Flexural Characteristics Research Articles

Low frequency vibration isolation characteristics and intelligent design method of hull grillage metastructures

In this paper, the wave propagation mechanics theoretical model of hull grillage metastructures with local resonators is established, and the intelligent design method of hull grillage metastructures is proposed based on deep learning. The flexural vibration isolation characteristics of periodic hull grillage structures and the proposed hull grillage metastructures are theoretically studied using the spectral element method. Numerical calculation and experimental tests of the flexural wave vibration transmission of hull grillage metastructures are conducted to validate the proposed theoretical model. In addition, the data set is constructed by using the wave mechanics theoretical model of hull grillage metastructures, and the forward prediction neural network model of vibration transmission characteristics as well as the inverse design neural network model of hull grillage metastructures are established. Results show that compared with periodic hull grillage structures, the proposed hull grillage metastructures possess significant low-frequency flexural wave vibration isolation characteristics which almost completely covers the low-frequency range from 27 Hz to 169 Hz. Both forward prediction and inverse design network models have good performance, which verifies the correctness of the intelligent design method based on deep learning, and provides a new direction for the structural design on demand of low-frequency vibration reduction of ship and offshore structures.

Experimental investigation of mechanical properties of jute/hemp fibers reinforced hybrid polyester composites

AbstractOne of the primary drawbacks associated with natural fiber reinforced composites is their relatively poor mechanical properties. One potential approach to overcome this challenge is to augment the fiber loading, thereby improving the interfacial characteristics and hybridization. In this study, hybrid polyester composite structures reinforced with jute/hemp fibers were fabricated via the hand layup process, with fiber loadings varying between 30%, 50%, and 70% by volume. Fibers were subjected to alkali solutions (NaOH) containing 3% and 5% alkali in advance of the composites' formation. The impact, flexural, and tensile characteristics of hybrid jute/hemp reinforced polyester composites were investigated via laboratory studies. The composite materials that underwent testing with a 50 vol% fiber loading and 3% NaOH exhibited the maximum tensile strength (26.6 MPa), tensile modulus (733.56 MPa), flexural strength (62.7 MPa), and flexural modulus (3.04 GPa).Highlights Hybrid polyester composite structures reinforced with jute/hemp fibers were fabricated. Hand layup method used with various fiber loadings (30%, 50%, and 70% by volume). Highest mechanical properties were obtained for 3% NaOH treatment and 50% fiber loading.

Flexural and Flammability Characteristics of Woven Jute Fabric Reinforced Vinyl Ester Treated with Ammonium Polyphosphate

The work aims to determine the optimum fire-retardant treatment for the jute/vinyl ester composites on the composites' flexural and flammability characteristics. Ammonium polyphosphate deposition in composite samples increased the thickness and weight, which led to an increase in their sample densities. The deposition of 10% ammonium polyphosphate (APP) resulted in the highest flexural strength. However, APP significantly increased the flexural modulus of all samples to the untreated sample. In terms of flammability properties, the deposition of APP increased composites' performance against fire. Incorporating 10% of APP provides good flexural and fire-retardancy properties for the woven jute/vinyl ester composites

Changes in flexural, tensile and impact characteristics of kerb concrete due to the addition of tyre-derived aggregates and polypropylene fibres

Kerb is an integral part of the roadway that provides structural support and facilitates drainage. When constructed over expansive soils, they face additional tensile stresses due to swelling and shrinkage caused by seasonal moisture variations. Tree roots can also exert additional tensile stresses that need to be absorbed by the kerb. Due to the relatively low deformation tolerance of concrete, premature failures are common. This study, a rigorous laboratory investigation, evaluates the effect of adding tyre-derived aggregate (TDA) and recycled polypropylene fibre on tensile strength, deformation tolerance, flexural toughness and impact resistance of concrete for potential use in road kerb construction. The effect of replacing natural coarse aggregates with recycled concrete aggregates has also been investigated. It has shown that TDA can improve deflection tolerance and polypropylene fibres can help resist larger tensile stresses. 5 % rubber with 0.66 % polypropylene fibres could be used as effective solutions in areas prone to expansive soil movement and tree root migrations.

