A simple repair method for GFRP delamination 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
Novel opt imization method of single square FSS impinged and cascaded radar absorbing composites
Ravi Panwa ra, Dae-Sung Sonb and Jung-Ryul Leeb*
aIndian Institute of Information Technology, Design & Manufacturing, Jabalpur, Madhya Pradesh, India; bOpto-Electro-Structural Lab, Korea Advanced Institute of Science & Technology (KAIST), Daejeon, South Korea
Abstract
It is well known that radar absorbing potentiality of existing magneto-dielectric composites can be significantly enhanced by the application of frequency selective surface (FSS) and cascaded electromagnetic (EM) structures. But the optimization of such complex EM structures and validation of the adopted optimization strategy is still a very challenging task for the researchers. Therefore, in this study, an effective effort has been made for the optimization and the corresponding validation for Single Square FSS (SS-FSS) impinged and cascaded radar wave absorbers using advanced computational EM software’s like FEldberechnung fur Korper mit beliebiger Oberflache – a German acronym (FEKO) and high frequency structure simulator (HFSS). In addition, a critical analysis of dielectric constant (ε′) has been carried out to select the best combination of composites for the development of efficient radar wave absorbers. A comparison between optimized and simulated results have been carried out to examine the effect of advanced EM approaches over reflection loss (RL) characteristics of composite radar absorbing materials (CRAMs). A rapid change in radar absorption properties of composites has been observed after the application of SSFSS and cascading. A SS-FSS impinged composite has been found to provide a wide absorption bandwidth of 3.6 GHz at X-band. A cascaded absorber having layer thickness 1.8 mm provides a peak RL of −42.6 dB at 10.6 GHz with an absorption bandwidth of 2.5 GHz. The strong agreement between mathematical model, HFSS and FEKO results clearly reflects the efficiency of adopted approach for distinct practical EM applications.
Keywords: Radar wave absorber; composite; stealth; frequency selective surface
Op timal fi ber distributio n for tensile propertie s of injection molded composite
Dong-Joo Lee*
School of Mechanical Engineering, Yeungnam University, Gyungsan 712-749, South Korea
Abstract
The survival rate of a composite is the residual fiber length divided by the initial fiber length, and it decreases with the initial fiber length and fiber volume content ( Vf) during injection molding processes. The degree of damage is higher for carbon fiber than for glass fiber, and the survival rate increases with a hyperbolic tangent relationship as the nozzle diameter increases. Higher survival rate corresponds to a stronger material. Five different lengths of fiber with 29 different size fibers were selected based on the distribution and shape of residual fiber in experimental works. These were examined to study the effects of fiber distribution on the tensile properties of a short-fiber reinforced composite (SFRC). Compared with the experimental results, the modulus predicted using the Halpin-Tsai relation shows reasonable agreement with the prediction obtained using the residual fiber length instead of the initial fiber length. It was found that the tensile modulus and strength generally differ by a factor of up to 3.2, depending on the fiber distribution patterns with Vf = 30%, and the trend is more significant as the fiber aspect ratio increases. The interactions between the fiber and matrix and the staggered-type distribution are the most important factors in the reinforcement of the SFRC. With the same combination of short fiber length, an optimized fiber distribution pattern is suggested.
Keywords: fiber aspect ratio; damage during injection molding; fiber distribution; tensile strength and modulus; prediction
Rayleigh waves at the boundary surface of modifi ed couple stress generalize d thermoela stic with mass diffusion
Rajnees h Kumara*, S.M. Abo-Dahabb,c and Shaloo Devid
aDepartment of Mathematics, Kurukshetra University, Kurukshetra, India; bMathematics Department, Faculty of Science, Taif University, Taif, Saudi Arabia; cMathematics Department, Faculty of Science, SVU, Qena, Egypt; dDepartment of Mathematics & Statistics, Himachal Pradesh University Shimla, Shimla, India
Abstract
In this problem, we have studied propagation of Rayleigh waves in an homogeneous isotropic modified couple stress generalized thermoelastic with mass diffusion solid half space in the context of Lord–Shulman (L-S), Green–Lindsay (G-L) theories of
thermoelasticity. Secular equations are derived mathematically by using appropriate boundary conditions. The values of determinant of secular equation, Rayleigh wave velocity and attenuation coefficient with respect to angular velocity for different values of wave number and relaxation times in the absence and presence of mass diffusion, are computed numerically. The numerical simulated results are depicted graphically for copper material.
