Flexural Strength Retention Research Articles

High performance phthalonitrile/phenolic epoxy (PNP/PEP) copolymers and their GFRP composites

In the design of advanced thermoset GFRP composites, balancing the processabilities of the resin and the comprehensive properties of final GFRP composites is the key. In this paper, phthalonitrile/phenolic epoxy (PNP/PEP) copolymers with well processabiliy have been designed for the GFRP composites. The resulted PNP/PEP GFRP composites not only exhibit high mechanical properties at room temperature; but also show excellent high-temperature mechanical performance. After 300 oC/72h aging, the flexural strength retention ratios maintains over 93% while those of flexural modulus is near to 100%. Advanced PNP/PEP GFRP composites can be employed in some critical circumstances that need high mechanical properties and service temperatures.

Oxidation behavior and high-temperature flexural property of CVD-SiC-coated PIP-C/SiC composites

Polymer infiltration pyrolysis (PIP) was used to prepare carbon fiber-reinforced silicon carbide (C/SiC) composites, and chemical vapor deposition (CVD) was employed to fabricate SiC coating. The oxidation behavior at 1700 °C and the flexural property at 1200 °C were tested. SiC coating exerted remarkable oxidation effects on PIP-C/SiC composites. In the absence of coating, PIP-C/SiC composites lost 29.2% of its mass, with merely 6.74% of the original flexural strength retained. In contrast, CVD-SiC coated PIP-C/SiC composites had the mass loss of 10.2% and the flexural strength retention ratio of 23.4%. In high-temperature tests, SiC coating played an important role in the flexural strength of PIP-C/SiC composites. The flexural strength of uncoated composites became 330.7 MPa, and that of coated ones reduced from 655.3 to 531.2 MPa.

Dense Mulliteceramic Sintered by SPS and Its Behavior Under Thermal Shock

This article studies the influence of raw material, sintering temperature, particle size, and Al2O3 content on densification of mullite ceramics. Thermal cycle treatments were conducted to evaluate thermal shock resistance of samples. Microstructures of samples were also investigated to reveal effects of various parameters and thermal test. Flexural strength retention rises while density decreases, resulting from increasing extra space for stress release. Tridymite precipitation is found to be harmful in improving thermal shock resistance.

Seawater ageing of glass fiber reinforced epoxy nanocomposites based on silylated clays

The performance of the fiber reinforced epoxy nanocomposites incorporating silylated clay minerals exposed to seawater ageing vis-à-vis the amount of grafted silanes has been studied. The novel glass fiber reinforced epoxy nanocomposites incorporating clay minerals treated with different concentrations of two different silane coupling agents (3-Aminopropyltriethoxysilane and 3-Glycidyloxypropyltrimethoxysilane) have been exposed to simulated seawater at two different temperatures i.e. 25 °C and 55 °C. All fiber reinforced epoxy-clay nanocomposites showed an increase in weight due to seawater absorption. The water uptake studies were analyzed with an assumption that weight loss due to hydrolytic degradation of epoxy would be insignificant as compared to weight gain by fiber reinforced composites due to absorption of seawater. The rate of diffusion of seawater in glass fiber reinforced epoxy-silylated clay nanocomposites was slightly less than that of glass fiber reinforced epoxy-clay nanocomposites incorporating a commercially available organically modified montmorillonite Cloisite 15A®. The water uptake behavior and durability of nanocomposites were significantly influenced by the polarity of the organic moieties, the morphology of clay minerals in epoxy and temperature of seawater. Clay minerals modified using small quantities of silane coupling agents in fiber reinforced epoxy-clay nanocomposites led to better retention of tensile and flexural strength after hygrothermal ageing owing to silanization effect on exfoliation, as well as forming covalent bonds with the matrix. However, if silane coupling agents are used in excess, it will lead to the development of siloxane network which will also encapsulate clay minerals. The presence of such networks would act as concentration sites and lead to a significant decrease in tensile and flexural strength, as observed.

