Good Stiffness Research Articles

A comparative experimental study on blind‐bolted beam connections to square steel tubular columns filled with polyurethane foam or concrete

AbstractIn the last two decades blind‐bolted connections have been developed to allow bolting of open section beams (e.g, I‐beam) to steel hollow section (SHS) columns where access from all sides of the column is not possible. Filling the tubular column with concrete in the vicinity of the beam‐to‐column connection has been shown to improve the anchoring mechanism of the blind‐bolted connection thereby increasing the strength and stiffness of the connection and reducing the column face deformation, however it adversely affects the joint ductility. This study introduces polyurethane foam filled steel tubular columns in combination with a new anchoring arrangement employing hollo‐bolts to develop a novel connection between the SHS columns and open section beams that provides a better combination of stiffness, strength and ductility. To investigate the behaviour of the proposed arrangement, monotonic pull‐out tests of blind bolted T‐stub connections anchored to foam‐filled steel tubular (FFT) and concrete‐filled steel tubular (CFT) columns using holloBolts were conducted. Benchmark tests on unfilled SHS columns were also conducted for comparison. The FFT in conjunction with the proposed anchoring mechanism was shown to provide a good stiffness as the CFT columns, and almost similar ductility to that of the unfilled steel tube blind‐bolted connection. Hence it is concluded that employing foam instead of concrete as an infill leads to favourable combination of strength and ductility, thus rendering FFT an attractive light alternative to CFT sections when ductility of the joint is an important design consideration.

Structural behavior of a fully assembled cable-piercing ridge-tube cable dome with modular assembly ring truss

There is yet to be a fully assembled long-span steel structure system. This paper proposes a fully assembled cable-piercing ridge-tube cable dome (FCRCD) with a modular assembly ring truss (MART). A scale model of FCRCD with MART with a span of 10 m and a rise-span ratio of 1/10 was designed and manufactured, the static test of the scale model was conducted, and the finite element model (FEM) was established and analyzed. The structural behavior under different vertical loads was studied by static test and finite element analysis. Simultaneously, to further investigate the mechanical properties of the FCRCD in detail, the FEMs of the ridge-tube cable dome (RTCD) with MART and ridge-cable cable dome (RCCD) with MART were established and analyzed for comparison with the FCRCD with MART. The research results verified that the innovative FCRCD has good stiffness, stability, bearing capacity, and resistance to uneven load; the FEM method is correct, and the FEM analysis is accurate. The cable-piercing ridge tube (CRT) can limit the relaxation of the ridge cable to about 10%, improve the mechanical properties and tensioning efficiency, and reduce the prestressing loss of the FCRCD. The FCRCD is more favorable to the force state of the MART, and it is more suitable for long-span and super-long-span spatial structures and can meet the requirements of rigid roof laying.

Biopolymeric conjugation with synthetic fibers and applications

Abstract Presently, several different kinds of polymer composite materials of varying properties have been developed and these composite materials play a vital role in construction and automotive industries. Polymer composites are normally preferred owing to some of their unique properties such as light weight, low cost, good surface finishes, more durability, and non-corrosiveness. But it is a challenge to environmental sustainability, therefore researchers are emphasizing on development of new modified biodegradable polymer composite materials. The biopolymer matrix reinforced by synthetic fibers is a viable alternative, which exhibits adequate mechanical properties and biodegradability. Although various advanced and improved composite materials are developed by using synthetic fibers, natural fibers, and nanoparticles, the use of synthetic fibers as reinforcing material is cost effective and shows improved performance. Among the various kinds of synthetic fibers, normally glass fibers (GF) in the form of short fiber are the most widely used reinforcing material, which is cost effective, provides good impact resistance, stiffness, strength, thermal stability, and chemical resistance. For requirement of high stiffness of the composite material, carbon fibers (CF) are more suitable than GF. Some other synthetic fibers such as aramid (AF), polypropylene fibers (PP-F), polyacrylonitrile fiber (PAN-F), basalt (BF), and polyethylene terephthalate fiber (PET-F) are some cases used as reinforcing material for synthesis of composites. The composite reinforced with synthetic fibers are used as a highly suitable material for manufacturing of various components in cars, space vehicles and railways. Recently some new hybrid composite materials are developed by using both natural and synthetic fibers as reinforcing material, which exhibits dynamic thermal, mechanical properties and potentially suitable from automobile to construction industry. Recently, numerous new biomaterial composite has been developed by using biopolymer as matrix with reinforcement of various kinds of synthetic fibers, which are used as good implant material for tissue engineering applications.

