A new approach for evaluating crack growth resistance curve of modeII delamination by doubly end-notched tension tests
Shigeki Yashiroa*, Toshihide Agatab and Akinori Yoshimurac
aDepartment of Aeronautics and Astronautics, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan; bGraduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, 432-8561, Japan; cAeronautical Technology Directorate, Japan Aerospace Exploration Agency (JAXA), 6-13-1, Osawa, Mitaka, Tokyo, 181-
0015, Japan
Abstract
Quantitative determination of interlaminar fracture toughness that governs onset and growth of delamination is essential for engineering of composite materials and structures. This study proposes a new approach to evaluate both the initial fracture
toughness and the crack growth resistance property of pure mode II delamination by tensile tests of specimens having two initial cracks, which were conceived from double-lap joints. The proposed test method achieves stable growth of mode II delamination using a fundamental testing system. This study presents the specimen configuration, the theory to evaluate the energy release rate, and experiment results. The mode II initial fracture toughness measured by the present approach agreed well with the results of conventional end-notched flexure tests. Furthermore, the crack growth resistance curves were evaluated by unloading-reloading tests of the proposed doubly end-notched tension specimens.
Keywords: polymer-matrix composites (PMCs); delamination; fracture toughness; mechanical testing
A parametric study of skin laminates used in the composite lay up of large-scale wind turbine blades
Khaza r Haya t* and Sung Ku Ha
Department of Mechanical Engineering, Hanyang University, 1271, Sa 3-dong, Sangnok-gu, Ansan, Kyeonggi-do 426-791, South Korea
Abstract
To reach an optimal design solution for the composite layup of large-scale wind turbine blades, subjected to various design load conditions, while, fulfilling numerous design requirements, is a challenging task to accomplish. Since, a large-scale blade is a slender beam structure, therefore, its thin composite layup can be assumed to be under plane stress condition. Consequently, a parametric study of the skin laminates used in the blade composite layup, is conducted to explore and identify the possible
design improvements. The results show that the use of off-axis fiber angles of the skin laminate lower than the conventional 45° are more favorable to achieve higher laminate stiffness, strength, bucking stability, fatigue resistance, and bend-twist coupling value, thereby, demonstrating the potential improvements to the existing composite layup design of large-scale wind turbine blade.
Keywords: skin laminates; large-scale wind turbine blades; parametric study
An efficient modal strain energy-based damage detection for laminated composite plates
Moham mad-Re za Ash ory*, Ahmad Ghasemi-Ghalebahman and Mohammad-Javad Kokabi
Department of Mechanical Engineering, Semnan University, Semnan, Iran
Abstract
Delamination damage has been recognized as a major source of failure that commonly occurs in laminated composites due to their relatively low inter-laminar fracture toughness. The present work deals with an investigation on performing a damage identification technique using a finite element model updating based on genetic algorithm, and providing an evaluation approach with improved sensitivity for detection of quantitative parameters. To this end, an appropriate objective function has been developed based on weighted strain energy, exhibiting the highest level of sensitivity compared to the other methods of damage diagnosis. It is shown that the accuracy of damage location and intensity identification is improved using the proposed method.
Keywords: composite laminate; damage identification; model updating; strain energy
Characteristic s of micro-glass bead/PLA porous composite prepared by electro spinning
Chang Ki Yoona, Byung Kyu Parkb and Woo Il Leea*
aSchool of Mechanical and Aerospace Engineering, Seoul National University, Seoul, 08826, Korea; bInstitute of Advanced Machine and Design Seoul National University, Seoul, 08826, Korea
Abstract
Electrospinning, which produces nano/micro-fiber in a remarkably simple and fast manner, has been applied for numerous materials in various areas. In this study, the characteristics of micro-glass bead/PLA porous fiber composite were studied. The
breath figure method was implemented to fabricate porous PLA fibers from PLA solution obtained by dissolving PLA in a solvent mixture (10:1 weight ratio) of dichloromethane (DCM) and N,N-dimethylacetamide (DMAc). The micro-beads
(60 μm) were used to make more gaps between fibers and the specific surface area was measured and compared. Furthermore, the sound absorption and the insulation property of the samples were also measured. The specific surface area of samples
increased from 1.45 to 4.39 m2/g with the addition of micro-glass beads and porous structure. The insulation property improved from 40 to 35 mW/m K with addition of micro-glass beads due to the formation of air layers.
