Pure Bending Tests Research Articles

500 μm heavy micro-alloyed Cu wire for IGBT application: The study on microstructure characteristics, electrical fatigue fracture mechanism and bonding reliability

In this study, we introduced trace amounts of silver and nickel into 500 μm diameter copper wires to form micro-alloyed copper wires used in insulated gate bipolar transistors (IGBT). The addition of silver and nickel enhanced the mechanical properties of the conductors and suppressed the work hardening effect, significantly improving the power cyclic lifetime. Additionally, this study conducted chlorination and high-temperature oxidation test to compare the application characteristics of the heavy micro-alloyed copper wires with pure copper wires, through tensile and bending test, as well as electrical property comparisons. Finally, Cu50Ni (50 ppm Ni) wires were selected and nickel ceramic substrates for wire bonding to evaluate module electrical properties and bonding reliability.In the chloride test, there was no significant pitting corrosion observed in copper wire, and the micro-alloyed copper wire outperformed the pure copper wires in terms of bending lifetime and power cycling performance. In the high-temperature oxidation test, an oxide layer of cuprous oxide formed on the surface of all wires. The pure copper wire exhibited a significant increase in resistance. Notably, the micro-alloyed copper wires had better resistance to oxidation. Regarding wire bonding, the use of Cu50Ni wires and nickel ceramic substrates reduced the diffusion rate of nickel atoms from the substrate to the copper wire, forming a thinner alloy diffusion layer. This prevented electrical degradation and achieved high bonding reliability, especially under higher bonding forces. These findings confirm that micro-alloyed copper wires are suitable for high-power applications.

Lateral buckling of the compressed edge of a beam under finite bending

This paper investigates the critical condition whereby the compressed edge of a beam subjected to large bending exhibits a sudden lateral heeling. This instability phenomenon occurs through a mechanism different from that usually studied in linear theory and known as flexural–torsional buckling. An experimental test device was specifically designed and built to perform pure bending tests on soft materials. Thus, the experimental campaign provides not only the moment-curvature behavior of beams of narrow rectangular cross section, but also information regarding the post-critical lateral buckling behavior. To study the local bifurcation phenomenon, an analytical model is proposed in which a field of small transversal displacements, typical of the linear stability of thin plates, is superimposed on the large vertical displacement field of an inflexed beam in the nonlinear elasticity theory. Furthermore, numerous numerical simulations through nonlinear FE analysis have been performed. Finally, the results provided by the different methods applied were compared and discussed.

Effect of connection and grouting level on mechanical behavior of pipe roof

ABSTRACT Pipe roof support suffers from engineering defects such as connection and insufficient grouting in tunnel engineering. To analyze the influence of connection and grouting level on the mechanical behavior of pipe roof support during tunnel construction, a series of pure bending tests were conducted to measure the mechanical property of pipe roof, and quantitatively analyze the influence of the connection and grouting level on the bearing capacity and bending stiffness of the pipe roof. In addition, the double shear mechanical analysis model of pipe roof based on the Timoshenko beam theory and the Pasternak elastic foundation theory was established by considering the shear deformation of pipe roof, the supporting effect of surrounding rock of tunnel face and the delayed effect of shotcrete for primary support. Then, the solution methods for pipe roof deflection and internal force were derived based on this model. Based on an engineering case, the deflection and internal force distribution, as well as the effect of connection and grouting levels on the pipe roof were discussed. Corresponding construction suggestions were proposed and had achieved good results in the case. This research can provide reference for the design and construction of pipe roof.

A methodological approach towards modelling Steel/CF hybrid damage behaviour under bending

This study presents a combined experimental-numerical approach to predict the load-displacement response of a steel/carbon fibre composite in bending-dominated forming. The 3D material and damage model consider the residual strength of kinked fibres through a deviation-based calibration method.For the first time, a special pure bending test that allows controlled forming to specific curvatures is combined with in situ damage analysis to test and calibrate a damage model for hybrid material forming.The results of this study show that the mechanical performance and damage mode in bending depends on the carbon fibre layup orientation and that the model accurately reproduces the load-bearing capacity, the load drop at fibre kinking and the mechanical behaviour post-forming induced damage.