Highly Impact‐Resistant Silk Fiber Thermoplastic Composites

Silk fibers combine good stiffness and strength with a very high strain to failure and are as such highly promising to realize composites with high impact resistance. It is shown that to realize this potential it is quite beneficial to employ matrix materials of high strain to failure, particularly thermoplastic matrices. High impact resistance is thus achieved, well above the values for the pure matrices. Below the glass‐transition temperature of the thermoplastic matrix, the impact energy absorption decreases. The adhesion between fiber and matrix also plays a significant role; lower adhesion typically increases the low‐velocity penetration impact resistance, due to the spread of damage. Finally, the fiber architecture is pivotal; when a woven fabric is used which is unbalanced in strength, the impact resistance reduces in correspondence with the weakest material direction. A quasi‐isotropic layup has a lower capacity for deformation than a balanced woven configuration which likely explains the observed lower penetration impact resistance.

An in-plane omnidirectional flutter piezoelectric wind energy harvester

Most wind energy harvesters that are based on wind-induced vibrations can only operate in a specific wind direction, which limits their application in environments with time-varying wind directions. Previously reported in-plane omnidirectional piezoelectric wind energy harvesters (PWEHs) based on vortex-induced vibrations can produce stable electrical output characteristics when the wind direction changes, but their output powers are relatively low and the working wind speed ranges are relatively narrow. To solve this issue, this work presents an in-plane omnidirectional flutter PWEH which is mainly composed of the bluff body of a hollow cylindrical shell and the inside elastic supporting structure of several piezoelectric composite beams. Finite element analysis shows that harvesters with both four and six supporting beams offer good stiffness and electromechanical conversion isotropies. Experiments demonstrate that both prototype devices are flutter PWEHs with rotation axes located on the rear of the geometrical center of the bluff body. The effect of wind speed on their directionality is small, and both prototypes show in-plane omnidirectional operation over a wide wind speed range, over which the electrical outputs remain relatively high. The prototype with six beams is preferred from the viewpoint of the wind direction adaptability. The onset wind speeds in different directions all range between 5.8 and 6.0 m/s, showing the good isotropy. The minimum and maximum powers are approximately 266.4 and 300.1 μW, respectively, at 10 m/s, and it shows in-plane omnidirectional energy harvesting performance in the wind speed range from 6.5 m/s up to more than 10 m/s.

Material properties of ITRAC and cyclic behavior of double steel plate composite shear wall filled with ITRAC

An innovative iron tailing and recycled aggregate concrete (ITRAC)-filled double steel plate composite shear wall (ITRAC-CSW) was proposed to promote the application of the fabricated composite structures and the green build materials. Firstly, the mix proportion of ITRAC was studied through the test of six groups of ITRAC samples by changing the recycled coarse aggregate (RCA) replacement ratio and water-binder ratio. Favorable mechanical properties and the corresponding mix proportion was obtained. The elastic modulus calculation and the constitutive model of the ITRAC were obtained based on the test results. Subsequently, three full-scale ITRAC-CSW specimens were fabricated using ITRAC with the 100% RCA replacement ratio and tested under the cyclic lateral load and constant axial load. The failure mode and deformation mechanism of the specimens were analyzed through experimental phenomena. The seismic performance of the specimen was explored by comparing the load–displacement curves, stiffness degradation, and energy dissipation capacity. The analysis revealed that the ITRAC-CSW exhibits good bearing capacity, stiffness, and energy dissipation capacity which can be used in practical project.

