Single Fiber Tensile Test Research Articles

Optimal synergy between micro and nano scale: Hierarchical all carbon composite fibers for enhanced stiffness, interfacial shear strength and Raman strain sensing

Multifunctional hierarchical reinforcements are fabricated by growing multi walled carbon nanotubes (CNTs) onto carbon fibers (CFs) via chemical vapor deposition. In contrast to typical hybrid multi scale reinforced composites, the biomimetic approach of hierarchical interconnection between CFs and CNTs is followed in order to provide the dimensional confinement required for the effective synergy between the nanophase i.e. the CNTs and the micron phase i.e. the CFs. Compared to the reference CF: (i) ASTM single fiber tensile tests reveal up to 50% increase in tensile modulus together with the expected decrease in tensile strength, (ii) Single Fiber Fragmentation Tests (SFFT) reveal up to 134% enhancement for Interfacial Shear Strength (IFSS), (iii) the frequency of the Raman 2D graphitic vibrational mode with strain shows a strain sensitivity enhancement up to 87.4% and (iv) fractographic investigation shows bridging of the CNTs only for specific growth conditions, which correspond to the optimal IFSS. Furthermore, a direct correlation between the Raman strain sensitivity with the young moduli of the CF and the hierarchical CF-CNT is found, proving the efficient stress transfer from the nano to micron scale in a “composite” fiber. Overall, an optimal synergy between the reinforcing graphitic phases is achieved, attaining for the first time an equivalent stiffness for the CNT reinforcement close to theoretically obtained values. Thus, biomimetic hierarchical reinforcements provide the roadmap for the full exploitation of the unique properties of the nanophase in advanced structural composites.

Study of composite-based natural fibers and renewable polymers, using bacteria to ameliorate the fiber/matrix interface

In this paper, bacteria belonging to the species Acetobacter xylinum were used to modify the surface of natural fibers by depositing nanosized bacterial cellulose around natural fibers which enhances their adhesion to renewable polymers. Single fiber tensile test was used in order to determine their mechanical properties and surface. The practical adhesion between the modified fibers and the renewable polymers cellulose acetate butyrate is quantified using the single fiber pullout test. Simple weight gain measurements before and after the modification show that about 4 and 6% bacterial cellulose adheres to the fibers as a result of the bacterial modification procedure. Scanning electron microscopy micrographs confirm the presence of attached bacterial cellulose on the surfaces of natural fibers.

Thermal and Mechanical Properties of Bamboo Fiber Reinforced Epoxy Composites.

Bamboo fibers demonstrate enormous potential as the reinforcement phase in composite materials. In this study, in order to find suitable NaOH concentration for bamboo fiber treatment, bamboo fibers were treated with 2 wt.%, 6 wt.% and 10 wt.% NaOH solutions for 12 h, respectively. We determined that 6 wt.% NaOH treated bamboo fibers were optimal for the fabrication of bamboo fiber composites by single fiber tensile test, single fiber pull-out test, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The short length bamboo fibers treated with 6 wt.% NaOH solutions were well dispersed in the epoxy matrix by a new preparation method. The effect of fiber content and fiber length on the mechanical behavior of bamboo fiber reinforced epoxy composites was investigated. The results confirmed that fracture toughness and flexural modulus of the composites monotonically increased with fiber length and content. However, for all samples, composites showed negligible difference on the flexural strength. The fracture surfaces of the composites were observed by SEM, revealing that fiber breakage, matrix cracking, debonding, and fiber pull out were major failure types. In addition, thermogravimetric analysis (TGA) was carried out to investigate the thermal behavior of both bamboo fibers and composites.

Continuous carbon nanotube synthesis on charged carbon fibers

Carbon nanotube grafted carbon fibers (CNT-g-CFs) were prepared continuously, spool to spool, via thermal CVD. The application of an in-situ potential difference (300 V), between the fibers and a cylindrical graphite foil counter electrode, enhanced the growth, producing a uniform coverage of carbon nanotubes with diameter ca. 10 nm and length ca. 125 nm. Single fiber tensile tests show that this approach avoids the significant reduction of the underlying carbon fiber strengths, which is usually associated with CVD grafting processes. Single fiber fragmentation tests in epoxy, with in-situ video fragment detection, demonstrated that the CNT-g-CFs have the highest interfacial shear strength reported for such systems (101 ± 5 MPa), comparable to state-of-the-art sizing controls (103 ± 8 MPa). Single fiber pull-out data show similar trends. The short length of the grafted CNTs is particularly attractive for retaining the volume fraction of the primary fibers in composite applications. The results are compared with a short review of the interfacial data available for related systems.

