Uniform Bending Research Articles

A new approach to improve the ductility of non-penetrating laser-welded lap joints of cold-rolled 301LN stainless steel

The aim of this work is to improve the fracture ductility of non-penetrating laser-welded lap joints. The 1.5 + 2.0 and 2.0 + 2.0 lap plates of cold-rolled 301LN stainless steel tilted 15° in the load direction and in the reverse load direction were welded by a vertical laser beam to prepare a positive-tilt weld (PTW) and negative-tilt weld (NTW). The tilt weld had a regular geometry, and the solidification centerline was tilted by approximately 15°. The laser-welded 301LN stainless steel was solidified by the primary ferritic mode with good resistance to thermal cracking, and the weld metal with ultrafine grains had excellent plasticity. The main weld in the penetrating plate of the NTW joints has a greater bending moment than that of PTW joints under tensile loading conditions, so the plastic deformation of the NTW is due to uniform bending, while that of the PTW is due to approximate parallel stretching. The bending deformation of the main weld of the NTW joint leads to a greater tensile stress ratio (decomposed normal stress to shear stress) in the interfacial weld metal than that of the PTW joint, so the interfacial fracture ductility of NTW joints is much greater than that of PTW joints.

Moving Accelerometers to the Tip: Monitoring of Wind Turbine Blade Bending Using 3D Accelerometers and Model-Based Bending Shapes.

Increasing the length of wind turbine blades for maximum energy capture leads to larger loads and forces acting on the blades. In particular, alternate bending due to gravity or nonuniform wind profiles leads to increased loads and imminent fatigue. Therefore, blade monitoring in operation is needed to optimise turbine settings and, consequently, to reduce alternate bending. In our approach, an acceleration model was used to analyse periodically occurring deviations from uniform bending. By using hierarchical clustering, significant bending patterns could be extracted and patterns were analysed with regard to reference data. In a simulation of alternate bending effects, various effects were successfully represented by different bending patterns. A real data experiment with accelerometers mounted at the blade tip of turbine blades demonstrated a clear relation between the rotation frequency and the resulting bending patterns. Additionally, the markedness of bending shapes could be used to assess the amount of alternate bending of the blade in both simulations and experiment.s The results demonstrate that model-based bending shapes provide a strong indication for alternate bending and, consequently, can be used to optimise turbine settings.

Reassesment of lateral torsional buckling in hot-holled I-beams

Lateral torsional buckling (LTB) of I-beams is characterized by simultaneous lateral deflection and twist. In this paper the influence of destabilizing and neutral effects of loadings and the possibility of the occurrence of web distortion, which characterizes the lateral distortional buckling (LDB), is numerically investigated. Recent research has shown divergences between the standard procedures of the American Institute of Steel Construction, Australian Standards and Eurocode with LTB numerical results. In addition, some procedures have recently been proposed for correcting possible deviations between the results of numerical analysis and standard procedures. In order to investigate this situation, elastic stability and physical and geometrical nonlinear analyzes are performed, using GBTul and ABAQUS softwares, respectively. The numerical model is calibrated considering experimental tests. The beams are simply supported, with fork supports at the ends, and subject to neutral and destabilizing effects of loading. The beams are subject to uniform bending, mid-span concentrated load and uniformly distributed loads. The parametric study is performed by varying the geometric cross section parameters. The results are compared with international standards and analytical procedures. It is concluded that the influence of destabilizing and neutral effects of loadings is responsible for providing non-conservative results when compared to the American Institute of Steel Construction procedure. The occurrence of LDB in hot-holled I sections influences the lateral stability strength of I-beams, but it is not predominant. With the possibility of using the elastic critical moment obtained by the elastic stability analysis, the conservative situation of EC3 is verified. The Australian Standards procedure is in agreement with all the situations analyzed.

