Epoxy Specimens Research Articles

Effect of biomass ash mixture composite on sound absorption

Given that noise is an unwanted variable in human comfort whether in industrial or in commercial application, biomass combustion in recent days has gained increased interest within the heat and power industries; moreover, the application of biomass ash is used widely in many sectors. However, the effectiveness of sound absorption by various biomass ash mixture remains unexplored. This research aims at evaluating the effect of biomass ash mixture composite, in particular, coconut coir and spent coffee ground, toward sound absorption. It is formulated on the ratios of 1:1, 1:2, 1:3, 2:1 and 3:1 of epoxy resin to biomass ash via standing wave tube according to ASTM E1050-98. The results obtained from the research’s experiments indicated that, at 5 kHz, the average sound absorption coefficients for epoxy specimen infused with coconut coir ash, coffee ash, and mixture of both ashes, are 0.1, 0.098, and 0.097, respectively, and that the unmingled epoxy specimen has an average sound absorption coefficient of less than 0.09. Therefore, the research concluded that coconut coir ash composite provides better sound absorption property, compared to coffee ash, mixture of both ashes, and purely epoxy composites.

Investigation of the Structure and Properties of SWCNT-Modified Epoxy Specimens

SWCNT-modified epoxy with advanced electrical properties was investigated in the paper. CFRPs have high specific strength and elastic modulus which are the most important properties for aerospace engineering. However a lack of electrical and heat conductivity makes efficient lightning strike protection and thermal de-icing complicated. In this research electric conductivity of epoxy binder for CFRP production is modified by addition of single-wall carbon nanotubes. Measurements of electrical conductivity of hardened epoxy binders are performed showing good increase of conductive properties.

Effect of Nanoiron Particles Reinforced Blended Polymer Nanocomposites on Mechanical Properties

We report on the preparation of nanocomposites using epoxy and vinylester blend in which nanoiron filler was dispersed to evaluate the mechanical performance. Different weight ratios viz.1,2,3,4,5 & 7wt.% of nanoiron particles were dispersed into the matrix to prepare different systems to evaluate the optimization of performance. Nanoiron was also prepared by chemical reduction method and nanocomposites were prepared by hand layup process. Three blade Mechanical stirrer and ultra-sonicator was used while preparing the modified to keep the non-homogeneity nanoparticle at bay. Mechanical properties such as hardness, tensile strength, flexural strength, impact strength and compression strength properties were performed. Nanoiron particles functionalization nepotisms the fabrication composites through the remedial temperature at low as associated to the as-synthesised nano particles occupied vinylester nano composites. Mechanical property values improved owing to the standardized nanoparticle chemical bonding and spreading between vinylester matrix and nanoparticles. Then the combination nanoiron particles into the vinylester resin matrix it becomes magnetically harder. Machines generated mechanical property values were compared and analysed with system generated software analysis of variance (ANOVA) values. Machine values and ANOVA values were measured for the specimens of epoxy+vinylester+nanoiron, where the nanoiron is varying viz. 1, 2, 3, 4, 5 and 7 wt.%.

In-situ Full Field Out of Plane Displacement and Strain Measurements at the Micro-Scale in Single Reinforcement Composites under Transverse Load

Micromechanics damage models applied to composites predict stresses and strains in the matrix and fibers as a function of the microstructure, constituting phases mechanical properties and load histories. Material parameters, like interface properties, are identified through inverse methods based on macroscopic stress-strain curves. Predictions are also benchmarked against macroscopic measurements. This situation does not capture local phenomena and hinders the robustness of the indentification/validation process. The purpose of this work is to provide full displacement and strain fields at the scale of a single fibre embedded into a matrix to allow the modelling community to either develop and identify micromechanics damage models or to benchmark their own predictions. Such data is critically lacking in the community. To that end, we have investigated three single fibers having radically different bonding strength with epoxy in addition to a bundle of about a hundred carbon fibers that were used as reinforcements of standard “dogbone” epoxy specimens. A laser scanning confocal microscope (LSCM) is used for micro digital image correlation (μDIC) during in-situ quasi-static tests of single-reinforcement dogbone specimens. For all specimens, damage initiated with fiber debonding at the free surface along the tensile direction. The crack then propagates around the interface while slightly growing along the fiber. The interfacial crack is shown to grow faster for couples with weak interfacial bonding. Strong fiber / matrix bonding is shown to stop Mode II transverse interfacial debonding which significantly delays specimen failure. Analysis of the LSCM micrographs with μDIC is used to provide measurements of displacements, strains, and measure depth during each test. The importance of out of plane displacements in interfacial debonding is highlighted. Out of plane displacement is shown to play a role in interfacial crack opening and growth and ought to be considered when studying or modeling damage in FRCs. μDIC is shown to be a promising technique to provide a better understanding of the damage mechanisms at the fiber or bundle scales and to determine interfacial toughness of a specific fibre / matrix couple in order to perform accurate damage modeling in FRCs. Displacement, strain, and confidence field results for each pixel from each experiment and at each time step are also provided in an extensive data package for detailed comparison with simulation results.

