Flexural Mechanical Properties Research Articles

Study on the tensile and flexural mechanical properties of TRE in freezing-thawing environments

Through tensile and four-point bending experiments, the effects of different freezing-thawing environments, freezing-thawing cycles, textile layers and types, textile surface treatment, and PVA fibre content on the tensile and bending mechanical properties of TRE were studied in freezing-thawing environments. The test results show that under the action of freezing-thawing cycles, the mechanical properties of the TRE specimens in sulfate-chloride solutions were significantly reduced. With the number of freezing-thawing cycles increases, the tensile and flexural mechanical properties of the TRE specimens presented a notable decreasing trend. The ultimate tensile stress and ultimate bending load of the double-layer textile TRE specimens were higher than those of the single-layer textile TRE specimens, but the ultimate tensile strain and ultimate mid-span deflection were decreased. Compared with carbon-glass textile-reinforced TRE specimens, the tensile and bending mechanical properties of the TRE specimens reinforced with basalt-glass textile were significantly reduced. The ultimate tensile stress and flexural load of the TRE specimens impregnated by epoxy resin and covered with sand decreased, while the ultimate tensile stress and ultimate mid-span deflection increased. When the PVA fibre content was increased from 1.0% to 2.0%, the tensile and flexural mechanical properties of the TRE specimens were also improved.

Influence of Sodium Hydroxide (NaOH) Treatment on Mechanical Properties and Morphological Behaviour of Phoenix sp. Fiber/Epoxy Composites

The purpose of this present research work is to assess the static and dynamic mechanical properties of an eco-friendly natural cellulosic fiber (Phoenix sp.) reinforced epoxy composites. The cellulosic fiber was isolated from Phoenix sp. plant petioles, and it was treated with various concentrations of sodium hydroxide (5, 10, 15 and 20%) solution. The impact of treatments on tensile, flexural, impact and dynamic mechanical properties of the fabricated composite was explored and optimized. Moreover, the mechanically tested samples were subjected to morphological analysis to predict the failure mechanisms. The outcomes revealed that the treated fibers had good interfacial bonding with epoxy matrix (confirmed through morphological and single fiber pull-out studies), reduced the failure mechanisms (fiber pull-outs and fiber debonding) and exhibited good static and dynamic mechanical properties of composite materials than untreated fiber composites. It is concluded that composites fabricated using 15% of sodium hydroxide treated fiber could be used to manufacture automotive panels and other lightweight industrial products.

Flexural Mechanical Properties of Natural Fibre Reinforced Polymer Composites — A Statistical Investigation

The objectives and novelty of this paper are to create a hybrid-natural fibre composite by the Response Surface Methodology RMS technique, and then compared this hybrid composite with the individual fibre reinforced composites in the bending test. The first aim of this study is devoted to analyse, modelize and optimise the various independent variables such as the type of fibres (X1), the types of chemical treatment (X2), the volume fraction of fibre (X3) and the treatment duration (X4) used on the output parameters which are the mechanical characteristics namely, ultimate flexural stress and flexural modulus in the bending test using a Box-Behnken experimental design. Mathematical models for ultimate flexural strength and flexural modulus were developed using the response surface methodology (RSM). These models would be helpful in selecting independent variables in order to maximize the flexural mechanical properties. Statistical analysis of the results showed that selected variables had a significant effect on the flexural properties, except the treatment time that has a very weak significance effect on the flexural properties. In the second section, the impact behaviors of the natural hybrid composites found by the RMS method were confirmed experimentally. Finally, the experimental results indicate that the flexural properties of the natural hybrid composites increase with an increase in the composition of jute fibres.

