Titles and Abstracts from Issue 3 of 2009:
Carbon Nanotube Reinforced Acoustically Transparent Epoxy Nanocomposites for Underwater Sonar Windows
Wei Chen, Shankar Rajaram, Shad Thomas, and Steven R. Nutt
Abstract: Oxidized multiwalled carbon nanotubes (o-MWCNTs) were incorporated into filled epoxy blends to develop acoustically transparent structural nanocomposites for sonar windows. The longitudinal wave speed, density, flexural mechanical properties, loss factor, and insertion loss were characterized for different compositions. The addition of 0.05wt% o-MWCNTs increased the composite flexural modulus and strength by 370% and 90% respectively with no change in the longitudinal acoustic wave speed. Analytical predictions also indicated that the higher shear loss factor provided by carbon nanotubes ameliorated shear resonance at oblique insertion angles. Carbon nanotube additions afford the ability to increase mechanical properties and acoustic transparency, both of which are critical for underwater sonar windows.
Effects of Heat Treatment on Microstructure and the Fracture Toughness
of SiCp/Al Alloy Metal Matrix Composites
D.P. Myriounis, S.T. Hasan, N.M. Barkoula, A. Paipetis, and T.E. Matikas
Abstract - The current study focuses on the fracture toughness behaviour of A359 aluminium matrix
reinforced with 31 wt. % SiC particulates subjected to different heat treatment conditions.
Unreinforced aluminium alloy fracture properties have been also determined for reference
purposes. Three different heat treatment conditions have been applied to the Al/SiCp composites
and the fracture toughness values have been determined for all specimens. Infrared thermography
was used to monitor the plane crack propagation behaviour of the materials and validate the
fracture toughness testing. As expected, the obtained KIC values were found to be lower than
those of the unreinforced matrix alloy. However, heat treatment considerably improved the
fracture toughness of the composites. In particular, the specimens heat treated under the T6
condition exhibited enhanced fracture toughness compared to the other two conditions. This
behaviour can be attributed to a mechanism related to alterations in the microstructure at the
vicinity of the interface induced by the heat treatment. This mechanism was associated with
precipitates accumulated at the interfacial region resulting in material hardening.
A Simple Method to Synthesize Nanocrystalline Hydroxyapatite
Zhengmao Li, Wen He, Yingjun Wang, Xudong Zhang, Hongshi Zhao, Shunpu Yan, and Weijia Zhou
Abstract - In this study, hydroxyapatite (HAp) particles with nanostructure have been synthesized from the calcium hydroxide and di-ammonium hydrogen phosphate via a precipitation method. The materials were characterized with X-ray diffraction (XRD), Fourier transform infrared spectrograph (FTIR) and transmission electron microscopy (TEM) to determine the particle properties (particle size, crystallinity, structural and morphology). This process represents a simple method, with no control of the solution pH needed, for the production of nanosized HAp. The results show that the products are monophase HAp of the diameter of 15~20 nm and 50~70 nm in length.
Synthesis and Characterization of Nanostructures Calcium Phosphates Powders and Calcium Phosphates/a-Al2O3 Nanocompsites
N.H.A. Camargo, S.A. Delima, J.F. Aguiar, E. Gemelli, M. Tomiyama, H. Oudadesse
Abstract - Nanostructured materials are of interest to different research laboratories and have widespread repercussions: science, politics, government, society and the economic market. Some of these materials are considered very important, namely the nanostructured and the microporous bioceramic, the hydroxyapatite, b-calcium phosphate and the calcium phosphate nanocomposites reinforced with nanoparticles of alumina and silica. They are important, mainly, because of their mineral characteristics which are similar to the bone structure of the human skeleton. Nanoparticle reinforcement of a-alumina has often been employed during the process of synthesis of nanocomposite powders to improve the mechanical properties of the bone matrix of calcium phosphate and to optimize the distribution and the interconnection of microporosity of these microbiomaterials. This paper deals with the method of synthesis and characterization of nanostructured powders of calcium phosphate and nanocomposites reinforced with 5, 10 and 15% (in volume of) sol-gel a-Al2O3. The present results focus on the morphological characterization, mineralogical and thermal behavior of nanostructured powders obtained from the process of synthesis and the microstructure of biomaterials sintered at 1150ºC for 4 hours and at 1200ºC for 2 hours. Results clearly show that the powder obtained from the synthesis is presented in the form of fine particle clusters in the composition of calcium phosphate hydrate; the nanoparticles were smaller than 20nm. The powder calcined at 900ºC for 2 hours consists mainly of hydroxyapatite (Ca5(PO4)3(OH)), the nanoparticles were smaller than 100nm. The micrographs from the fracture surface of the sintered nanocomposite biomaterials clearly show that the quantity (in volume) of reinforcement of a-alumina nanoparticle increased the interconnection of micropores of the hydroxyapatite matrix.
