On the build orientation effect in as-printed and as-sintered bending properties of 17-4PH alloy fabricated by metal fused filament fabrication

Purpose The purpose of this paper is to systematically investigate the influence of build orientation on the anisotropic as-printed and as-sintered bending properties of 17-4PH stainless steel fabricated by metal fused filament fabrication (MFFF). Design/methodology/approach The bending properties of 17-4PH alloy fabricated by low-cost additive manufacturing (MFFF) using three build orientations (the Flat, On-edge and Upright orientations) are examined at both as-printed and as-sintered states. Findings Unlike tensile testing where the Flat and On-edge orientations provide similar as-sintered tensile properties, the On-edge orientation produces a significantly higher bending strain with a lower bending strength than the Flat orientation. This arises from the printed layer sliding due to the Poisson's effect, which is only observed in the On-edge orientation together with the alternated layers of highly deformed and shifted voids. The bending properties show that the Upright orientation exhibits the lowest bending properties and limited plasticity due to the layer delamination. Originality/value This study is the first work to study the effect of build orientation on the flexural properties for MFFF. This work gives insight information into anisotropy in flexural mode for MFFF part design.

Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency

The paper presents a technique to obtain an electrically-tunable matching between the series and parallel resonant frequencies of a piezoelectric MEMS acoustic transducer to increase the effectiveness of acoustic emission/detection in voltage-mode driving and sensing. The piezoelectric MEMS transducer has been fabricated using the PiezoMUMPs technology, and it operates in a plate flexural mode exploiting a 6 × 6 mm doped silicon diaphragm with an aluminum nitride (AlN) piezoelectric layer deposited on top. The piezoelectric layer can be actuated by means of electrodes placed at the edges of the diaphragm above the AlN film. By applying an adjustable bias voltage Vb between two properly-connected electrodes and the doped silicon, the d31 mode in the AlN film has been exploited to electrically induce a planar static compressive or tensile stress in the diaphragm, depending on the sign of Vb, thus shifting its resonant frequency. The working principle has been first validated through an eigenfrequency analysis with an electrically induced prestress by means of 3D finite element modelling in COMSOL Multiphysics®. The first flexural mode of the unstressed diaphragm results at around 5.1 kHz. Then, the piezoelectric MEMS transducer has been experimentally tested in both receiver and transmitter modes. Experimental results have shown that the resonance can be electrically tuned in the range Vb = ±8 V with estimated tuning sensitivities of 8.7 ± 0.5 Hz/V and 7.8 ± 0.9 Hz/V in transmitter and receiver modes, respectively. A matching of the series and parallel resonant frequencies has been experimentally demonstrated in voltage-mode driving and sensing by applying Vb = 0 in transmission and Vb = −1.9 V in receiving, respectively, thereby obtaining the optimal acoustic emission and detection effectiveness at the same operating frequency.

Flexural–Torsional Free Vibration Analysis of a Double-Cantilever Structure

This paper aims to investigate the free coupled flexural–torsional vibrations of a double-cantilever structure. The structure consists of two identical Euler–Bernoulli cantilever beams with a piezoelectric layer on top. The beams are connected by a rigid tip connection at their free ends. The double-cantilever structure in this study vibrates in two distinct modes: flexural mode or coupled flexural–torsional mode. The flexural mode refers to the in-phase flexural vibrations of the two cantilever beams resulting in translation of the tip connection, while the coupled flexural–torsional mode refers to the coupled flexural–torsional vibrations of the cantilever beams resulting in rotation of the tip connection. The latter is the main interest of this research. The governing equations of motion and boundary conditions are developed using Hamilton’s principle. Two uncoupled equations are realized for each beam: one corresponding to the flexural vibrations and the other one corresponding to the torsional vibrations. The characteristic equations for both the flexural and the coupled flexural–torsional vibration modes are derived and solved to find the natural frequencies corresponding to each mode of vibration. The orthogonality condition among the mode shapes is derived and utilized to determine the modal coefficients corresponding to each mode of vibration. Moreover, the analytical and experimental investigations show that the coupled flexural–torsional fundamental frequency of the structure is dependent on dimensional parameters including the length of the cantilever beams and the length of the tip connection.

