Cantilever Structure Research Articles

Investigation of support structure configurations for selective laser melting of In718

The Selective Laser Melting (SLM), as a widely used metallic Additive manufacturing (AM) process, relies heavily on support structures. This study investigated the impact of different support structure configurations on the quality of In718 samples fabricated through SLM. On the basis of a comprehensive review of existing support structures configurations from the literature, three typical configurations: block, cone, and lattice, were designed to support cantilever parts for performance comparison. A coupled thermo-structural finite element simulation using ANSYS was performed to evaluate the temperature, deformation, and thermal stress evolution during the printing process of the three supported cantilever structures. The residual stress and deformation of the printed In718 cantilevers with different support structures were measured for validation. The results showed that block support exhibits the best strength and heat dissipation capability, making it the most effective support configuration for the SLM of In718 material. This research provides a fundamental procedure for evaluating the supporting performances among various support structures for the SLM process.

Optimized evaluation of ground motion intensity measures for the prefabricated cantilevered roadbed structure in mountainous areas

The prefabricated cantilevered roadbed structure (PCRS) is a novel design that addresses the significant excavation and embankment volume associated with traditional mountainous roadbeds. The seismic performance of it has not yet been fully investigated. Seismic fragility analysis is one of the main methods for assessing the damage pattern of a structure, and the ground motion intensity measure (IM) is a key parameter affecting the damage assessment results. To this end, a finite element model is first conducted based on structural load-bearing capacity verification experiments, relying on a prefabricated cantilevered roadbed structure in a mountainous region. Then, the nonlinear time-history analysis of the structure was carried out, and 20 common IMs were selected and compared from the perspectives of practicality, efficiency, proficiency, and sufficiency. Finally, the seismic fragility analysis of the structure is conducted based on the optimal IM. The analysis results indicate that the peak ground acceleration of response spectrum (PSA) is the optimal IM for such structures. Quadratic fitting exhibits higher accuracy compared to linear fitting. Among all components, fixed-end foundations are identified as the most vulnerable. Anchored reinforcement remains elastic throughout the seismic response calculations and suffers little damage.

WrapToR composite truss joints: Concept introduction and coaxial joint analysis and demonstration

This study focuses on the development of coaxial continuously wound joint structures for Wrapped Tow Reinforced (WrapToR) trusses, which are carbon fibre composite lattice beams fabricated through a unique winding process. WrapToR truss beams have shown very high levels of performance as beam-like structures, but their usefulness can be greatly extended by using them as members within hierarchical space frames, which can be made into more geometrically complex and generally useful structures. However, the key challenge lies in creating effective joint structures able to connect together multiple WrapToR beams of different sizes and orientations. This paper addresses this challenge by presenting a modified WrapToR winding process which enables three-dimensional winding of arbitrary space frame joints, with an initial focus here on a proof of concept coaxial joint. This includes the design and manufacturing of a coaxial joint demonstrator and the development of a finite element analysis tool to predict its mechanical performance. A cantilevered beam structure combining this joint with two different sizes of WrapToR truss is built and tested, showing high levels of bending rigidity and good agreement with numerical prediction. Following this, the analysis tool is used to explore the achievable design space for coaxial WrapToR joints.

Application of active piezoresistive cantilevers in high-eigenmode surface imaging

Abstract One of the most important limitations of the atomic force microscopy (AFM) is scanning speed, whose high values are required for contemporary high-resolution, long-range diagnostic applications. The measurement bandwidth of an AFM depends on several factors, but usually results from the time constant of the oscillating cantilever, which is correlated with its resonance frequency and quality factor. We propose a method to overcome this problem by performing the surface measurements when the cantilever is vibrating in higher eigenmodes. In this paper we demonstrate the application of active piezoresistive cantilevers operating in this mode. The active piezoresistive cantilever comprises a piezoresistive deflection sensor, a deflection actuator and a nanotip. It is a complete micro-electro-mechanical system (MEMS), ensuring the highest reliability of cantilever vibration control and detection. Higher eigenmode operations are usually difficult to implement as they usually result in lower deflection and lower sensitivity of the probe vibration deflection. Here we present an experimental modification of the structure of an active piezoresistive cantilever using focused ion beam (FIB) machining that mitigates both weaknesses. This has enabled the cantilever to scan the surface at a scanning rate of 10 lines/s with a maximum speed of 500 μm/s and a data acquisition rate of 10 kS/s, when the probe is vibrating at 380 kHz in the second eigenmode. We also describe a traceable calibration routine (based on analysis of the response of the piezoresistive detector, the output of the HeNe interferometer and precise control of the deflection actuator), together with the cantilever modification process and the development of the measurement setup. We show measurement results of dedicated calibration samples and silicon carbide crystal lattice references.

