J. R. Lee - Daejeon Pengarang T. Ogasawara Pengarang

A simple repair method for GFRP delaminati on using ultraviolet- curable resin Limin Baoa*, Takuya Okazawaa, Anchang Xub and Jian Shic aFaculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda-shi, Nagano Prefecture 386-8567, Japan; bCollege of Textile Science and Engineering, Wuhan Textile University, 1st FangZhi Road, Wuhan 430073, P.R. China; cFaculty of Systems Science and Technology, Akita Prefectural University, 84-4 Ebinokuchi Aza, Tsuchiya, Yurihonjo-shi, Akita Prefecture, Japan Abstract Fiber-reinforced plastic (FRP) composites are widely used in engineering because of their high strength and light weight in comparison to monolithic metal alloys. They are mostly used in laminate form and are stronger within layers than between layers, making them prone to cracking and peeling. This type of structural degradation can be dangerous during operation. For this reason, research on FRP composites with the ability to self-repair has attracted much attention. In this study, we developed a new method to repair glass fiber-reinforced plastic (GFRP) composites by using ultraviolet-(UV) cured resin. As GFRP composites are UV transmissive, the repair process can be carried out externally by exposing the damaged part to UV light. The transmittance of EP GFRP is about 40%. Holes were pre-drilled with wires in order to facilitate the injection of UV resin between the layers of the composite, and this process was accomplished without degrading the mechanical properties of the material. A double cantilever beam (DCB) test was performed on the GFRP composite to induce interlaminar fracturing. UV-curable resin was then injected between the layers of the composite through a series of pre-drilled holes. Following this repair, the DCB test was performed again to evaluate the repair rate. A compressive after impact (CAI) test was also performed on the GFRP composite to induce delamination. Compressive strength before and after the repair was also evaluated. Keywords: GFRP; repair method; ultraviolet-curable resin; DCB test; CAI test Effect of matrix ductility on fatigue strength of unidirectional jute spun yarns impregnated with biodegradable plastics Hideaki Katog ia*, Yoshinobu Shimamurab, Keiichiro Tohgob, Tomoyuki Fujiib and Kenichi Takemuraa aDepartment of Mechanical Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa 221-8686, Japan; bDepartment of Mechanical Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 432-8561, Japan Abstract Natural fiber-reinforced composites are carbon-neutral materials that are anticipated for use as an alternative to glass fiber-reinforced plastics. This study investigated the effects of matrix ductility on the fatigue strength of unidirectional jute spun yarns impregnated with biodegradable plastics. Polylactic acid (PLA) and polybutylene succinate (PBS) were used for the matrix. PLA is brittle, but it is widely used as a matrix of green composites. Because PBS has much higher ductility than that of PLA, it can be expected to have higher fatigue strength when subjected to the same strain amplitude as PLA. Fatigue tests were conducted with maximum stress set to 40–90% of the tensile strength. The stress ratio was set as 0.1. Results show that the matrix ductility strongly affects the fatigue strength and the fatigue mechanism of the composite. A matrix with better ductility was effective to improve fatigue strength. Keywords: jute spun yarn; unidirectional reinforcement; fatigue; biodegradable plastics; PLA; PBS Exper imental study of size effect on quasi-static strengths for short gla ss fi bre-reinforced plastics Takahik o Sa wadaa* and Takayuki Kusakab aCenter for Technology Innovation – Mechanical Engineering, Research & Development Group, Hitachi, Ltd., Hitachinaka, Japan; bDepartment of Mechanical Engineering, Ritsumeikan University, Kusatsu, Japan Abstract The present paper examines size effect on the strength of short glass fibre-reinforced phenolic resin (SGP) composites made by press moulding with different loading modes and specimen shapes. Three- and four-point flexural tests and tension–torsion combined tests were conducted at room temperature in order to evaluate the influence of Vf and loading mode on fracture strength. The obtained uniaxial strength data were analysed using the Weibull statistical theory. The relationship between fracture strength and effective volume was investigated based on the Weibull statistical theory and agreed well with the effective volume theory (EVT), regardless of specimen size, dimensions or loading mode. The experimental results revealed that the tension–torsion multiaxial SGP strength was in agreement with the Tsai–Hill failure criterion. The EVT was also applied to the Tsai–Hill failure criterion to consider the size effect, and the validity of the proposed method was confirmed experimentally. Keywords: short glass fibre-reinforced plastics; size effects; strength Improved adhesion betwee n nickel–titanium SMA and polymer matrix via