Interfacial properties and permeability of three patterned glass fiber/epoxy composites by VARTM

Abstract The interfacial properties for three different glass fiber (GF) mats were evaluated by examining permeability through combining the results of wettability and interlaminar shear strength (ILSS) testing. Three types of GF mats were studied: (1) unidirectional (UD), (2) bidirectional (BD, 0/90°), and (3) randomly-chopped (RC). Single fiber tensile tests were used to compare the fibers in the 3 mats, forty single fibers were extracted from each mat. FE-SEM was used to study damages on the GF in each of the mat types. Fibers from the UD mat exhibited the best mechanical properties and less damage was observed with the FE-SEM. Vacuum assisted resin transfer molding (VARTM) was used to manufacture glass fiber reinforced composite (GFRC) specimens, with the three different mat types. The permeability of the different GF mats was measured, during manufacture of the GFRC, and related to the spreading of the epoxy resins in the GF mats. Short beam tests were performed as a measure of interfacial properties and related to the observed permeability and spreading. GFRC manufactured with UD GF mat exhibited the best interfacial and mechanical properties and displayed the least physical damage while GFRC manufactured with BD GF mat had the poorest interfacial and mechanical properties while exhibiting the most visible damage. The UD GF mat also displayed the smallest change in contact angle and the best permeability. The longitudinal fiber pattern in the UD GF mat apparently promotes capillary effects leading to an increase in wetting rate. This study demonstrates that GF mat pattern affect the interfacial and mechanical properties as well as matt permeability and resin spreading.

Development and application of a quality control and property assurance methodology for reclaimed carbon fibers based on the HiPerDiF (High Performance Discontinuous Fibre) method and interlaminated hybrid specimens

To promote the usage of recycled composite material, it is of paramount importance to develop quality control and property assurance methodologies compatible with the format of reclaimed fibers. In this paper, the concept of using interlaminated hybrid specimens, whose tensile response has been tailored with the aid of the Damage mode maps, is exploited to unambiguously identify the reclaimed fibers failure strain. The interlaminated hybrid specimens are manufacturing by sandwiching a layer of aligned discontinuous reclaimed carbon fibers produced with the HiPerDiF (High Performance Discontinuous Fibre) method between continuous glass fibers. The reliability of the obtained results is compared with results obtained with single fiber tensile tests. The developed methodology is then applied to the investigation of the strength retention of carbon fibers reclaimed through a solvolysis process and to the effects of the fiber length on the HiPerDiF alignment process.

Melt electrowriting below the critical translation speed to fabricate crimped elastomer scaffolds with non-linear extension behaviour mimicking that of ligaments and tendons

Ligaments and tendons are comprised of aligned, crimped collagen fibrils that provide tissue-specific mechanical properties with non-linear extension behaviour, exhibiting low stress at initial strain (toe region behaviour). To approximate this behaviour, we report fibrous scaffolds with sinusoidal patterns by melt electrowriting (MEW) below the critical translation speed (CTS) by exploitation of the natural flow behaviour of the polymer melt. More specifically, we synthesised photopolymerizable poly(L-lactide-co-ε-caprolactone-co-acryloyl carbonate) (p(LLA-co-ε-CL-co-AC)) and poly(ε-caprolactone-co-acryloyl carbonate) (p(ε-CL-co-AC)) by ring-opening polymerization (ROP). Single fibre (fØ = 26.8 ± 1.9 µm) tensile testing revealed a customisable toe region with Young’s Moduli ranging from E = 29 ± 17 MPa for the most crimped structures to E = 314 ± 157 MPa for straight fibres. This toe region extended to scaffolds containing multiple fibres, while the sinusoidal pattern could be influenced by printing speed. The synthesized polymers were cytocompatible and exhibited a tensile strength of σ = 26 ± 7 MPa after 104 cycles of preloading at 10% strain while retaining the distinct toe region commonly observed in native ligaments and tendon tissue. Statement of SignificanceDamaged tendons and ligaments are serious and frequently occurring injuries worldwide. Recent therapies, including autologous grafts, still have severe disadvantages leading to a demand for synthetic alternatives. Materials envisioned to induce tendon and ligament regeneration should be degradable, cytocompatible and mimic the ultrastructural and mechanical properties of the native tissue. Specifically, we utilised photo-cross-linkable polymers for additive manufacturing (AM) with MEW. In this way, we were able to direct-write cytocompatible fibres of a few micrometres thickness into crimp-structured elastomer scaffolds that mimic the non-linear biomechanical behaviour of tendon and ligament tissue.

