Composite Pillars Research Articles

Deformation behavior of TiB reinforced Ti and Ti6Al4V composite particles under in-situ microcompression

To reveal the role of nano-TiB whiskers in micromechanical behaviors of two common titanium composite particles (TCPs), this paper presents experimental investigation on the elastic and plastic deformation of micron-sized Ti-TiBw and Ti6Al4V-TiBw particles. Scanning electron microscope with in-situ uniaxial compression experiment of single TCP was performed within a diameter range of ∼1–5 μm. This study enables detailed insights into the elastic and plastic deformation and geometrical shape evolution of TiBw reinforced TCPs. It is found that, when the particle size decreases, the flow stress and contact yield stress in microcompression for both TCPs exceed the yield strength of bulk composite pillars with identical content of TiB. The contact yield stress is as high as ∼1.5 GPa and ∼1.3 GPa for the smallest Ti-TiBw (D∼1.45μm) and Ti6Al4V-TiBw (D∼1.78μm) particles measured, respectively. In elastic-plastic and fully plastic regime, the steady plastic flow for both particles can be maintained over ∼2 GPa till the engineering compressive strain of εE ∼ -0.4. Compared with bulk composites, higher strain hardening rate of ∼34.2 and ∼37.5 GPa for Ti-TiBw and Ti6Al4V-TiBw particles demonstrate remarkable pinning capacity induced by nano-TiBw network. No structural damage and microcracks was observed in surface morphology of severely deformed Ti6Al4V-TiBw particles, showing distinctive microscale plasticity. The deformation and strain hardening mechanism for such composite particles have been discussed in terms of grain size, aspect ratio of TiBw and the network architecture.

The effectiveness of the composite educational pillars strategy in the artistic performance of sports performances and the development of perceptions of success among the fifth elementary students

The effectiveness of the composite educational pillars strategy in the artistic performance of sports performances and the development of perceptions of success among the fifth elementary students

Measuring Competitiveness at NUTS3 Level and Territorial Partitioning of the Italian Provinces

In this paper we propose a dashboard of indicators of territorial attractiveness at NUTS3 level in the framework of the EU Regional Competitiveness Index (RCI). Then, the Fuzzy C-Medoids Clustering model with multivariate data and contiguity constraints is applied for partitioning the Italian provinces (NUTS3). The novelty is the territorial level analized, and the identification of the elementary indicators at the basis of the construction of the eleven composite competitiveness pillars. The positioning of the Italian provinces is deeply analyzed. The clusters obtained with and without contraints are compared. The obtained partition may play an important role in the design of policies at the NUTS3 level, a route already considered by the Italian government. The analysis developed and the related set of indicators at NUTS3 level constitute an information base that could be effectively used for the implementation of the National Recovery and Resilience Plan (NRRP).

Strengthening effect of high-entropy alloys endowed by monolayer graphene

The graphene (Gr) can effectively confine the dislocation propagation, allowing for the pronounced strengthening effect. However, due to the technical limitations of atomic resolution, an in-depth understanding regarding the potential strengthening mechanisms at atomic level is still insufficiently comprehended. In this paper, molecular dynamics (MD) simulations were performed to investigate dislocation-Gr interactions and strengthening mechanisms in FeNiCrCoCu high-entropy alloy (HEA)/Gr nanopillars. The hindrance of Gr sheet to mobile dislocations was demonstrated to promote the onset of massive immobile dislocations, especially the Stair-rod dislocation which gave rise to the remarkable strengthening effect. The immobile Hirth, 1/3<110> and 1/6<301> dislocations exerted the subsidiary effect on strengthening the composite pillars. Meanwhile, the diminished dislocation length induced by dislocation reactions and the absorption effect to mobile dislocations was verified to endow a more appreciable dislocation starvation for composite pillars which was conducive to forming more Stair-rod dislocations. In addition, the results also confirmed that the reduction in Gr diameters would directly weaken the pillars attributing to the fact that the Gr edges acted as a dislocation source. These findings may contribute to the design of HEA/Gr composites toward better mechanical properties.

