Papers by Author: Yu Ting He

Abstract: Friction Stir Welding (FSW) is a new type of solid-state connection which can reduce structural weight significantly. In this paper, fatigue tests and finite element analysis were employed to study fatigue properties and residual stresses of aerial aluminum alloy 2524-T3 FSW joint. The residual stresses in FSW joint were obtained by a nonlinear direct coupled-field finite element analysis. On the basis of finite element analysis results, the fatigue life of FSW joint was estimated. It is verified that the analytic and estimated results agree with that of experiment.

Abstract: To monitoring of the crack damage located at the bolt hole of metallic bolted-joint structure in real-time, a fatigue crack monitoring scheme based on rosette eddy current sensor is put forward. The characteristics of sensor are analyzed via semi-analytic model, and feasibility of proposed scheme is verified through monitoring experiment using constructed fatigue crack monitoring system. The result of semi-analytic model shows that the magnitude of transimpedance is more sensitive to changing of conductivity and liftoff than phase of transimpedance, and the sensitivity of magnitude increases with the frequency. The result of fatigue crack monitoring experiment of 2A12-T4 aluminum alloy under constant load indicates that viewing the break point as indication of crack position, the rosette eddy current sensor achieves quantitative-monitoring capability of fatigue crack with precision of 1mm and the sensing-channels near fatigue source are capable of qualitative-monitoring of accumulated fatigue damage.

Abstract: Finite element method (FEM) is applied to analyze the buckling performance of alloy aluminum stiffened panel subjected to uniform axial compression. With the skin thickness and stiffener pitch unchanged, the influence of flange thickness, flange length, stiffener thickness and stiffener height on compress buckling critical loads are studied by FEM. Important parameters influencing the buckling performance are identified and the results offer a referenced measure for the optimization design and engineering application of the structure.

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: Finite element models of an eddy current sensor array are built up by electromagnetic-circuit couple method, and the influences of conformable substrate on sensor’s output characteristics are analyzed by those models. It is shown that the model contains the conformable substrate has almost the same output characteristics as the model without it, but the output amplitudes and phases of the former model are higher than the latter. Therefore we can simply the sensor as a single surface to facilitate the analysis, and then revise it to fit to the real sensor.

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: 2A12 specimens are selected in pre-corrosion fatigue test to get the ground corrosion effect coefficient, namely C(t) curve. Then, combining with Miner linear cumulative damage theory, theoretical fatigue life model is established based on the simulated corrosion-fatigue interactive process. Compared with actual corrosion-fatigue interactive test, theoretical life in short interactive periods is almost same, but actual life is higher in long interactive periods. Afterwards, a modified model based on C(t) curve at different interactive periods is established. The calculation shows that the modified results are in good agreement with the corrosion-fatigue interactive test.

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: A new approach to reflect the relation of aircraft structural calendar life and fatigue life is established by pre-corrosion and fatigue test with 2A12 alloy specimens. The corrosion factor curve is fitted from the test, and then aircraft structural corrosion and fatigue interactive process during actual in-service environment is simulated. Furthermore, combining with Miner linear cumulative damage theory and the method of ‘calendar life tending to minimum’, life envelope is found. The result shows that flight strength is the key factor for aircraft structural life, and the envelope can be used to realize single aircraft structural life surveillance.

Abstract: The three-dimensional finite element model of cabin glass with surface scratch is built using the finite element software ANSYS, which is aimed to analyze the detailed stress around the scratch route tip. Then the fatigue notch factor can be gained through utilizing of results from three-dimensional model, which is followed by the estimation of fatigue life based on local stress-strain method. It is found that the stress around scratch route tip is nearly linearly increased with the increasing of tip depth (0.2mm<h<0.8mm) and the fatigue performances of cabin glass with surface scratch are sensitive to scratch depth. Finally, fatigue tests are carried out with the specimens of different scratch route tip depths, and validation against fatigue life by local stress-strain method and experimental data shows a good agreement, which indicates that the scratch model and the local stress-strain method for the effects of scratch on cabin glass fatigue performances are valid.