Enhancing the mechanical and water resistance performances of bamboo particle reinforced polypropylene composite through cell separation

Abstract It is frequently observed that bamboo particle composites (BPCs) do not show higher mechanical performances than the corresponding wood particles composites (WPCs), although bulk bamboo is much stronger than wood in mechanical performances. Herein this phenomenon was demonstrated from the cell compositions in the applied bamboo particles. To address that, a simple method to physically separate bamboo fibers (BFs) and bamboo parenchyma cells (BPs) from a bamboo particle mixture was developed. Polypropylene (PP) composites with pure BFs, BPs, a mixture of BFs and BPs (BFs + BPs), wood particles (WPs) as fillers were prepared. The flexural and dynamic mechanical properties, water absorption, and thermal properties were determined. The BF/PP composites showed the best mechanical performances (MOR at 35 MPa, MOE at 2.4 GPa), followed by WP/PP, (BF + BP)/PP, and BP/PP. They also exhibited the lowest water absorption and thickness swelling. Little difference was found for the thermal decomposition properties. However, a lower activation energy of BF/PP compared with BP/PP implied an uneven dispersion of BFs and weaker interfacial interaction between BF and PP. The results suggest that the mechanical performances and water resistance of bamboo particle/polymer composites can be significantly improved through cell separation. However, interface modification should be applied if higher performances of BF/PP composites are required.

Effect of hot water on the mechanical performance of unidirectional carbon fiber-reinforced nylon 6 composites

One of the major concerns of carbon fiber-reinforced nylon 6 composites (CF/Nylon 6) is its sensitivity to environmental degradation, especially hygrothermal aging. In this study, neat nylon 6 plates and unidirectional CF/Nylon 6 laminates with different fiber orientations manufactured by hot compression method were subjected to water absorption tests by immersing them in 80 °C and 98 °C hot water for various time durations. The corresponding flexural mechanical properties, including the flexural modulus and flexural strength, of the as-prepared samples before and after water absorption were evaluated by using three-point bending tests. The effects of immersion time, fiber orientation, and water temperature on the flexural properties are discussed. Flexural cyclic tests were conducted to evaluate the stiffness degradation of neat nylon 6 and unidirectional CF/Nylon 6 laminates. Optical observation and scanning electron microscopy were used to observe the fracture behavior of unidirectional CF/Nylon 6 laminates before and after water absorption. Results indicated that the flexural modulus and strength of unidirectional CF/Nylon 6 laminates in different fiber orientations decreased by ≈ 8%–60% and ≈40%–60% after hot water immersion, which was mainly caused by the weakened matrix (the cleavage reaction of the main chain and plasticization of the matrix) and weakened interfacial properties (attack on the interface by hot water). The fracture behavior of 0° CF/Nylon 6 laminates after water immersion tended to be more ductile than those without hot water immersion.

A computational approach to design moisture-resistant wood polymer composites

This work computationally predicts the onset of moisture-induced damage for different wood polymer composite (WPC) formulations using an experimentally validated micromechanical model. For model validation, the flexural mechanical properties of a commercially available WPC were experimentally obtained after exposure to either moisture or combined moisture and freezing conditions. As expected, exposure caused a loss in mechanical properties, which was primarily attributed moisture-induced damage and not further exacerbated by freezing. Once validated, the model was used to predict that the WPC would incur damage when placed in a commonplace 40–45 % relative humidity environment. This work demonstrates that computational simulations can be used to design moisture-resistant WPC formulations given specific environmental conditions (i.e., relative humidity, temperature) of the intended target application.

Acrylic Bone Cements Modified with Graphene Oxide: Mechanical, Physical, and Antibacterial Properties.

Bacterial infections are a common complication after total joint replacements (TJRs), the treatment of which is usually based on the application of antibiotic-loaded cements; however, owing to the increase in antibiotic-resistant microorganisms, the possibility of studying new antibacterial agents in acrylic bone cements (ABCs) is open. In this study, the antibacterial effect of formulations of ABCs loaded with graphene oxide (GO) between 0 and 0.5 wt.% was evaluated against Gram-positive bacteria: Bacillus cereus and Staphylococcus aureus, and Gram-negative ones: Salmonella enterica and Escherichia coli. It was found that the effect of GO was dependent on the concentration and type of bacteria: GO loadings ≥0.2 wt.% presented total inhibition of Gram-negative bacteria, while GO loadings ≥0.3 wt.% was necessary to achieve the same effect with Gram-positives bacteria. Additionally, the evaluation of some physical and mechanical properties showed that the presence of GO in cement formulations increased wettability by 17%, reduced maximum temperature during polymerization by 19%, increased setting time by 40%, and increased compressive and flexural mechanical properties by up to 17%, all of which are desirable behaviors in ABCs. The formulation of ABC loading with 0.3 wt.% GO showed great potential for use as a bone cement with antibacterial properties.

