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Number of results: 5
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Abstract

The strength of conveyor belts splices made in mines rarely reaches full belt strength. It consists of a number of factors. The primary is the method of their construction and proper selection of ingredients. The significant impact has also has splice quality covering both keeping proper geometry matched to the belt construction and belts working conditions and adherence to the best practices in the field of technologies of their construction.Difficult conditions in underground mines and pressure on reducing conveyor downtime (avoiding production losses) is reflected by a drop in static and dynamic splices strength. This is confirmed by numerous studies of belt splices strength and fatigue life conducted in the Laboratory of Belt Conveying (LTT) within the framework of research and expert opinions commissioned by belt manufacturers and their users. The consequence of too insufficiently low belt splices strength is their low durability, decreasing reliability and, consequently, higher mining transportation costs. Belt splices are in fact the weakest link in the serial structure which form closed loops of interconnected belt sections working in series of conveyors transporting excavated material in the mine. The article presents the results of simulation analyzes analyses investigating how the increase of belt splices durability may contribute to the reduction of transportation costs in the underground mines.
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Abstract

Dynamic Mine disasters can be induced by the instability and failure of a composite structure of rock and coal layers during coal mining. Coal seam contains many native defects, severely affecting the instability and failure of the compound structure. In this study, the effects of coal persistent joint on the strength and failure characteristics of coal-rock composite samples were evaluated using PFC2D software. The results show that with the increase of included angle α between the loading direction and joint plane direction, the uniaxial compressive stress (UCS) and peak strain of composite samples first decrease and then gradually increase. The elastic moduli of composite samples do not change obviously with α. The peak strain at α of 45° is the lowest, and the UCS at α of 30° is the smallest. This is inconsistent with theoretical analysis of lowest UCS at α of 45°. This is because that the local stress concentration caused by the motion inconformity of composite samples may increase the average axial stress of upper wall in PFC2D software. Moreover, the coal persistent joint promotes the transformation from the unstable crack expansion to the macro-instability of composite samples, especially at α of 30° and 45°. The majority of failures for composite samples occur within the coal, and no obvious damage is observed in rock. Their failure modes are shear failure crossing or along the coal persistent joint. The failure of composite sample at α of 30° is a mixed failure, including the shear failure along the persistent joint in coal and tensile failure of rock induced by the propagation of coal persistent joint.
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Abstract

The paper presents the results of research on the modification of the face geometry of the refill friction stir spot welding tool sleeve for welding thin aluminum sheets with an Alclad and an oxide anode coating. The analysis of the impact of such modification on the process perform (tool motion parameters, temperature) and microstructure as well as mechanical strength of the lap joints were analyzed. The tests were carried out using aluminum alloy 2024-T3 sheets with thickness 1.27 mm. For comparative purposes, joints were also made using plates without an Alclad and without anodized coating with using unmodified tool and modified tools with developed 3 variants of face geometry. The samples with the joint were subjected to metallographic and strength tests. It has been shown that the use of modified geometry has a decisive influence on the performance of the process and the effect of softening and mixing of materials in the zone of point connection.
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Abstract

This paper presents an elasticity solution of adhesive tubular joints in laminated composites, with axial symmetry. In this model, adherends are orthotropic shells and the stacking sequences can be either symmetric or asymmetric. Adhesive layer is homogenous and made of isotropic material. They are modelled as continuously distributed tension/compression and shear springs. Employing constitutive, kinematics and equilibrium equations, sets of differential equations for each inside and outside of overlap zones are obtained. By solving these equations, shear and peel stresses in adhesive layer(s), as well as deflections, stress resultants and moment resultants in the adherends are determined. It is seen that the magnitude of peel stresses due to transverse shear stress resultant is much greater than that obtained from axial stress resultant. The developed results are compared with those obtained by finite element analysis using ANSYS software. The comparisons demonstrate the accuracy and effectiveness of the aforementioned methods.
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