Flexural, compressive and thermal characterization of hybrid composite materials

Resin-based materials used in restorative dentistry are introduced at a fast pace with limited knowledge about their properties. Comparing properties of these materials from different restorative categories is lacking but can help the clinician in material selection. This study aimed to compare mechanical properties and wear resistance of bis-acryl-, composite-, and ceramic-resin restorative materials. Bisacryl-resin (Bis-R, LuxaCrown, DMG), composite-resin (Com-R, Filtek Supreme Ultra, 3M Oral Care), and ceramic-resin (Cer-R, Enamic, VITA Zahnfabrik) specimens were prepared for mechanical tests: fracture toughness (FT) with and without initial thermomechanical loading using a mastication simulator, flexural strength (FS), and flexural modulus (FM), compressive strength (CS), and volumetric wear loss measurement. The datasets for FT and wear resistance were each analyzed using two-way ANOVA followed by pairwise comparisons or Tukey testing as appropriate. The datasets for FS, FM, and CS were analyzed using one-way ANOVA followed by the Tukey test. Analysis of FS, FM, and CS showed significant differences between materials, with all pairwise comparisons between materials showing significance. Analysis of FT resulted in a significant interaction between the material and treatment, with analysis of wear loss showing a significant interaction between the material and the number of cycles. Cer-R demonstrated superior FT, CS, and wear resistance compared to Bis-R and Comp-R materials. Fracture toughness of Bis-R increased after thermomechanical loading.

This work deals with the preparation and characterization of two different types of natural powder which is nano-thyme (NT) and nano-pumpkin (NP) and investigation of its adding on the mechanical properties of epoxy matrix composite at different weight fractions (0.5%, 1%, 1.5%, 2%). Hand Lay-Up method was utilized to prepare the nanocomposite samples. Flexural, compression, impact, hardness tests for these samples had been investigated. The results showed that flexural modulus and compressive strength incremented with the weight fraction of both powder types in epoxy composite. While the values of flexural strain, flexural strength, shear stress, impact strength, and hardness decreased. The nano-thyme powder showed a varied behavior in epoxy matrix compared with nano-pumpkin powder.

It was tried to prepare a carbon fiber reinforced carbon (CFRC) plate by the lamination of high performance carbon fiber (CF) paper.A carbon fiber reinforced plastics (CFRP) plate was prepared by laminating 80 sheets of the CF paper which was coated with phenol resin containing some amount of graphite powder, and carbonizing it into CFRC plate (3.5mm in thickness) at a temperature up to 1000°C under nitrogen (Fig.1).The CFRC plate underwent the densification, high temperature and hot-press treatments to improve its mechanical strength. The densification treatment did not improve the mechanical strength of the CFRC plate (Table 1).While, by the high temperature treatment (1500°C, 2200°C, and 2500°C), the flexural and shear strength of the CFRC plate remarkably increased and the modulus slightly decreased.The maximum flexural strength was obtained at 2200°C of HTT (Table 2).The thickness of CFRC plate decreased from 3.5mm to 3.2mm with the increase of the treatment temperature from 1000°C to 2500°C (Fig.4).The X-ray diffraction profiles of the CFRC indicated the growth of graphitic structure at the temperature over 2200°C (Fig.7).It suggests that the shrinkage of CFRC plate was due to the structural change of the matrix and CF by stress graphitization.By hot-press treatment (2200°C, 140kg/cm2), the thickness of CFRC plate decreased from 3.5mm to 2.5mm, the bulk density increased to 1.78, the porosity decreased to 12%, and the cross section texture became more homogeneous than that before the treatment.The mechanical properties of this CFRC plate was 150MPa in flexural strength, 39GPa in flexural modulus, and 200MPa in compressive strength, and these values obtained show narrower scatter than that in other cases (Table 2).On the bases of the best properties previously obtained on UD-CFRC samples and of the results in this work, it was assumed that the maximum value of quasi-isotropic CFRC plate is 150-200MPa in flexural strength.