In situ monitoring of quantum dot growth using a magnification inferred curvature method

The growth of InAs on a GaAs (001) substrate follows the Stranski–Krastanov (S–K) growth mode. Initially, the stress due to the lattice constant difference is small, resulting in two-dimensional growth. However, as the thickness of the growth layer increases, this stress accumulates, and upon reaching a critical film thickness, the growth transitions to three-dimensional, facilitating stress relaxation. Strain changes during crystal growth can be observed through variations in substrate curvature. However, in InAs/GaAs quantum dots (QDs), these changes are minimal, making observation challenging. Previously, the curvature of the substrate during InAs/GaAs QD formation could only be estimated with low precision, necessitating the use of very thin substrates with cantilever structures to achieve higher curvature. In this study, we applied the magnification inferred curvature (MIC) method, which allows for high-precision estimation of substrate curvature during molecular beam epitaxy growth. This method enabled us to observe strain changes during the formation and relaxation processes of QDs on standard-thickness GaAs (001) substrates. The results highlight the potential of the MIC method in investigating the complex interplay of strain and stress in semiconductor growth processes, emphasizing its suitability for fabricating next-generation QD devices.

Optimized design of mechanical cantilever structure parameters and stress field inversion study based on deep neural network

Optimized design of mechanical cantilever structure parameters and stress field inversion study based on deep neural network

A Polyimide Composite-Based Electromagnetic Cantilever Structure for Smart Grid Current Sensing.

Polyimides (PIs) have been extensively used in thin film and micro-electromechanical system (MEMS) processes based on their excellent thermal and mechanical stability and high glass transition temperature. This research explores the development of a novel multilayer and multifunctional polymer composite electro-piezomagnetic device that can function as an energy harvester or sensor for current-carrying wires or magnetic field sensing. The devices consist of four layers of composite materials with a polyimide matrix. The composites have various nanoparticles to alter the functionality of each layer. Nanoparticles of Ag were used to increase the electrical conductivity of polyimide and act as electrodes; lead zirconate titanate was used to make the piezoelectric composite layer; and either neodymium iron boron (NdFeB) or Terfenol-D was used to make the magnetic and magnetostrictive composite layer, which was used as the proof mass. A novel all-polymer multifunctional polyimide composite cantilever was developed to operate at low frequencies. This paper compares the performance of the different magnetic masses, shapes, and concentrations, as well as the development of an all-magnetostrictive device to detect voltage or current changes when coupled to the magnetic field from a current-carrying wire. The PI/PZT cantilever with the PI/NdFeB proof mass demonstrated higher voltage output compared to the PI/Terfenol-D proof mass device. However, the magnetostrictive composite film could be operated without a piezoelectric film based on the Villari effect, which consisted of a single PI-Terfenol-D film. The paper illustrates the potential to develop an all-polymer composite MEMS device capable of acting as a magnetic field or current sensor.

The mechanism and prevention of rockburst induced by the instability of the composite hard-roof coal structure and roof fractures

Despite the implementation of prevention and control measures, rockburst still occur. The characteristics of composite coal were analyzed by combining monitoring and early warning means. Two types of composite coal in the hard roof were distinguished based on their distinct initiation and destruction processes despite experiencing the same rockburst event. Rockburst caused by structural instability was studied in different mining stages, and the following conclusions were considered. 1) The mechanical model of the instability of composite coal in hard roof was established for different mining stages to reveal rockburst mechanisms. The high-speed advance of working faces changed the fractured structure of upper hard rocks in the pressure-relief protection range. The sudden fracture of long cantilever structures caused dynamic load disturbance to high-stress coal, which resulted in rockburst in the insufficient mining stage. The failure and deformation of coal under high-stress static loads created conditions for the instability and fractures of roof. The disturbance of low hard rock strata aggravated the deformations of damaged coal. Therefore, rockburst appeared in the full mining stage. 2) Structural instability and roof fracture caused by different factors were the main causes of rockburst for composite coal in hard roof in different mining stages. Relevant prevention and control measures were formulated to ensure the safety of working faces, which provided references for the prevention and control of rockburst in working faces under similar conditions.

