Round Bar Research Articles

Influence of tensile edge design and printing parameters on the flexural strength of ZrO2 and ATZ bars prepared by UV-LCM-DLP

Lithography based Ceramics Manufacturing (LCM), i.e., Digital Light Processing (DLP) is one of the Additive Manufacturing (AM) techniques that is being widely used for the production of ceramic parts. Additionally, the development of photocurable slurries and the influence of the printing parameters on the fabricated parts properties are also receiving high attention. In this work, ZrO2 and ATZ materials were used as a case of study to evaluate the flexural strength of the fabricated parts, using our own developed UV-curable slurries. The influence of the tensile edges shape of the bars, tilting speeds, layer thickness and printing direction were evaluated, obtaining the highest flexural strength values for the 200 ​μm round shape bars, faster tilting speeds, 25 ​μm layer thickness and printing in the Z direction for ZrO2 and in the Y for ATZ.

Measuring elastic moduli and loss tangent using a free-free resonant bar method.

A previously developed method for determining fundamental material properties has been employed to characterize several common materials used in loudspeaker fabrication, including plastics, wood, and metals. Through selective excitation of an elastically supported "free-free" bar in two different axial orientations we were able to quickly measure, calculate and plot the Young's, shear, and loss moduli (Tan δ) versus frequency in the audible range. Using coils adhered to both ends of a round bar suspended in a magnetic field, a material's response to torsional or flexural excitations can be measured quickly and repeatably. Since the method of determination is rapid (∼5 s) and nondestructive it provides a convenient way to assess a large selection of materials. The method also has a high signal to noise ratio allowing the tester to conveniently accommodate inevitable variations in the test setup and the dimensions of a specimen.

Evaluation of residual creep life of steels using macro-pillar creep testing and Omega method

Residual creep life evaluation is an essential part of Fitness-For-Service (FFS) assessment for engineering components operating at elevated temperatures. This paper elaborates a new evaluation approach based on macro-pillar compression testing (MPCT) and Omega method. The MPCT creep test was performed at the same stress level as the tensile creep test by adjusting the testing load using an algorithm, which is also provided in this paper. The barreling effect of MPCT creep test was corrected by two proposed parameters, which were calibrated using finite element method with 6 types of Cr-Mo alloys from API 579. Finally, a 1.25Cr-0.5Mo-Si steel was prepared for both MPCT and round bar tensile creep tests at 550 ℃ and different initial stress levels. The predicted residual creep life by MPCT has an error of 2.2% at 140 MPa, 6.4% at 160 MPa and 13.5% at 180 MPa.

Mode I stress intensity factors for semi-elliptical fatigue cracks in curved round bars

Some cyclically loaded components such as mooring chains can develop fatigue cracks in locations where the shape of the part is equivalent to that of a curved or bent round bar. Here we consider a semi-elliptical crack growing from the surface of a curved round bar. This geometry can for example represent a chain link segment with a crack located at its inner- or outer radius. The surface crack can be either almond shaped, sickle shaped or straight-fronted. Stress intensity factors (SIFs) over the fronts of such crack geometries are in the present work investigated for several elementary mode I stress distributions. Finite element analysis and linear elastic fracture mechanics methods are used to develop semi-analytical solutions for the SIF at any point on the crack front. Effects of relative bar curvature on numerical results are demonstrated. Relative to otherwise identical cracks in straight bars, SIFs for cracks in the curved bars considered here are found to differ by up to 8%. With an offshore mooring chain model as a case example, the estimation of SIFs for cracks in a complex residual stress field is furthermore demonstrated using a cubic polynomial stress approximation.

Effect of loading rate on the bond behaviour of plain round bars in concrete subjected to uniaxial lateral tension

The bond between reinforcement and concrete is one of the main factors affecting structural performance. In terms of the bond mechanism, the bond performance of plain round bars is especially sensitive to the stress state of the surrounding concrete. Lateral tensions have been confirmed to significantly weaken the bond properties of plain round bars but the effect of loading rate on such a condition is still not well understood. Experiments involving 178 pull-out specimens with various concrete strengths and bar diameters were performed to analyse the influence of loading rate on the bond behaviour of plain round bars embedded in concrete under uniaxial lateral tension. The main bond parameters were evaluated quantitatively. The results showed that bond strength was independent of loading rate and the ratio of residual strength to bond strength remained constant, but the slip at the peak bond stress decreased obviously with an increase in loading rate. An empirical constitutive model of bond stress–slip considering the concrete strength, bar diameter, uniaxial lateral tension and loading rate was developed and validated with experimental results.