Structural stiffness evaluation of suspension bridge based on monitoring data

For long-span suspension bridges, the structural deformation is significantly influenced by the environment. Therefore, evaluating the structural stiffness of suspension bridges is crucial. This paper takes a certain long-span suspension bridge over the sea as an example to discuss different methods for evaluating the structural stiffness of suspension bridges. A three-dimensional finite element model is established, and influential lines at key locations are extracted. The fitting accuracy of vertical deformation and environmental temperature data under different time windows is analyzed based on GPS deformation monitoring data. Furthermore, the spatial distribution of the maximum and minimum values of bridge deformation caused by vehicle loads is statistically analyzed. The results indicate that the displacement extreme value coefficient at the mid-span of the suspension bridge is relatively large compared to other locations. The measured displacement envelope curves are within the theoretical envelope curves, demonstrating good overall stiffness performance of the bridge. The research methodology in this paper accurately evaluates the overall structural stiffness of the suspension bridge, providing strong support for ensuring the safe operation of the bridge.

Investigation of New Material for Deterging Heat Exchanger Tube

This work represents new material can be used in cleaning process of heat exchanger tubes. Rubber projectiles are back bone of on line cleaning mechanism but it has poor mechanical and thermal features. Three materials have different properties with micro scale powder solid phase (aluminum, aluminum oxide and copper) had been added to (LSR) with different volume ratios (2%, 5%, 10%, 15%). specimens had been prepared with certain method and under specific conditions. Compression test was applied to identify stiffness factor of these new composite materials. Wear test was applied to finite the wear rare coefficient for these materials. Un certainty statistics was applied for measurements results so It's founded that with increasing volume ratio each of stiffness factor and wear rate coefficient increase linearity up to (15%) for all specimens. copper filler give best for stiffness that stiffness factor reaches about (30 (N/(mm/mm))) at volume ratio 15%) but poorest wear resistance with wear rate coefficient (9*10^-6) Mpa^-1 inversely aluminum filler gives best results in wear resistance with wear rate coefficient (6*10^-6) Mpa^-1 but weakest in stiffness test with stiffness factor (28 N/(mm/mm) at volume ratio 15%). Aluminum oxide was the best choice for new projectile material as it combines between good stiffness and wear resistance.

Bioderived Freestanding Film as a Robust Interfacial Protective Layer for Advanced Lithium Metal Anodes

Lithium metal is a potential candidate for anode material in next‐generation rechargeable batteries with high energy and power densities. However, the huge volume change caused by the uneven deposition of metallic Li leads to the cracking of the solid electrolyte interphase (SEI), which cannot prevent the reaction of inner fresh Li with electrolyte, resulting in severe dendrite growth and electrochemical degradation. Herein, a freestanding protein film derived from eggshell is reported as the protective layer on the electrode surface to form a robust artificial SEI layer. Benefiting from its 3D interconnected fiber framework along with good mechanical stiffness and softness, the Li‐ion flow is uniformly modulated, leading to the suppression of Li dendrite growth. The electrochemical performance of corresponding symmetric, asymmetric, and full cells is significantly enhanced. A high coulombic efficiency above 95% for nearly 700 cycles is achieved for the modified Cu/Li asymmetric cell at a current density of 3 mA cm−2 (with a capacity of 1 mAh cm−2). This study indicates a SEI reinforcement approach for the stabilization of the Li metal anode based on the freestanding structure derived from biomaterials.

A Wide-Scanning Array Antenna of Connected Vertical Bowtie Elements Structurally Integrated Within an Aircraft Fuselage

A low-profile, wide-scanning phased-array antenna of vertical bowtie elements fully integrated with a structurally efficient radome and ribs of an aircraft fuselage is proposed in this paper. The array is designed to simultaneously fulfil the electrical requirements of an airborne antenna sensor and the mechanical requirements of a load-carrying aircraft fuselage. The array antenna is capable of steering the beam up to ±80° in the azimuth plane over a 20% bandwidth (2.4 GHz to 3 GHz) with the active reflection coefficient (Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>act</i></sub> ) below –10 dB in an infinite array environment. Experimental results of a 16×16 element array demonstrator agree well with the simulation results. The 16×16 array antenna is capable of steering the beam up to ±60° and ±75° with the bandwidth of 20% and 10%, respectively at Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>act</i></sub> ≤ –10 dB. The array antenna also achieved good stiffness and performed well in the vibration loads of commercial transport aircraft.

Do the Mechanical Properties of Calcium-Silicate-Based Cements Influence the Stress Distribution of Different Retrograde Cavity Preparations?