The aim of this study was to assess the effect of printing orientation and water ageing on the flexural strength and flexural modulus of 3D printed resins for occlusal splints. Bar-shaped specimens were designed with dimensions of 64 × 10 × 3.3 mm according to ISO 20795-2:2013. Specimens were 3D printed with the Form 3B printer (Formlabs), using Dental LT Clear Resin (CL) or Comfort Resin (CO) (Formlabs), and 3 different printing orientations: as per manufacturer's recommendation (40° N = 20), parallel (0° N = 20), or perpendicular to the build platform (90° N = 20). To simulate intraoral ageing, half of the specimens per material and printing orientation (N = 10) were stored in distilled water at 37 °C for 30 days prior to testing. Specimens were tested in a three-point bending apparatus using a universal testing machine equipped with a 50 N load cell moving at a crosshead speed of 5 mm/min. Flexural strength (MPa) and flexural modulus (GPa) data were collected and statistically processed with separate analyses for unaged and aged specimens (Two-Way or One-Way ANOVA; Tukey test; p < 0.05). As for unaged specimens, both resin materials exhibited the highest flexural strength and modulus in the 90° orientation and the lowest values in the 40° orientation group. After water aging, all groups showed reduced flexural strength and modulus, with CO displaying up to 52% loss in flexural strength and values falling below ISO thresholds. CO consistently exhibited significantly lower flexural strength and modulus than CL, irrespective of aging.

This research examines the mechanical properties of composites made from flax fiber and polyester resin. Hybrid composites were produced by integrating flax fiber, known for its exceptional tensile and flexural strengths, with graphene oxide nanoparticles (nGO) and polyester resin. The flexural and ultimate tensile strengths of the composites were predicted using a multilayer perceptron (MLP) regression model, a type of artificial neural network (ANN). The composite material FGO-1, comprising 40 wt.% flax fiber, 1 wt.% graphene oxide nanoparticles, and 59 wt.% polyester resin, exhibited outstanding mechanical properties. The FGO-1 sample showed improvements in flexural modulus (46.80%), flexural strength (50.80%), tensile modulus (32%), and tensile strength (37.83%). The energy absorption rate was 32.69%, and its impact resistance exceeded that of the other composite formulations by 8.75%. The ANN model successfully predicted these strengths, achieving R2 values of 0.89 and 0.98 for flexural and tensile strengths, respectively. Microstructural analysis using a scanning electron microscope (SEM) was conducted alongside tensile, flexural, impact, and interlaminar shear strength tests to evaluate the composite’s performance.

Influence of polymerization mode on flexural properties of esthetic resin luting agents

In this study, lightweight polymer concrete samples were produced with limestone (Ceyhan, Adana), pumice (Nevsehir) and zeolite (Gordes, Manisa) as a binder resin, and compressive and flexural tensile strength of these samples were determined via laboratorial experiments. For the study, the cylinder and prismatic samples of polymer on normal aggregate concrete (NAC), polymer on normal and lightweight aggregate mixture concrete (NLAC) and polymer on lightweight aggregate concrete (LWAC) were prepared. The polymer concrete produced was cured 3, 7, 28 and 90 days. The concrete samples were cured at 65% relative humidity with 20°C temperature. The density and slump workability of concrete mixtures were also measured. Laboratory test results showed that lightweight polymer concretes can be produced by the use of limestone, pumice, zeolite andas a binder resin. The use of mixture was recommended due to its satisfactory strength development. Key words: Polyester resin, compressive strength, flexural tensile strength, aggregate type, curing time.