Elaboration of the Equipment and Technology for Cutting Rolled Round Bars and Pipes with the Cyclic Circular Bending Method

A brief overview of methods for cutting round bars and pipes is presented, their main advantages, disadvantages and field of application are considered. It is proposed to use the effect of fatigue fracture for round bars and pipes breaking. The task is to study this process under the action of cyclic loads. The possibility of applying the known provisions of calculating theory of strength analysis for low-cycle fatigue for this process is tested. A comparative assessment of theoretical and experimental data is given and their significant difference is established. New calculated dependences are proposed, which are in good agreement with the experimental data. A theoretical assessment of the productivity of the process of round bars and pipes breaking by the method of cyclic circular bending was carried out using new results and various options for the design of a device for breaking were considered with an analysis of the features of their operation. Based on the results of the analysis, a variant of the device for the implementation of a continuous process of breaking the pointed ends of thick-walled fuel pipes during drawing in coils and a diagram of the mechanism for breaking the ends of the pipe with its supply from the coil were selected. Samples of pipes obtained by brittle cyclic bending are presented.

Design of manually operated multiple-seed planting machine for an Ethiopian environment

The advancement of technology has been influenced and enhances the production rate and quality of industrial and agricultural products. This study aimed to design and manufacture portable and multiple seed planting machines from locally available materials. The paper deals principally with the design and manufacturing process of the seeder machine. The design feature considers the geometrical components, driving power determination, and stress and forces Analysis of each part. Pro-Engineer and solid work software were used for part details and assembly drawing. Materials were selected based on functionality, durability, cost, and local availability. Hence, Sheet metal steel was used for the fabrication of the seed and fertilized boxes, seed, and fertilizer metering disc were fabricated from polyvinylchloride (PVC) and the power transitions elements like transitions shafts and gears also fabricated from round steel bar. The seeder machine was assembled by the permanent joining of the frame (Arc welding), and the remaining components were bolted to each other in their places. Experimental tests have been performed to evaluate the performance and functionality of the seeder. It was observed that the machine had been put (dropped) the seed within the design space gap between the consecutive plants and the required amount of fertilizer were placed with the designed depth.

Fracture Toughness Measurement of Aluminium and Steel Inserted Aluminium Using Numerical Method

The aim of the current work is to test the possibility of improvement of fracture properties of a shaft fabricated by press fitting a rod inside a tube and explore the effect of interface on the crack propagation. Measurement of Mode II fracture toughness is considered for this purpose. In this study numerical method developed by Yong Li and Viola based on Kienzler and Herrmann’s method by conducting a simple shear test on round bar specimen is adopted. Round bar specimens with a circumferential notch are subjected to shear test. Three specimens are prepared using Al6061T6 alloy tube inserted with rod of three different materials A6061T6 alloy, commercial pure Copper, and AISI1045 steel. Also a plain rod of Al6061T6 alloy is tested under shear to compare the results. Shear tests are conducted on Universal Testing Machine and fracture toughness values are calculated using modified Kienzler and Herrmann’s equations. The results indicated an improvement of 18% in the fracture toughness values in the case of A6061T6 alloy rod inserted A6061T6 alloy tube compared to the fracture toughness of plain A6061T6 alloy rod. And when steel rod is inserted inside the A6061T6 alloy tube an improvement of 33.33% in the fracture toughness.

