Round Bar Research Articles

R curve obtained by a round bar with a circumferential crack and its effectiveness for a fracture toughness test (For a material with medium fracture toughness)

R curve obtained by a round bar with a circumferential crack and its effectiveness for a fracture toughness test (For a material with medium fracture toughness)

Determination of the optimal modes of operation of the clover grater and scarifier KS-0.3 P during scarification

The article provides information about the features of the device, the quality of work of the prototype of a new 25...30 % more productive clover grater and scarifier KS-0.3 P in comparison with the analogue KS-0.2 P. KS-0.3P includes a drum-type wiping and scarifying device, a pneumatic separation device, a two-stage exhaust air purification system containing a cyclone and a fabric filter. The increase in the productivity of the new machine is achieved by increasing the diameter of the drum with a solid wiping surface to 0.45 m and the length of the oval deck with scarifying plates to 0.7 m. The solid grating surface of the drum is welded from steel rods of hexagonal profile No. 12 mounted on an edge. The deck covering the drum from below by 180° is made of round bars with a diameter of 10 mm and nine steel plates with a thickness of 2 mm and a width of 11 mm, evenly distributed along the length of the deck. When studying the technological process of clover grater and scarifier the method of mathematic planning of the experiment was used. The quality of scarification done was evaluated using the GOST 12038-84, GOST 12036-85 methodologies and additionally introduced indicator of variation of the number of germinated seeds. The material supply was regulated by the degree of opening of the flap in the loading hopper in the range from 0.2 to 0.4 t/h. The rotation frequency of the drum was changed by a frequency converter from 550 to 650 min-1. Eastern galega seeds met GOST 52325-2005 requirements. The experiments were carried out in three-fold repetition. As a result of an experimental study of the KS-0.3P cloverworm-scarifier during the scarification of the seeds of the Eastern galega, the ranges of the optimal drum rotation speed of 550... 650 min-1 and the material supply of 0.3... 0.4 t / h were determined, when the specified agrotechnical indicators were provided: the degree of scarification not less than 95.0 % and crushing not more than 1.5 %.

General point load weight function for semi-elliptical surface cracks in round bars

Offshore mooring chains are continuously subjected to cyclic environmental loadings, resulting in fatigue cracks that always develop at the surface and grow across the circular cross-sections. To analyse the fatigue crack growth in a mooring chain based on a fracture mechanics-based approach, the evaluation of stress intensity factors (SIFs) of surface cracks in the chain segments becomes essential. A general point load weight function of SIFs for semi-elliptical surface cracks in straight and curved round bars was derived in this study. Parametric three-dimensional finite element (FE) models were developed to calculate the SIF solutions for determining the unknown parameters in the weight function. The analysis matrix covered wide ranges of aspect ratios 0.1 ≤ a/c ≤ 2.0, relative crack depths 0.03 ≤ a/D ≤ 0.6 and relative bar curvatures 0.0 ≤ D/Ri ≤ 1.5. The developed weight function was verified against the solutions available in the literature and FE results, indicating good accuracy. The proposed weight function can be used in SIF calculation and remaining fatigue life prediction of surface cracked round bar components under complex stress distributions, such as chain links.

Experimental and Theoretical Studies of the Thermal Contact Conductance for Bundles of Round Steel Bars.

The paper presents investigations devoted to the analysis of the thermal contact conduction in a bundle of round steel bars. The phenomenon can be expressed quantitatively with the use of thermal contact conductance (hct). The starting points for the presented analysis were the results of the experimental measurements of the effective thermal conductivity. The measurements were performed for samples of a medium in the form of flat packed beds of bars with three different arrangements: staggered, in-line, and crossed and four bar diameters: 10, 20, 30, and 40 mm. Next, a mathematical model was developed, thanks to which the values of the hct coefficient were calculated for the analyzed cases. This approach consists in analyzing thermal resistances in the medium model, which is defined with an elementary cell. It was established that the value of the hct coefficient in the temperature range of 50-600 °C changes within the range of 50-175 W/(m2·K), and it decreases with an increase in the bar diameter. The final effect of the present study was to develop generalized approximation equations describing changes in thermal contact conductance in the heated bar bundle simultaneously in the temperature and bar diameter function.

