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In this paper, a numerical modeling was developed to study (on the basis of the Paris law) the fatigue propagation paths of eccentric external (outer) cracks in circumferentially cracked round bars (CCRB) subjected to a cyclic type of loading in the form of either remote tensile loading or imposed axial displacement. Results show how the eccentricity (in relation to the wire axis) of the circular resistant ligament increases with the growth of outer circumferential cracks by subcritical fatigue mechanisms. This phenomenon is more pronounced when the solicitation consists of a remote tensile loading than when it is an axial displacement, when the initial eccentricity of the ligament increases (for a given initial diameter), and when the Paris exponent characteristic of the material rises. The paper also analyzes in depth the different situations regarding contact between crack faces during subcritical cyclic fatigue propagation, covering a wide range of cases including no contact, partial contact, and full contact depending on the ligament diameter (during the process of fatigue crack advance) and the relative eccentricity of the annular crack that loses its axial symmetry in relation to the round bar (cylinder) axis. In addition to the fatigue crack path study, closed-form stress intensity factor (SIF) solutions for the considered geometry (a cylinder with an outer annular crack) are provided in the form of third-degree polynomial expressions as a function of the ligament diameter and the crack eccentricity (both in dimensionless terms).

The modified Gurson–Tvergaard–Needleman model, that considers shear decohesion as an increment in the total void volume fraction, is used to investigate the effect of superimposed hydrostatic pressure on the ductility of a round bar specimen. Experiments indicate that the fracture mode is not uniform across the cross section of a round bar specimen–no shear damage exists at the center while it is pronounced at the edge. The damage mechanisms of shear decohesion and void growth are delayed by applying superimposed hydrostatic pressure, which leads to an increase in the fracture strain and ductility. However, the effect of pressure on ductility depends on the location within the cross section. Void growth at both the center and the edge becomes increasingly delayed with increasing pressure, but this effect is more significant at the edge because of the existence of shear stress. Shear decohesion at the edge becomes the dominant damage mechanism, rather than void growth, when pressure is increased. The numerical results presented herein are used to explain and discuss this phenomenon in depth.

The bond behavior of reinforcing bars is highly dependent on confinement conditions and is of great importance in the design and analysis of concrete structures. This paper presents an experimental investigation into the bond behavior of plain round bars subjected to uniaxial and biaxial lateral pressures with different pressure ratios. The bond parameters are analyzed with respect to the average lateral pressure. The results show that the residual and ultimate bond strengths increase with the increase of the average lateral pressure, but their ratio stays invariable. The slip at the ultimate bond stress first reduces remarkably, and then increases gradually with an increase in lateral pressure. Compared with lateral pressure, the bar size and the strength of concrete have little influence on the bond strength ratio. Finally, a constitutive model of bond stress-slip with the lateral pressure effect is presented and shown to correlate well with the experimental data for different pressure ratios and levels.

The evaluation of tube burring formability is a crucial task for finding a suitable material for tube-based automobile parts. The local strain at the ductile fracture site (fracture strain) should be evaluated for this purpose. Moreover, a cold-drawn steel tube has a strong anisotropic shaped microstructure and possibly causes anisotropic fracture strain behavior. Based on this background, the study evaluated the axial and hoop directional fracture strains of cold-drawn steel tubes using the small round-bar tensile specimen. The burnished surface ratio on the pierced surface was also investigated for possibility estimation of in-line formability inspection. As a result, three tubes are presented with inferior, nearly the same, and superior hoop directional fracture strains compared with the axial strains, where exceeding 40% deterioration in the hoop direction occurs by a combination of grain elongation and carbide aggregation. The scanning electron micrographs suggest that the microvoid growth and linkage percolated thorough carbides on the elongated grain boundaries. For the piercing test, the 30% fracture strain deterioration resulted in a 4% decrease in the burnished surface ratio on the pierced surface. This result suggested that the estimation of the pierced surface can detect material defects before the actual tube-burring process.

This study describes a semi-analytical method for determining the J -R curves of round bars with elliptical cracks. This method develops the semi-analytical equations for load, displacement, and J -integral for surface-cracked round bars considering different materials and crack sizes. The validation of the semi-analytical expressions evaluated by three-dimensional finite element analysis reveals that the load–displacement curves and J -integral-load curves anticipated by the equations match the simulation results well. The average J -R curves of the surface-cracked round bars are obtained from fracture toughness tests on carbon steel 45 and the semi-analytical equations. In addition, this study also measured the J -R curves at different positions on the crack-front using the distributions of the J -integral along the fracture front obtained from three-dimensional finite element analyses.

