Nonlinear Contact Interface Research Articles

Sensitivity and Forced Response Analysis of Anisotropy-Mistuned Bladed Disks With Nonlinear Contact Interfaces

AbstractA new method has been developed for the analysis of nonlinear forced response of bladed disks mistuned by blade anisotropy scatter and for the forced response sensitivity to blade material anisotropy orientations. The approach allows for the calculation of bladed disks with nonlinear friction contact interfaces using the multiharmonic balance method. The method uses efficient high-accuracy model reduction method for the minimization of the computational effort while providing required accuracy. The capabilities of the developed methods are validated and demonstrated using a two-blade model. A thorough study of the influence of the material anisotropy mistuning and its sensitivity on the characteristics of the forced response is carried out using finite element (FE) modes of anisotropy mistuned realistic bladed disk with nonlinear friction joints of blade roots and shroud contacts. The dependency of the nonlinear forced response on excitation level and contact pressure values has been carried out for anisotropy mistuned bladed disks.

Analytical and numerical modelling of wave scattering by a linear and nonlinear contact interface

A new analytical approach is presented for describing plane-wave scattering at a plane interface that is characterised by a linear or nonlinear traction law. The crucial step is a decomposition of the scattered field into two contributions that exhibit symmetries corresponding to Mode I or Mode II fields, in the terminology of fracture mechanics. As a consequence, the scattering problem for linear springs is reduced to determining two unknowns, corresponding to the normal and the tangential components of the relative displacement across the interface, thereby leading to an explicit analytical solution. By contrast, the conventional approach is formulated in terms of the four unknown amplitudes for the reflected and transmitted longitudinal and transverse waves, with the solution having to be determined numerically for particular values of the incident angle and material properties. Next, a perturbation approach is employed to derive analytical solutions for nonlinear springs. This approach leads to successive approximations that can also be solved analytically, thereby resulting in analytical formulae for scattering by weakly nonlinear springs. These analytical formulae are compared with computational results based on the finite element method, utilising parameter values that are representative of rough-surface contact. Excellent agreement with the computational results is demonstrated, thereby highlighting the practical value of the analytical formulae for parametric studies.

Fabrication of core–shell C/MnO nanocomposite by liquid deposition for high performance lithium-ion batteries

Energy storage materials with high energy density are highly desired due to the development of electrical vehicles. In this work, monomer aniline is driven to be carbon by a simple liquid deposition and carbonization. The C/MnO nanocomposite with a non-linear contact interface core–shell structure were successfully fabricated. It contains 92.5 wt% of MnO for the dry nanocomposite. When evaluate as anode materials for lithium ion battery, the C/MnO electrode exhibits excellent reversible capacity of 943.6 mAh g−1 at a current density of 100 mA g−1 after 100 cycles. Impressively, a capacity of 484 mAh g−1 retains at a high current density of 4000 mA g−1, indicating that the C/MnO nanocomposite is potential competitor for application in lithium ion battery.

Analysis of Flutter-Induced Limit Cycle Oscillations in Gas-Turbine Structures With Friction, Gap, and Other Nonlinear Contact Interfaces

A frequency-domain method has been developed to predict and comprehensively analyze the limit-cycle flutter-induced vibrations in bladed disks and other structures with nonlinear contact interfaces. The method allows, for the first time, direct calculation of the limit-cycle amplitudes and frequencies as functions of contact interface parameters and aerodynamic characteristics using realistic large-scale finite element models of structures. The effects of the parameters of nonlinear contact interfaces on limit-cycle amplitudes and frequencies have been explored for major types of nonlinearities occurring in gas-turbine structures. New mechanisms of limiting the flutter-induced vibrations have been revealed and explained.

