Plastic Bending Deformation Research Articles

Study on seismic performance of a novel connection for exterior wall panels

In order to avoid the damage of the external wall panel and connecting joints caused by the incompatibility between the steel structure and the external wall panel under earthquake loads, as well as to control the interaction between the structure and wall panel to ensure favorable impacts on the main structure, a new connection for external wall panel is proposed. This connection combines the features of the sliding connection and the energy dissipating connection. To investigate the deformation behavior, failure modes, and energy dissipation capacity of the connection, a total of ten specimens with different parameters were designed for cyclic loading. The results indicate that the new connection dissipates energy through bending plastic deformation and pull-bending plastic deformation of the side plate, demonstrating excellent deformation and energy dissipation capacity with noticeable post-yield strengthening effect. Additionally, the effects of different geometric parameters on the initial stiffness, yield load, bearing capacity and hysteretic properties of the connections are also analyzed. Finally, based on the theoretical model of the space rigid frame, the calculation formula of the characteristic parameters at elastic stage of the joint is proposed by the assumptions of ignoring torsion, axial and shear deformation, which is validated by the test results and finite element simulation.

ANALYSIS OF ASYMMETRIC PLASTIC BENDING DEFORMATION OF WELDED TUBE SHEETS AND DERIVATION OF A DAMAGE LAW FOR J SHAPE-C SHAPE -O SHAPE FORMING

The J shape-C shape -O shape (JCO) forming method of sheets for large-diameter longitudinally welded pipes has been widely used to manufacture oil and gas pipelines. The quality of welded pipes formed through the JCO process is directly affected by the accurate control of asymmetric bending springback and damage during the procedure. A finite element model (FEM) for JCO asymmetric bending was constructed to investigate the characteristics of asymmetric plastic bending deformation and the distribution laws of damage in JCO forming. This model was based on a nonlinear mixed hardening Lemaitre damage model coupled with the Quasi-Plastic-Elastic (QPE) model. Then, residual stress, forming shape, and damage degree of crimping, first bending, second bending, and third bending were analyzed. Moreover, the accuracy of the model was experimentally verified. Results demonstrate that, the asymmetric bending deformation process can be divided into five stages, including rigid body rotation phase, full elastic deformation phase, elastic–plastic uncladded deformation phase, elastic–plastic cladded phase, and springback phase. In the first bending, the stress centerline significantly misaligns with the mold centerline. Asymmetry is not evident in the second and third bending stages. Furthermore, the peak residual stress and peak damage can be effectively reduced by a larger punch radius, while the peak damage can be reduced by a larger die span. This study lays a foundation for optimizing the technical parameters of JCO forming. Keywords: JCO forming, asymmetric bending, finite element, QPE model, deformation characteristics

Study on the Influencing Factors and Forming Process Selection of Sheet Metal Bending Spring Back Defects

In recent years, with navigation, aviation, chemical manufacturing, and automobile bodies increasing requirements for lightweight, high efficiency, and energy saving, quality requirements in the selection of materials and manufacturing process are also improved. However, there is an unavoidable elastic deformation in the process of plastic bending deformation of the panel veneer, and the accuracy of the workpiece is impacted by the spring back phenomenon, which causes dimensional and shape inaccuracies in the panel veneer. The purpose of this paper is to summarize and analyze the phenomenon of flexural spring back caused by material selection and processing techniques and to discuss the solution of the flexion bounce problem from the material selection, processing method, and machining mold, which can be applied to avoid material wastage.

Ballistic response of a high-strength steel

Quasi-static compression/tension, dynamic compression/shear mechanical property tests, fracture morphology characterization, dynamic response experiment, numerical simulation, and calculation of the ultimate penetration velocity of the high-strength steel under the impact of large mass low-velocity fragments and small mass high-velocity fragments were carried out to study the ballistic performance of high-strength steel used for armor vehicle protection and clarify its dynamic response under Ballistic impact. The fracture mode of the high-strength steel under dynamic impact compression and shear was shear failure. A large number of fine parabolic shear dimples were formed on the fracture surface. The high-strength steel had an obvious strain rate strengthening effect and adiabatic shear sensitivity. The plug formed under the low-velocity impact of a large mass fragment was a cone shape, and the impact area of the target plate underwent slight bending plastic deformation. The damage of the fragment to the target plate includes both adiabatic shear failure and ordinary shear failure. Under the high-velocity impact of small mass fragments, the fragments were seriously deformed and destroyed, and the damage model of the target plate is adiabatic shear failure.