In engineering applications, steels are commonly used in various areas. The mechanical members are exposed to different loading conditions and this subject can be investigated in fracture mechanics. Fracture toughness (KIC) is the important material property for fracture mechanics. Determination of this properties is possible using a compact tension specimen, a single edge notched bend or three-point loaded bend specimen, which are standardized by different institutions. Researchers underline that these standardized methods are complex, the manufacturing process is difficult, they require special fixtures for loading during the experiment and the test procedures are time consuming. Alternative methods are always being sought by researchers. In this work, two different approaches are investigated for S355 steels. In the first method, a circumferentially cracked round bar was loaded in tensile mode and pulled till failure. Using suitable equations, fracture toughness can be calculated. In the second method, a circumferentially notched bar specimen without fatigue pre-cracking was loaded in a tensile machine. By means of fracture load values, fracture toughness was determined by the proposed equations. It can be stated that these two different approaches for calculating fracture toughness are simple, fast and economical.

In the factory, the steel round bar sawing machine is applied to finish the sawing mission. Due to the process of the sawing steel is operating in high speed, the grinding-wheel-saw (GWS) is quickly worn by the friction and replaced frequently. The automatic replacement system of GWSs is seldom built yet. To improve the efficiency of the replacement for GWSs, the machine-vision-based intelligent robotic replacement system (MIRRS) for GWSs is developed and reported in the study. The MIRRS is mainly consisted of the six degrees-of-freedom (DOF) manipulator and the six-axes mechanical arm system to successfully complete the task of the replacement. The finite element method (FEM) is applied to analyze and design the subsystem of the MIRRS. Besides, the machine-vision positioning system associated with the digital camera are also setup to provide the required feedback detections for the MIRRS. The hardware system architecture and the control flow chart are described in detail and the hundreds of realistic testing results are collected to verify the reliability and offer the well working efficiency of the designed MIRRS.

Reducing the deformation of the transport bracket was the basic means to improve the mate precision between the large tonnage round bar and the bracket. The finite element model of the bracket was established and the actual loading conditions of the bracket for transporting the large tonnage round bar were analyzed by ABAQUS. The deformation and the weak areas of the bracket were investigated by the finite element analysis. The optimization model was obtained by the methods of replacing the type of the channel steel, improving the bracket structure and arranging fulcrums. These methods were adopted selectively to optimize the bracket structure based on the bracket’s maximum deformation demand. The finite element analysis not only shortened the design cycle, reduced the design cost, but also provided technical support for the bracket structure design.

Shot peening is an effective and economical technique for improving the fatigue strength of metallic components by inducing compressive residual stress and hardening the layer near the surface. The effect is generally evaluated by main two parameters: coverage and peening intensity. However, the valuable coverage for improving the fatigue strength depends on the shape of the target material. In this study, the effect of coverage on fatigue limit in round bar of annealed medium carbon steel was experimentally studied. The fatigue limits for shot peened round bar specimens with 140–2300% coverage increased 14–25% by comparing those for non-peened round bar specimens. The valuable range of coverage was 280–60% in the used material and shot peening condition for improving the fatigue limit in short time. The result indicates that the valuable coverage of the round bar material is higher than full coverage to improve the fatigue limit of the material due to the effect of incident angle on round bar, even though the degree depends on the materials and shot peening conditions.

The shear pin of the friction pendulum bearing (FPB) can be made of 40Cr steel. In conceptual design, the optimal cut-off point of the shear pin is predetermined, guiding the design of bridges isolated by FPBs to maximize their isolation performance. Current researches on the shear pins are mainly based on linear elastic models, neglecting their plasticity, damage, and fracture mechanical properties. To accurately predict its cutoff behavior, the elastic-plastic degradation model of 40Cr steel is indeed calibrated. For this purpose, the Ramberg-Osgood model, the Bao-Wierzbicki damage initiation criterion, and the linear damage evolution criterion were selected to develop the elastic-plastic degradation model of 40Cr. Subsequently, parameter calibration of this model was performed through uniaxial tensile tests on two sets of six smooth, round bars with different diameters. Following this, finite element simulations were conducted for the pure shear test of grade 10.9 high-strength bolts made of 40Cr steel, aiming to verify the elastic-plastic degradation model. The results showed that the failure modes and force-displacement curves simulated by the finite element method were in good agreement with the test results. Moreover, the error between the primary characteristic parameters (initial stiffness, peak load, fracture displacement, and absorbed energy) obtained by finite element calculation and the test values was within 15%. These results demonstrated that the calibration elastic-plastic degradation model of 40Cr steel can predict the cutoff of the shear pin.