Residual stress states in cementite and ferrite in a combined cold drawing process of AISI 1045 steel using neutron diffraction and synchrotron radiation

The evaluation and control of residual stress states in manufacturing processes such as cold drawing can be difficult, especially in multi-phase materials. Diffraction methods are ideal for characterizing residual stresses in individual phases provided these phases scatter neutrons or X-rays well enough to obtain a good signal. Residual stresses determination problems in drawn components have been reported. Main constraints are measurements in the primary ferrite phase only. The presence of cementite in carbon steel is often neglected. A problem that has not yet been extensively investigated is how residual stresses in the ferrite and cementite phases develop in subsequent steps of material processing such as cold drawing. In this work a combined straightening and bar drawing process of AISI 1045 round bars from coils of a hot-rolled material was investigated. A careful characterization of the material, including residual stress states in the ferrite (α−Fe) and cementite (Fe3 C) phases, using neutron diffraction and synchrotron diffraction was performed for each of the different manufacturing steps. The drawing and polishing and straightening (P.S.) parameters by crossed rolls were changed to evaluate their influence on the α−Fe and Fe3 C residual stress distributions. After the drawing process, residual stresses in the cementite phase are highly tensile, as already reported, however it can be shown that after polishing and straightening steps residual stresses in the cementite phase decrease and residual stress distributions also depend on the tool angle used.

Protection of objects from local damage and destruction

The paper deals with the dynamic process of local destruction of an object of armor protection. It is modeled as an object of destruction in the form of a spherical shell, and the threat is represented in the form of a metal round bar. Formulas are given and an estimate of the acceleration rate at which the object of armor protection is guaranteed to lose continuity is made. It is shown that if the rod has a tip covered with a layer of iridium, then under certain conditions, due to the fact that this metal has a high dynamic viscosity under intense loads, the object of armor protection is highly likely to be hit.

Reduction of singular stress field of adhesive notched round bar

Reduction of singular stress field of adhesive notched round bar

Prediction of surface roughness in turning of duplex stainless steel (DSS) using response surface methodology (RSM) and artificial neural network (ANN)

In this present study, an experimental investigation has been done to predict surface roughness by taking into consideration of the following parameters: cutting speed, rate of feed, cutting depth and nose radius in the hard turning of Duplex 2205 (ASTM A276) round bar material utilizing carbide tip tool material. Machining of duplex stainless Steel is considered as an inefficient machinable material, low removal rate and requires more exertion to machine the item. For experimental purposes, the 4-factor and 5-level design matrix is structured using the Design-Expert software. The statistical method is used to analyze the variance using ANOVA technique to examine the unique performance character.The statistical method is employed to analysis of variance (ANOVA) in order to examine the performance uniqueness. A second-order mathematical model is created according to the Design of Experiments (DoE) of Response Surface Methodology (RSM) to anticipate surface roughness. In view of cutting test, the cutting speed is the parameter which has the greatest impact on the machining activity. The nose radius is a minor parameter that has a less impact on machining activity. For the best possible results, the cutting parameters leading to surface roughness, the Artificial Neural Network (ANN) model is trained and tested using MAT Lab. For this condition, the ANN suggests the utmost least predicted value of surface roughness. The results of the tests confirming the expected values proved to be in perfect agreement with the experimental values. Finally, efficiency of three different ANN transfer function were compared to choose the best predicted values. The Log-sigmoid is the most suitable transfer function that provides minimum surface roughness.

A small specimen testing method to determine tensile properties of metallic materials

Abstract A stable uniaxial tensile testing method has been proposed for small specimens that can obtain stress-strain relations and strength of metallic materials. Based on energy equivalent assumptions, a semi-analytical model with five parameters has been put forward. Those parameters can be determined by a small amount of finite element analysis (FEA), and more extensive numerical validation is carried out on the model. By designing a simple installation fixture for the small specimens of which the parallel section is 1.2 mm in width and 5 mm in length, a series of uniaxial tensile tests have been performed with small specimens. It shows that the stress-strain relations and strength obtained by the small specimen testing method are consistent with those from standard round bar specimens. The small specimen test method will help to obtain the mechanical properties of materials in nuclear industry and other fields.