Modified-Graphene-Oxide-Containing Styrene Masterbatches for Thermosets

Incorporating graphene-based nanomaterials into thermosetting resins is challenging at an industrial-scale. To address this issue, we prepared a styrene masterbatch containing chemically modified graphene oxide (mGO) and added it to unsaturated polyester and vinyl ester resins via simple mechanical mixing to generate homogeneous mGO/resin dispersions. For comparison, oven-dried or freeze-dried mGO was also blended into resin using the same mechanical mixing conditions. At low mGO loading levels of 0.02–0.08 wt %, composites made with oven-dried or freeze-dried mGO show the highest increase in fracture toughness but also the most severe decrease in flexural strength, whereas composites prepared from the mGO masterbatch show the best dispersion homogeneity and better retention of flexural strength while exhibiting only slightly less increase in toughness. The masterbatch process offers an economical way of producing high-quality mGO/resin dispersions.

The Degradation Behavior of SiCf/SiO2 Composites in High-Temperature Environment

SiCf/SiO2 composites had been fabricated efficiently by Sol-Gel method. The oxidation behavior, thermal shock property and ablation behavior of SiCf/SiO2 composites was investigated. SiCf/SiO2 composites showed higher oxidation resistance in oxidation atmosphere, the flexural strength retention ratio was larger than 90.00%. After 1300 °C thermal shock, the mass retention ratio was 97.00%, and the flexural strength retention ratio was 92.60%, while after 1500 °C thermal shock, the mass retention ratio was 95.37%, and the flexural strength retention ratio was 83.34%. After 15 s ablation, the mass loss rate was 0.049 g/s and recession loss rate was 0.067 mm/s. The SiO2 matrix was melted in priority and becomes loosen and porous. With the ablation going on, the oxides were washed away by the shearing action of the oxyacetylene flame. The evaporation of SiO2 took away large amount of heat, which is also beneficial to the protection for SiCf/SiO2 composites.

Residual mechanical properties of carbon fibre reinforced thermoplastics with thin-ply prepreg after simulated lightning strike

This study experimentally examined the residual mechanical properties of a carbon-fibre/polyamide-6 laminate and randomly-oriented carbon-fibre strand (ROS) thermoplastic composites with thin-ply prepreg after a simulated lightning strike, and compared the results with those of a carbon-fibre/epoxy laminate fabricated from thick-ply prepreg. The damage was characterized by visual inspection, ultrasonic scanning, and optical microscopy. The residual mechanical properties were evaluated using a four-point flexural test. The flexural strength of the carbon-fibre/epoxy laminate was considerably reduced due to delamination, whereas the carbon-fibre/polyamide-6 laminate with a thin-ply prepreg exhibited improved retention of flexural properties. Lightning damage to ROS composites was spread over larger areas and depths, while being scattered and spotted, consistent with superior retention of flexural strength. Moreover, the flexural properties of intact and damaged ROS composites were improved by thin-ply prepreg. These results suggest that the application of thin-ply prepreg to thermoplastics affords composites with superior mechanical properties and lightning resistance.

Oligomeric bisphenol A‐based PEEK‐like phthalonitrile‐cure and polymer properties

ABSTRACTThe cure behavior and properties of oligomeric bisphenol A‐based PEEK‐like phthalonitrile (PN) are thoroughly examined in this article. The resin is easily processed from the melt at a relatively low temperature (150–200 °C) and the monomer cure occurs in a controlled manner as a function of the amine content and processing thermal conditions. Dynamic mechanical measurements and thermogravimetric analysis show that the polymer properties improve as the maximum PN postcure temperature is increased to 415 °C. The effects of the amine and polymer postcure conditions on the flexural and tensile properties of the PN polymer are investigated. The mechanical properties of the polymer are maximized after postcuring to moderate temperatures (330–350 °C). The polymer exhibits an average flexural strength and tensile strength at break of 117 and 71 MPa, respectively. After oxidative aging at 302 °C for 100 h, the polymer retains excellent mechanical properties. The average flexural and tensile strength retention of the polymers are 81 and 75%, respectively. Microscale calorimetric measurements reveal that the flammability parameters of the oligomeric PN are low compared to other thermosets. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3769–3777