Buckling of welded high-strength steel I-beams

National constructional steel design standards preclude many high-strength quenched and tempered steel grades, and with the growth update of such steels in structural applications, revision or new guidance is needed. This paper reports experiments and presents numerical studies of welded high-strength steel (HSS) I-section beams fabricated by welding BISPLATE-80 (nominal yield stress fy = 690 MPa) and BISPLATE-100 (fy = 890 MPa) plates. For the experimental program, three BISPLATE-80 and five BISPLATE-100 I-sections were fabricated and tested under scenarios of uniform bending and moment gradient. The specimens were designed to develop either lateral-torsional or local buckling modes, with tensile fracture not being observed during the tests. The buckling capacity so obtained significantly exceeded the predictions of Eurocode 3 and of the Australian AS4100, especially for intermediate beam slendernesses, while the ANSI/AISC 360–16 guidelines marginally estimated the buckling resistance of specimens. It was also found that lateral-torsional buckling initiated after partial yielding of the compression flange. The numerical studies consisted of two ABAQUS finite element (FE) models, being a test simulation model as well as a generic representation, to facilitate extending the pool of experimental data, which showed that Eurocode 3 and AS4100 underestimate the buckling strength of intermediate and slender beams, while the ANSI/AISC 360–16 curves overestimate the FE predictions for lateral-torsional buckling capacities of beams in inelastic portions. A parameter that is dependent on the material properties is introduced in the AS4100 beam buckling strength formula and a new curve for the buckling of HSS flexural members is proposed.

Cylindrical shells under uniform bending in the framework of Reference Resistance Design

The resistance of cylindrical shells and tubes under uniform bending has received significant research attention in recent times, with a number of major projects aiming to characterise their strength through both experimental and numerical studies. However, the investigated cross-section slenderness ranges have mostly addressed low radius to thickness ratios where buckling occurs after significant plasticity and the influence of geometric imperfections is relatively minor. The behaviour under uniform bending of thinner imperfection-sensitive cylinders that fail by elastic buckling was largely omitted, as was the influence of finite length effects. The value of such resistance models that are only useful for thicker cylinders is therefore somewhat limited.This paper offers the most comprehensive known characterisation of the buckling and collapse resistance of isotropic cylindrical shells and tubes under uniform bending. Expressed within the modern framework of Reference Resistance Design (RRD), it holistically incorporates the effects of material plasticity, geometric nonlinearity and sensitivity to realistic and damaging weld depression imperfections. The characterisation was made possible by the authors' recently-developed novel methodology for mass automation of nonlinear shell buckling finite element analyses. A modification of the RRD formulation is proposed which facilitates its application to systems of low slenderness, and offers a compact algebraic characterisation of all potential imperfection amplitudes for this common shell structural condition. A reliability analysis is also performed.

Assessment of lateral distortional buckling resistance in welded I-beams

Lateral distortional buckling (LDB) of I-beams is characterized by simultaneous lateral deflection, twist and cross section change due to web distortion. The present study investigates the effect of web distortion in LDB resistance of doubly-symmetric welded I-beams. Elastic stability and physical and geometrical nonlinear analyses are performed, using GBTul and ABAQUS softwares, respectively. The numerical model is calibrated considering experimental tests. The beams are simply supported, with fork supports at the ends, and subject to neutral and destabilizing effects of loading. The beams are subject to uniform bending, mid-span concentrated load and uniformly distributed loads. The parametric study is performed by varying the geometric cross section parameters. The results are compared with international standards and analytical procedures. It is concluded that the occurrence of LDB is responsible for the resistance reduction, especially for the slender web sections. With the elastic stability analysis, it is possible to estimate the critical moment for the calculation of the ultimate moment considering the LDB. It is found that there is no need to propose a new solution for the determination of LDB resistance, since some procedures allow the use of the elastic stability analysis response for the calculation of the ultimate moment, such as EC3. However, some adjustments can be made to the ANSI/AISC 360–16 and AS 4100: 1998 standards, since the results compared to these procedures are not conservative.

