Ultimate Flexural Strength Research Articles

The effect of graphene nanoplatelet addition on the mechanical, durability and self-healing properties of engineered cementitious composites

Nanomaterial usage is an effective method to enhance the mechanical and durability properties of cementitious materials. Graphene Nanoplatelets (GNPs) are cost-efficient graphene-based nanomaterials that can exhibit graphene-like features. Although GNPs have been found to improve mechanical and durability properties, their effect on the self-healing behavior of cementitious materials, particularly Engineered Cementitious Composites (ECC), has not been examined in the literature studies. Therefore, this study aims to investigate the effects of GNP addition on mechanical, durability and self-healing behavior of ECC. During the study, the mechanical, durability, and self-healing characteristics of ECC with and without GNP were observed by using various mechanical and non-destructive test methods. Compression test, four-point bending test, resonance frequency test, ultrasonic pulse velocity test, sorptivity test, electrical impedance test and microscopic inspection were conducted. According to the test results, 0.05% GNP addition increased the compressive strength of ECC specimens. With the effect of GNP, first cracking strength, ultimate flexural strength and deformation values increased both for virgin and preloaded ECC specimens. The preloaded specimens with GNP performed similarly to virgin specimens under bending. The cracks of preloaded GNP specimens were either closed completely or extensively compared to control specimens. The crack numbers of GNP specimens after failure were also greater than that of control specimens. Accordingly, the flexural and self-healing behavior of the specimens improved with GNP addition. The effect of improvement by GNP addition was also evident in nondestructive tests. A considerable increment occurred in electrical resistance with GNP addition.

Ultimate flexural strength of rectangular concrete‐filled steel tubular beam‐columns using high‐strength materials

AbstractThe ultimate flexural strength of concrete‐filled steel tubular (CFST) beam‐columns is calculated using the full‐plastic strength as per the “AIJ Recommendations for Design and Construction of Concrete Filled Steel Tubular Structures”. However, the full‐plastic strength might overestimate the ultimate strength of rectangular CFST beam‐columns, when the width‐to‐thickness ratio is significant and/or high‐strength materials are used. The calculation of the ultimate flexural strength when it exceeds the applicable range of AIJ CFT recommendations is based on a method that considers the stress reduction on the compression side of the steel tube or outermost edge strain of the concrete. However, both stress reduction and outermost edge strain should be considered when high‐strength materials are used in CFST for accurate ultimate strength formulas. In this study, a simple evaluation method for the ultimate flexural strength of rectangular CFST beam‐columns was proposed using the maximum strain at the extreme concrete compression fiber and stress reduction on the compression side of the steel tube. In addition, the appropriate strain at the extreme concrete fiber needed to accurately calculate the ultimate strength was discussed.

Behavior of Engineered Cementitious Composites (ECCs) Subjected to Coupled Sustained Flexural Load and Salt Frost

The performance of engineered cementitious composites (ECCs) under coupled salt freezing and loaded conditions is important for its application on the transportation infrastructure. However, in most of the studies, the specimens were generally loaded prior to the freezing. The influence of sustained load was merely considered. To this end, four sustained deflection levels, i.e., 0%, 10%, 30% and 50% of the deflection at the ultimate flexural strength, and three salt concentrations (1%, 3% and 5%) were applied. Prior to the salt frost resistance test, the fluid absorption of ECC specimens under various conditions were measured. The changes in relative dynamic elastic modulus (RDEM) during the freeze-thaw cycles were captured. The depth and the content profile of free chloride were measured after the coupled sustained load and freezing and thawing cycles. It is shown that 3% NaCl solution leads to the largest deterioration in all cases. There is no visible flaking or damage occurring on the surface. The relationships between locally sustained flexural stress and RDEM loss and also locally sustained flexural stress and free chloride penetration depth were proposed and showed satisfactory results. It is concluded that when ECC is subjected to the FTCs under 1% de-ice salt solution, no depassivation of the steel is expected even under a large deflection level. In terms of 3% and 5% salt solution, the thickness of cover should be no less than 20 mm when a deflection level of 0.5 is applied.