Effect of harsh environments on mechanical properties of GFRP pultruded profiles

Abstract This paper presents an experimental investigation on the long-term mechanical performance, focusing on bending and compression of GFRP pultruded structural sections adopted as many structural constructions. Vinylester matrix has been used in combination with E-glass fibers. The degradation of the mechanical performance has been monitored through a process of accelerated artificial ageing by using aggressive environmental conditions, sea water set at different temperatures: 20, 40 and 60 °C, sea water wetting and drying cycles, alkaline solutions set at two different PH, 13.6 and 12.7 and acidic solution with PH = 3.5. In this study, flexural and compressive strength retention after about five months has been used as measurement of the imparted degradation and sea water absorption has been considered to define the diffusion coefficient and the activation energy for GFRP compositions. It was shown that the immersion of composites in alkaline solutions after 147 days, reduced the mechanical strength of sections more than the immersion in sea water and acidic solutions. And also results of the immersion in sea water solutions revealed that the strength reduction becomes larger in higher temperatures. The Arrhenius principle has been applied to estimate the long-term degradation of the GFRP profiles and predict the expected service life of such materials.

Influence of carbon nanofiber clustering on the chemo-mechanical behavior of cement pastes

The influence of carbon nanofiber (CNF) clustering on the chemo-mechanical behavior of cement pastes subjected to a decalcifying environment was studied. Portland cement pastes with and without CNFs were exposed to a concentrated solution of ammonium nitrate to accelerate decalcification. Microstructural changes and evolution of the porosity were examined as a function of exposure duration. Changes in the flexural response of the cement paste with CNFs were studied and reviewed in relation to CNF clustering and microstructural evolution. Results showed a strong coupling between decalcification, CNF clustering, microstructural evolution, and the flexural properties of the cement paste. After 7 days of decalcification by NH4NO3, the CNF clusters acted as weak zones that reduced the flexural strength retention of the cement paste. However, after 125 days of decalcification by NH4NO3, a dissolution-filling mechanism within the clusters created a better bond with the surrounding cement paste, slowing down the loss of flexural strength and providing added ductility to the cement paste.

Novel Biocomposites from Biobased Epoxy and Corn-Based Distillers Dried Grains (DDG)

The growing ethanol production around the world demands more value-added applications for its main byproduct, distillers grains. The present work reports the study of using corn based distillers dried grains (DDG) as biofillers for biobased epoxy resin and the mechanical, physical and thermal properties of the composites. The biobased epoxy resin is the blend of diglycidylether of bisphenol-A based resin and epoxidized soybean oil. The incorporation of DDG into the biobased resin accelerated the curing process as evident from the differential scanning calorimetry and temperature-modulated Fourier transform infrared spectroscopy. The 40 wt% DDG filled composite showed an excellent retention of flexural strength of up to 94 % of that of the neat epoxy. Furthermore, the composite filled with the DDG treated with epoxy functionalized oligomeric silsesquioxane showed even better flexural properties thanks to the improved wettability of the biobased resin with the filler. Dynamic mechanical analysis showed a 12 % increment in storage modulus for the surface-treated DDG composites over the biobased resin. The improved interfacial adhesion between the DDG and matrix through the surface modification was also observed in the morphological characterization with electron microscope. The study demonstrates the viability of combining DDG biofiller with the epoxy bioresin to produce novel biomaterials at low cost.

Long-term bending performance and service life prediction of pultruded Glass Fibre Reinforced Polymer composites

This paper presents an experimental investigation on the long-term mechanical performance, focusing on bending, of pultruded composite plates adopted as cladding in building constructions. Three matrices have been used in combination with E-glass fibres: isophthalic polyester, orthophthalic polyester and vinylester.The degradation of the mechanical performance has been monitored through a process of accelerated artificial ageing by using water baths set at different temperatures: 20°C, 40°C and 60°C.Flexural strength retention through time has been used as measurement of the imparted degradation and water absorption has been considered to define the diffusion coefficient and the activation energy for the three compositions. The Arrhenius methodology has been adopted to estimate the long-term degradation of the composites and to predict the expected service life of the materials. The outputs of the research show that isophthalic and vinylester systems have flexural strength retention of 65% for more than 75 and 100years, respectively, while the orthophthalic composite has the same retention for more than 20years.

