Showing papers by "Yichun Zhou published in 2015"

The effect of morphology of thermally grown oxide on the stress field in a turbine blade with thermal barrier coatings

Abstract: To study the effect of morphology of thermally grown oxide on the stress distribution and evolution under cyclic thermal loading, a three-dimensional finite element model of a turbine blade with thermal barrier coatings is developed, in which the coating deposition process, high temperature creep and elastic–plastic behavior are taken into account. Based on the simulation results, dangerous regions in thermal barrier coatings can be predicted. It is shown that, during the cooling stage, tensile stress occurs at the peak of thermally grown oxide/bond coating interface, and compressive stress lies in the valley. With the increase of thickness and amplitude of thermally grown oxide, both the maximum tensile and compressive stresses increase, and the stress distribution is more sensitive to its amplitude than thickness.

Frequency as a key parameter in discriminating the failure types of thermal barrier coatings: Cluster analysis of acoustic emission signals

Abstract: A key parameter in discriminating the failure types of thermal barrier coatings (TBCs) was found out by using the k -means cluster analysis of acoustic emission (AE) signals. It is shown that there are five classes of mechanisms, including surface vertical cracks, opening interface cracks, sliding interface cracks, substrate deformation and macroscopic cleavage or spallation. Except for the last one, the other four classes can be clearly distinguished from their peak frequency distributions in the ranges of 170–250, 400–500, 260–350 and 40–150 kHz, respectively. However, AE signals overlap with each other in other parameter spaces, e.g., amplitude, energy, rise time, and duration time. The results indicate that the frequency can be applied to identify the AE source mechanisms in TBCs.

Ice Regelation: Hydrogen-bond extraordinary recoverability and water quasisolid-phase-boundary dispersivity.

Abstract: Regelation, i.e., ice melts under compression and freezes again when the pressure is relieved, remains puzzling since its discovery in 1850’s by Faraday. Here we show that hydrogen bond (O:H-O) cooperativity and its extraordinary recoverability resolve this anomaly. The H-O bond and the O:H nonbond possesses each a specific heat ηx(T/ΘDx) whose Debye temperature ΘDx is proportional to its characteristic phonon frequency ωx according to Einstein’s relationship. A superposition of the ηx(T/ΘDx) curves for the H-O bond (x = H, ωH ~ 3200 cm−1) and the O:H nonbond (x = L, ωL ~ 200 cm−1, ΘDL = 198 K) yields two intersecting temperatures that define the liquid/quasisolid/solid phase boundaries. Compression shortens the O:H nonbond and stiffens its phonon but does the opposite to the H-O bond through O-O Coulomb repulsion, which closes up the intersection temperatures and hence depress the melting temperature of quasisolid ice. Reproduction of the Tm(P) profile clarifies that the H-O bond energy EH determines the Tm with derivative of EH = 3.97 eV for bulk water and ice. Oxygen atom always finds bonding partners to retain its sp3-orbital hybridization once the O:H breaks, which ensures O:H-O bond recoverability to its original state once the pressure is relieved.

Simulation of FeFET-Based Basic Logic Circuits and Current Sensing Amplifier

Abstract: The usage of ferroelectric-gate field effect transistors (FeFET) in digital circuits has typically been its applications in memory. The use of FeFET to implement logic circuits is neither completely understood nor extensively studied. This paper presents simulations of electrical properties of a single FeFET and the resulting behavioral characterizations of FeFET-based basic logic circuits in a commercially available TCAD environment. The all-FeFET current mirror, CMOS inverter, 2-input-NAND and 2-input-NOR logic circuits show almost the same electrical characteristics as standard MOSFET ones, except for the negligible clockwise hysteresis under the condition of low voltage supply. Moreover, the all-FeFET current mode sensitive amplifier whose component units were all-FeFET common-source amplifier, current mirror and differential amplification, also works reasonably.

Cutting ring type measurement method for residual stress of cylinder wall of cylindrical part

Abstract: The invention discloses a cutting ring type measurement method for residual stress of the cylinder wall of a cylindrical part. The cutting ring type measurement method includes the following steps of (1) forming a cutting ring, wherein a circular ring cut from the cylinder wall of the cylindrical part is used as the circular ring to be cut, and the circular ring to be cut is cut apart in the radius direction to form the cutting ring; (2) calculating the residual stress, wherein in the circular ring to be cut, a calculation formula for the radial residual stress sigma and a calculation formula for the circumferential residual stress sigma of the position spaced from the center of the circular ring by r in the radius direction are expressed in the specification. Multi-point measurement can be achieved without developing a special measurement device, operation is easy and convenient, efficiency is high, and results are accurate.

Design and Simulation of FeFET-Based Lookup Table

Abstract: Ferroelectric random access memory (FeRAM) is a promising candidate to substitute static random access memory (SRAM) in lookup table (LUT) design due to its high density, high speed operation, anti-radiation and non-volatility. Ferroelectric gate field effect transistors (FeFETs) have been extensively studied and its usage in memory elements and basic analog circuit configurations has gained much interests. Here, we propose a novel architecture of FeFET-based LUT. An improved timing mode of FeRAM chip is analyzed to satisfy the performance of the FeFET-based LUT. Decoder, driver circuit and sensitive amplifier for FeFET array are also proposed. All the simulation results show that the proposed LUT works properly when the frequency reaches 500 MHz at 0.3 V differential input signal.