Solid Round Bar Research Articles

Compressive creep buckling of single cell metamaterial at elevated temperatures

AbstractThe benefits of tailored lattice topologies are limited in elevated temperature conditions without a clear understanding about the interplay between the metamaterial structure and the creep response of the base material. This study showed that the metamaterial structure causes the lattice compressive creep behavior to differ largely from that of bulk structures of the same base material. Inconel 625 FCCZ lattices and solid round bar specimens were crept in compression at two elevated temperatures and at three stress levels. The solid round bar specimens experienced only small increases in the steady state creep rate with a steady state exponent of 0.35 and 0.63 at 550°C and 650°C. The solid round bar specimens did not exhibit a deformation mechanism change over the temperatures and stress levels tested. The FCCZ lattices exhibited much larger changes in creep rates with changing stress and temperature with a steady state exponent of 18.3 and 20.2 at 550°C and 650°C, respectively. Additionally, the lattice specimens experienced three different failure behaviors with increasing temperature and stress from stable creep, to progressive buckling, and finally rapid collapse.

Modes I-II-III stress intensity factors of a semi-elliptical surface crack at a round bar under torsion loading by FEM and DBEM

The corner point singularity of surface cracks by finite element method (FEM) has become a numerical concern decades ago. The literature showed that the stress intensity factors (SIFs) at the corner points were often excluded. Further, most SIFs were reported for larger ratios of the crack depth over cylinder diameter. This paper presents the SIFs (Modes I, II and III) of a semi-elliptical surface crack at a solid round bar under torsion. The tetrahedral and hexahedral elements were used in the finite element modelling. The effects of the loading mode and the crack aspect ratio on the corner point singularity were discussed. The tetrahedral meshing was generally observed to be more suitable for modelling relatively small surface cracks, particularly in respect to the corner point singularity. For all loading modes, the SIFs away from the corner points of using the tetrahedral meshing were found to have fairly good agreement with those by dual boundary element method (DBEM).

Effects of Stress Amplitude Ratio and Phase Angle on Short Fatigue Crack Behavior and Fracture Mode of EA4T Steel

The loads on railway axles in actual service conditions are complex and variable, which may lead to local changes in the fatigue performance, which then affect the fatigue reliability and safety evaluation results of the components and structures. At present, studies on the short fatigue crack behavior and fracture failure mode of EA4T steel, a common material for high-speed trains, are limited. Therefore, fatigue tests on smooth funnel solid round bar specimens under different stress amplitude ratios and different phase angles were performed. Replica technology was used to record the initiation and propagation information of short fatigue cracks. Due to the homogenous and fine microstructure of all the specimens, the same short fatigue crack behavior was observed regardless of the loading condition. The fracture morphology observed by a scanning electron microscope shows that the cracks initiated on the surface of the specimens, and the specific fracture morphology was exceedingly distinct in each region. In addition, the short fatigue crack growth rate and fatigue life were compared and analyzed. The results show that the stress amplitude ratio and phase angle have a considerable influence on the fatigue life and short crack growth rate of the specimens. The results of this research can provide a reference for practical engineering applications.

Hot Extrusion of a Commercial Aluminum Powder Metallurgy Metal Matrix Composite Material

Abstract Sintered preforms made of an aluminum powder metallurgy (PM) 2000 series metal matrix composite designed for press-and-sinter applications were forward extruded at 450°C under displacement rates of 254 mm/min and 2,032 mm/min. The material was highly responsive to extrusion under these conditions and was readily formed into products that included 10-mm and 15-mm solid round bars as well as C-channel and round tubing profiles, wherein extrusion ratios ranged from 11:1 to 76:1. Significant metallurgical improvements were also observed in the seemingly defect-free products. These included gains in tensile yield strength (10 %), ultimate tensile strength (20 %), and tensile ductility (400 %) when compared to the nonextruded T6 counterpart. Such enhancements were attributed to the attenuation of full theoretical density, disruption of the residual oxide network, and the development of a partial duplex fiber texture with strong <111> and moderate <100> fiber components within the extruded PM products.

