Image-based truss recognition for density-based topology optimization approach

Structural and Multidisciplinary Optimization - Topology optimization is a tool that supports the creativity of structural-designers and is used in various industries, from automotive to...     

Sequential approximate optimization of industrial hammer peening using finite element simulations

In this paper, the industrial hammer peening process is optimized using multi-objective, sequential approximate optimization, which is a mathematics- plus finite element- based algorithm. Since the number of design and objective variables is significant, the global optimization problem is split into two, more manageable multi-objective subproblems. The use of surrogate modelling together with an intensification and diversification strategy for solving the optimization subproblems allows for significant computational cost savings without loss of accuracy. Additionally, we propose a Bayesian inference criterion-based sensitivity approach for “filtering-out” design variables which do not significantly affect objectives variables. Finally, guidelines for selecting appropriate Pareto optima are given using \(N-1\) Pareto diagrams, where N is the number of objective variables.     

Finite element analysis and contact modelling considerations of interference fits for fretting fatigue strength calculations

This paper presents a 3D finite element study of an interference fit assembly subjected to bending. The results accuracy and the solution convergence are governed by mesh size and contact algorithms options. Their influences were investigated to evaluate displacements and stresses near the contact edge where fretting fatigue failure occurs. Four contact algorithms were tested: Penalty function, Augmented Lagrangian, Normal Lagrange and Pure Lagrange. Performance criteria such as precision and time were highlighted and specific convergence control parameters were found. Finally, best practice rules for interference fit FEA are specified.     

Fretting fatigue strength reduction factor for interference fits

This work is based on a comparison between experimental data and finite element analysis for many configurations of interference fits in rotating bending and alternated torsion. Refined mesh and sub modeling techniques were used to obtain converged results. Contact convergence was achieved using augmented Lagrangian algorithm, with penetration control equal to 0.1% on radial interference and allowable elastic slip of 0.1 μm. Fatigue results are presented for 4 different fatigue criteria: Von Mises, Sine, Crossland and Dang Van. Dang Van criterion gives the most consistent results and shows no evidence of a correlation between sliding amplitude and fatigue life. Relative slip seems to be a consequence rather than the cause, excluding cases with important wear. A fretting fatigue strength reduction factor was calculated for the fretting zone. Its value is between 0.35 and 0.69 depending on the chosen criterion, but varies for different materials and/or loading types. Results give a good fatigue life approximation and can easily be used to optimize the shape of the interference fits.     

Influence of the load modelling during gait on the stress distribution in a femoral implant

Introduction

When designing and installing implants, stress analyses should be performed in conditions close to those of everyday use. Specifically, for femoral implants, cyclic loading during gait has been demonstrated to produce fatigue failure. However, there is still no consensus in the literature regarding which modelling procedure is the most appropriate to simulate implant working conditions. This work proposes a method for realistic load modelling of the human body during gait based on flexible multibody dynamics.

Method

The proposed dynamic method was applied to a case study of a lower limb implant that failed by fatigue. The computed stresses were compared to the stresses obtained using the other three methods found in the literature, which are principally based on static or quasi-static load modelling.

Results

For all compared methods, the maximum computed stress was located in the same region of the implant. The maximum stress provided using flexible multibody dynamics was equal to 346 MPa, which was 355% greater than the maximum value given by the static method and 18% greater than the value given by the quasi-static method.

Discussion and conclusion

The proposed dynamic method was in agreement with the conclusions of the previous failure analysis performed on the broken implant. Conversely, the static and quasi-static methods were not representative of the real loading conditions induced by gait. Moreover, the dynamic method emphasizes the pertinence of evaluating the fluctuations in the critical stress during the gait cycle, which is mandatory when studying fatigue failures.

     

Rebuttal to comments by R. Dumas

Multibody System Dynamics -     

Optimal design of interference fit assemblies subjected to fatigue loads

This paper presents a methodology for an optimal design of interference fit subjected to fatigue loads. Optimization consists in finding a trade-off between mass and competing safety factors at hub and shaft contact zone as well as in shaft fillet. Developing an effective calculation method for fatigue strength of an interference fitted assembly using the finite element method is one of the main steps of the procedure. Meanwhile, coupling the finite elements model of interference fit with an optimization algorithm is not adequate considering the computing time and the significant number of calculations necessary to portrait the assembly behavior. Therefore, a sequential approximate multi-objective optimization algorithm (SAMOO) is presented. The method involves Design Of Experiments (DOE), interpolation with kriging functions, and multi-objective optimization. Preliminary study of parameter variance, and advanced post-processing of multi-objective optimization, provide engineers with valuable information for identifying an optimal design of interference fit assembly using fewer finite element calculations.