Fatigue Failure Load of a Bonded Simplified Monolithic Feldspathic Ceramic: Influence of Hydrofluoric Acid Etching and Thermocycling.

To evaluate the effect of hydrofluoric acid (HF) etching and thermocycling (Tc) on fatigue failure load of feldspathic ceramic restorations cemented with two resin cements. Disc-shaped feldspathic ceramic (Vitablocs Mark II; Ø=10 mm, 1.0-mm thick) and G10 epoxy resin (Ø=10 mm, 2.5-mm thick) specimens were made and randomly allocated considering three factors: ceramic etching (ie, with vs without 10% HF plus silane application), resin cement (ie, self-adhesive [RelyX U200; U200] or conventional [Multilink Automix; MA]), and Tc (ie, with vs without 5-55°C/12,000 cycles). Adhesive cementation followed each manufacturer's instructions. The fatigue test (n=20) was based on the staircase approach (250,000 cycles; 20 Hz). Contact angle, surface topography, and fractography analysis were also executed. Specific statistical tests were employed for each outcome (α=0.05). The interaction of HF and Tc factors decreased the fatigue resistance for both cements (U200 542.63>U200/HF-Tc 495.00; MA 544.47>MA/HF-Tc 506.84). Comparing the cements associated with HF or Tc, there was statistical superiority for MA (U200-Tc 537.37<MA-Tc 561.32; U200/HF 535.79<MA/HF 557.11), and no statistical difference was detected when only cement type or its association with HF-Tc was compared (U200 542.63=MA 544.47; U200/HF-Tc 495.00=MA/HF-Tc 506.84). The fracture always originated from defects at the ceramic-intaglio surface as radial cracks. HF etching plus silane agent increased the ceramic surface free energy and its wettability, but it did not provide better results in terms of fatigue resistance compared with silane agent application only. The association of HF etching and aging significantly reduced the fatigue resistance of the material, regardless of the resin cement used.

A two-step approach for synthesis, characterization and analysis of dicyclopentadiene–urea formaldehyde–siloxane-based double-walled microcapsules used in self-healing composites

Microencapsulation is a widely used method for making healing agents used in self-healing composites. In this study, a novel two-stage process was used to make double-walled microcapsules. Dicyclopentadiene–urea formaldehyde (DCPD–UF) microcapsules were synthesized by in situ polymerization of oil-in-water emulsion followed by siloxane coating through ‘sol–gel process’ (DCPD–UF–siloxane microcapsules). Average diameter of microcapsules, UF shell thickness and siloxane coating thickness were found to be 300, 1.4 and 16 µm, respectively. The effect of addition of microcapsules on rheological properties of epoxy was studied. Breaking pattern of single-walled and double-walled microcapsules immersed in epoxy was analyzed by continuous monitoring of the deformation behavior through a rheometer–microscope arrangement, confirming improved mechanical properties of the double-walled microcapsules. In this study, epoxy resin cast specimens with and without microcapsules were prepared and the effect of microcapsules on mechanical properties was examined. Epoxy specimens with double-walled microcapsules were found to be having improved mechanical properties compared to those with single-walled microcapsules. Finally, healing efficiency of DCPD–UF–siloxane microcapsules in epoxy was observed to be marginally higher, and therefore, this double-walled microcapsule system is shown to be a promising candidate for further self-healing composite investigations.

Experimental Study on Microwave-Based Curing Process with Thermal Expansion Pressure of PTFE for Manufacturing Carbon Fiber/Epoxy Composites.

Conventional composite curing incur high production costs because of their long processing times. In contrast, microwave curing process (MCP) can reduce the production costs because both the mold and the composite parts can be heated directly. In this study, a mold consisting of polytetrafluoroethylene (PTFE), quartz glass, and stainless steel clamps was manufactured to cure composite specimens of carbon fiber and epoxy resin. Flame test was conducted prior to the MCP to confirm whether the spark occurred in the mold and the composite prepreg. Uniaxial tensile tests and three-point bending tests were then conducted to obtain the mechanical properties of the composite specimens according to the input power and the processing time. The mechanical properties of the composite specimens fabricated by MCP were compared with those of composite specimens manufactured by PCF. The results show that MCP can cure the composite prepreg more rapidly than PCF and can attain comparable mechanical properties.

