nickel–graphene complex with the negative curvature is less than the corresponding value for the positive one. However, in both cases the equilibrium curvature radius of nickel-coated graphene is of the order of several nanometres. It is shown that both temperature and bending directions (zigzag and armchair) weakly affect the bending energy and do not change the equilibrium radius. Bending behaviour of the system is defined by the carbon–nickel interaction rather than the individual properties of isolated graphene and nickel films.

Reduction in holding time at bottom dead centre in hot stamping by water and die quenching

A water and die quenching process with submerged tools was developed to improve the productivity of hot stamping. Although heated steel sheets are cooled only by the tools in the conventional hot stamping operation, the bent sheets are cooled by water around tools in the water and die quenching process, and thus the holding time at the bottom dead centre is reduced. The sheets were bent into a hat shape to examine the quenchability and deformation behaviour. For 1.6 mm in thickness, the holding times for sufficient hardening and the prevention of springback were 5 s and 20 s with and without water, respectively. Furthermore, the holding time was reduced by bottoming due to the increase in heat transfer coefficient.

Investigation of sheet bending parameters on springback in nickel coated mild steel sheets using response surface methodology

Springback is the geometric change during forming process and it affects the dimensional accuracy of a finished product. This study aims to analyse the issue of springback in sheet bending by using response surface methodology (RSM). The effect of punch travel (d), strain hardening index (n), holding time (t), punch velocity (v) and width of the sheet (w) on the springback was explained by contour plots. The experiments were designed as per Centre Composite design and also linear and quadratic polynomial equations were used for developing the mathematical model. The experimental results of the punch travel, velocity, width of the sheets increased which increases the springback. The holding time increases when the springback decreases. ANOVA analysis was used to identify the most significant factor which affects the springback and it indicates that the springback is inversely proportional to the holding time and the springback is directly proportional to the width of the sheets. The results of scanning electron microscope (SEM) and energy dispersive analysis of X rays analysis for the nickel coated mild steel were also reported.

Deformation Type in Forming of Horn Tubes

The purpose of this research is the development of technology to make complex-shape closed-section parts directly from sheet blanks (direct sheet forming). It is expected to form closed-section parts with large expansion of the circumferential length by direct sheet forming. In this paper, the deformation type of horn tubes, which consists of circular, conical and transient portions, is studied. The horn tube is one of the typical shapes for automotive parts. With reference to deformation types in the conventional stamping process, those in the forming process of horn tubes are discussed on the basis of the results of FEM analysis. The validity of FEM analysis is confirmed by comparison with experimental results. It is clarified that the forming process can be broken down into several stages and deformation types (uniform bending of sheet, stretch flanging, axial bending of U-section, deformation into double curved surface and plane-strain compression).

Bending of sheet metals using plastic tools made with 3D printer

A plastic punch and die manufactured by a fused deposition modelling process were employed for a V-bending process of sheet metals. For the plastic tools, the production time and cost are low, whereas the yield stress and Young’s modulus are considerably lower than those for steel tools. The dimensional accuracy of the bent sheets by the plastic tools was examined. To improve the dimensional accuracy, a steel punch and plastic die were employed. The plastic tools underwent large elastic deformation during forming, whereas the springback was almost similar to that for the steel tools. It was found that the plastic tools are useful for bending sheet metals.

Laser edge forming to increase the bending radius in hemming

Hemming can be used, for example, to join dissimilar materials which cannot be welded by conventional laser or arc based processes. A critical value in hemming is the ratio of outer sheet bending radius and outer sheet thickness because cracks can occur in outer sheets with low ductility due to a small bending radius. In this study, a novel approach is introduced for increasing the bending radius by laser based edge forming. The laser beam melts the edge of the inner sheet prior to the hemming process. In laser edge forming, the edge thickness increases due to the surface tension of the melt. The edge cross-section has typically a nearly circular shape after solidification. Two laser beam irradiation strategies were investigated. In case of the first strategy, a defocused laser beam was applied. The second strategy combined a focused laser beam resulting in the formation of a vapor capillary (keyhole) with sinusoidal beam oscillation transversal to the sheet edge. The results show that the position of the cylindrical edge cross-section according to the sheet plane could be affected by the applied irradiation strategy. The needed laser power was significantly lower when using a focused laser beam due to the deep penetration effect. The potential of the laser edge forming technique for crack-free hemming processes was demonstrated with 1 mm thick aluminum alloy sheets by carrying out stripe tests.