Structure-property relationships of basalt fibers for high performance applications

Abstract Continuous basalt fibers present a unique combination of good mechanical and functional properties at an attractive cost level. These characteristics can be useful in high performance polymer matrix composites where cost orientation and function integration are becoming priority objectives. The present work examines a currently unresolved problem of basalt fibers regarding high performance applications: the variation of fiber structural and mechanical properties due to inhomogeneity of the natural raw material and the spinning process. Commercial basalt fibers from seven different manufacturers were investigated regarding their fiber chemistry, diameter distribution and occurrence of defects and crystallites. In a second step, structure-property relations on different scales were established with single fiber, impregnated roving and composite tensile test results.

Characteristics of oil palm empty fruit bunch fiber and mechanical properties of its unidirectional composites

The characteristics of waste oil palm empty fruit bunch fiber (OPEFB) including fiber morphology and mechanical properties were investigated for use as reinforcement in polymer composites. The mechanical properties of the OPEFB fiber were determined by the single fiber tensile test which was carried out at different span lengths (20, 40, and 60 mm) to obtain the reliable strength and stiffness of the fiber. The extrapolated E‐modulus at infinite fiber length was found to be around 4.36 GPa. The fiber strength was in the range of 150–190 MPa. The unidirectional (UD) composite of OPEFB fibers in various polymer matrices, namely polypropylene, poly(lactic acid), and epoxy, were prepared and characterized. Three‐point bending test (3PBT) was performed on the UD composites in both fiber transverse and longitudinal directions to determine fiber‐matrix interfacial adhesion and composite flexural properties, respectively. Besides, It was found that the efficiency factors achieved for OPEFB in poly(lactic acid) and epoxy were 0.72 and 0.87, respectively, which were significantly higher than that of OPEFB in polypropylene. This result was consistent with the interfacial strength measured by transverse 3PBT. The study provides fundamental understanding for design and application of OPEFB in polymer composites. POLYM. COMPOS., 40:1158–1164, 2019. © 2018 Society of Plastics Engineers

Scalable manufacturing of carbon nanotubes on continuous carbon fibers surface from chemical vapor deposition

A novel process has been successfully developed to grow carbon nanotubes (CNTs) on continuously moving carbon fibers (CF) surface by a unique open-ended chemical vapor deposition (CVD) furnace. Systematic researches were carried out under various deposition temperatures, velocities of continuous carbon fibers and catalyst concentrations. The morphologies and structures of CNTs were investigated by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM), which indicated clearly that carbon fibers with uniformly distributed CNTs were achieved, with the optimum parameters of 650 °C deposition temperature and 6 cm min−1 velocity of continuous carbon fibers and 0.05 M catalyst concentration, respectively. By means of the single fiber push-out tests, the interfacial shear strength (IFSS) of carbon fibers growing CNTs was increased significantly by 84.4% compared to the desized carbon fibers. Furthermore, the results of single fiber tensile test verified that there is scarcely any degradation in the mechanical properties of carbon fibers after the growth of CNTs with the optimum parameters. This study provides a new and original vision for scalable manufacturing of CNTs on continuous moving substrate, when compared to the traditional batch process.