Effect of thermo-oxidative aging on three-dimensional and four-directional braided carbon fiber/epoxy composite

An experimental study was performed to investigate the effect of high temperature exposure on flexural properties of the three-dimensional and four-directional braided carbon fiber/epoxy composite and the corresponding neat resin. For this purpose, samples were exposed to 90℃, 120℃, 150℃, and 180℃ (below and above the glass transition temperature of the matrix resin) for various periods of time up to 13 days. The flexural properties combining with Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), weight loss, scanning electron microscope (SEM), and optical microscope analyses were performed on the unaged and aged samples. The results revealed that the thermo-oxidative behavior of the braided composite was significantly different from the neat resin. The flexural strength of the neat resin decreased dramatically due to the oxidation degradation of the sample surface when the aging temperature was equal to its glass transition temperature. The extensive degradations of both the matrix and the fiber/matrix interface, especially for the interface, were responsible for the significant decrease in flexural strength of the braided composite. The flexural strength retention rates of the braided composite were higher than that of the neat resin after exposure to 90℃, 120℃ and 150℃ because the integral structure of the braided composite can make the fiber bear flexural force together although the matrix resin and the fiber/matrix interface had a certain degree of damage after longtime thermo-oxidative aging.

Influence of Oxygen Plasma Modification Carbon Fiber on Flexural Strength and Hydrothermal Properties of CF/PES Composite

In this paper, low temperature oxygen plasma treatment method was adopted to process the carbon fiber surface. Flexural Strength test method was utilized to represent f composite material flexural strength. This paper observed flexural failure morphology of composite material by aid of SEM, then it compared the mechanical property, hygroscopicitiy and flexural strength retention rate of composite material before and after the plasma treatment. Results showed that the optimum treatment conditions of carbon fiber were 300W treatment power and 15-minute treatment time. Under the condition, the highest flexural strength value be increased by 19.55%.Saturated bibulous is low and bibulous rate is slow, flexural strength retention rate is 94.9%. And at the same time PES-C resin matrix can be strengthened, which will further improve the mechanical properties of composite materials.

Open hole flexural and izod impact strength of unidirectional flax yarn reinforced polypropylene composites as a function of laminate lay‐up

An open hole flexural strength and impact energy of flax yarn‐reinforced polypropylene (PP) composites were studied in this work. Highest flexural strength and strength retention were observed for axial (06) and cross‐ply (0/90/0)s laminates, respectively, while also examining the influence of laminate lay‐up and open hole size on flexural strength. It was found that maleic anhydride‐grafted polypropylene (MAPP)‐treated composite laminates achieved marginal improvement on flexural strength for all kinds of laminate lay‐up. Off‐axial laminates (±456) showed a good strength retention for open hole laminates after MAPP treatment. The fractography study confirmed microbuckling and matrix crack propagation over the compressive and tensile side of the laminate, respectively. Furthermore, severe surface damage was detected over the tensile side of 8‐mm hole size laminates. Impact test of the flax/PP laminates showed slight improvement by MAPP treatment. High‐ and low‐impact energy was experienced for axial and off‐axial laminates. The damaged impact sample shows evidence of fiber pull‐out for untreated flax yarn reinforced laminates. POLYM. COMPOS., 34:1912–1920, 2013. © 2013 Society of Plastics Engineers

Influence of dip-coated boron nitride interphase on mechanical and dielectric properties of SiCf/SiC composites

The utilization of urea and boric acid solutions as precursors via dip-coating method for synthesis of BN coatings on KD-I SiC fibers was demonstrated. The effects of precursor compositions of BN on coatings microstructure, coatings morphology, mechanical and dielectric properties of SiCf/SiC composites were investigated. XRD, FT-IR and Raman spectra results show that the crystalline degree of t-BN decreases with urea and boric acid mole ratios increase from 3:1 to 12:1. The surface of as prepared BN coatings is smooth and its thickness is uniform when the ratio is higher than 6:1. From mechanical properties measurements, the higher mole ratio helps to improve the flexural strength and fracture ductility of the composites. The flexural strength and failure displacement of SiCf/SiC composites with 0.2μm thickness BN interphase reach 278MPa and 0.29mm, which are both much higher than those of the composites without interphase, whose ultimate values are only 191MPa and 0.13mm, respectively. The flexural strength retention of the composites with BN interphase is higher than that of the composites with PyC interphase below 800°C and there is no significant difference at higher temperatures. The BN coatings have little influence on the complex permittivity of SiC fabrics.