Nanolayered CoCrFeNi/Graphene Composites with High Strength and Crack Resistance.

Emerging high-entropy alloy (HEA) films achieve high strength but generally show ineludible brittle fractures, strongly restricting their micro/nano-mechanical and functional applications. Nanolayered (NL) CoCrFeNi/graphene composites are elaborately fabricated via magnetron sputtering and the transfer process. It is uncovered that NL CoCrFeNi/graphene composite pillars exhibit a simultaneous ultra-high strength of 4.73 GPa and considerable compressive plasticity of over 20%. Detailed electron microscope observations and simulations reveal that the monolayer graphene interface can effectively block the crack propagation and stimulate dislocations to accommodate further deformation. Our findings open avenues for the fabrication of high-performance, HEA-based composites, thereby addressing the challenges and unmet needs in flexible electronics and mechanical metamaterials.

Machine learning-based optimization of the design of composite pillars for dry adhesives

A machine learning-based optimization strategy was used to find optimal designs for adhesive composite pillars with either high adhesion strength or high adhesion tunability. Neural networks were trained with data generated by finite element analysis to predict the adhesion strength of composite pillars with different designs; an average prediction error of less than 1% was achieved. Through a sensitivity study with the trained neural networks, it is found that the geometry of the stiff core above a critical cut off height has no effect on the interfacial stress distribution and the adhesion of the pillar. A randomly initialized constrained optimization algorithm was then applied to the trained neural networks to find the optimal composite pillar design. A composite pillar design with a stiff core that has an enlarged tapered flat end is optimal for realizing robust and high adhesion, since it can achieve high adhesion under different loading and contact conditions. The optimized pillar has a critical normal detachment force that is nearly 11 times that of a homogenous pillar and 1.7 times that of a composite pillar with a simple wide rectangular core under normal loading. A composite pillar with a thin flat stiff core shows the highest effective adhesion difference between being loaded with a normal force and being loaded with a moment.

Enhanced damping capacity of nanolaminated graphene (reduced graphene oxide)/Al-Mg-Si composite

Cyclic uniaxial compression tests were carried out on micro-pillars fabricated from reduced graphene oxide (RGO)-reinforced Al-Mg-Si alloy that went through peak-ageing treatment. The composite pillars were found to have a significantly better damping capacity and improved resistance to plastic deformation as compared to the unreinforced matrix. These observations were further corroborated by the much higher damping coefficient of the composite pillars (η = 0.3081 ± 0.0803), almost doubled that for the alloy matrix alone (0.1560 ± 0.0457). Site-specific TEM analysis revealed that the enhanced damping property of the composite came from a combined effect of dislocation impedance at the RGO/Al interface, the dislocation looping and cutting at the precipitates, and the formation of nano-twins in the alloy matrix upon deformation.

Dynamically Tunable Dry Adhesion through a Subsurface Thin Layer with Tunable Stiffness

AbstractRecently, a novel concept to realize dynamically tunable dry adhesion via subsurface stiffness modulation (SSM) in a composite core–shell structure has been introduced and demonstrated for gripping and release of objects. Here, a variant form of the composite core–shell design is proposed to significantly improve the performance of dynamically tunable dry adhesion in terms of activation time and activation voltage. Specifically, composite pillars with an embedded microfluidic channel filled with a low melting point alloy (LMPA) are fabricated, and the adhesion of the pillars is characterized as a function of LMPA state: either melted or solid. The effects of the thickness and in‐plane pattern of the LMPA channel, as well as the depth at which it is embedded on tunable adhesion are investigated. Experiments show that the effective adhesion strength can be reduced up to 50%, equivalent to a 2× change in dry adhesion when the LMPA is melted. Finite element analysis of the stress distribution change under SSM shows that the experimentally observed tunable adhesion is primarily due to stiffness change close to the interface. In addition, two technology demonstrations of composite pillars picking and releasing objects with fast activation (≈1 s) and low activation voltages (≈1 V) are included.