ANALYSIS OF RESIDUAL STRESS BY X-RAY DIFFRACTION AND STUDY OF MICROSTRUCTURE IN WELDED JOINT OF ASTM A-36 MARINE STEEL

ASTM A-36 marine steel is one of the most used and classified as a medium strength carbon steel. Its characteristics and purpose are in common applications and in metallic structures in general, sawmills, walkways, agricultural machinery and implements, road, rail and oil implements. It is used in angles, round, flat and square bars and I, U and T profiles. In this work, 10 mm sheets, with a V chamfer, were welded using the MIG/MAG process and X-Ray Diffraction measurements were carried out to study of residual stresses caused by the welding process. Then samples were taken for metallography and microscopy in the Scanning Electron Microscope (SEM). They were also performed in the three regions of the weld: base metal (MB); thermally affected zone (ZTA) and in the molten zone (ZF) Brinell hardness tests, to determine the energy stored in the regions of the weld bead. Vickers Microhardness measurements were also made at the ZTA, as it is a very narrow range, to give more precision to the hardness measurements. The X-Ray Diffraction test showed that the air-cooled samples are compressive and the water-cooled samples are tensile. The micrographs of the samples, in the region of the weld, showed that the ferritic phase prevailed in the molten zone. It was also observed the precipitation of carbides and alloying elements, in addition to the presence of martensite. It is concluded, therefore, that the results for the MIG/MAG welding were satisfactory and recommended for the welding of ASTM A-36 Steel.

The influence of longitudinal rebar type and stirrup ratio on the bond performance of reinforced concrete with corrosion

This study investigated the bond-slip mechanism of eccentrically pulled out rebar under different corrosion level. The variation patterns of the bonding performance between two types of steel rebars (i.e., plain round rebar and ribbed rebar) and concrete with different stirrup ratios were obtained with respect to the amount of steel rebar corrosion. The differences in bonding performance between plain round rebars and ribbed rebars with concrete were compared, and the bond-slip mechanisms of plain round rebars and ribbed rebars with concrete were elucidated. The influence of longitudinal bar type and stirrup ratio on the ultimate bond strength and bond-slip constitutive curve was analyzed. It has been determined that in the case of uncorroded specimens featuring ribbed bars, the ultimate bond strength exhibits an approximately linear increase in relation to the stirrup ratio. Conversely, the stirrup ratio does not have a significant impact on the ultimate bond strength of uncorroded specimens with plain round bars. Transverse reinforcement plays a crucial role in mitigating the effects of cracked concrete by delaying the reduction in bond stress caused by the corrosion rate of longitudinal reinforcement. This phenomenon becomes increasingly prominent when higher stirrup ratios are utilized in the case of plain round reinforcement. Transverse reinforcement serves to suppress the occurrence of the brittle failure stage that follows the peak bond stress in specimens exhibiting a low corrosion rate. The magnitude of this effect becomes more pronounced as higher transverse reinforcement ratios are employed.

A novel approach for study of straightness in commercially produced round metal bars based on deflection measurements

Round metal bars are available at various sizes at commercial markets and in industries. These bars are used in various branches of industry, for instance in automobile, aerospace, power and manufacturing engineering as well as paper industry, printing and packaging industry and construction industry. It is often found that round bars as available in open market are not often straight at various sections along the length. As the round bars usually fulfil responsible functions, their surface irregularities should be precisely measured. In the present investigation, straightness of bars is measured section-wise across the length of the bar in order to understand the actual scenario of production quality. An attempt has been made by choosing various different types of materials of different sizes to ascertain the actual availability of bar sizes at commercial market and also to understand the level of straightness of these bars along the axis of the bar. 3D surface plot is also used here to find out whether such bars as commercially available can be utilised for precision industrial applications or not. Finite element analysis is also performed to compare the deformations of different solid round metal bars. Results show that commercially available aluminium bars are showing nearly straight having less deformations compared to bars of other materials.

