Jai Sug Hawong

A Study on the Development of Reflective Photoelastic Experimental Hybrid Method on the Static Plane Problems of Isotropic Material

The reflective photoelastic experiment can be used more effectively than the transparent of photoelastic experimental method in industrial fields. Therefore the reflective photoelastic experimental hybrid method for the fracture mechanics of isotropic material was developed in this research. Using the reflective photoelastic experimental hybrid method we can obtain stress intensity factors and separate stress components from only the isochromatic fringe patterns. The errors between the experimental values and theoretical values for stress intensity factors are less than 10%. It was verified that the reflective photoelastic experimental hybrid method is very useful for the static plane fracture problems, for the stress intensity factors and for the stress components at the vicinity of the crack-tip in isotropic materials.

Reliability Estimation of Solder Joint by Using the Failure Probability Models

The differences in the coefficient of thermal expansion (CTE) between the chip and the FR-4 board generate the shear strains and the bending moment in the solder joint. It seems to be a main cause of failure in the solder joint when the chip and the FR-4 board are heated repeatedly. Thus, the fatigue loading induced by thermal cycling is a major concern in the reliability of the solder joint. The magnitude of shear strain and the final failure are known to be influenced by varying boundary conditions such as the difference of CTE, the height of solder, the distance of the solder joint from the neutral point (DNP) and the temperature variation. In this paper, the effects of boundary conditions on the failure probability of the solder joint are studied by using the failure probability models such as the First Order Reliability Method (FORM) and the Monte Carlo Simulation (MCS). Furthermore, the stiffness of the solder joint is considered to investigate the influence at the failure probability.

A Study on the Cracked Specimen for Biaxial Tensile Loading Test

In the recent years, the studies on the mechanical behaviors of various materials subjected to biaxial loading have been worked since they are more complicated and intrinsically different from those under the simple uniaxial condition. The cruciform specimen without any slots has been commonly used for the goal so far. We prepare improved biaxial specimen with slots and make sure its validity by means of finite element analysis and photoelastic experiment. Even though the equal load biaxiality was applied to the specimens, as the results, we found that the stress biaxiality ratios in central region of specimen differ according to the position from the center of them, the specimen with slots in the arms is more effective to make state stress uniform than the specimen without slot.

Calculation of Stress Intensity Factor under Mixed Mode Biaxial Tensile Load by Photoelastic Hybrid Method

In this study, the photoelastic experiment hybrid method was introduced and applied to the fracture problems of the isotropic polycarbonate plate with a central crack under the uniaxial and equibiaxial tensile load. The influences of equibiaxial tensile load on the isochromatic fringes and stress fields, stress intensity factors near the mixed mode crack-tip were investigated. As the results, without relation to the inclined angle of crack, the asymmetric isochromatic fringes around the crack propagation line under uniaxial tensile load has become symmetric and the slope of isochromatic fringe loop has inclined toward crack surface when an equal lateral tensile load was added. Furthermore, the distribution of all stress components have changed from asymmetric shape to symmetric shape, and only the range of compressive stress of σχ/σ0 have changed as compared with the mode I condition under unaxial load with β = 0°. When an equal lateral tensile load was added to uniaxial load, the value of stress intensity factors are little changed when β = 0° but the values of KI /K0 are increased and KII /K0 are become zero, that is, mode I situation when β = 15°~45°.

Development of Dynamic Photoelastic Experimental Hybrid Method for Orthotropic Material

In this paper, transparent dynamic photoelastic experimental hybrid method for propagating cracks in orthotropic material was developed. Using transparent dynamic photoelastic experimental hybrid method, we can obtain stress intensity factor and separate the stress components from only isochromatic fringe patterns without using isoclinics. When crack is propagated with constant velocity, the contours of stresses components in the vicinity of crack tip in orthotropic material are similar to those of isotropic material or orthotropic material with stationary crack under the static load. Dynamic stress intensity factors are decreased as crack growth. It was certified that the dynamic photoelastic experimental hybrid method was very useful for the analysis of the dynamic fracture mechanics.

A Study on the New Static Photoelastic Experimental Hybrid Method

In photoelastic experimental method, until now, we have used the Newton-Raphson numerical method in analysis of photoelastic experimental data such as the non-linear least square method for the photoelastic expreriment. We used the Hook-Jeeves’ numerical method in stead of Newton-Raphson numerical method for the non-linear least square method for photoelastic experimental method. The new photoelastic experimental hybrid method, that is, the photoelastic experimental hybrid method with Hook-Jeeves’ numerical method has been developed in this research. Applying the new photoelastic experimental hybrid method to stress concentration problems and plane fracture problems, it’s validity was assured. The new photoelastic experimental hybrid method is more precise and stabler than the photoelastic experimental hybrid method with Newton- Raphson numerical method (the old photoelastic experimental hybrid method)

Development of photoelastic experiment model material for Ti50Ni50 SMA-FRP

Photoelastic model material with shape memory effect and molding processes of the material is developed in this research. Matrix and fiber of the photoelastic model material developed in this research are respectively epoxy resin and wire of Ti50Ni50 shape memory alloy. It is called Ti50Ni50 shape memory alloy fiber epoxy composite. It is assured that Ti50Ni50 SMA-FEC is satisfied with the requirements of photoelastic model material and can be used as photoelastic model material and can be used as photoelastic model material. The maximum recovering strain of Ti50Ni50 SMA-FEC is occurred at 80 degrees in any prestrain of Ti50Ni50 shape memory alloy wire fiber and in any fiber volume ratio. Recovering strain is increased with the increment of the prestrain and the fiber volume ratio.