Dayi Zhang

A nonlinear auxetic structural vibration damper with metal rubber particles

The work describes the mechanical performance of a metal rubber particles (MRP) damper design based on an auxetic (negative Poisson’s ratio) cellular configuration. The auxetic damper configuration is constituted by an anti-tetrachiral honeycomb, where the cylinders are filled with the MRP material. The MRP samples have been subjected to quasi-static loading to measure the stiffness and loss factor from the static hysteresis curve. A parametric experimental analysis has been carried out to investigate the effect of relative density and filling percentage on the static performance of the MRP, and to identify design guidelines for best use of MRP devices. An experimental assessment of the integrated auxetic-MRP damper concept has been provided through static and dynamic force response techniques. (Some figures may appear in colour only in the online journal)

A novel smart rotor support with shape memory alloy metal rubber for high temperatures and variable amplitude vibrations

The work describes the design, manufacturing and testing of a smart rotor support with shape memory alloy metal rubber (SMA-MR) elements, able to provide variable stiffness and damping characteristics with temperature, motion amplitude and excitation frequency. Differences in damping behavior and nonlinear stiffness between SMA-MR and more traditional metal rubber supports are discussed. The mechanical performance shown by the prototype demonstrates the feasibility of using the SMA-MR concept for active vibration control in rotordynamics, in particular at high temperatures and large amplitude vibrations.

A probability method for prediction on High Cycle Fatigue of blades caused by aerodynamic loads

A probability method for prediction on High Cycle Fatigue (HCF) of blades caused by aerodynamic loads (PHBA) is erected and two approaches are adopted: improving the numerical method to obtain the dynamical responses of blades caused by aerodynamic loads and introducing probability theory into predicting HCF. The basic governing equations of fluid domain, solid domain and fluid-solid interface are given for flow-blade interaction system. Furthermore a numerical method named bidirectional sequential method is illuminated, and the corresponding physical process of vibration from unsteady state to steady state is described. The dynamical response can be obtained by this time domain method conveniently by the use of commercial softwares. Then PHBA is put forward based on vibration stress according to the probabilistic accumulative damage model. Finally an engineering sample is discussed to illuminate PHBA flow clearly. PHBA is performed on two types of second-stage stators to evaluate the operation security, thus the probabilistic accumulative damages altering with operation time are calculated, and the operational reliabilities are also obtained. The results can describe the possibility of HCF intuitively and quantitatively, which shows PHBA is very helpful in the HCF prediction and failure analysis.

Interfacial contact stiffness of fractal rough surfaces

In this work we describe a theoretical model that predicts the interfacial contact stiffness of fractal rough surfaces by considering the effects of elastic and plastic deformations of the fractal asperities. We also develop an original test rig that simulates dovetail joints for turbo machinery blades, which can fine tune the normal contact load existing between the contacting surfaces of the blade root. The interfacial contact stiffness is obtained through an inverse identification method in which finite element simulations are fitted to the experimental results. Excellent agreement is observed between the contact stiffness predicted by the theoretical model and by the analogous experimental results. We demonstrate that the contact stiffness is a power law function of the normal contact load with an exponent α within the whole range of fractal dimension D(1 < D < 2). We also show that for 1 < D < 1.5 the Pohrt-Popov behavior (α = 1/(3 − D)) is valid, however for 1.5 < D < 2, the exponent α is different and equal to 2(D − 1)/D. The diversity between the model developed in the work and the Pohrt-Popov one is explained in detail.

Experimental investigation on the vibration tuning of a shell with a shape memory alloy ring

This paper presents a new design of a smart ring with motion actuators made of a shape memory alloy (SMA). The mechanical properties of the SMA actuator were investigated at room (25 °C) and high (90 °C) temperatures to better understand its characteristics. The results show that the smart ring with an SMA not only shows good stability and rapid effectiveness in the vibration control of the test shell, but observably eliminates the nonlinear vibration characteristics due to contact and rubbing between the ring and shell during the heating process. The smart ring also shows excellent performance in the isolation of transient vibration resulting from impact or random loads. With regard to impact loads, the response peak value can reduce by 57.4% in most cases, while the value is 38.7% for random excitations. The study shows the feasibility of using the SMA material for potential applications of vibration tuning the casings of aero-engines.