Mechanical properties and constitutive model of filling medium in hot casting socket at elevated temperatures

Hot casting sockets have been commonly applied in the prestressed structures to anchor steel cables. However, the study on the fire behaviour of hot casting sockets is limited, particularly in relation to the thermo-mechanical properties of the filling medium. This paper experimentally investigates the mechanical properties of a zinc copper alloy (employed as the filling medium) at varying target temperatures. A comprehensive range of stress–strain curves are obtained by using a digital image correlation measurement system. The elastic modulus, proportional limit, effective yield strength and ultimate strength are presented and compared to those of steel cables. It is found that the strain hardening effect diminishes as the temperature increases. Reduction factors of elastic modulus, effective yield strength and ultimate strength of the zinc copper alloy are smaller than those of steel cables at elevated temperatures, indicating the vulnerability of the filling medium in fire scenarios. Mathematical formulas of reduction factors of mechanical properties are proposed. Furthermore, a novel constitutive model is proposed by modifying the Johnson-Cook model. Parameters involved in the stress–strain relationship are determined by the smooth round bar test results, whereas those in the failure criterion are determined by the notched round bar test results. Finally, the modified constitutive model is applied in a finite element model, and the numerical results have good agreement with the test results.

Unstable stress-triaxiality development and contrasting weakening in two types of high-strength transformation-induced plasticity(TRIP) steels: Insights from a new compact tensile testing method

The impact of high stress triaxiality on work hardening in transformation-induced plasticity (TRIP) steel has been widely acknowledged, particularly through measurements of the austenite fraction. Understanding this TRIP behavior is crucial for predicting material fracture in press-forming processes. However, the actual flow stresses under high-stress-triaxiality conditions remain largely undetermined. To address this gap, we developed a new tensile testing method using tiny notched round bars to investigate stress-triaxiality-induced work hardening in TRIP steels. The specimens were analyzed using two-dimensional micrometry to allow finite element analyses to identify the flow stress. Additionally, we conducted in situ tensile tests in which their crystal lattice stresses were monitored using synchrotron X-ray diffraction (XRD) to realize mechanism analyses of the unexpected work-hardening behavior identified by the developed tensile testing method. Our combined approach revealed a mutual, unstable increase in the flow stress and stress triaxiality in the TRIP-aided bainitic ferrite steel, which reduced the hardening exponent coefficients and thus induced a higher stress triaxiality. In contrast, the TRIP-aided martensitic steel exhibited a weakening behavior, characterized by a significant decrease in the hardening exponent coefficients in the case of the sharpest notch. XRD analyses showed that microstructural heterogeneity led to an extraordinarily high hydrostatic stress in the austenite phase, accounting for these contrasting behaviors. This finding challenges the established consensus on TRIP steels and suggests the need for a revised framework for their application in press-forming, taking into account stress-triaxiality conditions.

A cyclic GTN model for ultra-low cycle fatigue analysis of structural steels

Ultra-low cycle fatigue (ULCF) is a critical concern in the seismic design of steel structures due to its adverse effects on the ductility and energy dissipation capacity of steel connections. The Gurson-Tvergaard-Needleman (GTN) model, a well-accepted micromechanical fracture model, cannot be applied directly to ULCF analysis, as it requires proper estimation of the effects of cyclic loadings on the ductile fracture of materials. In this paper, a cyclic GTN (C-GTN) model was proposed for the ULCF prediction of materials, in which the evolution of microvoids during ULCF loadings was addressed for tensile and compressive half load cycles, respectively, and the effect of the cumulative plastic strains on the material’s resistance to ductile fracture was considered by the reduction of the critical void volume fraction for void coalescence. Then, a VUMAT subroutine was programmed for the C-GTN model, in which the cyclic hardening behavior of materials was simulated with the Voce-Chaboche model. Finally, the C-GTN model was calibrated for the G20Mn5QT cast steel based on previous tests on notched round bar specimens of the material. The applicability of the C-GTN model and the VUMAT subroutine were validated in the ULCF analysis of double-hole plate specimens of the G20Mn5QT cast steel.

Synergistic Effect of Strontium and Melt Quenching on the Solidification Microstructure of Hypereutectic Al-Si Alloys.