Keywords: BET specific surface area; electrospinning; micro-glass beads; sound absorption; PLA; porous structure; thermal conductivity
Fabrication and mechanical characterization of continuous carbon fiber-reinforced thermoplastic using a preform by three-dimensional printing and via hot-press molding
Masao Yamawakia* and Yousuke Kounob
aElectrical Engineering & Information Science, National Institute of Technology, Kure College, Kure city, Japan; bWestern Region Industrial Research Center, Hiroshima Prefectural Technology Research Institute, Kure city, Japan
Abstract
A new 3D printer equipped novel nozzle structure for continuous carbon fiberreinforced thermoplastics (C-CFRTP) was developed and the suitable printing conditions were studied. C-CFRTP filament and additional matrix resin were supplied independently using each extruder, which is useful for variety printing and precise form control in 3D printing. To measure the mechanical properties, specimens for tensile strength testing were fabricated using C-CFRTP filament (Vf:50%) without additional matrix resin. The experimental results indicate that the tensile strength and Young’s modulus were approximately 700 MPa and 53 GPa, respectively. The recrystallization effect through annealing after 3D printing yielded no drastic improvement. The mechanical properties were considerably improved by a hot-press treatment after 3D printing. The tensile strength and Young’s modulus increased to approximately 1400 MPa and approximately 90 GPa, respectively. These results suggest that one of the useful applications of C-CFRTP 3D printing technology is preforming of small parts in industrial products.
Keywords: composite materials; additive manufacturing; 3D printing; fabrication condition; mechanical properties
Impact study on sandwich panels with and without stitc hing
R. Santhan akris hnan*, Stanley Samlal, A. Joseph Stanley and J. Jayalatha
Department of Aerospace Engineering, Hindustan University, Chennai 603103, India
Abstract
The low velocity impact responses of sandwich panels with and without stitching were investigated using an instrumented drop weight impact tower. A novel stitching technique was developed to stitch the sandwich panel. Unstitched and stitched sandwich panels with pile orientation of 90°, 45° and 90°/45° were fabricated using vacuum infusion process. Low velocity impact test were carried out with different energy levels of 2, 5, 10, 20, 30, 40 and 50 J. The increase in the impact performances generated by the introduction of these reinforcements compared to a traditional sandwich (unstitched) was quantified. The results also show that the ballistic limit of the sandwich panels were improved by employing piles in different orientation.
Keywords: impact; sandwich panels; novel; pile; ballistic limit
Improving bending characteristics of FRP sandwich structures with reinforcement webs
Limi n Bao*, Yuki Miura and Kiyoshi Kemmochi
Faculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Nagano-ken 386-8567, Ueda-shi, Japan
Abstract
Sandwich-structure materials consist of a high-strength skin material and a lightweight core material. The advantages of sandwich structures are known to include excellent mechanical properties and low weight. Sandwich structures are lightweight because of their lightweight core; meanwhile, the skin structure provides mechanical strength and bears bending stress. Carbon-fiber reinforced plastic (CFRP) is a highspecific-strength and high-specific-rigidity material. In recent years, CFRP sandwich structures have been used in aerospace applications due to their lightweight properties. However, soft-core members such as plastic foam materials have low rigidity and therefore may not exhibit adequate function as a sandwich structure. Webs can make up for the lack of rigidity of soft core members. Consequently, sandwich structures with reinforcement webs offer higher strength than sandwich structures without reinforcement webs. This study focused on reinforcement webs suitable for use in CFRP sandwich structures by evaluating the bending characteristics of CFRP sandwich structures with reinforcement webs. Experimental results demonstrated that CFRP sandwich structures with reinforcement webs had improved bending strength. The effects of the spacing interval of reinforcement webs and the number of layers of carbon fiber fabric on the bending characteristics of CFRP sandwich structures were also examined. Finally, an optimal condition model was created for CFRP sandwich structures with reinforcement webs.
Keywords: sandwich structures; webs; CFRP; bending strength; bending rigidity; buckling analysis; strength analysis
Non-contact visualization of fiber waviness distribution in carbon fiber composites using eddy current testing
Koichi Mizu kami* and Keiji Ogi
Department of Civil and Environmental Engineering, Graduate School of Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
Abstract
Fiber waviness is a process-induced defect that greatly decreases the compressive strength of carbon fiber composites. In this study, we developed eddy current techniques that enable non-contact visualization of waviness distribution. To visualize in-plane waviness in a carbon fiber composite, we visualized the path of eddy current flowing along the carbon fiber by measuring the magnetic field. Finite element analyses show that the shape of the in-plane waviness can be visualized in the distribution of the magnetic field from the eddy current. However, with increasing distance between the surface of the tested material and measurement plane, the visualization increasingly underestimates the in-plane waviness angle. To avoid this underestimation, we propose a magnetic imaging method that can reconstruct the magnetic field at the surface. The surface magnetic field was reconstructed by using the magnetic field data measured away from the surface. Experiments were performed on a cross-ply laminate with artificially induced in-plane waviness. The distribution of in-plane waviness can be successfully visualized from the measured magnetic field. Using this magnetic field imaging method to enable non-contact measurements, the angle of waviness can be measured with an error of only 1°.
Keywords: carbon fiber composite; non-destructive testing; waviness; eddy current
