Sustainable Foam Core Chair

Gerard Simon Prosper

Abstract— This report describes how to design a lightweightchair which weighs less than 500g and able to support an 81kgperson without using any glues, tapes and fasteners. Stressanalysis was used to determine the concentration of stress andto help to get rid of unnecessary parts of the chair and to helpto get rid of unnecessary parts of the chair. Truss structures,gussets, and fillets are used to keep the weight down and rigidityup. These are also added to remove concentrations of stress.Final design is able to support an 81kg person without the legsand back support failing.

I. INTRODUCTION

This project requires a formal understanding of the termsustainability. Sustainability or sustainable is defined byOxford Dictionary as ’Conserving an ecological balanceby avoiding depletion of natural resources’. In order tobe sustainable, efficiency has to be fully utilized so thatminimum input is used to maximize the output. The processfrom input to output should done in the right steps to preventuse of excessive material and hence, keeping the weight ofthe chair to a minimum weight.

The final design of the chair ( see Fig 1 ) is able tosupport a weight of an 81kg person. Requirements for theheight of the chair is set up to be between 480mm to530mm, the seat depth and width to be between 380mmto 420mm, and the back height to be between 250mmto 450mm. This paper is organized as follows, Section 2describes the concept generation and evaluation, Section 3describes analysis, Section 4 describes experimental results,Section 5 is a discussion, and Section 6 is a conclusion.

II. CONCEPT GENERATION AND EVALUATION

Three designs ( see Fig.2, Fig.3, Fig.4 ) and Pugh chart (Table 1 ) were used to determine the most suitable chair. Thedecision matrix contained considerations which were weight,stability, simplicity, appearance and ease of assembly. Thefirst chair design was stable but it was not easy to build itup and it will be heavy. The second chair design is mucheasier to assemble, stable and weighs less. The third chairdesign is stable and weighs less but not easy to assemble.The second chair design was picked due to it highest markand it also contained the most stable leg and back support,which was able to support an 81kg person.

III. ANALYSIS

Before starting to build the chair , the lines of forces hadto be done. From that figure the base leg was changed froma square shaped to a cross shaped leg due to a it being morestable in this circumstance ( see Fig. 5 ). In order to getthe precise results of the stress concentration acting on thechair, stress analysis was done by Autodesk Inventor. This

Fig. 1. Final Design

TABLE IPUGH CHART

Criteria Design 1 Design 2 Design 3Weight - 1 1Stability 1 1 1Simplicity - 1 -Appearance 1 1 -Ease of Assembly - 1 -Total 3 5 2

program provides assistance to identify stress concentrationand the results showed that there were no significant failurewhen it was being tested ( see Fig. 6 ). This also includedthe rear end of the chair. Due to the simplicity of the designand the connection between the 2 legs being rigid , it wasable to support the person weighing 81kg.

IV. EXPERIMENTAL RESULTS

The chair was able to support an 81kg person and no partsfailed or crashed when it was being tested. The weight ofthe chair was 0.397kg which met the requirement, and the

Fig. 2. Design 1

Fig. 3. Design 2

Fig. 4. Design 3

Fig. 5. Cross Shaped Leg

Fig. 6. Stress Analysis

legs were stable enough. However the initial back supportwas changed because it easily failed when someone leanedits back. Improvement was made when an extra support wasadded to the back support to ensure that it did not fail whenit was leaned upon. In order to make the chair lighter, holescan be cut at specific places in the legs and the edges of theseat can be trimmed.

V. DISCUSSION

In order to make the chair light, we used the least amountof pieces that was possible. For this chair, only four foambaords were used to cut out the necessary parts. Even thoughonly two pieces were used for the legs of the chair, itmanaged to support of the weight of 81kg person. By doingthis, the weight was substantially reduced and it was notnecessary to cut out smaller pieces from other parts of thechair.

VI. CONCLUSIONS

The chair design was able to meet the functional require-ments and it exceeded the weight requirement being less than400 grams. Being a simple yet stable chair, it was able tosupport an 81kg person without failure on the legs, seat andback support.

VII. APPENDIX

1) Engineering drawings with dimensioning2) Bill of materials