Pultruded FRP Beams with Embedded Fibre Bragg Grating Optical Sensors for Strain Measurement and Failure Detection.

Composites have added new dimensions to the design and construction of buildings and structures. One of the wider spread composite applications in the construction industry is composite beams or pillars, which can be manufactured through pultrusion processes. These types of construction elements are usually used to withstand the weight of large loads, so their integrity must be guaranteed. Due to optical sensors’ advantages over their electrical counterparts—small sizes, low weight, non-conductive, and immunity to electromagnetic interference—and FBGs having an outstanding position among optical fibre sensors—due to their multiplexation capability and relatively easy monitoring—in this study, we propose the integration of FBG sensors for the observation and analysis of the integrity of structures made with composite beams over time. The validation test results showed the successful embedding integration of FBG-based fibre optical sensors in an FRP pultrusion beam and strain transmission up to 7500 µɛ from the composite test piece to the sensor. Additionally, we were able to anticipate the piece failure by the FBG spectrum deformation.

Plane and Surface Acoustic Waves Manipulation by Three-Dimensional Composite Phononic Pillars with 3D Bandgap and Defect Analysis

The current century witnessed an overwhelming research interest in phononic crystals (PnCs) and acoustic metamaterials (AMs) research owing to their fantastic properties in manipulating acoustic and elastic waves that are inconceivable from naturally occurring materials. Extensive research literature about the dynamical and mechanical properties of acoustic metamaterials currently exists, and this maturing research field is now finding possible industrial and infrastructural applications. The present study proposes a novel 3D composite multilayered phononic pillars capable of inducing two-dimensional and three-dimensional complete bandgaps (BGs). A phononic structure that consisted of silicon and tungsten layers was subjected to both plane and surface acoustic waves in three-dimensional and two-dimensional periodic systems, respectively. By frequency response study, the wave attenuation, trapping/localization, transmission, and defect analysis was carried out for both plane and surface acoustic waves. In the bandgap, the localized defect state was studied for both plane and surface acoustic waves separately. At the defect state, the localization of both plane and surface acoustic waves was observed. By varying the defect size, the localized frequency can be made tailorable. The study is based on a numerical technique, and it is validated by comparison with a reported theoretical work. The findings may provide a new perspective and insight for the designs and applications of three-dimensional phononic crystals for surface acoustic wave and plane wave manipulation, particularly for energy harvesting, sensing, focusing and waves isolation/attenuation purposes.

Friction behavior of gecko-inspired polydimethylsiloxane micropillar array with tailored Young’s modulus by incorporation of ZrO2 particles

Here we present a simple route to improve the stiffness of polydimethylsiloxane (PDMS) gecko-inspired micropillar with high friction by incorporation of ZrO2 particles. Young’s modulus of PDMS composite pillar is increased due to the presence of three-dimensional network between fillers and free PDMS segments, and the composite pillar with ZrO2 nanoparticles has the largest Young’s modulus due to the high specific surface area of nano-size fillers. The patterned composite pillars with various diameters of ZrO2 particles exhibit high friction force, which is attributed to the strong interconnection between hydroxyl groups on ZrO2 surface and silanol units in PDMS matrix. This particle-embedded elastomer micropillar delivers a universal strategy to increase Young’s modulus with high friction performance in gecko-inspired adhesive.

Soft and flexible sensor array using carbon black pillars for object recognition via pressure mapping

Soft and flexible arrays of pressure or force sensors are particularly useful for wearable and robotic applications. This article presents a soft and flexible sensor array made from carbon black composite pillars. These pillars allows more sensing elements to be constructed in a given planar area. A prototype sensor consisting of a 3 × 3 array of carbon black composite pillars is used to demonstrate their potential. Each pillar shows a reliable corresponding change in resistance with instantaneous pressure or force applied on it. With a sensor array, the pressure distribution across the contact surface of the sensor can be represented as a pressure map allowing the recognition of the shape of an object applying the pressure on the sensor array. The soft and flexible nature of the sensor array allows it to be easily deployed and enables prediction of the shape of an object through the 3D pressure map.