Impact of weave architecture on the mechanical performance of carbon-aramid/PVB hybrid composites

Continuous fiber-reinforced thermoplastic composites having superior mechanical properties are preferred for lightweight architectures. Rising demands for enhanced mechanical performance under certain types of loadings have focused researchers toward the hybridization of composite materials. In this study carbon and aramid fibers were employed to produce hybrid fabrics by weaving in two different woven architectures, 1/1 plain and 2/1 twill. Polyvinyl butyral (PVB) matrix was reinforced with these woven fabrics and hybrid composites were fabricated by compression molding. Un-hybrid carbon and aramid composites were fabricated using PVB matrix, as control samples. Tensile characteristics of hybrid composites offered intermediate strain at failures of 0.5% due to the combined rigid and ductile natures of carbon and aramid, respectively. Flexural strength and absorbed impact energy (200 MPa and 97 kJ/m2) were higher for hybrid composites, and quick elastic recoveries were experienced in hybrid composites after impact. Plain woven reinforced hybridization had about 25% and 5% lower tensile and flexural characteristics respectively, as more interlocking zones of warp and weft yarns reduced strength. However, these interlocking zones positively contributed to impact performance by 11.5% higher energy absorption.

Effect of Benzoyl Chloride and Fiber Loading on Mechanical Properties and Biodegradation of Poly Lactic Acid/Sugarcane Bagasse Fibre Composites

This study aimed to investigate the properties of benzoyl chloride modified and unmodified poly lactic acid and sugarcane bagasse fibre composites (PLA/SCBF), as well as the impact of chemical treatment on the mechanical and biodegradation properties of these composites. In this study, Fourier Transform Infrared (FTIR) Spectroscopy was employed to examine the benzoyl chloride modified and unmodified fibre samples. Additionally, Scanning Electron Microscope (SEM) and Thermal Gravimetric Analysis (TGA) techniques were utilised to investigate the morphology and thermal behaviour of the Poly lactic/SCBF composites. The results indicate that the use of benzoyl chloride treatment resulted in an increase in the tensile, flexural characteristics, impact strength, and hardness strength. The treatment with benzoyl chloride resulted in a reduction in both water absorption and biodegradability. The research also elucidated the impact of increasing the quantity of sugar cane bagasse on the aforementioned qualities. The addition of SCBF at higher loading resulted in a decrease in the tensile strength, biodegradability, flexural strength, and impact strength. The water absorption and hardness exhibited a positive correlation with the increase in fibre loading. The observed improvement in mechanical characteristics indicates that the treatment effectively enhanced the interfacial adhesion between SCBF and the PLA matrix. The enhancement of the interfacial adhesive forces was observed by the examination of scanning electron microscopy (SEM) micrographs. The Fourier Transform Infrared (FTIR) spectrum of the treated solvent-cast bamboo fibre (SCBF) exhibited the presence of a benzoyl group attached to the fibre, indicating successful benzoyl chloride treatment. Additionally, a modest reduction in hemicellulose content was seen following the treatment. The thermal characteristics of the modified PLA/SCBF composites were found to be enhanced based on the results obtained from the TGA-DTA analysis.

Chopped carbon fibre reinforcement in high-strength concrete: Flexural characteristics

In this study, the flexural behaviour of high-strength concrete was tested with chopped carbon fibres that were 30 mm long and added in amounts of 0.2%, 0.4%, 0.6%, 0.8%, and 1%. Thirty-six prisms were evaluated experimentally for flexural strength at 28 days using an ultrasonic pulse velocity test and a flexural testing machine. X-ray diffraction and linear regression analysis were carried out to characterise crystalline material and linear correlation amongst different mixes. Increasing the number of carbon fibres in high-strength concrete led to unexpected and innovative findings, such as lower pulse velocities and improved flexural characteristics up to an optimum dosage point. In SEM images of chopped carbon fibres, debonding was the most prevalent cause of failure.

