Progress Report Week 2

8/10/2019 Progress Report Week 2

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Noel Le CE 221LArevik Sargsyan Date assigned: October 1stS asha Kornilova Date completed: October 9thCesar Flores

Weekly Progress Report #2

Objective

The purpose of this weeks lab was to determine an unknown specimens material

properties by putting the specimen through series of loading and unloading conditions,

and ob taining the specimens strain at the applied stress.

Preparation: measurements

At the start of the experiment, we measured the diameter, height and perpendicularcross sectional area of the cylinder in order to be able to observe the changes once

force was applied. The measurements were taken using a caliper device, as shown in

Figure 4. The measurements were taken three times, as shown in Table 1, to ensure

accuracy. In Table 2 we calculated the average diameter at 2.87 in, height of 5.68 in,

and a cross sectional area of 6.46 in^2. Standard deviation was used to compare the

accuracy of the measurements.

Preparation: set up

In order to prepare the specimen for loading we placed it onto a rubber plate prior to

loading it into the device. This diminished the specimen s bottom surface irregularities

and ensured that the applied vertical force applied evenly onto the cylindrical surface.

We moved the specimen upwards until it touched the metal plate, as shown in Figure 5.

The meter read 2 lbs. force being applied onto the object. We labeled that as our initial

loading, zeroed the displacement, and began Trial 1.


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Trial 1.

We gradually increased the force applied and read the vertical displacement with a

meter and measured the diameter at the center of the block. Once the specimen was

approximately half its original volume, we began to decrease the loading. It is important

to note that the viscosity of the object may have affected the discrepancy in the resulting

diameters. The initial diameter measurement was always the outlier in comparison to

the other two measurements. The professor adjusted the specimen during its unloading

stage because it was no longer centered. Once the loading reached 10 lbs., the cylinder

lost contact with the metal plate, and we took our final reading of deformation. Therewere total of 7 readings in Trial 1, and it served as a testing trial due to so many errors.

Trial 2.

Trial 2 was performed similarly to Trial 1 and because of the students exp erience in the

previous trial, Trial 2 produced higher accuracy results. Similarly to the first trial, we

zeroed the machine at 2 lbs. force as an initial reading. We gradually increased the

force to 20 lbs. We then unloaded the specimen without losing contact, reaching 0 lbs.

Calculation

After organizing the data in a spreadsheet in Table 4, we calculated stress and strain.

Stress was calculated using given loading force divided by the calculated cross

sectional area. The strain was calculated by dividing the vertical deformation by the

original height.

Analysis

Figure 1 illustrates the stress vs. strain relationship of Trial 1 during loading and

unloading. The graph was manipulated to connect the lines from the initial to the final,


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Solution: to mark the spot on the cylinder with a pen where the measurements should

be taken, to assign measurement reading to one group member rather than trading

within the group to gain experience. In order to reduce the effect of viscosity, the group

member must wait a full minute after the force has been applied before they take a

measurement

4. Error: the cylinder was pressed against the edge of the rubber plate, which may

cause a resistance of bulging in that area.

Solution: similarly to solution to error number 3, if the specimen has a marking of the

spot in which the group member must take the measurement it will prevent unclearreadings.

Conclusion

The purpose of this weeks lab was to determine the properties of an unknown

specimen by subjecting it to loading and unloading conditions and observing the

materials reaction through stress vs. strain curves. We found that the material exerted a

higher viscosity property due to the changing diameter readings from earlier to a later

time. The specimen deformed at a varying rate under the increasing stress and

therefore it is a nonlinear material. Because there was no permanent deformation after

the specimen has undergone loading and unloading conditions, the specimen is an

elastic material. Besides the experience of gathering data, this week taught our group

about the value of experience to produce better results, as illustrated by the difference

in Trial 1 and 2.

Documents

Progress Report Week 2