Novel screen-printed ceramic MEMS microhotplate for MOS sensors

We developed a new approach to the fabrication of MEMS substrates for MOS gas sensors. This full screen-printing process is based on the application of sacrificial material, which is solid at the near-room temperature of printing and turns to powder after the firing of the elements of the sensor. Therefore, this sacrificial material can be removed from under the suspended elements of the MEMS structure in ultrasonic bath. The glass-ceramic MEMS is a cantilever structure equipped with a Pt-based microheater made of Pt resistive material with sheet resistance of about 4 Ohm/square fabricated using core-shell technology. It is located at the end edge of the cantilever and is isolated from the contacts to the sensing layer by glass-ceramic insulation. Screen-printing provides cheap fabrication, robustness and low power (∼120 mW@450°C) of the sensing element. The functionality of the microhotplate was checked using ZnO nanomaterial deposited by microextruder, it demonstrated high response and selectivity of ZnO material to NO2 (response 41.6 at 200°C for 10 ppm).

Thermomechanical modelling of residual stresses and distortion in laser powder bed fusion: Assessment of the effect of build plate preheating on the behaviour of Inconel 718

The fabrication of complex metallic parts via laser powder bed fusion (L–PBF) is becoming more mainstream to overcome the limitations of traditional manufacturing methods. However, L–PBF induces undesirable residual stresses (RS) and possible geometric distortion of the component. This study aims to show the capabilities of build plate preheating in mitigating both defects. A thermomechanical finite element model is developed to investigate the outcomes of various preheating conditions when producing Inconel 718 samples consisting in a base and an overhanging beam restricted with support structures. Initially, the model is calibrated against the deflection result of an academic work employing a resemblant geometry. Our study is then performed. The as–built von Mises stress evolution along two paths as well as part distortion are assessed at 100, 300, and 500°C, then compared to the reference “no preheating” case results. A peak top surface RS of 803MPa was reached without preheating and reduced by 48.69% at 500°C. Along the vertical path, the mean stress value went from 897MPa at 20°C to 474MPa at 500°C. Distortion of the as–built part is essentially a non–uniform contraction of the beam along the x–direction due to progressive bending of the supports about y–axis. Once the beam is unrestricted from the substrate, it deforms as a cantilever structure. Increasing the preheating temperature decreases the maximum build direction deflection by 14.56% at 100°C, up to 76.94% at 500°C in comparison to the 4.12mm reached at 20°C. In conclusion, preheating the substrate is a very effective way to mitigate RS and distortion in L–PBF of Inconel 718. Even the relatively low 100°C showed a notable improvement in this regard.

Safety and high-recovery mechanisms and application research for initial mining of thick-coal-seam with complex structure and thick-hard roof

Thick-coal-seam with complex structures and thick-hard roof in the initial mining phase pose various challenges, including a long weighting interval, strong rock pressure, poor top coal caving performance (TCCP), and significant coal loss. These problems directly affect the safety and efficiency of the mining operations. This study employs the principles of elastic thin plates and ellipsoidal bodies to unravel the formation mechanism of strong rock pressure in thick-hard roof and the influence of parting on the TCCP. In addition, a hydraulic fracturing technique is proposed for safe-efficient recovery during the initial mining phase. The reliability of this technique is verified through numerical simulations and field experiments. The research findings reveal the following. (1) The primary causes of strong rock pressure in the mining face are attributed to a long weighting interval and wide collapse range of the main roof, and the weighting interval is primarily influenced by the thickness and tensile strength of the main roof. (2)The key factor affecting the TCCP is the cantilever beam structure formed by the fracture of the thick-hard parting, as it intersects the ellipsoidal body during coal caving. The simultaneous fracturing of both the top coal and roof can reduce the weighting interval on the working face. This process effectively decreased the strength of the thick-hard parting within the top coal, while simultaneously enhancing its load strength and eliminating the cantilever structure resulting from the parting fracture. It not only reduces the first weighting intensity but also promotes the early and proper coal release, thereby enhancing the TCCP and ensuring safe-efficient mining during the initial mining phase. (3) Aiming at the difference in the strengths of the top coal and roof, a graded hydraulic fracturing technique and system were proposed. Fracturing boreholes with a diameter of 60 mm, spacing of 10 m, and height of 20.85 m, which can economically and effectively ensure the fracturing results. Field applications have demonstrated that fractured coal and rocks in fracturing areas exhibit well-developed fractures. During the initial mining phase, the weighting interval in the working face was reduced by 20 m, resulting in a decrease in the overburden pressure and 26.9% reduction in the lumpiness of the top coal. Additionally, the recovery rate increased by 31.19%.