Regulation of posterior body and epidermal morphogenesis in zebrafish by localized Yap1 and Wwtr1.

The vertebrate embryo undergoes a series of dramatic morphological changes as the body extends to form the complete anterior-posterior axis during the somite-forming stages. The molecular mechanisms regulating these complex processes are still largely unknown. We show that the Hippo pathway transcriptional coactivators Yap1 and Wwtr1 are specifically localized to the presumptive epidermis and notochord, and play a critical and unexpected role in posterior body extension by regulating Fibronectin assembly underneath the presumptive epidermis and surrounding the notochord. We further find that Yap1 and Wwtr1, also via Fibronectin, have an essential role in the epidermal morphogenesis necessary to form the initial dorsal and ventral fins, a process previously thought to involve bending of an epithelial sheet, but which we now show involves concerted active cell movement. Our results reveal how the Hippo pathway transcriptional program, localized to two specific tissues, acts to control essential morphological events in the vertebrate embryo.

Numerical investigations into influence of scanning path curvature on deformation behavior during curvilinear laser bending of magnesium sheets

ABSTRACTIn laser bending process, metal sheets are deformed by using thermal stresses induced due to controlled laser heating. Straight line heating is used to manufacture simple shapes while curvilinear irradiation is used to generate 3D complex shapes. Scanning path curvature is an important parameter that controls the deformation profile of a worksheet. This article presents systematic investigations into influence of scanning path curvature on the thermal stresses based deformation behavior, temperature distribution and warping of the magnesium M1A sheets. Initially, a three-dimensional nonlinear thermomechanical finite element model of curvilinear laser bending process has been developed. Mathematical correlations have been derived to model the curvilinear irradiations. The developed model has been validated by using experimental studies. Then, numerical investigations have been performed on temperature distribution, stress–strain distribution and distortions occur in the laser bent magnesium alloy sheets. Results indicated that sheet bends away from the scanning path. One of the key findings is that low to medium levels of arc height reduce the edge effect during laser bending, while higher values of arc height produce warping at the free edge. It is envisaged that presented results will be useful to manufacture 3D complex shapes and to align complex geometry sheets.

Processing and Analysis of Experimental Data for the Impact Toughness of the Steel Quality J55 API 5CT Using Design Expert Software

In this paper the plate from the steel of quality grade J55 API 5CT and the process of pipe forming O139.7x7.72 mm and O219.1x7.72 mm with rectilinear seam is analysed. The impact of deformation level in the cold and mechanical properties of the steel coils before and after the forming of the pipes are elaborated and processed through Design Expert Software. For analysis it was used the planning method of the experiment. It was built the mathematical model for the experiment with one index (impact toughness - Kv) and with one factor (level of deformation in the cold), and with few levels and two blocks (before and after the forming of the pipes). Statistical analysis of experimental data for models of plate and pipe were obtained through Design Expert Software. Based on such date graphic representation for the influence of deformation rate on Charpy-V notch energy was generated. Application of the Design Expert Software helps quick and correct combinations of three criteria (treatments) in order to estimate the level of deformation throughout the bending of sheet and calibration, influence of the decrease of impact toughness during the forming of pipes.

Feedforward control of sheet bending based on force measurements

The accuracy which can be reached with feedback control in industrial metal forming processes is limited by product-to-product variations in the process. These variations may be controlled with a feedforward control system. To do so, a measurement system and a process estimator are needed to measure and correct for these variations. In this work, the use of force measurements for feedforward control of a steel sheet bending process is investigated. A multi-stage demonstrator process is developed with cutting, deep drawing and bending stages and a large number of force sensors. Several relations between process forces and the product geometry are studied in an extensive analysis of measurement data from the production process. It is proposed to build a moving window process estimator using the LASSO regression method. The parameters of the regression model are updated during production based on historical data of the production line. Several simulation runs are performed to estimate the effect of feedforward control on the process accuracy. These simulation runs are based on measurements from the real production line and minor assumptions. The proposed approach leads to an estimated decrease of 24% in the root mean square error of the final angle with respect to a simulation run with feedback control only.

