Issue 3
JTAM, Sofia, vol. 45 Issue 3 (2015)

Maximum Allowable Dynamic Load of Mobile Manipulators with Stability Consideration

H. R. Heidary
College of Mechanical Engineering, Malayer University, Malayer, Iran


High payload to mass ratio is one of the advantages of mobile robot manipulators. In this paper, a general formula for finding the maximum allowable dynamic load (MADL) of wheeled mobile robot is presented. Mobile manipulators operating in field environments will be required to manipulate large loads, and to perform such tasks on uneven terrain, which may cause the system to reach dangerous tip-over instability. Therefore, the method is expanded for finding the MADL of mobile manipulators with stability consideration. Moment-Height Stability (MHS) criterion is used as an index for the system stability. Full dynamic model of wheeled mobile base and mounted manipulator is considered with respect to the dynamic of nonholonomic constraint. Then, a method for determination of the maximum allowable loads is described, subject to actuator constraints and by imposing the stability limitation as a new constraint. The actuator torque constraint is applied by using a speed-torque characteristics curve of a typical DC motor. In order to verify the effectiveness of the presented algorithm, several simulation studies considering a two-link planar manipulator, mounted on a mobile base are presented and the results are discussed.

JTAM, Sofia, vol. 45 Issue 3 pp. 03-22 (2015), [Full Article]

Analysis of the Nonlinear Elastic Response of Rubber Membrane with Embedded Circular Rigid Inclusion

Sang Jianbing1, Xing Sufang1, Wang Ling1, Wang Jingyuan2, Zhou Jing2
1School of Mechanical Engineering, Hebei University of Technology, Tianjin, 300130, China
2School of Civil Engineering, Hebei University of Technology, Tianjin, 300130, China

Rubber membranes exhibit a particular nonlinear elastic behaviour known as hyper elasticity. Analysis has been proposed by utilizing the modified strain energy function from Gao’s constitutive model, in order to reveal the mechanical property of rubber membrane containing circular rigid inclusion. Rubber membrane is taken into incompressible materials under axisymmetric stretch, based on finite deformations theory. Stress distribution of different constitutive parameters has been analyzed by deducing the basic governing equation. The effects on membrane deformation by different parameters and the failure reasons of rubber membrane have been discussed, which provides reasonable reference for the design of rubber membrane.

JTAM, Sofia, vol. 45 Issue 3 pp. 23-36 (2015), [Full Article]

Influence of Thin-Wall Structure on Stress Distribution of Curvic Couplings

Shuxia Yuan1, Youyun Zhang2, Yongsheng Zhu2
1School of Mechanical Engineering, Xi’an Shiyou University, Xi’an, PR China
2Theory of Lubrication & Bearing Institute, Xi’an Jiaotong University, Xi’an, PR China

The objective of this paper is to investigate the influence of transition structure between curvic teeth and disk on stress distribution of curvic couplings, and provide data to help improving the design of curvic couplings. In this work, the three-dimensional finite element method was used, and Augmented Lagrange Algorithm was adopted to the contact algorithm during the analysis. According to the results of this paper, designing thin-wall structure reasonably can avoid detaching of contact interface at external diameter during preload process; reduce stress fluctuation of curvic teeth caused by circumferential bolts structure; and balance stress difference of each contact pair caused by different disk quality under the action of the centrifugal force.

JTAM, Sofia, vol. 45 Issue 3 pp. 37-52 (2015), [Full Article]

Investigation on Influence of Speed on Rolling Resistance of Belt Conveyor Based on Viscoelastic Properties

Yan Lu, Fu-Yan Lin, Yu-Chao Wang
School of Mechanical Electronic & Information Engineer, China University of Mining and Technology, Beijing, Beijing, 100083

Since indentation rolling resistance accounts for the major part of total resistance of belt conveyor, it is important to compute it using a proper method, during the design and application study of the belt conveyor. Firstly, an approximate formula for computing the indentation rolling resistance is offered. In this formula, a one-dimensional Winkler foundation and a three-parameter viscoelastic Maxwell solid model of the belt backing material are used to determine the resistance to motion of a conveyor belt over idlers. The velocity of belt is an important operating parameter in the working conditions of the belt conveyor. What’s more, a set of experimental apparatus, which can measure the value of indentation rolling resistance is designed. Author obtains a series of measured data under the different belt speeds with the help of experimental apparatus. Finally, a computation example, that is provided for a typical rubber compound backing material, shows the comparison between the measured and the theoretical results, which offers the influence of speed on the rolling resistance.

JTAM, Sofia, vol. 45 Issue 3 pp. 53-68 (2015), [Full Article]

Analysis of Mixed Mode I/II/III Fracture in Foam Core Sandwich Structures Using Imposed Displacement Split Cantilever Beams

V. Rizov
Department of Technical Mechanics, University of Architecture, Civil Engineering and Geodesy, 1, Chr. Smirnensky Blvd, 1046 Sofia, Bulgaria

Static fracture in foam core sandwich structures under mixed mode I/II/III loading conditions was studied theoretically. In order to generate such loading conditions, a thread guide was used to impose inplane displacements of the lower crack arm of a sandwich Split Cantilever Beam (SCB). The upper crack arm was loaded by a transverse force. A three-dimensional finite element model of the imposed displacement sandwich SCB configuration was developed. The fracture was studied applying the concepts of linear-elastic fracture mechanics. The strain energy release rate mode components distribution along the crack front was analyzed using the virtual crack closure technique. The influence of the imposed displacement magnitude and the crack length on the fracture was evaluated. The effect of the sandwich core material on the mixed-mode I/II/III fracture was studied. For this purpose, finite element simulations were carried-out assuming that the core is made by different rigid cellular foams. It was found that the strain energy release rate decreases when the foam density increases.

JTAM, Sofia, vol. 45 Issue 3 pp. 69-82 (2015), [Full Article]

Behaviour of Bi-Adhesive in Double-Strap Joint with Embedded Patch Subjected to Bending

Semsettin Temiz1, Hamit Adin1, Ismail Yasin Sulu2
1Department of Mechanical Engineering, Faculty of Engineering, Batman University, 72060 Batman, Turkey
2Department of Mechanical Engineering, Faculty of Engineering, Inonu University, 44280 Malatya, Turkey

In this study, behaviour of bi-adhesive used in the repair of damaged parts was analyzed, using the finite element method. In a double-strap joint with an embedded patch, patch is embedded into the adherents for structural requirements. In addition, to increase the strength of the joint, two adhesives are used to bond the adherents. This approach reduces stress concentration at the overlap ends, increases the load capacity and delays the failure. These effects give rise to higher joint strength. For this purpose, a stiff adhesive, FM73 produced by Cytec Fiberite, was applied in the middle portion of the overlap, while a softer adhesive, SBT9244 from 3M, was applied towards the edges, prone to stress concentrations. Non-linear finite element analyses were carried out to predict the failure loads, to assist with the geometric design and to identify effective ratios of sizes to maximize joint strength.

JTAM, Sofia, vol. 45 Issue 3 pp. 83-96 (2015), [Full Article]