Papers by Keyword: Void

Abstract: 2D kinetic Monte Carlo simulation has been used to study the void distribution of nickel thin film prepared by physical vapor deposition, and embedded atom method (EAM) was used to represent the interatomic interaction. Packing density and surface roughness were studied as the functions of deposition rate, substrate temperature and incident angle. The results reveal the existence of critical substrate temperature and critical incident angle, and higher substrate temperature, lower deposition rate and appropriate incident angle are advantaged to prepare the compact thin film with excellent mechanical properties.

Abstract: In this paper, the micro-damage mechanisms of 5A06 Al alloy weld joints have been studied under the condition of constant load and cyclic thermal load. The mechanical performance variation of the base material and its weld joint are analyzed and compared. Microstructure analysis reveals that the main damage mechanism in weld joints is the interior voids nucleation and growth. The voids distribution and evolution govern the damage process. Test results also show most fractures occur at HAZ near the welding fusion line. The development of these voids results in the performance deterioration of the weld joints under thermal cycling condition.

Abstract: Ultrasonic is one of the most wide use of nondestructive evaluation technique. Voids and cracks are the most common defects in a solid. In this investigation, the ultrasonic technique is used to distinguish the defects between the void and crack. As an incident wave impinges on the crack tip, the diffractive wave can be detected from various angles. The amplitude of the diffraction is dependent on the receiving angle. For a void, the incident wave is scattered, the amplitude of the scattering wave is also dependent on the receiving angle. By comparing the amplitudes between the diffractive wave and the scattering wave, one is able to identify the defect of a void or a crack from the other. In this work, 5MHz of longitudinal and shear transducers are used and placed in a variety of incident and receiving angles to examine the difference between the void and crack. The experimental results are validated by the theoretical calculation. In order to identify the void and crack, it is required to have significant difference between the diffractive and scattering waves. The range of the detecting angle, which possesses a meaningful difference between the diffractive and scattering waves, is proposed through the numerical and experimental study to help the identification of the void and crack.

Abstract: High resolution phase contrast imaging technique has been applied to obtain clear crack images together with the detailed of microstructural features in a cast aluminum alloy. Crack opening/closure, crack extension and damage evolution in the vicinity of a crack-tip is observed three-dimensionally (3-D). 3-D image analysis is performed to evaluate void initiation and growth near the crack-tip. The information on physical displacement of each microstructural feature is provided for analyzing local crack driving forces at crack front. This technique has been identified to provide a unique possibility to quantitatively interpret the 3-D cracking behavior in bulk materials.

Abstract: The effects of void formation on the joint strength and failure mode of the solder joints were examined. A computational modeling technique, i.e., finite element modeling, was employed to investigate the effects. The effects of location, size and number of void were also investigated and compared with the case that has no void in the solder ball. When there was 1 or more voids in the solder ball, the joint strength decreased regardless of the location, size, and number of voids. Especially, the shear force of the joints decreased about 50% when 3 voids were formed in the solder ball. From the stress analyses, the possibility of preliminary brittle interfacial failure should be lower when voids were formed in the solder ball.

Abstract: Recent progress is presented in the understanding of grown-in defects in Czochralskigrown germanium crystals with special emphasis on intrinsic point defects, on vacancy clustering and on interstitial oxygen. Whenever useful the results are compared with those obtained for silicon.

Abstract: In this work, we investigate the effect of performing a high dose 20 keV He+ implant before the implantation of B at low energy (3 keV) in silicon and the subsequent thermal annealing at 800 °C. The implants were performed in laterally confined regions defined by opening windows in a SiO2 mask, in order to evidence the impact on a realistic configuration used in device fabrication. High resolution quantitative scanning capacitance microscopy (SCM) combined with cross-section transmission electron microscopy (XTEM) allowed to clarify the role of the voids distribution produced during the thermal annealing on the diffusion and electrical activation of implanted B in Si. Particular evidence was given to the effect of the uniform nanovoids distribution, which forms in the region between the surface and the buried cavity layer.

Abstract: The behaviors of a material are nonlinear in the large deformed region. The hyper elastic models can describe such non linear materials. If the hyper elastic material is applied to the hydrostatic tensile load, the void begins to grow when the load exceed the critical value. It is important to study the coalescence of the void growth in order to consider the destruction of the material. In this paper, the void growth simulations in the hyper-elastic material with multiple seeds are studied. The unit rectangular cell with small voids is subjected to the hydrostatic tensile load. This problem can be analyzed by FEM. However, the simulation with the larger number of the voids is not possible. Thus, the CA (Cellular Automaton) is used to describe the behaviors of the void coalescence and the possibility of CA is discussed.