Mechanical properties of silicon nitride using RUS & C-Sphere methodology

Silicon Nitride is a type of engineering ceramics which has been used in ball bearing and other rolling contact applications due to its good fatigue life, high temperature strength and tribological performance. In this paper, the mechanical properties of Hot Isostatically Pressed (HIPed) and Sintered and Reaction Bonded Silion Nitride (SRBSN) have been studied. The elastic modulus and poisson’s ratio of three type of commerical grade HIPed silicon nitride, and groudn SRBSN with three surface condidtions were measured using a Resonance Ultrasound Spectroscopy (RUS). The RUS measurement reveals the variation of elastic properties across different types of HIPed silicon nitride specimens. The surface strength of silicon nitride are studied using a C-Sphere specimen, and the results show that different commercial grade HIPed silicon nitride show varying surface strength. The surface conditions of ground SRBSN have an effect on the surface strength of the specimens. The RUS and C-Sphere techniques can potentially be used to sample the quality and consistency of ball bearing elements

Direct-Cooled Power Electronics Substrate

The goal of the Direct-Cooled Power Electronics Substrate project is to reduce the size and weight of the heat sink for power electronics used in hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs). The concept proposed in this project was to develop an innovative power electronics mounting structure, model it, and perform both thermal and mechanical finite-element analysis (FEA). This concept involved integrating cooling channels within the direct-bonded copper (DBC) substrate and strategically locating these channels underneath the power electronic devices. This arrangement would then be directly cooled by water-ethylene glycol (WEG), essentially eliminating the conventional heat sink and associated heat flow path. The concept was evaluated to determine its manufacturability, its compatibility with WEG, and the potential to reduce size and weight while directly cooling the DBC and associated electronics with a coolant temperature of 105 C. This concept does not provide direct cooling to the electronics, only direct cooling inside the DBC substrate itself. These designs will take into account issues such as containment of the fluid (separation from the electronics) and synergy with the whole power inverter design architecture. In FY 2008, mechanical modeling of substrate and inverter core designs as well as thermal and mechanical stress FEA modeling of the substrate designs was performed, along with research into manufacturing capabilities and methods that will support the substrate designs. In FY 2009, a preferred design(s) will be fabricated and laboratory validation testing will be completed. In FY 2010, based on the previous years laboratory testing, the mechanical design will be modified and the next generation will be built and tested in an operating inverter prototype

C-Ring Strength of Advanced Monolithic Ceramics

Alumina, silicon carbide, silicon nitride, and zirconia are common candidate ceramics for load-bearing tubular components. To help facilitate design and reliability modeling with each ceramic, Weibull strength distributions were determined with each material using a diametrally compressed c-ring specimen in accordance with ASTM C1323. The investigated silicon nitride and zirconia were found to exhibit higher uncensored characteristic strengths than the alumina and silicon carbide. The occurrence of chamfer-located fracture initiation was problematic, and hindered the ability to generate valid design data in some of these ceramics. Fractography and stress modeling results suggest that some aspects of ASTM C1323 should be revised to further minimize the frequency of chamfer-located failure initiation in c-ring test specimens

In-Situ Mechanical Property Evaluation of Dielectric Ceramics in Multilayer Capacitors

The Young's modulus, hardness, and fracture toughness of barium titanate dielectric ceramics in three commercially available multilayer capacitors (MLCs) were measured in-situ using indentation and a mechanical properties microprobe. The three MLCs were equivalent in size (0805), capacitance (0.1 uF) and dielectric type (X7R). The Young's modulus and hardness of the dielectric ceramics in the three MLCs were similar, while there were statistically significant differences in their fracture toughnesses. The results provide insight into the assessment of MLC mechanical reliability, and show that equivalent electrical MLC rating is not necessarily a guarantee that the dielectric ceramics in them will exhibit equivalent mechanical performance

Mode I Fracture Toughness of a Small-Grained Silicon Nitride: Orientation, Temperature, and Crack Length Effects

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65267/1/j.1151-2916.1999.tb02134.x.pd

Sintered silver finite element modelling and reliability based design optimisation in power electronic module

This paper discusses the design for reliability of a sintered silver structure in a power electronic module based on the computational approach that composed of high fidelity analysis, reduced order modelling, numerical risk analysis, and optimisation. The methodology was demonstrated on sintered silver interconnect sandwiched between silicon carbide chip and copper substrate in a power electronic module. In particular, sintered silver reliability due to thermal fatigue material degradation is one of the main concerns. Thermo-mechanical behaviour of the power module sintered silver joint structure is simulated by finite element analysis for cyclic temperature loading profile in order to capture the strain distribution. The discussion was on methods for approximate reduced order modelling based on interpolation techniques using Kriging and radial basis functions. The reduced order modelling approach uses prediction data for the thermo-mechanical behaviour. The fatigue lifetime of the sintered silver interconnect and the warpage of the interconnect layer was particular interest in this study. The reduced order models were used for the analysis of the effect of design uncertainties on the reliability of the sintered silver layer. To assess the effect of uncertain design data, a method for estimating the variation of reliability related metrics namely Latin Hypercube sampling was utilised. The product capability indices are evaluated from the distributions fitted to the histogram resulting from Latin Hypercube sampling technique. A reliability based design optimisation was demonstrated using Particle Swarm Optimisation algorithm for constraint optimisation task consists of optimising two different characteristic performance metrics such as the thermo-mechanical plastic strain accumulation per cycle on the sintered layer and the thermally induced warpage