The synergistic effect between strontium (Sr) and melt quenching on the solidified microstructure of hypereutectic Al-Si alloys was investigated by optical and scanning electron microscopy. The results indicate that melt quenching can suppress the growth of primary Si particles in the solidified structure of the hypereutectic Al-Si alloy, resulting in a significant decrease of in the average size of primary Si particles in Al-(18~22)Si alloys from 30.35~66.31 μm to 15.13~34.63 μm. The synergistic effect between Sr and melt quenching can further inhibit the precipitation of primary Si particles in the Al-18Si alloy. After the addition of Sr to Al-18Si alloy and undergoing melt quenching, the area fraction of primary Si clearly decreases. When the added amount of Sr increases from 0.1 wt.% to 0.5 wt.%, the area fraction of primary Si decreases from 1.13% to 0.16%. With 0.5 wt.% Sr in the tested alloy, the inhibiting effect on primary Si precipitation was significantly improved. Research has shown that the cooling rate has a significant impact on the solidified structure of the melt-quenched Al-18Si-0.5Sr alloy. There exists no primary Si in solidified structures on the area of 1/8R and 1/4R from the surface of the round bar sample, but the area fraction of primary Si increases, respectively, to 1.97% and 12.48% on the area of 1/2R and R from the surface. The higher the cooling rate, the higher the inhibitory effect on the primary Si precipitation in the Al-18Si-0.5Sr alloy.

Effect of stress triaxiality on the hydrogen embrittlement micromechanisms in a pipeline steel evaluated by fractographic analysis

Hydrogen gas, as an energy carrier, is expected to play an important role in the storage and transport of energy produced by renewable sources. The transport of hydrogen gas can be managed through the use of existing pipeline networks. However, the uptake of hydrogen in steel structures is known to cause a degradation of mechanical properties, a phenomenon called hydrogen embrittlement (HE). In this study, the hydrogen-assisted ductility loss of an API 5L X70 pipeline steel is investigated. The influence of hydrogen on mechanical behavior is evaluated by tensile tests on uncharged and hydrogen charged specimens. These tests are performed on notched round bar specimens with different notch radii, allowing for a range of positive stress triaxialities to be examined. Notched samples are more embrittled than unnotched specimens after hydrogen charging. Hydrogen signatures in the form of fisheyes and quasi-cleavage are detected on the fracture surface. Fisheyes initiate primarily at segregation bands in the steel for all specimen geometries. Fisheyes can also be linked to different inclusion types present in the steel, depending on notch geometry. For unnotched as well as the least sharply notched specimens tested in this study, the embrittlement can be correlated with the area fraction of fisheyes on the fracture surface.

Ductile fracture of LYP225 steel: Effects of stress states and loading histories

This paper presents the experimental and modeling studies of the ductile fracture initiation of LYP225 steel, considering the stress state and loading history dependency. The monotonic material tests, including the notched round bars (NRBs), flat grooved plates (FGPs), and the shear plates (SPs), confirm the prominent stress state dependency of the ductile fracture. The increased stress triaxiality will significantly reduce the fracture strain, and the shear effect quantified by the Lode angle parameter will degrade the deformability under similar triaxiality. The Hosford-Coulomb fracture criterion can well characterize the relationship between fracture strain and stress state variables. Regarding the cyclic loading, a generalized expression of the cut-off region is proposed to consider the temporarily frozen damage accumulation under compression applied. In addition, the premature cyclic fracture initiation predicted by the monotonic fracture criterion highlights the necessity of considering the loading history effect. Based on the plastic strain memory surface, a reduced factor is introduced for the lower damage accumulation rate under cyclic loading. By comparing the testing and predicted plastic deformation corresponding to fracture initiation, the proposed fracture model is validated under different stress states and loading protocols, as indicated by the low average percentage errors of 4.02% for monotonic loading and 16.7% for cyclic loading.

