A finite element model is developed for the process of squeeze casting of metal matrix composites in cylindrical molds. The fluid flow and the heat transfer are fundamental phenomena in squeeze casting. To describe heat transfer in the solidification of molten aluminum, the energy equation written in terms of temperature and enthalpy are applied in an axisymmetric model which is similar to the experimental system. A 1-D flow model simulates the transient metal flow. A direct iteration technique was used to solve the resulting nonlinear algebraic equations, using a computer program to calculate the enthalpy, temperature and fluid velocity. The cooling curves and temperature distribution during infiltration and solidification were calculated for pure aluminum. Experimentally, the temperature was measured and recorded using thermocouple wire. The measured time–temperature data were compared with the calculated cooling curves. The resulting agreement shows that the finite element model can accurately estimate the solidification time and predict the cooling process.
This study investigated acoustic emission behavior during fatigue crack growth test under constant and variable amplitude loading in 304 stainless steel. To describe the acoustic emission behavior, counts rate(dη/dn) was related with stress intensity factor range (SIFR, ΔK) in log-log plot. As a result of test, the relationship was represented a curve, which forms rise and fall behavior in counts rate as the SIFR increases. AE response to a single overload was sudden drop and slow recovery in counts rate, which was similar to crack growth retardation behavior. Under block loading, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental results indicated that stress intensity factor controls the counts rate (dη/dn) as well as crack growth rate (da/dn) regardless of load range or crack length.
An axisymmetric finite element (FE) model is developed for the process of squeeze casting the metal-matrix composites (MMCs). The flow in the mold, the infiltration into the porous preform, and the solidification of the molten metal are studied numerically. The saturated porous flow model is adopted to simulate metal infiltration into the fibrous preform. To track the fluid front during the mold filling and infiltration, the level-set method is used. The enthalpy method is used to deal with transient heat transfer, including phase changes. Also, a simple preform deformation model is used to predict the permeability change caused by preform compression during infiltration. A numerical model representing the experiment setup is proposed. The infiltration and cooling behaviors during a process were calculated using pure aluminum as the matrix and a Saffil fiber preform. To validate the assumptions used in the numerical model, a series of infiltration experiments was carried out. The infiltration kinetics and the preform deformation were studied at different inlet pressures and at different preheat temperatures of the aluminum and the mold. A comparison with the experimental data shows that the developed FE program successfully predicts the actual squeeze casting process.
Synopsis :An on-line model predicting the residual stress in roller leveling process is developed. In order to simplify the formulation, the plain strain (de z ϭ0) condition is assumed and the stress in thickness direction is ignored (s y ϭds y ϭ0). The camber and gutter deformation of the real sized plate are measured and compared with the prediction values of the model to validate the accuracy of the model. The variations of residual stress are studied according to the entry and the delivery intermeshes, respectively. The camber deformation decreases linearly as increasing the entry intermesh. But the gutter deformation does not vary directly as the intermesh. Therefore, the optimum intermesh values should be found to minimize both the camber and the gutter deformation.
Acoustic emission (AE) technique was applied as a non-destructive test method to detect and evaluate the localized damage at high temperature environment. The creep-fatigue crack growth tests were carried out with the acquisition of AE signal at 1000°F. Under trapezoidal waveform loadings, AE results showed different features according to each damage mode. During the creep period, low and steady emissions were shown, while emissions were burst and high counts rate was recorded during the fatigue loading. Based on these characteristics, damage contribution was expressed in terms of acoustic emission parameter as a part-time monitoring method. Comparisons of damage contribution with respect to lifetime showed the transient behavior from cycle-dependent to time-dependent process. In case of full-time monitoring, bilinear behavior between AE counts and life was represented. From both monitoring results, it was confirmed that creep and fatigue damage can be characterized by means of emission features and AE is possible way to evaluate the localized damage at elevated temperature.
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