Balsawood Structure Design Essay Research Paper 1

Balsawood Structure Design Essay, Research Paper

1. Introduction:

This report is the first stage of the design, construction and testing

of a balsa wood structure. In April, the design will be tested against

classmates. designs, where the design with the highest load/weight ratio

wins. The information gained from this report will be used in the

construction of the structure. The report is composed of two sections.

The first is an evaluation of material properties of balsa, glues and

different joint configurations. The second section consists of a

discussion on a preliminary design that is based on conclusions drawn

from the testing section.

Common material tests of tension, compression and bending were

performed and analyzed. The qualities of three different adhesives were

tested and evaluated, and finally, three different joint configurations

were tested. Illustrations of each test setup are included. Whenever

possible, qualitative results will be given as opposed to strictly

quantitative values. A qualitative result is much more useful in

general design decisions. Experimental results from the testing stage

combined with experiences is working with the materials offered clues

for the preliminary design.

The design section mixes both practical and experimental experience

together to present the best possible solution for the structure. It

also offers additional insights that were not considered in the initial

material testing procedure. The design presented in the this section,

is likely to be similar the final model, however modifications may be

needed for the final design that were unforeseeable at the time of this

report.

This report generally functions as a guide for the construction stage of

the project. Its role is to provide useful information and a basis for

the final design. Before the final design is tested, prototypes will be

constructed to test the principles discussed in this report. The goal

of this report is to combine the results from testing and experience to

produce a working preliminary design.

2. Material Testing

All standard testing was performed on the Applied Test System located in

room XXXXXXXXXXXXXX. The goal of this section is to determine the

material strengths of balsa, and how balsa responds to different

loading. Before testing, the basic structure of balsa needs to be

considered. Wood grain is composed of bundles of thin tubular

components or fibers which are naturally formed together. When loaded

parallel to this grain, the fibers exhibit the greatest strength. When

loaded perpendicular to the grain, the fibers pull apart easily, and the

material exhibits the least strength.

Generally, for design considerations, the weakest orientation should be

tested. However, testing procedure called for testing of the material

in the greatest strength orientations; torsion and compression, parallel

to the grain, and bending with the shear forces perpendicular to the

grain. Testing the materials for their “best direction” characteristics

can produce results that are not representative of real behavior. To

expect uniform stress distributions and to predict the exact locations

of stresses prior to testing prototypes is generally not a good idea.

However the values obtained from these tests can give a general idea of

where the structure may fail, and will display basic properties of the

material.

Tension Test

In tension testing, it is important to have samples shaped like the one

in Figure 1, or the material may break at the ends where the clamps are

applied to the material. Failure was defined to occur when the specimen

broke in the center area, and not near the clamps. The machine records

the maximum load applied to the specimen and the cross sectional area

was taken of the central area prior to testing. These two values are

used to compute the maximum stress the material can withstand before

failure.

Figure 1: Sample Torsion Specimen

In general, the material failed at the spaces with the smallest

cross-sectional areas, where imprecisions in cutting took place or the

material was simply weaker. It took many tests to get breaks that

occurred in the center section instead of at the ends, perhaps with an

even smaller center section this would have been easier. It should also

be noted that two different batches of balsa were tested and there was a

notable discrepancy between the results.

Table 1: Tension Tests Results

Specimen # Strength (psi)

1 1154

2 1316

3 1830

4 1889

Specimens 3 and 4 were from a different batch of balsa and were thicker

pieces in general, although thickness should have had no effect on

maximum stress, it is assumed that the second batch simply has a

greater density than the f

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