Sub-modeling approach for obtaining structural stress histories during dynamic analysis

Abstract

Abstract. Modern machine structures are often fabricated by welding. From a fatigue point of view, the structural details and especially, the welded details are the most prone to fatigue damage and failure. Design against fatigue requires information on the fatigue resistance of a structure's critical details and the stress loads that act on each detail. Even though, dynamic simulation of flexible bodies is already current method for analyzing structures, obtaining the stress history of a structural detail during dynamic simulation is a challenging task; especially when the detail has a complex geometry. In particular, analyzing the stress history of every structural detail within a single finite element model can be overwhelming since the amount of nodal degrees of freedom needed in the model may require an impractical amount of computational effort. The purpose of computer simulation is to reduce amount of prototypes and speed up the product development process. Also, to take operator influence into account, real time models, i.e. simplified and computationally efficient models are required. This in turn, requires stress computation to be efficient if it will be performed during dynamic simulation. The research looks back at the theoretical background of multibody simulation and finite element method to find suitable parts to form a new approach for efficient stress calculation. This study proposes that, the problem of stress calculation during dynamic simulation can be greatly simplified by using a combination of Floating Frame of Reference Formulation with modal superposition and a sub-modeling approach. In practice, the proposed approach can be used to efficiently generate the relevant fatigue assessment stress history for a structural detail during or after dynamic simulation. Proposed approach is demonstrated in practice using one numerical example. Even though, examples are simplified the results show that approach is applicable and can be used as proposed.

Random multiaxial fatigue: A comparative analysis among selected frequency and time domain fatigue evaluation methods

“…For instance during the first stages of the design, the reduced computational effort is probably the major aspect to be addressed, as an algorithm should process the huge amount of information obtained by the FEA (Finite Element Analysis) and MBS (MultiBody Simulation) simulation on the system and the component [5,8] and it should supply quickly the estimated damage on every point of the model [1,6,7]. The algorithm shall be used continuously during this first stage, due to the high number of the system degrees of freedom and the needs for comparisons of several design parameters.…”

“…The virtual evaluation of the mechanical component fatigue behavior has improved significantly during the last years [1][2][3][4][5][6][7][8]. Efficient and time-saving techniques have been developed in order to perform a reliable estimation of the fatigue damage within the different parts of a component and during the different stages of the design process [1,6,7].…”

Instability load analysis of a telescopic boom for an all-terrain crane

“…This substructure, formed by condensation, is called the super element, which is regarded as an individual element in the whole structural model during the modeling or analysis procedure (Li and Zhao, 2006). The substructure is defined by the characteristic points on a single boom section, and the nodal degrees of freedom in the substructure are statically condensed to form a super element, which reduces the computational burden for solving the global system variables (Mäkinen, 2007;Ghosh and Roy, 2009;He et al, 2010;Rantalainen et al, 2013). The precondition of adopting the static condensation method is that the nodal displacements and rotational angles are small in substructure, and the static condensation must be implemented in local coordinate systems.…”

Random fatigue. A new frequency domain criterion for the damage evaluation of mechanical components

“…The evaluation of the fatigue behavior of mechanical systems and components subjected to random loads is increasingly being addressed to the frequency domain environment, both in terms of dynamic analysis [1][2][3][4][5][6] and in terms of results post-processing [7][8][9][10][11][12][13][14][15][16][17][18][19].…”