Numerical investigation of the combined effects of curvature and normal stress on sheet metal formability

A number of parts and components involved in the automotive industry are made of thin bent sheets, which are subjected to out-of-plane compressive stresses in addition to traditional in-plane stresses. Unfortunately, the classical predictions based on the conventional concept of Forming Limit Diagram (FLD) are no longer relevant when the strain distribution is heterogonous over the sheet thickness. Therefore, this conventional FLD concept is not capable of accounting for the effect of out-of-plane stresses on the onset of localized necking. The aim of the present contribution is to propose an extension of the well-known Marciniak–Kuczynski approach to simultaneously account for the effect of curvature and normal stress on formability prediction. The new developed tool allows predicting the limit strains for the whole range of strain paths. The mechanical behavior of the studied sheets follows the rigid–plastic flow theory. Through numerical results, it is shown that both curvature and normal stress tend to increase the formability limit of the sheet metal.

Axial crushing of tubes fabricated by metal sheet bending

Energy absorption characteristics of thin-walled tubes fabricated by bending of metal sheets are studied in this work. Square tubes are prepared by folding aluminum alloy 3003 H12 sheets and quasi-static axial crushing tests are then performed with universal material testing machine. The energy absorption capacity and deformation of these folded tubes are analyzed and compared with traditional square tubes. Nonlinear finite element code LS-DYNA is employed to simulate the crushing tests and the numerical results are compared with the experiment. The influences of various factors, including the boundary condition, loading speed, fillet radius and sectional shape, on the crushing force and deformation of the folded tubes are investigated numerically. In addition, folded tubes with multi-cell sections are also analyzed and compared with traditional tubes. Some suggestions are provided for the design of folded single or multi-cell tubes. Since the folded tubes are easily prepared, cost-effective for small-scale production and flexible in both sectional shape and geometric parameters, they are quite promising to be applied widely in various engineering fields.

An analytical model for the response of carbon/epoxy-aluminum honeycomb core sandwich structures under quasi-static indentation loading

An analytical model is developed to predict the loading and unloading response, as well as the residual dent diameter and dent depth, of carbon/epoxy-aluminum honeycomb core composite sandwich structures undergoing quasi-static indentation loading. The model considers damage created using spherical indenters and is valid up to the barely visible external damage threshold. The initial low load regime (until the onset of core crushing) is modeled using a combination of local Hertzian indentation of an elastic half-space and small deflection plate theory of a circular plate on an elastic foundation. For loads above those required to cause core crushing, the model uses the Rayleigh-Ritz method of energy minimization with the total system energy determined using a combination of face sheet bending energy, face sheet membrane energy and work done to the core during both elastic deformation and crushing. Degraded face sheet properties are used in the model beyond the onset of face sheet delamination, which is predicted using Griffith’s energy criterion. The model is validated using experimental results for sandwich structures consisting of quasi-isotropic 8- (thin) and 16- (thick) ply carbon/epoxy face sheets and aluminum honeycomb cores. The results show that the overall mechanics of the model are fundamentally correct and reflective of physical behavior. Thus, in its present form the model shows promise as a preliminary design tool.

Springback-free mechanism in hot stamping of ultra-high-strength steel parts and deformation behaviour and quenchability for thin sheet

The springback-free mechanism in hot stamping of ultra-high-strength steel parts was clarified by the mechanical, thermal and transformation viewpoints. In hot stamping, the effects of elastic recovery during unloading and thermal shrinkage on the springback are comparatively small, but the effect of the phase transformation is critical. Volume expansion occurs primarily upon the start of the martensitic transformation, and plastic deformation is induced by the volume expansion during holding at the bottom dead centre, causing the springback including the post-stamping deformation to disappear. It was observed from well-organised experiments that holding at the bottom dead centre until the martensite finish temperature prevents the springback, and the springback-free mechanism in hot stamping of ultra-high-strength steel parts was clarified from the observation. The springback behaviour in hot stamping of a thin steel sheet with 0.6 mm thickness was explained from the above mechanism, and the deformation behaviour and quenchability for the thin sheet were examined. A sufficient holding time at the bottom dead centre was more closely associated with the prevention of springback rather than sufficient hardening. Additionally, local thinning around the bottom corner of a bent thin sheet was prevented by optimising the transfer time from the furnace.

