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Title Product development of a chair and experimental testing of wood
Translated title Produktudvikling af en stol og experimentel testing af trae
Author Sorensen, Kasper (Copenhagen University College of Engineering, IHK)
Supervisor Schreiber, Mads Peter (Copenhagen University College of Engineering, IHK)
Institution Ingeniørhøjskolen i København, IHK, DK-2750 Ballerup, Denmark
Thesis level Bachelor thesis
Education Diplomingeniør, Maskiningeniør
Education Bachelor of Mechanical Engineering
Publication date 2013-12
Abstract Empirisk testing af traepaneler gennemfoert for at udlede mekaniske egenskaber. Disse egenskaber blev anvendt i CAD analyse af modeller og i statiske FEA. En model valgt over de andre udfra et design brief og denne model blev skaeret paa en 3 akse CNC maskine og derefter samlet.
Abstract In order to successfully design a chair to be manufactured from a CNC-machine, it was a pre-requisite to know the mechanical properties of available materials, which were in consideration for usage. The data was not made available by the suppliers; therefore, it was needed to conduct tests in order to determine the mechanical properties of the materials. These properties was used to ensure the chair was structurally rigid, thus safe to use, and not wasting excess material.

The data was gathered empirically and the testing followed the general principles of the EN310 standard for a 3 point bending test set-up. The materials that were investigated were plywood and MDF, chosen due to their price tags and expected difference in properties. Each material was tested from both a 11mm board and a 15mm board, with four different widths and four samples of each width, totalled at 64 tests. From the test results yielded, it was possible to determine the modulus of elasticity and the modulus of rupture through standardized formulas, which were applying classic mechanics.

For the tested plywood the results varied quite a lot, and in general the 11mm samples were found to bend much than the thicker samples, which would start to creep. The average MOE was found to be 6770 MPa and 3786 MPa for the 11mm and 15mm plywood respectively. The MDF behaved more predictable with fewer anomalies and the results for those were 3799 MPa and 2243 MPa for the 11mm and 15mm respectively. These values were averaged once again and a safety factor of 3 was chosen as an appropriate measure against these variations.

A comparison in-between the different ways of connecting the materials were applied to understand the ways of failure, which would occur and at which stress level. The results from this were merely applied as guidelines, rather than numerical values. However, the results corresponded well to the theory, and the tenon-mortise joint was found to be the strongest of the four fasteners tested and looked into.

Ergonomics and anthropometrics considerations and studies were discovered and applied to have references to dimension the final model more appropriately in accordance with the selected user.

The selected material’s properties were not used as input in development of the initial three CAD models, but rather the SolidWorks material “Balsa”. This was done for three reasons, one being that it would result in completely identical studies and the second reason being, that the results from the testing were being interpreted in parallel of the CAD studies. Finally, it was the only option from the solidworks library with sufficient information.

Three cad models with their own distinct features were developed, so that their individual performance could be evaluated and compared to another through finite element analyses and against the initial design brief. The designs were evaluated for their performance to handle a uniform load applied to the seat and backrest in the CAD software. The extent of completion of the design brief was assessed personally. This combined made for the initial selection process, and a single model was chosen to be developed further.

With a design chosen superior to the two other options, the results for the plywood wood panel was chosen as a material, so that critical component can be indentified and modelled more accurately, ensuring a durable and efficient design. This material was quite stronger than Balsa, and allowed for a slimmer design, and thus cheaper and arguably prettier as well.

In the further development process, a new problem was identified, which was the lateral force the chair could support. With this found insufficient, new iterations were made and the reinforcement bars were added to the chair. The general dimensioning was also altered due to ergonomics and anthropometrics.
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Admin Creation date: 2013-12-17    Update date: 2014-01-10    Source: ihk    ID: ihk-21628291    Original MXD