An enhanced method to determine the Young’s modulus of technical single fibres by means of high resolution digital image correlation

To obtain mechanical tensile properties of materials it is customary to equip the specimen directly with a device to measure strain and Young’s modulus correctly and only within the measuring length defined by the standards. Whereas a variety of tools such as extensometers, strain gauges and optical systems are available for specimens on coupon level, no market-ready tools to measure strains of single fibres during single fibre tensile tests are available. Although there is a standard for single fibre testing, the procedures described there are only capable of measuring strains of the whole testing setup rather than the strain of the fibre. Without a direct strain measurement on the specimen, the compliance of the test rig itself influences the determination of the Young’s modulus.This work aims to fill this gap by establishing an enhanced method to measure strains directly on the tested fibre and thus provide accurate values for Young’s modulus. It is demonstrated that by applying and then optically tracking fluorescing polymeric beads on single glass fibres, Young’s modulus is determined directly and with high repeatability, without a need to measure at different measuring lengths or compensating for the system compliance. Employing this method to glass fibres, a Young’s modulus of approximately 82.5 GPa was determined, which is in the range of values obtained by applying a conventional procedure. This enhanced measuring technology achieves high accuracy and repeatability while reducing scatter of the data. It was demonstrated that the fluorescing beads do not affect the fibre properties.

Effects of Styrene-Acrylic Sizing on the Mechanical Properties of Carbon Fiber Thermoplastic Towpregs and Their Composites.

Thermoplastic towpregs are convenient and scalable raw materials for the fabrication of continuous fiber-reinforced thermoplastic matrix composites. In this paper, the potential to employ epoxy and styrene-acrylic sizing agents was evaluated for the making of carbon fiber thermoplastic towpregs via a powder-coating method. The protective effects and thermal stability of these sizing agents were investigated by single fiber tensile test and differential scanning calorimetry (DSC) measurement. The results indicate that the epoxy sizing agent provides better protection to carbon fibers, but it cannot be used for thermoplastic towpreg processing due to its poor chemical stability at high temperature. The bending rigidity of the tows and towpregs with two styrene-acrylic sizing agents was measured by cantilever and Kawabata methods. The styrene-acrylic sized towpregs show low torque values, and are suitable for further processing, such as weaving, preforming, and winding. Finally, composite panels were fabricated directly from the towpregs by hot compression molding. Both of the composite panels show superior flexural strength (>400 MPa), flexural modulus (>63 GPa), and interlaminar shear strength (>27 MPa), indicating the applicability of these two styrene-acrylic sizing agents for carbon fiber thermoplastic towpregs.

SIFAT MEKANIS SERAT ENCENG GONDOK SEBAGAI MATERIAL KOMPOSIT SERAT ALAM YANG BIODEGRADABLE

The Eichornia crassipes fiber have potentially as a composite reinforcing material. The advantage of composites with natural fibers like to light weight, corrosion resistance, water resistance, attractive performance, and without machining process. The purpose of using natural fiber as an alternative material to replace glass fiber composite material with Eichornia crassipes fibers are friendly and cheap. The research material used Eichornia crassipes fiber, NaOH, Etanol, and H2O. Processing of Eichornia crassipes fiber is washing with water, natural drying ± 10 days in eviromental, fiber taking with steel brush. Dry fibre were subjected to 10%, 20%, 30% NaOH and ethanol solution with variations of immersion time of 2, 4, 6 hours, neutralization with H20, and drying at room temperature. The Single fiber tensile test specimens were made with variations of treatment type in NaOH and Ethanol solution (10%, 20%, 30%), immersion time of 2, 4, and 6 hours. Single fiber test specimens refer to standard ASTM D 3379. Optimum tensile strength test results on NaOH treatment 20% variation of immersion time 4 hours: 28.402 N / mm2 and on ethanol treatment 20% variation of immersion time 2 hours: 48.197 N / mm2.