Experimental Study and an RSM Modelling on Drilling Characteristics of the Sheep Horn Particle Reinforced Epoxy Composites for Structural Applications

Recent environmental concern has been raised about the development of biocomposites because of their low cost, eco-friendliness, and biodegradability. Machining of polymeric composite is inevitable during assembly of structural components. In view of creating holes in structural composites, drilling is necessary and it is essential to carry out research to find the optimal machining parameters. The experimental assessment and prediction of the thrust force and torque involved in drilling composites reinforced with sheep horn are presented in this work. The matrix and sheep horn particles were combined in the right proportions before being moulded and poured into a mould, then allowed to cure at room temperature. Investigated properties included ultimate tensile strength, flexural strength, and hardness. To evaluate the quality of the hole, micrographs of the drilled hole were employed. When the mixture was optimised based on the properties, it was found that a 70:30 ratio produced the best results. Thrust force and torque of 58 N and 4.8 N-mm, respectively, were observed for sheep horn filler laminates which were drilled using the combination of 6 mm diameter, 0.1 mm/rev feed rate, and 400 rpm speed. This is by far the best among the combinations used in the experiment. Additionally, the experimental outcomes indicate that the feed rate and spindle speed are the most significant factors affecting the thrust force. Since there were minimal errors in the comparison, the central composite design modelling is consummate. Overall, the extensive experimental effort offers several options to utilise this composite material in future applications across a wide range of fields.

Investigations on tensile and flexural properties of wheat straw fibre reinforced polymer composite

ABSTRACT There are needs and challenges in using natural resources to produce advanced materials with sustainability. So, in this modern time, natural fibres are used as reinforcement in composites because of their excellent properties, such as lower costs, biodegradability, lightweight, high corrosion resistance, high wear resistance, fewer health hazards and availability. However, greenhouse gases are released by the open burning of crop residues, such as wheat straw, rice straw, barley and many others, which increases global warming and declines air quality. So, in this experimental work, wheat straw fibres (WSFs) were used as natural fibres because of several factors, such as abundant availability, promoting of green composites and keeping rural areas clean (i.e. pollution-free) by reducing open burning. The same weight percentage of WSFs of different uniform mesh sizes was used with epoxy resin to fabricate the specimens for measuring the tensile and flexural properties as per the ASTM D 638 and D 790 standards. The results show that different behaviour of all specimens was observed under tensile and flexural loading. However, a specimen devoid of WSFs has the highest ultimate tensile and flexural strength, which were 25.064 MPa and 70.25 MPa, respectively.

An investigation on the effects of in vitro induced advanced glycation end-products on cortical bone fracture mechanics at fall-related loading rates

It has been suggested that adverse changes in bone quality due to the accumulation of advanced glycation end-products (AGEs) may play a role in the increased skeletal fragility. These non-enzymatic glycation mediated crosslinks are caused due to the presence of sugars in the extracellular space and can be induced in-vitro. AGEs exist naturally in bone, but with diseases such as type-2 diabetes, they are found at higher levels. While previous studies have examined the relationships between AGE accumulation and some mechanical properties, there is a lack of understanding of how AGE accumulation affects the fracture mechanics behaviour of bone tissue at fall-related loading rates. The objective of this study was to investigate the relationship between AGE accumulation and the fracture mechanics of cortical bone tissue. An in vitro glycation model was used to simulate diabetic conditions in twenty anatomically adjacent pairs of bone from a single bovine femur, which reduced the possibility of inter-specimen variability. Mechanical characterisation was carried out using 3-point bend, fracture toughness and nanoindentation testing, while bone composition was analysed by quantifying the accumulation of fluorescent AGEs. Under three-point bend testing, it was found that the yield stress, ultimate flexural strength, and secant modulus of the glycated samples were significantly higher than the controls. Furthermore, fracture toughness testing showed that the critical fracture toughness was increased by 16% in glycated samples compared to controls. These results provide no evidence that AGEs alone play a role in bone fragility at fall-related loading rates, with AGE accumulation actually found to enhance several pre- and post-yield properties of the tissue.

