Bend Bars Research Articles

Straight and Bent Bars Buckling Considered as the Axial Displacement of One Bar End

Abstract A new approach has been taken to the problem of straight and bent bar buckling, where bar buckling is considered as a function of axial displacement of one end. It was assumed that the length of a bar being buckled at any instant of buckling is the same as that of a straight bar, regardless of the size of axial displacement of one end of the bar. Based on energy equations, a formula was derived for the value of axial displacement of one bar end or buckling amplitude in the middle of bar length as a function of compressive force. The established relationships were confirmed by simulation tests using the finite element software Midas NFX and by experimental tests.

Fatigue Behavior of Welded API 5L X70 Steel Used in Pipelines

In this study, fatigue failure behavior of welded X70 pipeline steel was investigated by rotating bar bending fatigue tests performed at room temperature. S–N curves of base metal, weld and heat-affected zone (HAZ) were plotted. Tension tests, hardness measurements and Charpy V-notched impact tests were carried out for mechanical characterization. Samples were examined with optical microscope and scanning electron microscope (SEM) microstructurally. Fracture surfaces were examined with SEM. In addition to fractographic analysis, striation counting method was used to estimate the crack growth rate of base metal, weld and HAZ. Stress intensity factor (∆K) ranges were also calculated. Tensile properties and hardness values of base metal and weld were found to be almost the same. Charpy impact test results show that base material has approximately twice impact energy than weld and HAZ at room temperature. However, Charpy impact energies of HAZ and weld decreased noticeably at − 30 °C, while very slight decrease was observed for base metal. The comparison of high-cycle fatigue and crack growth behaviors shows that base metal has better fatigue behavior of all from the point of crack initiation and propagation. Moreover, our findings also support the idea that striation counting can be used as a fractographic approach to estimate the crack growth behavior of materials.

Prediction of residual stresses of second kind in deep drawing using an incremental two-scale material model

ABSTRACT For modern engineering applications, the prediction of residual stresses is a starting-point for the subsequent optimisation of the design with regard to the process induced stresses on the macro and the grain scale. In this paper, a new approach for the numerically efficient prediction of phase-specific residual stresses (residual stresses of second kind) in two-phase materials is presented. The proposed model allows for a two-scale simulation of complex forming processes, solely based on the phase-specific constitutive equations. This enables the calculation of the average stresses and strains in each phase during the entire process and the prediction of the macroscopic material response. The numerical results are compared to experimental diffraction-based data of a bending bar and a deep drawn cup and are aligned better compared to existing models.

A Rectangular End-Winding Model for Enhanced Circulating Current Prediction in AC Machines

The end-winding region is usually overlooked in the roebel design of large AC machines. However, saturated stator slots cause overhang parts to impact the circulating currents significantly. In fact, a precise knowledge of the winding overhang strand inductances is crucial when optimising the transpositions of large roebel bars, especially in the case of under-roebeling (having less than 360-transposition in the active part) where the goal is to compensate the winding overhang parasitic field with the slot-parasitic field. In this article, a rectangular inductance calculation model (R-ICM) is proposed. It results in a circuital lumped-element model (LEM) that takes the strand dimensions, the bar bending, as well as small-scale effects into account. Moreover, the work describes how to model finite current-carrying rectangular segments (straight and arced) from first principles. Finally, the methodology was demonstrated for two prototype specimens with different bending-shapes corresponding to the fundamental elements on a stator bar in the winding overhang of large electrical machines.

Novel residual stress measurement technique to evaluate through thickness residual stress fields

In this present study, a novel approach of measuring through-thickness residual stresses based on the general strain relaxation methodologies has been described. This new method is an amalgam of the conventional deep hole drilling technique and the contour method with a reduced degree of damage to the component made during measurements. The annular deformation of a reference hole made at the measurement location has been interpreted as the displacement boundary conditions in a two-dimensional finite element model. In this regard, a thick, partially plastic four-point bent bar specimen was used to validate the proposed method. Through-thickness axial residual stresses induced in the bar were measured using the proposed technique and were observed to be in a reasonably close match with the theoretical and DHD results.

Influence of the Infill Orientation on the Properties of Zirconia Parts Produced by Fused Filament Fabrication.