Engineering application study of high-performance aluminum alloy 6A13-T6

To address the application challenges of the novel high-strength aluminum alloy material 6A13-T6 in engineering, experimental and numerical simulation studies were conducted. Firstly, material tensile tests, axial compression tests, and pure bending tests were conducted, and the applicability of the specification was evaluated. Subsequently, finite element models were employed to analyze the overall mechanical performance and economic indicators of three typical engineering structures (grid shells, grid trusses, and glass curtain walls) based on the test results. The findings indicate that 6A13-T6 exhibits a non-proportional yield strength (f0.2) of 340 MPa, an ultimate strength of 352 MPa, and a post-necking elongation of 14.5%. Design calculations for axially compressed and flexural members made of 6A13-T6 high-strength aluminum alloy can be conservatively carried out following Chinese design specification. The use of 6A13-T6 aluminum alloy can reduce material consumption in structures, with a maximum reduction of up to 29% compared to other commonly used aluminum alloys and up to 72% compared to common steel materials. Therefore, the new high-strength aluminum alloy 6A13-T6 has obvious engineering application value and has been used in a hotel curtain wall project.

An experimental and numerical study on the rotational behavior of bolted glulam beam-to-column connections reinforced by double U-shaped welded steel sections

The study presented the results of the experimental and numerical study on the rotational behavior of the bolted glulam beam-to-column connections reinforced by double U-shaped welded steel sections. To demonstrate the enhancement efficiency of double U-shaped steel sections on the performance of bolted glulam beam-to-column connections, both unreinforced and reinforced bolted glulam connections were tested under the monotonic pure bending scenario and the cyclic loading scenario with combined shear and bending, respectively. Besides, detailed finite element (FE) models of the reinforced bolted glulam beam-to-column connections were developed and then validated by the experimental results. The rotational behavior of the unreinforced connections and that of the reinforced connections were compared in terms of damage modes, performance parameters, stiffness degradation, and cumulative energy dissipation, respectively. The effects of two configurational parameters on the rotational behavior of the reinforced connections were analyzed, which were the diameter of the holes predrilled in the beams and the width-to-thickness ratio of the top plates of the U-shaped steel sections. In the monotonic pure bending tests, the rotational stiffness of the reinforced connections is 1.20–2.22 times that of the unreinforced connections. The rotational stiffness of the reinforced connections is enhanced as the width-to-thickness ratio of the top plates is reduced. Furthermore, when the diameter of the holes predrilled in the beams is enlarged from 22 mm to 30 mm, the rotational stiffness and the ultimate moment resisting capacity of the reinforced connections are reduced by 27.8% and 16.6%, respectively. As for the cyclic loading tests, when reinforced with U-shaped steel sections, the ultimate moment resisting capacity and the rotational stiffness of the bolted glulam connections are enhanced by 26.7% and 17.0%, respectively. The degradation of the secant stiffness of the unreinforced connection is more severe, indicating that the reinforcement with double U-shaped steel sections is an efficient damage-resistant technique for both new and existing bolted glulam connections. based on the developed FE models, both the failure modes and the moment-rotation curves of the reinforced connections under the monotonic pure bending scenario can be predicted.

Research on the Flexural Performance of Steel Pipe Steel Slag Powder Ultra-High-Performance Concrete Components.

In order to study the flexural performance of the combined structure of steel-pipe and steel slag powder ultra-high-performance concrete (UHPC), nine round steel-pipe beams filled with steel slag powder UHPC of different types were fabricated according to the orthogonal test method with the steel pipe type, coarse aggregate content, steel fiber admixture, and curing system as parameters. The broken ring morphology, deformation characteristics, deflection distribution, and flexural bearing capacity of the steel-pipe-UHPC beams were analyzed via a pure bending test and a finite element simulation. The results show that the damage morphology of the round steel-tube-UHPC beams prepared by using steel slag powder UHPC as the inner filling material was "bow damage" under the pure bending load, and the load capacity was higher. When the cross-sectional deflection reached L/30, the external load was still not reduced, and the steel-tube-steel-slag powder-UHPC beam had a better plastic deformation capacity and a later flexural bearing capacity. The type of steel tube had a significant influence on the flexural bearing capacity of the steel-tube-UHPC beam, and the larger the diameter of the steel tube section and the thicker the tube wall, the higher its flexural bearing capacity. The calculated ultimate flexural bearing capacity by the finite element software and the test results had a stable error between 5.6% and 11.2%, which indicates that the model was reasonably established. The research results can provide a reference for the application of steel pipe UHPC engineering.

