The surface absorption coefficient of S304L stainless steel during Nd:YAG pulse laser welding process was derived by using the inverse engineering technique. The thermal-elastic-plastic finite element method is employed to calculate the temperature distribution, melting pool depth and shape with specific heat source. The derived melting pool depths and diameters with different values of absorption coefficient were compared with experimental results. In this study, the least square error method is used to obtain the equivalent absorption coefficient. The results show that the equivalent absorption coefficient of S304L stainless steel is in the range of 0.1~0.25 for low power intensity Nd:YAG impulse laser welding.

The dynamic characteristics of nonlinear composite helicoper blades are solved by using the differential quadrature method (DQM). The bending-torsion coupled beam model is proposed to characterize the composite blade. The Kelvin-Voigt internal and linear external damping coefficients are also employed. The DQM is used to transform the partial differential equations of a composite rotor blade into a discrete eigenvalue problem. The Chebyshev-Gauss-Lobatto sample point equation is used to select the sample points. Numerical results indicate that even nine sample points can provide the convergent results by employing this DQM for the blade analysis. The difference between the responses derived from the linear and the nonlinear models have been compared to illustrate the significance of the nonlinear effect in this case. The transitional dynamic responses of the derived systems are calculated by using Newmark method. In this study, the effects of the fiber orientation, internal damping, external damping, pre-twisted angle and the rotation speed on the dynamic behavior for a composite beam are studied. The effect of the number of sample points on the accuracy of the calculated natural frequencies is also discussed. The integrity and computational efficiency of the DQM in this problem will be demonstrated through a number of case studies. Numerical results indicated that the DQM is valid and efficient for a composite blade formulation.

Both experimental and numerical analyses into the shear toughness parameter for Sn/3.0Ag/0.5Cu and 63Sn/37Pb solder ball joints are performed. The ball shear tests are conducted at the loading speeds of 200μm/s and 300μm/s using ball joint specimens with diameters of 300, 600 and 760 μm. The failure behavior of the solder joints is quantified in terms of their fracture toughness. The results show that the shear toughness increases with an increasing solder ball diameter. Furthermore, it is shown that the Sn/3.0Ag/0.5Cu solder ball has a greater ductility than the eutectic 63Sn/37Pb solder ball. It is found that the shear toughness with great differentiability is relatively insensitive to the loading speed, and is therefore a suitable parameter with which to evaluate the ductility of solder ball joints in ball shear tests. Finally, the finite element analysis is further employed in the simulation with the software of MSC, Marc. Numerical predictions have good agreements compared with experiment ones.

The effects of isothermal aging and the thermal cycling loading on the shear toughness of different solder materials and ball sizes have been explored. The difference between shear toughness values of traditional Sn/37Pb eutectic solder ball joints and the lead free Sn/3.0Ag/0.5Cu solders are chosen for discussion. The experiment measurements under the ball shear test (BST) have been compared and studied for both solder joints. The fracture behaviors of the solder joints under the high temperature aging and thermal cycling testing are examined by scanning electron microscope (SEM). The variation of shear toughness of different ball joints reveals that the high temperature aging and thermal cyclic loading reduce the shear toughness significantly. The measured shear toughness values indicate that the Sn/3.0Ag/0.5Cu solder joints have better ductility for the joints undergoing the high temperature aging and the thermal cycle loadings. Based on the measured results, the better reliability for the Sn/3.0Ag/0.5Cu ball joints is expected, due to the aging and cycling load testing.

When fabricating laser diode transceiver modules, the coupling efficiency can be improved via a laser hammering process, in which additional, calculated spot welds are performed at key locations within the package in order to compensate for post-weld shift. The present study performs a numerical investigation into the post-weld-shift compensation of a butterfly laser module package incorporating a lensed optical fiber and a laser diode with a central wavelength of 980 nm. In performing the simulations, the deformation of the package components during the welding process is modeled using Marc finite element software. Furthermore, the laser power coupling efficiency is estimated using the commercial Zemax optical design program. It is shown that the numerical predictions for the coupling power in the laser diode transceiver module are in good agreement with the experimental results. The optimal welding sequence which minimizes the post-weld shift of the optical fiber relative to the laser diode is determined. It is shown that the corresponding coupling efficiency is equal to 69%. Finally, it is shown that by performing an optimized laser hammering process, the coupling efficiency can be improved to around 99%.