The aim of the present study was to investigate the influence of the mechanical properties of three different calcium-silicate-based cements on the stress distribution of three different retrograde cavity preparations. Biodentine™ "BD", MTA Biorep "BR", and Well-Root™ PT "WR" were used. The compression strengths of ten cylindrical samples of each material were tested. The porosity of each cement was investigated by using micro-computed X-ray tomography. Finite element analysis (FEA) was used to simulate three retrograde conical cavity preparations with an apical diameter of 1 mm (Tip I), 1.4 mm (Tip II), and 1.8 mm (Tip III) after an apical 3 mm resection. BR demonstrated the lowest compression strength values (17.6 ± 5.5 MPa) and porosity percentages (0.57 ± 0.14%) compared to BD (80 ± 17 MPa-1.22 ± 0.31%) and WR (90 ± 22 MPa-1.93 ± 0.12%) (p < 0.05). FEA demonstrated that the larger cavity preparation demonstrated higher stress distribution in the root whereas stiffer cement demonstrated lower stress in the root but higher stress in the material. We can conclude that a respected root end preparation associated with cement with good stiffness could offer optimal endodontic microsurgery. Further studies are needed to define the adapted cavity diameter and cement stiffness in order to have optimal mechanical resistance with less stress distribution in the root.

Design and Characterization of a Low-Cost and Efficient Torsional Spring for ES-RSEA

The design of torsional springs for series elastic actuators (SEAs) is challenging, especially when balancing good stiffness characteristics and efficient torque robustness. This study focuses on the design of a lightweight, low-cost, and compact torsional spring for use in the energy storage-rotary series elastic actuator (ES-RSEA) of a lumbar support exoskeleton. The exoskeleton is used as an assistive device to prevent lower back injuries. The torsion spring was designed following design for manufacturability (DFM) principles, focusing on minimal space and weight. The design process involved determining the potential topology and optimizing the selected topology parameters through the finite element method (FEM) to reduce equivalent stress. The prototype was made using a waterjet cutting process with a low-cost material (AISI-4140-alloy) and tested using a custom-made test rig. The results showed that the torsion spring had a linear torque-displacement relationship with 99% linearity, and the deviation between FEM simulation and experimental measurements was less than 2%. The torsion spring has a maximum torque capacity of 45.7 Nm and a 440 Nm/rad stiffness. The proposed torsion spring is a promising option for lumbar support exoskeletons and similar applications requiring low stiffness, low weight-to-torque ratio, and cost-effectiveness.

A Study on the Structural Characteristics of the Blades of Wind Turbines under Static Load Condition

The study of the structural strength and stiffness of wind turbine blades is an important foundation and guarantee for analyzing the stability and reliability of the complete wind turbine. By analyzing the results of static load experiments and finite element calculation, the stress, strain and deflection of blades can be more precisely determined so as to assess the structural characteristics of blades. We conducted static load tests on the medium-size experimental blades developed by the Institute of Engineering Thermophysics, Chinese Academy of Sciences, and obtained the deflection conditions of flap-wise and edgewise bendings, as well as the analytic results on the strain of the main beams and trailing edges. Meanwhile, a finite element model of blades was built using ANSYS to analyze the maximum deformation, stress, and strain. The corresponding results were compared with those of static load experiments. Then the strain and bending properties of blades under the static load were investigated, and the characteristics of the safety application of blades were verified. The results show that: 1)Within the range of 100% design load, the deflection of edgewise and flapwise directions presented a linear relationship with the applied loads. 2) After the loads in the flapwise direction exceeded 100% design load, a non-linear relationship between the blade bending and the applied loads were found. 3)The blade beam and trailing edge retain good stiffness properties under big strain conditions, and the maximum deformation appeared at the maximum chord length of the trailing edge of the blades. Our results on the static load experiments were basically consistent with the finite element model simulation, which verified the accuracy of the results of the static load experiment and finite element simulation of blades.

The Influence of Glass Fiber/Glass Fiber Powder with β-Nucleating Agent on the Properties of Polypropylene

Glass fiber-reinforced polypropylene (PP/GF) has been widely used due to its high stiffness, but for some applications that need low-module characteristics, PP/GF will have limitations due to its lower toughness, so it is necessary to develop glass fiber-modified polypropylene with good stiffness–toughness balance performance. In this study, two average length glass fibers (4.5 mm and 12 mm) and glass fiber powder, combined with β-nucleating agent, were used to investigate the effects on the crystallization and mechanical properties of polypropylene. The results show that compared with glass fiber, glass fiber powder cooperates with β-nucleating agent reinforced polypropylene composite showed good stiffness–toughness balance performance, and β-crystals were found in the composite measured by Differential Scanning Calorimetry (DSC), the presence of β-crystals can improve the toughness of the composite.