Tailored glass fiber interphases via electrophoretic deposition of carbon nanotubes: Fiber and interphase characterization

Electrophoretic deposition (EPD) has been used to deposit carbon nanotubes (CNTs) onto glass fibers to strengthen the fiber/matrix interphase of glass/epoxy composites. CNTs were functionalized using an ultrasonicated-ozonolysis followed by polyethyleneimine (PEI) treatment, creating a stable, aqueous dispersion suitable for EPD. Single E-glass fiber filaments were successfully coated with the functionalized CNTs using EPD. Single fiber tensile and microdroplet debond tests were conducted to investigate the tensile properties of the CNT modified E-glass fibers and their interfacial structure and properties in an epoxy matrix, respectively. Weibull analysis of the fiber testing revealed no detrimental effects resulted from the CNT coating, with some evidence to suggest slightly improved strength. Microdroplet tests revealed changes in the fracture modes due to the application of the CNT coating. The interfacial shear-sliding shifted from the fiber/resin interface to the CNT/resin interphase for the CNT modified fibers. Higher effective interfacial shear strength corresponded to the results where fracture propagated deeper into the CNT-rich interphase layer, confirming the trends observed in previous model interphase studies.

Mechanical Characterization of Carbon Fibres Recycled by Steam Thermolysis: A Statistical Approach

The recent development of technologies for recycling carbon fibre reinforced plastics (CFRPs) leads to the need to evaluate the mechanical response of recycled carbon fibres. As these fibres are likely to be degraded during the recycling treatment, it is very important to determine their tensile residual properties so as to evaluate their ability as reinforcement for new composite materials. Carbon fibres reclaimed by a steam‐thermal treatment applied to degrade the epoxy resin matrix of a CFRP are here analysed. Two conditions were chosen so as to reach two degradation efficiency levels of the steam thermolysis. Several carbon fibre samples were selected for mechanical testing carried out either on single filaments using single fibre tensile tests or on fibre tows using bundle tensile tests. It is shown that the single fibre tensile test leads to a wide variability of statistical parameters derived from the analysis. Bundle tensile tests results were able to indicate that fibre strength of recycled carbon fibre is similar to corresponding as‐received carbon fibres thanks to a statistically relevant database. Wide number of tested filaments enabled indeed to obtain low scatters.

Effect of thermoplastic polyurethane (TPU) on the thermal and mechanical properties of polylactic acid (PLA)/curcumin blends

Polylactic acid (PLA) is known to be brittle by nature and thus limits the flexibility of the polymer. A possible solution to enhance the flexibility of PLA is to add a flexible polymeric based material such as thermoplastic polyurethane (TPU). In this study, 30-50 wt% of TPU was added into PLA/curcumin blends to improve its flexibility. Thermal analysis using differential scanning calorimetry shows that further additions of TPU at the expense of PLA did not affect the glass transition temperature, crystallisation temperature and melting temperature of the blends. Fibers of PLA/curcumin/TPU were successfully drawn and Single Fiber Tensile Test (SFTT) showed vast improvement in elongation at break. The initial addition of 30 wt% of TPU to the brittle PLA/curcumin composition causes a significant increase in elongation at break by 39 times and further additions at 50 wt %, the elongation at break increases by 105 times. However, with the increase in elongation, a decrease in strength and Young’s modulus was observed.

An effective non‐covalent grafting approach to functionalize carbon fiber with polyethyleneimine in supercritical fluid to enhance the interfacial strength of carbon fiber/epoxy composites

A facile and effective approach to functionalize carbon fiber (CF) by non‐covalent grafting branched polyethyleneimine (PEI) in conventional and supercritical methods was proposed. Fourier transform infrared (FTIR) spectrometry, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic contact angle analysis (DCA), and single fiber tensile testing were carried out to characterize the CF reinforcements. Interfacial shear strength (IFSS) and transmission electron microscopy were performed to investigate the composites interfacial properties. Experimental results indicated that the non‐covalent grafting polyethyleneimine on CF–COOH increased the polarity, wettability, and roughness of carbon fiber surface. The interfacial shear strength improved significantly using the two methods, especially in supercritical methanol, which further confirmed the previous study. Single fiber tensile strength did not deteriorate owing to the green modification. Moreover, this convenient project was believed to have widely potential applications in high performance composites. POLYM. COMPOS., 39:E2381–E2389, 2018. © 2017 Society of Plastics Engineers