acid treatment and nano-silica particles coating Bi n Yanga*, Yongchao Zhangb, Fu-Zhen Xuana, Biao Xiaoa, Liang Heb and Yang Gaoa aSchool of Mechanical and Power Engineering, East China University of Science and Technology, Meilong Road 130, Shanghai, 200237, China; bCollege of Aerospace and Civil Engineering, Harbin Engineering University, Harbin, China Abstract Shape memory alloy (SMA) composites are the desirable candidate for smart materials that used in intelligent structures. However, the overall mechanical performance of SMA composites depends immensely on the quality of the interaction between SMA and polymer matrix. Therefore, it is necessary to find out an approach to enhance the interfacial property of this composite. In this paper, we modified nickel–titanium SMA wire with nano-silica particles before and after acid treatment. The modification effect on the interfacial strength between SMA and epoxy resin was evaluated. Contact angle analysis, scanning electron microscopy (SEM) observation, and single fiber pull-out test were carried out. The bonding characteristics between modified wire and liquid/cured resin were investigated. We then embedded SMA wire into woven glass fabric/epoxy composite laminates, and manufactured this hybrid composites via vacuum assisted resin transfer molding processing. Three-point-bending test of the hybrid composites was performed to validate the modification effect. Fiber pull-out experiment demonstrates that the interfacial shear strength increases by 6.48% by nano-silica particles coating, while it increases by 52.21% after 8 h acid treatment and nano-silica particles coating simultaneously. For hybrid composites, flexural strength of the two specimens increases by 19.8 and 48.2%, respectively. In SEM observation, we observed large debonding region in unmodified composites, while interfacial adhesion between modified wire and epoxy keeps strong after flexural damage. Keywords: shape memory alloy; surface modification; interfacial adhesion strength; SMA hybrid composites; fiber pull-out test Matrix crack evolution in m ulti-directional c omposite laminates c o n s i d e r i n g t h i c k n e s s e f f e c t s N. Jagannathana∗ , S. Gururajab and C.M. Manjunathaa aStructural Technologies Division, CSIR-National Aerospace Laboratories, Bangalore 560017, India; bDepartment of Aerospace Engineering, Indian Institute of Science, Bangalore 560012, India Abstract A probabilistic strength-based predictive model for matrix crack evolution in a multidirectional (MD) composite laminate considering thickness effect has been presented in the current work. Weibull distribution has been assumed for the in situ ply strength variation commonly observed in polymer composite laminates. The statistical parameters have been estimated from a master laminate. The crack density evolution has been simulated for cross-ply laminates containing varying thicknesses of 0◦ and 90◦ plies. The crack density evolution and associated stiffness degradation predictions have been compared with existing experimental values. The model has been extended to MD laminate containing plies of varying thicknesses to estimate the stiffness degradation under in-plane loading. The bounds on the stiffness have also been estimated. Good correlation is found to exist between the experimental data and simulation predictions. Keywords: Matrix cracking; Probabilistic strength; MD laminates; Thickness effect Evaluation of measurement method for car bon fi ber length using an optical image scanner Mariko Teradaa*, Atsuhiko Yamanakaa, Yukitane Kimotob, Daisuke Shimamotoc, Yuji Hottaa,c and Takashi Ishikawaa aNational Composites Center Japan, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan; bAutomotive Center, Toray Industries, Inc., 9-1, Oe-cho, Minato-ku, Nagoya 455-8502, Japan; cNational Institute of Advanced Industrial Science and Technology, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan Abstract Fiber length and its distribution are important factors to determine the mechanical properties of discontinuous carbon fiber-reinforced composites. For the efficient and easy measurement of fiber length, an optical image scanner was introduced into the measurement procedure. The scan image allowed to measure approximately 25,000 carbon fibers. The measured values (Lsc) and mean value of these () were evaluated by comparison with reference values (Lmi) obtained using an optical microscope. Lsc were dependent on the angle between fiber and sub-scanning direction. Furthermore, the relative errors between and Lmi were less than 2.5% in case that Lmi were 0.226 mm or more. The sample standard deviations of Lsc were approximately constant and their values were ca. 0.010 mm. Therefore, it was found that the relative error of measurement value derived from the scan image was dependent on the measured fiber length. Keywords: discourteous carbon fiber; scanner; fiber length distribution; measurement errors Effect of poly(ether imide) blends on the physical propertie s of thermoplastic