Combined use of novel chitosan-grafted N-hydroxyethyl acrylamide polyurethane and human dermal fibroblasts as a construct for in vitro-engineered skin

A rich plethora of information about grafted chitosan (CS) for medical use has been reported. The capability of CS-grafted poly(N-hydroxyethyl acrylamide) (CS-g-PHEAA) to support human dermal fibroblasts (HDFs) in vitro has been proven. However, CS-grafted copolymers lack good stiffness and the characteristic microstructure of a cellular matrix. In addition, whether CS-g-PHEAA can be used to prepare a scaffold with a suitable morphology and mechanical properties for skin tissue engineering (STE) is unclear. This study aimed to show for the first time that step-growth polymerizations can be used to obtain polyurethane (PU) platforms of CS-g-PHEAA, which can also have enhanced microhardness and be suitable for in vitro cell culture. The PU prepolymers were prepared from grafted CS, polyethylene glycol, and 1,6-hexamethylene diisocyanate. The results proved that a poly(saccharide-urethane) [(CS-g-PHEAA)-PU] could be successfully synthesized with a more suitable microarchitecture, thermal properties, and topology than CS-PU for the dynamic culturing of fibroblasts. Cytotoxicity, proliferation, histological and immunophenotype assessments revealed significantly higher biocompatibility and cell proliferation of the derivative concerning the controls. Cells cultured on (CS-g-PHEAA)-PU displayed a quiescent state compared to those cultured on CS-PU, which showed an activated phenotype. These findings may be critical factors in future studies establishing wound dressing models.

Preparation of high-performance epoxy materials with remarkable negative thermal expansivity

In this study, a simple but effective strategy to synthesize epoxy materials with negative thermal expansion (NTE) performance was proposed. The thermal expansion coefficient of epoxy material was turned from positive (154.5 ppm/K) to negative (−492.6 ppm/K) by introducing eight-membered carbocyclic (EMCC) structure into bisphenol-A epoxy resin system. The NTE performance can be well regulated by controlling the ratio of EMCC-polyamide. Molecular simulation was also carried out, suggesting that the system with the 15 wt% EMCC-polyamide mass fraction gives the lowest energy as compared to those with 7.5 and 10 wt%. Improvements of thermal stability and mechanical properties of the synthesized negative thermal expansion epoxy material were achieved by further composited with nano-TiO2. With the combination of EMCC unit and nano-TiO2, the prepared epoxy materials can possess good hardness and stiffness, meanwhile, have acceptable flexibility and toughness. The modified epoxy materials were successfully used as coating materials for the encapsulation of monocrystalline silicon. This study provides a new strategy for the preparation and regulation of polymer composites with excellent NTE performance.

Fabrication and characterization of polylactic acid/natural fiber extruded composites

AbstractIn this work, the fabricated polylactic acid (PLA) and hybrid natural fiber (NF) biocomposites via a melt extrusion method were investigated. NFs from locally grown plants were utilized as fillers. Polyethene glycol (PEG) was used as the plasticizer to improve the processability of the PLA. The effect of PLA/NF biocomposite processing was assessed by mechanical characterization (tensile, modulus, strain at break, and impact tests), and thermal properties (thermogravimetric analysis and differential scanning calorimetry [DSC] analysis). The dynamic mechanical analysis (DMA), and thermo‐mechanical analysis (TMA) of the samples were also analyzed. The mechanical properties of PLA/NF biocomposites improved as compared with that of PLA. The DMA findings show that the storage modulus and loss modulus exhibited a slight reduction for PLA/NF biocomposites compared with the PLA sample. In opposite, the glass transition temperature (Tg) from DSC thermogram results showed no obvious changes in values compared with the PLA sample. Furthermore, the findings of TMA showed a significant decrease in coefficient of thermal expansion values of PLA/NF biocomposites compared with those of PLA samples. The overall findings from this work indicated that PLA/NF biocomposites have the potential to make novel biocomposites and suitable for further application especially in biomedical applications due to its good stiffness, tensile strength, and dimensional stability.