FLEXURAL AND DURABILITY CHARACTERIZATION OF CONCRETE REINFORCED WITH TREATED BAMBOO AS AN ALTERNATIVE BUILDING MATERIAL

Abstract The cost and environmental problems associated with steel as a reinforcement material in concrete has necessitated the need to research for alternative reinforcement materials, and bamboo is one of them. The flexural and durability characteristics of bamboo reinforced concrete (BRC) samples under harsh environmental condition was simulated by curing samples in an alkaline solution. Bamboo splints that were coated with sanded bitumen were used to reinforce the concrete samples with unreinforced concrete (UC) serving as control. The BRC samples were cured in normal water and an equal number were cured in 5% Sodium Hydroxide (NaOH) alkaline solution. Samples from both curing conditions and another of the control were tested for flexural strengths after 7, 14, 28, 56, and 76 days of curing respectively and results compared. Water absorption rates after each curing period were also taken. Ultrasonic pulse velocity (UPV) tests were also conducted on the samples to find out the composite qualities. The results showed that BRC had twice as much flexural strength than UC but reduced in strength by 17.9% in the alkaline environment after 28 days of curing. In addition to possessing acceptable strength values under normal water and alkaline solution curing situations by ponding, all the samples had elastic dynamic modulus and static modulus values that exceeded minimum recommended values by the relevant standards.

Flexural characteristics of a polypropylene fibre concrete topping on a precast concrete slab

Flexural characteristics of a polypropylene fibre concrete topping on a precast concrete slab

Influence of Treatments on the Mechanical Properties of Epoxy Resin Hybrid Composites Reinforced with Pineapple Fiber and Snail Shell Particulates

The growing environmental concern regarding synthetic materials in various engineering applications is driving increased research into the production of green composites. In this study, pineapple leaf fiber (PLF) and snail shell powder amended with sodium hydroxide (NaOH) solution, at concentration levels of 0, 2, 4, 6 and 8% for 30, 60 and 90 minutes, respectively, were used to produce various composite samples; and their mechanical properties tested in agreement with American Society for Testing and Materials (ASTM) International approved procedures. The laboratory test results revealed that both the NaOH concentration and treatment period considerably influenced the tensile and flexural strengths of the composite samples. It was observed that the composite samples, made with reinforcement materials modified with NaOH concentrations of 0%, 2%, 4%, 6%, and 8% for durations of 30, 60, and 90 minutes, exhibited tensile strengths of 8.12, 9.88, 11.04, 14.11, and 16.74 MPa; 10.93, 14.22, 17.04, and 15.71 MPa; and 12.27, 15.19, 14.06, and 13.84 MPa, respectively. Similarly, the results portrayed that the composite samples produced with reinforcement materials treated with 2%, 4%, 6% and 8% sodium hydroxide concentrations for durations of 30, 60 and 90 minutes, developed flexural strength of 31.98, 38.82, 43.97 and 49.03 MPa; 36.55, 44.17, 53.38 and 47.93 MPa; and 39.62, 46.08, 48.17 and 43.66 MPa, respectively. It was also interesting to observe that 6% NaOH treatment for 60 minutes yields the optimum tensile and bending strengths of 17.04 and 53.38 MPa respectively. This finding revealed the potential of using bio-composites for engineering applications, mostly where moderate tensile and flexural strengths characteristics are sought after.

Experimental study of dynamic mechanical properties and damage mechanism of textile reinforced concrete

The flexural characteristics of alkali-resistant (AR) glass textile reinforced concrete slabs (GTRC) at static-to-dynamic loading rates are investigated in the present study. The fabricated GTRC slabs were manufactured with four and six textile layers as reinforcement. Static flexural testing is conducted at 0.5 mm/min, while dynamic flexural tests are conducted at five loading velocities of 1, 2, 3, 4, and 4.5 m/s. The corresponding strain rates at selected impact velocities are 4, 8, 12, 16, and 18 s-1. Two separate mechanical setups, including (i) the MTS load frame and (ii) Instron drop-weight impact system, are used for distinct experimental testing. Furthermore, the mechanical properties of flexural strength, maximum strain, ultimate strain, flexural modulus, and toughness are calculated by using mathematical relations. In addition, failure patterns and the load-bearing intrinsic mechanisms of GTRC samples are analyzed in detail. Flexural experiments at various loading rates revealed that the loading rate and the number of reinforcing layers significantly influence the bending characteristics and mechanical properties of GTRC samples. In addition, the mechanical response is comparatively reduced at six layers of reinforcement than GTRC with four layers, proving better mechanical properties in flexural load at static and dynamic loading conditions.