Investigation into the Flexural Toughness and Methods of Evaluating Ductile Concrete

The main purpose of this study was to investigate the flexural behavior of high-ductility fiber-reinforced concrete (HDC) and propose a suitable method for evaluating flexural toughness. The flexural strength, deformation, and toughness of HDC were investigated through four-point bending tests with specimens of 40 × 40 × 160 mm. The test parameters were fiber volume fractions (0%, 1%, 1.5%, and 2%), water–binder ratios (0.24, 0.26, 0.29, and 0.32), and ages (28 d and 56 d). The experimental results showed that polyvinyl alcohol (PVA) fibers led to significant improvement in the flexural behavior of HDC due to its strain-hardening behavior and excellent crack dispersion capacity. The ultimate flexural strength of HDC with 2% PVA fibers of about 15.32 MPa showed an increase of up to 221%. The deformation and flexural toughness ratios were 23 times and 1.43 times higher, respectively, than the specimens without fibers. A simple and practical method for evaluating the flexural toughness of HDC was proposed, which solved many problems with the existing methods. This method made full use of the peak load, which overcame the difficulty of identifying the initial crack information, solved the insufficient deflection limit, and provided a more comprehensive and accurate evaluation by selecting characteristic points evenly distributed throughout the loading process.

Effect of High Strength Concrete Prepared from Recycled Aggregates on the Behavior of Reinforced Concrete Beams Under Flexure

Experimental study of the flexural implementation of high-strength reinforced recycled aggregate mixture is investigated for 100 × 150 × 1000 mm beams of reinforced concrete with different coarse recycled aggregate ratios plus three steel reinforcement ratio (ρ) casting and testing at 28 days. The aim of this research is to use coarse recycled aggregate ratios as a natural coarse aggregate replacement by (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100%) in high strength concrete. Former investigations experiments have been carried out and provided on the characteristics of the mixture prepared with recycled aggregates, such as strength in compressive, workability, flexural tensile strength, and splitting tensile strength. Prism and cylinders have been prepared, and specimens have been tested at ages 7, 14, 28 days of curing. This investigation considers the flexural efficiency of reinforced recycled aggregate mixture beams in describe as cracking and ultimate flexural strength, and load-deflection correlation, the moment at mid-span, and ductility and failure modes. Results show that 100% recycled coarse aggregate degrades the concrete strength relevant to 18.0, 18.9, and 19.3%, 16.2, 16.6, and 19.4% and 16.0, 16.2, and 18.2% in expression of compressive, splitting and flexural strength with tensile for 7, 14 and 28 days, reduces the workability by 33.3% and decreases the cracking and ultimate load with the improved rate of recycled coarse aggregate regarding of 39.4 and 45.1% and 10.9% for ductility for the beams with ratio of reinforcement of ρ=0.0157%. Decreasing the reinforcement ratios with ρ=0.0105 and 0.0067% while keeping the strength of concrete constant 100% recycled coarse aggregate decreases the cracking and ultimate load of about 11.3 and 20.8% and 15.6 and 24.4% respectively and 2.0 and 4.3% for ductility.

Different Fiber Reinforcement Effects on Fly Ash-Based Geopolymer Long-Term Deflection in Three-Point Bending and Microstructure

This study investigated the effect of a low amount of polyvinyl alcohol (PVA) and steel fiber reinforcement on fly ash-based geopolymer composite long-term deflection and its microstructure. For testing purposes, specimens with different amounts and types of fiber reinforcement as well as plain (reference) were prepared. The long-term deflection test was performed by loading specimens with 40% of the ultimate flexural strength. A microstructure analysis was performed using polished section specimens, and images were acquired at 25-times magnification on a scanning electron microscope. The results of the flexural strength test show that all geopolymer composites with fiber reinforcement have lower flexural strength than plain geopolymer composites. The long-term deflection tests show that the highest deflections exhibit 1% PVA fiber-reinforced specimens. The lowest amount of deflection is for 1% steel fiber-reinforced specimens. Specific creep shows similar results to plain, and 1% steel fiber-reinforced specimens, while 1% PVA and 0.5% PVA/0.5% steel fiber-reinforced specimen exhibits the same properties. The quantitative microanalysis of the polished section further confirms the deflection results. Specimens with 1% PVA fiber reinforcement have significantly higher porosity than all other specimens. They are followed by plain specimens and 1% steel fiber, and 0.5% PVA/0.5 steel fiber-reinforced specimens have almost the same porosity level.