High Temperature Mechanical Properties of a Vented Ti-6Al-4V Honeycomb Sandwich Panel.

For aerospace applications, honeycomb sandwich panels may have small perforations on the cell walls of the honeycomb core to equilibrate the internal core pressure with external gas pressure, which prevent face-sheet/core debonding due to pressure build-up at high temperature. We propose a new form of perforation on the cell walls of honeycomb sandwich panels to reduce the influence of the perforations on the cell walls on the mechanical properties. In this paper, the high temperature mechanical properties of a new vented Ti-6Al-4V honeycomb sandwich panel were investigated. A vented Ti-6AL-4V honeycomb sandwich panel with 35Ti-35Zr-15Cu-15Ni as the filler alloy was manufactured by high-temperature brazing. The element distribution of the brazed joints was examined by means of SEM (scanning electron microscopy) and EDS (energy-dispersive spectroscopy) analyses. Compared to the interaction between the face-sheets and the brazing filler, the diffusion and reaction between the honeycomb core and the brazing filler were stronger. The flatwise compression and flexural mechanical properties of the vented honeycomb sandwich panels were investigated at 20, 160, 300, and 440 °C, respectively. The flatwise compression strength, elastic modulus, and the flexural strength of the vented honeycomb sandwich panels decreased with the increase of temperature. Moreover, the flexural strength of the L-direction sandwich panels was larger than that of the W-direction sandwich panels at the same temperature. More importantly, the vented honeycomb sandwich panels exhibited good compression performance similar to the unvented honeycomb sandwich panels, and the open holes on the cell walls have no negative effect on the compression performance of the honeycomb sandwich panels in these conditions. The damage morphology observed by SEM revealed that the face-sheets and the brazing zone show ductile and brittle fracture behaviors, respectively.

Improved Interlaminar Fracture Toughness and Electrical Conductivity of CFRPs with Non-Woven Carbon Tissue Interleaves Composed of Fibers with Different Lengths.

Non-woven carbon tissue (NWCT) with different fiber lengths was prepared with a simple surfactant-assistant dispersion and filtration method and used as interleaving to enhance both delamination resistance and electrical conductivity of carbon fiber reinforced plastics (CFRPs) laminates. The toughing effect of NWCT on both Mode I and Mode II interlaminar fracture of CFRPs laminate is dependent on length of fibers, where the shorter carbon fibers (0.8 mm) perform better on Mode I interlaminar fracture toughness improvement whereas longer carbon fibers (4.3 mm) give more contribution to the Mode II interlaminar fracture toughness increase, comparing with the baseline composites, and the toughness increase was achieved without compromising of flexural mechanical properties. More interestingly, comparing with the baseline composites, the electrical conductivity of the interleaved composites exhibited a significant enhancement with in-plane and through-the-thickness direction, respectively. Microscopy analysis of the carbon tissue interleaving area in the laminate indicated that carbon fibers with shorter length can form into a 3D network with more fibers aligned along through-the-thickness direction compared with longer ones. The shorter fibers thus potentially provide more effective fiber bridges, pull-out and matrix deformation during the crack propagation and improve the electric conductivity significantly in through-the-thickness direction.