Wave propagation in tapered periodic curved meta-frame using Floquet theory

In this work, the elastic wave propagation and dispersion characteristics of a curved tapered frame structure is investigated analytically. Separately, wave propagation through uniform curved and straight tapered beam were reported in the existing literature; however, no literature reports the influence of simultaneous bent and taper on the wave propagation. In particular, the band characteristics for the curved and tapered beam with two types of cross-sections, i.e., rectangular and circular, are presented. The paper elucidates that introducing a small periodic bent angle cross-section produces a complete, viz. axial and flexural band gap in the low-frequency region, and conicity enhances the width of the band. It is also evidenced that a curved tapered frame with a solid circular cross-section induces a wider band gap than the rectangular section. A complete first normalized bandwidth of 159% is achievable for the circular cross-section and 123% in the case of the rectangular section. The complete result is presented in a non-dimensional framework for wider applicability. An analysis of a finite tapered curved frame structure also demonstrates the attenuating characteristics obtained from the band structure of the infinite structure. The partial wave mode conversion, i.e., generation of coupled axial and flexural mode from a purely axial or flexural mode in an uncoupled medium is observed. This wave conversion is perceived in reflected and transmitted waves while this curved tapered frame is inserted between the two uniform cross-section straight frames.

Demystifying Openhole and Outer Casing Geometry and Annulus Material Characterization with Third Interface Echo TIE Response

Ultrasonic imaging based tools have been used for long for delivering high-resolution, comprehensive real-time confirmation of the pipe-to-cement bond quality and downhole pipe condition. However, for comprehensive analysis of cement barriers in challenging scenarios like lightweight cement and for better distinction between different annular materials downhole, a multi-physics evaluation has been developed which combines the measurements taken in thickness-mode with measurements taken in flexural-mode of the casing. Signals from these independent measurements are then processed to provide robust interpretation of solid-liquid-gas behind casing using acquired flexural attenuation and acoustic impedance data. The information provided by the flexural attenuation is related to the state of the material in contact with the casing and does not probe deeper into the cement sheath. However, the pulse radiated by the flexural wave packet into the annulus may be reflected by the third interface, the interface with the formation or outer casing. The inner casing is fairly transparent to this reflected pulse so that it can also be picked by the receivers with significant amplitude. Since this reflected pulse propagate through the thickness of the annulus layer it may bring valuable information about the annulus geometry and material, and about the formation or outer casing geometry. This paper demonstrates third interface echo principles and showcases several case studies for evaluating the outer casing geometry, annular material characterization, casing cut and pull depth suggestion and determining open hole size.

Mode-Dependent Selective Detection of Humidity and Helium Using Electromagnetically Actuated Clamped Guided MEMS Resonators

In this work, we demonstrate a selective gas sensor based on monitoring two different detection mechanisms; absorption and thermal conductivity. To illustrate the concept, we utilize a resonator composed of a clamped-guided arch beam connected to flexural beams and a T-shaped moveable mass. The resonator has two distinct out-of-plane modes in which the mass motion dominates the first mode while the motion of the flexural beam dominates the second mode. A highly disperse graphene oxide (GO) solution is prepared and drop-casted over the moveable mass structure using the inkjet printer for humidity sensing. On the other hand, the He is detected using the hot flexural beams. The results show no significant effect of humidity on the flexural mode (FM) nor for He on the mass mode (MM). This indicates a new technique for selectivity and identification. The device shows good sensitivity (50.1% to 50% RH @ MM and 39.2% to 50% He @ FM: (Vac = 1.5V)), linearity, and repeatability with excellent selectivity. It is demonstrated that the FM has great potential for detecting and categorizing different gases according to their thermal conductivity. The demonstrated multimode MEMS resonator can be a promising approach for the development of smart, highly selective, and sensitive gas/chemical sensors.

A Study on the Detection of Internal Defect Types for Duct Depth of Prestressed Concrete Structures Using Electromagnetic and Elastic Waves

Prestressed concrete (PSC) is widely used for the construction of bridges. The collapse of several bridges with PSC has been reported, and insufficient grout and tendon corrosion were found inside the ducts of these bridges. Therefore, non-destructive testing (NDT) technology is important for identifying defects inside ducts in PSC structures. Electromagnetic (EM) waves have limited detection of internal defects in ducts due to strong reflections from the surface of the steel ducts. Spectral analysis of the existing impact echo (IE) method is limited to specific conditions. Moreover, the flexural mode in upper defects of ducts located at a shallow depth and delamination defects inside ducts are not considered. In this study, the applicability of the elastic wave of IE was analyzed, and multichannel analysis of surface, EM, and shear waves was employed to evaluate six types of PSC structures. A procedure using EM waves, IE, and principal component analysis (PCA) was proposed for a more accurate classification of defect types inside ducts. The proposed procedure was effective in classifying upper, internal, and delamination defects of ducts under 100 mm in thickness, and it could be utilized up to 200 mm in the case of duct defect limitations.

