Zhu Feng Yue

Experimental Study of the High Temperature Mechanical Behaviors of TLP Bonding of Two Ni-Base Single Crystals

In this paper, the mechanical behavior of Ni-base single crystals joint created by TLP bonding is presented. Experimental study has been performed on the TLP single crystal under loading conditions of static uniaxial tension, creep and Three-points-bending (T-P-B) at temperature of 850 °C. Specimens made of the base material, Ni-base single crystal specimens without bonding, were also tested under the same loading conditions. The mechanical behaviors of TLP single crystal is compared to the behaviors of base material. It was found that the static strength of the TLP specimens with the boundary normal to the tensile direction was 63% of the strength of the base material. The creep strength and the fracture ductile strength was more than 57% and 55% of that of the single crystal base material, respectively. The macro and micro graphs of fracture surfaces of specimens indicated that the fracture modes of the samples were brittle fracture.

The Effects of Cooling Holes on the Creep Life in a Modeling Specimen of Single Crystal Air-Cooled Turbine Blade

This paper presents the study of the influences of cooling holes on the creep life behavior in the modeling specimen of single crystal cooling turbine blade at high temperature. Thin-walled cylindrical specimens with holes are tested to model the air-cooled turbine blade. Specimens without holes are also studied to make comparisons. Experimental results show that at 900°C, the creep lives of specimens with holes are longer than those of specimens without holes. Scanning Electron Microscopy (SEM) analyses reveal that creep deformations occur firstly around the cooling holes and finally rupture at the region with low stress and strain. Finite element analyses are used to study the creep damage development by a K-R damage model which has been implemented into the Abaqus user subroutine (UMAT). Simulation results show that stress concentration and redistribution occur around the cooling holes during the creep development. It is also shown that the maximum strain and stress are around the cooling holes which are the initial rupture region in the experiments.

Experiment and FEM Simulation on Residual Stress of Cold Expansion Hole

A 2D cylindrical plate model has been established to study the distribution of residual stress of cold expansion hole under different interference values. In addition, the effects of material models on residual stress fields are considered also. Experiments are carried out to measure the residual stress of cold expansion hole and verify simulation results. FEM results show, with interference values increasing, the higher residual radial and circumferential stresses are obtained. At same interference value, the residual stress of Hardening Material( HM ) model is much larger than that of Elastic Perfectly Plastic Material( EPPM ) model.

Numerical Study on Elastic-Plastic Stress Field Near the Cooling Holes of Nickel-Based Single Crystal Air-Cooled Blades

In this paper, a plate containing a central hole was used to simulate gas turbine blade with cooling hole. Numerical calculations based on crystal plasticity theory have been performed to study the elastic-plastic stress field near the hole under tension. Two crystallographic orientations [001] and [111] were considered. The distributions of resolved shear stresses and strains of the octahedral slip systems {110}<112> were calculated. The results show that the crystallographic orientation has remarkable influence on both von Mises stress and resolved shear stress distributions. The resolved shear stress distributions around the hole are different between the two orientations, which lead to the different activated slip systems. So the deformed shape of the hole in [001] orientation differs from that in [111] orientation.

Constitutive Relationship and Applications of Shape-Memory Alloys

A constitutive relationship has been applied to study the behavior of structures and composites of the shape-memory alloy (SMA). The predictability o f he constitutive relationship is confirmed by the uniaxial and multiaxial examples. The paper gives out the finite element algorithmic implementations, which is applied to implement as umat of ABAQUS. As two kinds of applications, CT (compact tensile) and TPB (three point bending) sp ecimens and SMA-fiber enforced metal matrix and metal-fiber reinforced SMA-matrix composites are analyzed. The different distributions of martensite fraction of the CT specimens a d TPB-specimens made of SMAs are explained by the different stress characteristics before the cracks. The study on the SMA-related composites shows that the bulk mechanic behavior depends on t he volume of SMA and the non-SMA matrix/fiber properties. Introduction Shape-memory alloys (SMAs) belong to a class of materials t h t can undergo reversible phase transformations between martensite and austensite. These transform ations are solid-solid displactive-diffusionless (or lattice-distortive). Austensite is a crystallographically more-ordered phase, which is stable at high temperatures and low values of the st ress. Martensite is a crystallographically less-ordered phase, which is stable at low emperatures and high values of the stress. Shape memory effect and superelasticity are the two most unusual effects of SMAs. The description of the phase transformation is the basic work in the constitutive r elationship. So far, there are many constitutive relationships. The second step is the implementation of the constitutive relationship into a finite-element scheme. The objective of this paper is to apply a constitutive relationship and the algorithmic form of finite-element scheme to SMA structure and composites . Constitutive Relationship and Models Three phase transformations are considered (1) austensite into si ngle-variant martenste (A->S), (2) martensite into austenite (S->A) and (3) martensite reorienta t o (S->S). This assumption is a good approximation and to be appropriate to Nitinol and other SMAs frequently us ed. Generally, the materials are considered to be isotropic. Auricchio [1]’s model is applied here. Please refer to the reference for the detail about the model. It should be pointed out the finite element algorithmic implementations have been changed according our understanding of the model. The integration algorithm for the time-discrete model is given out as following 7 steps. It is suitable for the writing of umat of ABAQUS. (1) Trial state Key Engineering Materials Online: 2003-07-15 ISSN: 1662-9795, Vols. 243-244, pp 487-492 doi:10.4028/www.scientific.net/KEM.243-244.487