Imperfection Insensitivity of Thin Wavy Cylindrical Shells Under Axial Compression or Bending

Abstract The presence of imperfections significantly reduces the load carrying capacity of thin cylindrical shells due to the high sensitivity of thin shells to imperfections. To nullify this unfavorable characteristic, thin cylindrical shells are designed using a conservative knockdown factor method, which was developed by NASA in the late 1960s. Almost all the design codes, explicitly or implicitly, follow this approach. Recently, a new approach has emerged to significantly reduce the sensitivity of thin cylindrical shells. In this approach, wavy cross sections are used instead of circular cross sections for creating thin cylinders. Past studies have demonstrated the effectiveness of wavy cylinders to reduce imperfection sensitivity of thin cylinders under axial compression assuming linear elastic material behavior. These studies used eigenmode imperfections which do not represent realistic imperfections found in cylinders. In this paper, using a realistic dimple-like imperfection, new insights are presented into the response of wavy cylinders under uniform axial compression and bending. Furthermore, the effectiveness of the wavy cylinders to reduce imperfection sensitivity under bending load is investigated assuming a plastic Ramberg–Osgood material model. The effect of wave parameters, e.g., the amplitude and the number of waves, is also explored. This study reveals that wavy thin cylinders are insensitive to imperfections under bending in the inelastic range of the material. It is also found that the wave parameters play a decisive role in the response of thin wavy cylinders to imperfections under bending.

Springback Analysis of AA5754 under Warm Stamping Conditions

Prediction of springback has been thoroughly investigated for cold forming processes; however with the rising prominence of lightweight materials and new forming technologies, predicting springback at elevated temperatures has become essential. In this paper, three analytical models and one empirical model were proposed to predict springback of an aluminium alloy AA5754 at warm forming conditions. The analytical models developed were based on the effect of the linear bending moment, uniform bending moment and through-thickness stress gradient respectively on springback, while the empirical model was developed using the results of L-shape bending tests. The model predictions were compared with the experiment results for various forming conditions. At room temperature, all four models had very good agreement. At elevated temperatures, the linear bending moment model was preferred for a die radius of 8mm, whereas empirical and stress gradient models were more suitable for a die radius of 4mm; in both cases, very close agreement was achieved where errors were within 5%.

Folding a ridge-spring

A ridge-spring is a thin-walled bent strip with flat side panels. It may be folded elastically along its length, to create a localised hinge region of mostly uniform cylindrical curvature and bending moment, which do not vary with the fold angle of hinge. A simple analysis shows a common grouping in closed-form expressions; α4/3 · (b/t)1/3, where α is the pitch angle of the ridge line, b is the strip width and t its thickness. More accurate calculations of the hinge curvature and moment confirm the robustness of simpler expressions, which are compared to data obtained from finite element simulations. It is shown that, for many initial geometries, theoretical predictions of curvature and moment are typically within 10% of the computational results—which project the same dimensional performance. We also compare a ridge-spring to a more familiar tape-spring of equal cross-sectional proportions. For moderate pitch angles and relatively small thicknesses, it is shown that a ridge-spring has a higher folded hinge curvature and bending moment, comparatively, which may prove attractive for certain applications.

On the post‐buckling rotational capacity of square hollow sections in uniform bending – An initial study of the impact of initial imperfections on deformation paths

On the post‐buckling rotational capacity of square hollow sections in uniform bending – An initial study of the impact of initial imperfections on deformation paths

Inelastic lateral buckling of steel cantilevers

Steel cantilevers are very different from the simply supported beams under uniform bending which provide the basis for designing steel members against lateral buckling. Cantilevers have different end restraint conditions, while the most critical loading condition for cantilevers is one of concentrated end load leading to a linear moment distribution. Thus the elastic lateral buckling formulations for uniform bending of simply supported beams used more generally for design are inappropriate for cantilevers.The mono-symmetric yield patterns in simply supported beams with residual stresses in uniform bending are of opposite sense to those of cantilevers because of the opposite sense of the bending moments. Thus formulations which take account of the effect of mono-symmetry on the inelastic lateral buckling of simply supported beams are inappropriate for cantilevers. Further, the linear cantilever moment distribution leads to very localised yielding instead of the uniform yielding of beams under uniform bending.This paper studies the inelastic lateral buckling of cantilevers in order to produce better design guidance than that currently based on the inelastic buckling of simply supported beams in uniform bending. The effects of mono-symmetry on the elastic buckling of beams and cantilevers are first investigated, and then the effects of the mono-symmetric non-uniform yielding patterns which complicate the prediction of the inelastic buckling resistances of cantilevers are studied. Cantilevers with reduced (instead of rigid) end warping restraints occur in overhanging beams, and so the effects of yielding on overhanging segments are also studied.These studies are used to develop simple approximate methods for designing cantilevers and overhanging segments against inelastic lateral buckling.