AUTOMATIC LOGGING-WHILE-DRILLING DIPOLE SONIC SHEAR PROCESSING ENABLED BY PHYSICS-DRIVEN MACHINE LEARNING

Logging-while-drilling (LWD) dipole sonic tools have been introduced to the industry as a supplement to monopole and quadrupole measurement because they can provide shear slowness anisotropy, which is essential for formation characterization and well completion applications. Due to the presence of the collar, which acts as a strong waveguide, the recorded formation signal is significantly affected at low frequencies. Consequently, an automated interpretation of LWD dipole sonic data re-mains a challenge. The traditional dispersive semblance-based method requires accurate estimates of parameters such as borehole size and/or mud slowness to avoid bias in the dispersion model used in the processing. Recently, a frequency-slowness domain inversion scheme has been developed that can invert for both the formation shear slowness and mud slowness by minimizing the guidance-mismatch cost function. However, this method uses an isotropic dispersion model and requires selecting narrow-band dispersion data in the low-frequency range with good-quality, which can limit the range of applicability of the method and also requires user input through-out the process. We have previously developed a physics-driven machine learning-based method to enhance the interpretation of wireline dipole sonic data. However, the LWD scenario introduces additional complexity. This work extends the method to support the interpretation of LWD dipole sonic. An anisotropic root-finding mode-search algorithm is first used to generate extensive synthetic formation flexural dispersion curves that can match dispersion measurements in strong anisotropic formations in high-angle and horizontal wells, with a known tool model. Special care needs to be taken to pick the formation flexural mode from several co-existing modes arising from the strong coupling between tool and formation. After quality control and verification, this comprehensive synthetic dataset is used to train a neural network model. We then develop an inversion-based algorithm, taking advantage of this efficient neural network model and combining it with a clustering algorithm, to reliably label and ex-tract the formation flexural mode, processed from either the modified Prony’s method, or a broadband dispersion analysis algorithm. The extraction around the formation flexural kick-in frequency is used for developing a quality control method. The strongest collar arrival, on the other hand, can be confidently removed due to the fundamental difference in its dispersion characteristics from the formation flexural mode. This novel method can automatically and efficiently label the formation flexural mode and simultaneously invert it for formation shear slowness together with other relevant parameters such as mud slowness without user intervention. Since this method is built upon an anisotropic model, it can be applied to the full frequency range of the data spectrum without the traditional isotropic model assumption. Additionally, the regression analysis of the inverted mud slownesses can further provide physical constraint to reduce uncertainties in the inverted shear slowness. The algorithm has been tested on field data showing good performance. It makes edge deployment possible so that LWD telemetry can be optimized to transmit the processed data to the surface in real-time, which is essential to leverage the advantages of the conveyance method.

Spontaneous Curvature Induced Stretching-Bending Mode Coupling in Membranes

In this paper, a simple example to illustrate what is basically known from the Gauss’ times interplay between geometry and mechanics in thin shells is presented. Specifically, the eigen-mode spectrum in spontaneously curved (i.e., up-down asymmetric) extensible polymerized or elastic membranes is studied. It is found that in the spontaneously curved crystalline membrane, the flexural mode is coupled to the acoustic longitudinal mode, even in the harmonic approximation. If the coupling (proportional to the membrane spontaneous curvature) is strong enough, the coupled modes dispersions acquire the imaginary part, i.e., effective damping. The damping is not related to the entropy production (dissipation); it comes from the redistribution of the energy between the modes. The curvature-induced mode coupling makes the flexural mode more rigid, and the acoustic mode becomes softer. As it concerns the transverse acoustical mode, it remains uncoupled in the harmonic approximation, keeping its standard dispersion law. We anticipate that the basic ideas inspiring this study can be applied to a large variety of interesting systems, ranging from still fashionable graphene films, both in the freely suspended and on a substrate states, to the not yet fully understood lipid membranes in the so-called gel and rippled phases.

Coupled longitudinal-flexural vibration characteristics of a piezoelectric structure with losses

The dynamic characteristics studies of piezoelectric structures usually focus on the single vibration modes such as the longitudinal or the flexural mode, and the losses that cause heat generation and energy waste are generally neglected, which leads to discrepancies compared with experiments. In the present paper, a beam-type piezoelectric structure with four kinds of losses under coupled longitudinal-flexural vibration mode is investigated. In this approach, first, impedance matrix of the structure is obtained based on the motion equation and the electrical-mechanical boundary conditions. Secondly, admittance curves of this piezoelectric structure under different boundary conditions are simulated by the equivalent circuit methods that contain four losses—piezoelectric and dielectric losses, as well as two elastic losses. The simulation results by equivalent circuit methods has good agreement with COMSOL results, which demonstrate the effectiveness of the proposed method.