Dynamics and Morphology of Cracks in Silicon Nitride Films: A Molecular Dynamics Study on Parallel Computers

1. The mechanism of the effect of the frequency and form of trajectory of cyclic loading upon the speed of crack propagation was examined from the fracture mechanics viewpoint. 2. In steel 00Kh12N3D a reduction in sinusoidal loading frequency of 20 times (from 2000 to 100 cycles/min) leads to an increase of 1.6 times in the speed of crack development. 3. The speed of fatigue crack propagation in steel 00Kh12N3D is expressed by the following experimentally obtained relationship:C=1.61.10−10‡K3.07n−0.22 4. In steel 15Kh2NMFA the speed of crack growth does not depend upon the frequency of sinusoidal loading and is expressed by the relationshipC=3.86.10−11‡K3.16. 5. A reduction in the frequency of loading with a rectangular form of trajectory leads to a reduction in the speed of crack development in steels 00Kh12N3D and 15Kh2NMFA. 6. The speed of the fatigue crack is less with impact loading than with a sinusoidal form of load trajectory.

A fractal aggregation behavior in amorphous silicon nitride (SixNy) films deposited by microwave electron cyclotron resonance plasma chemical vapor deposition is reported. The fractal structure and dimension of 1.45 obtained by experiment and computer simulation are all in excellent agreement with the result predicted by the cluster-cluster-aggregation model. The forming of fractal structure is related to the change of discharge mode between ring plasma and bulk plasma.

Study on dynamic fracture behavior of mode I crack under blasting loads

This paper deals with a non-destructive detection method of the generation time, the crack length and the propagation speed of fatigue crack in spot-welded joints under tensile-shear load.In case of spot-welded joints, fatigue cracks generate usually at the neighborhood of nugget tips of the weld interface, and propagate toward outer surfaces of the sheets. Accordingly, it is very difficult to observe and measure the crack length, consequently the generation time and the propagation speed of crack by using conventional measuring devices.Authors developed a non-destructive method of fatigue crack, which the generation time, the crack length and the propagation speed of fatigue crack can be quantitatively estimated by utilizing infomation obtained from the strain gages bonded on the electrode indentations of spot welds. Specimens used in this experiment are made of various kinds of thin steel sheets.Main conclusions obtained in this study are as follows:(1) The propagation length of fatigue crack is related with both mean strain and strain range of out-put of the strain gage, and the changing rate of strain range is specially useful for fatigue crack detection.(2) The generation time and the propagation speed of fatigue crack can be estimated easily from relationship between the number of cycles and the crack length, which is established in advance for an individual test piece.

Characterization of thin-film amorphous semiconductors using spectroscopic ellipsometry

Dynamic crack propagation and bifurcation phenomena are investigated analytically by utilizing the strain energy density fracture criterion in the framework of catastrophe theory. The effect of biaxial stress, loading imperfections (mixed-mode loading), Poisson's ratio, state of stress as well as crack tip propagation speed on the crack path directional stability is analyzed. Special crack path stability charts for (un)stably propagating cracks are obtained, and their connection with the experimentally recorded crack tip stress field is addressed. It is shown that a slight change of the normal stress acting parallel to a crack at its tip (crack-parallel stress) may be able to affect the crack surface roughening and/or branching velocity considerably. It is also indicated that under small tensile crack-parallel stress, the crack propagation is stable only when the crack propagation speed is less than about 30% of the relevant shear wave speed. The crack becomes unstable, and its surfaces roughen severely at a higher speed, and the crack bifurcates at the highest propagation speed, some 45% of the shear wave speed. It is suggested that superimposing mode-II (shear) loading will enhance the dynamic crack path stability while increasing crack propagation speed will reduce the stability of crack propagation. It is expected that under compressive crack-parallel stress no crack surface roughening will occur before the crack stably bifurcates.

