Fiber Composite Samples Research Articles

Mechanical properties of chemically-treated hemp fibre reinforced sandwich composites

In this study, hemp fabrics were used as reinforcements with polyester resin to form composite skins while short hemp fibres with polyester as a core for making composite sandwich structures. To improve the fibre matrix adhesion properties, alkalisation, silane and acetylation treatments on the fibres surface were carried out. Examinations through fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to investigate the physical and thermal properties of the fibres. Mechanical properties such as flexural and compressive strengths of the sandwich structures made by treated and untreated hemp fibres were studied. Based on the results obtained from the experiments, it was found that the fibre treated with alkalic solution and post-soaked by 8% NaOH exhibited better mechanical strength as compared with other treated and untreated fibre composite samples. Besides, DSC and TGA analysis showed that the thermal stability of all treated fibre was enhanced as compared with untreated samples.

Flexural Mechanical Characteristic of Sawdust and Chipwood Filled Epoxy Composites

A study was conducted with the objective of gathering the information through flexural (three-point bending) testing. This research presents the testing results concerning the mechanical properties, modulus of elasticity (MOE) and modulus of rupture (MOR) of natural fiber reinforced composite. Resin were used as a matrix and untreated wood fibres contents 14% by weight as a filler treatment parameters to obtain better compatibility involving wood fibres Sawdust (SW) and Chipwood (CW) and epoxy. The feasibility of processing the composite prepared manually from waste wood and epoxy using open molding was investigated. The tests that have been conducted are in according to ASTM (D790-97) for flexural properties test method. Statistical analysis using ANOVA one way and two way showed that the differences of results obtained from those SW and CW fiber composite samples are significant, which confirm a very firm mechanical performance of the composites through flexural tests. This shows the producing a good quality of SW and CW fibre composite which maybe can use for furniture utilities.

Tensile Properties and Micromorphologies of Sawdust and Chipwood Filled Epoxy Composites

In this study, waste wood product obtained from the timber industry originating from various type of wood has been investigated. Research work carried out on the three different sizes of fiber derived from the sawdust (SW) and chip wood (CW). The SW and CW fiber and epoxy resin were blended together respectively using hand tools machine, all specimens of fiber composite were prepared accordance to the ASTM standards. Tensile and morphological properties provide an excellent measure of the degree of reinforcement provided by the fiber to the composite. The tensile modulus increased with the filler size from coast to rough of composites both SW and CW but decreases steadily with the wood–fiber size from rough to soft content. Statistical analysis using one way and two ways analysis of variances (ANOVA) showed that the differences of results obtained from those SW and CW fiber composite samples are significant, which confirm a very firm mechanical performance of the composites through tensile tests. This shows the producing a good quality of SW and CW fibres composite which maybe used for home furniture utilities.

Deuterium inventory in plasma facing materials by means of NRA: A microbeam probe approach

Particle retention in tokamak walls is a key issue for long time discharges in future thermonuclear fusion reactors. Plasma wall interactions drive the fuel retention through two major mechanisms: co-deposition with carbon produced by wall erosion and particle retention in wall materials. In this study, we report results obtained from the tokamak Tore Supra, from which two types of samples were analyzed by means of micro-NRA: (i) small pieces of deposited carbon layers were collected after cumulative discharges and deuterium contents were measured; (ii) carbon fiber composite (CFC) samples, immersed in the plasma during an experimental campaign were also analyzed. 3D deuterium elemental mapping demonstrated that deuterium can be trapped at depths much higher than usual implantation depths and deep local retention sites have been evidenced and localized.This study demonstrates that μNRA can be used for assessment of deuterium post-mortem inventory in tokamaks, both by measuring uniformly distributed deuterium in small fragments of deposited carbon layers and by locally describing deuterium 2D and 3D distributions in complex structures.

FIRE DAMAGE ON CARBON FIBER MATERIALS CHARACTERIZED BY THZ WAVES

We apply THz imaging technology to evaluate fire damage to a variety of carbon fiber composite samples. The majority of carbon fiber materials have polarization-dependent reflectivities in the THz frequency range, and we show how the polarization dependence changes versus the burn damage level. Additionally, time domain information acquired through a THz time-domain spectroscopy (TDS) system provides further information with which to characterize the damage. The technology is discussed in terms of non-destructive testing applications to the defense and aerospace industries.

