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The purpose of this lab was to learn how to create accurate testing environments to precisely test the strength of (a) specific material(s)/structure(s). As well as how to collect and use the data from those tests. In this case being 6 wooden truss structures built in class out of matchsticks.
I started out by building 6 trusses of my own design, with the goal of making them as consistent as possible for more accurate testing results.
Next I supported each end of the structures as symmetrically as possible by placing them between two level surfaces, with a gap in between them.
To measure any deflection in the bridge under load, we first need to find our 'zero'. To do this, before any load has been placed on the truss, we will use a height indicator and place the tip as close to the top or bottom as possible, then set the device to zero. Using this as a reference, we can measure any difference in height which would be our deflection.
(Weights hanging off one of the trusses)
(Me placing weights on one of my trusses)
Now we can start hanging weights off our structure.
(Broken trusses)
(Simple glue bond failure)
(You can see the breaking point of this truss towards the middle of the lower beam)
As you can see, eventually the trusses would break:
Data collected from the experiment:
Raw data:
The raw data represents the data directly collected from the testing. The grams next to each sample number represent the max weight each truss could handle before failing. The mm represents the current millimeter deflection measurement before the truss failed. The number of increments represents the number of times we increased the weight on the truss plus 500 grams.
Graphs:
This graph shows the average max number of grams the truss design could hold.
Each bar represents the individual trusses max weight.
The orange line represents the number of times we incremented the weight for each truss.
This bar graph shows the Average max amount of weight the truss could hold (left bar), as well as the average number of times we incremented the weight 500 grams (right bar).
Notes:
For each and every truss in the experiment, I made observations, and wrote them down as further data that can be utilized in the experiment.
Free Body Diagram:
I also included a free body diagram of the truss. This shows how the forces in the truss are reacting to the load.
Analysis:
Going into this, the only theory I had was that the advanced construction would hold some kind of weight that would be more than the simple construction completed the week before. The results showed us that the average max weight an advanced construction could hold before it failed was about 3000 grams, compared to the simple construction which was about 270 grams. This was no surprise as we utilized triangles, and the benefits of trusses, without even adding a significant amount of weight to the structure as a whole.
Conclusion:
To have stronger, more consistent trusses, as you can see from the notes, there is a direct correlation to how well the cuts on the ends of the individual members were done, and what their max breaking point was. So, to have better results, I would give the glue more time to dry, and only apply what glue is needed. But above all, cut the ends of each member at the appropriate angle so that they are flush when glued together.
Though some failed prematurely, overall, I would say we have a decent idea what the average weight one of these structures can hold, and a general idea on how to improve them in the future.
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