Flexural Mechanical Properties Research Articles

Effect of Thermal Aging on Mechanical Properties and Morphology of GF/PBT Composites.

The effects of thermal aging at 85~145 °C in air on the tensile and flexural mechanical properties of 20% glass fiber (GF)-reinforced commercial grade polybutylene terephthalate (PBT) composites were studied. The results showed that as the aging temperature increased, the tensile and flexural strength of the GF/PBT composites significantly decreased. However, the elastic modulus of the composites was almost independent of aging. As the aging temperature increased, the separation between GF and the PBT matrix became more pronounced, and the fibers exposed on the surface of the matrix became clearer and smoother, indicating a decrease in interfacial adhesion between the PBT matrix and GF. The reason for this decrease in strength and brittle fracture of composites is the interface damage between the GF and PBT matrix caused by the difference in their thermal expansion coefficients during thermal aging.

12-Month flexural mechanical properties of conventional and self-adhesive flowable resin composite materials.

The aim of this study was to investigate the 12-month flexural mechanical properties of 23 flowable resin-based composites (FRBC) that included 5 self-adhesive FRBC materials. Specimens were evaluated following ISO 4049:2019 guidelines, but additionally stored in physiologic 0.2M phosphate buffered saline solution being tested at 24 h, 1 week, 1 month, and at 3-, 6-, 9-, and 12-months. While some deviation and degradation were noted at testing intervals, conventional FRBC materials overall demonstrated greater flexural strength than the self-adhesive and compomer materials. Three self-adhesive materials and the compomer were below recommended ISO 4049:2019 flexural strength values at 24 h with another after 6 months storage. Conventional FRBC materials, except at 1 month, overall demonstrated increased flexural modulus than the self-adhesive FRBC materials. Although results were material dependent, conventional FRBC materials demonstrated overall greater flexural mechanical properties as compared to the self-adhesive FRBC materials and the compomer evaluated.

HDPE/Cherry Tree Fiber Composites: Size Particle Effect in the Flexural Mechanical Properties.

HDPE/Cherry Tree Fiber Composites: Size Particle Effect in the Flexural Mechanical Properties.

Effect of multi-walled CNTs polyurethane mats lamination with basalt fabrics reinforced-epoxy composites reviewed on tension and bending properties

Material technology continues to develop with various innovations and engineering to improve weaknesses in both mechanical and physical properties. In this study, electrospun fibres containing a multi-wall blend of CNT and Polyurethane (PU) with or without surfactant that laminated into a basalt fibre-reinforced composite were uniquely demonstrated. Multi-wall CNT 3wt% was added to the PU/MEK/DMF solution and produced using an electrospinning process. PU fibre mat containing 3wt% CNT was made without and with surfactants. Also, Basalt fibre reinforced epoxy composite as a control sample was produced. In addition, vacuum-assisted resin transfer printing has been used in the manufacture of composite panels containing both fibres. The aim of combining basalt fibre and PU CNT spun mats was to investigate their effect on the tensile and flexural mechanical properties. Tensile and flexural tests were carried out on a universal testing machine (UTM) in accordance to ASTM D 638 and ASTM D790 standards. FESEM and TEM on composite morphology test were done after testing. The results indicated that the basal matting fibre-reinforced epoxy composites stacked by PU mats with or without surfactants were affected by CNT inclusions. Nanofiber spun mats laminated in a basalt fibre composite lead to a considerable increase in both loads (i.e. tensile and flexural properties). The highest tensile and flexural load values occurred in the BF+PU-mat-2 sample with triton-x 100 surfactants compared to BFRP. The increase in tensile and flexural modulus values was at 13% and 17.3%, respectively. On the other hand, there was a decrease in shear failure due to tensile and bending loads due to the brittleness of the composite reinforcement. In conclusion, this CNF-mat lamination is highly suitable to be used to improve the strength properties of BFRP composites. It is highly recommended for automotive parts, marine compartments and storage insulation.