Flexural wave propagation characteristics of metabeam with simultaneous acoustic black hole and local resonator

This paper studies the flexural wave propagation in a metamaterial beam with the coupled acoustic black hole and local resonators (ABHLR). The main objectives are to derive the dynamic stiffness matrix of the coupled ABHLR unit cell and analyse its wave propagation characteristics. Initially, a closed-form solution of Euler–Bernoulli’s beam with an indented acoustic black hole is derived. From this, an exact dynamic stiffness matrix, incorporating local resonator effects, is derived using the spectral element method. Dispersion diagrams are generated by combining Bloch’s theorem with ABHLR transfer matrix. The coupled effects of acoustic black hole (ABH) and local resonator (LR) on the bandgap characteristics are investigated. The coupled ABHLR metamaterial shows either a positive or negative effect on bandgap formations, depending on the parametric values of the unit cell. As a positive effect, for some parametric values, the coupled ABHLR cell simultaneously produces bandgaps at lower frequencies (LR-based) and higher frequency ranges (ABH-based). Similarly, for other parametric value, as a negative effect, the bandgaps of ABHLR cell get merged but the pass bands appear on the overlapping region. This pass-band appears due to the constructive interference of ABH and LR, on each other. However, the attenuation bandgap with a higher attenuation rate is obtained on the overlapping region due to the destructive interference of LR and ABH effect. Finally, the global stiffness matrix of a finite beam with 30 unit cells is developed to analyse the frequency domain response and the results are validated with band gap analysis of the unit cell. The frequency domain response is also validated with finite element simulations using the commercial software. Results show that ABH and LR parameters have to be optimally designed to utilize the attenuation effects and avoid constructive interference due to coupling effects. The coupling of metamaterials can aid in vibration suppression and multiple-frequency filtering in mechanical and aerospace applications.

Flexural behaviour of GFRP-reinforced concrete pontoon decks under static four-point and uniform loads

Concrete pontoon decks are subject to flexural loading actions under concentrated and uniform loads caused by self-weight, live loads, and wave actions. This study investigated the structural behaviour of concrete pontoon decks reinforced with glass fiber-reinforced polymer (GFRP) bars under static four-point and uniform loading conditions. Five large-scale GFRP-reinforced concrete decks with a length of 2400 mm, width of 1500 mm, and thickness of 125 mm were tested to evaluate their moment capacity, strain behaviour, cracking propagation, and failure mechanism. The effects of the loading configurations, reinforcement arrangement, and cutout simulating the piles' location were evaluated. The edge cut-out initiated flexural-shear cracks, causing the pontoon decks to fail at an effective bending stress 10% lower than the solid decks. Decreasing the span-to-depth ratio from 5.6 to 4.0 increased the induced shear stress of a section and caused the deck to fail by shear compression. Uniform loading resulted in an even load distribution and minimized the stress concentration around the cutout. An increase in the effective depth improved all deck flexural characteristics. The equations in ACI 4401. R-15 and CSA S806–12 provided an accurate prediction for solid decks but overestimated the ultimate flexural strength of the GFRP-reinforced concrete decks with a cutout.

