1. Sustainable Foam Core Chair
Gerard Simon Prosper
Abstract— This report describes how to design a lightweight
chair which weighs less than 500g and able to support an 81kg
person without using any glues, tapes and fasteners. Stress
analysis was used to determine the concentration of stress and
to help to get rid of unnecessary parts of the chair and to help
to get rid of unnecessary parts of the chair. Truss structures,
gussets, and fillets are used to keep the weight down and rigidity
up. These are also added to remove concentrations of stress.
Final design is able to support an 81kg person without the legs
and back support failing.
I. INTRODUCTION
This project requires a formal understanding of the term
sustainability. Sustainability or sustainable is defined by
Oxford Dictionary as ’Conserving an ecological balance
by avoiding depletion of natural resources’. In order to
be sustainable, efficiency has to be fully utilized so that
minimum input is used to maximize the output. The process
from input to output should done in the right steps to prevent
use of excessive material and hence, keeping the weight of
the chair to a minimum weight.
The final design of the chair ( see Fig 1 ) is able to
support a weight of an 81kg person. Requirements for the
height of the chair is set up to be between 480mm to
530mm, the seat depth and width to be between 380mm
to 420mm, and the back height to be between 250mm
to 450mm. This paper is organized as follows, Section 2
describes the concept generation and evaluation, Section 3
describes 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. The
decision matrix contained considerations which were weight,
stability, simplicity, appearance and ease of assembly. The
first chair design was stable but it was not easy to build it
up and it will be heavy. The second chair design is much
easier to assemble, stable and weighs less. The third chair
design is stable and weighs less but not easy to assemble.
The second chair design was picked due to it highest mark
and 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 had
to be done. From that figure the base leg was changed from
a square shaped to a cross shaped leg due to a it being more
stable in this circumstance ( see Fig. 5 ). In order to get
the precise results of the stress concentration acting on the
chair, stress analysis was done by Autodesk Inventor. This
Fig. 1. Final Design
TABLE I
PUGH CHART
Criteria Design 1 Design 2 Design 3
Weight - 1 1
Stability 1 1 1
Simplicity - 1 -
Appearance 1 1 -
Ease of Assembly - 1 -
Total 3 5 2
program provides assistance to identify stress concentration
and the results showed that there were no significant failure
when it was being tested ( see Fig. 6 ). This also included
the rear end of the chair. Due to the simplicity of the design
and the connection between the 2 legs being rigid , it was
able to support the person weighing 81kg.
IV. EXPERIMENTAL RESULTS
The chair was able to support an 81kg person and no parts
failed or crashed when it was being tested. The weight of
the chair was 0.397kg which met the requirement, and the
3. Fig. 6. Stress Analysis
legs were stable enough. However the initial back support
was changed because it easily failed when someone leaned
its back. Improvement was made when an extra support was
added to the back support to ensure that it did not fail when
it was leaned upon. In order to make the chair lighter, holes
can be cut at specific places in the legs and the edges of the
seat can be trimmed.
V. DISCUSSION
In order to make the chair light, we used the least amount
of pieces that was possible. For this chair, only four foam
baords were used to cut out the necessary parts. Even though
only two pieces were used for the legs of the chair, it
managed to support of the weight of 81kg person. By doing
this, the weight was substantially reduced and it was not
necessary to cut out smaller pieces from other parts of the
chair.
VI. CONCLUSIONS
The chair design was able to meet the functional require-
ments and it exceeded the weight requirement being less than
400 grams. Being a simple yet stable chair, it was able to
support an 81kg person without failure on the legs, seat and
back support.
VII. APPENDIX
1) Engineering drawings with dimensioning
2) Bill of materials