Influence of Bending-Twisting Coupling Deformation on Pure Bending Strength and Fracture Morphology of CFRP Angle-Ply Laminate

The purpose of this study is to investigate the effect of bending-twisting coupling deformation on the bending strength of CFRP in which laminate configuration has symmetricity and angled fiber orientation. In this study, a novel type of test fixture for pure bending test that permit the coupled bending-twisting deformation is newly developed. Test results showed that the pure bending strength of the angle-ply laminates was decreased when bending-twisting coupled deformation was permitted. The normalized bending strength when the bending-twisting coupled deformation is permitted was decreased with increase of coupled component of angle-ply laminate. Observations of fracture morphology of specimen also showed that the specimen was firstly failure at the 0° layer on the compression side, no matter if the coupled deformation was permitted or constrained. However, when the coupled deformation was permitted, the failure was occurred at lower applied bending stress compared with when coupled deformation was constrained. Moreover, when the coupled deformation was permitted, the failure of 0° layer was occurred at the diagonal portion of specimen. These results suggested that the existing of in-plane shear stress at 0° layer affects the fracture morphology of specimen.

Random forest-based algorithms for accurate evaluation of ultimate bending capacity of steel tubes

Despite the existence of methods for estimating the behavior of steel circular tubes subjected to pure bending, analytical models are still restricted due to the problem’s complexity and significant nonlinearity. Using the random forest (RF) as the basic model, novel intelligent models are constructed to estimate the ultimate pure bending capacity of circular steel tubes in this study. The RF model’s parameters are optimized using three nature inspired optimization algorithms, namely, the particle swarm optimization (PSO), ant colony optimization (ACO) and whale optimization algorithm (WOA). In the experimental part, a database of 104 tests that comprise 49 and 55 pure bending tests conducted on fabricated and cold-formed steel circular tubes, respectively, are evaluated and utilized to investigate the applicability of the hybrid RF-models. A single RF model is also built for comparative reasons in order to estimate the ultimate pending capacity. Various statistical and graphical measures are used to evaluate the performance of the developed models. The results show that the proposed RF-based nature-inspired algorithms can outperform the original RF predictive model. When the hybrid-RF models were assessed, it was discovered that the RF-WOA performed best. In addition, the influence of each parameter on the prediction findings based on the best RF-model is investigated via sensitivity analysis. Taking into account the overall findings, the hybrid RF-models may be used as powerful tools to predict the ultimate bending capacity of circular steel tubes and may be viable to aid technicians in making proper judgments.

Fibre-Reinforced Grout for Micropile Construction

Hollow bar micropiles (HBMP) are increasingly used to support heavy structures owing to their ability to carry considerable axial loads. However, their lateral capacity is relatively small due to their small flexural strength, which could limit their application for structures subjected to large lateral loads. Enhancing the micropile flexural strength by utilizing fibre-reinforced grout in its construction can thus improve its lateral performance. This study investigates the use of four types of fibers in grout mixture with different dosages to enhance the strength of grout used for micropile construction. Plastic, basalt, steel and micro-steel fibers were applied with dosages of 1%, 1.5% and 2%. Based on the obtained results, steel fibers were selected for further investigation. Nine model micropiles 1000 mm long and 76 mm in diameter were casted and tested in a laboratory environment with two different types of steel fibers. The micropiles were subjected to pure bending tests and the moment – curvature curves were extracted. The moment – curvature results indicated that the micropiles moment capacity increased and their post-cracking behaviour improved by adding steel fibers to the grout mix. As part of a large-scale study of lateral performance of single and grouped micropiles installed in cohesionless soil, one micropile was constructed with 1% micro-steel fiber to investigate its effect on its lateral performance. The lateral load test results indicated that the lateral capacity of the reinforced micropile improved by 10% over that of the non-reinforced micropile.

A dynamic finite element procedure for bending collapse of composite thin-walled lenticular tubes

This paper presents an explicit dynamic procedure based finite element framework to investigate the quasi-static bending collapse behavior of composite thin-walled lenticular tubes (CTLTs). A detailed description of the boundary conditions and loads adopted for pure bending tests, and of determining appropriate analysis parameters that control the quasi-static process, such as the simulation time duration and damping coefficient, is given with simulation tests. The quasi-static condition is ensured by using energy balance assessments and the accuracy of the results is verified against true static simulation results reported previously. The collapse performances of a particular CTLT were evaluated numerically in two bending directions. Two distinct regimes were observed, namely, a pre-collapse regime and a post-collapse regime, and the collapse peak moment and critical bending angle that mark the division of the two regimes were predicted. It is shown that as the bending angle increases progressively, the CTLT first bends and buckles into periodic wrinkling patterns at the locally compressed region in the pre-collapse stage, and then after collapsing into the post-collapse stage, the bending moment drops rapidly and the wrinkling patterns evolve into localized ridges and folds, and finally the deformation is concentrated at a certain position of the compressed region.