Extraction and investigation of lightweight and porous natural fiber from Conium maculatum as a potential reinforcement for composite materials in transportation

Abstract The aim of the study is to evaluate the use of undervalued Conium maculatum plant fibersas a new potential for the reinforcement of composite materials. In this research, new natural cellulosic fibers were extracted from Conium maculatum plant using conventional water retting method. Mechanical strength, crystallography, thermal stability and chemical structure of Conium maculatumfibers were investigated by single fiber tensile testing, X-Ray Diffraction Analysis (XRD), Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR), respectively. Additionally, surface topography and surface chemistry were analyzed by Scanning Electron Microscope (SEM) and X-Ray Photoelectron Spectroscopy (XPS), respectively. SEM images revealed that the fiber has a porous structure which is very critical for the transportation industry. XPS results indicated that the fiber surface is hydrophobic which is very critical for the composites prepared with hydrophobic matrices like polyolefin materials. Chemical composition of the fibers was also determined. The main components of Conium maculatumfibers such as cellulose, hemicellulose and lignin were reported to be 49.5, 32.2 and 8.6%, respectively. The crystallinity index was stated as 46.4%. The fibers are thermally stable up to 260 °C. Tensile strength of Conium maculatum fibers were determined as 327.89 ± 67.41 MPa. This research paper suggests a novel sustainable ecological material for reinforcement in polymeric composites.

Modification of carbon fibers surfaces with polyetheramines: The role of interphase microstructure on adhesion properties of CF/epoxy composites

Interface construct plays a vital role in developing superior mechanical performance of carbon fibers (CFs)/resin composites. Herein, a facile approach for incorporation of polyetheramine (PEA) onto CFs surface by covalent bond (CF‐g‐PEA) was proposed, and compared to the adsorption one via Van der Waals' force (CF‐c‐PEA). FTIR, X‐ray photoelectron spectroscopy, Raman spectra, scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis, single fiber tensile testing, and interfacial shear strength were carried out to characterize the CF reinforcements and composites. Experimental results showed that both of coating and grafting PEA on CFs increased the polarity, wettability, roughness of CF surface, and interfacial shear strength, especially CF‐g‐PEA, which indicated covalent bond interaction can combine more PEA on CF surface than that of Van der Waals. While single fiber tensile strength of CF‐c‐PEA increased due to the structure of CF without destruction. Meanwhile, the reinforcing mechanisms and interfacial failure modes of composites were also explored. The results suggest that the interphases between the CFs and resin matrix can be adjusted by varying the bonding natures between CF and grafted modifiers, thereby offering a new route for appropriate designing and development of CF‐based composite materials. POLYM. COMPOS., 39:E2346–E2355, 2018. © 2017 Society of Plastics Engineers

Effect of oxygen plasma treatment on tensile strength of date palm fibers and their interfacial adhesion with epoxy matrix

Abstract In recent years, natural fibers have received much attention from various industrial applications. As these fibers are lightweight, nonabrasive, low cost, ecofriendly and biodegradable, they can be sometimes considered as alternatives to synthetic fibers in lightweight composite structures. In this work, date palm fibers (DPFs) were treated by oxygen plasma at various plasma discharge power and exposure time. The effects of plasma treatment on tensile strength of DPF and interfacial adhesion between DPF and epoxy were determined by single fiber tensile test and microbond test, respectively. Scanning electron microscopy was used to investigate the surface morphologies of DPFs before and after the plasma treatment. The functional groups on the surface were studied by attenuated total reflectance-Fourier transform infrared spectroscope (ATR-FTIR). Decrease in hemicellulose and lignin content of DPF was indicated in ATR-FTIR spectra of the treated sample with plasma treatment. The results show that plasma treatment cleans the fiber surface and increases the surface roughness by etching effect. Moreover, fiber surface modification significantly improves tensile properties of DPFs and interfacial shear stress (IFSS) of fiber/matrix. However, the effects of plasma power and exposure time on tensile properties and IFSS values of DPFs are not found significant. Moreover, Weibull statistics show that plasma treatment could not decrease the variability in fiber strength due to the nature of fibers.