A statistical analysis on effect of process parameters on tensile, flexural, and hardness characteristics of wood–polylactic acid composites using FDM 3D printing

A statistical analysis on effect of process parameters on tensile, flexural, and hardness characteristics of wood–polylactic acid composites using FDM 3D printing

Effects of fiber properties on flexural and fracture characteristics of manufactured sand concrete based on acoustic emission

Fiber-reinforced concrete (FRC) with natural sand (NS) as fine aggregate has been regarded as an favorable cementitious composites in engineering application due to its superior mechanical and fracture properties, etc. As a promising substitution for NS in conventional concrete, manufactured sand (MS) presents great potential in minimizing environmental impacts and increasing economic benefits. This paper presents the effects of fiber type (steel fiber, basalt fiber, glass fiber), fiber content (0 %, 1 %, 2 %) and fiber length (6 mm, 13 mm, 20 mm) on mechanical and fracture characteristics of manufactured sand concretes (MSCs) with 100 % replacement ratio of NS with MS. The entire fracture processes of MSCs were monitored using acoustic emissions (AE) in real time. The results showed that flexural strength of MSC increases with the addition of three different fibers, and steel fiber exhibits the best reinforcement effect. MSC with 1 % steel fiber content exhibits the highest flexural strength. Meanwhile, the longer the fiber length is, the smaller the flexural strength presents. The effects of fiber properties on AE parameters (count, b-value, information entropy) revealed that the addition of fibers reduces the fluctuation of counts and information entropy. The MSC with 2 % steel fiber content exhibits more dramatic fluctuations of b-value and information entropy after post-peak, which reveals greater internal damage in specimen. The longer the steel fiber is, the more dramatic the AE signal fluctuations and the more severe the damage inside the specimen emerge. Parametric analysis of rise angle (RA) and average frequency (AF) for classifying fracture modes (tensile and shear cracks) show that the incorporation of fibers can reduce the tensile cracks of MSC specimen under four-point bending. With the increase of fiber content, the tensile cracks first decrease and then increase. The longer fiber length is, the more tensile cracks generate during the fracture process.

Investigating the Effect of Polypropylene Fiber on Mechanical Features of a Geopolymer-Stabilized Silty Soil

This study investigates the stabilization of silty soil using alkali-activated fly ash and fibers with lengths of 3 mm and 12 mm. The study examines the effects of hybrid fiber length, fiber content, fly ash content, and activator content on the mechanical properties of the geopolymerstabilized samples. The objectives of this paper are 1) to examine the effect of activator content and fly ash content on the UCS, Al/Si ratio, and SiO2/Na2O ratio of the stabilized samples using a statistical approach, 2) to investigate the effect of hybrid fiber length on UCS, secant modulus, flexural strength, toughness, and flexural load-deformation characteristics of the stabilized soil. A statistical approach was employed to investigate the relationship between fly ash content, alkali activator content, and UCS value. Optimal fly ash content and alkali activator content were determined based on the statistical model. The geopolymer structure of the stabilized soil was characterized via SEM, EDS, XRD, and FTIR analyses. The effects of fly ash and alkali activator content on UCS, Al/Si ratio, and SiO2/Na2O ratio were determined using the derived statistical model. The study demonstrated that activator content, a critical factor in compaction, significantly influences the UCS value, as much as the effect of the Si/Al and SiO2/Na2O ratios. Additionally, variations in fly ash content led to an increase in the UCS value of up to 15%. Moreover, changing the activator content resulted in a maximum 12-fold increase in UCS value. Incorporating hybrid fibers for stabilization led to higher secant modulus (up to 30%), flexural strength (up to 6%), and ductility without compromising UCS.

Experimental investigations on mechanical properties of sisal and coir fiber reinforced hybrid bio composites

Nowadays, natural fibres have emerged as a new category of material, gradually displacing synthetic fibres in a variety of contexts. Synthetic fibres have the potential to lower the price of hybrid composites while enhancing their use with natural fibres. Coir and sisal fibres were used to create the hybrid composites in this investigation. Epoxy LY556 and Hardener HY951 were used in a hand lay-up process to create composites with alternating stacks of coir and sisal fibres. The produced composites were tested in accordance with the ASTM standards for tensile strength, flexural strength, impact strength, compression strength, water absorption, and biodegradability. The mechanical characteristics of composites were shown to be significantly influenced by the orientation of the fibres through experimentation. When compared to their angle-ply and cross-ply equivalents, unidirectional hybrid composites prove to be the superior material. Flexural and impact characteristics of hybrid composites are greatly affected by the hand lay-up method, whereas tensile strength and water absorption % are unaffected. These hybrid composites have shown promise as a lightweight load-bearing structural material, and this is something that should be noted.