Prediction of crack shape in a cylindrical bar under combined fatigue tension and torsion loading

Most of the existing theoretical studies to predict 3D-crack-front shape change are confined to plate-like structures. In this paper, a transient three-parameter geometric model with fewer constraints located on equivalent deflected crack planes is developed by using space oblique extension circles for a transverse surface crack in a solid round bar under fatigue tension–torsion loading. The results show that the proposed mathematical and numerical analysis method can get more effective prediction with fewer iterations. It is verified by comparing the formation outcome of crack growth obtained by visualization of the predicted crack-front shapes with other numerical solutions and experimental results.

Multiaxial fatigue life assessment in notched components based on the effective strain energy density

This paper presents a methodology to predict the fatigue lifetime in notched geometries subjected to multiaxial loading based on the effective strain energy density concept. The modus operandi consists of defining a fatigue master curve that relates the strain energy density with the number of cycles to failure from standard cylindrical specimens tested under low-cycle fatigue conditions. After that, the multiaxial loading history at the geometric discontinuity is reduced to an equivalent uniaxial loading scenario via the calculation of an averaged value of the strain energy, which is done by combining the equivalent strain energy density concept along with the theory of critical distances. Then, this energy is inserted into the fatigue master curve to estimate the fatigue lifetime. The method is tested in solid round bars with lateral notches subjected to in-phase bending-torsion loading. Overall, the comparison between the experimental and predicted fatigue lives shows a very good agreement. Additionally, the proposed approach enables the determination of the most likely initiation sites as well as the crack angles at the early stage of crack growth.

Surface residual stresses induced by torsional plastic pre-setting of solid spring bar

Residual stresses could be induced by the plastic torsion loading of a solid round bar. This article deals with the residual stresses generated at the surface during the process of plastic pre-setting. Residual stresses were measured on the surface of a specimen by x-ray diffraction for different angles of subsequent plastic pre-setting. In addition, the residual stresses were calculated using analytical and numerical modelling by finite element methods. The analytical approach was based on the torsional characteristic, τ–γ, of the material and tension test results. It has been found that the direction of cold rolling on the surface has a significant influence on residual stresses, as it is reflected in the initial stress state. A good agreement between analytical modelling, finite element analysis, and experimental residual stress measurement was obtained.

J-Integral Evaluation of Surface Cracks in Round Bar under Mode III Loadings

Fracture mechanics approach has successfully used to characterize the existing cracks in engineering materials and structures. Tremendous number of publications on surface cracks can be found for crack behaviour which was assumed to behave linear elastic. However, lack of information on elastic-plastic crack behaviour or <em>J</em>-integral was demanded especially for 3D surface cracks. In this present study, semi-elliptical surface cracks embedded in a solid round bar subjected to mode III loadings are considered. Then, <em>J</em>-integral or <em>h</em>-function and limit load were determined and analyzed. In order to predict <em>J</em>-integral along the crack front, a mathematical model was then developed. It is found that the developed model capable to predict <em>J</em>-integral well. However, the predictions breakdown occurred when the elastic dominated region of cracks.

Design and construction of Shoreditch High Street Bridge, UK

The £500 million East London railway works contract in the UK includes the design and construction of a series of underline bridge structures, carrying the upgraded and extended railway between the refurbished Kingsland viaduct at its northern end and the former Great Eastern railway. One of these is Shoreditch High Street Bridge, a bowstring arch bridge forming a landmark where a new section of the railway crosses Shoreditch High Street just north-east of the City of London. It is an unusual form of railway bridge, chosen primarily for its appearance, having solid round bar hangers and no bracing between arch ribs above deck level. The East London railway Balfour Beatty–Carillion joint venture directed the design and constructed the bridge, while the bridge design was undertaken by URS. This paper describes the design and construction of Shoreditch High Street Bridge, highlighting some of the more unusual features.

The crack growth behavior after overloading on rotating bending fatigue

Most of the crack propagation behavior relating to the variable amplitude load is conducted in flat specimens such as centered-crack specimens or compact test specimens with various thicknesses. For that reason, it is also important to understand the crack growth behavior relating to the overload on other geometry which differs from the previous investigation. In the present study, the crack growth behavior after being overloaded was investigated on a solid round bar. It was found that the size of diameter influences the crack growth behavior. The retardation or acceleration depends on the residual stress state in front of the crack tip. If the residual stress state developing was compressive, retardation was observed, and if the tensile residual stress state developed, the acceleration of the crack occurred after overloading. In addition, the shape of the component has to be taken into consideration for evaluating fatigue life in association with the crack growth.

