Thermo-elastic Finite Element Method Research Articles

FEM Study of a Steel Corrugated Web Plate Girder Subjected to Fire

The main aim of this work is a computational nonlinear analysis of a high strength steel corrugated-web plate girder with a very detailed and realistic mesh including vertical ribs, all the fillet welds and supporting areas. The analysis is carried out to verify mechanical structural response under transient fire temperature conditions accounting for an efficiency and accuracy of three various transient coupled thermo-elastic models. All the resulting stress distributions, deformation modes and their time variations, critical loads and eigenfrequencies as well as failure times are compared in all these models. Nonlinearities include material, geometrical and contact phenomena up to the temperature fluctuations together with temperature-dependent constitutive relations for high strength steel. They result partially from steady state and transient experimental tests or from the additional designing rules included in Eurocodes. A fire scenario includes an application of the normative fire gas temperature curve on the bottom flange of the entire girder for a period of 180 minutes. It is computed using sequentially coupled thermo-elastic Finite Element Method analyses. These account for heat conductivity, radiation and convection. The FEM model consists of a combination of 3D hexahedral and tetrahedral solid finite elements and uses temperature-dependent material and physical parameters, whose values are taken after the experiments presented in Eurocodes. Numerical results presented here demonstrate a fundamental role of the lower flange in carrying fire loads according to this scenario and show a contribution of the ribs and of the welds to the strength of the entire structure.

Roll deformation and stress distribution under thermo-mechanical loading in cold rolling

Tool deformation in metal forming is an important phenomenon that is critical not only for controlling the shape and size of final product but also for minimizing its cost. Under the assumption of an elastic roller and including the heat transfer effects, in this paper we determine the distribution of elastic deformation of the roller when it comes in contact with the strip in cold rolling. Using a coupled approach, the heat transfer phenomenon between roll and strip has been modeled analytically to predict roll temperature distribution by simulating non-uniform heat flux at the interface. This temperature distribution along with the mechanical load results in roll deformation with large localized stresses. Roll deformation has been modeled by using a thermo-elastic finite element method. Thermal and deformation models have been coupled and an iterative procedure has been developed to calculate optimum roll diameter. Finally, the deformed roll radius is utilized for calculating the exit strip thickness. It is found that the calculated thickness under thermo-mechanical load agrees very well with the experimental value reported in the published literature. The developed combined analytical–numerical model can easily be implemented on a personal computer and takes less memory and computational time, which is a marked advantage over pure numerical schemes.

FEM stress analysis and sealing performance improvement of box-shaped bolted flanged joints using silicone sealant under internal pressure and thermal conduction conditions

Interface stresses and sealing performance of thin-wall box-shaped bolted flanged joints using silicone sealant under internal pressure and thermal conduction conditions are analyzed by the thermo-elastic finite element method. The flexible flanges were fastened by M8 bolts and nuts with an initial clamping force (bolt preload) after being joined with the silicone sealant. In the elastic and thermo-elastic Finite Element Method (FEM) calculations, the effects of the bolt pitch distance, flange rigidity and flange thickness were examined on the interface stress distributions. In addition, the effects of the linear thermal expansion coefficient and Young's modulus of the silicone sealant in the steady temperature state were also examined from a design standpoint. In the experiments, leakage pressure was measured when the silicone sealant was applied between an aluminum flexible flange with 1 mm thickness and an aluminum flange (body) with 10 mm thickness. Measurements of sealing performance with the silicone sealant and a sheet gasket were also conducted. In addition, strains in the joint in steady temperature states were also measured by strain gauges to understand the effect of the operative temperature on the sealing performance. The experimental results were found to be in fairly good agreement with the calculated results. From the results, it was found that the effect of the thermal conduction condition was greater than that of the internal pressure on both the interface stress distributions and the sealing performance. In addition, the sealing performance was found to be better in the joint with the silicone sealant than that with the sheet gasket.

High strength FGM cutting tools: finite element analysis on thermoelastic characteristics

In general, a metal cutting tool is composed of tip and shank of different materials, thus it exhibits crucial stress concentration near the material interface under thermomechanical loading while at work. Such an inherent defect is caused solely by the material composition discontinuity across two different material components, but it could be minimized by enforcing the material composition distribution be continuous. This would be achieved by inserting a graded layer between shank and tip, according to the concept of functionally graded material (FGM), in which the material composition varies continuously such that no discontinuity exists over the entire tool region. This paper intends to explore the possibility of FGM for improving the thermal strength of metal cutting tools, according to the parametric analysis by two-dimensional thermoelastic finite element method.

Mechanism of transient thermal cycle failure in ZrO2 /NiCrAl functionally graded thermal barrier coatings

In this paper, the failure mechanism under transient thermal cycle loading is studied for a functionally graded thermal barrier coating (FGTBC) system consisting of ZrO2 and NiCrAl plasma sprayed on a steel substrate. Controlled experiments and numerical analysis (thermoelastic finite element method) were performed and the results indicate that the surface tensile stress is responsible for the initiation of surface cracks and the tensile stress normal to the interface is large enough to break the interfacial bond (the magnitude of the interfacial bond strength of the ZrO2 layer in the FGTBC is below the strength of the ZrO2 , i.e. the interface is weaker than the ZrO2 material). By comparing the mode I stress intensity factor and the fracture toughness, the surface cracks are considered to be arrested, this characteristic is confirmed by SEM studies. The interfacial crack propagation causes a segment of the ZrO2 layer in the FGTBC to spall.

