Mladenko Kajtaz

A collaborative FEA platform for rapid design of lightweight vehicle structures

This paper presents a novel methodology for rapid design of sustainable vehicle structures using a collaborative Finite Element Analysis (FEA) platform. The developed platform utilises FEA substructures in a novel way to increase the vehicle development efficiency by speeding up analysis and reducing the number of iterations in the product development process. It also allows rapid validation of design changes early in a design and therefore reduction of computational effort and time without compromising accuracy. The underpinning methodology was described and illustrated here using a case study dealing with the design and optimisation of a car seat actuator assembly.

Creep and Recovery Behaviour of Polyolefin-Rubber Nanocomposites Developed for Additive Manufacturing

Nanocomposite application in automotive engineering materials is subject to continual stress fields together with recovery periods, under extremes of temperature variations. The aim is to prepare and characterize polyolefin-rubber nanocomposites developed for additive manufacturing in terms of their time-dependent deformation behaviour as revealed in creep-recovery experiments. The composites consisted of linear low density polyethylene and functionalized rubber particles. Maleic anhydride compatibilizer grafted to polyethylene was used to enhance adhesion between the polyethylene and rubber; and multi-walled carbon nanotubes were introduced to impart electrical conductivity. Various compositions of nanocomposites were tested under constant stress in creep and recovery. A four-element mechanistic Burger model was employed to model the creep phase of the composites, while a Weibull distribution function was employed to model the recovery phase of the composites. Finite element analysis using Abaqus enabled numerical modelling of the creep phase of the composites. Both analytical and numerical solutions were found to be consistent with the experimental results. Creep and recovery were dependent on: (i) composite composition; (ii) compatibilizers content; (iii) carbon nanotubes that formed a percolation network.

Comparative Evaluation of Engineering Design Concepts Based on Non-Linear Substructuring Analysis

The paper presents a novel approach to comparative evaluation of engineering design concepts that exhibit non-linear structural behaviour under load. The developed method has extended the substructures technique in order to apply the Finite Element Analysis (FEA) method to complex non-linear structural problems in the conceptual design phase. As conventional FE models based on substructures allow only linear analysis, it was necessary in this research to introduce a new algorithm capable of linearizing non-linear structural problems with sufficient accuracy in order to enable comparative evaluation of design concepts relative to each other under the given constraints and loading conditions. A comparative study with respect to model size, efficiency, accuracy and confidence was performed to validate the developed method. Obtained results indicate significant improvement over more traditional approaches to applying FEA in the conceptual design phase. The improvements achieved using the developed method compared to the traditional FE based approach are superior by a factor of 2.7 in efficiency and by a factor of 4.5 in confidence while not sacrificing the optimality of the solutions.

Optimising the multiplicative AF model parameters for AA7075 cyclic plasticity and fatigue simulation

Purpose This study presents the improvements of the multicomponent Armstrong–Frederick model with multiplier (MAFM) performance through a numerical optimisation methodology available in a commercial software. Moreover, this study explores the application of a multiobjective optimisation technique for the determination of the parameters of the constitutive models using uniaxial experimental data gathered from aluminium alloy 7075-T6 specimens. This approach aims to improve the overall accuracy of stress–strain response, for not only symmetric strain-controlled loading but also asymmetrically strain- and stress-controlled loading. Design/methodology/approach Experimental data from stress- and strain-controlled symmetric and asymmetric cyclic loadings have been used for this purpose. The analysis of the influence of the parameters on simulation accuracy has led to an adjustment scheme that can be used for focused optimisation of the MAFM model performance. The method was successfully used to provide a better understanding of the influence of each model parameter on the overall simulation accuracy. Findings The optimisation identified an important issue associated with competing ratcheting and mean stress relaxation objectives, highlighting the issues with arriving at a parameter set that can simulate ratcheting and mean stress relaxation for load cases not reaching at complete relaxation. Practical implications The study uses a strain-life fatigue application to demonstrate the importance of incorporating a technique such as the presented multiobjective optimisation method to arrive at robust parameters capable of accurately simulating a variety of transient cyclic phenomena. Originality/value The proposed methodology improves the accuracy of cyclic plasticity phenomena and strain-life fatigue simulations for engineering applications. This study is considered a valuable contribution for the engineering community, as it can act as starting point for further exploration of the benefits that can be obtained through material parameter optimisation methodologies for models of the MAFM class.

AN EXTENDED SUBSTRUCTURING TECHNIQUE FOR EFFICIENT EVALUATION OF NONLINEAR LOAD-BEARING STRUCTURES IN THE CONCEPTUAL DESIGN STAGE

The research presented in this paper has extended the substructuring technique into the nonlinear domain in order to apply the finite element analysis (FEA) method to complex nonlinear structural design problems in the conceptual design stage. As conventional FE models based on substructures allow only linear analysis, it was necessary in this research to introduce a new algorithm capable of linearizing nonlinear structural problems with sufficient accuracy in order to enable evaluation of engineering design concepts in a more objective and rigorous manner in the early stages of design. The developed method was implemented within a commercial FE solver, and validated using a select number of case studies. The results obtained for the two sample solutions indicate that the new method has achieved an improvement in accuracy of 90% and 98% respectively compared to the conventional FE-based approach applied to the same class of design problems.

Extension of Substructuring Technique in the Nonlinear Domain

Conventional finite element models based on substructures allow only linear analysis. Some load-bearing structures such as energy absorbers and impact attenuators are designed to perform their useful functions in the nonlinear domain. Evaluating engineering design concepts of those structures objectively and with a certain rigour is challenging. Finite element analysis (FEA) as a potentially suitable tool for the evaluation typically is not computationally efficient and affordable in the conceptual design phase. An idea of extending the substructuring technique to be used for the concept evaluation by allowing substructures to exhibit a nonlinear response and use them in finite element models to reduce the computational cost is investigated in this chapter. For this reason, it was necessary to introduce a new algorithm capable of substructuring nonlinear structural models with sufficient accuracy. The main requirement for successful application of substructuring to this class of design problems is the definition of structural stiffness within an engineering design concept, which is, in fact, the minimal requirement for FEA functionality as well. In this work, the expansion of the substructuring technique beyond the linear response expectancy application is achieved by employing a scalar qualifier to economically modify original substructure matrix for substructures to exhibit a nonlinear response. This extension and integration of substructuring are crucial in allowing FEA to become more computationally efficient and affordable in the conceptual design phase. This chapter provides a comprehensive overview of the traditional substructuring process, followed by a detailed description of the developed method that extends substructures beyond the linearity domain. The implementation of the extended substructures within a commercial FEA code (ABAQUS) is then presented.

Conceptual Design Evaluation of Lightweight Load Bearing Structural Assembly for an Automotive Seat Adjuster Mechanism

An application of a novel methodology in a redesign of the load bearing subassembly of an automotive seat adjuster is presented. This novel methodology efficiently evaluated concept variations at a higher rate than the traditional approach based on FEA and therefore enables a comparison of the objective spaces rather than undesirable point design comparisons. This significant increase in efficiency increased the amount of generated knowledge that was presented to the design engineer in a form of the Pareto front comparisons. The comparisons of the Pareto fronts allowed for a clear identification of Concept #3 as the preferred solution, given the load-bearing and the light weighting criteria only. The results also indicated that Concept #2 could also be promising solution after major enhancements, as it showed potential to outperform the current solution in some cases.