Shape Memory Effect and Hysteresis Behavior of Shape Memory Alloy Metal Rubber

The present work focuses on the shaping craft of shape memory alloy metal rubber (SMAMR) and its temperature dependent mechanical properties. Heat treatment process was conducted to form a stable SMAMR sample beyond the general procedure of metal rubber (MR) in order to resist the shape memory effect (SME). The influence of the heat treatment procedure on the mechanical properties was tested. The quasi-static experimental investigations were carried out to obtain the storage modulus and energy loss factor varying with the structural parameter, strain amplitude, and material temperature.It is found from the experiment results that the SMAMR sample which underwent the heat treatment was able to remember its original moulding shape and recover from the overloading plastic deformation when heated above the phase transition temperature. For comparison, another sample without the heat treatment was heated to the same temperature after the plastic deformation, but the final shape deviated from the original one. It is also confirmed that the heat treatment procedure obviously increased the storage modulus and loss factor of SMAMR.Just like the variety elastic modulus of shape memory alloy (SMA), the storage modulus of SMAMR increased obviously while the material was heated above the phase transformation temperature due to the elastic modulus change of SMA wire. The quasi-static experiments showed a hysteretic property of the stress–strain curve in a certain temperature. But the hysteretic curve was temperature and structural parameter dependent.It is concluded that the heat treatment process is necessary to obtain a stable SMAMR during the phase transformation. The varying storage modulus and superior loss factor performances of SMAMR make itself a kind of attractive functional material which will be available in the active suppression of vibration. For example, it can be fabricated to a rotor bearing with changeable stiffness and damping, which is of practical significance in the active control of synchronous vibration of rotors crossing resonance condition.Copyright

Size-dependent mechanical behavior and boundary layer effects in entangled metallic wire material systems

This paper describes the influence on the compressive and dissipative behavior of entangled metallic wire material (EMWM) samples provided by their size and mutual connectivity. The mechanical properties of EMWM specimens with different thicknesses are obtained from quasi-static compressive and cyclic loading. The behavior of the stress–strain curves, tangent modulus, and loss factor are strongly dependent on the thickness of the samples. The analysis from samples connected in different layouts shows that apart from the global thickness, size scale effects and contact interface also play important roles in controlling the behavior of EMWM systems. The importance of the sample size and its connectivity with adjacent different layers are defined by the unique microstructure and contact properties of the wires near the specimen boundary layer. The boundary layer produces different mechanical behaviors and a distinct structural configuration compared to the EMWM bulk solid. These peculiar characteristics are confirmed by microstructural and qualitative observations obtained from computed tomography scanning. The results and analysis presented in this work are relevant to designing EMWM material systems with adaptive performance under different loading and geometric constraints.

Tunable mechanical characteristics of a novel soft magnetic entangled metallic wire material

This article proposes a novel soft magnetic entangled metallic wire material(SM-EMWM) for the first time, and describes the manufacturing and quasi-static tests of its samples produced from soft magnetic metal wires. The mechanical properties of three batches of SM-EMWMs with different porosity have been investigated at different maximum strains in different external magnetic fields. The result shows that its properties (tangent modulus, loss factor) can be tunable in the magnetic field rapidly and reversibly. Compared with no magnetic field condition, the tangent modulus of SM-EMWM samples in a magnetic field of 500 mT can increase 2 ~ 7 times on the average, while the loss factor averagely raises 10% ~ 30%. The results show that the application of SM-EMWM, as a novel magneto-sensitive smart material, is feasible and applicable.

Interval Analysis on Aero-Engine Rotor System With Misalignment

Misalignment is a usual phenomenon in rotating machines. The rotor centerlines are not collinear at the couplings and the rotors operate in incorrect axial positions in a multi-span rotor. The effects of misalignment of flexible rotor system are summarized as the variation of joint stiffness and additional misalignment excitation force based on the dynamic model established.The variation of joints stiffness is difficult to describe, meanwhile the misalignment excitation and rotor unbalance changes with different assembly and operating conditions. The distributions of these parameters which have significant effect on rotor dynamics are unknown, but the intervals of uncertain parameters are usually easier to get. An interval analysis method based on Taylor expansion and direct integration, which solves the dynamic response of rotor system under complex excitations including misalignment and multi unbalance with different frequencies and excitation points is presented. The differential equation of rotor system is formulated by combination of the matrixes of an actual rotor system finite element model and interval excitation vectors. The responses of a single spool and two spools with misalignment and unbalance are calculated by the interval analysis method. The results indicate that the method is effective and reflects some dynamic influence of misalignment and unbalance on rotor system. Second harmonic frequency appears, and rotor orbit is irregular. The response reflects the uncertain interval distribution characteristics, and the frequency components on different locations of the rotor have different characteristics.Copyright

Constraint Mechanical Model and Investigation for Rub-Impact in Aero-Engine System

A mechanical model for rub-impact was proposed considering the additional constraints caused by rubbing. Based on the constraint mechanical model, some characteristics of response such as resonant range expansion, contact unstability and amplitude jump during rubbing were studied. The influences of typical parameters on rotor’s vibration response with rub constraint were also evaluated. The result reveals that additional constraint stiffness causes the unstable contact range and the resonant range to be wider. While greater friction coefficient between rotor and casing results in smaller response and narrower resonant range.A simplified dynamic model for the aero-engine was built, which takes the constraint effect into account. The numerical simulation result shows that in addition to the resonant range expansion caused by the constraint, the rotor response is also closely related to rubbing location and mode shapes. The rotor response shows a feature of quasi-periodic in slight rubbing, while the rotor motion tends unstable in heavy rubbing.© 2015 ASME