LRFD for Lateral-Torsional Buckling Resistance of Cellular Beams

Cellular beams are those that present sequential web openings along the span, and are produced by thermal cutting and welding. Studies addressing the lateral-torsional buckling resistance curve of cellular beams according to the American standard are scarce. The objective of the present study is to investigate the lateral-torsional resistance in cellular beams, considering the Load and Resistance Factor Design. To this end, geometrical and material nonlinear analyses are conducted. The cellular beams are simply supported, with fork supports at the ends, and subjected to three types of loading: uniform bending, mid-span concentrated load and uniformly distributed loads. The geometric parameters of cross section and unrestrained length are varied. Results are compared with the nominal and design flexural strength. Failure modes are associated with non-dimensional lateral-torsional stiffness. Considering the application of uniform bending moment, failure modes such as LTB and WDB + LTB occurred. In contrast, considering the presence of shear stress, failure modes such as the Vierendeel mechanism, WPB, and WPB + LTB occurred. It was concluded that when compared with the numerical model results, the design flexural strength was ineffective under inelastic buckling regime, a situation in which interaction of modes of failure can occur. When considering only the pure lateral-torsional bucking, the Load Resistance Factor Design variation was observed. This variation presented an average value equal to 0.83, differing from the procedure in question by approximately 7.8%.

Symmetry-adapted real-space density functional theory for cylindrical geometries: Application to large group-IV nanotubes

We present a symmetry-adapted real-space formulation of Kohn-Sham density functional theory for cylindrical geometries and apply it to the study of large X (X=C, Si, Ge, Sn) nanotubes. Specifically, starting from the Kohn-Sham equations posed on all of space, we reduce the problem to the fundamental domain by incorporating cyclic and periodic symmetries present in the angular and axial directions of the cylinder, respectively. We develop a high-order finite-difference parallel implementation of this formulation, and verify its accuracy against established planewave and real-space codes. Using this implementation, we study the band structure and bending properties of X nanotubes and Xene sheets, respectively. Specifically, we first show that zigzag and armchair X nanotubes with radii in the range 1 to 5 nm are semiconducting. In particular, we find an inverse linear dependence of the bandgap with respect to the radius for all nanotubes, other than the armchair and zigzag type III carbon variants, for which we find an inverse quadratic dependence. Next, we exploit the connection between cyclic symmetry and uniform bending deformations to calculate the bending moduli of Xene sheets in both zigzag and armchair directions. We find Kirchhoff-Love type bending behavior for all sheets, with graphene and stanene possessing the largest and smallest moduli, respectively. In addition, other than graphene, the sheets demonstrate significant anisotropy, with larger bending moduli along the armchair direction. Finally, we demonstrate that the proposed approach has very good parallel scaling and is highly efficient, enabling ab initio simulations of unprecedented size for systems with a high degree of cyclic symmetry. In particular, we show that even micron-sized nanotubes can be simulated with modest computational effort.

Pore structure of reactively synthesized nanolaminate Ti3SiC2 alloyed with Al

Ti3SiC2 has the unique properties integrating the advantages of metals and ceramics, and good open pore structure when alloyed with Al. In this work, porous Ti3SiC2 compounds with different Al/Si atom ratios were prepared through the reactive synthesis of elemental powders at 1300 °C. The results indicate that the phase compositions are determined by Al element mole number, and that the pore structure can be controlled through varying Ti particle size. The MAX phase transits from Ti3SiC2 with Al element mole number no more than 0.6 to Ti3AlC2 with Al element mole number in the range of 0.8–1.2. When Al element mole number is 0.6, the porous compound has a single MAX phase of Ti3SiC2 with uniform microporous structure and high bending strength. Porous Ti3SiC2 alloyed with 0.6Al has a slow linear increase rate of 0.0083%/μm in open porosity with increasing Ti particle size, and a strict linear relationship between the maximum aperture and Ti particle size with the increase rate of 0.0342 μm/μm. The pore structure formed by the phase transition mechanism for porous MAX phase has the smallest tortuosity factor compared with that formed by the clearance mechanism and the Kirkendall effect.