The fused filament fabrication (FFF) of ceramics enables the additive manufacturing of components with complex geometries for many applications like tooling or prototyping. Nevertheless, due to the many factors involved in the process, it is difficult to separate the effect of the different parameters on the final properties of the FFF parts, which hinders the expansion of the technology. In this paper, the effect of the fill pattern used during FFF on the defects and the mechanical properties of zirconia components is evaluated. The zirconia-filled filaments were produced from scratch, characterized by different methods and used in the FFF of bending bars with infill orientations of 0°, ±45° and 90° with respect to the longest dimension of the specimens. Three-point bending tests were conducted on the specimens with the side in contact with the build platform under tensile loads. Next, the defects were identified with cuts in different sections. During the shaping by FFF, pores appeared inside the extruded roads due to binder degradation and or moisture evaporation. The changes in the fill pattern resulted in different types of porosity and defects in the first layer, with the latter leading to earlier fracture of the components. Due to these variations, the specimens with the 0° infill orientation had the lowest porosity and the highest bending strength, followed by the specimens with ±45° infill orientation and finally by those with 90° infill orientation.

An approach for objective and automated identification of pork belly firmness

A series of studies was performed to develop and test a method adaptable for early automated sorting of pork bellies based on firmness. Flattened and non-flattened, bone-in, skin-on primal bellies were fed skin-down, caudal end foremost on to a horizontal (0°) or raised (30°) conveyor with an adjustable nosebar (ø = 14 mm). The drop angle, after 24 cm of belly had passed the nosebar, was strongly correlated with subjective floppiness (r = 0.77–0.82; P ≤ .0001) and moderately correlated with fat thicknesses (r = 0.47–0.67; P ≤ .0001). On a 0° conveyor, drop angle relationships were generally weakest for non-flattened bellies, but moderate and similar for flattened bellies at 0°, as well as for both flattened and non-flattened bellies at 30°. The method appears to show promise for commercial production use. Further work is required on the impact of belt speed, firmness categorization, and the relationship to the current bar bend research method.

Seismic performance of strengthened reinforced concrete columns

Post-earthquake reconnaissance studies have reported severe damage to reinforced concrete buildings. In a moment resistant framed building, columns are the critical members of the load path. Shear failure of a column is brittle, leading to quick degradation of the lateral strength and vertical load carrying capacity. The reported study focuses on seismic strengthening of a short shear-critical column by concrete jacketing technique. For a shear-critical jacketed column, the integrity of the new and old concrete depends on any slippage at their interface. The investigation on the effects of three different interfaces such as surface roughening, providing dowel bars or bent shear connector bars in addition to surface roughening, on the seismic performance of jacketed columns, is presented in this paper.Large-scale column specimens were tested to shear failure under lateral monotonic and cyclic loads, in presence of estimated service level axial loads. The details of the experiments and the comparison of their results in terms of shear strength, stiffness and behavior are included. The specimens with different interfaces were found to be similar in their lateral load resistance, showing negligible difference in strength. However, the specimens with bent bars showed higher stiffness compared to the specimens with other two types of interfaces. The strengths of the specimens were predicted using codal provisions and a strut-and-tie model. Their behavior was traced using a piecewise linear model. The predictions were compared with the test results. The proposed method of analysis for shear deformation can be used in developing non-linear shear hinge properties for short jacketed columns, in a pushover analysis of a building.

Designing Robotically‐Constructed Metal Frame Structures

AbstractWe present a computational technique that aids with the design of structurally‐sound metal frames, tailored for robotic fabrication using an existing process that integrate automated bar bending, welding, and cutting. Aligning frames with structurally‐favorable orientations, and decomposing models into fabricable units, we make the fabrication process scale‐invariant, and frames globally align in an aesthetically‐pleasing and structurally‐informed manner. Relying on standard analysis of frames, we then co‐optimize the shape and topology of bars at the local unit level. At this level, we minimize combinations of functional and aesthetic objectives under strict fabrication constraints that model the assembly of discrete sets of bent bars. We demonstrate the capabilities of our global‐to‐local approach on four robotically‐constructed examples.

Performance and Durability of In-Plant Partially Cured GFRP Bent Bars in Steam-Cured Precast Concrete Elements

Abstract Glass fiber-reinforced polymer (GFRP) bent bars were used as shear reinforcement for precast/prestressed concrete box beams in Ontario, Canada. Differential scanning calorimetry (DSC) test...

