Реферат: Balsawood Structure Design Essay Research Paper 1

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 first one, or perhaps that it had not been

affected by air humidity as much as the first batch. (See the design

concepts section for more discussion of moisture content in the

specimens.)

Compression

Compression testing was also performed parallel to the wood?s grain

(See Figure 2). The specimen used must be small enough to fail under

compression instead of buckling. For analysis of compression tests,

failure was defined as occurring when little or no change in load caused