EXPERIMENTAL CHARACTERIZATION OF THE STRENGTH OF HAND-LAMINATED AND VACUUM BAGGED QUASI-ISOTROPIC GLASS-EPOXY COMPOSITES AGAISNT THE ISO 12215-5

Glass fibre reinforced polymer composites are the most common materials employed for the manufacturing of small crafts. Their hull construction and scantlings are governed by the ISO 12215-5. The latest version of the standard introduced a new methodology to assess the ultimate strength of composites laminates. The regression equations based on the fibre weight fraction of the former version have been replaced by a more detailed ply-by-ply analysis. However, no validation data is available to ascertain the relevance of the default ultimate strengths provided by the ISO 12215-5:2019. This paper employs destructive testing to experimentally characterize the ultimate flexural, tensile and compressive strength of a quasi-isotropic glass-epoxy laminate. Experiments were undertaken in accordance with the ISO 178 for flexural properties, the ISO 527-4 for tensile properties, and the ISO 14126 for compressive properties. Two manufacturing techniques are investigated, namely hand lamination and vacuum bagging. The former represents a cheaper and therefore more common manufacturing option, while the latter is representative of an advanced manufacturing process. The key results show that the ISO 12215-5:2019 default ultimate strengths for the quasi-isotropic composite laminate tested are (i) conservative for the ultimate flexural strength, (ii) appropriate for the ultimate tensile strength, and (iii) optimistic for the ultimate compressive strength, especially for vacuum bagged samples, with the main cause identified as the value of the ultimate compressive breaking strain for chopped strand mat. These findings provide validation data for the ISO12215-5:2019. They may inform designers, compliance assessors and policy makers in the selection of relevant factors of safety for composite structures, and it is anticipated the results may contribute to future improvements in small craft regulations.

Three point bending and tensile properties of bio‐additive polydopamine‐coated 3D printing‐based distal ulna small locking bone plates: Future need of orthopedic implants

AbstractPolylactic acid (PLA)‐based implants fabricated by 3D Printing process are biocompatible, porous in nature and light in weight. These biomimetic implants can be used as an alternative to metallic implants. However, such PLA‐based implants lack mechanical strength, limiting their application in biomedical field. In the present study, direct immersion coating technique has been used for application of polydopamine coating followed by studying the effect of input process parameters such as infill density, immersion time, speed of incubator shaker and concentration of coating solution using response surface methodology (RSM)‐based approach. Analysis of variance (ANOVA) has been applied for prediction of statistical models with respect to ultimate tensile and flexural strengths. The effect of individual process parameters has been discussed using main effect plots and the interactions occurring between significant parameters has been discussed using response surface and contour plots. From the findings, it was evident that infill density was highly significant parameter followed by immersion time, speed of incubator shaker and concentration of coating solution. Also, the mechanical properties improved with increase in infill density and immersion time. However, they initially increased and then decreased with increase in speed of incubator shaker and concentration of coating solution.