Characterization of a silicon nitride ceramic material for ceramic springs

Under extreme working conditions such as high temperature, strong electric and magnetic fields and acidic or basic environments, ceramic springs offer a clear advantage over conventional steel springs. In this study, a tailored grade of silicon nitride ceramic was characterized as spring material. The basic characterization was complemented with component tests. Bend bars, helical springs and conical disk springs were manufactured and tested under various loading scenarios.Manifested by the smallest effective volume of the three tested geometries, helical springs showed the highest fatigue strength. Nevertheless, the complexity involved in manufacturing helical springs pertaining to their geometrical features resulted in a relatively large scatter in fatigue data. The results pointed out the importance of proper design and machining of the contact surface edges in disk springs, which bear the highest stresses.This work demonstrates the potential of producing ceramic springs with broad applicability and sufficient strength and fatigue resistance.

Automatic Bar Bending Machine using Pneumatic System

The main intention of this project is to automate the bar bending process using pneumatic system to reduce the cost and enhance the productivity. Conventional Methodologies involve major labour work, layout setup, high cost etc. Hence to reduce labour cost, Automation is preferred. Existing hydraulic system are cost high enough, so to make cost effective, Pneumatic bar bending system is proposed here. Sample bar is taken about 8mm and pressurized with a compressor of about 25-30mm. Entire test setup size assembled is 2*2 square feet. This project discuss about the construction and process of pneumatic based bar bending system, also the associated practical implications during implementation.

Fatigue damage of PBH shear connector of steel-concrete composite structure

Perfobond Leiste (PBL) shear connector is a widely-applied shear connector that rely on the concrete tenons and penetrating steel bars in the open hole steel ribs to resist slipping. Perfobond Hoop (PBH) shear connector uses the stirrups in the concrete structure to replace the independent penetrating straight reinforcement in the PBL shear connector, which has better spatial rigidness, and shear performance. In this paper, the static and fatigue tests of PBH shear connector are designed to analyze the static and fatigue failure characteristics and study the fatigue damage mechanism and fatigue damage evolution model of PBH shear connector. The study found that PBH shear connector has higher shear stiffness and fatigue properties than PBL shear connector. The concrete tenon in the open-hole steel rib plate is the key part of the PBH shear connector, and its failure form is different during static and fatigue failure. The fatigue shear stiffness of the PBH shear connector is shown as a jump reduction, which is different from the static shear stiffness as a smooth decline. The fatigue damage process of PBH shear connector is divided into three stages according to the failure mechanism: the bond failure stage of the steel-concrete composite interface, the crushing and migration stage of the concrete tenon, and the bending and failure stages of the penetrating steel bar. The three stages take up 10%, 80% and 10% of the fatigue life in turn. With the damage degree as the fatigue process variable, a two-line fatigue damage evolution model of the PBH shear connector is established, which can be used to predict the final interface slip value and fatigue life.

On the Applicability of Thermoforming Characterization and Simulation Approaches to Glass Mat Thermoplastic Composites

Chopped fiber composite materials offer the potential to be used for complex geometries, including local thickness changes, ribs and beads, offering significant potential for functional lightweighting. Depending on the initial mold coverage and flowability of the material, the processing behaves either more like a compression molding or a thermoforming process. The latter is applicable to high initial mold coverages and includes typical thermoforming defects such as local wrinkling. Such defects are not predictable by conventional compression molding simulation approaches usually adopted for this material class. Therefore, thermoforming characterization and simulation approaches and their applicability to glass mat thermoplastic (47 vol.% long glass fiber, Tepex Flowcore) for high initial mold coverages is investigated. Abaqus in combination with several user-subroutines is applied. Valid material characterization results from torsion bar and rheometer bending tests are obtained and applied to an automotive structure in thermoforming simulation. Results indicate that the high stiffness and high viscosity captured by the rheometer bending test at low shear-rates are necessary to reproduce the wrinkling behavior observed in the experimental results. Discrepancy is most likely reducible to thermomechanical effects, and that the modelling approach does not account for thickness deformation due to transverse compression.

