G. Mansour

Position analysis in polynomial form of planar mechanisms with Assur groups of class 3 including revolute and prismatic joints

This paper presents the position analysis in analytical form of the Assur group of class 3 and order 3 with four links and six revolute/prismatic joints (triad). The aim of this position analysis is to determine all possible configurations of the Assur group, for a given position of its external joints. Four kinds of the Assur group of class 3, with one, two and three prismatic joints are investigated. The analysis leads to a nonlinear system of three equations with three unknown parameters. Using a successive elimination procedure, a final polynomial equation in one unknown is obtained. The real solutions of the polynomial equation correspond to assembly modes of the Assur group. Three numerical applications of the proposed methods are presented. Finally, a numerical application for position analysis of a planar mechanism with eight links including a triad with three external prismatic joints is also given.

Position analysis in polynomial form of planar mechanism with an Assur group of class 4 including one prismatic joint

This paper presents the solution in polynomial form to the position analysis of the Assur group of class 4 (tetrad) with four links, one prismatic and five revolute joints. The aim of this position analysis is to determine all possible configurations of the Assur group, for a given position of its external joints. The analysis leads to a non-linear system of three equations with three unknown parameters. Using a successive elimination procedure, a final polynomial equation of sixth order in one unknown is obtained. The roots of the polynomial equation lead to, at most, six different configurations of the Assur group in the complex field. Two kinds of the Assur group of class 4, the first with one external and the second with one internal prismatic joint, are investigated. In both cases, the numerical examples lead to two real solutions, which correspond to assembly modes of the Assur group. An application of the proposed method is also given for planar mechanism including such groups.

Optimization of robot links motion in inverse kinematics solution considering collision avoidance and joint limits

Abstract The present paper solves the inverse kinematic problem of a spatial redundant or nonredundant manipulator taking into account as criteria the collision avoidance and the joint functionality limits. A simulating manipulator-obstacle model with convex volumes in order to avoid a collision is used. The solution of the inverse kinematics has been conducted by the penalty function method. The developed procedure is demonstrated by solving a spatial manipulator with five revolute joints and for the off-line programming of this manipulator, which is used in a work station for various manufacturing processes. The results obtained can be checked by graphical simulation of the manipulator motion, and guarantee for a prescribed position and orientation of the end-effector a collission avoidance, respecting the joint limits.

Nanoindentation measurements of fumed silica epoxy reinforced nanocomposites

Nanoindentation testing is used in this paper in order to investigate the mechanical properties of specimens with varying weight percentage of fumed silica using a low-viscosity liquid epoxy resin as a matrix. Controversial results are reported in the literature regarding the elastic modulus of fumed silica epoxy nanocomposites using conventional tensile tests, thereby there is much scope in investigating comparatively such systems in a nanometer scale. The results show that the hardness and modulus of the nanocomposites steadily decrease with increasing fumed silica content which was attributed to the severe tendency for cluster formation as studied by optical microscope and scanning electron microscope analysis. The variations in elastic modulus as measured using the nanoindentation testing technique revealed small differences from the tensile test data. A material-depending calibration procedure has been used by utilising the epoxy elastic modulus as measured by the tensile tests in order to account for the indentation inherent uncertainties in the tip shape calibration. The results demonstrate that the nanoindentation testing technique is an effective mechanical testing method for epoxy nanocomposites when an appropriate calibration procedure is followed.

Nanomechanical Characterization of Hybrid Multiwall Carbon Nanotube and Fumed Silica Epoxy Nanocomposites

The efficiency of epoxy reinforcements provided by multiwall carbon nanotubes (MWCNTs) and fumed silica particles as well as hybrids of these two materials was assessed. Also, comparisons between the mechanical properties were performed as obtained from macroscale and nanoscale experimental methods in the form of uniaxial tensile tests and instrumented nanoindentation testing. The results showed that the material stiffness and hardness is higher for nanocomposites having 1%wt MWCNTs while the lowest values were obtained for the hybrid nanocomposites. The nanoindentation technique proved an effective method of measuring the mechanical properties providing that a suitable calibration method is followed.

Modal testing of epoxy carbon–aramid fiber hybrid composites reinforced with silica nanoparticles

In the current paper, the modal characterisation of aramid–carbon fiber hybrid composites (ACFRP) and ACFRP reinforced with silica nanoparticles (nACFRP) is investigated through the analytical-experimental transfer function method. The modal properties, such as resonant frequencies and modal loss factors, are measured by vibrating cantilever beam specimens with an impact hammer, while the vibratory response is detected through an acceleration transducer. The procedure for the identification of analytical-experimental transfer functions is carried out using a genetic algorithm by minimising the difference between the measured response from tests and the calculated response, which is a function of the modal parameters. The analytical transfer functions provide a substructuring process to identify modes, as a function of damped natural frequencies and loss factors of a complex structure, and it is insensitive to experimental noise as well as the modal coupling effect. The validation of the proposed method is verified with 10 degrees of freedom mass-spring dashpot model. The effectiveness of the proposed method is demonstrated by investigating the static and dynamic behaviour of the ACFRP and nACFRP specimens. Results indicate that the inclusion of nanosilica particles increase the stiffness of the ACFRP, although the damping response of the reinforced specimens is moderately improved.