Assessing the effect of PLA, cellulose microfibers and CaCO3 on the properties of starch-based foams using a factorial design

The effect of polylactic acid (PLA), cellulose microfibers (CEL), and calcium carbonate (CaCO3) on the equilibrium moisture content (EMC), density and flexural mechanical properties of starch-based bio-foams was studied using a full factorial design 23. Also, a moisture aging study was carried out. The results show the three factors studied changed the bio-foams morphology, contribute to density increment, enhance dimensional stability and improve both the moisture resistance and the mechanical flexural properties. The moisture aging studies show that, although the flexural mechanical properties decrease with increasing humidity, the bio-foams exceed the mechanical properties of commercial expanded polystyrene (EPS) trays. These findings suggest the bio-composites could be used in regions where the humidity conditions are moderate to very humid, guaranteeing their dimensional stability and functional properties. Thus, these new bio-foams are an attractive and sustainable option to replace the non-biodegradable EPS commercial trays.

Mechanical and Electrical Properties Investigation of 3D-Printed Acrylonitrile–Butadiene–Styrene Graphene and Carbon Nanocomposites

Acrylonitrile–butadiene–styrene (ABS) nanocomposite filaments for 3D-printing were produced by melt compounding and extrusion. Two types of nanoadditives were employed: (a) graphene nanoplatelets (GnP) at various concentrations and (b) carbon nanotubes (CNTs). Fused filament fabrication (FFF) 3D printer was used for the fabrication of specimens, according to international standards to be employed for the determination of the tension and flexural mechanical properties of the specimens and the correlation with their microstructure. Nanocomposite filaments were also tested in tension, to evaluate the effect of 3D printing on the material. Moreover, the electrical properties of the specimens were also determined. As found out, a decrease in the tensile strength, the tensile modulus of elasticity, the flexural strength, and the flexural modulus of elasticity can be observed with the increase in the GnP concentration, in every case. ABS specimens filled with CNTs exhibited higher tensile and flexural strength and a more brittle behavior when compared to pure ABS and ABS with GnP. Regarding the electrical properties of the composites, it was found that dielectric constant increases by increasing GnP content, the specimens remaining at the same time rather nonconductive, even at a concentration of 10 wt.% in GnP. In contrast, ABS filled with CNTs at a concentration of 10% illustrated a large conductivity.

Experimental Cold-Cured Nanostructured Epoxy-Based Hybrid Formulations: Properties and Durability Performance.

Different hybrid epoxy formulations were produced and cold-cured, monitoring the properties development during low temperature curing and aging. All systems were based on silane functionalized bis-phenol A (DGEBA) resins (Part A), cured at ambient temperature with two amine hardeners (Part B). The different components of the formulations were selected on their potential capability to bring about enhancements in the glass transition temperature. The durability of the produced hybrids was probed in comparison to the corresponding neat epoxies by monitoring changes in glass transition temperature (Tg) and flexural mechanical properties after exposure to different levels of humidity and immersion in water and at temperatures slightly higher than the local ambient temperature, in order to simulate the conditions encountered during summer seasons in very humid environments. The thermal degradation resistance of the hybrid systems was also evaluated by thermogravimetric analysis.

Effect of free-volume holes on static mechanical properties of epoxy resins studied by positron annihilation and PVT experiments

The tensile, flexural, and fracture toughness properties of seven chemically different amine-cured epoxy resins were studied. Positron annihilation lifetime and pressure–volume–temperature (PVT) experiments were performed on each epoxy resin to characterize the average size and fraction, respectively, of free-volume holes. A negative correlation between hole fraction and hole size was revealed for these chemically different epoxy resins. Better tensile and flexural mechanical properties (higher tensile modulus and lower tensile strain at break; higher flexural modulus, higher flexural strength, and lower flexural strain at break) were clearly observed for epoxy resins with smaller hole size and higher hole fraction. However, no clear relationship between fracture toughness and hole properties was found. The correlations between (tensile and flexural) static mechanical properties and hole properties for chemically different epoxy resins should provide guidance for further improvements in the mechanical properties of carbon-fiber-reinforced polymers.