A Statistical Approach for Study of Roundness in Commercially Produced Round Metal Bars

Commercially produced ferrous and non-ferrous metal round bars are available at various sizes. These bars have tremendous engineering use in multiple areas like automobile, aerospace, power, manufacturing, paper, printing, packaging and construction industries. Due to its wide range of utility of round bars, it is naturally pertinent to understand and ascertain quality aspect of these bars. Quite often it has been observed that round bars as available are not completely geometrically round at various sections along the length, also straightness is also somewhat compromised. Therefore, it is necessary to check the uniformity of diameters at various sections. In this paper statistical process control has been used to ascertain whether such round bars as commercially available can be utilized for industrial application or not. Control limits in terms of diameter measurement along the length of bars help to evaluate the characteristics of data variation which is needed to take decision about confirmation of utility of commercially produced bars

Miniature specimen tests and fracture model of heat affected zone material

AbstractThe paper investigates the mechanical properties of the heat affected zone (HAZ) material near welds and compares the properties to those of the base metal and weld materials. A dedicated experimental set‐up was designed and manufactured to test miniature specimens with a cross‐section width in the range of 1 mm to 2.5 mm and a parallel gauge length of less than 10 mm. To identify the HAZ of the welded connections, a macro‐etching technique was adopted, and the shape and size of the HAZ were measured. Afterwards, miniature specimens were extracted from the base metal, weld and HAZ in both the longitudinal and transverse directions of the weld, and subsequently tested in the specialised experimental set‐up. The miniature specimens not only included the normal rectangular plate‐type specimen, but also the notched round bar and grooved plane strain types of specimens. Hence, the stress‐strain curve and fracture strains under various stress states were obtained from the tests. The validity of the Lode angle Modified Void Growth Model (LMVGM) was investigated using the experimental data, and the fracture loci of the base metal, weld and HAZ in both the longitudinal and transverse directions were identified.

Insert Molding of Aluminum Alloy A7075 and Alumina Plate by Semi-Solid Forging

Industrial, electric railway, and automotive applications of inverters and converters use case-type semiconductor packages called power modules. Power modules have multiple joint points, and among them, from the viewpoint of reliability and bonding strength, many studies on metal-ceramic substrate bonding have been reported. Alumina Al203 or aluminum nitride AIN are mainly used for ceramics, and copper or aluminum are mainly used for metals, although alumina and aluminum have a price advantage. The joining methods are generally brazing and AMB (Active Metal Brazing), but there is a need to improve the joint strength, heat dissipation characteristics, and productivity, i.e., a joining method that does not use brazing material. The purpose of this study is to achieve direct joining of alumina A1203 and aluminum alloy A7075, and semi-solid forging [1, 2, 3, 4, 5, 6] was used as the method. The A7075 used in this study is considered to be suitable for this application because of its high strength and thermal conductivity among aluminum alloys. In this study, solid phase ratio 30 % semi-solid forging was actually performed using a servo press and a die, and the results were evaluated by observing the cross section of the fabricated specimens. The punches and dies were circular in shape to ensure uniform spreading of the molten material, and carbon steel S50C with high thermal conductivity was used to quickly dissipate the heat of the semi-solid slurry during the pressing process. The thickness of 99.6 % Al2O3 alumina plate was 2.5 mm. The semi-automatic stirring device was modified to stir the molten metal by attaching a 1000 mm round bar to the rotating part of a tabletop drilling machine and attaching a stirring blade to the tip of the bar. Debonding between aluminum alloy and alumina plate was not confirmed. There was no gap between the aluminum alloy and the ceramic plate.

Development and preliminarily tests of superelastic Ni-Ti SMA ribbed bars for reinforced concrete applications

The research on superelastic shape memory alloy (SMA) bars reinforced concrete members and structures has received a great deal of attention recent years. In this study, novel superelastic Ni-Ti SMA ribbed bars were developed and investigated to improve the bonding performance and to avoid the problem that the threaded or mechanical anchorage parts of the SMA plain round bars (used in many previous studies) were easy to break in advance. A comprehensive experimental program was conducted to characterize the cold-rolled superelastic Ni-Ti SMA ribbed bars, including scanning electron microscopy to observe the micromorphology, differential scanning calorimeter tests to analyze the phase transformation temperatures, and cyclic tensile tests to examine their mechanical properties. Moreover, five reduced-scale concrete beams were prepared and tested to verify the advantages of the superelastic SMA ribbed bars as bottom longitudinal reinforcements. Results shown that the cyclic tensile response of the cold-rolled SMA ribbed bar subjected to some degree of annealing can be similar with that of the annealed SMA plain round bar. Compared with the beam specimen incorporating ECC and superelastic SMA plain round bars and the beam specimen incorporating normal concrete and superelastic SMA ribbed bars, the specimen incorporating ECC and superelastic SMA ribbed bars exhibited a significantly improved deformation ductility, ultimate bearing capacity, energy dissipation ability, self-centering capability, and cracking performance under the cyclic flexural loads. Besides, no reinforcement slippage or fracture were observed during the entire loading process in all beams, suggesting satisfactory bonding effect and uniformity.