Experimental study on the longitudinal shear transfer mechanisms and resistance in CSTC composite beams

This contribution presents an experimental study on composite steel truss in concrete (CSTC) beams consisting of prefabricated structural steel latticed girders embedded in concrete. Unlike typical composite beams with downstand steel profiles using headed stud shear connectors, CSTC beams are composed of straight and sinusoidally bent bars with a circular cross-section, in which the transfer of the longitudinal force is ensured via a mechanical interlock between the steel diagonals and the surrounding concrete slab. Because of the lack of specific tests, it is necessary to comprehend the local behaviour (stiffness, resistance and slip capacity) through new experimental investigations which support the development of a reliable design model able to predict the respective longitudinal shear resistance.This paper presents and discusses the setup and results of a wide experimental campaign of more than 30 push-out tests on CSTC beams. Different geometrical and mechanical parameters were varied in accordance with their typical range of application. Based on the experimental results, it was found that the shear transfer mechanism and resistance is governed by localized concrete failure combined with plastic bending deformation of the diagonal bars. The load-slip behaviour was found to be qualitatively comparable with headed stud shear connectors and the significant slip capacity, in most cases beyond 20 mm, indicates that the sinusoidal web bars lead to a shear transfer mechanism that may be considered to be ductile according to EN 1994-1-1. In addition, to isolate the local contribution to the resistance provided by the bars near the weld seams, the diagonal bars of some specimens were intentionally sawed off in some of the specimens, resulting in a “steel tooth”. The load carried by this isolated component was found to be about 58 % of the full longitudinal shear resistance. The experimental values of the resistance were finally used to calibrate statistically an analytical equation for predicting the design of longitudinal shear resistance in compliance with the reliability levels given in EN 1990. Additional considerations concerning the potential interaction with the vertical shear load capacity given by the diagonal bars were included in the final design proposal.

Seismic application of steel rocking column bases with replaceable cover plates in steel MRFs

This paper presented unidirectional and bidirectional cyclic loading test results of a novel steel rocking column base. Feasibility of the column base in steel moment-resisting frames was verified through nonlinear static and time history analysis. It was found that the column base was capable of dissipating seismic energy through plastic bending deformation of the replaceable cover plates and flag-shaped hysteretic curves can be observed. Nevertheless, it is not expected to provide much energy dissipation for the whole structural system, since the plastic bending deformation of each cover plate is only in one direction. A three-dimensional simplified numerical model of the column base was developed and validated against the test results. Following that, nonlinear static and time-history analysis were conducted on prototype steel moment-resisting frames with and without the rocking column bases. In general, replacing some column bases with the rocking ones (i.e., 4/24 of all in this study) did not cause much reduction in lateral resisting stiffness and capacity. Moreover, this reduction was even slighter when the loading direction was perpendicular to the weak axis of the rocking column section. On the other hand, replacing all fixed column base with the proposed rocking column base may cause drift concentration in the ground storey, which is too radical for the prototype building. The seismic responses of modified frames were generally very close to that of the original frame with all fixed column bases. Even though the maximum drifts in the ground storey of these frames were larger than that of the original frames with fixed bases, the maximum drifts of the whole structures were not expected to be amplified. • Bidirectional cyclic loading tests on a novel steel rocking column base were conducted. • The column base showed flag-shaped hysteretic cures and dissipated seismic energy through plastic deformation of the replaceable cover plates. • Feasibility of the column base in steel moment-resisting frames was verified through nonlinear static and time history analysis. • Replacing some column bases with the rocking ones did not cause much reduction in lateral stiffness and capacity.

Research on Damage Assessment of Concrete-Filled Steel Tubular Column Subjected to Near-Field Blast Loading