Keywords: Rayleigh waves; modified couple stress theory; thermoelastic diffusion; Rayleigh wave velocity; attenuation coefficient
Analysis of structure characteristics in laminated graph ene oxide nanocomposites using molecular dynamics simulation
Yutaka Oyaa*, Kyosuke Inuyamaa, Tomonaga Okabea, Jun Koyanagib and Ryosuke Matsuzakic
aDepartment of Aerospace Engineering, Tohoku University, 6-6-01 Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan; bDepartment of Material Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan; cDepartment of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510,
Japan
Abstract
The characteristics of laminated graphene oxide (LGO) nanocomposite, which are expected to be used for highly functional composites, are known to be related to its microstructure. In this study, we investigate the influences of hydrogen-bonding and
cross-linked network structures on the initial stiffness and yield stress, using molecular dynamics simulations. Our results show that each structure increases the mechanical properties, and the combination of these structures strengthens the properties. Moreover, we found that the physical origin of the enhancement is cross-linked networks that generate stretched polymers connecting graphene sheets. Our study concludes by suggesting an appropriate selection of materials for high-performance
LGO nanocomposites.
Keywords: graphene oxide nanocomposites; molecular dynamics simulations; mechanical properties
Experimental and numer ical analysis of fl exural and impact behav iour of glass/pp sandwich panel for autom otive structu ral applicatio ns
M.A . Khana* , A.K. Syeda, H. Ijazb and R.M.B.R. Shahc
aFaculty of Engineering, Environment and Computing Coventry University, Coventry CV1 5FB, UK; bDepartment of Mechanical Engineering, University of Jeddah, Jeddah, Saudi Arabia; cCharge Automotive Ltd, Banbury OX16 2DJ, UK
Abstract
Cost and recyclability are among the primary factors on exploiting the engineering materials for their new applications. In this context, glass/pp-based sandwich panel has been studied experimentally and numerically with the aims of its potential applications in the automotive structures. The first part of this work presents the experimental results achieved for the load-carrying capacity of panels using three-point bend tests for its static flexural behaviour. Static behaviour is studied to compare the top-roller diameter effect on the flexural behaviour of the panels and shows a significant difference in the results. Impact behaviour of the panels is explored using three different types of impactor end-shapes that generate different levels of damage in the material with the same level of impact energy. The second part of this paper deals with the development of numerical models for the three-point bend and impact behaviour of the panels using a commercial finite element code of Abaqus. Strain energy-based homogenisation technique is employed to determine the equivalent orthotropic properties of complex circular honeycomb core material. The finite element models predict to a good level of the static and impact behaviour of the material when compared with the experiments.
Keywords: glass/pp sandwich panel; three-point bend test; flexural behaviour; low-velocity impact; FE modelling
Experimental chara cterization of dynamic crack growth behav ior in CFRP adhesi ve interface
Sota Oshim aa, Hisayoshi Ishidab, Takayuki Kusakac* and Tomo Takedad
aGraduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16, Naka-cho, Koganei, Tokyo 184-8588, Japan; bGraduate School of Science and Engineering, Ritsumeikan University, 1-1-1, Noji-Higashi, Kusatsu, Shiga 525-8577, Japan; cDepartment of Mechanical Engineering, Ritsumeikan University, 1-1-1, Noji-Higashi, Kusatsu, Shiga 525-8577,
Japan; dAeronautical Technology Directorate, Japan Aerospace Exploration Agency, 7-44-1, Jindaiji Higashimachi, Chofu, Tokyo 182-8522, Japan
Abstract
The dynamic crack growth behavior of adhesively bonded joints under mode I and mixed mode (I + II) loading were investigated. The split Hopkinson pressure bar (SHPB) apparatus and the digital image correlation (DIC) technique were employed to determine the mode I fracture toughness of the adhesively bonded joints during crack propagation under impact loading. The dynamic crack growth behavior for carbon fiber reinforced plastics (CFRP) adhesively bonded joints under mode I loading was studied using this method. In order to verify the proposed method, the dynamic crack growth behavior of titanium alloy adhesively bonded joints was also studied. Moreover, the crack growth behavior of CFRP adhesively bonded joints
under mixed mode loading was studied using the SHPB technique. For the considered CFRP adhesively bonded joints, the fracture toughness decreased under both mode I and mixed mode loading as the loading rate increased. Microscope observation showed that a shift in the crack location occurred in the high loading tests.