Cold-formed stainless steel RHS members undergoing combined bending and web crippling: Testing, modelling and design

The behaviour and resistances of cold-formed stainless steel rectangular hollow section (RHS) members undergoing combined bending and web crippling were studied based upon experimental and numerical investigations. A test program consists of 4 pure bending tests, 7 pure web crippling tests and 23 web crippling-bending interaction tests was conducted. The RHS specimens were cold-rolled from lean-duplex and ferritic stainless steel sheets. Numerical models were built and validated against the test results. Upon validation, parametric studies comprised of 312 finite element analyses were undertaken. The obtained test and numerical results were compared with nominal resistances predicted from the American, Australian/New Zealand and European design standards for stainless steel structures. Moreover, the provisions in the North American Specification for cold-formed steel members were also evaluated. The comparison results indicate that the codified design provisions are generally safe to use for design of cold-formed stainless steel RHS members undergoing combined bending and web crippling, among which the European provision yields overly-conservative predictions. The codified web crippling-bending interaction curves can be applied for designing the stainless steel RHS members undergoing combined bending and web crippling, whilst improved predictions could be achieved by employing recently proposed bending and web crippling design rules.

A modified bond model for describing isotropic linear elastic material behaviour with the discrete element method

Recently, the discrete element method is increasingly being used for describing the behaviour of isotropic linear elastic materials. However, the common bond models employed to describe the interaction between particles restrict the range of Poisson’s ratio that can be represented. In this paper, to overcome the restriction, a modified bond model that includes the coupling of shear strain energy of neighbouring bonds is proposed. The coupling is described by a multi-bond term that enables the model to distinguish between shear deformations and rigid-body rotations. The positive definiteness of the strain energy function of the modified bond model is verified. To validate the model, uniaxial tension, pure shear and pure bending tests are performed. Comparison of the particle displacements with continuum mechanics solution demonstrates the ability of the model to describe the behaviour of isotropic linear elastic material for values of Poisson’s ratio in the range 0 le nu < 0.5.

Numerical Simulation for the Honeycomb Core Sandwich Panels in Bending by Homogenization Method

Nowadays, with the continuous development of science and technology, computer software has been widely applied and is increasingly popular in many fields such as the automobile, aviation, space, and shipbuilding industries. Numerical simulation is an important step in finite element analysis and product design optimization. However, it is facing challenges of reducing CAD model building time and reducing computation time. In this study, we have developed a homogenization model for the honeycomb core sandwich plate to reduce the preparation of the CAD model as well as the computational times. The homogenization consists of representing an equivalent homogenized 3D-solid obtained from the analysis calculation in-plane properties of honeycomb 3D-shell core sandwich plate. This model was implemented in the finite element software Abaqus. The simulations of tensile, in-plane shear, pure bending, and flexion tests for the case of the 3D-shell and 3D-solid models of the honeycomb core sandwich will be studied in this paper. Comparing the results obtained from the two models shows that the 3D-solid model has close results as the 3D-shell model, but the computation time is much faster. Thereby the proposed model is validated.

Experimental study on bending resistance of steel-UHPC composite slabs

The local cracking problem of steel-UHPC composite slab structure layer under negative bending moment is a basic research topic for the application and development of this new type composite bridge deck structure system. Combined with the performance of UHPC, the mechanical behaviour of composite slab before ultimate load was analysed by designing a pure bending test model, and the mechanical indexes such as cracking load and ultimate load were obtained. The results show that the reinforcement and the combination effect can effectively limit the development of tensile crack in UHPC layer and improve the bearing capacity of the slab. The reinforced steel-UHPC composite slab ears good ductility. The material properties of UHPC should not be ignored in the analysis and calculation of mechanical properties of composite slabs. The combined effect can limit the development of tensile cracking and change its failure mode of the UHPC layer. The thickness of longitudinal reinforcement protective layer of steel-UHPC composite slab can significantly affect its flexural behavior. The application range of the equivalent section method based on linear elasticity is limited, and it is necessary to develop the analysis and calculation method that can accurately reflect the cooperative working effect of each member of the steel-UHPC composite plate.

Proposal of a pure bending test method for advanced composite materials

This paper proposes a simple and precise pure bending test method for composite materials. With CFRP as the subject, we compare conventional bending test methods and extract issues for each of them. Based on the results, we propose a test method that can solve the complexities of the conventional pure bending test method and can also accurately measure the characteristics of the pure bending property. The proposed test method is simpler than the conventional ones and agrees well with the theoretical values.

