Abstract:Linear dynamic finite element analysis can be considered very reliable today for the design of aircraft engine components. Unfortunately, when these individual components are built into assemblies, the level of confidence in the results is reduced since the joints in the real structure introduce nonlinearity that cannot be reproduced with a linear model. Certain types of nonlinear joints in an aircraft engine, such as underplatform dampers and blade roots, have been investigated in great detail in the past, an… Show more
“…Next, contact was enabled along the full length of the beams with a coefficient of friction µ = 0.6 [24]. Abaqus allows several methods for addressing the tangential and normal behavior of contact, where the default method is a Penalty method in both directions.…”
Section: Figure 1 Finite Element Model Of 2d Bolted Structure Model mentioning
Bolted joints are common in assembled structures and are a large contributor to the damping in these assemblies. The joints can cause the structure to behave nonlinearly, and introduce uncertainty because the effective stiffness and damping at the joint are typically unknown. Consequently, improved modeling methods are desired that will address the nonlinearity of the jointed structured while also providing reasonable predictions of the effective stiffness and damping of the joint as a function of loading.
A method proposed by Festjens, Chevallier and Dion addresses this by using a sort of nonlinear modal analysis based on the response of the structure to quasi-static loading. This was further developed by Allen and Lacayo and thoroughly demonstrated for structures with discrete Iwan joints. This work explores the efficacy of quasi-static modal analysis for 2D and 3D finite element models in which the geometry, contact pressure and friction in the joint are modeled in detail. The mesh density, contact laws, and other solver settings are explored to understand what is needed to obtain convergence for this type of problem. For the 2D case study, the effect of bolt preload and coefficient of friction are explored and shown to produce reasonable trends. Three dimensional models prove far more challenging and significant effort was required to obtain convergence and then to obtain results that are physically realistic; these efforts are reported as well as the lessons learned.
“…Next, contact was enabled along the full length of the beams with a coefficient of friction µ = 0.6 [24]. Abaqus allows several methods for addressing the tangential and normal behavior of contact, where the default method is a Penalty method in both directions.…”
Section: Figure 1 Finite Element Model Of 2d Bolted Structure Model mentioning
Bolted joints are common in assembled structures and are a large contributor to the damping in these assemblies. The joints can cause the structure to behave nonlinearly, and introduce uncertainty because the effective stiffness and damping at the joint are typically unknown. Consequently, improved modeling methods are desired that will address the nonlinearity of the jointed structured while also providing reasonable predictions of the effective stiffness and damping of the joint as a function of loading.
A method proposed by Festjens, Chevallier and Dion addresses this by using a sort of nonlinear modal analysis based on the response of the structure to quasi-static loading. This was further developed by Allen and Lacayo and thoroughly demonstrated for structures with discrete Iwan joints. This work explores the efficacy of quasi-static modal analysis for 2D and 3D finite element models in which the geometry, contact pressure and friction in the joint are modeled in detail. The mesh density, contact laws, and other solver settings are explored to understand what is needed to obtain convergence for this type of problem. For the 2D case study, the effect of bolt preload and coefficient of friction are explored and shown to produce reasonable trends. Three dimensional models prove far more challenging and significant effort was required to obtain convergence and then to obtain results that are physically realistic; these efforts are reported as well as the lessons learned.
“…It requires input parameters for the contact surfaces, such as friction coefficient and contact stiffness. Schwingshackl et al [19] took advantage of the third approach to consider good nonlinear modeling practice and obtain the required nonlinear data. Kim et al [20] introduced four kinds of finite element models to investigate modelling techniques for bolted joints.…”
“…Thus, scholars studied nonlinear stiffness and energy dissipation of joint. [8][9][10][11] Since there are several bolts distributing in the joint, the characteristic of bolted joints has a great influence on the stiffness of the joint. Existing researches point out that hysteresis appears whenthe bolt was under the transverse harmonic load.…”
As an important component in aero-engine, the stiffness of the flange joint has a direct impact on vibration characteristics. The paper studies the stiffness characteristics of the flange joint which includes a snap by nonlinear transient analysis in ANSYS. The angle of rotation-load curves under harmonic transverse load are obtained. It is discovered that there are different routes of curves in the process of uploading and unloading, and that the curves form a closed cycle, which is called hysteresis loop. Then, the paper also analyses the hysteresis's generation mechanism and the influence of joint parameters -preload of bolts and interference of the snap -on the shape and area of hysteresis loop. Finally, a model, which is comprised of the three-dimension finite element (namely, the joint) and beam element, is built to study the influence of hysteresis on vibration. The results show that the hysteresis of joint can be aroused under the circumstance of certain vibration amplitude and that the hysteresis can rapidly accelerate the amplitude attenuation by the mean of energy dissipation. The research results can be applied to vibration suppression design of aero-engine.
NOMENCLATUREICE Infinitesimal Contact Element. Fcr Critical Force.
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