Durability of glass‐fiber‐reinforced polymer nanocomposites in an alkaline environment

AbstractThis study was conducted to determine the effect of clay content in GFRP (glass‐fiber‐reinforced polymer) composite samples as they were aged in an alkaline solution. Two kinds of GFRP composite samples were prepared. One was E‐glass‐fiber‐reinforced vinyl ester polymer, and the other was nano‐GFRP composites prepared with the addition of 1 and 2 wt% of montmorillonite clay to the polymer matrix. These samples were aged in alkaline solution of pH 13.2 with and without sustained load. The load was 1335 N or 18.7% of the tensile strength of the composite samples. The aging was evaluated by measuring the reduction in tensile strength after 6 months. Also, absorption of alkaline solution into the plain and nano‐GFRP samples was investigated so as to elucidate the diffusion behaviors. It was found that for a short exposure time (e.g. 1 month) and without sustained load, dispersing 2 wt% of the nanoclay in the polymer matrix of the GFRP samples reduces the diffusivity by 39%. However, with the application of sustained load, the glass fiber composite samples deteriorate more with increasing clay content. The reduction in tensile strength was 7.1%, 12.1%, and 18.1% for the samples containing 0, 1, and 2 wt% of clay, respectively. J. VINYL. ADDIT. TECHNOL., 12:25–32, 2006. © 2006 Society of Plastics Engineers

Manufacturing carbon nanofibers toughened polyester/glass fiber composites using vacuum assisted resin transfer molding for enhancing the mode-I delamination resistance

Abstract Polymer composite materials reinforced by continuous fibers have excellent in-plane strength but are usually weak against delamination. This paper presents an experimental study of using carbon nanofibers (CNF) to improve the interlaminar fracture properties of polyester/glass fiber composites. Surfactant-treated CNF were dispersed in polyester resin and then the CNF-resin suspension was infused to impregnate a glass fiber preform using vacuum assisted resin transfer molding (VARTM). The manufacturability of using VARTM for thick and large CNF toughened composite parts has been experimentally investigated. The influence of CNF concentration on the CNF filtration in the glass fiber preform, the resin viscosity, and the micro-void formation has been examined. By choosing appropriate manufacturing parameters, we were able to use VARTM process to infuse the surfactant-treated CNF/resin matrix into the glass fiber preform and successfully manufactured the CNF toughened polyester/glass fiber composite specimens for mode-I delamination tests. The critical energy release rates of mode-I delamination ( G IC ) were characterized for several composite specimens with 1 wt% CNF concentrations and for those with pure resin. Significant improvement in the G IC was consistently observed as 1 wt% CNF were added to toughen the polyester resin. Microscopy pictures showed that the fracture surfaces of the 1 wt% CNF toughened polyester/glass fiber composite samples were more complex than the fracture surfaces of regular polyester/glass fiber composites.

Environmental fatigue of unidirectional glass–carbon fiber reinforced hybrid composite

Abstract Unidirectional glass fiber reinforced and glass–carbon fiber reinforced (glass to carbon fiber volume ratio 3:1) epoxy matrix composite samples were subjected to tension–tension fatigue in air and in distilled water at 25°C. While no significant change in fatigue life was observed for both types of samples tested in air and in water when cyclically tested at 85% of average ultimate tensile strength (UTS), the detrimental effect of water becomes apparent at lower stress levels of 65 and 45% UTS. Compared to samples tested in air, cyclic loading in water results in shorter fatigue lives for both glass and hybrid samples. While all of the glass fiber composite samples did not survive to 106 cycles when loaded in water, hybrid samples showed better retention in structural integrity under environmental fatigue for lives up to 107 cycles, a consequence of the corrosion resistant of carbon fiber. Thus, by incorporating appropriate amount of carbon fibers in glass fiber composite, a much better performance in fatigue can be achieved for glass–carbon hybrid composite.

Effect of transcrystallization in carbon fiber reinforced poly(p-phenylene sulfide) composites on the interfacial shear strength investigated with the single fiber pull-out test

The effect of transcrystallinity in carbon fiber reinforced poly(p-phenylene sulfide (PPS) composites on the apparent shear strength was investigated with the single fiber pull-out test. Transcrystalline zones around the reinforcing fibers do not seem to improve the adhesion level significantly. Neighbor fibers hinder the formation of the transcrystalline zone and a ductile fracture behavior can be observed. However, the apparent strength level is slightly higher for composites containing such reinforcing neighbor fibers compared with single fiber composite samples. During annealing a brittle interface can be formed in the multifiber composite yielding a higher level of the apparent shear strength.

Transportable infrared line scanner based equipment for thermal nondestructive testing

Abstract Transportable equipment for on-site thermal nondestructive testing is described. The equipment is constructed from two separate units: a hand-held infrared line scanner and a remote unit containing all the necessary control devices. The sample surface is heated by manually scanning a line source over the surface and the resulting surface temperature rise is simultaneously measured with the line scanner. The heating line is generated either by a line-focused laser beam or by a radio frequency induction coil. The obtained surface temperature distribution of the monitored area is presented as a pseudo-color image. The feasibility of the method is demonstrated with a carbon-glass fiber composite sample.

Crystallization and chain adsorption of poly(etheretherketone) in discontinuous pitch‐derived carbon fiber composites

AbstractThe crystallization kinetics of poly(etherether ketone) (PEEK) in chopped mesophase pitch‐derived carbon fiber/PEEK composites have been studied. Various processing techniques are used in order to obtain controlled fiber length in the composites. Scanning electron microscopy performed on properly etched long fiber composite samples reveals that the nucleating sites density is low at the carbon fiber surface: transcrystalline layers are rarely observed. This is confirmed by differential scanning calorimetry. However, samples processed by mixing carbon fibers and molten polymer in a high temperature mixer have a widely different behavior: the nucleation density and the crystallization rate increase, the glass transition of these samples is displaced towards higher temperatures, and the solubility is dramatically lowered. We ascribe these phenomena to the adsorption of the polymer chains on carbon particles created by attrition during the mixting.