Numerical and experimental study on multi-pass laser bending of AH36 steel strips

Laser bending is a process of bending of plates, small sized sheets, strips and tubes, in which a moving or stationary laser beam heats the workpiece to achieve the desired curvature due to thermal stresses. Researchers studied the effects of different process parameters related to the laser source, material and workpiece geometry on laser bending of metal sheets. The studies are focused on large sized sheets. The workpiece geometry parameters like sheet thickness, length and width also affect the bend angle considerably. In this work, the effects of width and thickness on multi-pass laser bending of AH36 steel strips were studied experimentally and numerically. Finite element model using ABAQUS® was developed to investigate the size effect on the prediction of the bend angle. Microhardness and flexure tests showed an increase in the flexural strength as well as microhardness in the scanned zone. The microstructures of the bent strips also supported the physical observations.

Evaluation of the VDA 238-100 Tight Radius Bending Test using Digital Image Correlation Strain Measurement

The VDA238-100 standard for tight radius bending (v-bending) of sheet materials has received widespread acceptance with automotive suppliers and material producers to characterize local formability. However, the test fixture and tooling in the v-bend test standard is not amenable to direct strain measurement and the operator cannot terminate the test at the onset of crack initiation as the outer bend surface is not visible. Consequently, fracture is identified using a load threshold and the bend angle estimated from an analytical formula based upon the punch displacement and tooling geometry. Bend angles are not directly transferable and must be interpreted relative to the sheet thickness and bend radius unlike a strain measurement. By obtaining an in-situ strain measurement on the surface using digital image correlation (DIC), the plane strain fracture limit can be accurately identified at the onset of cracking and remove ambiguity in translating the bend angles to practical forming operations and simulations. A novel inverted VDA test frame was developed to incorporate DIC strain measurement during the bend test and a variety of advanced high strength sheet materials were evaluated. It was observed that the VDA bend test creates a homogeneous strain state of plane strain across the width of the sample along with a proportional strain path to fracture without necking that is ideal for fracture characterization. A correlation is developed to relate the bend angle with the major strain for the materials considered and accounts for the sheet thickness and bend radius. A comparison of the bend angle obtained using the formula in the VDA standard based on the punch displacement was in very good agreement with manual measurements and an algorithm to measure the bend angle using DIC analysis was developed.

Electrodeposition of Nickel on Titanium in Aqueous Acidic Electrolytes

Nickel may be produced in acidic chloride-sulfate based electrolytes. Nickel is initially deposited on stainless steel or titanium cathodes to produce starting sheets while chlorine gas is evolved on DSA anodes. Stress in the nickel deposit may cause bending of the cathode sheet. In addition, irregular growth such as dendrite formation may occur. In extreme cases, short-circuiting of electrodes will happen. Fundamental electrochemical studies of the initial stages of the electrodeposition process may give valuable information for obtaining smooth nickel deposits. Electrochemical experiments of nickel deposition were carried out on titanium substrates using cyclic voltammetry and potential step, and examined with SEM imaging. The measurements were performed at different deposition potentials and times to get an overall picture of the nucleation and growth of nickel on titanium substrates. Further deposition studies have been performed using in situ AFM to study the whole process from single nickel nuclei to a cohesive layer, and determine the nucleation mode and characteristics. The effects of electrolyte composition and pH will be presented. The pre-treatment of the substrate is important for the nucleation and properties of the nickel deposit. The figure illustrates the different nucleation overpotential for a smooth and rough titanium substrate. Figure 1

Thermo-mechanical vibration, buckling, and bending of orthotropic graphene sheets based on nonlocal two-variable refined plate theory using finite difference method considering surface energy effects

In this article, the influence of temperature change on the vibration, buckling, and bending of orthotropic graphene sheets embedded in elastic media including surface energy and small-scale effects is investigated. To take into account the small-scale and surface energy effects, the nonlocal constitutive relations of Eringen and surface elasticity theory of Gurtin and Murdoch are used, respectively. Using Hamilton’s principle, the governing equations for bulk and surface of orthotropic nanoplate are derived using two-variable refined plate theory. Finite difference method is used to solve governing equations. The obtained results are verified with Navier’s method and validated results reported in the literature. The results demonstrated that for both isotropic and orthotropic material properties, by increasing the temperature changes, the degree of surface effects on the buckling and vibration of nanoplates could enhance at higher temperatures, while it would diminish at lower temperatures. In addition, the effects of surface and temperature changes on the buckling and vibration for isotropic material property are more noticeable than those of orthotropic. On the contrary, these results are totally reverse for bending problem.