Enhanced Damping Capacity in Graphene-Al Nanolaminated Composite Pillars Under Compression Cyclic Loading

Cyclic compression tests were conducted on 2.5-μm-diameter nanolaminated graphene-aluminum (Al) composite pillars. The composite possessed three times higher damping coefficient than its pure Al counterpart, which was rationalized by the enhanced dislocation hindrance at the graphene/Al interfaces in the composites. Moreover, the cyclic compression of micro-pillars produced similar damping coefficients as the corresponding bulk sample, providing a novel and convenient approach to assess the cyclic deformation behavior and damping properties of structural materials.

Microstructure Formation and Micropillar Compression of Al-TiC Nanocomposite Manufactured by Solidification Nanoprocessing

The microstructure and mechanical responses of a pseudo-dispersed Al-TiC nanocomposite were thoroughly studied using micropillar compression and high-resolution transmission electron microscopy (HRTEM). The microstructure of the Al-7 vol pct TiC nanocomposite comprised the α-Al matrix, DO22-Al3Ti platelet and Al4C3, along with TiC domains in which ~ 30 vol pct TiC nanoparticles were loaded without sintering contact. The pseudo-dispersion of TiC nanoparticles was rationalized by the relationship between Van der Waals attraction, Brownian motion, and energy barrier. The microscale tetragonal DO22-Al3Ti compound exhibited excellent yield strength (YS) (1400 to 1667 MPa) and microplasticity (10.8 pct). Intermittent discrete strain bursts and size effects were observed in the single-crystalline Al/Al3Ti pillars. The remarkable YS (720 MPa) of the 3 μm Al-30 vol pct TiC composite pillars was attributed to Orowan strengthening and load transfer. The crystallographic orientation relationship at the Al/TiC interface was identified to be $$ \left[ { 1 1 0} \right] (\bar{1}\bar{1}1 )_{\text{Al}} \parallel [ 1 1 0 ] (\bar{1}\bar{1}1 )_{\text{TiC}} $$, while the solid bonding guaranteed the effective load transfer and prevented the dislocation avalanche. Nano-twins and edge dislocations were observed in the HRTEM images of TiC NPs and [Al + TiC] mixture, which suggested that the major deformation mechanisms of the Al-30 vol pct TiC composite pillars were dislocation ‘pile-up’ and twins.

Strengthening and deformation mechanisms in nanolaminated graphene-Al composite micro-pillars affected by graphene in-plane sizes

Graphene is considered to be an ideal reinforcement in metals, and its strengthening to the metal matrix is found to be the combined effect of load-sharing and the alteration of dislocation activity in the matrix. In this study, uniaxial compression tests were performed on graphene (reduced graphene oxide, RGO)-Al nanolaminated composite micro-pillars with different RGO in-plane sizes and laminate orientations. We elaborately controlled the processing parameters so that the composites with different RGO in-plane sizes shared the same RGO volume concentration and total RGO/Al interface area. It was found that the strength of RGO-Al composite pillars increased with decreasing RGO in-plane size, regardless of the laminate orientations relative to the loading direction (iso-strain or iso-stress). A clear transition in deformation mechanism existed in RGO-Al composite pillars having iso-strain configuration, from shear fracture in pillars with larger RGO in-plane size, to kink banding in pillars with smaller RGO nanosheets. These observations were interpreted by isotropic and kinematic hardening mechanisms, the superior constraining effect of smaller RGO nanosheets over dislocation transmission and motion, and the crack propagation in Al lamellae across the pillar interior. This work indicates that the mechanical behavior of graphene-reinforced metal matrix composites (MMCs) can be tailored by carefully tuning the geometry of the graphene nanosheets, without changing their type and concentration.