Experimental behavior of iron-based shape memory alloys under cyclic loading histories

The present paper investigates the behavior of iron-based shape memory alloys (Fe-SMAs) subjected to cyclic inelastic straining by means of uniaxial coupon experiments. The tests feature round bar coupons subjected to a broad range of uniaxial cyclic strain histories representative of earthquake loading. The experimental results suggest that the Fe-SMA under investigation exhibits an asymmetric stress-strain relation, with limited superelastic behavior. It was found that the post-yield/phase transformation behavior of the Fe-SMA alloy is both strain-rate and temperature-dependent. Quantitative comparisons with structural steels subjected to nominally identical cyclic strain histories indicate that, although the studied Fe-SMA has a similar energy dissipation per loading excursion with respect to conventional S355J2+N, the Fe-SMA’s hardening response is appreciably higher, leading to comparatively larger elastic strain energies being stored.

INFLUENCE FRONT TENSION ON DEFORMED STATE DURING ROLLING ROUND BARS IN OVAL CALIBER

The purpose of this work is to study the effect of forward tension on the deformed state when rolling round bars in an oval caliber. The work includes experimental and theoretical parts. The experimental part of the work was done in the laboratory. Theoretical part is divided into two other parts - computer modeling and calculations using empirical formulas. The mathematical model was developed in the software package QForm 2D / 3D wich using for modeling and optimization of metal forming processes. Modeling was made for a quarter of the sample, which allowed reducing the time of task solution. Based on previous studies for the conditions of the real experiment on the contact of the sample with the rolls chose the law of friction Coulomb’s with a coefficient of friction of 0.45, most accurately corresponds to the conditions of the experiment. Other boundary conditions are selected from the standard libraries of the QForm software system according to the conditions of the real experiment. Comparison of the calculation results with the experimental data shows that the error does not exceed the engineering accuracy, that is, the process of rolling round samples in an oval caliber with a tension can be studied, based on the results of simulation in QForm. Comparison of the calculation results by the proposed formula and as a result of mathematical modeling showed that the error of determining the profile width by the empirical formula and when modeling in the software package QForm 2D / 3D are close to each other. In other words, both formula and model can be used in engineering calculations anyway. The results of theoretical and experimental studies show that under the influence of front tension reduces the value of widening when rolling round samples in oval calibers. This influence must be taken into account when calculating the deformation mode in finishing wire blocks. The results of work can be used in automated systems of modern rolling mills, which will allow to develop innovative resource-saving technologies of wire rod production on the existing equipment with lower consumption factor as compared to the existing equipment.

Effect of cladding parameters on microstructure and defects in direct laser metal deposition of 24CrNiMo steel

Direct laser metal deposition of a medium carbon low alloy steel was performed on a round bar sample. Taguchi design was used to investigate the effect of three process parameters with three different levels on the microstructure and properties of single- and multitrack clad samples. Microstructural analysis showed that coalesced bainite and lath martensite exist in the clad area. Two different kinds of cracks occurred in multitrack clad samples. When laser power is not sufficient or scanning speed is high, cracks can occur in the laser clad area because of the accumulation of trapped defects inside the molten pool, e.g., inclusions, voids, and low melting point constituents alongside insufficient molten metal back-filling at interdendritic regions. These cracks can be considered as solidification cracks. Another type of cracks can occur in previous tracks of multitrack clads which actually are the heat affected zones (HAZ) of newly deposited clad tracks, because of high tensile stress on HAZ and the presence of oxide and sulfide constituents at interdendritic regions. These cracks can be considered as reheating cracks. According to the result of Taguchi design experiments, using optimum laser parameters like high laser power, medium scanning speed, and sufficient powder feed rate, crackfree clad layers can be obtained via the prevention of formation of unfavorable constituents at interdendritic regions.

Stochastic assessment of bond-slip behavior of plain round bars in low strength concrete

The effect of inherent uncertainties in material properties on the global response of beam-type bond-slip specimens constructed from the low strength concrete and plain round bar was investigated by the stochastic study. First, the substandard specimens were tested up to failure under monotonic loading. Bond-slip models, which were derived from the experimental data, were proposed for confined and unconfined RC members with poor concrete quality and plain round bars. Then, the proposed bond-slip relations were implemented in numerical models. The experimentally validated finite element (FE) models were combined with a suitable stochastic sampling technique (Latin Hypercube Sampling (LHS)). Therefore, the variability in the identical tests was characterized by stochastic computational mechanics. The load–displacement curves in the stochastic analysis formed a band around the deterministic model which also simulated the dispersion in the experimental capacity. Besides, the randomized behavior provided the basic statistical parameters of the response quantity. Finally, the partial correlation coefficient between input variables (i.e., material parameters) and response variable was evaluated to outline the material parameters which mainly govern the global response (i.e., sensitivity analysis). It is found that the relative impact of the concrete tensile strength on the ultimate capacity was the most significant.