The aim of the present work is to evaluate the mechanical properties of banana and S-glass fiber-reinforced hybrid nanosilica composite. The glass and other synthetic fiber-reinforced polyester composites give high strength when compared with the natural fiber-reinforced composite, but their applications are limited because of the high cost of fabrication. So to overcome the cost of fabrication and to meet the high strength as of synthetic composite, a new hybrid composite is fabricated by using 50% of natural fiber and 50% of synthetic fiber. The new composite is fabricated by reinforcing the stacking layers of woven banana and s-glass fibers with the polyester resin as a matrix and nanosilica as filler material. Different samples were prepared by changing the stacking sequence of fiber placed in the composite and weight percentage of nanosilica powder that is mixed into the resin. The fabrication is done by the hand layup method. The mechanical properties like tensile strength, flexural strength, tensile modulus, and flexural modulus were studied. The morphological study is done through a scanning electron microscope to observe the fibers pullout, stacking of fibers, and the behavior of matrix in the hybrid composite. The change of weight percentage of nanosilica and the stacking sequence of fibers in the composite show the improvement in mechanical properties.

The waste produced by bamboo stick production processing was collected from a Vietnamese craft village and used as a source of microfibril cellulose (MFC) for a filler of unsaturated polyester (UP) resin based composites in this study. A mixture of MFC in UP was obtained by directly introducing the bamboo pulp into UP resin followed by a grinding process using a ball-grinding machine. A master batch method was also adopted for composite preparation, in which a high-content solution of MFC in UP resin was first fabricated and then diluted to prepare another solution with the desired content. Morphology and mechanical characteristics of UP resin based composites were investigated. Effect of different methods of preparation, such as hand lay-up and vacuum bagging methods, on the mechanical properties of glass fiber reinforced UP resin composites was also examined, showing that the tensile strength of composite materials with 0.3 wt% MFC was increased by 10.24% (for the hand lay-up method) and 19.62% (for the vacuum bagging method) when compared with the pristine composite material. The flexural strength increased from 192.40 MPa to 208.63 MPa and the impact strength increased by 19.6% from 158.28 kJ/m2 to 186.84 kJ/m2 for the hand lay-up method.

Laminated composites based on polyetheretherketone (PEEK) and polyimide (PI) matrices were fabricated by hot compression. Reinforcing materials (unidirectional carbon-fiber (CF) tapes or carbon fabric) and their layout patterns were varied. Stress–strain diagrams after three-point flexural tests were analyzed, and both lateral faces of the fractured specimens and fractured surfaces (obtained by optical and scanning electron microscopy, respectively) were studied. It was shown that the laminated composites possessed the maximum mechanical properties (flexural elastic modulus and strength) in the case of the unidirectional CF (0°/0°) layout. These composites were also not subjected to catastrophic failure during the tests. The PEEK-based composites showed twice the flexural strength of the PI-based ones (0.4 and 0.2 GPa, respectively), while the flexural modulus was four times higher (60 and 15 GPa, correspondently). The reason was associated with different melt flowability of the used polymer matrices and varied inter- (intra)layer adhesion levels. The effect of adhesion was additionally studied by computer simulation using a developed two-dimensional FE-model. It considered initial defects between the binder and CF, as well as subsequent delamination and failure under loads. Based on the developed FE-model, the influence of defects and delamination on the strength properties of the composites was shown at different stress states, and the corresponding quantitative estimates were reported. Moreover, another model was developed to determine the three-point flexural properties of the composites reinforced with CF and carbon fabric, taking into account different fiber layouts. It was shown within this model framework that the flexural strength of the studied composites could be increased by an order of magnitude by enhancing the adhesion level (considered through the contact area between CF and the binder).