Concrete-filled steel tubular (CFST) columns are widely used in engineering structures, and they have many different cross section types. Among these, normal solid sections and concrete-filled double-skin steel tubular sections are often used. Although many studies have been conducted on CFST columns with these two section types, no studies have been conducted on their damage assessment under blast loading. In this study, experimental analysis and a numerical simulation method were integrated to evaluate the responses and assess the damage of two concrete-filled steel tubular (CFST) columns with different cross sections subjected to near-field blast loading. The results showed that for a scaled distance of 0.14 m/kg1/3, plastic bending deformation occurred on the surfaces of the two CFST columns facing the explosive. The antiexplosion performance of the normal solid-section (NSS) CFST column was better than that of the concrete-filled double-skin steel tubular (CFDST) column. The explosion centre was set at the same height as the middle of column, and the distributions of the peak pressure values of the two columns were similar: the peak pressures at the middle points of the columns were the greatest, and the peak pressures at the bottom were higher than those at the top. With the analysis of the duration of the positive pressure, the damage at the middle was the most severe when subjected to blast loading. Using pressure-impulse damage theory and the validated numerical simulations, two pressure-impulse damage evaluation curves for NSS and CFDST columns were established separately by analysing the experimental and simulation data. Finally, based on the two pressure-impulse damage evaluation curves, the two pressure-impulse damage criteria for these two different fixed-end CFST columns were defined based on the deflection of the surfaces facing the explosives. Furthermore, the mathematical formulae for the two different column types were established to generate pressure-impulse diagrams. With the established formulae, the damage of the CFST columns with these two cross section types can be evaluated. Damage to other similar CFST columns with different cross section types due to near-field blast loading can also be evaluated by this method.

The Cooling Media Influence on Selected Mechanical Properties of Steel

Abstract The aim of experiment was to analyse the structural transformations and changes in mechanical properties of K720 steel during heat treatment (quenching). Three types of cooling medium were selected. The heating parameters and subsequent delays at the recrystallisation temperature were the same for all samples and were observed in a laboratory furnace. Water with the highest cooling capacity was selected as the benchmark cooling medium. Subsequently, the hardening oil TK – 46 was used. Sunflower oil was selected as the last quenching medium, which can be considered an ecological replacement of quenching oil with possibility of biological disposal. The microstructure and microhardness of individual samples were subjected to a metallographic evaluation and evaluated according to ČSN EN ISO 6507, respectively. The impact toughness analysis was performed according to the ČSN EN ISO 148-1 and a three-point bending test was performed according to ČSN EN ISO 7438. This test specifies a method for determining the ability of metallic materials to undergo plastic deformation in bending. The bend test includes subjection of round, square, rectangular or polygonal cross-section to plastic deformation by bending, without changing the direction of loading, until the specified angle of bend is reached.

Improving bistable properties of metallic shells using a nanostructuring technique

A localized nanostructuring approach is proposed to manufacture bistable metallic shells and improve bistable properties of conventional cylindrical bistable shells. The stable configurations and transition processes of bistable shells based on three different mechanisms are experimentally and numerically investigated. Compared to conventional bistable cylindrical shells produced by plastically bending, the bistable shells with a nanostructured region can have much higher load bearing capacities and stiffness, and consume more energy before shape transition, no matter in a domelike shape or a cylindrical shape. Numerical modelling is developed using two equivalent inelastic strains for the plastic bending deformation and accumulated plastic deformation in nanocrystallization process. For nanostructured bistable shells, the internal stress fields are found to play important roles for the transition features, which are considerably affected by eccentric loading, while the eccentric loading has little effect on transition processes of the cylindrical bistable shells made by plastically bending. The influences of the size of the nanostructured region, the plate thickness and different nanostructuring processes on the bistable behaviors are further experimentally studied. In addition, the bistable properties of the bistable shells based on different mechanisms after thermal treatment from 200 °C to 700 °C are investigated. The applied nanostructuring process largely improves the bistable properties of bistable metallic shells, which can sustain severe environment of high temperature (about 500 °C).

An optimization approach by Finite Element Analysis, using Design of Experiments and Response Surfaces- a survey

The deformation of an aluminum plate, called in this paper, a support plate, which is part of a bending plastic deformation device, is studied in this paper using the Finite Elements Method, respectively design points of the design by optimization using features such as Design of Experiments and Response Surfaces. The start of the analysis was determined by a functional requirement in the design and construction of a sophisticated bending device controlled by steel plates for the production of exhausts for cars. To optimize the project, it was necessary to analyze the behavior of the active material and components of the device. The analysis of material and piece behavior, in working conditions, has been developed by addressing the facilities offered by Ansys software. Following FEA analysis, optimizing the active components of the device has provided proven results in practice through the execution and operation of the device, according to the technology required by the product designer.