Preliminary study on the impact of initial imperfections on the post‐buckling rotation of square hollow sections in uniform bending

ABSTRACTWith increasing use of high‐strength steel grades, the need for more accurate design specifications arises, with the aim of fully exploiting the material benefits and create economic advantages. According to Eurocode 3, the maximum rotational capacity is limited and linked to the definition of cross‐sectional classes. For class 1, the rotation θ is assumed to be “infinite”, while it drops significantly for class 2 and 3 to a maximum rotation of θpl and θel, respectively. In reality, in spite of their lower hardening capacity and ultimate strains, high‐strength steel sections display a non‐negligible rotational capacity that exceeds these code predictions, which were developed for mild steel and with a level of analysis in mind that is suitable for hand calculations. For an increased use of high‐strength steel sections, it is thus very important to understand and to be able to predict a more realistic deformation and rotation capacity, with the aim of implementing the findings in tools for advanced, FEM‐based Design by Analysis (DbA) approaches. As an initial step in this direction, the proposed paper shows the results from numerical calculations on the rotational capacity of HSS rectangular hollow sections. The numerical results are calibrated against laboratory tests. Consequently, different rectangular cross section dimensions but also variations of the steel grade and the thickness are chosen and calculated in the finite element program ABAQUS.

Stability Analysis of Compression Member on Elastic Springs

Part of the large parametric study focused on the stability behaviour of compression single members and the member structures with various loadings and boundary conditions is presented here. This part relates to the stability analysis of the compression member on elastic springs. The span of the member L = nℓ, where ℓ is the length of the field which equals to the distance between the neighbouring elastic springs. The members under investigation have seven various numbers of the fields n = 2, 3, 4, 5, 6, 7 and ∞. The members have uniform bending rigidity EI, uniform normal force N and (n – 1) elastic springs with equal spring stiffness Cw. The results are presented in the form of eight diagrams. The curves of diagrams were replaced by the straight lines to be able derived approximate formulae for calculation of the critical force. It is shown that approximate formulae give the values of the critical forces Fcr.a which differ from diagram values Fcr less than 3.3 %, being slightly on the safe side. The values of the critical forces Fcr obtained from the solution of the stability equation are verified by comparisons with results Fcr.IQ of the computer program IQ 100. Excellent agreement is achieved between Fcr.IQ and Fcr. The presented solution of the compression member on elastic springs may be used also for the calculation of the critical force of the compression member on elastic foundation. The solution given in the paper creates scientific background needed in the design of the semi-through bridge trusses.

Research on Four-Point Air Bending Process and Contour Detection Method for JCO Forming Process of LSAW Pipes

Aiming at the forming efficiency and roundness of the longitudinal submerged arc welded (LSAW) pipes in JCO (J-shape to C-shape to O-shape) forming process, this paper proposes a four-point air bending process. Compared with the traditional three-point air bending process, The new process can provide a more uniform bending moment, does not need to crimp the edges of steel sheet, shorten the residual straight segment length, and lengthen the forming length in single pass. The mechanical model is established to analyze the static equilibrium conditions and elastic–plastic deformation. The process is simulated by using the software package ABAQUS, to find the maximum punch spacing, and further determine the formulation principles of other process parameters. In addition, a contour detection method for the LSAW pipes in forming process is proposed based on machine vision (planar-array CCD camera produced by Gray Point Corporation, Vancouver, Canada). This method can not only quickly detect the contour of each pass, but also splice the detected contours together to obtain the overall contour with the given splicing algorithm. According to the measured contour, the bending angle, radius, and roundness can be calculated, to correct the punch reduction in the next pass and improve the forming accuracy of the pipes. Finally, an experimental system is designed to verify the proposed four-point bending JCO forming process and contour detection method. The result shows that the error between the contour detection method and CMM (coordinate measuring machine) is less than 0.5% for the overall contour, the two experimental pipes require 13 and 15 passes respectively, the roundness of pipes are less than 1.1%, which is much better than that of traditional three-point bending JCO forming process.