Detecting localized damage in cantilevered structures under nonstationary ambient excitations via Gabor spectral mode transmissibility functions

A method based on Gabor spectral mode transmissibility functions (GSMTFs) is proposed to detect local damage in a cantilevered structure under nonstationary ambient excitations. Gabor transformation and singular value decomposition are used to reduce the influences of other vibration modes on Gabor spectral mode transmissibility functions and process nonstationary structural responses, respectively. A new state characteristic based on the fundamental structure frequency is formulated on the basis of the GSMTFs, eventually leading to the development of a new damage indicator. The probability density functions of the damage indicator for healthy and damaged states can be estimated from the measured data, and the receiver operating characteristic (ROC) curve derived from these probability distributions and the corresponding area under the ROC curve (AUC) are used to determine the damage location. A six-degree-of-freedom system and a typical transmission tower are numerically studied, and the results show that the proposed method can estimate the structural damage location under nonstationary random loads. The proposed method is further validated with a planar frame in the laboratory, which exhibits multiple damage elements via random force hammer excitations. The results show that the AUC values computed for certain parts of the structure containing the damaged elements are greater than those for other parts of the structure, indicating the effectiveness of the proposed method. Moreover, the proposed method is compared with the dot product difference (DPD) index, and the results from the laboratory planar frame demonstrate that the proposed method can better identify damage.

Dynamics of resonant magnetoelectric effect in a magnetoactive elastomer based cantilever: Magnetic field induced orientation transition and giant frequency tuning

Magnetoelectric (ME) effects in composite heterostructures containing mechanically coupled ferromagnetic and piezoelectric layers enable the mutual transformation of magnetic and electric fields and form the basis for the development of magnetic field sensors, actuators and energy harvesters. Promising materials for such composite structures are magnetoactive elastomers (MAE), which are silicone matrices with ferromagnetic particles uniformly distributed within them. The strong dependence of MAE properties on magnetic fields and their low rigidity enable contactless control of ME effects characteristics within such structures. In this work we have experimentally investigated the dynamics of resonant ME effects in a structure consisting of a MAE layer with carbonyl iron particles and a layer of polyvinylidene fluoride piezopolymer in a cantilever geometry. For the structure magnetized in a plane along the axis, the frequency tuning of the bending oscillations reached 360 % at the fields up to 2 kOe, and the maximum ME conversion coefficient was 1.74 V/(Oe·cm). For the structure magnetized perpendicular to the plane, an orientation transition was observed, which manifested itself as a jump-like bending of the structure to the angle up to ∼850 at magnetic field above the critical value. The frequency tuning by the magnetic field reached 185 %, and the maximum ME conversion coefficient was 135 V/(Oe·cm). A model has been developed that qualitatively describes the dynamics of ME effect in composite cantilever structures with a MAE layer for different orientations of the applied magnetic field.

Characterization and Theoretical Analysis of the Venus Flytrap Trigger Hair

The Venus flytrap, which possesses a number of mechano-sensitive trigger hairs, is a typical carnivorous plant that effectively senses and catches insects to survive in nutrient-poor habitats. When insects touch the trigger hairs on a leaf, once they reach the threshold, the Venus flytrap induces an action potential and sharply closes to capture the prey. In this paper, the trigger hairs obtain a special cantilever beam structure with a stiff hair lever and a flexible basal podium, and there is a noticeable notched structure at the basal podium, which differs from a common homogeneous hair. Based on the characteristics of the Venus flytrap trigger hairs, we established a three-dimensional model and conducted theoretical and finite element analysis. The results show that the unique hollow heterogeneous cantilever structure of the Venus flytrap trigger hair can achieve high sensitivity and optimal tactile perception. Overall, the morphology, structure and mechanical characteristics of Venus flytrap trigger hairs were characterized in detail, which may provide a deeper understanding of the trigger hairs’ tactile perception mechanism. And the mechanical simulation and optimization analysis of Venus flytrap trigger hairs had an important theoretical basis and parameter support for the further design of state-of-the-art tactile sensors with high sensitivity inspired by Venus flytrap trigger hairs.