Dynamic Mechanical Properties and Damage Parameters of Marine Pipelines Based on Johnson–Cook Model

A comprehensive understanding of the dynamic behavior of materials and structures under impact loads is paramount for the design and maintenance of reliable marine pipelines and associated structures. However, there is a lack of comprehensive research on the full characterization of constitutive and failure models of carbon steels, which are commonly used in marine pipelines. In this paper, Q235 steel was subjected to quasi-static tensile tests at room temperature on smooth specimens to obtain the constitutive parameters using the Johnson–Cook (J-C) model. Subsequently, quasi-static tensile tests were conducted on notched specimens, and dynamic tensile tests were performed on smooth round bars to obtain stress triaxiality and failure strain. The acquired data were then utilized to fit the failure parameters using the Johnson–Cook (J-C) damage model, a widely accepted constitutive model employed in high-strain rate applications through the least squares method. Finally, the tensile test is numerically simulated based on the acquired experimental parameters. The obtained results reveal a remarkable agreement between the curve fitted by the J-C constitutive model and the experimental tensile curve. Additionally, a high degree of correlation between the load-displacement curves of the tests and simulations provides robust validation of the accuracy of the dynamic mechanical parameters for Q235 steel. These findings contribute valuable insights into the behavior of carbon steels commonly used in marine pipelines, enhancing the overall understanding of their response to impact loads and informing more reliable design and maintenance practices.

Ultra-flexible self-supporting Ag2Se/nylon composite films for wearable thermoelectric devices

Recently, flexible thermoelectric (TE) generators (f-TEGs) have received a lot of attention. Compared with TE films on flexible substrates, self-supporting composite films prepared by combining TE materials with soft fabrics and thus retaining the inherent advantages of fabrics, such as stretchability, breathability, and flexibility, are more practical and may significantly expand the application of f-TEGs in smart wearable devices. Hence, in this work, a facile and rapid method for preparing ultra-flexible self-supporting Ag2Se/nylon composite films is developed. The composite films with both TE properties and flexibility were obtained by fast selenization of commercial Ag/nylon fiber fabrics in a short time (60 s) at room temperature and then hot pressing at 230 °C in a vacuum. The maximum power factor of an optimized composite film at room temperature can reach 73.7 μW m−1 K−2. Meanwhile, the film exhibits excellent flexibility with the Seebeck coefficient and electrical conductivity decreased by only 7.37 and 8.48% after being bent 4000 repetitions around a round bar with a radius of 4 mm, which exceeds most reported flexible TE films. The ultra-high flexibility is mainly attributed to its high content of the nylon matrix (∼85.05 wt%), the tight bonding between Ag2Se grains, and the good combination between the Ag2Se and nylon matrix. In addition, a 3-leg f-TEG assembled with the optimal film produces a maximum power of ∼1.524 μW (corresponding to a power density of ∼0.47 W m−2) at a temperature gradient of 40.6 K, verifying the good TE performance of the composite film. This f-TEG can also be used as a self-powered temperature sensor, showing potential applications in daily life.

Round bar notch shape optimization for tensile stress concentration testing

Abstract Notched structures in machine parts for several reasons cause discontinuity and stress concentration. It is essential to optimize these stress concentrations in notched parts. This study determined the best notch shape by creating different notch shapes by keeping two key points fixed on the spline curve in the notched region. This paper involves optimizing the shape of a fillet in a notched tension bar. An optimal shape was aimed to minimize the notch factor without causing yield anywhere in the bar by parametrically controlling the spline of the fillet via ANSYS parametric design language code. Optimal shapes of B-spline curves were obtained for round bars subject to axial tension loadings. Changing the code can also be used for bending or combined loading conditions other than tensile loading.