Keywords: adhesive joints; split Hopkinson pressure bar; fracture toughness; impact strength; loading rate dependence; digital image correlation
Optimisation of hybridisa tion effect in graphene reinforced pol ymer nanocom posites
Velram Balaji Mohan* , Reuben Brown, Krishnan Jayaraman and Debes Bhattacharyya
Centre for Advanced Composite Materials, Department of Mechanical Engineering, The University of Auckland, 314–390 Khyber Pass Road, Newmarket, Auckland 1023, New Zealand
Abstract
This article focuses on the optimisation of electrical and mechanical properties of hybrid blends of polyoxymethylene (POM) as primary thermoplastic matrix, polypyrrole (PPY) as secondary conducting polymer and graphene (G) as reinforcement. An initial Taguchi analysis was performed with a focus on improving electrical conductivity (σ) and tensile strength. A mixture analysis using ‘simplex’ statistical design was applied to develop an experimental subset that identified an optimal combination in weight-percentage. Both electrical and mechanical properties were improved by the addition of PPY and graphene particles due to hybridisation mechanism as well as double percolation threshold. The maximum electrical conductivity of 0.95 S cm−1 was achieved with POM reinforced with 3 wt.% of G and 2.5 wt.% of PPY loading. The mechanical properties were found to be increased with increase in addition of both G and PPY.
Keywords: hybridisation; graphene composites; electrical conductivity; ultimate tensile strength; statistical analysis; morphology; sub-set optimisation
Prepara tion and characterization of ZnO/Zn S core/shell nanocomposites through a simple chemical method
Bing Yan, Yongqia n Wang* and Xiuling Wu*
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, China
Abstract
In this paper, we reported the preparation of ZnO/ZnS core/shell nanocomposites by sulfidation of ZnO nanostructures via a simple hydrothermal method. The precursors of bare ZnO nanoparticles and ZnO nanorods were synthesized by a surfactant-assisted hydrothermal growth. The structural, morphological, and element compositional analysis of bare ZnO nanostructures and ZnO/ZnS core/shell nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy techniques. The XRD results indicated that the phase of bare ZnO nanoparticles and ZnO nanorods was wurtzite structure, and the phase of coated ZnS nanoparticles on the surface of bare ZnO nanostructures was sphalerite structure with the size of about 8 nm. Photoluminescence measurement was carried out, and the PL spectra of ZnO/ZnS core/shell nanocomposites revealed an enhanced UV emission and a passivated orange emission compared to that of bare ZnO nanostructures. In addition, the growth mechanism of ZnO/ZnS core/shell nanostructures through hydrothermal method was preliminarily discussed.
Keywords: ZnO/ZnS core/shell; hydrothermal; photoluminescence; growth mechanism
Strength evaluation of unidirectional carbon fi ber-reinforced plastic laminates based on tension–compression biaxia l stress tests
Kei ta Gotoa*, Masahiro Araia, Masaomi Nishimurab and Kazuki Dohib
aDepartment of Aerospace Engineering, Nagoya University, Nagoya, Japan; bDepartment of Mechanical Systems Engineering, Shinsyu University, Nagano, Japan
Abstract
Biaxial stress tests of carbon fiber-reinforced plastic (CFRP) laminates were performed to investigate failure criteria under biaxial loads. Specimens of unidirectional CFRP laminates were subjected to a tensile load in the longitudinal fiber direction and a compressive load in the transverse fiber direction. An exclusive jig was used to perform biaxial stress tests with a commonly used single-axis testing machine. Measurements were obtained by controlling the displacement ratio between compressive and tensile displacements. The critical tensile and compressive stresses were then calculated using a constitutive equation. The critical longitudinal tensile stress markedly dropped with increasing the compressive load. The failure criteria of the biaxial stress tests were expressed as the ellipse, of which the major and minor axes were the longitudinal tensile/transverse compressive strengths or fracture strains, respectively. Scanning electron microscope observations suggest that fiber/matrix interfacial debonding due to the compressive load could decrease the critical longitudinal tensile stress.
Keywords: CFRP; unidirectional laminate; biaxial load; failure criterion
