Parametric study on the fatigue life of railways under rolling contact fatigue by three-dimensional numerical analysis

The current paper presents the results of parametric analyses on the stress intensity factor (SIF) of railways with inclined cracks under rolling contact fatigue (RCF). A 3D finite element (FE) model was proposed to demonstrate the shear mechanism in RCF. The feasibility of the suggested numerical model was verified through the SIF (K) obtained from advanced 3D FE analysis compared with existing 2D FE results. Based on the series of FE analyses, the sensitivity analysis on the cracked depth, surface/crack friction coefficients, and inclined angle, which mainly affected SIF history at the cracked tip, was examined. SIF distributions for various locations of the wheel along the cracked tip were also presented.     

A two surface plasticity model for the simulation of uniaxial ratchetting response

In this study, a two surface plasticity model was developed and used to simulate the uniaxial ratchetting response of CS 1026 steel. Most cyclic plasticity models used in ratchetting simulations are Chaboche-type nonlinear kinematic hardening models, which deal with dynamic recovery terms considering the back stress tensor. This paper describes the ratchetting simulation of steel by the two surface model based on yield theory following both isotropic and kinematic hardening rules in order to obtain enhanced ratchetting response. The parameters used in the simulation were obtained from a parametric study and were determined from the initial range and stabilized range of CS 1026 steel. In addition, the two surface model was validated by comparing the results of a ratchetting simulation with experimentally determined maximum axial strain per cycle. The ratchetting responses obtained from the two surface model are an improved simulation results compared with results from bilinear and kinematic hardening models.     

Friction Force Measurement at Windscreen Wiper/Glass Contact

In the present study, a novel windscreen wiper-on-cylinder machine has been used to investigate the influence of sliding speed and normal force on the coefficient of friction. Using this machine it is possible to measure the friction force not only on specimen level, as in former studies to be available in the literature, but also on structural level by considering the whole windscreen wiper. As measurement results are strongly influenced by both the real, non-circular cross-section, and the eccentricity of the rotating glass cylinder an analytical model has been developed to explain the measurement results. The good agreement to be found between theory and experiment confirms the validity of the model. Majority of the results belongs to partial contact where the wiper blade is not in contact with the glass countersurface along its total length. After the discussion of experimental results, as a last step, authors made an attempt to compare quantitatively the predictive capability of two different contact models widely used in mixed friction model of sliding rubber components. The results show that the difference in film thickness due to solid–solid contact can be larger than three orders of magnitude in case of a typical windscreen wiper.     

Crack tip shielding and anti-shielding effects of parallel cracks for a superconductor slab under an electromagnetic force

In this letter, the shielding or anti-shielding effect is firstly applied to obtain the behavior of two parallel cracks in a two-dimensional type-II superconducting under electromagnetic force. Fracture analysis is performed by the finite element method and the magnetic behavior of superconductor is described by the critical state Bean model. The stress intensity factors at the crack tips can be obtained and discussed for decreasing field after zero-field cooling. The shielding or anti-shielding effect at the crack tips depend on the distance between two parallel cracks and the crack length. The results indicate that the shielding effects of the two parallel cracks increase when the distance between the two parallel cracks decreases. It can be also obtained that the superconductors with shorter cracks has more remarkable shielding effect than those with longer cracks.     

Friction and Wear Characteristics of Haynes 25, 188, and 214 Superalloys Against Hastelloy X up to 540 <Emphasis Type=Bold>°</Emphasis>C

As demand for more power increases, compression ratios, and operating temperatures keep rising. High speeds combined with high temperatures make turbomachinery sealing applications even more challenging. In order to confirm sufficient service life material pairs should be tested under conditions similar to engine operating conditions. This study presents high temperature friction and wear characteristics of cobalt/nickel superalloys, Haynes 25 (51Co–10Ni–20Cr–15W), Haynes 188 (39Co–22Ni–22Cr–14W), and Haynes 214 (75Ni–16Cr–3Fe–0.5Mn) sheets when rubbed against Hastelloy X (47Ni–22Cr–18Fe–9Mo) pins. Tests are conducted at 25, 200, 400, and 540 °C with a validated custom design linear reciprocating tribometer. Sliding speed and sliding distance are 1 Hz and 1.2 km, respectively. Friction coefficients are calculated with friction force data acquired from a load cell. Wear coefficients are calculated through weight loss measurements. Results indicate that Haynes 25 (H25) has the lowest friction coefficients at all test temperatures. Above 400 °C, H25 and Haynes 188 (H188) exhibit the best wear resistance. Protective cobalt oxide layers are formed on the H25 and H188 at 540 °C in addition to nickel, chrome, and tungsten oxides. Although, it has better oxidation resistance, Haynes 214 has relatively higher wear rates than other tested materials especially at low temperatures. However, its wear performance improves beyond 200 °C.     