DVC analysis of a polymer material subjected to tensile loading with synchrotron radiation tomography

Subsurface deformation behavior of a polymeric material is studied through the digital volume correlation (DVC) technique. Fundamental principles of the DVC technique are presented and the supplemental state-of-the-art algorithmic schemes to improve the efficiency and accuracy of the DVC analysis are also introduced. Tensile tests on an epoxy material are performed in conjunction with synchrotron radiation tomography. In order to create randomly distributed grayscale values in the tomograms for the following image analysis, microscale high-density particles are embedded when the epoxy specimens are fabricated. 3D tomographic images taken at multiple loading steps are utilized for the DVC analysis. The performance of the present DVC analysis is evaluated with the experimental data.

Effect of load parameter on tribological behavior of UHMWPE/Pongamia oil-cake incorporated basalt epoxy composites

The wear nature of basalt epoxy specimens incorporated with both POC and UHMWPE was studied by using wear test tribometer. The wear rate was calculated with respect to applied load. The test specimens were formulated using VARTM technique. The % of filler material in the specimen was varied from 0 wt% to 6 wt% (POC and UHMWPE). The outstanding wear behavior was recovered with basalt composites with the fillers. The fracture surface of the specimens was examined by using high resolution scanning electron microscope to analyze the wear data. It was observed that addition of fillers is very important when the worn out of the specimen at initial stages. The process of tribo-film, fibre breakages accounts for wear at much later stages.

Nanomechanical Properties of a Bicomponent Epoxy Resin via Blending with Polyaryletherketone

In order to investigate the nanomechanical behaviors and nanotribological properties of bicomponent epoxy resin (BE) blends, which were filled with thermoplastic polyaryletherketone (PAEK) powders, nanoindentation and nanoscratch tests were performed. The brittle fractured morphologies of bicomponent epoxy resin blends were studied. The microhardness and elastic modules of the materials were measured using the nanoindentation technology. The hardness, elastic modulus, and other mechanical properties of materials on a nanoscale were determined. Nanoindentation and scratch experiments showed that the indentation response is dominated by plastic deformation. The microhardness is the lowest as the content of PAEK powders is increased to 30 parts per hundred parts of resin (phr), while that of the neat bicomponent epoxy resin specimen is the highest. Furthermore, the pristine bicomponent epoxy resin (BE) exhibited better load-carrying and indentation recovery capacity than the other three samples. The nanoscratch results indicate that the frictional coefficient of the BE/PAEK-30 blend is the lowest, and while that of the pristine bicomponent epoxy resin is the highest, with better scratch/wear resistance.

Effects of environmental exposures on carbon fiber epoxy composites protected by metallic thin films

Carbon fiber epoxy composites have a wide range of applications in aerospace, construction, and automotive industries due to their good mechanical properties and lightweight characteristics. Carbon fiber epoxy composite structures are typically intended for service in corrosive and hostile environmental conditions. Therefore, development of coatings which are able to protect carbon fiber epoxy composite laminates against prolonged and harsh environmental conditions such as ultraviolet radiation and moisture deems critical. This paper offers a novel method for environmental protection of fiber-reinforced polymer composites by applying thin metallic films on composites' surface as coating materials. In order to investigate the protective properties of metallic thin films, copper and aluminum coatings were deposited on the surface of carbon fiber epoxy specimens by using direct current magnetron-sputtering technique, and then mechanical properties and surface morphology of specimens were monitored during the course of accelerated environmental exposure. Both metallic coatings showed good adhesion to carbon fiber epoxy samples during environmental aging and provided protection for the specimens' surface against environmental degradation. The correlation between flexural properties and surface morphology of carbon fiber epoxy specimens is also presented.