Self-supporting lamellae: Shape variation methods for the 3D concrete printing of large overhang structures

3D Concrete Printing (3DCP) is considered a solution to confront both labor shortages and material waste in the construction industry. However, to realize non-standard, large-scale buildings, substantial amounts of supporting material and manual assembly are still required to print structures with significant overhangs, including the inclined structure and the cantilever structure. In response, the study draws inspiration from mushroom lamellae and proposes a geometry-based approach to adjusting the large-overhang shape into a self-supported one. This approach imitates lamella morphology by creating folds on the given geometry based on constraints established through empirical studies, thereby reducing overhangs and improving printability. Specifically, the proposed approach includes two shape variation methods. The first method generates lamellae perpendicular to the inclined shape, thereby providing lateral support to the filament. The second method creates lamellae under the cantilever, facilitating a seamless horizontal-to-vertical transition. The effectiveness of these methods is demonstrated through the generation and printing of four column capital samples. Upon evaluating the overhang mechanisms of these geometries, an approachable optimization method is also presented to further minimize the amplitude of lamellae while maintaining self-supporting ability. Compared with control groups that focus on either maximizing printability or minimizing material usage, the optimal result for the inclined structure prototype showcases an over 75 % overhang reduction on the critical layer with just about 15 % use of additional material. As for the cantilever prototype, an over 75 % overhang reduction is achieved on the critical layer with about 35 % additional material usage. Various large-scale structure examples are presented at the end of the research, illustrating the applicability and scalability of the lamella-inspired method in a wider range of building types.

Modelling and characterisation of a magnetically coupled piezoelectric beam for energy harvesting gear meshing motion

Gear transmission systems are crucial components for transmitting power and motion in a host of engineering applications. Recently, the potential to embed sensors into transmission components has attracted significant attention for accurate condition monitoring of system health. As a result, embedded sensors must operate in a safe and stable manner, whilst being able to provide a continuous power-supply and ensure operational autonomy. In this work, a magnetically coupled beam-type piezoelectric energy harvester is developed for energy harvesting of rotational centrifugal forces and individual gear meshing excitation events. A new coupled electromechanical dynamic model is developed to explain the working principle and response of the harvester when excited by a combination of gear meshing excitation events, a centrifugal force, and a magnetic force. Since gear meshing events are observed to lead to an increased hardening nonlinearity of the energy harvester, and a decrease in power output, a novel variable-section cantilever structure was developed. Our detailed theoretical analysis demonstrates that the novel variable stiffness structure improves both the power output and bandwidth, with excellent agreement with experimental measurements. This work provides new theoretical insights into the application of magnetically coupled piezoelectric energy harvesters for self-powered sensing systems for critical gear transmission systems.

Ultrahigh Electrobending Deformation in Lead-Free Piezoelectric Ceramics via Defect Concentration Gradient Design.

Recent breakthroughs in defect-engineered lead-free piezoelectric ceramics have reported remarkable electrostrain values, surpassing the limit of lattice distortion. This has aroused wide concern on bending deformation and the associated underlying mechanism. Herein, via designing lead-free piezoelectric ceramics with varying volatilization characteristics, it is uncovered that the ultrahigh electrobending deformation is primarily attributed to a large strain gradient induced by unevenly distributed defect dipoles. In 0.5 mm thick Sr/Sn co-doped potassium sodium niobate ceramics featuring volatile K/Na elements, the inherent bipolar electrostrain value can reach 0.3% at 20kV cm-1 due to the existence of defect dipoles, while the gradient distribution of defect dipole generates significant bending displacement, amplifying apparent electrostrain value to 1.1%. Notably, nonvolatile Ba0.99TiO2.99 ceramic with homogeneous defect dipole distribution does not present electrobending. Of particular interest is that the electrobending phenomenon can be observed through introducing a defect dipole gradient into barium titanate ceramic. A monolayer ceramic with defect dipole gradient can generate large tip displacement (±1.5mm) in cantilever structure, demonstrating its promising potential in precise positioning. This study delves into the underlying mechanism driving electrobending deformation and its impact on the apparent electrostrain measurement in defect-engineered piezoelectric ceramics, providing fresh perspectives for the development of piezoelectric bending actuators.

