Yann Ledoux

Multi-scalar analysis of hip implant components using modal decomposition

This paper presents a metrological analysis of hip prosthesis components. When changing ceramic prostheses, the surgeon sometimes finds traces of alloy lying in the insert or the femoral head. These traces can be thin and accurate or as a wide band. From the measurements made on the contact areas of hip prosthesis components, we analyse these phenomena by highlighting the defects of form, waviness and roughness of these surfaces using a novel geometric parameterization (namely modal parameterization). The aim of this work is to isolate these defects to characterize the prostheses components. We show that this parameterization allows a multi-scale analysis of surfaces regardless of the type of wear of the prosthesis, and that the results offer some relevant explanations to the analysis of visible damage on the prostheses. In a later study, we are going to analyse the defects influence on the alteration of the performance of hip prostheses.

Integrating Risks in Project Management

Risk is an inherent property of every project. In many cases, project management and risk management are applied quite independently. On the one hand, the traditional tools of project management do not include the notion of risk. On the other hand, the tools of risk management focus on the representation of risks without explicitly representing the project, which leads to implement the risk management process independently of the project management process. Methods and tools are needed to manage and represent risk project. The absence of such techniques is a concern because there is no risk without project and no risk-free project. This paper discusses the need to develop an integrated approach to project risk management. This method must be able to represent the risks, but also the project, its components and its environment. The paper concludes by showing the importance of developing an integrated approach to risk management and project management processes.

A trade-off function to tackle robust design problems in engineering

In this paper, an original trade-off function is proposed to deal with robust design in engineering. Robust design in engineering aims at sizing systems with a low variation in all performance measures under uncertainties. It is mainly related to the generation and evaluation of candidate solutions. However, it is also suitable to consider the robustness in the decision-making process to ensure the selection of the most preferred design in the early stages of the design process. The purpose of our research work consists in tackling the robust design problem as a trade-off between two design objectives: (i) improve the global level of performance of the system and (ii) reduce the sensitivity of the performance with regard to uncertainty sources. The robustness of the candidate solutions is evaluated by a trade-off function modelling the designers intention with an a priori articulation of preferences. Design objective formulation is based on the concept of desirability function and indices. Candidates solutions are ranked according to their ability of reducing the design sensitivity while remaining highly desirable. The developed approach is illustrated on an example of a truss structure design problem which is numerically solved by a genetic algorithm.

Global optimisation of functional requirements and tolerance allocations based on designer preference modelling

ABSTRACT The allocation of design and manufacturing tolerances has a significant effect on the final performance of products and the associated manufacturing costs. Although this phase is crucial in the early stages of product design, there is a lack of tools to provide support for designers. The main originality of this study is to propose an integrated optimisation scheme based on a particular ontological model, which structures the design problem from the functional requirements stage to the definition of quantified objectives for optimisation. Design priorities are integrated by weighting every design objective. The mechanism studied here is a helicopter turboshaft engine. The aim is to determine optimal tolerance values according to several scenarios. A comparison between classical distribution of tolerance values (iso-distribution) and a tolerance distribution subject to manufacturing costs is proposed. Finally, ontological modelling is used to optimise the position of the mechanical joints of the mechanism, the tolerance values and the associated costs. This last result demonstrates the advantage of integrating both the tolerance optimisation related to manufacturing cost and the joint positions of the mechanism in the early phase of the design.

Genetic algorithm for design and manufacture optimization based on numerical simulations applied to aeronautic composite parts

A key challenge for the future is to reduce drastically the human impact on the environment. In the aeronautic field, this challenge aims at optimizing the design of the aircraft to decrease the global mass. This reduction leads to the optimization of every part constitutive of the plane. This operation is even more delicate when the used material is composite material. In this case, it is necessary to find a compromise between the strength, the mass and the manufacturing cost of the component. Due to these different kinds of design constraints it is necessary to assist engineer with decision support system to determine feasible solutions. In this paper, an approach is proposed based on the coupling of the different key characteristics of the design process and on the consideration of the failure risk of the component. The originality of this work is that the manufacturing deviations due to the RTM process are integrated in the simulation of the assembly process. Two kinds of deviations are identified: volume impregnation (injection phase of RTM process) and geometrical deviations (curing and cooling phases). The quantification of these deviations and the related failure risk calculation is based on finite element simulations (Pam RTM® and Samcef® softwares). The use of genetic algorithm allows to estimate the impact of the design choices and their consequences on the failure risk of the component. The main focus of the paper is the optimization of tool design. In the framework of decision support systems, the failure risk calculation is used for making the comparison of possible industrialization alternatives. It is proposed to apply this method on a particular part of the airplane structure: a spar unit made of carbon fiber/epoxy composite.