In-Situ Reduced Graphene Filled Epoxy NanoComposite With Highest Storage Modulus

Reduced graphene fillers were integrated into epoxy nanocomposites by solvent exchange of GO solution to acetone, ethanol and DMF, and subsequent in-situ thermal reduction and curing. The comparative fracture specimens of neat epoxy, acetone-rGO/epoxy, and DMF-rGO/epoxy showed ethanol-rGO/epoxy had greater load transfer by bonding and functionalization of the rGO surface with polymer chains from the epoxy via the solvent. The TGA and DTG showed marginal drop in the stability of the nanocomposites behind the neat epoxy, and DSC heat loss magnitude showed superior chemical bonding within ethanol-rGO/epoxy. The modulus increased with rGO content from 0, 0.05, 0.1, 0.2, 0.3 and 0.4 wt%, while the highest tensile strength was at 0.2 wt%. Thereafter, the dynamic and viscoelastic mechanical characteristics of rGO-epoxy nanocomposites: while the 0.4 wt% of rGO in ethanol-rGO/epoxy exhibited the highest storage modulus of 4144 MPa 0.91 tan delta, and a marginal decrease in glass transition temperature, Tg, while highest Tg was 115 ⁰C at 0.05 wt%. The dynamic mechanical storage moduli were fairly constant with increased amplitude from 0 to 4 µm, while loss moduli and tan delta only reduced at lower amplitudes from 0-4 µm.

Detection of Delamination in Polymer Composites by Digital Image Correlation-Experimental Test.

Fiber-reinforced polymer composite structures are frequently used in industries where personal safety is critical; therefore, it is important to periodically estimate or monitor the condition of high value, load bearing structures. The digital image correlation (DIC) is well known as an effective method to obtain full field surface strains; in this paper, it was used to detect artificial damage inside the structures. Carbon or glass fabric reinforced epoxy specimens were produced and tested. All specimens contained an artificial through-delamination which was created by the insertion of different foils of a mould release agent during production. Tensile and compression tests were done while the camera system collected the images of the deformed surface to be analyzed posteriorly. In most cases the approximate locations of delaminations could be effectively detected from strain maps by the localization of zones showing different strain values than intact zones.

Effect of gamma irradiation on the optical properties of epoxy resin thin films

The optical properties of irradiated epoxy resin films with different thickness were carried out using a UV spectrophotometer. epoxy-resin specimens were subjected to gamma- rays with doses varying from 0 to 120 kGy. The optical parameters were evaluated in a wavelength range between (190 to 1100 nm). The optical parameters such as; absorption coefficient (α), optical density (OD), skin depth (SD), extinction coefficient (k), refractive index (n), optical band gap Eg, dielectric constant (ε1), and dielectric loss (ε2) were determined. The results indicate that the optical behavior of epoxy thin films is a good transparent in the low wavelength region. It was found that the evaluated optical band gap (Egdir, Egin) decreases with increasing thickness and gamma irradiation doses. In addition, the type of electronic transmission is indirect.

Effect of Hydraulic Liquid and Sea Water on the Mechanical Characteristics of Polymeric Fibrous Structures

The degradation of the mechanical characteristics of typical composite materials under the action of the working liquid is studied. Polypropylene and epoxy specimens reinforced with a glass fabric with the warp fiber orientation 0, ± 45, and 90° have been investigated according to the ISO 527-4 standard. The materials were a polypropylene composite based on stitched glass fabric and an epoxy-bonded glass fabric and carbon fabric reinforced composite. The basic mechanical characteristics of the materials under investigation have been determined. The specimens were kept in an AMg10 hydraulic liquid and in sea water for 910 hours with periodic weighing. The characteristics of the process of adsorption of working liquids by the materials under investigation: adsorption rate coefficient and the maximum amount of the adsorbed liquid have been determined. An investigation to detect damages caused by the liquids adsorbed by materials has been carried out. The specimens with adsorbed liquids were held at 255–373 K with subsequent tensile test. It has been found that the liquid in the material causes its swelling owing to liquid pressure. It is assumed that the characteristics degrade in proportion to swelling pressure. The effect of the above liquids on the strength characteristics of the materials under investigation has been studied by keeping them in these liquids for different time intervals (0–840 h), followed by a tensile test. The effect of through-thickness stitching along the test direction 90° on the mechanical characteristics of a material with a liquid in comparison with other test directions has been studied. The laws governing the effect of the above liquids on the mechanical characteristics of materials in time have been established. Based on experimental data, a model of the behavior of the composite under investigation under the above conditions has been developed, and numerical calculations have been performed. The calculated curves give a fairly good fit to experimental data, which confirms the described approach to be correct.

