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Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Titanium (Ti) and its alloys are attracting special attention in the field of dentistry and orthopedic bioengineering because of their mechanical adaptability and biological compatibility with the natural bone. The dental implant is subjected to masticatory forces in the oral environment and transfers these forces to the surrounding bone tissue. Therefore, by simulating the mechanical behavior of implants and surrounding bone tissue we can assess the effects of implants on bone growth quite accurately. In this study, dental implants with different gradient pore structures that consisted of simple cubic (structure a), body centered cubic (structure b) and side centered cubic (structure c) were designed, respectively. The strength of the designed gradient porous implant in the oral environment was simulated by three-dimensional finite element simulation technique to assess the mechanical adaptation by the stress-strain distribution within the surrounding bone tissue and by examining the fretting of the implant-bone interface. The results show that the maximum equivalent stress and strain in the surrounding bone tissue increase with the increase of porosity. The stress distribution of the gradient implant with a smaller difference between outer and inner pore structure is more uniform. So, a-b type porous implant exhibited less stress concentration. For a-b structure, when the porosity is between 40 and 47%, the stress and strain of bone tissue are in the range of normal growth. When subject to lingual and buccal stresses, an implant with higher porosity can achieve more uniform stress distribution in the surrounding cancellous bone than that of low porosity implant. Based on the simulated results, to achieve an improved mechanical fixation of the implant, the optimum gradient porous structure parameters should be: average porosity 46% with an inner porosity of 13% (b structure) and outer porosity of 59% (a structure), and outer pore sized 500 μm. With this optimized structure, the bone can achieve optimal ingrowth into the gradient porous structure, thus provide stable mechanical fixation of the implant. The maximum equivalent stress achieved 99 MPa, which is far below the simulation yield strength of 299 MPa.

Calculation of load-carrying capacity of old railway masonry arch bridges as crucial infrastructures is one of the vital issues in the railway industry. The field test of the 2PL20 bridge reveals important properties such as the initial stiffness and cracking pattern, but the ultimate capacity of the bridge under static loading was not achieved due to the field limitations. Therefore, the present study aims to predict the total nonlinear response of the 2PL20 bridge up to the failure status. All the geometrical characteristics of the 2PL20 bridge are modeled precisely and the failure state is predicted using the three-dimensional nonlinear finite element analysis. Moreover, to determine the load-carrying capacity of the 2PL20 bridge, the behavior of materials is regarded nonlinearly in which the Williams and Warnke and the Drucker-Prager failure criteria are taken into account for concrete and soil materials, respectively. To obtain precise results of ultimate capacity of the 2PL20 bridge under field test, the vertical and horizontal displacements of the crown on the northern span are chosen as the calibration criterion and, consequently, the vertical and horizontal load-deformation curves are verified based on the field test results. The obtained results indicate that the load-carrying capacity of the 2PL20 bridge equals 8880 kN under the static field test. Finally, the calculated safety factor is equal to 3.2 and increasing axial load up to 35-ton is admissible based on UIC 776-1 for a 25-ton axial load. [ABSTRACT FROM AUTHOR]

Ultra-high-speed grinding is a significant method for the advanced manufacturing of the difficult-to-machine material components, e.g., nickel-based superalloy. However, unclear mechanism of material removal behavior is still the main problem. The present work intends to establish the three-dimensional (3D) finite element simulation model of ultra-high-speed grinding with single abrasive grain. The effects of undeformed chip thickness and grinding speed on the morphology of grinding traces and chips are investigated. The parameters, such as pile-up ratio and shear slip frequency, are characterized experimentally, and the mechanism of material removal behavior in the process of ultra-high-speed grinding has been accordingly researched deeply. The results indicate that the pile-up ratio decreases firstly and then increases with an increase of undeformed chip thickness; the lowest pile-up ratio would be obtained when the undeformed chip thickness is 0.8~1 μm. When the grinding speed is below 240 m/s, with the increase of grinding speed, the distance between the sawtooth of the grinding chips is reduced, while the sawtooth degree is increased. When the grinding speed exceeds 400 m/s, the chip shape changes from serrated fracture to banded continuity, and the frequency of adiabatic shear slip goes up with the increase of grinding speed, which helps to reduce the grinding force, making the grinding process more stable and decreasing the difficult machinability of Inconel 718 nickel-based superalloy. [ABSTRACT FROM AUTHOR]