Embedded piezoresistive pressure sensitive pillars from piezoresistive carbon black composites towards a soft large-strain compressive load sensor

Soft robotics is a rapidly expanding field that aims at replacing rigid robotic components in a wide range of applications with more compliant, organic and functional components. The limited availability actuator-compatible sensors that can provide real-time feedback limits large scale implementation of these soft robots. A secondary sensing layer that encompasses the soft actuator or a sensor embedded soft actuator would enhance the suitability of soft robots in a wider range of applications. This article describes the design, fabrication and characterization of a carbon composite elastomeric force sensor, which aims to be a free standing film than can be cut into desired shape and embedded into soft robots while manufacturing for imparting self-sensing capabilities. Various concentrations of carbon black in the elastomer composite have been studied and the ideal concentration is derived. Carbon composite pillars as soft sensors with conductive tracks on top and bottom were fabricated and embedded in a soft elastomer matrix for analysing the sensor response under physical loading. The sensitivity of these sensors were identified and characterised, and were found to be capable of detecting forces as small as 0.1 N. The thin-film free-standing architecture of sensing element allows embedding the fabricated sensing element into any elastomer matrix improves the applicability of these sensors in a wide range of soft robotic applications.

Dynamically switchable polarization-independent and broadband metasurface perfect absorber in the visible and near-infrared spectra regime

Abstract An electrically tunable absorber in the visible (Vis) and near-infrared (NIR) regime is theoretically investigated. The absorber is composed of aluminum (Al)-indium tin oxide (ITO) composite square pillars on top of thin dielectric layer and Al substrate. Significant tuning of absorption with modulation ratio of 86% can be achieved. The modulation ratio above 75% can be maintained from 1427 to 1795 nm and over 90% absorbance at the NIR regime from 1500 to 1800 nm can also be achieved. The symmetry of the absorber eliminates the polarization dependence and the near unity absorption efficiency can be maintained by incidence angles up to 70°. The presented method will enhance the functionality of absorber and has the potential for the applications that require active control over light absorption.

Investigation of adhesion and friction of an isotropic composite pillar

In this work, studies are carried out on the adhesion and friction of composite pillars contact with a smooth flat surface. The composite pillar is obtained by allocating additive metal particles to a polymer matrix. The aluminum micron-sized particles are added to a polymer matrix in different mass ratios, which is aimed at an alteration of structural properties such as the stiffness and damping that is likely to permit adhesion and friction properties to be tuned accordingly. The results demonstrate that incorporating aluminum particles to a polymer matrix yields a loss of adhesion, and metal particles have a minor influence on the change of friction force for different sliding velocities.

Strain-rate dependent deformation mechanism of graphene-Al nanolaminated composites studied using micro-pillar compression

Uniaxial compression tests conducted at various strain rates were performed to uncover the strain-rate dependent deformation mechanism of micro-pillars fabricated from bulk nanolaminated graphene (reduced graphene oxide, RGO)-Al composites. It was found that in both RGO-Al composite and pure Al pillars, compression at high strain rates resulted in a relatively smooth stress-strain response, as opposed to the jerky deformation at low strain rates. At any given strain rate, the RGO-Al composite pillars had significantly higher strengths than their pure Al counterparts, and this reinforcing effect grew to be more pronounced with increasing strain rate. In addition, the composite pillars were characterized by considerably higher strain rate sensitivity index (m) and correspondingly lower activation volume (V*) than the pure Al pillars. These observations were interpreted by a competition between dislocation generation and annihilation, a transition in the deformation mechanism over different strain rates, and the dislocation obstruction by the inter-lamella interfaces.

Investigation of surface acoustic wave propagation in composite pillar based phononic crystals within both local resonance and Bragg scattering mechanism regimes

We investigate the propagation of surface acoustic wave through phononic crystals (PCs) that consist of composite pillars, comprising of a cap metallic pillar and a bottom epoxy pillar on the semi-infinite substrate. The computation of band structures, together with measured transmission spectra, shows the important role of the bottom pillar in engineering the band structures for its Young’s modulus one order of magnitude smaller than that of the cap pillar. We also discuss the conditions of ignoring the influences of the bottom pillar in PCs featuring extremely high cap pillars. We finally modify the height of the bottom pillar to engineer the band structures of PCs, leading to, in both the simulation and experiment, Fano resonance-like transmission in the long wavelength regime.