Synthesis and study of mechanical properties of polypropylene (PP)/banana nano-filler biocomposites

A novel sustainable biocomposite (Polypropylene/banana fiber) material was synthesized by using polypropylene (PP) reinforced with banana fibers (BF) with permeation of nano manganese oxide (MnO2). The different samples of the biomaterial were synthesized with varying percentages of PP, BF, and MnO2. The various mechanical properties of the developed biomaterial were studied by using suitable methodology. The maximum tensile strength is demonstrated with a fiber length of 15 mm and reinforcement of 20 % of banana fiber. The flexural strength increases with an increase in fiber loading up to 15 %, and then decreases. The ultimate flexural strength was achieved with a fiber length of 10 mm and a loading rate of 15 %. The absorption of impact energy is maximum with a fiber length of 15 mm and a loading rate of 20 %. Because of the improvement in mechanical properties with an increase in concertation of banana fiber up to a certain extent, it is concluded that this biomaterial can be used in various important applications after suitable treatment.

Behavior of Steel Beams Subjected to Bending and Shear Loading Under Localized Fire Conditions

Civil structures were designed to carry a variety of loading during their service life, including fire hazards. As a result, providing fire safety to structural members is one of the most important tasks in civil infrastructure design. Steel structural members are subject to fire-induced damage or collapse due to their high heat conductivity and quick loss of strength and stiffness qualities. Furthermore, the failure in steel beams under the combined effects of bending, shear, and fire loading is poorly understood in the literature. A present study consists of experimental investigations on the fire response of steel beams under bending and shear dominant loading. The specimens have a constant length of 1250 mm. The total depth of the specimens was changed according to the section chosen: 4 in, 6 in, and 8 in (10 cm, 15 cm, and 20 cm). The results of tests show that beams can fail suddenly due to a high drop in yield and ultimate strength of the steel beam. the increase in temperature degree reduced greatly the yield and ultimate flexural strength of the steel beams with different sizes (for all groups). This reduction reached at some times to 50% for the ultimate strength capacity of the specimen. Shear strength is also affected greatly by fire exposure and the reduction reached to about 38%. Furthermore, the design strength capacity can only tolerate loads at low temperatures. This reduction in strength was noted under flexural and shear dominant loading. Moreover, the design strength capacity can withstand against loading at low-temperature degrees only.

Experimental and numerical evaluation of the structural performance of corroded reinforced concrete beams under different corrosion schemes

The effect of steel corrosion on the structural performance of reinforced concrete (RC) beams is a complex phenomenon concerning all types of reinforcing steel (tension, compression, and shear reinforcement) which has not been fully investigated experimentally or through modelling. The parameters used in models have not been fully employed in the non-uniform corrosion of steel bar, the buckling effect of corroded compression reinforcement or bond slip at the steel to concrete interface due to the combined effects of longitudinal and shear reinforcement corrosion. The objectives of this paper are i) to experimentally investigate the effect of three corrosion schemes (tension reinforcement corrosion; tension and compression reinforcement corrosion; tension, compression and shear reinforcement corrosion) on the structural performance of RC beams through the investigation nine beams, each with dimension of 150 mm width, 200 mm height and 2100 mm length ii) to employ a finite element method (FEM) to model both the control and corroded RC beams in which non-uniform corrosion of steel bars has been modelled by varying the bar diameters and the locations of corrosion pits including the buckling effect of compressive reinforcing steel bar, iii) to propose a modified bond slip model at the longitudinal steel–concrete interface due to the combined effect of longitudinal and shear reinforcement corrosion. The experimental results show that the yield and ultimate strength of the RC beams reduced under the three corrosion schemes. The yield strength of corroded RC beams is affected by the tension reinforcement corrosion while the ultimate strength is influenced by both the tension and compression reinforcement corrosion. Shear reinforcement corrosion contributes to the reduction in flexural strength of the RC beams due to the reduction in confinement of concrete. The failure modes and the ductility of the corroded RC beams are influenced by the non-uniformed corrosion and its distribution along the steel bars. The proposed FEM demonstrates good correlation with the experimental results, with the difference in ultimate flexural strength from the FEM and the experimental test in the range of 0.1 % to about 4 % for small pitting corrosion beams and up to 10 % for critical pitting corrosion beams.