The Effect of Fibre Length on Flexural and Dynamic Mechanical Properties of Pineapple Leaf Fibre Composites

The present paper deals with the effect of loading different pineapple leaf fibre (PALF) length (short, mixed and long fibres) and their reinforcement for the fabrication of vinyl ester (VE) composites. Performance of PALF/VE composites was investigated through three-point bending flexural testing and viscoelastic (dynamic) mechanical properties through dynamic mechanical analysis (DMA). DMA results revealed that the long PALF/VE composites displayed better mechanical, damping factor and dynamic properties as compared to the short and mixed PALF/VE composites. The flexural strength and modulus of long PALF/VE composites were 113.5 MPa and 14.3 GPa, respectively. The storage (E′) and loss (E″) moduli increased to 2000 MPa and 225 MPa respectively for PALF/VE composites. Overall result analysis indicated that increasing the length of the reinforcement fibre results in satisfactory mechanical performance and dynamic properties of composites.

Flexural Behavior and Mechanical Properties of Steel Fibers Ferro Geopolymer One Way Slabs Mortar

Flexural Behavior and Mechanical Properties of Steel Fibers Ferro Geopolymer One Way Slabs Mortar

Mechanical, elution, and antibacterial properties of simplex bone cement loaded with vancomycin

Prosthetic joint infection (PJI) is one of the most devastating failures in total joint replacement (TJR). Infections are becoming difficult to treat due to the emergence of multi-drug resistant bacteria. These bacteria produce biofilm on the implant surface, rendering many antibiotics ineffective by compromising drug diffusion and penetration into the infected area. With the introduction of new antibiotics there is a need to create benchmark data from the traditional antibiotic loaded bone cements. Vancomycin, one of the commonly used antibiotics, shows activity against Methicillin-resistant Staphylococcus aureus (MRSA) and S.epidermidis. In our study, vancomycin added to bone cement was evaluated for elution properties, antimicrobial properties, and mechanical properties of the bone cement. Vancomycin at five different loading masses (0.125, 0.25, 0.5, 1.0 and 2.0 g) was added to 40 g of Simplex™ P cement. Addition of vancomycin affected the mechanical properties and antimicrobial activity with significant differences from controls. Flexural and compression mechanical properties were compromised with added vancomycin. The flexural strength of samples with added vancomycin of 0.5 g and greater were not greater than ISO 5833 minimum requirements. 2.0 g of vancomycin added to bone cement was able to eliminate completely the four bacterial strains tested. 2.0 g of vancomycin also showed the highest mass elution from the cement over a 60-day period. Given the reduced flexural strength in samples with 0.5 g and greater of added vancomycin and the inability of vancomycin in amounts less than 2.0 g to eliminate bacteria, this study did not find an ideal amount of vancomycin added to Simplex™ P that meets both strength and antibacterial requirements.

A multi-scale method for predicting ABD stiffness matrix of single-ply weave-reinforced composite

Single-ply weave-reinforced composites (SWRC) with asymmetric large textile unit cells are increasingly used in thin-walled aerospace structures because of the high specific stiffness than the plain weave-reinforced composites. The microstructural heterogeneity makes SWRC possess different tensile, flexural, shear and torsional mechanical properties, enabling the ABD stiffness matrix in classical laminate theory (CLT) to become a suitable candidate for the description of homogenized properties. As CLT is limited for SWRC, a multi-scale method to predict the homogenized ABD matrix is concentrated in the paper, and the whole process is captured through the single-ply broken twill 1/3 weave-reinforced composite. The representative volume element is generated with realistic internal geometry, and the periodic boundary conditions are extended to include the rotational degrees of freedom. The asymmetric weave architecture makes the neutral plane shift from the midplane, if this is not considered, the inaccurate coupling effects arise and the calculation error of tensile modulus reaches 35.9%. The obtained ABD matrix is macroscopically similar to those from two-ply cross-ply [0/90] laminate with only two small entries B12 and B21 in the B coupling matrix. The predicted values agree well with experimental results, and the reasonable strain distributions under various deformations are addressed thoroughly.