Surface Roughness Optimization of some Machining Parameters in Turning Operations Using Taguchi Method

In this study, an attempt has been made to optimize cutting parameters (cutting speed, depth of cut, and feed rate) in conventional turning operations. A Taguchi orthogonal array (L933) was used in surface roughness optimization of a solid round bar of mild steel material. The experimental runs were randomized; two skilled machinists were involved in the turning operation using the same machining parameters. ANOVA analysis was performed to identify the percentage contribution of the factors affecting surface roughness during machining. The optimal cutting combination was determined by using the signal-to-noise ratio and the following results were obtained; speed (level 2) = 55.m/min, depth of cut (level 3) = 0.08mm, and feed rate (levels 3) = at 0.08mm/rev. A prediction of surface roughness was carried out using the optimal setting followed by a confirmatory test on the lathe. The result shows that the confirmatory runs compared favourably (96.44%) with the predicted surface roughness.

Effect of inner diameter on friction torque in the friction welding of pipes

To clarify the joining mechanism of friction welding, the authors have previously investigated joining phenomena in the first phase of friction welding using solid round bars.1–5 The results obtained in these studies have led to the proposal of a method for simulation of friction torque in the first phase of friction welding with the friction welding conditions and the physical values of the base metals adopted as key parameters of interest. Results have also led to the development of a method for simple estimation of the initial torque based on the base metal yield strength at the seizure temperature of the faying surfaces.6

Compressive Strength of Solid Round Steel Bars

In the era of modernization, solid round steel bars are widely used in communication towers, which play a vital role in today's world. Solid steel round bars are used as leg members, diagonal members, and horizontal members of a communication tower. Canadian Standard for Antenna towers and Antenna Supporting Structures, CAN/CSA-S37-01, specifies empirical expressions for the compressive strength of solid rounds based on the well-known Structural Stability Research Council column strength curves for nonsolid-round members as well as on the results from an experimental investigation on the compressive resistance of solid rounds carried out back to 1965. This paper provides a summary of the available literature on the compressive strength of solid rounds. Also, the results of the recently tested six large solid round bars at Ryerson University, Toronto, are presented. Correlation between the results from these tests and the current practice for the design of solid rounds is investigated. It is expected that the results from this paper direct the attention of code writers to more economical and safe empirical expressions for the ultimate compressive resistance of solid rounds. This would assist the practicing engineers in the evaluation of the load-carrying capacity of existing antenna towers since even a small increase in strength for live load can make the difference between demolishing a tower or leaving it in service.

Delayed Fracture of High Strength Steel having Thin Thickness.

A study of hydrogen embrittlement on high strength steels was carried out with thin walled hollow and thin plate specimens, of which stress state would be plane stress condition, to compare them with solid round bar specimens which had been subjected to plane strain condition. The specimens were cathodically charged with hydrogen under sustained load conditions. The delayed fracture life of thin walled hollow and thin plate specimens lasts longer compared with the solid bar specimens. SEM fractographic examination showed that the essential process of delayed fracture, in which a formation of quasi-cleavage (QC) crack triggers the intergranular (IG) crack after subcritical propagation into a critical size, is unchangeable irrespective of the stress condition. Consequently, total life of the hydrogen charged steel is mainly determined by the period of crack initiation and subcritical growth of the QC crack.

Biaxial Fatigue of A533B Pressure Vessel Steel

The low-to-intermediate cycle fatigue behavior of A533B steel is investigated using solid round bar specimens tested in combined bending and torsion. Loadings are applied in-phase and 90 deg out-of-phase to produce cases of proportional and nonproportional biaxial fatigue. Out-of-phase loadings are found to be more damaging than in-phase loadings. Two equivalent strain criteria similar to those in the ASME Boiler and Pressure Vessel Code and a newer approach based on cyclic plastic work are used to correlate fatigue lives. The equivalent strain criteria are found to underestimate the fatigue damage in out-of-phase tests, but to provide reasonably good correlations overall. The plastic work approach provides a conservative treatment of the out-of-phase data and somewhat better overall correlation. Cracking behavior observed during the tests is also summarized.