An improved methodology for determining tensile design strengths of Alloy 617

This paper presents an improved methodology for determining high-temperature tensile design strengths of Alloy 617, which is regarded as one of main structural materials for very high temperature reactor (VHTR) system. In establishing time-independent allowable stress values, an existing ASME standard procedure is preliminarily analyzed and their limitations are pointed out. Then, an improved methodology, which has a consistent and quantifiable design margin at low and high temperatures for tensile strengths, is proposed and compared with the ASME method. To find suitable curves of temperature trend to the tensile strength data, three fitting methods are demonstrated, and a statistical technique is adopted for design use. The results will be utilized to reasonably determine the tensile design strengths of Alloy 617 for application in the VHTR system.     

Laminar and turbulent channel flow simulation using residual based variational multi-scale method

We present a residual-based isogeometric variational multiscale method to solve laminar and turbulent channel flow. Residual-based variational multiscale method is a new finite element formulation for solving turbulent flows using a large-eddy simulation type modeling. Isogeometric analysis, a new finite element method using CAD blending functions as its basis functions, is employed for higher order approximation of the solution. First, laminar flow with Re _τ 0.55 = through flat channel is considered and linear, quadratic and cubic basis functions, which are C ⁰, C ¹, and C ²-continuous across element boundaries, respectively are employed and their accuracy is presented by the comparison with analytical result. Next, same methodology is applied to the turbulent channel flow with Re_r = 180. Current results are validated by the comparison of turbulence statistics using available DNS data.     

Inspection method of cable-stayed bridge using magnetic flux leakage detection: principle,sensor design,and signal processing

A nondestructive testing technique based on magnetic flux leakage is presented to inspect automatically the stay cables with large diameters of a cable-stayed bridge. Using the proposed inspection method, an online nondestructive testing (NDT) modular sensor is developed. The wreath-like sensor is composed of several sensor units that embrace the cable at equal angles. Each sensor unit consists of two permanent magnets and a hall sensor to detect the magnetic flux density. The modular sensor can be installed conveniently on cables with various diameters by increasing the number of sensor units and adjusting the relative distances between adjacent sensor units. Results of the experiments performed on a man-made cable with faults prove that the proposed sensor can inspect the status signals of the inner wires of the cables. To filter the interfering signals, three processing algorithms are discussed, including the moving average method, improved detrending algorithm, and signal processing based on a digital filter. Results show that the developed NDT sensor carried by a cable inspection robot can move along the cable and monitor the state of the stay cables.     

A study to maximize the crash energy absorption efficiency within the limits of crash space

The design of an engine room is important to protect the passenger from a crash impact by improving the absorption of the crash impact energy. The side member in the engine room absorbs most of the crash impact energy when the vehicle experiences a frontal crash. The side member is of two types: hat and ‘U.’ Analysis of the extent of energy absorption and the mechanism of the side member are necessary through a collapse mode in various load conditions. In this study, the design of experiments was used for evaluating the characteristics of the absorption of crash energy by side members through design variables. First, crash analysis was performed by experiment number extracted from the design of the experiment. Then, using the results of crash analysis, multiple regressions were conducted and sensitivity analysis performed for each design variable. Finally, the optimum design was developed for maximizing the absorption energy per unit weight considering various boundary conditions. In the present study, as a basic step for modeling the fatigue behavior of an extruded Al alloy cylinder, the fatigue crack growth data of the alloy was collected in two orientations. Microstructural analysis revealed that the material had recrystallized grains and clusters of constituent particles aligned in the direction of extrusion. Fatigue life of the samples revealed a shorter fatigue life representing a higher fatigue crack growth rate in the transverse direction.     

Anti-plane moving crack in a functionally graded piezoelectric layer between two dissimilar piezoelectric strips

The dynamic propagation of a crack in a functionally graded piezoelectric material (FGPM) interface layer between two dissimilar piezoelectric layers under anti-plane shear is analyzed using integral transform approaches. The properties of the FGPM layers vary continuously along the thickness. The FGPM layer and two homogeneous piezoelectric layers are connected weak-discontinuously. A constant velocity Yoffe-type moving crack is considered. The Fourier transform is used to reduce the problem to two sets of dual integral equations, which are then expressed to the Fredholm integral equations of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGPM to show the effects on electric loading, gradient of the material properties, crack moving velocity, and thickness of the layers. The following are helpful to increase resistance to crack propagation in the FGPM interface layer: (a) certain direction and magnitude of the electric loading, (b) increasing the thickness of the FGPM interface layer, and (c) increasing the thickness of the homogeneous piezoelectric layer to have larger material properties than those of the crack plane in the FGPM interface layer. The DERR always increases with the increase of crack moving velocity and the gradient of the material properties.