Papers by Keyword: Microtensile Test

Abstract: The Quenching and Partitioning (Q&P) process is known as a promising method for producing steels with superior mechanical properties. Developing Q&P steels with optimized mechanical properties requires well understanding of the relation between their microstructural and mechanical properties. The microstructural evolution during different Q&P processes in a 0.3C-1.5Si-3.5Mn (wt.%) steel was analysed. Mechanical properties of the developed microstructures were measured by using microtensile test. The influence of volume fractions and carbon contents of the phases on the ductility and strength of the microstructures was investigated. Furthermore, the effect of the specimen size on the tensile properties was discussed and a correction procedure was applied to convert the measured microtensile properties to the standard ones. A comparison with the measured mechanical properties of other type of Advanced High Strength Steels (AHSS) shows the improved properties of the Q&P steels.

Abstract: Platinum (Pt) thin film microheater is designed for integration in a well-known dog bone-like microtensile test structure for high temperature tensile properties measurement. COMSOL Multiphysics tool with electro-thermal modeling was employed to predict the Joule heating capability of three different configurations of Ptmicroheater. The temperature of the test structure resulted from the three micorheater configurations as a function of total dissipated power was plotted for comparison. The microheater with the dendritic-like configuration was found to have the highest power efficiency of 3.19°C/mW in heating up the microtensile test structure.

Abstract: Ti-6242 alloys have been widely used in aero-engine applications due to high temperature strength and creep resistance. The γ-TiAl based intermetallics are considered as candidate materials to replace the current materials weed at high temperatures. The present paper reports on the microstructural and mechanical characterization of γ-TiA/Ti6242 diffusion bonds. The emphasis is put on the better understanding of microstructural development during diffusion process and mechanical properties of diffusion bonds. The process variables of temperature, pressure and time were optimized to produce joints with sound microstructure and bond quality for mechanical characterization. The micro and standard tensile tests were applied to determine bonding strength of joints. Metallographic and fractographic examinations on diffusion joints and tested specimens were carried out using SEM coupled with EDX. The concentration profiles of elements from EDX analysis combined with SEM/BSE investigation demonstrated that the strong inter-diffusion of main elements Al and Ti across the bonding interface occurred during DB process leading to the formation of a noticeable diffusion zone consisting of fine* α2/α grains. The micro tensile tests showed that the preference of fracture on base materials far from the bonding line, but a more marked tendency to brittle failure along bonding interface shown by the standard tensile test results, indicating a significant sample size effect on mechanical property measurements.

Abstract: Fracture behaviors of silicon films were evaluated by microtensile methods. We fabricated two types of specimens using surface micromachining, one for a test device for microtensile testing only and the other for a microtensile-compatible resonating device driven by alternating electrostatic force. The piezoelectric-driven uniaxial stress-strain measurement system was designed to evaluate the mechanical properties of thin films. We used UV adhesive to grip the device to the microtensile system, and the grip was made of UV-transparent glass in order to cure the underlying UV adhesive layer. To assess fracture toughness, we used newly proposed methods combining resonance frequency and microtensile methods. The fracture strength of single- and polycrystalline silicon showed dependence on geometry and doping condition. By varying the geometry, we analyzed the effect of the CMP side and the dry-etched side on changes in the mean fracture strength. Atomic force microscopy observation showed that the larger flaws of the dry-etched side were significant in decreasing the mean fracture strength. Fracture toughness based on fracture mechanics with a precrack was evaluated by newly proposed methods combining resonance frequency and microtensile techniques. The measured toughness was independent of specimen geometry but dependent on doping condition. The measured fracture toughness of notched specimens was 33% higher than that of pre-cracked specimens, even though the notch radius was as small as 1.4µm. The effects of notch-tip radius and doping on fracture toughness of silicon film were also analyzed.

Abstract: A free-standing photosensitive polyimide film with thickness of 10µm is fabricated with the different curing temperatures using a micro fabrication process. The microtensile specimens of a strip type are made to facilitate a tensile testing. The Young’s modulus and yield strength of photosensitive polyimide film are measured with various strain rates from 10-4 /s to 10-3 /s by using a microtensile test. Also, the hardness and Young’s modulus of polyimide films are obtained from nanoindentation test. Finally, the mechanical properties measured from microtensile test are compared with those from nanoindentation test.