Impact of PVDF and its copolymer-based nanocomposites for flexible and wearable energy harvesters

Encountering the consumption of fossil fuels on a large scale and contamination of the environment due to chemical batteries, along with the rapid growth of various wearable devices and IoT-enabled devices, researchers are urged to discover lightweight, flexible, biocompatible wearables which can be self-powered. Currently, flexible piezoelectric, triboelectric and hybrid nanogenerators are good power sources to integrate into self-powered wearable devices that can even monitor human health conditions. PVDF and its copolymers are widely used materials in self-powering wearable technology, as it is flexible, biocompatible, easily processable and is of low cost. PVDF has five crystalline phases, among them the β phase has strong electroactive and piezoelectric properties. Several attempts have been made to enhance the β phase of PVDF by incorporating different nanofillers for implementation in energy harvesting applications. This review focuses on the recent advancements in energy harvesting by using various additives like Mxene, ZnO, hBN, TMDCs and QDs. Mxene has superb mechanical properties that include good bending stiffness, good Young’s modulus, high thermal conductivity, absorptivity, intrinsic hydrophilicity etc. ZnO is a piezoelectric material with good electrical, chemical, thermal stabilities and optical as well as photocatalytic properties. It is a less toxic material with good resistance against microbes. hBN is an electrical insulator which possess good thermal conductivity, is transparent to visible light and exhibits a high Young’s modulus of ∼1TPa. TMDCs are non-toxic materials with an ultrathin structure and good surface area to mass ratio, exhibiting good mechanical, optical and electronic properties. The current review briefly discusses the deformation sensing mechanism, various methods of β phase enhancement in PVDF, fabrication of PVDF based energy harvesting devices and material selection criteria of nanofillers. A dedicated section is presented for humidity sensors as wearable devices are prone to sweating conditions. The authors hope this review brings a general understanding of PVDF and its copolymer-based nanocomposites for flexible and wearable energy harvesters.

Novel electrochemiluminescence biosensor of fumonisin B1 detection using MWCNTs-PDMS flexible bipolar electrode

A novel portable and disposable bipolar electrode (BPE)-electrochemiluminescence (ECL) device was fabricated for fumonisin B1 (FB1) detection. BPE was fabricated by using MWCNTs and polydimethylsiloxane (PDMS) due to their excellent electrical conductivity and good mechanical stiffness. After the deposition of Au NPs on the cathode of BPE, the ECL signal could be improved 89-fold. Then a specific aptamer-based sensing strategy was constructed by grafting capture DNA on Au surface, followed by hybridizing with aptamer. Meanwhile, an excellent catalyst, Ag NPs was labeled on aptamer to activate oxygen reduction reaction, leading to a 13.8-fold enhancement in ECL signal at the anode of BPE. Under the optimal conditions, the biosensor exhibited a wide linear range of 0.10 pg/mL to 10 ng/mL for FB1 detection. Meanwhile, it demonstrated satisfactory recoveries for real sample detection with good selectivity, making it to be a convenient and sensitive device for mycotoxin assay.

Pengujian Kekuatan Tarik Komposit Serat Kayu Mahoni Tanpa Pengaruh Alkali

Composite is defined as a combination of two types of materials, namely matrix and reinforcement which have different properties. Composites have the advantage that they are resistant to corrosion and also have good strength and stiffness. This study aims to determine the tensile strength of mahogany fiber composites without alkali, with variations in fiber volume of 10%, 30%, 50%, and variations of mesh 30, 50, and 80. The reinforcing particles are made in powder form by means of a blender with a matrix. BQTN 157 EX polyester resin was used. The results showed that the highest tensile strength was found in the mesh 80 experiment of 43.07 MPa. This shows that the smaller the composite reinforcing particles, the greater the tensile strength. While the smallest tensile strength is at 10% fiber volume, namely 14.21 MPa. Tensile strength reaches its maximum at 30% fiber volume, which is 32.76 MPa. The addition of fiber volume to 50% actually lowers the tensile strength to 20.69 MPa.