Buckling-restrained steel bar damper for spine frame system

This paper presents an experimental investigation on buckling-restrained steel bar dampers used at the lower sides of a spine frame. The dampers are mainly composed of round steel bar cores restrained by round steel tubes, and additional components called supporters that provide the lateral support against flexural buckling of the round steel tube. One characteristic of the proposed damper is that its buckling length can be controlled by using supporters. Cyclic loading tests were conducted on 10 scaled specimens to assess the functionality and energy dissipation performance of the proposed damper. The test specimens differed mainly with regard to the number of supporters, number of contraction allowance zones, type of connection to the base beam, and damper length. The performance of the damper was extensively discussed base on the cyclic behavior of the different specimen configurations and the mechanical performance of the different damper components. Furthermore, the supporter connection was assessed via collapse mechanism analysis to determine strength requirements. The test results revealed the optimal configurations, the functionality, and the plastic deformation capacity of the proposed system.

Crack shape evolution and stress intensity factors for opposite surface cracks in aircraft shaft under tension and combined loading

Stress Intensity Factor (SIF) of opposite surface cracks presented in an un-notched round bar has been determined under tension and combined load conditions. The influence of loading modes on SIF of opposite surface cracks has been attempted using numerical method. Crack depth ratio [(a/d); ‘a’ crack depth and ‘d’ diameter of the bar] ranging 0.1 to 0.4 and crack aspect ratio [(a/c); ‘a’ crack depth and ‘c’ semi major axis of the ellipse] ranging 0.2 to 1.0 were considered. Mixed mode SIF was calculated with consideration of mode-II and mode-III fractures. When the bar was subjected to pure tensile loading, as the crack depth ratio (a/d) increases, a crossover (higher SIF value changes from middle region to surface region) in SIF distribution was observed for an aspect ratio of 0.6. This implies that the growing crack has changed its propagation behavior as the depth ratio increases. In addition to tension, when torque was applied, nonuniform and asymmetric SIF spread was observed for semi elliptic crack [(a/c) = 0.2] compared to semi-circular [(a/c) = 1.0] crack. It was also noted that mode-I fracture is higher at the middle region [P/P0 = 0] of the rack border, whereas mode-II and mode-III fracture is higher at the crack surface region [P/P0 = ±1]. Due to combined loading, more influence of mode-II and mode-III fracture failure was observed and their effect is marginal at the middle region [P/P0 = 0] of the crack border. Using surface plots, SIF of opposite cracks located in un-notched round bar has been determined.

On the fracture response of shape memory alloys by void growth and coalescence

Although Shape Memory Alloys (SMAs) belong to a relatively brittle class of materials, that of intermetallics, their fracture surfaces are characterized by both cleavage and dimples, with the latter being indicative of ductile rupture. Two clear differentiators of SMAs from other intermetallics, which may contribute to the presence of ductile rupture are their ability to transform their crystallographic structure and the presence of precipitates in large volume fractions. In this paper, unit cell simulations are employed in an effort to quantify the relative importance of the two fracture mechanisms in the overall failure response of these materials. The numerical simulations involve a single pre-existing void, assumed to have initiated from a second phase particle, embedded in a SMA matrix material. Thus, the unit cell studies allow for an investigation of void growth and coalescence, ignoring void formation and its footprint in the subsequent microstructure evolution. The numerical studies show that void growth is rather limited before the peak stress-value in the effective stress–effective strain response of the unit cell for initial void-volume fractions representative of precipitation-hardened SMAs. Given the available experimental observations on notched round bars, which indicate that precipitation-hardened SMAs fail in a stress-controlled manner, the numerical studies suggest that void growth and coalescence should play a minor role in the formation of dimples, as compared to that of void nucleation and cleavage, and in turn into the fracture response of precipitated SMAs.