Bio-Based White Eggshell as a Value-Added Filler in Poly(Lactic Acid) Composites

Based on its positive environmental impact, poly(lactic acid) (PLA) has been a gradual substitute for synthetic plastics used in diverse applications. The use of industrial limestone (ILS) as a filler in polymers can have advantages of changing the properties of pure polymers. Waste eggshells (WE) can be seen as an alternative filler to ILS as they are also a source of calcium carbonate. To assess the feasibility of both filler types and sizes, PLA composites were manufactured by injection molding with filler contents of 5, 10, and 20 wt.%. Tensile, flexural, and impact mechanical properties were evaluated in addition to water absorption. One-way analysis of variance (ANOVA) was performed to determine whether statistically significant differences among the measured mechanical properties existed. Scanning electron microscopy (SEM) was used to view the morphology of the fillers and fractured surfaces. The composite tensile strengths and flexural strengths performed the best when filler loadings were 5 wt.% and 10 wt.%, respectively, for both filler types. The tensile and flexural modulus both increased with filler loadings. The impact strength for the composites was obtained at a threshold level of 5 wt.% filler loadings for both filler types and slightly better for smaller particles sizes. ANOVA identified statistically significant differences for the mean mechanical property values evaluated. SEM showed the fractured surfaces of the PLA composites were different from the pure PLA indicating some transformation occurred to the matrix. The weight gains due to water absorption were observed to increase with increase in content of both filler types while the smaller particles had slightly higher water weight gains. Although the composites containing ILS fillers had somewhat enhanced mechanical properties over the WE-filled composites, the end application will dictate which filler type to use in PLA.

Anisotropy attenuation of reconstituted bamboo lumber by orthogonal layup process

Current reconstituted bamboo lumber materials have significant anisotropy as the strength along the fiber is much stronger than that perpendicular to the fiber, which will bring a lot of mechanical limitations in actual applications. A new kind of cross laminated bamboo (CLB) was designed and four-point bending properties of this CLB were investigated. Flexural mechanical properties of the CLB and traditional parallel bamboo strand lumber (PBSL) were tested both parallel to and perpendicular to the fiber direction to explore the effect of the cross-laminated structure in reducing the anisotropy of bamboo products. The ratio of the parallel strength (0°) to the transverse (90°) is reduced from 8.32 of the PBSL to 1.52 of the CLB in bending. A laminated composite theory with strain failure criterion was developed and consistently predicts the flexural failure of the CLB. With balanced mechanical properties in all directions, the new CLB could be widely applied as plated structures in building engineering.

Screw Extrusion Additive Manufacturing of Carbon Fiber Reinforced PA6 Tools

The creation of tools by additive manufacturing is becoming increasingly convenient for CFRP one-off and small batch production. Screw extrusion additive manufacturing of thermoplastic polymers has boosted the development of large format manufacturing solutions. Interlayer adhesion and anisotropic properties of a 3D printed part are indisputably key aspects of tool manufacturing process. In this study, thermal and mechanical properties of large format 40% carbon fiber reinforced polyamide 6 3D printed tools were determined. Moreover, the influence on part performance of two main printing parameters, deposition temperature and extruding pressure, was analyzed with respect to polymer melt rheology. The printed material revealed a highly anisotropic thermal and mechanical behavior associated with the alignment of the high carbon fiber content. The optimal process window was identified in terms of substrate deposition temperature. Along the print direction, no major impact on tensile and flexural mechanical properties was detected, while the injection molding values were exceeded by approximately 10%. The layer adhesion was estimated by measuring the stress at break on transversely Z-oriented specimens. Higher deposition temperatures and pressures, combined with lower viscosity, promote wetting and bond formation between layers, ultimately leading to more consistent performances. The best results in the transverse direction were achieved between 140 and 160 °C, reaching roughly a fifth of the longitudinal values. A significant drop in performance was detected below 120 °C, which was identified as the minimum process temperature. A post-process annealing heat treatment was also investigated, no beneficial outcomes were reported.

Flexural mechanical properties of Ti-6Al-4V multilayer micro-lattice biomaterials for skull repair

Flexural mechanical properties of Ti-6Al-4V multilayer micro-lattice biomaterials for skull repair

Effect of platelet length and stochastic morphology on flexural behavior of prepreg platelet molded composites

AbstractPrepreg platelet molding compound (PPMC) can be used to create structural grade material with a heterogeneous mesoscale morphology. The present work considered various platelet lengths of the prepreg system IM7/8552 to study the effect of platelet length on the flexural behavior of PPMC composite. A progressive failure finite‐element analysis was used to understand competing failure modes in PPMC with the different platelet length. The interlaminar and in‐plane damage mechanisms were employed to describe complex failure modes within the mesostructure of PPMCs. Experimental results of the flexural tests of the PPMC with different platelet length sizes were used to validate the modeling prediction. The experimental and modeling results revealed complex behavior of the flexural mechanical properties (modulus and strength) on the platelet length. The experimental results indicate that PPMC composites processed with a plate length of 12.7 mm have a higher flexural modulus and strength than 25.4 and 6.35 mm. The platelet length effect on the flexural mechanical behavior was attributed to interactions between various damage mechanisms and the stochastic fiber orientation distribution variability in the material.

