An analytical approach for local buckling analysis of initi ally delaminated composite thin-walled columns with open and closed sections
M. Taherzade h Esfahania, M.Z. Kabirb and M. Heidari-Raranic*
aMechanical Engineering Department, Amirkabir University of Technology, Tehran, Iran; bCivil Engineering Department, Amirkabir University of Technology, Tehran, Iran; cFaculty of Engineering, Department of Mechanical Engineering, University of Isfahan, 81746-73441 Isfahan, Iran
Abstract
Local buckling of intact thin-walled columns is generally performed by modeling the wall segments as long plates and by assuming that edges common to two or more plates remain straight. Thus, the buckling load can be determined by considering the wall segments as individual plates rotationally restrained by the adjacent wall segments. This technique is combined with plate theories as a new analytical method to predict the buckling load of an initially delaminated column with any arbitrary sections (open or closed). First, moments at the rotationally restrained edges of delaminated segment (web or flange) are obtained from the curvature and stiffness of the adjacent laminates. Then, the strain energy of this delaminated segment with distributed moment at edges is calculated based on the first-order shear deformation theory. Using the principal of minimum potential energy, the governing equations are obtained and solved by the Rayleigh–Ritz approximation technique. Results of the present approach are compared with three-dimensional finite-element results obtained from eigenvalue buckling analysis in ANSYS software for both
box- and channel-section columns with cross-ply and angle-ply stacking sequences. Finally, the effects of delamination size and location are investigated on the buckling loads.
Keywords: buckling; delamination; thin-walled columns
Identifying through-thickness material properties of carbon-fi ber-reinforced plastics using the virtual fi elds method combined with mo iré interferometry
S. Yoneyam aa,b*, P.G. Ifjub and S.E. Rohdeb
aDepartment of Mechanical Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara 252-5258, Japan; bDepartment of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA
Abstract
An investigation into the use of a novel curved-beam composite specimen is conducted to measure the interlaminar (through-thickness) tensile properties of carbon-fiber-reinforced plastic. A combination of a numerical model and full-field displacement/strain measurement with moiré interferometry is utilized in this study. Through-thickness material properties are identified from the measured displacement distribution using the virtual fields method. Because of the shape and the loading
condition of the proposed curved composite beam, both tensile and shear stresses exist in the through-the-thickness direction. Therefore, the interlaminar tensile modulus, as well as the interlaminar shear modulus, can be evaluated. The measurement
results by moiré interferometry provide the material properties through inverse analysis.
Keywords: inverse problem; material properties; carbon-fiber-reinforced plastics (CFRP); moiré interferometry; virtual fields method
Characteristic length determinati on of notched woven composites
F. Taheri-B ehrooz* and H. Bakhshan
Department of Mechanical Engineering, Iran University of Science and Technology, P.O.B. 6846-13114, Tehran, Iran
Abstract
In this manuscript, the progressive failure analysis was employed to predict the final failure of notched woven glass/epoxy composite laminates under tensile loading. A user-defined material model (UMAT) in the Abaqus finite-element package was
developed to utilize the 3D progressive failure analysis feasible. Three types of stress-based failure criteria as Max. Stress, Yamada-Sun, and Tsai-Wu were implemented in Abaqus to predict the damage initiation in the notched woven composites.
Instantaneous and recursive property degradation rules were employed to simulate damage propagation. A numerical procedure was developed to find the characteristic length (CL) in the notched woven composite laminates without test. The various
notched and unnotched woven glass/epoxy specimen were fabricated by vacuumassisted hand layup technique. Four groups of experiments were performed to predict the hole size effect on the strength of the notched laminates and verify the strength predicted by the progressive damage modeling. Numerical results were in good agreement with the test results. More than above, it was verified by the experiment that the CL obtained by the progressive damage analysis is a reliable and simple method to design notched woven laminates.
Keywords: notched woven composites; progressive damage analysis; UMAT; characteristic length
Mechanical properties of carbon fi ber paper reinforced thermoplastics using mixed discon tinuous recycled carbon fi bers
Haowen Weia*, Wataru Nagatsukaa, Hooseok Leea, Isamu Ohsawaa, Ken Sumimotob, Yi Wana and Jun Takahashia
aDepartment of Systems Innovations, School of Engineering, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656, Japan; bDepartment of Research and Development, Awa Paper Mfg. Co., Ltd., 3-10-18, Minami-yaso-cho, Tokushima-shi, Tokushima 770-0005, Japan
Abstract
Market demand for carbon fiber (CF) increases annually. Therefore, owing to the growing amount of carbon fiber-reinforced plastic (CFRP) waste, CFRP manufacturers are attempting to develop and design materials and products by paying greater
attention to ecological and economic factors. In this report, recycled CF (rCF) varieties with differing mechanical properties are mixed to determine the possibility of rCF application in future structural materials. 1, 3, 5, 8 and 10 MPa are investigated
for proper compression molding pressure. The range of 5–8 MPa is recommended. Mixing different rCFs can control the mechanical properties of the material, which is valuable for current rCF applications. A modified rule of mixture (ROM) is used
to discuss flexural modulus and flexural strength. The coefficients for ROM are given for different rCF.
