Stress Intensity Factor Of V-notch Research Articles

Method to calculate stress intensity factor of V-notch in bi-materials

Based on Zak's stress function, the eigen-equation of stress singularity of bi-materials with a V-notch was obtained. A new definition of stress intensity factor for a perpendicular inter-facial V-notch of bi-material was put forward. The effects of shear modulus and Poisson's ratio of the matrix material and attaching material on eigen-values were analyzed. A generalized expression for calculating K I of the perpendicular V-notch of bi-materials was obtained by means of stress extrapolation. Effects of notch depth, notch angle and Poisson's ratio of materials on the singular stress field near the tip of the V-notch were analyzed systematically with numerical simulations. As an example, a finite plate with double edge notches under uniaxial uniform tension was calculated by the method presented and the influence of the notch angle and Poisson's ratio on the stress singularity near the tip of notch was obtained.

A New Method to Calculate Dynamic Stress Intensity Factor for V-Notch in a Bi-Material Plate

The stress singularity eigen-equation for V-notch in a bi-material plate is obtained. A new definition of dynamic stress intensity factor of a crack perpendicular to bi-material interface is put forward, and then is extended to any V-notch in bi-material plate. A formula of stress extrapolation method to calculate dynamic stress intensity factors of V-notch in bi-material plate is obtained. As an example, the three points bending sample with two materials is investigated.

Finite Geometrically Similar Element Method for Dynamic Fracture Problem

A finite geometrically similar element method is proposed to determine the dynamic stress intensity factor. A group of geometrically similar elements is automatically generated layer by layer around the point of singularity. The large number of degrees of freedom around the tip of singularity is transformed to a small set of generalized coordinates by means of the series expansion formulas of the displacement field. By taking advantage of the same stiffness and similar mass of similarly shaped elements, the combined stiffness matrix of super-element is obtained directly. The small set of generalized coordinates can be obtained through solving the equation, and then the dynamic stress intensity factor of V-notch (crack) will be obtained. There are some advantages for this method such as good adaptability, high precision and good convenience.

Strength Evaluation of Plastic Packages During Solder Reflow Process Using Stress Intensity Factors of V-Notch

A crack initiated from a V-notch corner in the molding resin, such as a corner of die pad, is one of the main causes of the failure in plastic packages. The stress intensity factors of the asymptotic solution of a corner of jointed dissimilar materials are utilized for the evaluation of a solder reflow crack in a quad flat package (QFP). First, we estimate the critical vapor pressure, which causes a crack from a corner in the molding resin, using the critical stress intensity factor of a V-notch corner. This critical factor was measured by V-notched three-point bending tests and the displacement extrapolation method along with the three dimensional (3-D) finite element method (FEM). Moisture concentration in the QFP after absorption is analyzed, and vapor pressure caused by the solder reflow process is estimated. The critical moisture absorption time, which results in crack occurrence during the solder reflow process, can be predicted using this evaluation technique. Furthermore, we perform infrared solder reflow tests of the QFP for verifying the present failure evaluation technique.

Strength Evaluation of Electronic Plastic Packages Using Stress Intensity Factors of V-Notch

Strength Evaluation of Electronic Plastic Packages Using Stress Intensity Factors of V-Notch