Experimental and numerical study on the flexural mechanical properties of bioinspired composites with suture structures

Composite structures inspired by the suture line in the beak of woodpeckers, which is composed of stiff material (mimicking keratin) and compliant material (mimicking collagen), are proposed in this article. The flexural mechanical properties as well as the deformation and failure modes are investigated combining experiments and simulations, which are also compared with conventional laminated structures. First, three-point bending test is performed to characterize mechanical properties such as flexibility, stiffness, strength, and energy dissipation. Experimental results confirm that the suture structure affects the flexural properties significantly. Then, a finite element (FE) model is established to present the strain and stress fields inside the composite beams. The strain distribution demonstrates a shear mechanism in suture structures to dissipate energy, while the stress distribution reveals that the soft layers act as shock absorbers to release stress transmitted through the structure. At last, the failure mode and toughening mechanism of the composite structures is discussed. The mechanism responsible for the mechanical performance of biological structures can be generalized to design architectures with customized mechanical performances.

Role of discontinuous fiber core material on the mechanical behavior of hybrid sandwich polyester composites

This study investigated the potential for improving the mechanical behavior of glass fiber polyester composites by using symmetric hybrid sandwich configurations that combine continuous woven composite and different discontinuous reinforcements used as a core. The discontinuous reinforcements included sheet molding compound (SMC), bulk molding compound (BMC), and the discontinuous prepreg based platelets that were chopped from the woven trim scrap. Hybrid sandwich configurations using different core materials exhibited improvements in flexural mechanical properties, while providing more progressive failure under both flexural and compressive loading. Compressive strength in polyester SMC and woven laminate was significantly lower than flexural strength, while BMC and chopped platelets exhibited similar levels of strength in flexure and compression. Overall, hybridized compression molding produced sandwich structures can be used to control the failure progression and to improve the structural characteristics of composite, especially under flexural loads. The trim scrap core sandwich configuration had mechanical properties comparable with the BMC core hybrid. Therefore, trim scrap upcycling can be an efficient approach to reducing the amount of material waste during the manufacturing.

Development of Hybrid Composite Utilizing Micro-Cellulose Fibers Extracted from Date Palm Rachis in the Najran Region.

Environmental effects can be reduced by using renewable resources in various applications. The date palm fibers (DPF) used in this study were extracted from waste date ranches of the Najran region by retting and manual peeling processes. The biocomposites were developed by reinforcing the silane-treated DPF (SDPF) at different wt.% in eugenol phthalonitrile (EPN) and difunctional benzoxazine (BA-a) copolymer. The impact strength, tensile, flexural, and dynamic mechanical properties and thermogravimetric analysis were evaluated to understand the mechanical, thermomechanical, and thermal properties. Results confirmed that 30 wt.% SDPF-reinforced poly (EPN/BA-a) composites produced the highest mechanical and thermomechanical properties, and were considered optimized SDPF reinforcement. Furthermore, hybrid composites with 30 wt.% SDPF and 15 wt.% silane-treated glass fibers (SGF) reinforcement having different lamination sequences were also studied. The lamination sequences showed a significant impact on the mechanical and thermomechanical properties, as properties were further enhanced by adding a core layer of SGF in hybrid composites. However, the thermal properties of SDPF/SGF laminates were higher than SDPF biocomposites, but the SGF lamination sequence did not produce any impact. According to the limiting oxygen and heat resistance indexes, the developed SDPF/SGF laminates are self-extinguishing materials and can be used in temperature-tolerant applications up to 230 °C.

Strength Evaluation of Functionalized MWCNT-Reinforced Polymer Nanocomposites Synthesized Using a 3D Mixing Approach.