This article presents the correlation of vibration signal feature, that is, displacement due to vibration (microns) during the machining and three-dimensional finite element simulations in tool wear monitoring of a metal turning operation. Machining of AISI 1040 has been carried on using an uncoated inserts and online vibration signals acquired using a laser Doppler vibrometer. The measured tool wear forms correlate to features in the vibration signals in frequency domains. Analyses of the results suggested that the vibration signals’ features are effective for use in cutting tool wear monitoring and wear qualification. Present work demonstrates the three-dimensional finite element analysis to predict the workpiece displacements in feed direction and corresponding tool wear with the help of induced vibrations in face turning under dry machining conditions. Vibration-assisted turning model is developed and validated by comparing the simulation results with experimental results. In this research, three-dimensional finite element modelling and simulation issues for vibration-assisted turning are explored in detail. Machine dynamic effects are taken into account to predict the outcomes such as tool wear displacements and chip formation. The model can be implemented in an online tool wear monitoring system which predicts the actual state of tool wear in real time by correlating displacement variations during the machining. The correlation between the displacement due to vibration and flank wear has been evaluated through three-dimensional finite element modelling and simulation. Comparisons of simulations with experimental results demonstrate their predictive capability. From the results, useful conclusions may be drawn, and it can be stated that the proposed models can be used for industrial application. [ABSTRACT FROM AUTHOR]

[Display omitted] • We demonstrate a single-step process approach to fabricate disordered pyramidal nanostructures for large-scale broadband visible light absorber. Utilizing physical vapor deposition technology, the absorber consisting of a single layer of refractory metal (chromium) film is fabricated on 4-inch silicon (Si) wafer. The fabrication of the disordered pyramidal nanostructures is quite facile, low-cost, and compatible with mass production and CMOS process. • Benefiting from disordered pyramid nanostructures with distributed rough texture and gaps, this absorber achieves beyond 90% absorption in the range of 300 to 850 nm. Compared to the chromium film without pyramid nanostructures, it not only improves the absorption by more than 80%, but also obtains a more uniform absorption with relative absorption bandwidth (RAB) of 96.3%. Since the Cr is a refractory metal with high melting points (2180 K), the proposed absorber is extraordinarily resistant to heat which makes it a great candidate in solar absorbers for high-temperature photothermal conversion. • An improved three-dimensional finite element model is developed that is capable of simulating disordered pyramidal nanostructures with appropriate simplification. This model provides more insights into broadband absorption mechanism and can be used to predict optical performance for other disordered nanostructures. While the advances in material science have led to excellent absorption and bandwidth for visible light absorbers, the sophisticated and time-consuming fabrication in micro and nano scales makes it the bottleneck of large-scale manufacturing. Without complex structural patterning, an absorber consisting of a single layer of chromium film is fabricated on a 4-inch silicon wafer by single-step physical vapor deposition. Benefiting from disordered pyramidal nanostructures, this absorber achieves beyond 90% absorption in the range of 300 to 850 nm. Compared to the chromium film without nanostructures, it improves the absorption by more than 80%, and obtains a more uniform absorption with relative absorption bandwidth (RAB) of 96.3%. Simulated results demonstrate the excellent absorption is attributed to numerous disordered pyramidal nanostructures with rough texture and random gaps. This absorber shows the great potential of broadband absorption with angle insensitivity in visible region and sustainable light capture at high temperatures, and its fabrication is facile, low-cost, and compatible with mass production and CMOS process. [ABSTRACT FROM AUTHOR]

