Papers by Author: Shun Fa Hwang

Abstract: The purpose of this work is to study a new composite material consisting of polyurethane (PU) resin and carbon fiber fabric. This PU resin is superior in impact, viscosity, low curing temperature, and short curing time. If this resin is combined with fiber fabric by vacuum assisted resin transfer method, the fabrication time will be short. Since it is a braided composite, it’s important to have a model to predict the elastic constants for different braid angels. To predict the elastic constants including Young’s modulus, shear modulus, and Poisson’s ratio, a finite element model is established. In this model a braided layer is treated as two uni-directional layers. Then, the elastic constants of this composite with different braid angels are estimated. After that, the composites with different braid angels are fabricated and tested to obtain the elastic constants, and the comparison with the finite element results is made. The results indicate that the agreement is very good for the Young’s modulus. For the Poisson’s ratio, the difference between the prediction and the measurement is reasonable. From the comparison, it can be concluded that the finite element model is good. Then, this model is used to predict all in-plane elastic constants for arbitrary braid angles.

Abstract: Molecular dynamic simulation for Co cluster deposition on Si substrate was investigated in this work. The surface roughness and the interface mixing will be evaluated for the deposited film quality under different incident energies and substrate temperatures. The effect of thermal annealing on the ability of gap filling will be discussed by a slip vector. The results indicate that the incident energy has dominant effect on the surface roughness, and there is a minimum surface roughness value around the incident energy of 8 eV. However, the substrate temperature has little effect on the surface roughness. For interface mixing, the simulation indicates the easy diffusion of Co atoms into Si substrate. However, increasing either the incident energy or the substrate temperature could not change much the mixing conditions. As for the ability of gap filling, it is clear that the thermal annealing does improve this ability and obtains better surface roughness and interface mixing.

Abstract: A molecular dynamic (MD) method is used to simulate Al atom depositing on Cu substrate by controlling the incident energy and the deposition rate for dual-target magnetron sputtering. At the interface, functional graded material (FGM) will be created to reduce the residual stress after the deposition process. The results indicate that the surface roughness of the deposited film will be reduced with the assistance of FGM, and more layers of FGM will reduce more the root-mean-square (RMS) value and the residual stress to obtain excellent quality of the deposited film.

Abstract: The mixing situation of Co atoms implanting onto Cu(001) substrate is investigated with regard to incident energy and substrate temperature by molecular dynamics. The results indicate that higher substrate temperature and/or incident energy will result in higher intermixing between the incident atoms and the substrate atoms. Furthermore, the value of the first peak of the radial distribution function (RDF) becomes lower and wider for the Co-Cu system as the substrate temperature and/or incident energy are increased.

Abstract: Combining vibration testing and numerical method is a potential inverse technique for determining elastic constants of materials because of its nondestructive characteristic, single test, and producing average properties. In order to simplify the modeling processes and to reduce complicated derivation in the numerical method, the combination of finite element analysis and optimum design is adopted in this work. A finite element package, ANSYS, is used to do the modal analysis of the composite plate. A hybrid genetic algorithm, in which a simulated annealing mutation process and adaptive mechanisms are added to the real-parameter genetic algorithm, is used to search the possible elastic constants. After obtaining the natural frequencies of the composite plates from vibration testing, this inverse technique could predict the elastic constants of the composite plate. The inverse technique is verified by comparing with other methods and by determining the elastic constants of aluminum plates, and the excellence of including the hybrid genetic algorithm is proved. The results also indicate that the present technique could obtain very accurate elastic constants of composite plates.

Abstract: Composite materials using polymer resins as matrices have viscoelastic behavior. This behavior has effects on the fatigue properties of composite materials. Therefore, one can accelerate the fatigue testing if the loading frequency or temperature is changed. The purpose of this work is to investigate the accelerated fatigue properties of glass/fiber composites. In order to establish the accelerated fatigue properties of glass/epoxy composites, the fatigue testing of unidirectional specimens with different angles is conducted at room temperature under different stresses, stress frequencies, and stress ratios. The results indicate that the fatigue life increases with the increasing of stress frequency or stress ratio for the three types of unidirectional specimens. The reasons for these increasing effects are also discussed.

Abstract: Digital image correlation (DIC) is a whole-field and non-contact strain measuring method. It could provide deformation information of a specimen by processing two digital images that are captured before and after the deformation. In this work, a hybrid genetic algorithm, in which a simulated annealing mutation process and adaptive mechanisms are added to the real-parameter genetic algorithm, is used to search the corresponding subset after deformation. To invest the accuracy and reliability of this method, some key parameters are considered. The results indicate that the out-of-plane shift should be included, and a subset with 30x30 pixels should be recommended. The population size of 500, 100 generations, and 60 iterations are good enough. As for the searching strategy, it is recommended that the design variables are divided into three groups, each time only one group is under search, and they takes terms consecutively.

Abstract: Compression tests are conducted on composite laminates consisting of 16 unidirectional carbon/epoxy layers with two through-width delaminations. Two types of delamination length and location are considered. One is that a short delamination is located at the middle surface along the thickness direction and a long delamination is positioned between the second layer and the third layer. The other is that a long delamination is located at the middle surface and the position of the short elamination is between the second layer and the third layer. The results indicate that if the long delamination is close to the surface of the laminate, the inner, short delamination has no effect on the critical buckling stresses. However, the presence of inner, short delamination may significantly change the critical delamination growth stresses. If the short delamination is above the long delamination that is located on the middle surface, the presence of the short delamination may significantly reduce the critical buckling stresses. But its effects on the critical delamination growth stresses are minor.

Abstract: Valve-less micropumps with one or two piezoelectric buzzers are manufactured and tested. Piezoelectric buzzers are chosen as actuation elements because they are cheap and with high actuation amplitude. The micro-chamber with nozzle and diffuser is fabricated by employing UV photolithography and film mask. A negative photoresistive material, SU8-50, is used as a structure material, and exact angles in the inlet/outlet elements can be obtained. PDMS is chosen to bond different parts of the micropump. The piezoelectric buzzer does have nice actuation amplitude of 40.4 μm after the assembly with the chamber. The results indicate that the micropump with one piezoelectric buzzer has a maximum flow rate of 90.28μl/min when the buzzer is actuated at 100 V and 20 Hz. A maximum backpressure of 50 mm H2O occurs as the buzzer is actuated at 100 V and 30 Hz. For the micropump with two piezoelectric buzzers, it has a maximum flow rate of 165.32 μl/min when the buzzer is actuated at 100 V and 20 Hz and has a maximum backpressure of 84 mm H2O as the buzzer is actuated at 100 V and 30 Hz.