Papers by Author: Rong Hong Cui

Abstract: This paper applies the fracture-mechanics-based analysis and the crack-closure concept to naturally occurring small cracks and large crack growth, and to make total fatigue life predictions solely based on crack growth from the assumed initial materials defect. The equation of total fatigue crack propagation life under constant amplitude loading is presented. And the total fatigue propagation lives of LY12-BCZYU aluminium alloy SENT specimens by this equation and validated by experimental results. Validation against calculations by the model and experimental data shows a good agreement.

Abstract: There are some deficiencies in the former designed crack monitoring sensor, especially when crack initiates from both sides of hole. To solve this problem, a new scheme of the sensor is presented and corresponding finite element model (FEM) is established. Then the output characteristics of the sensor are analyzed by FEM. It is shown that the sensor is sensitive to cracks, and can be used to monitor the cracks initiating from the edge of the hole, no matter from left or right side. The relationship between crack length and sensor’s output is established by polynomial fitting, and it can be employed in further crack monitoring.

Abstract: The finite element model of a symmetric tapered attachment lug is built by using the finite element software ANSYS, a cosine pin-bearing pressure distribution is applied on the surface of the pin-hole as a boundary condition. The stress intensity factor (SIF) expression for a single through-the-thickness crack in a symmetric attachment lug subjected to an oblique pin-load less than 45 degrees is determined by studying on the effect of the dimensionless crack length (a/R₁)，the ratio of outer radius to inside radius (R₂/R₁), the inside radius (R₁), the tapered angle (β) of lug and the load degree (α) on SIF value. The paper can be helpful in assessing and designing damage tolerant attachment lugs.

Abstract: The finite element model of a straight attachment lug subjected to an oblique loading less than 45 degrees is built by using the finite element software ANSYS, a cosine pin-bearing pressure distribution is applied on the hole of lug as a boundary condition. The stress intensity factor (SIF) expression for the straight attachment lug with a single through-the-thickness crack, which is subjected an oblique pin-load less than 45 degrees, is determined by studying on the influence law of dimensionless crack length (a/R₁)，ratio of outer radius to inside radius (R₂/R₁), inside radius (R₁) and pin-load angle (β) on the SIFs values. The expression is validated by contrasting with the ANSYS results and the data of residual strength test. The stress intensity factor’s amplitude (ΔK) are calculated by the SIF equation to get the values of the Paris constants. The fatigue crack growth model of attachment lug subjected to oblique pin-load is established, offering an analytical as well as experimental method for assessing and designing damage tolerant attachment lugs.

Abstract: Metal structural crack monitoring is a significant and difficult task for structural health monitoring. A special coating sensor was employed in this study to monitor aluminum structural cracks. The coating sensor was deposited on the hot spots of the aluminum structure by modern surface technology. Fatigue experimental results show that the information of the structural crack origination and propagation can be obtained through analyzing the changes of the electrical conductivity of the coating sensor, and the fatigue performance of the specimen is not obviously changed after the coating sensor deposited on it.

Abstract: The electrical potential technique was applied to monitor the crack initiation and propagation in LY12-CZ plates. The feasibility of this method was validated by a simulation experiment firstly. Then fatigue crack monitoring experiment based on LY12-CZ aluminum alloy center-hole plate specimen was carried out. After a special coating sensor was prepared on the monitoring area of the specimen by surface technology, a set of fatigue crack monitoring experiments were carried out. The changes in the potential values of the coating sensor resulting from crack damage were documented. Since the property of the coating sensor and the introduced current were constant, the measured voltage values would only relate to the crack’s length and position. Based on the experimental results, the relation curves between voltage values and crack lengths were obtained, and a set of empirical formulae were deduced.

Abstract: A kind of copper multilayer coating was prepared on stainless steel substrate using ultrasonic-electrodepositing method. The microstructure, hardness, wear resistance, adhesion and corrosion resistance of it were investigated respectively. The results show that the coating exhibits a multilayer structure and the thickness of each layer is about 0.3µm. The crystallite average diameter of it is obviously smaller than that of the ordinary electrodeposited copper coating. The diffraction peaks of Cu (200) and Cu (111) for it are obviously stronger, while Cu (220) for it is much weaker. Comparative investigations on the mechanical properties show that only the hardness of it is a little lower, whereas the wear resistance and the adhesion of it to the substrate are all evidently enhanced. The average start corrosion time of it in 20％ HNO3 solution is nearly three times delayed, and the corrosion rate is obviously decreased; anode polarization curves in 3.5% NaCl solution also show that the corrosion resistance of it is greatly improved.

Abstract: The equation of fatigue crack propagation rate is indispensable to precisely predict the fatigue life of structure containing three-dimensional crack under constant amplitude loading. Considering the crack closure effects and thickness effects in real structures, the equation of fatigue crack propagation rate under tri-axial stress state is presented. And the fatigue propagation lives of LY12-BCZYU aluminium alloy plate specimens with central through crack are predicted by this equation and validated by experimental results. Validation against calculations by the model and experimental data shows a good agreement.

Abstract: Interfacial delamination is a recognized failure mode in Integrated circuits (ICs). A major cause for this failure is the mismatch of Thermal Expansion Coefficients, Young’s modulus, and Poisson’s ratios of the package materials. Here, the influence of delamination between epoxy and dielectric layers on pattern shift and passivation cracking in IC package under aeronautical conditions, mainly temperature and load cycles, is studied by maximum plastic strain and maximum principal stresses theory using a certain 2D FEM model with different delamination length “L_c.right”. Delaminations are easy to introduce more dangerous impact to the package, because the IC microstructures endure serious thermo-mechanical loading under aeronautical working conditions. The method can be used to find the dangerous designed structure schedules and will provide a basis for selecting passivation materials of aeronautical IC packages.

Abstract: This paper presents our effort to reduce thermo-mechanical failures related IC packaging reliability problems. These reliability problems are driven by the mismatch between the different material properties. First of all, finite element analysis are adopted to investigate the influence of encapsulation structures and material properties on the stress distribution in dielectric layers and plastic strain distribution in die for a typical stacked package of IC microstructures. Results show that thinner package body, lower thermal stress and smaller plastic strain can be realized in this micro-structure with the different design geometry parameters and materials properties. Secondly, it was also found that the transition layer of TiN between the die and dielectric layer has a pronounced influence on decreasing the local stress in the passivation layer by comparison analysis. These studies would be beneficial to improve the reliability of stacked IC micro-structure packages.