Elastic–Plastic Deformation of Flexible Plates With Spatial Reinforcement Structures

A mathematical model for the elastic–plastic bending deformation of spatially reinforced plates is constructed based on a leap-frog numerical scheme. The elastic–plastic behavior of the component materials of the composition is described by the theory of flow with isotropic hardening. The low resistance of the composite plates to transverse shear is taken into account using Reddy’s theory and the geometric nonlinearity of the problem using the von K´arm´an approximation. The dynamic elastic–plastic bending deformation of flat and spatially reinforced metal composite and fiberglass rectangular plates exposed to an air blast wave is investigated. It is shown that for relatively thick plates, replacing a flat leap-frog reinforcement structure by a spatial one leads to a decrease (of a few tens of percent for metal composite structures and a few hundred percent for fiberglass structures) in strain intensity in the binder and to a decrease (insignificant for metal composite structures and a factor of almost 1.5 for fiberglass) in the compliance of the plate in the transverse direction. It has been found that for relatively thin plates, replacing the flat reinforcement structure by a spatial one leads to a slight decrease in its compliance.

Experimental and numerical investigations of the plastic response and fracturing of an aluminium-plated structure with transition circular arcs subjected to impact loading

A new aluminium-plated structure with transition circular arcs used for railway vehicles is presented. Two impact experiments were performed using a test trolley to examine the plastic response and fracturing of the aluminium-plated structure. The results show that the deformation mode of the aluminium-plated structure switches from global plastic bending deformation to local fracturing at the transition circular arc region, which is consistent with the design. Numerical results are presented in terms of deformation modes, force responses and levels of absorbed energy, demonstrating good agreement with the experimental results. From the results of the numerical simulation, fracturing processes and variations in element stress triaxiality are presented. It is found that the stress state of elements affecting the initiation of cracking is of a tension state, while the stress state of elements affecting the end of cracking is of a shear state. A validated finite element analysis of an aluminium-plated structure with right-angled, circular arcs and chamfering transition sections is presented. Plastic and fracture energy levels of the aluminium-plated structure with three transition sections are measured as 2.56, 27.62, and 30.13 kJ and 0.98, 2.41, and 2.16 kJ, respectively, as the second fracturing point. Finally, the finite element analysis illustrates the impact energy effects involving different combinations of trolley mass and velocity, and experimental boundary conditions for varying bolt yield stress and pre-stress levels are defined in the finite element model to investigate the effects of bolted joints on the dynamic responses of an aluminium-plated structure with transition circular arcs.

Theoretical and Experimental Investigation of Coiled-Tubing Deformation Under Multiaxial Cyclic Loading

Summary Coiled tubing is continuous thin-walled steel tubing several thousands of meters in length without screwed connections. Cyclic plastic-bending deformation occurs during tubing spooling on the reel and when passing through the gooseneck arc guide. The coupling effect of cyclic plastic bending and internal pressure causes coiled-tubing diametral growth and wall thinning (referred to as ratcheting). This paper presents a numerical algorithm to calculate the deformations of the diameter and wall thickness on the basis of the incremental plasticity theory and the principle of virtual work. It is shown that predictions with the algorithm correlate well with experimental results.

A bonded sphero-cylinder model for the discrete element simulation of elasto-plastic fibers

Based on the Discrete Element Method (DEM), a bonded sphero-cylinder model is developed to simulate flexible fibers that can undergo plastic bending deformation. In the model, a fiber is formed by connecting a number of identical sphero-cylinders using virtual bonds, which can experience bending, axial extension/compression, and twisting deformations. The elastic deformation and vibration of a single fiber are simulated and validated against elastic beam theories. In addition, an elasto-plastic constitutive model is implemented to simulate the elasto-plastic bending deformation of a fiber. The DEM results compare well with Finite Element Method (FEM) simulations, verifying the proposed elasto-plastic fiber model. By using bonded sphero-cylinders as opposed to more traditional bonded spheres, large aspect ratio fibers with smooth surfaces can be simulated effectively with fewer elements. The new constitutive model allows for the simulation of elasto-plastic materials, such as metals, plastics, and biomass.

Plastic deformation analysis and forming quality prediction of tube NC bending

Plane strain assumption and exponent hardening law are used to investigate the plastic deformation in tube bending. Some theoretical formulae including stress, curvature radius of neutral layer, angle of neutral layer deviation, bending moment, wall thickness variation and cross-section distortion, are developed to explain the phenomena in tube bending and their magnitudes are also determined. During unloading process, the springback angle is deduced using the virtual work principle, and springback radius is also given according to the length of the neutral layer which remains unchanged before and after springback. The theoretical formulae are validated by the experimental results or the validated simulation results in literature, which can be used to quickly predict the forming quality of tube numerical control (NC) bending.

Linear, non-linear and plastic bending deformation of cellulose nanocrystals.