glass mat composites Se Hyun Kima,b, Je Sung Youmb , Moo Sung Leea and Jeong Cheol Kimb* aDepartment of Advanced Chemicals & Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, Republic of Korea; bKorea Institute of Industrial Technology, 6 Cheomdangwagiro 208gil, Buk-gu, Gwangju 61012, Republic of Korea Abstract Glass mat thermoplastic composites (GMTs) were prepared from poly(ether imide/ poly(ethylene naphthalate) (PEI/PEN) and PEI/poly(ethylene terephthalate) (PET) blends using compression molding. The thermal stability, surface hardness, rheological, mechanical, and gas barrier properties and the coefficient of thermal expansion (CTE) for various composites were analyzed. Differential scanning calorimetric and thermogravimetric analysis showed that PEI blends with 30% PEN or PET retained 80% of the thermal stability of virgin PEI. PEI melt viscosity significantly decreased with addition of PEN and PET, which greatly improved impregnation during GMT manufacture. The tensile strength and CTE of GMTs containing up to 30% PEN or PET remained similar to that of PEI/GM, while the flexural modulus increased and the gas barrier properties improved two fold. Scanning electron microscopy confirmed that interfacial adhesion improved for surface-modified GMs. We demonstrated that inexpensive GMTs could be prepared while retaining the superior properties of PEI. Keywords: PEI; PET; PEN; glass mat; blend; composite; gas barrier; CTE Cross-section analy sis of wind turbine blades: comparison of failure between glass and carbon fi ber Georgios Balokas and Efstat hios E. Theotoko glou* Department of Mechanics, Laboratory of Testing and Materials, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, 5, Heroes of Polytechnion Avenue, Athens 15773, Greece Abstract Wind energy stands as one of the most important renewable energy sources. Large scale wind turbine blades are mainly based on fiber reinforced polymer composites, as an efficient way to further improve their performance reducing the weight of their blades. The problem of the microstructure material failure of the interior support mechanism for a – high power – horizontal axis wind turbine blade is investigated in this study. A finite element model is developed, simulating the load-bearing box girder of the blade with a given airfoil shape, size, type, and position of the interior longitudinal beams and shear-webs. Previous work showed the challenging topics of material properties, design, computational analysis techniques, and load response of a blade cross section. In order to shed some light at a local level, a comparison of the most common composite blade materials concerning stress distributions and also displacements, which are critical for optimal blade design, is presented. A failure criterion is applied based on the shell finite element analysis of the model, in order to demonstrate the stress levels throughout every ply of the composite materials of the box girder and locate the initiation of fracture. Failure results concerning both glass and carbon materials are presented. Keywords: computational analysis; composite materials; glass and carbon fiber reinforced plastics; failure criteria; ply-drop analysis; wind turbine blades; failure criteria Computation of energy release rates for composite beam through cross-sectional analysis and virtual crack closure techniq ue Jun Hwan Janga and Sang Ho Ahnb* aDefense Acquisition Program Administration, Gwacheon-si 13809, Gyeonggi-do, Korea; b Department of Mechanical & Automotive Engineering, Shinhan University, Uijeongbu-si, Gyeonggi-do, Korea Abstract This study theoretically describes VCCT (virtual crack closure technique) as well as the dimensional reduction and recovery relations of cross-sectional blades, composed of composite materials, like a wind turbine blade that has a high aspect ratio and initial twist. Besides, to verify the efficiency and accuracy of dimensional reduction and recovery analysis of such a wind turbine blade, this study compared the recovery analysis results of a dimensionally reduced 1-D beam with the analysis results of a 3-D finite element model. Then, this study extracted nodal loads and nodal displacements of cracks, which are required for VCCT, using the recovery analysis results, and then conducted VCCT using the relations between nodal loads and displacements of extracted cracks, further suggesting a process of calculating ERR (Energy Release Rates) through the results of VCCT. As a numerical model and a turbine blade model, having initial cracks on the rectangular cross-section, are needed when ERR is calculated with VCCT applied to the finite element model and the dimensional reduction model, this study applied dimensional reduction & recovery technique and VCCT to these models and verified the efficiency and accuracy by comparing recovery analysis results and ERR. Keywords: composite beam; turbine blade; virtual crack closure technique; crosssectional analysis; recovery analysis; reducible modeling; energy release rates