Effects of friction welding conditions and weld flash on fatigue strength of steel friction‐welded joints

Summary As‐welded hot‐ and cold‐drawn mild steel solid round bar specimens are used to determine the effect of flash on the fatigue strength of friction‐welded joints in rotating bending fatigue tests. The results obtained may be summarised as follows. The fatigue strength of the hot‐ and cold‐drawn friction‐welded joints with flash decreases with an increasing upset pressure. The fracture location of friction‐welded joints with flash is the flash toe. The upset pressure has a pronounced effect on the fatigue strength, whereas the friction pressure and burn‐off have little effect. The toe radius of the flash decreases with an increasing upset pressure, whereas the toe angle conversely increases. Stress concentration in the flash toe is therefore considered to be the main cause of the greater loss of fatigue strength in friction‐welded joints with flash than in the base metal. The fatigue strength of the hot‐drawn joints recovers to the base metal level under any welding conditions so long as the flash is ...

ELLIPTICAL‐ARC SURFACE CRACKS IN ROUND BARS

AbstractThe crack aspect ratio influence on the stress‐intensity factor of elliptical‐arc edge flaws in solid round bars under tension or bending loading is discussed. The relative crack depth ξ=a/D between the depth a of the crack's deepest point and the bar diameter D ranges from 0.1 to 0.6, while the aspect ratio a/b of the flaw is made to vary from 0.0 (straight crack front) to 1.0 (circular‐arc crack front). For each value of ξ being considered, the maximum stress‐intensity factor is attained in correspondence to the deepest point on the crack front in the case of a/b= 0.0, while it is attained near the external surface in the case of a/b= 1.0. For intermediate aspect ratios, the stress‐intensity factor presents the maximum value at the crack's deepest point for ξ≤ξCR and near the free surface for ξ≥ξCR, with the critical relative crack depth ξCR getting lower and lower as the parameter a/b is increased.

Fatigue Crack Propagation in cylindrical bars

AbstractCrack propagation calculations were conducted to describe a developing surface crack in a solid round bar. The theoretical basis is a stress intensity factor solution in weighted average for the center and the surface points of a so called “almond‐shaped” crack under Mode 1 loading. This solution was obtained by use of approximate weight functions. With these weight functions stress intensity factors for tension and bending were calculated. Predictions for the developing crack shape and the crack growth rate can be made utilizing a da/dN‐ΔK relation. Experimental results for a 42 CrMo4 steel are in excellent agreement with these predictions.

An analysis of flow localization during torsion testing

A general analysis of the occurrence of flow localization during the torsion testing of solid round bars is presented. The formulation is based on equations which enforce torque equilibrium during straining and which account for the thermal effects resulting from heat generation and transfer via conduction and convection. These equations are solved in conjunction with the appropriate boundary conditions and a torque relation in the form of either an “evolutionary” differential equation or an expression in terms of the twist, twist rate, temperature, and specimen radius. To illustrate the use of the present formalism, several predictions are made for hypothetical and real materials. A qualitative analysis of flow localization in the special cases of 1. (a) isothermal and 2. (b) adiabatic conditions demonstrates that, irrespective of the material flow law, unbounded strain concentrations can only occur under the latter conditions. The analysis is applied to the problem of flow localization during the room temperature torsion of 304 stainless steel bars containing an initial geometric defect. To this end, finite difference forms of the governing equations are derived which were utilized in computer simulations. The simulations also employed analytic expressions for the material properties and a torque relationship obtained from nominally isothermal tests on samples without defects. A comparison of measured and predicted torque-twist curves and strain histories within and exterior to the defect shows excellent agreement when the effects of length changes during testing are taken into account.

Stress Intensity Factors for Single-Edge-Crack Solid and Hollow Round Bars Loaded in Tension

AbstractDimensionless stress intensity factors were determined for single-edge-crack solid and hollow round bars loaded in tension. These factors were calculated from experimental compliance (inverse slope of load-displacement curve) measurements made over a range of dimensionless crack depths (lengths) from 0.05 to 0.65. The tests were made with 76-mm (3-in.) diameter solid and hollow round bars notched on one side and loaded in axial tension. The hollow bar had an inner to outer diameter ratio of 0.33. A comparison was made with data in the literature for rectangular bars; for a crack depth to diameter ratio of 0.0001 the dimensionless stress intensity factor for a solid round bar is 0.55 compared with 2.0 for a rectangular bar.