The deformation behaviour of cellulose nanocrystals under bending loads was investigated by using atomistic molecular dynamics (MD) simulations and finite element analysis (FEA), and compared with electron micrographs of ultrasonicated microfibrils. The linear elastic, non-linear elastic, and plastic deformation regions were observed with increasing bending displacements. In the linear elastic region, the deformation behaviour was highly anisotropic with respect to the bending direction. This was due to the difference in shear modulus, and the deformation could be approximated by standard continuum mechanics using the corresponding elastic tensors. Above the linear elastic region, the shear deformation became a dominant factor as the amplitude of shear strain drastically increased. Plastic deformation limit was observed at the bending angle above about 60°, independent of the bending direction. The morphology of the atomistic model of plastically deformed cellulose crystals showed a considerable similarity to the kinked cellulose microfibrils observed by transmission electron microscopy. Our observations highlight the importance of shear during deformation of cellulose crystals and provide an understanding of basic deformations occurring during the processing of cellulose materials.

Analysis of Feed-Direction Burr Formation in Micro-Turning

A three-dimensional model of micro-turning using the finite element method (FEM) is created in this paper to analyzed the formation mechanism and influencing factors of feed-direction burr in micro-turning. According to the simulation and analysis result, in micro-turning,the deformation of the workpiece feed direction end is the combined action of the plastic bending deformation and shear slip deformation, and plastic bending deformation influences burr height and shear slip deformation affects the burr root thickness. Meanwhile, due to the amount of material involved in different deformation actions is changed, compared with conventional scale cutting, the various influencing factors have significant differences effect on the size of burr.

Computational micromechanics of bioabsorbable magnesium stents

Magnesium alloys are a promising candidate material for an emerging generation of absorbable metal stents. Due to its hexagonal-close-packed lattice structure and tendency to undergo twinning, the deformation behaviour of magnesium is quite different to that of conventional stent materials, such as stainless steel 316L and cobalt chromium L605. In particular, magnesium exhibits asymmetric plastic behaviour (i.e. different yield behaviours in tension and compression) and has lower ductility than these conventional alloys. In the on-going development of absorbable metal stents it is important to assess how the unique behaviour of magnesium affects device performance. The mechanical behaviour of magnesium stent struts is investigated in this study using computational micromechanics, based on finite element analysis and crystal plasticity theory. The plastic deformation in tension and bending of textured and non-textured magnesium stent struts with different numbers of grains through the strut dimension is investigated. It is predicted that, unlike 316L and L605, the failure risk and load bearing capacity of magnesium stent struts during expansion is not strongly affected by the number of grains across the strut dimensions; however texturing, which may be introduced and controlled in the manufacturing process, is predicted to have a significant influence on these measures of strut performance.

Research on the Hole Shape Distortions Near the Bending Plastic Deformation Area

In this paper, a research work on the hole shape distortion of commercial-purity aluminum plates in the bending process was carried out. The bending process was simulated by using ABAQUS software in order to reveal the phenomenon and law of hole shape distortions near deformation area. A series of bending tests were conducted for the comparison of simulation results. By measuring the hole diameter under different conditions, the factors that affect distortion level were obtained, including hole distance and initial plate thickness. The rationality of this distortion law was proved by finite element simulation. This research provided the plate with a hole of theoretical basis for bending process selection of the most suitable process parameters.

Modelling Bending Behaviour in Cloth Simulation Using Hysteresis

AbstractReal cloth exhibits bending effects, such as residual curvatures and permanent wrinkles. These are typically explained by bending plastic deformation due to internal friction in the fibre and yarn structure. Internal friction also gives rise to energy dissipation which significantly affects cloth dynamic behaviour. In textile research, hysteresis is used to analyse these effects, and can be modelled using complex friction terms at the fabric geometric structure level. The hysteresis loop is central to the modelling and understanding of elastic and inelastic (plastic) behaviour, and is often measured as a physical characteristic to analyse and predict fabric behaviour. However, in cloth simulation in computer graphics the use of hysteresis to capture these effects has not been reported so far. Existing approaches have typically used plasticity models for simulating plastic deformation. In this paper, we report on our investigation into experiments using a simple mathematical approximation to an ideal hysteresis loop at a high level to capture the previously mentioned effects. Fatigue weakening effects during repeated flexural deformation are also considered based on the hysteresis model. Comparisons with previous bending models and plasticity methods are provided to point out differences and advantages. The method requires only incremental extra computation time.