Assessing provisions in Eurocode2 for anchoring reinforcing bars with bends

In Eurocode2, the design provisions allow for the anchorage length of reinforcing bars with bends to be calculated as the center line of the bar from the critical section of the member to the end of the straight portion of the bar beyond the bend, with no limit on the maximum value of the length beyond the bend (extension length). This paper thus presents statistical analysis for test results of reinforcing bars anchored with bends, collected from the literature, as a means to assess the performance of the provisions of Eurocode2. Strength of bent bars at an anchorage length depends on many parameters, including concrete compressive strength, embodied as a constant bond stress along the anchorage length; diameter of the bar; concrete side cover; spacing between bars, and confining reinforcement. Test results incorporated in this analysis include 113 simulated beam-column joint specimens with 16, 19, 22, 25, and 36 mm beam bars with stresses at anchorage failure ranging from 213 to 943 MPa, and concrete compressive strengths ranging from 18 to 114 MPa. Each specimen contained 2, 3, or 4 bent beam bars with clear spacing between them ranging from 2db to 11.4db. All specimens contained no confining reinforcement within the joint region and a constant concrete side cover of either 65 mm or 90 mm. The analysis showed that, for a given bar diameter, the predicted bar stress at anchorage failure with limitations as originally integrated on bond stress, concrete cover, and spacing between bars is reasonably safe. However, the ratio of test-to-calculated bar stress decreases as the ratio of extension to embedment length increases, resulting in an unconservative design when the extension length exceeds half of the embedment length. For rational designs, an upper limit on the extension length of half the embedment length is thus suggested.

Behavior of Laminated Wooden Beam with Variable Section Subjected to Bending

The paper presents the theoretical and experimental study on the bending behavior of cantilever wood laminates beam with variable section from the classical guitar structure. During bending, normal stress and tangential stresses develop. As a viscous elastic material, in time the wood deforms in the plastic domain, causing permanent deformations. The theoretical study aimed the rheologic behavior of bending bars, and from the experimental point of view, five types of guitar neck probes were tested at bending on the ZWICK-Roell universal machine. The five categories of samples were differentiated by the geometry of the inserts and the material used for them. As the test samples showed a variable section with respect to both the longitudinal axis and the height, the displacements along the bars were measured in 7 points. The experimental results revealed the non-linear behavior of the structures and the influence of the reinforcement type used in the structure of the wooden beams.

Analytical Solutions for Bending of Nanoscaled Bars Based on Eringen’s Nonlocal Differential Law

The one-dimensional nanoscaled bar is commonly seen in current nanodevices, and it plays a significant role in nanoelectromechanical system (NEMS) and related nanotechnology. Motivated by this, the paper is concerned with the bending and stability of a nanoscaled bar especially a flexible bar subjected to vertical concentrated, vertical linearly distributed, and horizontal concentrated forces simultaneously. The theoretical model is developed by employing Eringen’s nonlocal differential law. Hence, the nonlocal differential constitutions in terms of stress and bending moment at a nanoscale are applied to the classical equilibrium formulation in order to construct the nonlocal constitutive model and then determine the analytical solutions for bending of such a nanoscale bar. Subsequently, the effect of a nonlocal scale on the midpoint deflections and internal forces is shown numerically, and the internal and external characteristic length scales are also examined. It is revealed that the capacity of resisting compression decreases with increasing the nonlocal effect since the internal characteristic scale cannot be neglected by comparing with the external characteristic scale. There exists a threshold value for bending stiffness. Both the midpoint deflection and bending moment vary monotonously when the material bending stiffness exceeds the threshold value, while the mechanical quantities fluctuate when the bending stiffness is less than its threshold value, namely, for a flexible nanoscaled bar. Accordingly, two different kinds of nonlocal predictions and the related disputes are resolved in the context of Eringen’s nonlocal differential law. The work is expected to be useful for the design, application, and optimization of nanoscaled bars sustaining bending with linear vertical and horizontal forces.

MakeSense: Automated Sensor Design for Proprioceptive Soft Robots.

Soft robots have applications in safe human-robot interactions, manipulation of fragile objects, and locomotion in challenging and unstructured environments. In this article, we present a computational method for augmenting soft robots with proprioceptive sensing capabilities. Our method automatically computes a minimal stretch-receptive sensor network to user-provided soft robotic designs, which is optimized to perform well under a set of user-specified deformation-force pairs. The sensorized robots are able to reconstruct their full deformation state, under interaction forces. We cast our sensor design as a subselection problem, selecting a minimal set of sensors from a large set of fabricable ones, which minimizes the error when sensing specified deformation-force pairs. Unique to our approach is the use of an analytical gradient of our reconstruction performance measure with respect to selection variables. We demonstrate our technique on a bending bar and gripper example, illustrating more complex designs with a simulated tentacle.