Oxidation behavior of C/SiC composites with a SiC/Mo–Si multilayer coating

A SiC/Mo-Si multilayer coating was prepared on the surface of C/SiC composites by chemical vapor deposition (CVD) combined with slurry painting. The coating was composed of a dense CVD SiC coating alternating with a porous Mo-Si layer. From inside to outside the coating consisted of CVD SiC,Mo-Si,CVD SiC,Mo-Si and CVD SiC. The coating remained intact and no obvious failure such as destruction or spalling was found during oxidation at 1 400 ℃ and thermal shock between 1 400 ℃ and room temperature. The mass loss and mass loss rate of the coated sample were only 0.25% and 6.61×10-6 g·cm-2·h-1,respectively after oxidation at 1 400 ℃ for 150 h. The flexural strength retention was 95.73% and 81.61% after 25 and 50 thermal cycles respectively and mass of the coating generally increased after oxidation. The SiC/Mo-Si multilayer coating showed excellent anti-oxidation ability and a thermal shock resistance and could effectively protect the C/SiC composites at 1 400 ℃ for a long time.

Encapsulating fly ash and acidic process waste water in brick structure

Fly ash contains metals such as cadmium, iron, lead, aluminum and zinc in its structure in appreciable amounts. These metals can leach out into surface and ground waters if fly ash is not properly disposed of. A similar problem also exists for acidic process waste waters discharged by numerous industries. The purpose of this study was to utilize such wastes as additives in the production of construction quality bricks for the purpose of waste elimination. The bricks produced were subjected to flexural strength and water retention capacity tests along with heavy metal leaching experiments in order to determine the applicability of the procedure and the best possible recipes. This paper summarizes the results obtained in these tests along with the possible mechanisms involved in stabilizing the two wastes in the brick structure.

Bismaleimide‐modified methyl‐di(phenylethynyl)silane blends and composites: Cure characteristics, thermal stability, and mechanical property

AbstractReactive blends of organic‐inorganic hybrid monomer, methyl‐di(phenylethynyl)silane (MDPES) and a modified bismaleimide resin (BMI/DBA) have been prepared. The thermal and oxidative stabilities of MDPES‐BMI/DBA blends were characterized by thermogravimetric analysis, derivative thermogravimetry, differential thermal analysis, dynamic mechanical analysis, and flexural strength retention at 240°C. Scanning electron microscopy was employed to study the surface morphology of MDPES‐BMI/DBA composite after thermal oxidative treatment. With the increase of concentration of BMI/DBA, flexural strength of composites increased from 78 to 331 MPa. The results showed that MDPES‐BMI/DBA blends exhibited excellent thermal and thermal oxidative properties, and the interface between MDPES and glass fiber was improved by the incorporation of BMI/DBA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Effect of Modified Intumescent Flame Retardant via Surfactant/Polyacrylate Latex on Properties of Intumescent Flame Retardant ABS Composites

In order to prepare intumescent flame retardant acrylonitrile-butadiene-styrene (ABS) composites with only a small decrease in their mechanical properties, we investigated the effect of adding an elastomeric polyacrylate latex and the surfactant TX-10 phosphate to modify the ammonium polyphosphate, melamine, and calcium 3-hydroxy-2, 2-bis(hydroxymethyl) propyl phosphate normally used, which resulted in an intumescent flame retardant composite (IFRC) powder with the aim of improving compatibility. These ABS/IFRC composites were compared with standard material containing unmodified intumescent flame retardant (NIFR) by investigating their thermal properties, melt characteristics, mechanical properties, and microstructure. The data showed that the glass transition temperature of the ABS/IFRC composites decreased slightly in all cases, the complex viscosity of the ABS/IFRC composites was remarkably reduced, and the mechanical properties improved in comparison with the material containing NIFR. A slight increase in impact strength retention, as well as a remarkable increase in tensile and flexural strength retention of ABS/IFRC, was achieved due to superior compatibility between ABS and IFRC in comparison with ABS/NIFR.