Digital light processing in photoelastic models production for material behavior modeling

Material behavior modeling for additive manufacturing (AM) technology represents a challenge because the manufacturing process and post-processing parameters strongly influence the mechanical properties of the part. Photoelasticity is a well-known full-field optical technique used for direct stress/strain determination and design evaluation purposes. A novel use of digital light processing (DLP), a form of vat polymerization AM technologies in photoelastic specimen production is discussed in this paper. A number of preliminary experiments were undertaken to address critical issues related to DLP process. It was concluded that the UV exposure time, dependent mostly on layer thickness, and orientation are the main factors affecting the mechanical properties and the accuracy of the printed samples. Pure bending test was used to determine mechanical and photoelastic properties of a commercially available acrylic-based photopolymer, not previously reported in the literature. The rectangular beam sample used was built in vertical layer orientation and fully-cured. The estimated value of Young’s modulus was within the expected range for acrylics, and the photoelastic constant obtained provides increased confidence in the investigated acrylic polymer for photoelastic stress analysis purposes, and consequently for validation of computer-based models.

Flexural capacity and bending stiffness of welded hollow spherical joints with H-beams

Eight specimens were designed, and pure bending tests were completed to study the mechanical properties of welded hollow spherical joints (WHS joints) with an H-beam subjected to pure bending. Parametric analyses of the joints under pure bending were conducted in consideration of the diameter(D) and wall thickness (t) of the welded hollow sphere(WHS), and height (h) and width (b) of the H-beam to validate the numerical model. Calculation methods for the flexural capacity and bending stiffness of the H-beam WHS joints were proposed. Results revealed two failure modes of the joints under pure bending, namely, (1) concave at the connection between the WHS and upper flange and external heave at the connection between the WHS and lower flange and (2) small concave at the connection between the WHS and upper flange and tensile fracture of the welding seam at the connection between the WHS and lower flange. The joints demonstrated good ductility under pure bending. The flexural capacity and bending stiffness of the joints were positively related to the wall thickness of the WHS and to the height and width of H-beam but were negatively correlated with the diameter of the WHS. The errors between proposed formulas and FEA for calculating flexural capacity and bending stiffness are very small, indicating the formulas can be employed in structural calculation instead of FEA.

An Experimental Study on the Ductility and Flexural Toughness of Ultrahigh-Performance Concrete Beams Subjected to Bending.

Ultrahigh-performance concrete (UHPC) and high-strength concrete (HSC) are currently widely used because of their distinct superior properties. Thus, a comprehensive comparison of the flexural behavior of UHPC and HSC beams is presented in this study. Nine UHPC beams and three HSC beams were subjected to pure bending tests to investigate the effect of various reinforcement ratios and steel fiber volume contents on the cracking and failure patterns, load-deflection behavior, ductility, and flexural toughness of these beams. The addition of steel fibers in the UHPC improved the energy absorption capacity of the beams, causing the UHPC beams to fail via rebar fracture. The deflection and curvature ductility indices were determined and compared in this study. The ductility indices of the HSC beam tended to decrease sharply as the rebar ratio increased, whereas those of the UHPC beam did not show a clear trend with respect to the rebar ratio. In addition, a comparison between the results in this study and the results from previous studies was performed. In this study, the addition of steel fiber contents up to 1.5% in UHPC increased the load capacity, ductility, and flexural toughness of the UHPC beams, whereas the addition of a steel fiber content of 2.0% did not significantly increase the ductility or flexural toughness of the UHPC beams.

Bending rigidity of yarns using beam method on a two-support configuration

This paper reports a simple, quick and reasonably accurate approach for measuring the bending rigidity of yarns. The beam method has been adapted and applied using a bending frame that has a fixed support and a simple support. The yarns are left to bend under the effect of their own weight. The accuracy and the precision of that bending frame are assessed over the time using an isotropic material and then compared against the ring-loop method and the KES-FB-2 pure bending tester. The findings show that the precision of this bending frame is acceptable. However, this bending frame gives at least 1.6 times greater values of bending rigidity than the KES-FB-2 pure bending tester, though the relationship between these two methods is linear and significant. Moreover, the spun yarns appear to have high levels of variability of the bending rigidity. This study is important as it overcomes the challenges faced while using other methods to measure the bending rigidity of yarn. It also provides a comprehensive account of the variation in this property. Further, it gives an indication of the highly non-uniform structure of spun yarns and the impact of yarn defects on the bending properties of yarns.