The interaction of Lamb wave A0 mode with delamination and delamination detection in 16-ply carbon fiber–reinforced epoxy composite beams are investigated through three-dimensional finite element simulation and experimental studies in this article. Wave propagation in composite beams with delamination with different lengths and located at different interfaces are investigated in finite element simulations, and some unique mechanisms of interaction between A0 mode and delamination are revealed in detail. Experimental results obtained with air-coupled ultrasonic transducers are well in accordance with finite element simulation results. In an experimental study, an air-coupled ultrasonic transducer is oriented at a coincidence angle such that it generates a pure fundamental antisymmetric Lamb wave mode A0 for delamination detection in laminated composite beams. The receiving transducer can be oriented either to detect the transmitted wave propagating in the same direction as incident wave or to detect the reflected wave in contrast to incident wave. The location and size of delamination can be evaluated quantitatively using the time-of-flight of reflected wave from both ends of the delamination. [ABSTRACT FROM PUBLISHER]

Air-coupled ultrasonic transducers are used to generate and receive Lamb waves in quasi-isotropic laminated composite beams for delamination detection. The influence of incident angle on the excited mode is studied. Numerical calculation and experimental results show that a pure Lamb wave mode can be generated if the transmitting transducer is oriented at a specific angle, and the receiving transducer can either be oriented to detect the same mode as that generated by the transmitter or to detect another mode generated by mode conversion at a defect. A three-dimensional finite element model is created to predict the interaction of Lamb waves with delamination, and some unique mechanisms of interaction between A mode Lamb waves and delamination are revealed in detail. The experimental results obtained on laminated composite beam using air-coupled ultrasonic transducers are well in accordance with finite element simulation results. Research results show that air-coupled ultrasonic guided waves can be used for delamination damage detection effectively in laminated composite beams. [ABSTRACT FROM AUTHOR]

Abstract: The formability in three-dimensional rectangular cup drawing of AZ31 magnesium alloy sheet is successfully predicted by the Drucker–Prager plasticity (DP model). Numerical results show that the punch corner shoulder is under the condition of high tension bending and the die corner shoulder is on pure bending regardless of constitutive models. The failure is attributed to the competition between the biaxial tension bending induced fracture on the punch corner shoulder and the through-thickness shear induced fracture on other shoulders in the sheet forming. Taking the yield surface asymmetry into consideration, in a way of the friction angle in the coordinate of compressive and tensile strengths in the DP model, the accuracy of plastic strain is improved remarkably. The fracture locates on the punch corner shoulder where the strain reaches its fracture limit earlier than the die corner shoulder''s. The predictions of forming limit and fracture locus in the DP model simulation are in good agreement with the experimental results. [Copyright &y& Elsevier]

A three-dimensional model based on the finite-element method is developed to simulate the temperature field and stress distribution in the welding and heat-affected zones during fusion welding of thin plates. The governing equations are solved using the SYSWELD program commercial code. The model's predictions are tested and verified against the experiments. Angular distortion and longitudinal bending are measured, the results are compared with those obtained from the mathematical model, and a relatively good agreement between them is found. The verified model is used to evaluate the effects of various parameters on the temperature and stress distributions in the welding and heat-affected zones of a thin austenitic stainless steel plate. [ABSTRACT FROM AUTHOR]

Abstract: In circumferential welding of a pipe component, it is often considered that axisymmetric model can provide a reasonable prediction of the residual stress distributions. However, in general, the axisymmetric model cannot reproduce the traveling arc along circumferential welds and rapid change of residual stresses that can be observed in the overlapping region. Moreover, it tends to overestimate the hoop residual stresses in circumferential welds. Therefore, three-dimensional finite element (FE) model is essential for the accurate simulation of circumferential welding which can incorporate the three-dimensional effects. This paper presents the three-dimensional FE simulation of circumferential butt welding of a steel pipe. The thermo-mechanical model used as well as the simulation methodology is detailed, and the results are discussed. In addition, parametric studies with inside radius to wall thickness ratio ranging from 10.0 to 100.0 have been presented to investigate the effects of pipe diameter on residual stresses. Axial and hoop residual stresses are plotted for the considered range of pipe diameters, and the differences are discussed. [Copyright &y& Elsevier]