Key Engineering Materials Vols. 326-328

Abstract: A unique interferometric system utilizing thermal-conduction loading is developed and implemented to investigate the effect of ramp rates of accelerated test profiles on the thermal deformation of flex package assemblies. The system provides extreme ramp rates to simulate the thermal shock condition with a temperature control much finer than the conventional convection based system can provide. The in-plane and out-of-plane displacements of the flex package are documented through moiré interferometry and Twyman/Green interferometry, respectively. Deformation measured under a thermal shock condition is compared with that under the conventional thermal cycling condition to assess the effect of ramp rates on package deformation. The comparison reveals that a low ramp rate of typical accelerated thermal cycling (ATC) tests causes significant reduction in the maximum level of elastic energy in the package assembly.

Abstract: In MEMS, packaging induced stress or stress induced structure deformation becomes increasing concerns since it directly affects the performance of the device. The conventional MEMS SOI (silicon-on-insulator) gyroscope, packaged using the anodic bonding at the wafer level and EMC (epoxy molding compound) molding, has a deformation of MEMS structure caused by thermal expansion mismatch. Therefore we propose a packaged SiOG (Silicon On Glass) process technology and more robust spring design.

Abstract: The predicted fatigue life of packaging structures using conventional procedures of finite element analysis (FEA) would be higher than an actual condition as a result of the perfect bonding interface assumed in the modeling. Actually, the crack extension of the solder joints along with the bi-material interface during the thermal cycling test had been observed. And, the crack models with an assumed crack length had widely adopted which only responded to the stress distribution at that moment instead of considering the effect of the whole stress history on the crack advancement. For this reason, a node tie-release crack prediction technique integrated with a nonlinear FEA was established in this research to further estimation for the thermo-mechanical reliability of solder joints. To proof our proposed technique, a double-layer wafer level chip-scaling package (DLWLCSP) was implemented as a testing vehicle to demonstrate the difference between the solder joint reliability, which was compared to the application of conventional FEA. Combined with the fracture criterion, the predicted result of using the present technique shown a lower fatigue life of solder joints than another, which using conventional one when the phenomenon of crack growth in dummy solder joints were considered. Finally, the actual experimental test showed the similar results as presented tie-release crack prediction analysis.

Abstract: This study tries to obtain the spring constant of welded metal bellows through experimental and numerical method respectively. The prediction of spring constant plays a great role in the design and application of the welded metal bellows. To derive the spring constant of the bellows, we employ commercial package to build up 2 axi-symmetric FEM models by using plane 42 and shell 51 elements. In the experiment, we use UTM to measure the spring constant of the bellows. And, the predicted spring constant resulting from the analysis is compared with the experimental one to discuss the rationality of spring constant analysis. The analytical results correspond well with experimental data and hence explaining the validity of FEM model.

Abstract: Thermal deformation of cast iron exhaust manifold for turbo diesel engine is investigated by finite element analysis (FEA). The FE model includes the temperature dependent material properties as well as the interactions between exhaust manifold, cylinder head and fasteners. It also considers the sliding behavior of the flanges of exhaust manifold on cylinder head when either expansion or contraction of the exhaust manifold exceeds the fastener pretension. The result of analysis revealed that remarkable thermal deformation occurred along the longitudinal direction. The amount of deformation was predicted and compared with experimental results. The new design of fastener hole, which allows sliding behavior, is expected to reduce thermal stress in turbo diesel engine exhaust manifold.

Abstract: A statistical assessment model for structural integrity of steam generator tubes with axial cracks at the top of the tubesheet was proposed using Monte Carlo method. In the model, a method for estimating the number of "real cracks" from in-situ inspection (ISI) data was used. Based on the estimated "real cracks", the number of newly detected cracks and growth of cracks during arbitrary operating period were simulated using the Monte Carlo method. The flaw growth rate used in the simulation was statistically calculated from the periodic in-service non-destructive inspection data. The number of cracks, the probabilistic distribution of crack sizes at the end of next operating interval and the probability of burst during operation were calculated from numerously repeated simulations using the proposed model.

Abstract: The paper discusses the problem of reliability calculation for mechanical units under load. Because the rated reliability of the unit as a system with many independent elements can tend to zero, the methods of reliability calculation of the units as real objects with the common factors (loads, operation conditions) are proposed. The choice of the life test modes and test time depends essentially on unit-related information like their operation conditions. The paper describes one of approaches, passing to this problem. Within its framework, the accumulations of damages are made at several typical points of the loaded system.

Abstract: This paper deals with the statistical properties of short time creep rupture characteristic values (for example, creep rupture time, steady state creep rate, total creep rate, initial strain, etc.) in STS304 stainless steels. From short time creep rupture tests performed by constant stresses at three different elevated temperatures 600, 650 and 700
, the scatter and probability distributions were investigated for rupture time, total creep rate, steady state creep rate, initial strain, and others. The effect of temperature on the statistical scatter of rupture time was the smallest at 700
. The effect of stress on the statistical scatter of rupture time was smaller with increasing stresses. The probability distributions of short time creep rupture data were well followed 2-parameter Weibull.

Abstract: Geomechanics model test has some distinctive advantages in simulating changing laws of stress and strain of rockmass as well as failure mechanism of surrounding rockmass of tunnel. In order to systematically study mechanics deformation properties of a large-scale offspur tunnel under excavation state, we design and manufacture a large scale 3D model test rack installation with hydraulic equipment. The test rack is 3.7 meters long, 2.2 meters wide and 4 meters high, which is the largest 3D geomechanics model test rack in present Chinese communication trades. The new-type similar material of model is a kind of cementitious composite which is mixed with iron ore powder, blanc fix, quartz sand, rosin, industrial alcohol and gypsum powder. 3D geomechanics model test for a large-scale offspur tunnel is carried out by utilizing the test installation and the similar material. The original design and construction of the offspur tunnel has been effectively optimized by results from model test.

Abstract: Stochastic simulation method considering the heterogeneity of hydraulic conductivity is suggested in this paper. Hydraulic field is simulated by using our FEM code for THM coupling processes. The results show that hydraulic gradient at different location around the cavern is differently dependent on water-curtain pressure in deterministic model. A probability range of hydraulic gradient at each point with 10m space between each was examined by means of stochastic realization of spacial variability of hydraulic conductivity. These analyses are contributed to determine the values interval of water-pressure and groundwater flux into the cavern with a given security for LPG containment design and evaluation considering the spacial variability of hydraulic conductivity.