Shu Xuefeng

THERMOELASTIC FREE VIBRATION OF CLAMPE CIRCULAR PLATE

An analysis was given for the free vibration of clamped circular plate when temperature and stress fields were coupled. A nonlinear differential equation about time was obtained by using Galerkins method. The numerical results of vibration amplitude vs time were compared with the uncoupled case. It is found that if the given initial displacement is small, the effect of thermoelastical coupling will make the natural frequency increase; if the given initial displacement is large, it will be the opposite case. Effects of some different vibration factors are also discussed.

The double mode model of the chaotic motion for a large deflection plate

The primary aim of this paper is to study the chaotic motion of a large deflection plate. Considered here is a buckled plate, which is simply supported and subjected to a lateral harmonic excitation. At first, the partial differential equation governing the transverse vibration of the plate is derived. Then, by means of the Galerkin approach, the partial differential equation is simplified into a set of two ordinary differential equations. It is proved that the double mode model is identical with the single mode model. The Melnikov method is used to give the approximate excitation thresholds for the occurrence of the chaotic vibration. Finally numerical computation is carried out.

Analysis of thermal-elastic coupling vibration of large deflection cylindrical shell

The governing equation and energy equations for thermal-elastic coupling vibration of cylindrical shell were developed. The Garlerkin method was used in numerical process. Some useful result can be concluded from numerical result. With the increase of the amplitude of temperature and coupling coefficient, the speed of vibration decaying becomes slower and the coupling effect becomes weaker. The larger the ration of length to radius and length to thickness, the faster the decaying of the vibration amplitude and the vibration frequency increase. It means the coupling effect gets stronger. The larger the coupling coefficient, the smaller the axial stress, the axial force and the bendind moment are.

Analysis of influence parameters on massloss of projectiles based on Jones abrasion model

During the high speed penetration into concrete targets, the head of projectiles will suffer different degrees of mass abrasion which affect the property of penetration. Based on Jones Model of mass abrasion, the effect of shear and wear causing mass loss is uniformly considered as friction per unit. Through the analysis of penetration experiment data, parameters of friction are discussed, and an empirical equation is imposed through linear fit of the relations between f and parameters for ratio of the yielding strength and hardness of target materials and projectile materials. Limiting the size scope Young Equation, calculating results are used for modifying the shear stress relating to the diameter of projectiles. A prediction formula of projectile mass abrasion is imposed with different scope of size.

Cleaning technology of the steel tube based on AFM

The paper presents a new point that Abrasive Flow Machining is first applied in cleaning the leftover such as copper on the abdominal wall of the steel tube. Analyze the principle of removing copper stains theoretically, the mechanical model of the removal of copper by abrasive is derived in detail. Automatic cleaning mechanism based on AFM and its system are designed, and the suitable technique parameters of AFM are selected. And then an application sample is presented. Experiments indicated that roughness is decreasing 50 percent after cleaned by AFM and reaches the requirement of technology.

Mechanical characterization of the IMC layer by using Nano-indentation tests

The IMC has become an important criterion when assessing the reliability of portable electronics. The quality of solder joints directly determines the drop-impact reliability of the product. As a structural member of the electronic product, IMCs are used to connect the solders and the associated printed circuit board by a proper joining technique such as the surface mount technology (SMT). Inter-metallic Compound, which is between lead-free solder Sn3.OAg0.5Cu and Cu-pad, were measured by using nano-indentation tests, while the load-displacement curves, displacement-elastic modulus curve and displacement-hardness curves were recorded. Modulus and hardness of these IMCs were characterized by Nano-indentation CSM from plan view in this study. Basing on these experimental data, The calculation of modulus and hardness for IMC layers was based on nano-indentation CSM test results and was compared with reported results.

Elasto-plastic analysis of popcorn failure caused by cavitition unstable growth in plastic IC packaging material

Popcorn failure in Hyperelastic-plastic electronic packages under thermal load and Moisture is studied. Using the theory of finite deformation, we obtain the analytical relation between void growth and the sum of the vapor pressure induced by moisture and thermal stress induced by heat mismatch. Numerical analyses show that the critical traction decreases with decreases of yield stress-shear modulus ratio when plastic behavior of material is considered. On the other hand the critical traction decreases with increase of the initial porosity when yield stress-shear modulus ratio is given.

Characterization of the creep constitutive behavior of SnAgCu solder in flip chip joints from the indentation creep testing

In this paper, creep behavior of the lead-free SnAgCu solder alloy after reflow process was investigated by use of Nano Indenter XP technology. Based on the steady-state power law creep relationship, the creep strain rate sensitivity exponent was determined from the indentation creep testing using dimensionless analysis method. Then, combining numerical simulation with dimensional analysis, the value of C in creep constitutive equations are obtained using search method. So power law creep constitutive equations for micro-solder joint can be obtained. The creep time-creep displacement curves calculated from numerical simulation match well with those measured from indentation experiment in room temperature, the results indicating that the steady-state creep model is valid in describing the creep mechanical properties of solder joints.

Investigation of the stress-strain curves of lead-free solder alloy

In this paper, a new methodology to extract the elasto-plastic properties of lead-free solder materials from an instrumented sharp indentation loading curve has been proposed using dimensional analysis and finite element computation. The nano indenter XP technology is used to test samples of lead-free eutectic SnAgCu solder alloys to obtain a load-displacement curve, which can be used to calculate its hardness, elastic modulus and contact stiffness using the Olivers method. Then, a group of dimensionless functions Pi (proposed by Dao et al.), that relate the characteristic parameters of indentation load- unloading curves to the mechanical properties obtained from the stress-strain curves, is used to predict the representative strain, the representative stress, strain hardening exponent and yield stress. Finally, according to the obtained parameters of materials, the 2D axial symmetrical element model was adopted to simulate the nanoindentation process by using the ANSYS finite element code. The validity of the new methodology is checked using the agreement of comparing the load-displacement curves of nanoindentation impressions in the experiments with FEM results. Eutectic SnPb solder was also examined for comparative purpose.

Moisture absorption and void growing effects on failure of electronic packaging

The purpose of this paper is to study the combined effect of moisture absorption and void growing on the reliability of electronic packaging. Finite element simulation on a plastic PBGA package was carried out for moisture history from the moisture preconditioning (85 degC / 85 % RH for 168 h) to subsequent exposure to a lead-free soldering process, and the rule of moisture diffusion and the change of stress was found. Then, with the implementation of interface properties into the model study, the critical stress that results in the unstable void growth and the delamination at interface is significantly reduced and comparable to the magnitude of vapor pressure. Finite element results give a good guideline on the underfill material selection, and also give an insight of the failure mechanism associated with moisture absorption.