An Approach for Estimating the Reliability of IGBT Power Modules in Electrified Vehicle Traction Inverters

The reliability analysis of traction inverters is of great interest due to the use of new semi-conductor devices and inverter topologies in electric vehicles (EVs). Switching devices in the inverter are the most vulnerable component due to the electrical, thermal and mechanical stresses based on various driving conditions. Accurate stress analysis of power module is imperative for development of compact high-performance inverter designs with enhanced reliability. Therefore, this paper presents an inverter reliability estimation approach using an enhanced power loss model developed considering dynamic and transient influence of power semi-conductors. The temperature variation tracking has been improved by incorporating power module component parameters in an LPTN model of the inverter. A 100 kW EV grade traction inverter is used to validate the developed mathematical models towards estimating the inverter performance and subsequently, predicting the remaining useful lifetime of the inverter against two commonly used drive cycles.

Reissner’s Mixed Variational Theorem for Layer-Wise Refined Beam Models Based on the Unified Formulation

The present paper proposes the application of the Reissners Mixed Variational Theorem (RMVT) for the accurate stress analysis of general multi-layered beam problems. Laminated materials usually differ from homogeneous materials in that they exhibit much higher transverse shear and transverse normal deformabilities. These characteristics, and others such as the Transverse Anisotropy (TA) and the Interlaminar Continuity of transverse stresses (IC), make Classical Laminated Theories (CLT) inappropriate for the analysis of multi-layered structures. The Carrera Unified Formulation (CUF) sets a framework in which classical-to-refined beam models can be generated by expanding the unknown variables over the cross-sectional domain by means of arbitrary functions. A LW expansion is adopted for both displacements and transverse stresses over the cross-section section domain. In this manner, the ZZ condition is automatically satisfied through the use of independent kinematics for each layer in a LW sense, with no need of introducing ad-hoc ZZ functions.

Biaxial Contractile Mechanics of Common Carotid Arteries of Rabbit

Few multiaxial constitutive laws under the vasoactive condition have been proposed as compared with those under the passive condition. The biaxial isometric properties of vasoactive rabbit arteries were studied, although the constitutive law was not proposed. The purpose of the present study is also to describe the multiaxial active mechanical properties of arteries. A novel strain energy function for the active stress has been proposed. This function is simple and may describe the multiaxial characteristics of constricted vessels. Although this study used mean stress and mean stretch ratio to determine the mechanical properties of vessels, a triaxial constitutive law of constricted vessels may be developed. There remains the subject of residual strains under active condition. If this problem will be solved, the accurate stress analysis under vasoactive conditions is possible.

Determination of Tensile Creep and Stress Relaxation of Concrete by Ring Test

The understanding of stress relaxation and tensile creep behavior is extremely important in accurate stress analysis and crack prediction of early-age concrete. The free shrinkage deformations of concrete with different strength grade were examined. The early-age tensile elastic modulus of concrete was investigated through temperature-stress testing machine. The tensile creep and shrinkage stress were obtained through the modified restrained ring test. The results indicate that the development of free shrinkage coordinates well with the inner strain of steel ring. Tensile creep decreases as water-binder ratio increases. Creep counteracts tensile stress of concrete by 28%~40% , decreases the possibility of cracking of concrete at early ages.

Finite Element Prediction of Mechanical Behaviour under Bending of Honeycomb Sandwich Panels

This paper outlines a finite element procedure for predicting the mechanical behaviour under bending of sandwich panels consisting of aluminium skins and aluminium honeycomb core. To achieve a rapid and accurate stress analysis, the sandwich panels have been modelled using shell elements for the skins and the core. Sandwich panels were modelled by a three-dimensional finite element model implemented in Abaqus/Standard. By this model the influence of the components on the behaviour of the sandwich panel under bending load was evaluated. Numerical characterization of the sandwich structure, is confronted to both experimental and homogenization technique results.

Stress Intensity Factors for Axial Cracks in Pressurized Cylindrical Elements Using the Boundary Element Method

Pressure vessels and pipes are inspected to establish the presence of cracks that could affect their integrity for a reliable operation avoiding the possible negative impact of their failure. The Boundary Element Method (BEM) is a relatively new numerical method in this kind of applications, which is based on Integral Equations (IE), considering only the contour of the solid (meaning an easier meshing). The BEM has a good accuracy that promotes its use in stresses analysis. Crack growth modeling is one of the most important applications for the BEM, since it allows an accurate stress analysis in the crack faces and crack propagation analysis without re-meshing. This paper focuses on modeling an inside surface axial crack in a cylindrical element under internal pressure using 2D-BEM, to determine the mode I Stress Intensity Factors (KI) at the crack tip. These factors are used to predict the mechanical behavior of the element and its residual life when is subjected to cyclic loadings The BEM generates less conservative results than API 579 rules for Ri/t ≤ 10, meanwhile for Ri/t ≥ 12 the results are in a good agreement with that standard. New simple correlations to calculate KI for 5≤Ri/t≤10 and 10<Ri/t≤25, are offered.

Design of Unpartitioned, Plug Type Header Boxes for Air-Cooled Heat Exchangers in Refinery Service

Dry air-cooled heat exchangers (ACHE) form an integral part of refinery cooling systems of which the header boxes form an important component. It is commonly designed as an ASME Section VIII Division 1 pressure vessel, but unfortunately neither ASME nor the American Petroleum Institute (API) provide guidance regarding to the methodology which should be used in the assessment of nozzle loads on the header box design. Subsequently, the designer must rely either on empirical guidelines or Finite Element Analysis (FEA) in line with the requirements of ASME Section VIII U-2(g). The aim of this project therefore was to develop an analytical design methodology that accounts for the effects of these nozzle loads on the header box. A new mechanical model was derived by extending the existing ASME Section VIII rigid frame theory model and the result was tested against an FEA case study to determine whether the model was useable. It was found that the new model makes some useful qualitative statements but cannot be used for accurate stress analysis of the stresses near the base of the nozzle on the header box. The case study was also used to examine the effectiveness of a commonly used empirical guideline.

DESIGN OF ASYMMETRIC GEAR AND ACCURATE BENDING STRESS ANALYSIS USING THE ES-PIM WITH TRIANGULAR MESH

This paper proposes a novel design of an asymmetric gear that applies a larger pressure angle in the drive side and a standard pressure angle in the coast side via accurate stress analysis using the edge-based smoothed point interpolation method with triangular mesh (ES-PIM-(T3)). An asymmetric rack cutter is first developed. Then, the governing equations of the tooth profiles cut by the rack cutter are derived. Finally, five sets of asymmetric gears with the pressure angles of 20° /20°, 25°/20°, 30°/20°, 35°/20°, and 40°/20° are established to quantitatively check the stress distributions at the fillet of the drive side of these teeth. The best point for applying force in a static bending stress analysis and the best pressure angle in the drive side for a gear design are suggested.

Finite Element Analysis of Elastic Membrane Coupling Based on MSC.patran

The membrane coupling plays an essential role in the transfer process of the wind wheel torque. In order to meet the design requirements and get more accurate stress analysis state of membrane, based on the finite element software HyperMesh, membrane and the surrounding model is regularly meshed into hexahedral element, and to MSC.patran analysis platform, to check the strength of the coupling. The result of analysis showed that, the maximum stress and deformation of coupling can be met to the design standards and reach the requirements also. Using of hexahedral element, analysis time of CPU can be reduced and smoother stress and strain contours cloud can be also obtained, so it provides a more scientific basis for the design and manufacture of membrane coupling.