Antibacterial, ester-free monomers: Polymerization kinetics, mechanical properties, biocompatibility and anti-biofilm activity

ObjectivesQuaternary ammonium (QA) methacrylate monomers have been extensively investigated and demonstrate excellent antibacterial properties. However, the presence of ester bonds makes them prone to degradation in the oral cavity. In this study, ester-free QA monomers based on meth-acrylamides were synthesized and screened for polymerization kinetics, mechanical properties and antibacterial effects. Materials and methodsTertiary quaternary ammonium acrylamides (AM) and methacrylamides (MAM) with alkyl side chain lengths of 9 and 14 carbons (C9 and C14) were synthesized and incorporated at 10 wt% into experimental composites based on BisGMA:TEGDMA (1:1), camphorquinone/ethyl-4-dimethylaminobenzoate (0.2/0.8 wt%) and 70 wt% barium glass fillers. Analogous methacrylate versions (MA) were used as controls. Degree of conversion (DC) and rate of polymerization (RP) during photoactivation (800 mW/cm2) were followed in real-time with near-IR. Flexural Strength (FS) and Modulus (E) were measured on 2 × 2 × 25 mm bars in 3-point bending after 24 h dry storage and 7-day storage in water at 37 °C. Antimicrobial properties and biofilm adhesion (fouling) were evaluated by bioluminescence (Luciferase Assay) and biofilm removal by water spray microjet impingement test, respectively. Cytotoxicity was assessed by MTT assay on dental pulp stem cells (DPSC). Data were analyzed with one-way ANOVA/Tukey's test (α = 0.05). ResultsDC was similar for all groups tested (∼70%). Both MAMs and C14-AM presented significantly lower RP. Under dry conditions, FS (110–120 MPa) and E (8–9 GPa) were similar for all groups. After water storage, all materials presented FS/E similar to the control, except for C14-AM (for FS) and C14-MAM (for E), which were lower. All C14 versions were strongly antibacterial, decreasing the titer counts of biofilm by more than two orders of magnitude in comparison to the control. C9 monomers did not present significant antibacterial nor antifouling properties. And biofilms had approximately equivalent adhesion on the C9 composites as on the control. Cytotoxicity did not show significant differences between the MA and AM versions and the control group. ConclusionsC14-QA monomers based on methacrylates and meth-acrylamides present strong antibacterial properties, and in general, similar conversion/mechanical properties compared to the methacrylate control. Statement of SignificanceThis work demonstrates the viability of methacrylamides and acrylamides as potential components in dental restorative materials with antimicrobial properties. The use of ester-free polymerizable functionalities has the potential of improving the degradation resistance of these materials long-term. The use of (meth)acrylamides did not interfere with the antimicrobial potential of quaternary ammonium-based materials.

Microstructure-based multiscale modeling of large strain plastic deformation by coupling a full-field crystal plasticity-spectral solver with an implicit finite element solver

We present a fully embedded implementation of a full-field crystal plasticity model in an implicit finite element (FE) framework, a combination which realizes a multiscale approach for the simulation of large strain plastic deformation. At each integration point of the macroscopic FE model a spectral solver, based on Fast Fourier Transforms (FFTs), feeds-in the homogenized response from an underlying full-field polycrystalline representative volume element (RVE) model which is solved by using a crystal plasticity constitutive formulation. Both, a phenomenological hardening law and a dislocation density based hardening model, implemented in the open source software DAMASK, have been employed to provide the constitutive response at the mesoscale. The accuracy of the FE-FFT model has been benchmarked by one-element tests of several loading scenarios for an FCC polycrystal including simple tension, simple compression, and simple shear. The multiscale model is applied to simulate four application cases, i.e., plane strain deformation of an FCC plate, compression of an FCC cylinder, four-point bending of HCP bars, and beam bending of a dual-phase steel. The excellent capabilities of the model to predict the microstructure evolution at the mesoscale and the mechanical responses at both macroscale and mesoscale are demonstrated.