Design methods

Résumé

Design methods are procedures, techniques, aids, or tools for designing. They offer a number of different kinds of activities that a designer might use within an overall design process. Conventional procedures of design, such as drawing, can be regarded as design methods, but since the 1950s new procedures have been developed that are more usually grouped together under the name of "design methods". What design methods have in common is that they "are attempts to make public the hitherto private thinking of designers; to externalise the design process". Design methodology is the broader study of method in design: the study of the principles, practices and procedures of designing. Background Design methods originated in new approaches to problem solving developed in the mid-20th Century, and also in response to industrialisation and mass-production, which changed the nature of designing. A "Conference on Systematic and Intuitive Methods in Engineering, Industrial Design, Arch

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https://en.wikipedia.org/wiki/Design_methods

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Influence of residual stresses on the buckling capacity of axially loaded steel columns

Gabriele Falconi

Over the past 60-80 years, the design methodology of steel structures comprising conventional steel profiles, such as HEA, HEB or HEM, has remained unchanged. However, during the 21st century, production methods have improved considerably. The aim of this study is to develop the basis for evaluating and refining the design methodology of steel members by considering realistic residual stress distributions generated during the fabrication process. Out of the numerous production methods, in this study we focus on hot rolled wide flange cross sections which are the most commonly used profiles in construction. Design specifications vary from one country to another. A comparison of the Swiss, European, Canadian, and Japanese approaches would help towards understanding the factors influencing the sizing of steel profiles. Simplified methods based on analytical and semi-experimental models have been developed over time to help engineers consider the phenomenon of lateral buckling by ensuring a sufficient degree of safety. Considering that the above design specifications have been developed based on experimental research of steel profiles and materials characteristic of old practices, this study investigates potential updates in the current design practices. To succeed in this challenge, it is imperative that the residual stress distributions of current cross-sectional and material characteristics are explained. Several studies throughout the past years have tried to focus on formulating simplified models that consider residual stress distributions. The accuracy of these models is investigated and recommendations are provided based on the best fits to measured residual stress distributions. These have explicitly been collected from nearly 10 experimental programs leading to more than 30 measured distributions with 𝐻/𝐵 (where 𝐻 is the height of the wide flange section and 𝐵 is the width) ranging from 0.95 to 2.22 (where 𝑡𝑓 is the thickness of the flange) ranging from 6.30 to 40mm. To supplement the knowledge regarding the residual stress distributions of current material specifications and to widen the cross-sectional range of available distributions, five additional wide flange residual stress distribution measurements (i.e., HEA160, HEM500, IPE120, IPE200 and IPE360) are implemented for the sake of this study. These distributions have been precisely determined through destructive laboratory measurements (i.e., cutting method) that are thoroughly explained in this thesis. In the advent of new technology and software development, structural element simulation can be performed in a thorough and precise manner. With the aid continuum finite element analysis (CFEA), the influence of residual stresses on lateral buckling of columns under axial load will be investigated. Eight cross-sectional profiles (i.e., HEA160, HEB500, HEM300, HEM500, IPE120, IPE200, IPE 360 and IPE400) are investigated. The CFEA consider realistic residual stress distributions that have been conducted by RESSLab, EPFL. The ultimate compressive load of these profiles considering varying buckling lengths (𝜆̅𝑘 ranging from 0.49 to 1.93, where 𝜆̅𝑘 is the normalised buckling length) are determined and compared with available design specifications.

2021

Chargement

Gene-disease associations studies are performed in an increasing number since the creation of the HapMap Project. These studies are used to investigate regions or genes in the genome for which one has an indication or a belief that they can be associated with a particular disease. The aim is to identify the genes that cause the disease. The approach that is commonly used in such studies is the two-stage design method.

2011

Chargement

The research presented in this thesis addresses the design of gear drives for micro engineering applications, and was performed in collaboration with a watch manufacturer. Gears have long been found in many fields of mechanical engineering. Their use in watches satisfy specific constraints: small dimensions, little or no lubrication and unusual performance specifications. A literature review allows us to establish a catalogue of existing gear profiles, and a synthesis of profile analysis and generation methods. On the basis of this assessment, we define knowledge gaps which we propose to bridge in the present work by reaching the following objectives: 1. Characterize the behavior of existing gear profiles used in the watchmaking industry (nominal profiles, but also profiles affected by shape errors and axes misalignment errors); determine their kinematic and static performances, and their transmission efficiency. Use these results to compare various profiles on an objective and rigorous basis. 2. Formulate the equations necessary to calculate the tooth profiles using conjugate conditions differing from the tradition-al kinematic conditions ( i.e. imposing the transmission ratio) 3. Work out a design methodology for gear profiles relying on the results obtained while working on the first two objectives To reach those objectives, we develop a computer code allowing us to evaluate the performances of the profiles. The diversity of existing profiles led us to formulate a generic geometrical representation applicable to all profiles, while allowing us to use the same analysis code. The developed tool is then validated by simulating profiles, the behavior of which is known analytically. To calculate conjugate tooth profiles respecting a static criterion, we use the classical theory again, adding a new equation to it, which we derive from a balance of power. We present this equation for the three dimensional case, and the planar case. The resolution method for this equation, valid for static conjugated cams (i.e. a unique pair of teeth), must satisfy a supplementary condition that ensures that the imposed torque ratio leads to an average kinematic ratio compatible with the desired number of teeth. A numerical method was developed for the planar gears case that establishes the range of torque ratios satisfying the imposed average transmission ratio. The lower and upper bounds of the range of solutions are defined in terms of geometric and efficiency considerations, respectively. The proposed approach is illustrated and validated by some profiles computations. In parallel to those theoretical developments, we designed and built a test bench to characterize experimentally the performances of gear profiles, (altered or not by various shape or misalignment errors) under operating conditions similar to those prevailing in a watch. The last part of the thesis provides a critical discussion of these developments places them in a broader context and comments how they could be generalized in future research works.

EPFL2016

Chargement

Influence of residual stresses on the buckling capacity of axially loaded steel columns

Gabriele Falconi

2021

EPFL2016