The evolution of fracture process zones in as-received and oxidized air plasma sprayed TBCs

The evolution of the fracture process zones as precursor to fracture was elucidated in as-received and oxidized air plasma sprayed (APS) Thermal Barrier Coating (TBC) specimens. Multiple techniques of Digital Image Correlation (DIC), Acoustic Emission (AE), Finite Element Analysis (FEA) and Scanning Electron Microscope (SEM) micrographs were combined together to obtain in-depth understanding of the failure mechanisms involved in a TBC component under uniform bending stress field. Both sides of specimens were monitored simultaneously during loading and it is shown that within a uniform applied strain, the localized zones of non-symmetric strains with the different lengths were initiated and growth within the ceramic top coat perpendicular to the principle stresses. The process zones were initiated in both as-received and oxidized specimens upon yielding the substrate. However, different strain localization areas were observed on two sides of each specimen. It was observed that separations in each localized zone were resisted by cohesive tractions controlled by the material microstructural features and not the applied external load. One of these localized strains was then rotated parallel to the interface propagating until the final delamination. In the oxidized specimen, the delamination was faster and spallation of top coat ceramic layer followed immediately after cracks reached the bond coat interface. The cohesive properties were determined using a hybrid experimental-numerical approach.

On the post‐buckling rotational capacity of square hollow sections in uniform bending

AbstractNominated for the Bernt Johansson Outstanding Paper Awards at Nordic Steel 2019The growing popularity of high‐strength steel grades leads to the need for more accurate design specifications, with the aim of fully exploiting the material benefits and creating economic advantages. According to Eurocode 3, the maximum rotational capacity of a section is limited and linked to the definition of cross‐sectional classes. For class 1, the rotational limit θ is assumed to be ”infinite“, whereas it drops significantly for classes 2 and 3 to a maximum rotation of φpl and φel, respectively. In reality, despite their lower hardening capacity and ultimate strains, high‐strength steel sections exhibit a non‐negligible rotational capacity that exceeds these code predictions, which were developed for mild steel and with a level of analysis in mind that is suitable for hand calculations. In order to achieve greater use of high‐strength steel sections, it is thus very important to understand and be able to predict a section's deformation and rotational capacity more accurately, with the aim of implementing the findings in tools for advanced, FEM‐based design by analysis (DbA) approaches. As an initial step in this direction, this paper shows the results from numerical calculations of the rotational capacity of HSS rectangular hollow sections. The numerical results were calibrated against laboratory tests. Consequently, different rectangular cross‐section dimensions and variations of the steel grade and thickness were chosen and analysed in the ABAQUS finite element software.

Bilayer tunneling field effect transistor with oxide-semiconductor and group-IV semiconductor hetero junction: Simulation analysis of electrical characteristics

Operation mechanisms and electrical characteristics of tunneling field-effect transistors (TFETs) employing a hetero tunneling junction by utilizing an n-type oxide-semiconductor (OS) and a p-type group-IV-semiconductor are comprehensibly analyzed. Gate-normal band-to-band tunneling (BTBT) has high potential for the superior TFET performance such as high on-state current and small sub-threshold swing (S.S.). Additionally, a hetero tunneling junction with type-II energy band alignment is promising to exponentially increase tunneling probability with keeping small off-state current. Therefore, in this study, we investigate the impact of key material and device parameters such as energy band alignment of source/channel regions and thickness of the OS channel layer or gate insulator based on technology computer aided design (TCAD) simulation. The gate-controlled uniform band bending along the source-drain direction realizes uniform BTBT in the entire region of the hetero tunneling junction. Also, the reduction of the tunneling barrier height, which is continuously controlled by the conduction band minimum of the OS-channel and the valence band maximum of the IV-source, is effective to increases on-state current and decrease S.S. value. On the other hand, the thicknesses of OS channel layer and gate insulator have strong influences on tunneling probability and threshold voltage. Therefore, the sub-threshold characteristics of TFETs are sensitive to non-uniformities in the tunneling junction such as channel thickness fluctuation and surface potential fluctuation at the metal-oxide-semiconductor (MOS) interfaces. These numerical analyses of the device operation are essentially important to understand the effects of key device parameters on the TFET performance and to realize the superior electrical performance.