Keywords: recycled carbon fibers; discontinuous reinforcement; carbon fiber paper; thermoplastic resin
Optimum structu ral design of CFRP isogrid cylindrical shell using genetic algorithm
Kazuhiro Sakata*, Takashi Suzuki and Goichi Ben
Department of Mechanical Engineering, College of Industrial Technology, Nihon University, 1-2-1, Izumicho, Narashino, Chiba, 275-8575 Japan
Abstract
This paper describes an optimum structural design of a CFRP isogrid cylindrical shell using a genetic algorithm (GA). When the CFRP isogrid cylindrical shell receives a prescribed uniaxial compressive load, an objective is to minimize weight of the CFRP isogrid cylindrical shell subjected to the constraint conditions of no buckling and no material failure. The buckling and material failure loads were approximated by a response surface method combined with partitioning of design spaces and these approximated values were used in the process of GA instead of FEM calculations in order to reduce the computational time. Furthermore, the differences from the constraint conditions of the linear or the non-linear (local) buckling loads were also calculated and their results were compared with each other.
Keywords: CFRP; isogrid cylindrical shell; optimum design; genetic algorithm; response surface method; FEM
Study of chemical and mecha nical properties of Dharbai fi ber reinforced polyester composite s
S. Kalyana Sundarama*, S. Jayabalb, N.S. Balajib and G. Bharathirajac
aDepartment of Mechanical Engineering, Madanapalle Institute of Techonolgy and Science, Madanapalle 517 325, Andhra Pradesh, India; bDepartment of Mechanical Engineering, A.C. College of Engineering and Technology, Karaikudi 630 004, Tamilnadu, India; cDepartment of Mechanical Engineering, C. Abdul Hakeem College of Engineering and Technology,
Melvisharam 632 509, Tamilnadu, India
Abstract
This investigation is focused on identifying a new variety of natural fiber (Dharbai fiber) for reinforcement in polymer matrix composites. An investigation on extraction procedure of Dharbai fibers has been undertaken. The chemical properties of
Dharbai fibers were determined experimentally as per TAPPI standards. The FT-IR Spectroscopy was used to study the chemical structure of Dharbai fibers and the tensile properties of these fibers were studied using single filament test. The fibers extracted were reinforced in polyester matrix by varying the fabrication parameters namely fiber weight content (%) and fiber length (mm). The effect of fiber weight content and fiber length on the mechanical properties of Dharbai fiber-polyester composites were evaluated as per ASTM standards. Scanning electron microscope was used to characterize the interfacial bonding between Dharbai fibers and polyester matrix. This study confirmed that, the Dharbai fibers could be used as an effective reinforcement material for making low load bearing polymer composites.
Keywords: polymer matrix composites (PMCs); chemical properties; mechanical properties; Dharbai fibers; scanning electron microscope (SEM)
The effect of multi-walled carbon nanotubes/hydroxyapatite nanoc omposites on bio compatibility
Jung-Eun Parka , Yong-Seok Janga,‡, Il-Song Parkb, Jae-Gyu Jeonc, Tae-Sung Baea
and Min-Ho Leea*
aDepartment of Dental Biomaterials and Institute of Biodegradable Materials, Institute of Oral Bioscience and BK21 Plus Project, School of Dentistry, Chonbuk National University, Jeonju 54896, South Korea; bDivision of Advanced Materials Engineering, Research Center for Advanced Materials Development and Institute of Biodegradable Materials, Chonbuk National University, Jeonju 54896, South Korea; cDepartment of Preventive Dentistry, School of Dentistry, Institute of Oral Bioscience and BK 21 Plus Project, Chonbuk National University, Jeonju 54896, South Korea
Abstract
In the present study, multi-walled carbon nanotubes/hydroxyapatite (MWCNTs/HA) nanocomposites with various MWCNT contents were manufactured by sol-gel processing. The MWCNTs/HA powder was characterized using field-emission scanning
electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman analysis. The results show that the MWCNTs were fully covered with HA nanoparticles and help forming the crystallized hydroxyapatite. In addition, in vitro
tests highlighted the excellent biocompatibility of the MWCNTs/HA composite.
Keywords: biomaterials; carbon nanotubes; hydroxyapatite; nanocomposites; bioactivity