Design for early-age structural performance of 3D printed concrete structures: A parametric numerical modeling approach

This paper presents a design framework based on structural performance of 3D concrete printing (3DCP) that considers three strength criteria for early-age failure modes: plastic collapse, elastic buckling, and flexural collapse. A simulator of structural behavior during printing was developed to take any shell or linear model, slice it into layers, perform incremental structural analysis layer by layer, and assign the respective material properties by adjusting the age of each layer when a new one is added. Then, finite element analysis for each printing stage indicates whether collapse might occur based on rheological and mechanical material properties over time. Printing experiments validated the criteria based on collapse layer estimation for a solid cylinder (plastic collapse), a thin-wall structure (elastic buckling), and an overhang structure (flexural collapse). Plastic collapse was most accurately predicted by a Drucker-Prager yield criterion for an unrestrained base and by a Modified Lade and Mohr-Coulomb criterion for a partially restrained base, while elastic buckling was predicted by linear elastic analysis. Additionally, this paper introduces flexural collapse as a distinct failure mode in early age 3DCP, proposing design criteria for overhang structures based on printing experiments. Experimental lessons learned were used to establish design constraints to aid the design of 3DCP structures, which were tested in the design of a hollow column and a cantilever structure. This study advances computational design for 3DPC structures with a new design methodology that combines constrained design and parametric numerical modeling.

An adaptive modeling method with a local choice of optimal displacement fields for finite element analysis of structures

In the standard finite element procedure, the user chooses himself which mechanical theory will be used for a given application. To this end, he relies on some rules acquired through experience or some theoretical consideration. But choosing an appropriate theory may be a difficult task when geometry, boundary conditions, loadings, and materials are complex. This paper aims to define an adaptive methodology to identify, in the context of linear static analysis, optimal finite element models from a theory choice point of view. A criterion is defined to choose, in each part of the structure, the relevant mechanical theory: solid, shell or beam. A solid mesh is defined for the whole structure while specific solid-shell or solid-beam approaches are used in shell or beam areas respectively. This avoids the construction of mid-surface or mid-axis geometries from solid ones, which is a complicated task, in particular for industrial applications. Kinematic relations between nodes are imposed to apply the displacement fields of shell or beam theories. This leads to a set of linear equations which are used for eliminating slave degrees of freedom. The methodology proposed can also be interpreted as a model size reduction method, compared to a complete solid approach. The effectiveness of this approach is demonstrated through two numerical examples, including academic cantilever structures and an industrial multilayered composite structure.

1D Topological Interface States for Improving Optical Sensors

AbstractThe field of compact optical microcavities has received significant research in the past decades, and a broad range of cavity‐based micromechanical sensors has been demonstrated. The present approach replaces the frequently employed, complex etched cantilever and membrane structures with a simple thin‐film system based on a compressible photonic microcavity to achieve pressure‐sensitive wavelength shifting of resonant modes. The effects of a topological dielectric mirror architecture on the light propagation in the system are extensively investigated. Topologically improved light‐matter interaction is experimentally demonstrated for systems where thin‐film devices are mounted on one side of the photonic cavity due to mechanical constraints. Coupled topological states are examined under the aspect of mode splitting and exhibit advantageous splitting tunability compared to non‐topological systems. The findings are complemented by the proposal of a simple spectral evaluation method allowing significant improvement in the precision of integrated Fabry‐Pérot sensors. The readout concept of the presented sensor allows a scalable improvement of the measurement precision by evaluating the resonant‐mode order in the deformable cavity. The experimental results and conceptual advancements provide pathways for significant improvements addressing the efficiency of light‐matter interaction in Fabry‐Pérot cavities and the readout precision of sensors incorporating thin‐film photodiodes in multimode photonic cavities.