The incorporation of carboxyl functionalized multi-walled carbon nanotube (MWCNT- COOH) into a polymethyl methacrylate (PMMA) has been investigated. The resultant tensile and flexural mechanical properties have been determined. In this paper, a novel synthesis process for a MWCNT-reinforced polymer nanocomposite is proposed. The proposed method significantly eliminates the most challenging issues of the nano-dispersed phase, including agglomeration and non-homogeneous mixing within a given matrix material, and also resolves the issues occurring in conventional mixing processes. The results of scanning electron microscopy support these claims. This 3D-mixing process is followed by an extrusion process, using a twin-screw extruder for pristine MWCNT, and a compression molding process for COOH-MWCNT, to prepare test specimens for experimentally determining the mechanical properties. The test specimens are fabricated using 0.1, 0.5, and 1.0 wt.% MWCNT, with a remaining PMMA phase. The testing is conducted according to ASTM D3039 and ASTM D7264 standards. Significant improvements of 25.41%, 35.85%, and 31.75% in tensile properties and 18.27%, 48%, and 33.33% in flexural properties for 0.1, 0.5, and 1.0 wt.% COOH-MWCNT in PMMA, respectively, compared to non-functionalized MWCNTs, were demonstrated. The highest strength was recorded for the nanocomposite with 0.5 wt.% f-MWCNT content, indicating the best doping effect at a lower concentration of f-MWCNT. The proposed CNT-PMMA nanocomposite may be found suitable for use as a scaffold material in the domain of bone tissue engineering research. This type of research possesses a high strength requirement, which may be fulfilled using MWCNT. Furthermore, this analysis also shows a significant amount of enhancement in flexural strength, which is clinically required for fabricating denture bases.

Three-dimensional pore characterization of poly(lactic)acid/bamboo biodegradable panels

In the context of novel environmental and energy regulations in construction (RE2020), biocomposites derived from bamboo fibers, bamboo powders, and biodegradable poly(lactic)acid polymer, all of which are renewable resources, have been investigated to meet the criteria of the novel regulations. In this work, the biocomposites were manufactured by twin-screw internal mixing at 170 °C for 5 min with a rotation speed of 60 rpm. The composites sheets were then shaped on a hydraulic press at 185 °C. Pore characterization including pore volume fraction, 3D-pore structure and morphology, and pore distribution of these materials were investigated using X-ray tomography combined with image processing (Avizo). The results show that when the bamboo fibers content is increased, an augmentation in the pore volume fraction and the number of large-volume pores could be observed. In turn, the bamboo powder-containing sheet had a significant increase in pore volume fraction, while a higher quantity of smaller pores, with uniform size, could be observed. The water absorption capacity of these composite increases with the increase of the amount of pore distribution, pore connection, and pore volume fraction. In addition, the orientation of the fibers in 3D observation, flexural mechanical properties, and thermal stability of the biocomposites are also reported in this study.

A study on graphene reinforced carbon fiber epoxy composites: Investigation of electrical, flexural, and dynamic mechanical properties

AbstractIn this study, graphene nanoplatelets (GNPs) added to epoxy matrix composite reinforced by aeronautical grade carbon fibers (CFs) were fabricated by the vacuum infusion method, and the effect of different GNPs contents (0.05, 0.25, and 1.25 wt%) on electrical conductivity, flexural properties, and dynamic mechanical properties were investigated. The results revealed an 8‐ and 73‐times improvement in conductivity values across the thickness with the addition of 0.05 and 0.25 wt% GNPs, respectively, compared to the neat composite. Flexural test results showed that with the addition of 0.05 GNP, only 6% increase in flexural strength was obtained, while with the addition of 0.25 wt% GNP flexural strength remained almost the same as for the neat composite. On the contrary, the addition of GNPs (1.25% by weight) causes a reduction in the flexural strength with respect to the neat composite. This was confirmed by the fractured surfaces examined by scanning electron microscope which reveals that considerable amount of fiber‐matrix debonding was observed with 1.25 GNPs loading. Dynamic mechanical analysis (DMA) revealed that the storage modulus of the neat composite increased by 12.6% with the addition of only a small amount of GNP (0.05% wt) compared to the neat composite. Composite with 1.25 GNP shows upward bending, affecting the shape of the cole–cole plot obtained from DMA results, indicating inappropriate interactions of GNPs in both the matrix and CF in the composite.