A study of stress concentration s around fi ber breaks in unidirectional CF/epoxy composites using double-fi ber fragmentation tests J. Watanabea*, F. Tanakaa, R. Higuchib, H. Matsutania, H. Okudaa and T. Okabeb aComposite Material Research Laboratories (CMRL), Toray Industries, Inc., 1515, Tsutsui, Masaki-cho, Iyogun, Ehime 791-3193, Japan; bDepartment of Aerospace Engineering, Tohoku University, 6-6-01 Aoba-yama, Aoba-ku, Sendai 980-8579, Japan Abstract The prediction of tensile strength of unidirectional CF/epoxy composites requires appropriately determining the tensile strength distribution of carbon fibers and calculating the stress concentrations around the fiber breaks. In this study, double-fiber fragmentation tests were performed to investigate the stress concentration factor in adjacent fibers around a broken fiber. Simulation results obtained by considering the additional stress concentration due to the matrix cracks correspond well with the fiber breakage behavior observed in experiments. Furthermore, using an additional stress concentration factor and a bimodal Weibull distribution, which has a narrow strength distribution at the short gauge length, the prediction of tensile strength of the unidirectional CF/epoxy composite exhibited a good agreement with experimental results. These results showed that double-fiber fragmentation tests are a valid means of estimating the stress concentrations around fiber breaks. Keywords: carbon fiber; stress concentration factor; matrix crack; bimodal Weibull distribution Energ y absor ption behaviour of braided basalt composite tube M. Nazr ul Roslana,b , M. Yazid Yahyab*, Z. Ahmadb and A.R. Azrin Hania aAdvanced Technology Centre, Faculty of Engineering Technology, Universiti Tun Hussein Onn Malaysia, 84600 Batu Pahat, Johor, Malaysia; bCentre for Composite, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia Abstract Braided composite had been proven to have a great potential as energy absorber. However, the past studies done were limited to synthetic fibre as the reinforcement composite. In this study, we focused on a natural fibre, namely basalt, as the reinforcement material. The effects of braid thickness, braid angle and braid tow density of the basalt composite tube subjected to quasi-static crushing response were investigated. Crushing failure mode had been observed in comparing those braid parametric effects. Moreover, the analysis of variance was used to analyse the main and interaction effects subjected to specific energy absorption (SEA) response for the test. Three crushing modes had been observed. The splayed and diamond shape of progressive folding were reported for the braid angles of ±30° and ±45°, respectively, and fibre micro-cracking mode effects for the ±60° braid angle. Furthermore, SEA increased with the decrease of braid angle and increase of diameter-to-thickness ratio. On the other hand, the highest braid angle demonstrated the lowest crush efficiency and poor triggering crushing progression. Keywords: basalt fibre; braided tube; crushing Eco-friend ly pol yvinyl alcohol (PVA)/bamboo charcoal (BC) nanoc omposites with superior mechanical and thermal properties Mohana d Mousa , Yu Dong* and Ian J. Davies Department of Mechanical Engineering, School of Civil and Mechanical Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia Abstract Carbon-based nanofillers, such as carbon nanotubes (CNTs) and graphene sheets are considered as effective nanoreinforcements due to their unique structures and material performance. However, the utilisation of such nanofillers can be hindered owing to a high level of nanotoxicity via human inhalation and high material cost for CNTs, as well as the tendency to form agglomerates of graphene sheets in polymer matrices. Bamboo charcoals (BCs) are eco-friendly and sustainable carbon-based particles, which possess good affinity with polyvinyl alcohol (PVA), one of popular water soluble biopolymers, to achieve excellent properties of PVA/BC nanocomposites. In particular, porous structures of BC particles enable polymeric molecules to easily penetrate with the strong internal bonding. In this study, fully eco-friendly PVA/BC nanocomposite films were successfully fabricated using a simple solution casting method to achieve the high dispersibility of BCs. With the inclusion of only 3 wt% BCs, tensile modulus and tensile strength of PVA/BC nanocomposite films were enhanced by 70.2 and 71.6%, respectively, when compared with those of PVA films. Better thermal stability is manifested for resulting nanocomposite films as opposed to that of pristine PVA, which is evidenced by the maximum increase of 17.8% in the decomposition temperature at the weight loss of 80%. It is anticipated that BCs can compete against conventional carbon-based nanofillers with a great potential to be developed into eco-friendly nanocomposites used for thin-film packaging application. Keywords: Polyvinyl alcohol (PVA); bamboo charcoals (BCs); nanocomposites; mechanical properties; thermal stability