Evaluation of Flexural Behavior of Prestressed Concrete (PSC) Hollow-Core Slabs (HCSs)

This study aimed to evaluate the flexural behavior characteristics of prestressed concrete hollow-core slabs (HCSs) through bending experiments. Six specimens were used as variables, both with and without reinforced concrete, in the HCS. A four-point load was applied in the form of a simple support beam to assess the flexural behavior and ultimate strength of HCS. The results demonstrate that, compared to non-reinforced specimens, the reinforced HCS exhibited higher maximum loads and better ductility performance. The experimental outcomes demonstrate that HCS showed an average of 10% higher capacity than the maximum load of the concrete structure standards (KDS 14 20 20, ACI 318-19, and PCI handbook), with or without reinforced concrete, leading to relatively safe predictions. This study’s experimental findings are anticipated to aid in evaluating structural safety in a relatively secure way. The findings indicate that the HCS structural system is excellent at sustaining the weight of a structure and ensuring its safety. Additionally, this investigation is anticipated to furnish practical guidance for optimizing the use of HCS systems in structural design and construction.

Energy-Dissipation Support Technology for Large Deformation Tunnels Based on the Post-Peak Behavior of Steel Plate Buckling: A Case Study

Large deformations can easily occur when tunneling through weak surrounding rock with high underground stresses. Under high-stress environments, the surrounding rock stores a large amount of strain energy, and the strain energy stored in the soft and weak surrounding rock enclosure is dissipated through the large traveling plastic deformation. Therefore, the effective use of the surrounding rock’s bearing capacity and energy dissipation is a feasible solution to the large deformation problem. Based on the energy principle, this study designs a high compressibility, large stroke energy-dissipation element, which transforms the traditional support into energy-dissipation support and solves the problem of large deformation by reasonably utilizing the “displacement” of the surrounding rock. The experimental results showed that the steel plate assembled structure had an initial peak value of about 15 MPa, a constant resistance of about 2 MPa with a large stroke, and a compression rate of more than 75%, with good post-compression flexural peak characteristics. Elastic–plastic buckling analyses of defective steel plate composite structures were carried out using finite element analysis software, and the deformation and force characteristics of a variety of steel plate composite structures after buckling under actual field conditions were investigated. Based on the 3D laser scanning system, the thickness of the upper and lower steel plates of the steel plate composite structure was set to 1 cm, the height of the vertical plate was set to 28 cm, and the thickness was set to 8 mm. The original rigid supporting method was converted into one of compression support by circumferentially embedding the steel plate composite structure into the initial support structure. The resulting support configuration offered a high safety factor because the pressure of the surrounding rock was released by the deformation of the steel plate composite structure.

Performance of carbon fiber (CF)/Ceiba petandra fiber (CPF) reinforced hybrid polymer composites for lightweight high-performance applications

Natural and synthetic fibers have their own advantages and disadvantages. For this reason, hybridization was performed to combine the two fibers to get composite reinforcement with high mechanical properties. It is used to synergize the two fibers aiming to create a higher performance than that of natural fiber-reinforced composites. This study used carbon fiber and natural fiber namely Ceiba petandra fiber (CPF). Compared to hybrid and CPF reinforced composites, carbon fiber (CF)-reinforced composites had superior mechanical properties, especially in terms of tensile and flexural characteristics. However, it is more brittle and expensive. In contrast, CPF composite has the lowest tensile strength, flexural quality, and abundance. The optimal value was shown in CF/CPF reinforced hybrid composites with a composition of 15 % CF and 15 % CPF, with tensile and flexural strength reaching 130.16 ± 17.37 MPa and 98.53 ± 12.2 MPa. Hybrid composite improves the thermal stability of the composite. Findings showed that incorporating natural and synthetic fibers produced composite materials with acceptable and ideal mechanical performance.