A novel heterogeneous-particle model based on peridynamics for flexural mechanical properties of randomly oriented fiber reinforced composites

On the basis of peridynamic (PD) theory, a heterogeneous-particle model is proposed to investigate the flexural mechanical properties of a chopped carbon fiber tape reinforced thermoplastic (CTT). In contrast to the numerical analysis on the tensile behavior, the simulation of flexural behavior of CTT is challenging because a full-scale model rather than a representative volume element (RVE) is required in the modeling. The novelty is that the mesoscopic structure, such as the random orientation of fibers and the thickness of tapes, are represented in the simulation of flexural mechanical behavior. This model successfully simulates the flexural fracture morphologies, well predicts the flexural mechanical properties, and effectively captures the characteristic of the scatter in flexural properties. The effects of tape thickness, fiber orientation, support span and specimen thickness on the flexural behavior of CTT are investigated by this model. The influencing mechanism of these factors is revealed through this model.

Experimental Research on Flexural Mechanical Properties of Ultrahigh Strength Concrete Filled Steel Tubes

Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (fcu) of the core concrete reached 80.3–115.2 MPa. The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure.

Mechanical properties of fully recycled coarse aggregate concrete with polypropylene fiber

Incorporating polypropylene fiber as an additive material into the mixture can effectively improve the mechanical properties of concrete. In this paper, in order to investigate the mechanical properties of fully recycled coarse aggregate (FRCA) concrete with PP fiber, four groups of specimens with different volume ratio of PP fiber were designed and manufactured to conduct experiments of uniaxial compression and bending respectively. Based on the test results, the influence of volume ratio of PP fiber on the compressive and flexural mechanical properties of FRCA concrete were analyzed. The results showed that the integrity of compression specimens with PP fiber was better after failure and the flexural failure of the specimens without fiber or with PP fiber was brittle after the peak value. Moreover, with the increase of volume ratio of PP fiber, the slump of specimens presented a downward trend, the cube compressive strength increased continuously, and the cylinder compressive strength first decreased and then increased. Besides, with the increase of volume ratio of PP fiber, the static pressure elastic modulus increased as a whole, and the flexural strength increased.

Effects of jute fiber length and weight percentage on quasi-static flexural and dynamic mechanical properties of jute/polyester composites for thin-walled structure applications

Natural fiber reinforced polymer composites are being widely used in aerospace and automotive applications. These are due to their low density and cost, better biodegradability and higher specific strength and modulus, which replace E-glass fiber reinforced polymer composites. Moreover, quasi-isotropic properties can be achieved with randomly orientated short natural fiber composites. These composite structures are subjected to dynamic loading and exposed to different temperatures and frequencies during their service. In this research, the influence of fiber parameters (fiber length and loading) on quasi-static flexural and dynamic mechanical properties of jute/polyester composites was studied. Dynamic mechanical properties were investigated at different frequencies (0.2, 0.5, 1.0, 2.0 and 5 Hz) and temperatures from 35 °C up to 190 °C. It has found that the composite sample with 5 mm length and 25 wt% (5JP25) exhibited the highest flexural strength of 94 MPa and flexural modulus of 7.45 GPa. However, the composite sample with 15 mm length and 25 wt% (15JP25) exhibited a higher average storage modulus and a lower average loss factor indicating the good fiber–matrix adhesion, compared with the other samples. The Cole-Cole plot of the composite sample with the fiber weight percentage of 25 wt%, indicated a perfect semi-circle. Good correlations were observed between the flexural and initial storage moduli values of pure polyester and composites.

Graphene oxide bulk material reinforced by heterophase platelets with multiscale interface crosslinking.

Graphene oxide (GO) and reduced GO possess robust mechanical, electrical and chemical properties. Their nanocomposites have been extensively explored for applications in diverse fields. However, due to the high flexibility and weak interlayer interactions of GO nanosheets, the flexural mechanical properties of GO-based composites, especially in bulk materials, are largely constrained, which hinders their performance in practical applications. Here, inspired by the amorphous/crystalline feature of the heterophase within nacreous platelets, we present a centimetre-sized, GO-based bulk material consisting of building blocks of GO and amorphous/crystalline leaf-like MnO2 hexagon nanosheets adhered together with polymer-based crosslinkers. These building blocks are stacked and hot-pressed with further crosslinking between the layers to form a GO/MnO2-based layered (GML) bulk material. The resultant GML bulk material exhibits a flexural strength of 231.2 MPa. Moreover, the material exhibits sufficient fracture toughness and strong impact resistance while being light in weight. Experimental and numerical analyses indicate that the ordered heterophase structure and synergetic crosslinking interactions across multiscale interfaces lead to the superior mechanical properties of the material. These results are expected to provide insights into the design of structural materials and potential applications of high-performance GO-based bulk materials in aerospace, biomedicine and electronics.