Effect of Adhesive Layer’s Voids on Stress Distribution of Adhesively Bonded Joints

The stress distribution of adhesively-bonded single lap joints under tensile shear loading is analyzed using 2-dimensional elastic-plastic finite element method (FEM). Special attentions have been put on the influence of void in adhesive on the stress distribution of adhesively-bonded joints. The results show that the stress concentration of the void is less than that of the end part of the joints when adhesive layer’s deformation was in the range of elastic. Moreover, the influence of the void on the stress distribution becomes less when the void moving from the end-part to the middle. The stress concentration becomes larger and the stress distribution of adhesive’s mid-thickness region becomes flatter when adhesive layer has biggish plastic deformation. Finite element results show an agreement with the theoretical results.

Pressure Pulsation Analysis of Aircraft Hydraulic Power Pipelines System

The output pressure pulsation model for the aircraft hydraulic power pipelines was established by the methods of transfer function and fluid network chain-rules; the dissipation caused by frequency-dependent friction was taken into account. Dynamic characteristics of hydraulic system were discussed in frequency-domain and time-domain respectively, the pumping excitation frequency influenced the frequency-response of hydraulic pipeline system, and several resonance frequency bands were obtained. The inverse fast Fourier transform was applied to simulate the transient pressure pulsation waves under pump starting and steady-running state.

Creep Behaviors of Nickel-Based Single Crystal Superalloys Compact Tension Specimen at High Temperature

Based on the microstructure change and damage characteristics of single crystal, a two-state-variable crystallographic creep damage constitutive model has been developed to investigate crack growth behaviors of single crystal compact tension specimen at 760 for two crack orientations: (001)[100] and (011)[100]. Numerical simulation results show the crack-tip stress fields are dependent on crack crystallographic orientation. Observations performed on the real single crystal specimens reveals that the macroscopic crack growth path appears as zigzag wave. The creep deformation at crack tip takes place in specific slip plane, and the deflection angles of crack initiation direction from the crack plane are 45º or 135 º and 53.7ºor 127.3º in the crack orientations (001)[100] and (011)[100]. A good agreement between experimental observations and numerical results is found.

Supports’ Dynamical Optimized Design for the External Pipeline of Aircraft Engine

A three dimension model of some aircraft engine’s pipeline has been established to study dynamic characteristics of the pipeline under random excitation. The relationship between the supports’ parameters and the dynamic characters of the pipeline was also presented. In order to avoid the harmful resonance, depress the vibration level and reduce the dynamic stresses of the pipeline, a specific dynamical optimized method was proposed and the supports’ layout and parameters (location, quantity) were analyzed and optimized. The results show that 1) Under random excitation, the maximum stresses are located near the bushing with serious stress concentration and the ends of pipeline. Fracture failure easily occurs in these parts. 2) The supports’ optimized method of the pipeline proposed in this paper is reasonable and effective. And the optimized pipeline has less dynamic stress and better anti-vibration capability.

Reliability-Based Multidisciplinary Design Optimization for Centrifugal Compressor Using the Fourth Moment Method

A reliability-based multidisciplinary design optimization (RBMDO) frame work for Centrifugal compressor was presented. Multidisciplinary feasible method was used to decouple the multidisciplinary analysis and the fourth moment method for reliability analysis was recommended systematically. Based on the approximation, the RBMDO framework was finished. The case study shows that optimization efforts could improve obviously the performance of centrifugal compressor under the requirements of reliability. This framework could make the design reach the best performance with a good reliability. It indicates that the proposed optimization method is available and feasible for the engineering application.