Dynamic mechanical properties of epoxy based PALF/basalt hybrid composite laminates

The focal point of this study is the usage of Pine apple leaf fiber (PALF) from the agricultural waste to produce epoxy based composites and to gauge the hybridizing effect and stacking sequences on the performance of PALF (P)/basalt (B) fiber composites, specifically their static and dynamic mechanical properties. High modulus unidirectional basalt fabric layers were added to PALF composite to achieve better specific properties and to retain its damping properties. Pure PALF, pure basalt and PALF/Basalt hybrid laminates of approximately constant thickness were prepared using the hand layup method followed by compression moulding technique. Properties like, tensile, flexural and dynamic mechanical properties of these composite laminates were experimentally assessed as per ASTM standards. From the outcomes it is exhibited that hybridization of PALF with basalt fibre improves the tensile, flexural and dynamic mechanical properties. Furthermore, the hybrid composite with basalt as skin exhibited better properties than PALF as skin.

Bending shape memory behaviours of carbon fibre reinforced polyurethane-type shape memory polymer composites under relatively small deformation: Characterisation and computational simulation

Shape memory polyurethanes (SMPU) have been of great interest in biomedical applications because of their unique ability to recover a primary shape by external actuation. This advantage can allow for easy suture and minimum tissue damage caused by surgery. Since SMPU suffer from low stiffness and low strength, carbon fibres have been widely used to reinforce SMPU, and their shape memory properties have been investigated using thermomechanical tensile tests. In reality, however, bending situations are more common than tensile situations, such as human skulls. In this study, carbon fibre reinforced SMPU (CF/SMPU) composites were studied as promising cranial implants that can offer shape memory properties, shape flexibility and high strength. First, the basic properties of pristine SMPU and CF/SMPU composites were characterised, including glass transition temperature (Tg), the viscosity of SMPU, the morphology of CF/SMPU, and their tensile and flexural mechanical properties. Then, a new method using rheometer was developed to study the shape memory behaviours of SMPU and CF/SMPU with three-point bending under relatively small deformations (≤1%), including flexural stress during programming and cooling, and bending recovery force during shape recovery. Finally, due to the invisibility of recovery process that was conducted in an enclosed temperature-controlling chamber of rheometer, the finite element method (FEM) was used to simulate the bending recovery test. The results showed carbon fibres significantly enhanced the mechanical properties (Young's modulus and flexural modulus) of SMPU. In terms of bending shape recovery, compared to pristine SMPU, CF/SMPU composites obtained substantially higher flexural stress during programming and cooling processes, and larger, more stable recovery force during recovery. The FEM results consolidated the peak recovery force of SMPU and the continuously growing recovery force of CF/SMPU as the temperature increased. Our findings on the improved mechanical and shape memory properties can provide a solid foundation for the potential applications of CF/SMPU composites as cranial implants.

Constrained Mixture Design to Optimize Formulation and Performance of Foams Based on Cassava Starch and Peanut Skin

Foams composed of cassava starch, peanut skin, and glycerol were developed by thermal expansion process. A constrained mixture design was applied to evaluate the effect of components on flexural mechanical properties and water absorption capacity (WAC). The interaction between cassava starch and peanut skin exhibited a significant antagonistic effect in WAC. Effects of the concentration of cassava starch, glycerol and the interactions between cassava starch–glycerol and peanut skin–glycerol were significant to mechanical properties. Desirability function was applied to optimize the formulation in order to obtain less hydrophilic, more flexible and more resistant foams. Optimized formulation consisted of 23.71% (w/w) peanut skin and 12.68% (w/w) glycerol, based on solids content (cassava starch + peanut skin). Optimized foam showed experimental values similar to those predicted, validating the fitted models for defined constraints. This foam showed an important improvement in hydrophilicity indicated by a decrease in WAC, compared to cassava starch-based foams without peanut skin.