Effects of Carbon Fiber Hybridization on the Compressive Strength of Glass-Carbon/Epoxy Hybrid Composite Pipes before and after Low Velocity Impact

In this paper, the effect of carbon fiber hybridization on the compressive strength of glass-carbon/epoxy hybrid filament wound pipes before and after low velocity impact was investigated experimentally. Specifically, the effects of different stacking sequence and fiber content ratio on the compression and compression after impact (CAI) behavior of hybrid glass-carbon fiber reinforced polymer pipes were analyzed. Hybrid composite pipes composed of eight layers of / reinforced with thin HDPE liner were manufactured utilizing filament winding technique. A series of axial compressive tests were carried out on the composite pipes for the non-impacted and impacted specimens under 100 J of impact energy. Residual compressive strength, damage tolerance and failure modes were examined and analyzed for different pipe configurations, before and after the impact. The failure modes of non-impacted and impacted composite pipes under compressive loading were analyzed visually. The results show that, under the same conditions of impact energy, specimens with alternative fibers exhibited better impact resistance regardless of fiber content ratio. Moreover, carbon fiber reinforced epoxy specimens exhibited the worst impact damage tolerance for a given impact energy level although having the highest compressive strength before impact among the samples, with the highest percentage reduction of 62% in residual compressive force after impact.

Shape recovery characteristics of shape memory epoxy composites reinforced with chopped carbon fibers

Epoxy resin, which demonstrates a shape memory effect, is reinforced by chopped carbon fibers (CCFs) to improve the thermal and mechanical properties. The interfacial interactions between 2-mm-long CCFs and epoxy make an impact on not only molecular motion but also the physical behaviors of CCFs/epoxy composites. In particular, shape recovery ability of CCFs/epoxy composites is enhanced with an increase in thermal conductivity generated by crossing CCFs in the epoxy system, although CCFs/epoxy composites containing small amounts of CCFs, such as 1 or 3 phr (parts per hundred rubber), show slower recovery rates than those of raw epoxy specimens due to the difficulty of making heat bridges in composites. With these results, it is confirmed that for specific time-dependent purpose, the shape recovery vector of CCFs/epoxy can be controlled using the amount of CCFs.

State of water in void-free and void-containing epoxy specimens

The effect of voids on the state of water absorbed in epoxy has been examined using differential scanning calorimetric analysis for a range of void contents (0 to 50%). For void-free specimens, water absorbed is classified as bound water (nonfreezing). Analysis of the medium and high void content specimens revealed water absorbed in three states: free water, freezable bound water, and nonfreezable bound water. The differential scanning calorimetric results show that the proportions of free water and freezable bound water increase with increasing void content, while the content of nonfreezable bound water decreased. Moisture-induced swelling decreased with increasing void content. The swelling is attributed to the content of nonfreezable bound water as determined by differential scanning calorimetric analysis.

Formulation of a mixed-mode multilinear cohesive zone law in an interface finite element for modelling delamination with R-curve effects

A constitutive model for an interface finite element is proposed to enable simulation of delamination in composite materials with R-curve effects. The constitutive model is formulated in the framework of cohesive zone modelling (CZM). In essence, a multilinear CZ law with an arbitrary number of line segments is developed. The CZ law seeks to enable constitutive modelling of failure mechanisms on multiple scales within the fracture process zone and reduce conventional a priori assumptions regarding the shape of the CZ law. The CZ law relies on damage mechanics, an equivalent one-dimensional formulation, and criteria for mode interactions to simulate delamination under mixed-mode loading. Special emphasis is put on the derivation of interpolation formulas and a constitutive tangent stiffness tensor for the multilinear formulation. The constitutive model is implemented in the commercial FE program ANSYS Mechanical, for implicit finite element analysis (FEA), using user-programmable features. The implementation is verified through single interface element numerical studies, and its applicability is demonstrated by simulating an experiment of quasi-static delamination showing large-scale fiber bridging in pure mode I DCB glass-fiber epoxy specimens. Experimental measurements and simulation outputs using the novel cohesive element is compared to those of the conventional bi- and trilinear CZ laws.

Optical Fiber Sensors for the Detection of Hydrochloric Acid and Sea Water in Epoxy and Glass Fiber-Reinforced Polymer Composites.

Optical fiber sensors (OFSs), which rely on evanescent wave sensing for the early detection of the diffusion of water and hydrochloric acid through glass fiber-reinforced polymers (GFRPs), have been developed and tested. Epoxy and GFRP specimens, in which these sensors were embedded, were subjected to tests in artificial sea water and hydrochloric acid. The sensors were able to detect the diffusion of chemicals through the epoxy and GFRP samples on the basis of a drop in the reflected signal from the tip of the optical sensor probe. Water and hydrochloric acid diffusion coefficients were calculated from gravimetric measurements and compared with the experimental response of the OFSs. Furthermore, mechanical tests were carried out to assess the influence of the sensors on the structural integrity of the GFRP specimens.