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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.11, #6)
Ultrasonic Study of Elastic Anisotropy of Material Composite by A. Mouchtachi; R. El Guerjouma; J. C. Baboux; P. Santini; P. Merle; D. Bouami (pp. 341-351).
The anisotropic elastic properties of two Aluminium Matrix Composites (AMC) were characterised using an ultrasonic method. The composite materials, fabricated by squeeze casting included aluminium matrix reinforced by alumina fibre and carbon fibre, respectively. The elastic constants were determined using an optimisation method associated to a classical ultrasonic immersion device. The methodology to recover the elastic constants consists in minimising the square deviation between calculated velocities and the experimental ones, measured under variable incidence from a computer controlled ultrasonic immersion device. The method of optimisation we use in this work is based on Levenberg–Marquard algorithm allowing a better convergence to the physical solution of the inverse problem. The elastic anisotropy of the two materials is discussed and the results are compared to experimental data taken from tensile tests and to values obtained by two models: the rule of mixture and a simplified Eshelby model.
Keywords: anisotropy; elastic constant; composite; optimization
Mechanical Properties and Failure Behavior of Cord/Rubber Composites by Shiguo Rao; Isaac M. Daniel; Emmanuel E. Gdoutos (pp. 353-375).
The mechanical properties and failure behavior of single tire belts with different cord angles were investigated. The cords consisted of two pairs of twisted steel wires. Geometric moiré and the grid method were used to measure small and large deformations, respectively. The stress–strain curves of all samples tested display three typical deformation stages, initial nonlinear deformation, followed by an intermediate stage of approximately linear deformation and a final stage of approximately linear deformation with increased modulus. The transition strain from the first to the second stage increases linearly with cord angle and the ultimate strength is found to follow the Tsai–Hill failure criterion. Failure mechanisms varied with cord angle. They are classified into four modes including failure within the cord, shear failure at the interface between cord and rubber, a combination of the above two modes and cord breakage. In-plane shear properties were obtained using both the Arcan pure shear and the 22° off-axis tests. They were found to be in good agreement. A nonlinear micromechanics model was proposed to predict the properties of single belts with different cord orientations by taking into consideration both the material and geometric nonlinearities.
Keywords: tire belts; cord/rubber composites; failure modes; micromechanical model; Tsai–Hill criterion; steel cords
Damage Mechanisms in Injection Molded Unreinforced, Glass and Carbon Reinforced Nylon 66 Spur Gears by S. Senthilvelan; R. Gnanamoorthy (pp. 377-397).
Application of short fiber reinforced thermoplastic materials are limited to functionally less important components due to heterogeneous characteristics of material and incomplete understanding of failure mechanisms involved. Reinforcement not only affects mechanical and electrical properties but also the failure mechanisms. Gears used in power/motion transmission may fail in many ways. This paper discusses the various types of failures exhibited by unreinforced and fiber reinforced Nylon 66 gears. Injection molded unreinforced, glass reinforced and carbon reinforced Nylon 66 spur gears were tested in a power absorption type gear test rig. Failed gears were observed under optical and scanning electron microscope to understand the damage mechanism. Different types of failures such as gear tooth wear, cracking at the tooth surface, tooth root cracking and severe tooth shape deformation were observed. Material compositions and applied torque decides the type of failure mechanism. Low interfacial strength between fibers and matrix in the reinforced gears causes fiber pullout. Reinforced gears exhibited longer life compared with the unreinforced gears due to superior mechanical strength and thermal resistance.
Keywords: damage mechanism; gear; unreinforced; fiber reinforced; Nylon 66; injection molded
Friction Stir Welding of Ceramic Particle Reinforced Aluminium Based Metal Matrix Composites by P. Cavaliere; E. Cerri; P. Leo; L. Marzoli; J. Dos Santos (pp. 399-399).
The mechanical and microstructural properties of 6061+20% Al2O3p and 7005+10% Al2O3p aluminium based metal matrix composites joined by friction stir welding were analyzed in the present study. The two materials were welded into the form of sheets of 7 mm thickness after T6 treatment and were tested in tension at room temperature. The microstructure of the joints was observed by optical microscopy and the fracture surfaces were analyzed by employing a scanning electron microscope equipped with field emission gun in order to study the micromechanisms involved during the deformation.
Keywords: MMCs; friction stir welding; FEGSEM