Cork is an ecological, natural, and renewable additive, an excellent thermal and acoustic insulator. All these attributes encourage its use in the building sector. Adding this additive to the Earth leads to a more lightweight composite with better thermal performance than the Earth alone. Unfortunately, the mechanical performance of this composite is degraded significantly, limiting its use in construction applications. The authors propose in this study to stabilize the clay-cork composite using natural stabilizers. A chemical stabilization was tested using local quick-lime, in addition to a physical stabilization using natural sheep-wool fibers. The primary purpose is to propose eco-friendly construction material with enhanced thermal and mechanical properties and the lowest environmental impact based on local and ecological raw materials to encourage more sustainable and low-energy constructions. First, physicochemical and mineralogical characterization of used clay was investigated. Then, an experimental investigation was conducted to identify the lime content that allows the optimal stabilization for the used clay. In this context, many different specimens of Bensmim soil stabilized with lime at six many contents 0, 10, 20, 30, 40, 50, and 70% were prepared and tested. The obtained results showed that the optimal lime content for the better stabilization of the used soil is about 30%. Next, an experimental study of thermomechanical properties was conducted on unfired clay bricks mixed with expended cork granules and stabilized by the addition of variable proportions of quick-lime 0, 10 and 30% and sheep-wool fibers 0, 1, and 2%. The mechanical performance of the specimens was investigated in terms of compressive and flexural strengths. At the same time, thermal quality was qualified through evaluating thermal conductivity using the steady-state Asymmetrical Hot Plate test method. The very encouraging experimental findings showed that using lime and sheep-wool fibers at the studied addition content resulted in lightweight composites with lower thermal conductivity and higher compressive and flexural strength than reference samples. The highest thermomechanical performances are obtained with clay-cork blocks reinforced with 30% lime content and 2% sheep-wool fibers. This block recorded values of 583 kg/m3, 0.155 W/m/K, 1.55 MPa, and 3.91 MPa, for bulk density, thermal conductivity, flexural and compressive strength respectively, compared to 765 kg/m3, 0.238 W/m/K, 0.96 MPa and 2.29 MPa for control samples. New material presents lightweight material for both improved thermal and mechanical qualities encouraging its use in building applications. Doi: 10.28991/cej-2021-03091778 Full Text: PDF

&lt;p&gt;Geopolymers have been suggested in the literature as matrix materials for fibre reinforced composites due to a unique combination of low-temperature synthesis and high temperature stability. This study investigated several key aspects of fibre reinforced geopolymer matrix composites in order to improve the basic knowledge of these materials. It was demonstrated that geopolymer matrix composites show great potential as fire-resistant materials for near room temperature applications. In particular, basalt fibre composites were of great interest due to their comparatively low cost and good mechanical performance. Microstructural investigations indicated that basalt fibres can potentially be used in geopolymer matrices up to 600°C. However, the success of the application of geopolymer matrix composites at higher temperatures is seen as critical and depends on further development of suitable matrices. Several compositions within a sodium-metahalloysite model matrix system were evaluated in order to identify a suitable formulation for composite fabrication. An average compressive strength of ~ 79 MPa and flexural strength and modulus of ~ 10 MPa and 8.5 GPa, respectively, were achieved for the best batch of the main matrix composition. By optimising the matrix composition, the mechanical properties could be significantly improved, achieving an extremely high maximum compressive strength value of 145 MPa. Issues with reproducibility and the influence of various aspects of the fabrication process are discussed. The room temperature flexural properties of unidirectional fibre reinforced composite bars with basalt, carbon and alumina fibres were investigated. Besides the fibre type, the effects of several other parameters including fibre sizing, matrix strength, span-to-depth ratio and specimen dimensions on the flexural properties and the failure behaviour of the composites were studied. Significant improvements to the mechanical properties were achieved with all fibre types. However, the mechanical behaviour was highly influenced by the elastic modulus of the fibre. Furthermore, it was shown that the composite properties were affected by the overall sample dimensions, the testing span and the mixing time of the geopolymer binder. The alumina fibre composites achieved the highest flexural stress with a maximum value of 470 MPa and a fibre content of ~ 30 vol.-%. Basalt and carbon fibre composites showed maximum flexural strength values around 200 MPa. Although all composite types displayed considerable post-fracture strength, only the basalt composites failed in tensile mode. The applicability of the weak matrix composites (WMC) concept to describe the mechanical behaviour of geopolymer matrix composites was discussed. The fibre-matrix interactions were analysed between room temperature and 1000°C by means of electron microscopy, EDS and x-ray diffraction. All fibres were found to be chemically stable under the highly alkaline conditions of the geopolymer synthesis and showed no significant reaction with the geopolymer matrix at room temperature. The results indicate that basalt fibre composites may be used up to 600°C without significant degradation of the fibre. The heating of the carbon fibre composites to 600°C had drastic effect on the strength and integrity of the composite, in particular, when using sized carbon fibres. The alumina fibres showed good wetting and bonding behaviour but otherwise little reaction with the matrix even after heating to 1000°C.&lt;/p&gt;