Nanoindentation, compression and fractural characterization of highly dispersed epoxy silica nanocomposites

Uniaxial compression tests were conducted in this study in order to investigate the compressive properties of the unmodified and nanomodified epoxy with silica nanoparticles. An instrumented nanoindentation technique was also used to investigate its applicability for measuring mechanical properties for such nanocomposite systems. Additionally, the fracture toughness of the unmodified and nanomodified epoxy was measured with single-edge-notch bending tests. The Young’s modulus was found to significantly improve with addition of silica nanoparticles and increase with increasing filler content when measured with both compression and nanoindentation tests. The modulus obtained from the nanoindentation testing was 4–8% higher than the one obtained from the compression tests. As expected, the addition of silica nanoparticles had a significant impact on the fracture toughness and fracture energy and increased with increasing filler content, while observation of the fracture surfaces using SEM suggested that the nanoparticles affected the fracture behavior of such epoxy systems. Implementation of an analytical model in the current nanomodified epoxy network as compared with the experimental fracture energy results showed that the 15% matrix void growth, from debonded nanoparticles, as well as the matrix shear banding are the governing mechanisms of energy absorption.

Dynamic Mechanical Characterization of Polyurethane/Multiwalled Carbon Nanotube Composite Thermoplastic Elastomers

ABSTRACT An effective analytical–experimental test method is used in the current work to characterize the vibration isolation behavior of thermoplastic polyurethane multiwalled carbon nanotube nanocomposites with five different concentrations. To determine the static compression stiffness and hysteresis of the specimens, compression and cyclic tests were conducted. The vibration isolation properties were determined through the analysis of transmissibility of a suitably designed test system. Thermoplastic polyurethane’s mechanical properties and vibration isolation properties were improved with the addition of multiwalled carbon nanotubes. Considering the obtained results, the dynamic stiffness of thermoplastic polyurethane and its capacity to isolate vibration can be adjusted by controlling the proportion of multiwalled carbon nanotubes. GRAPHICAL ABSTRACT

Investigation of the Electro-Discharge Open-Hole Machining on the Structural Behavior of Carbon Fiber Reinforced Polymers

The current work investigates the electro-discharge machining (EDM) of plain woven carbon reinforced polymer composites with pulse durations of 100 μs, 200 μs, 300 μs, currents 1 A, 3 A and 5 A, and a voltage of 100 V. An x-ray computed tomography (CT) is employed to examine the delaminations, while a delamination factor model utilizing the equivalent delamination diameter provides the measuring quantity for assessment. Finite element simulations compute the stress concentrations around the holes by taking into account the delamination equivalent diameters of the open-holes, as monitored from the x-ray CT. The Whitney-Nuismer point stress criterion is utilised in order to predict the failure strength of the machined open-hole laminates and it is compared with the experimentally derived mechanical strength values. The results reveal that EDM is a feasible method for open-hole machining of composites, however proper selection of the operational parameters is needed. By accurately measuring the peripheral delamination areas of the machined holes, it is shown that the analysis of the mechanical behaviour of the plain woven laminates by the means of finite element method and the Whitney-Nuismer criterion can accurately predict the response of such composites when subjected to tensile loads.

Mechanical and vibration isolation behaviour of acrylonitrile-butadiene rubber/multi-walled carbon nanotube composite machine mounts

ABSTRACT An effective analytical-experimental test method is used in the current work to characterize the vibration isolation performance of nitrile-butadiene rubber (NBR) reinforced with multi-walled carbon nanotubes (MWCNTs). A series of specimens were manufactured with 10 different NBR/MWCNTs concentrations (0 to 20wt% MWCNTs). In order to determine the static compression stiffness and hysteresis of the mounts, compression and cyclic tests were conducted. The vibration isolation properties were determined through the analysis of the transmissibility of a suitably designed test system. NBR’s mechanical properties and vibration isolation properties were improved with the addition MWCNTs, suggesting that the enhancement of NBR with MWCNTs was rather effective. Considering the obtained results, the dynamic stiffness of NBR and its capacity to isolate vibration can be adjusted by controlling the proportion of MWCNTs.