Linear fracture mechanics analysis on growth of interfacial delamination in lsi plastic packages under temperature cyclic loading

A study is made of the tendency of growth of delamination between dissimilar materials occurring in large scale integration (LSI) plastic packages under temperature cyclic loading. Two groups of delamination growth processes are considered; one along the interface between the top surface of the die pad and the die-bonding layer, and the other along the interface between the bottom surface of the die pad and the encapsulant resin. In each group several different initial patterns of delaminations are assumed. Stress intensity factors and their mode ratios at the tips of growing delaminations are calculated by combining a thermoelastic finite element method for nonlinear contact problems and a linear interface fracture mechanics approach. The effects of geometries of delamination and leadframe materials on the tendency of delamination growth are clarified.

Linear Fracture Mechanics Analysis of Interfacial Delamination in LSI Packages under Temperature Cyclic Loading.

A study is made for interfacial delaminations between dissimilar materials in LSI plastic packages caused by temperature cyclic loading. Combining a thermoelastic finite element method for nonlinear contact problems and linear fracture mechanics approach, stress intensity factors at the tips of growing delaminations are obtained for the packages with Cu alloy or 42 alloy (Fe-42%Ni) leadframe. The tendency of delamination growth are compared for the two configurations of delamination ; one along the interfaces between the top surface of the die pad and die-bonding layer and the other along those between the bottom surface of the die-pad and encapsulant resin. It is concluded that the former case is more likely to occur for the package with Cu alloy leadframe while for packages with 42 alloy leadframe, the latter case is more likely to occur.

Numerical and Experimental Analysis of Resin Cracking in LSI Packages under Temperature Cyclic Loading.

Numerical stress analysis of resin cracking occurring in LSI packages during temperature cycling tests was carried out using a thermoelastic finite element method for nonlinear contact problems. Through the use of the linear fracture mechanics approach, the analysis provides a fracture parameter and indicates the direction in which resin cracking occurs. Temperature cycling tests using actual LSI packages were also performed to verify the validity of the analyses. It was found that the test results agreed well with the analytical results and that leadframe materials and the delamination occurring between dissimilar materials determine quantitatively the tendency of resin cracking. The resin cracking mechanism was also studied and countermeasures against it were proposed.

Numerical stress analysis of resin cracking in LSI plastic packages under temperature cyclic loading

Numerical stress analysis of resin cracking occurring in plastic packages during temperature cyclic loading was carried out using a thermoelastic finite-element method (FEM) for the nonlinear contact problem. Through the use of the linear fracture mechanics approach to the bimaterial problem, the analysis provides a fracture parameter and indicates the direction in which resin cracking occurs. Temperature cycling tests using actual plastic packages were also performed to verify the validity of the analysis results experimentally. It was found that the test results agreed well with the analytical results. It was also clear that the delamination occurring between dissimilar materials determines the degree to which resin cracking occurs quantitatively and the most harmful delamination occurs in the die bonding layer. The resin cracking mechanism was studied and a countermeasure against it was proposed.

Analytical Evaluation of Residual Stress Singularity with Interfacial Slip in Dissimilar Material Bonded Joints

It is important to obtain information on the effect of interfacial slip on the interfacial stress field, which is induced by the thermal activation processes in the bonding process of dissimilar materials, for performing interfacial fracture analysis. In this paper, the effect of the interfacial slip occuring in the bonding processes of dissimilar materials on the stress singularity near the free edge was studied by thermoelastic finite-element method (FEM), and the characteristics of interfacial mechanics were simulated by modified bond-element method, of which fundamental types were often used for contact problems. The results are as follows. When the slip occurred near the bonded free edge, another singular stress field was produced at the slip tip, although the interfacial slip releaved the singular stress at the free edge, and the order of the singular term was found to decrease as the slip region extended. For this reason, if the interfacial slip did not accompany interfacial peel, the interfacial slip occurring in bonding processes would be effective in preventing interfacial fracture in cooling periods of bonding processes. In addition, since the stress field was found to resemble a crack problem, the singular stress field was estimated by stress intensity factor K.

Application of the Finite Element Method to the Quasi-Static Thermoelastic Analysis of Prestress in Multilayer Pressure Vessels

Abstract Multilayered wrapped vessel technology utilizes the compressive prestress induced during construction process to gain a considerable advantage over the monoblock vessels. The compressive prestress allows for more efficient use of construction material and more uniform distribution of stress throughout the vessel’s cross section. Analysis of the magnitude of prestress throughout the vessel’s thickness has been previously reported (Rasty, 1988). However, one major idealization in such analysis has been the assumption that the magnitude of induced prestress is constant around the circumference of the vessel. In this research, thermoelastic finite element method was utilized to simulate the construction process of one layer of the vessel. It was concluded that the compressive residual stress induced by the weld shrinkage varies through the circumference of the vessel by as much as 13.5 percent. Circumferential distributions of the prestress are presented and compared to the closed-form solutions (constant prestress assumption) in earlier works.