Stress and Vibration Analysis of Composite Propeller Blades and Helicopter Rotors
Yosif Golfman
Abstract - Composite propeller blades, helicopter rotors and fans have been manufactured in a laminate form from carbon fiber reinforced epoxy where the blade skin is made of aramid fiber reinforced epoxy resin. Additional reinforcement in the nose and trailing edge is made for the protection of the laminated layers. The carbon fibers with reinforced epoxy have been oriented in various directions. The torsion and bending stiffnesses of composite blades can be turned by changing the fiber direction of the layers. Therefore, the natural frequencies of propeller blades can be favorably placed in an area outside the operational r.p.m. range.
This paper relates the evaluation of the force and free vibration frequencies for the purpose of avoiding the air and ground resonance.
The Effects of Hybrid Laminate Structures on the Compression and Fatigue Properties of Helical Composite Springs
Chang-Hsuan Chiu, K.-H Tsai, Yong-Chi Lee, Chung-Li Hwan
Abstract - In this study, three groups of helical composite springs including CG (Carbon/Glass), CK (Carbon/ Kevlar), and HCG (High Modulus Carbon/Glass) groups were fabricated by hybrid laminates. The hybrid laminates of CG, CK, and HCG groups use carbon fibers and glass fibers, carbon fibers and kevlar fibers, and high modulus carbon fibers and glass fibers, respectively, with various volume ratios between those two fibers. In total, thirteen different hybrid laminate structures were made into helical composite springs. This study aims to investigate the effects of those hybrid laminate structures on the compression and fatigue properties of helical composite springs. According to the experimental results, all the helical springs of CK group either broke or cracked under compression before the coils were compressed into a compact state at which each spring coil contacted with its neighboring coils. However, those of CG and HCG groups with higher volume ratio of glass fibers sustained without crack until the coils were compressed into a compact state. Among them the spring C50G50 made using carbon fiber and glass fiber with volume ratio of 50/50 not only sustained without crack but also showed the highest spring constant of 469.3 lb/ in. In compression fatigue testing of helical composite springs the precompression displacement and the maximum compression displacement were set to be 10% and 70% of the maximum static compression displacement, respectively. Three hundred thousands fatigue cycles were applied on each specimen. The experimental results show that the decrease of the maximum compression loads after fatigue test was less than 5% of the maximum compression loads at the beginning of fatigue test for the composite springs C50G50, C30G70, HC50G50, and HC30G70, which satisfied the requirement of commercial standard.
Use of the Hybrid-Stress Finite Element Method in the Crack Propagation Analysis of Unidirectional Fibre-Reinforced Composite Plate
S.O. Edelugo
Abstract - Starting from the super-element concept of Tong and the Stress Intensity Factor Equations as derived by Sih et al., a hybrid-stress finite element set of equations for the stress intensity factors. K1 and K11 are developed. This approach utilizes the polynomials of two complex variables S1 and S2 in the transformed x-plane for the stress and displacement fields. The stiffness matrix was determined using a line integral on the boundary of the element whereas a properly selected shape function was used in the definition of the boundary element itself. Nodal displacement vector (q) was expressed in terms of the element displacement vector. Tabular comparisons with the results of the Boundary Value Collocation equations of Gandhi and plots of numerical results of glass-epoxy and graphite-epoxy for K1 and K11 in a unidirectional composite plate with elliptical crack in the center are also presented.