Characterization of polypyrrole-fibre composites by time-of-flight secondary ion mass spectrometry and vibrational spectroscopy

We have examined polypyrrole-polyester and polypyrrole-quartz fibre composite samples using time-of-flight secondary ion mass spectrometry (TOF-SIMS). This technique has allowed us to confirm that in each composite the conducting polymer overlayer of cationic polypyrrole chains is doped with 5-sulphosalicylate dopant anions, at least to a sampling depth of 10 Å. Surprisingly there is no detectable presence of the second aromatic sulphonate dopant anion utilized in the Milliken synthetic procedure (1,5-naphthalenedisulphonic acid, disodium salt). Our Fourier transform ( FT) Raman spectra of these polypyrrole-fibre composite contain strong spectral bands due to the cationic polypyrrole chains, several weak features due to the underlying fibre substrate (particularly in the case of the polyester fibres), and no bands attributable to the dopant anions. These observations suggest that the Raman scattered light from the substrate component is largely reabsorbed by the polypyrrole overlayer. Thus we conclude that there must be extensive coverage of the fibre substrate by the conducting polymer with few, if any, ‘bare’ patches. Finally, our FTi.r. microscopy studies on these coated composites produced good quality spectra of the underlying substrate with few features attributable to the polypyrrole overlayers.

Stiffness matrix invariants to validate the characterization of composite materials with ultrasonic methods

This paper presents a method of testing the ultrasonic measurements of the stiffness matrix, and the identification of the anisotropic behaviour, of composite materials. Some linear combinations of elastic constants are invariants for a rotation around an axis of symmetry. If the stacking sequence is the only parameter which changes in a set of long-fibre composites made of the superimposition of plies, the composites must own these invariants. So, PEEK-carbon fibre composite samples were constructed in this way to measure their elastic properties by immersion and contact ultrasonic methods, and to compare the results with predicted invariants. By changing the stacking sequence of plies three anisotropic models are tested: orthotropic, hexagonal and quadratic. Measurements of ultrasonic velocities in various planes of propagation permit the identification of the elastic constant and invariants. From the invariance of these linear combinations, the precision of the three-dimensional effective moduli can be estimated.

Transverse loading of monofilament reinforced microcomposites: a novel fragmentation technique for measuring the fibre compressive strength

Carbon/J-polymer single fibre composite samples were tested under tensile conditions with the fibre direction perpendicular to the tensile loading axis. The Poisson ratio effect induced a compression strain field in the fibre, resulting in a fragmentation phenomenon similar to that observed in a fibre subjected to tensile loading. This observation introduces a novel technique for the measurement of the compressive strength of single fibres, calculated either from the stress at first break, or from the Weibull scale parameter obtained from the fragmentation data produced at various stress levels. The special sample loading configuration used here also provides the first measurement of the effect of the length of the fibre on its compressive strength value.

Damping characteristics of fabric and laminated Kevlar composites

A set of experimental tests on damping coefficient measurements for Kevlar fibre composite samples, both fabric and laminated, is presented. The damping coefficient values, which are independent of the composite Young's modulus value and of the type (fabric or laminate), are greater than typical values for carbon or glass fibre composites. This behaviour can be explained by realizing that in Kevlar composites the fibre behaves as a viscoelastic material and its damping coefficient is of the same order as that of the matrix. The prediction of the damping coefficients by an energy approach validates the experimental results.

Wide‐angle x‐ray scattering study of heat‐treated peek and peek composite

AbstractWe report the results of a study of poly(etheretherketone) (PEEK) neat resin and APC‐2 carbon fiber composite samples which were processed from the melt and then subjected to a variety of thermal treatments. Wide‐angle x‐ray scattering was used to study the effects of quenching and annealing treatments. For both neat resin and composite, annealing resulted in perfection of the crystalline microstructure. In addition to the crystalline and amorphous scattering usually observed, disorder is frozen‐in by fast cooling after heat treatment. The disordered component is detected as an additional low‐angle scattering peak at 14 degrees, well separated from the crystalline reflections, and is observed in low molecular weight material synthesized in our laboratory, and in commercially available neat resin PEEK and APC‐2 carbon fiber composite samples. When disordered material was subsequently heated above the glass transition, and then cooled very slowly, only the crystalline and amorphous scattering remained. Application of stress also resulted in formation of the disorder in the necked down regions of samples drawn in tension, suggesting that residual stresses may occur as a result of rapid cooling after heat treatment.

A symmetrical straining jig for use under the microscope

A small, stiff rig is described which enables polymer or fibre composite samples to be strained symmetrically under the microscope. This ensures that the field of view remains central and facilitates both observation and measurement.