The aim of the article is to analyze the influence of short coir, glass and carbon fiber admixture on the mechanical properties of fly ash-based geopolymer, such as: flexural and compressive strength. Glass fiber and carbon fibers have been chosen due to their high mechanical properties. Natural fibers have been chosen because of their mechanical properties as well as for the sake of comparison between their properties and the properties of the artificial ones. Fourth series of fly ash-based geopolymers for each fiber was cast: 1, 2, and 5% by weight of fly ash and one control series without any fibers. Each series of samples were tested on flexural and compressive strength after 7, 14, and 28 days. Additionally, microstructural analysis was carried out after 28 days. The results have shown an increase in compressive strength for composites with fibers—an improvement in properties between 25.0% and 56.5% depending on the type and amount of fiber added. For bending strength, a clear increase in the strength value is visible for composites with 1 and 2% carbon fibers (62.4% and 115.6%). A slight increase in flexural strength also occurred for 1% addition of glass fiber (4.5%) and 2% addition of coconut fibers (5.4%). For the 2% addition of glass fibers, the flexural strength value did not change compared to the value obtained for the matrix material. For the remaining fiber additions, i.e., 5% glass fiber as well as 1 and 5% coconut fibers, the flexural strength values deteriorated. The results of the research are discussed in a comparative context and the properties of the obtained composites are juxtaposed with the properties of the standard materials used in the construction industry.

In the present study, an experiment was conducted to investigate the mechanical properties such as fluidity, compressive strength and flexural performance (flexural strength and toughness) of a single fiber-reinforced mortar (FRM) using only macro steel fiber (SF) or micro carbon fiber (CF) with different material properties and SF-CF hybrid FRM using a mixture of macro SF and micro CF. The specimens incorporated macro SF and micro CF in the mix proportions of 100-0%, 75-25%, 50-50%, 25-75% and 0-100% by volume at a total fiber volume fraction of 1.0%. Their mechanical properties were further compared and reviewed with the plain mortar at 28 days of age. The experimental results of fresh mortar showed that the table flow of mortar using only macro SF was slightly reduced compared to plain mortar, whereas the table flow of mortar using only micro CF and SF-CF hybrid mortar decreased significantly with increase of micro CF. It was revealed from the test of the hardened mortar that the SF-CF=75-25% (M3) specimen showed the highest compressive and flexural strength, and the SF-CF=50-50% (M6) specimen obtained the highest flexural toughness. Therefore, it was possible to confirm the synergistic reinforcement effect of that enhanced the strength and improved the flexural performance by hybrid of macro SF and micro CF. Based on the results of this experiment, the optimal mix proportion of SF-CF hybrid FRM is proposed in this paper to improve the compressive strength, flexural strength and flexural toughness.

During the pultrusion process, there are some parameters that influence the mechanical performance of pultruded composites. The pultruded kenaf composites processing parameter such as pulling speed influenced the pressure and curing behavior of the pultruded composites. The optimal pulling speed leads to the sufficient pressure and temperature and facilitated curing the pultruded composites. Mechanical properties such as tensile strength and modulus, flexural strength and modulus, and compressive strength of kenaf pultruded composites were analyzed in this study and the optimal pulling speed of pultruded composites was determined. The tensile strength and tensile modulus showed the optimal pulling speeds at 0.3 and 0.1 m/min, respectively, while, flexural strength, flexural modulus, and compressive strength were at 0.4, 0.2, and 0.3 m/min, respectively. Scanning electron microscopy images were utilized to study the effect of pulling speed on the morphology of the tensile fracture sample. Fiber wetting, fiber matrix adhesion, the gaps within the samples, and fiber breakages were among the phenomena occurring in the composites . J. VINYL ADDIT. TECHNOL., 24:E13–E20, 2018. © 2016 Society of Plastics Engineers