Effect of High Strength Concrete Prepared from Recycled Aggregates on the Behavior of Reinforced Concrete Beams Under Flexure

Experimental study of the flexural implementation of high-strength reinforced recycled aggregate mixture is investigated for 100 × 150 × 1000 mm beams of reinforced concrete with different coarse recycled aggregate ratios plus three steel reinforcement ratio (ρ) casting and testing at 28 days. The aim of this research is to use coarse recycled aggregate ratios as a natural coarse aggregate replacement by (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100%) in high strength concrete. Former investigations experiments have been carried out and provided on the characteristics of the mixture prepared with recycled aggregates, such as strength in compressive, workability, flexural tensile strength, and splitting tensile strength. Prism and cylinders have been prepared, and specimens have been tested at ages 7, 14, 28 days of curing. This investigation considers the flexural efficiency of reinforced recycled aggregate mixture beams in describe as cracking and ultimate flexural strength, and load-deflection correlation, the moment at mid-span, and ductility and failure modes. Results show that 100% recycled coarse aggregate degrades the concrete strength relevant to 18.0, 18.9, and 19.3%, 16.2, 16.6, and 19.4% and 16.0, 16.2, and 18.2% in expression of compressive, splitting and flexural strength with tensile for 7, 14 and 28 days, reduces the workability by 33.3% and decreases the cracking and ultimate load with the improved rate of recycled coarse aggregate regarding of 39.4 and 45.1% and 10.9% for ductility for the beams with ratio of reinforcement of ρ=0.0157%. Decreasing the reinforcement ratios with ρ=0.0105 and 0.0067% while keeping the strength of concrete constant 100% recycled coarse aggregate decreases the cracking and ultimate load of about 11.3 and 20.8% and 15.6 and 24.4% respectively and 2.0 and 4.3% for ductility.

Increasing density and mechanical performance of binder jetting processing through bimodal particle size distribution

Binder jetting is an additive manufacturing (AM) technology that has gained popularity and attention in recent years for production applications in tooling, biomedical, energy, and defense sectors. When compared to other powder bed fusion-based AM methods, binder jetting processes powder feedstock without the need of an energy source during printing. This avoids defects associated with melting, residual stresses, and rapid solidification within the parts. However, one of the challenges of this process is the relatively lower densities which impacts part density, and subsequently, sintering and mechanical properties. In this study, we investigated the influence of bimodal powder size distributions (a mixture of coarse to fine particles) as a method for increasing part density and mechanical strength, and used stainless steel (SS) 316L bimodal mixtures in this case. Four unimodal and two bimodal groups were evaluated under similar AM processing conditions for sintered density measurements and flexural strengths. Our results demonstrated that bimodal size distributions showed a statistically significant increase in density by 20% and ultimate flexural strength by 170% when compared to the highest performing unimodal group. In addition to experimental findings, reactive molecular dynamics simulations showed that the presence of finer powders along with coarser particles in the bimodal particle mixture contribute to additional bonds that are stronger across the particle interfaces. Findings from this study can be used to design bimodal particle size distributions to achieve higher density and better mechanical properties in binder jetting AM process.

Effect of Stacking Sequence on Long-Term Creep Performance of Pultruded GFRP Composites.

Pultruded glass-fibre reinforced polymer (pGFRP) composites are classified as lightweight material, which exhibit high strength-to-weight ratio for structural usage. This composite material has been applied as cross-arm members in transmission towers due to its ability in thermal and electrical insulation. However, the influence of the stacking sequence of pGFRP composite on its mechanical performance has not been fully covered in the literature to explain the long-term durability of the current cross-arm designs. The study expected to evaluate five fiber layers with various stacking sequences in terms of quasi-static and creep tests in a four-point bending mode. The creep test was performed for 1440 h (60 days). These composites were fabricated using the pultrusion process in the form of a square hollow structure. Later, it was cut into composite coupons with various sizes depending on the test conducted. The results showed that nine layers with 0°/45°/0°/−45°/0°/−45°/0°/45°/0° had the ultimate flexural strength. This stacking sequence configurations seemed to be optimally manufactured in continuous roving fibre by alternating between 0° and ±45° fiber orientations. Additionally, the S-9 pGFRP composite sample showed that it had a low-creep deflection with high elastic and apparent creep moduli in 1440 h. In terms of strength reduction factor, this configuration was recorded as the highest. The findings showed that the nine layers of pGFRP composites with alternation of 0° and ±45° fiber orientations were highly suitable for structural application at transmission towers for a long-term operation.