Controlling factors for roughness increases on cleavage fracture surfaces and crack branching in polycrystalline steel

Ceramic Materials have been widely used in many fields of engineering, It is necessary to research the process of crack propagation of ceramic materials at high temperature by numerical simulation. The numerical model is applied to investigate the formation, extension and coalescence and crack propagation in ceramic materials at high temperature. A numerical model of ceramic materials is proposed to investigate thermally-induced damage and crack propagation at high temperature. The numerical simulations show that when the tensile stress exceeds its phase transition threshold, it produces tensile failure, in the specimen surface more and more the impact cracks are appear, the crack spacing’s are basically equal and parallel to each other, with the elapse of time, the main cracks continue to expand, small part of the cracks expansion are subjected to limited, there are the classifications of cracks. With the elapse of time, crack propagation speed gradually slows down, and eventually reaches a steady state. The numerical simulation demonstrates that the model proposed can visually replicate the thermal cracking propagation process of ceramic materials at high temperature. The result of our numerical simulation shows that thermal cracking propagation process in ceramic materials at high temperature is in good agreement with the real experimental thermal cracking result of crack propagation in ceramic materials at high temperature.

Temperature of thermal spikes in amorphous silicon nitride films produced by 1.11 MeV C603+ impacts

Dynamic crack propagation in elastic-perfectly plastic solids under plane stress conditions

In this paper, we report the reflectance spectra of hydrogenated amorphous silicon nitride(a-SiNx:H) film grown on GaAs substrate using Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Fourier Transform Infrared (FTIR) spectroscopy has been used explicitly to resolve the LO and TO phonon mode contributions. The results of variable angle polarized IR reflectance on a-SiNx:H/GaAs samples are obtained for two different orientations. The calculated results for polarized reflectance are in good agreement with experimental measurements by choosing suitable frequencies and damping as fitting parameters.In this paper, we report the reflectance spectra of hydrogenated amorphous silicon nitride(a-SiNx:H) film grown on GaAs substrate using Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Fourier Transform Infrared (FTIR) spectroscopy has been used explicitly to resolve the LO and TO phonon mode contributions. The results of variable angle polarized IR reflectance on a-SiNx:H/GaAs samples are obtained for two different orientations. The calculated results for polarized reflectance are in good agreement with experimental measurements by choosing suitable frequencies and damping as fitting parameters.

Thin films deposited on crystalline silicon surfaces are critical components of many silicon‐based devices, including high‐efficiency photovoltaic cells. Knowledge of their optical and electronic properties is important in designing and fabricating efficient solar cells, especially as the device complexity increases and includes micron‐scale features. Here, a camera‐based photoluminescence (PL) technique is developed to image the thickness of specific passivating films on silicon wafers. The technique is entirely contactless and nondestructive, requires minimal sample preparation, and provides a large dynamic range in terms of field of view, with micron‐scale spatial resolution possible. It retains the advantages of PL imaging, a mainstream technique for photovoltaic material and device characterization, and it has some extra capabilities similar to those of ellipsometry. This newly developed technique is demonstrated on hydrogenated amorphous silicon and silicon nitride films, two important passivation technologies for high‐efficiency silicon solar cells.

Evolution of Crack Propagation Rate in Notched Specimens Using XFEM Method under Bending Load Condition

Patterned or unpatterned silicon nitride films are used as masks in structured or unstructured, epitaxial or amorphous growth of semiconductor layers on single-crystal or amorphous substrates. The silicon nitride mask is stable compared to the conventionally used silicon oxide mask. Amorphous silicon nitride films are a constituent element of superlattice structures which are base materials for novel devices.

Fractal geometry is a non‐Euclidean geometry which has been developed to analyze irregular or fractional shapes. In this paper, fracture in ceramic materials is analyzed as a fractal process. This means that fracture is viewed as a self‐similar process. We have examined the fracture surfaces of six different alumina materials and five glass‐ceramics, with different microstructures, to test for fractal behavior. Slit island analysis and Fourier transform methods were used to determine the fractal dimension, D , of successively sectioned fracture surfaces. We found a correlation between increasing the fractional part of the fractal dimension and increasing toughness. In other words, as the toughness increasing the fracture surface increases in roughness. However, more than just a measure of roughness, the applicability of fractal geometry to fracture implies a mechanism for generation of the fracture surface. The results presented here imply that brittle fracture is a fractal process; this means that we should be able to determine processes on the atomic scale by observing the macroscopic scale by finding the generator shape and the scheme for generation inherent in the fractal process.