Scattering of Magnetoacoustic Waves and Dynamic Stress Concentration around Double Openings in Piezomagnetic Composites

Based on the magnetoacoustic coupled dynamics theory, the wave function expansion method is used to solve the problem of acoustic wave scattering and dynamic stress concentration around the two openings in e-type piezomagnetic composites. To deal with the multiple scattering between openings, the local coordinate method is introduced. The general analytical solution to the problem and the expression of the dynamic stress concentration are derived. As an example, the numerical results of the dynamic stress distribution around two openings with equal diameters are given. The effects of the parameters, such as the incident wave number and the spacing between the openings, on the dynamic stress concentration factor are analyzed.

Empirical Analysis of the Impact Strength of Textile Knitted Barrier Meshes

The assumptions of instrumental methodology for measuring dynamic loads of knitted barrier meshes were defined. A test stand was built, original in terms of both mechanical construction and electronic measuring system, connected to a computer data analysis system. Maximum values of dynamic forces in the mesh fastening strings were determined. The correctness of the strain gauges construction and measurement data transmission systems was confirmed. Tests of multidirectional resistance to dynamic loads in the mesh fastening strings were carried out. The experiment involved dropping a ball with a mass of 5 kg and a diameter of 10 cm, from a height of 1 m and 2 m onto the mesh surface. The potential impact energy equaled Ep1 = 49.05 J and Ep2 = 98.1 J. The tests showed that the highest force values were observed for meshes with square-shaped a-jour structure, and for mesh with diamond-shaped a-jour geometry the force values were lower. A symmetrical forces distribution was observed in all the strings. The highest forces were recorded in the middle strings and the lowest in the outer ones. The conducted tests confirmed the correctness of the adopted constructional solutions of test stand for identification of dynamic stress distribution in mesh fastening strings. The developed method is a useful verification tool for numerical analysis of mechanical properties of barrier meshes.

THE EFFECT OF MANDIBLE VISCOELASTICITY ON DYNAMIC STRESS DISTRIBUTION IN OSSEOUS TISSUE ADJACENT TO DENTAL IMPLANT

Mandible consists considerable amount of water together with solid phase of hydroxyapatite and collagen fibrous. Such composition causes the bone tissue to exhibit time-dependent viscoelastic behavior in response to external dynamic loads for instance mastication. In this study, we aimed to evaluate the effect of mandible viscoelasticity on dynamic stress distribution in osseous tissue adjacent to dental implant with the aid of finite element analysis method. The von-Mises stress profile within the surrounding bone tissue of Titanium dental implant was investigated in two different elastic and viscoelastic models of mandible. The two models had identical boundary conditions and geometrical features but different mechanical properties. There were no obvious changes in the location of vulnerable area in both models. But in comparison with the elastic model, a considerable drop in peak stress values accompanied with a smoother stress contours was observed in the viscoelastic model. It can be concluded that the viscoelasticity of mandible plays a vital role in the evaluation of subsequent response of implanted mandible to external cyclic loads and thus in detecting the long-term success of dental implantation. Significant reduction of stress exerted on mandible bone, particularly in the area adjacent to the location of applied force, may result in a longer fatigue life as a main index of long-term success of dental implantation.

A Green’s Function Approach for Dynamic Stress Analysis of Spherical Shell under the Isotropic Impact Load

A Green’s function approach is developed for the analytic solution of thick-walled spherical shell under an isotropic impact load, which involves building Green’s function of this problem by using the appropriate boundary conditions of thick-walled spherical shell. This method can be used to analyze displacement distribution and dynamic stress distribution of the thick-walled spherical shell. The advantages of this method are able(1)to avoid the superposition process of quasi-static solution and free vibration solution during decomposition of dynamic general solution of dynamics,(2)to well adapt for various initial conditions, and(3)to conveniently analyze the dynamic stress distribution using numerical calculation. Finally, a special case is performed to verify that the proposed Green’s function method is able to accurately analyze the dynamic stress distribution of thick-walled spherical shell under an isotropic impact load.

Failure Prevention on Application of Flexible Printed Circuits

With the compact nature and the high electrical-connection density, flexible printed circuits (FPC) can achieve considerable weight, space and cost savings over the use of traditional rigid printed circuit boards. In recent years, it becomes impossible without flexible printed circuit technology in electronic products especially for Flip mobile phones. Whereas, its application is not always satisfied the engineering of assembly and reliability due to the existing of mechanical stress in soldering process and service environment. In this paper, through analyzing the common failures in mass production including via interconnection, trace crack and black pad, some preventions were suggested to improve the quality and reliability at the aspect of manufacture, process, mechanical design and dynamic stress distribution philosophy.