Hybrid Interfacial Transition Zone between Wet-On-Wet Casted Concrete-Microstructure and Mechanical Properties.

The manufacture of elements containing two types of concrete allows for the minimization of the amount of Portland cement by matching the properties of concrete with local structural and durability requirements. The most common production method of the hybrid element is wet–on–hard and wet–on–wet. Casting wet–on–dry is the most common approach while casting wet–on–wet has been used mostly for concrete overlays and screeds. The study focuses on the wet–on–wet method but is applied in the production of vertical and horizontal elements. Bond-behavior and micro properties of the wet–on–wet casting interface of ultra–high–performance concrete (UHPC)–normal strength concretes are investigated. The obtained results indicate the formation of a hybrid interfacial transition zone between the two types of casted concrete. The binder matrix located in this zone appeared to combine properties of both used concrete. Porosity, phase composition, and presumably also strength, changed gradually. Furthermore, despite significant differences in shrinkage, no microcracking or delamination was observed in that zone. The ultimate flexural and compressive strength of the produced elements were either equal to the stronger concrete or were higher than the weaker of the used concrete.

Flexural Strength of Concrete Beams Made of Recycled Aggregates: An Experimental and Soft Computing-Based Study

The implementation of recycled concrete aggregates (RCAs) in the construction industry has been highlighted in the literature recently. This study aimed to propose an intelligent model for predicting the ultimate flexural strength of recycled reinforced concrete (RRC) beams. For this reason, a database comprising experimental tests on concrete beams was compiled from the literature. Additionally, two experimental tests were performed in the laboratory to enhance the aforementioned database. The flexural test results showed a 10% reduction in flexural strength when the RRC beam was tested instead of a conventional beam (constructed with natural aggregates). Nevertheless, an artificial neural network (ANN) improved by particle swarm optimization (PSO), as well as an imperialist competitive algorithm (ICA), were utilized for developing the predictive model. The inputs of the hybrid predictive models of flexural strength were the beam geometrical properties, reinforcement ratio, RCA percentage, compressive strength of concrete, and the yield strength of steel. The overall findings (e.g., correlation coefficient values of 0.997 and 0.994 for the testing data) showed the feasibility of the PSO-based ANN predictive model, as well as the ICA-based ANN predictive model in the flexural assessment of RRC beams. Furthermore, comparing the prediction performances of PSO-based ANN with ICA-based ANN and the conventional ANN showed that the PSO-based ANN model outperformed the predictive model built with the conventional ANN and the ICA-ANN.

Polylactic acid‐based composite using fused filament fabrication: Process optimization and biomedical application

AbstractBiopolymer‐based composites, which are being employed extensively in biomedical applications have exceptional physical and mechanical properties. However, printing composites is a challenging task for biomedical applications. The current work highlights the impact of process parameters of fused filament fabrication (FFF) technology, that is, layer height, number of loops, nozzle temperature, and a nonprocess parameter, that is, weight percentage of alumina on ultimate tensile strength, ultimate flexural strength, and ultimate compression strength of polylactic acid (PLA)‐alumina composite. Response surface methodology (RSM) has been implemented to construct the tests. The regression model demonstrated how various parameters and their interaction affected output responses. The surface plots for noticeable interactions have also been plotted. The outcome revealed that parameter control and optimization have vital impact on mechanical properties. The optimum value for maximum mechanical strengths has been obtained at layer height 0.1 mm, number of loops 4, nozzle temperature 195°C, and weight percentage of alumina as 1.5%. Later a case study has been performed with obtained optimized parameters with porous structures for biomedical applications and found that the properties such as surface finish, and dimensional accuracy were unaltered during the optimization process.