닫힘균열의 1차원 모델을 이용한 고조파 발생에 대한 파라미터 연구

균열이 용접부 내와 같은 잔류응력의 영향을 받는 곳에 존재할 경우, 균열은 닫힘균열로 존재할 수 있으며, 인장과 압축에 대하여 비대칭적인 거동을 보이게 된다. 이러한 비선형 균열에 대하여 균열면에서 발생하는 고조파를 이용한 초음파 탐지 기법이 활발히 연구되고 있다. 본 연구에서는 비선형 접촉면에서 발생하는 고조파에 대한 파라미터 연구를 수행하였다. 본 연구는 일반적인 3차원 균열로 나아가기 위한 기초연구의 성격을 띄고 있다. 압축과 인장에 대해 각기 다른 선형 거동을 나타내는 접촉면을 가정하였고 1차원 문제를 고려하였다. 기본주파수 성분에 대한 2차고조파 성분의 비를 다양한 강성비, 입사파의 주파수, 접촉면의 두께에 대하여 조사 하였다. When a crack exists under a residual stress, for example in welds, the crack can be closed and it shows non symmetric behavior for tension and compression. Ultrasonic detection method for those nonlinear cracks has been developed recently. The method uses the higher order harmonics generating at the crack surface. In this study, parameter study was carried out for the analysis of the harmonics generation at a nonlinear contact interface as a preliminary study for general 3-dimensional cracks. One-dimensional problem with simple bilinear behavior for the contacting surface was considered. The amplitude of second harmonic to the fundamental wave was obtained for various stiffness ratios, incident frequencies, and the contacting layer thicknesses.

Method for Sensitivity Analysis of Resonance Forced Response of Bladed Disks With Nonlinear Contact Interfaces

An effective method has been developed to calculate the sensitivity of the resonance peak frequency and forced response level to variation of parameters of nonlinear friction contact interfaces and excitation. The method allows determination of the sensitivity characteristics simultaneously with the resonance peak frequency and response level calculated as a function of any parameter of interest and without significant computational expense. Capabilities of the method are demonstrated on examples of analysis of large-scale finite element models of realistic bladed disks with major types of the nonlinear contact interfaces: (i) a blisk with underplatform dampers, (ii) a bladed disk with friction damping at blade fir-tree roots, and (iii) a high-pressure bladed disk with shroud contacts. The numerical investigations show high efficiency of the method proposed.

Mechanical tests and finite element models for bone holding power of tibial locking screws

Objective. To investigate the bone holding power of tibial locking screws. Design. The bone holding power was assessed by mechanical testing and finite element analysis. Background. Screw loosening might threaten fracture fixation and bone healing. Methods. In mechanical tests, six types of different tibial locking screws were inserted into low-density polyurethane foam tubes, which simulated osteoporotic bone. The screws were pushed out of the foam bone by an axial load, and the maximal pushout load was recorded. In finite element analysis, three-dimensional finite element models with a nonlinear contact interface between the screws and the bones were created to simulate the mechanical testing. The total strain energy of the bone and total reaction force of the screws were recorded. The contribution of the design factors was analyzed by the Taguchi method. Results. In the mechanical tests, foam bone was stripped by the screw threads without screw deformation. The testing results were closely related to those of finite element analysis. The Taguchi analysis showed that the descending order of contribution of the design factors was outer diameter, pitch, half angle, and inner diameter. Root radius and thread width had minimal effects. Conclusions. The bone holding power of the screws could be reliably assessed by finite element models, which could analyze the effects of all the design factors independently and were potentially applicable to screws with irregular thread patterns. RelevanceThe finite element models built in this study may help manufacturers in evaluating new designs of locking screws and assist surgeons in selecting suitable devices for patients with severe osteoporosis.

Pushout strength of tibial locking screws: Development of finite element models

This study investigated the bone holding power of tibial locking screws by mechanical testing and finite element analysis. In mechanical tests, five types of commercially available tibial locking screws: Howmedica, Osteo AG, Richards type I, Richards type II, and Synthes were inserted in a cylinder of polyurethane foam bone. Axial load was applied to the screw tip to push the screws out of the foam bone by a material testing machine. The pushout strength of each screw was recorded. In finite element analysis, three‐dimensional finite element models with nonlinear contact interface between the screws and the bones were created to simulate the mechanical testing. The results showed that the order of the pushout strength of the locking screws from high to low was Osteo AG, Richards type II, Richards type I, Howmedica, and Synthes. The results of mechanical tests were highly correlated to the results of finite element analysis. Finite element models with low elastic modulus of bone and no frictional force between the screws and bones can better simulate the situations of mechanical testing. The finite element models built in this study may help the manufacturers evaluate new designs of locking screws before manufacture and assist surgeons to select suitable devices for their patients.