Fatigue failure experiment - Experiment first PDF

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It is the first experiment on MAE 101 course....

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Fatigue failure

MAE 101 09/23/2021 Roja Adhikari

Abstract: This experiment helps to understand the fatigue failure with the help of paper clips. The fatigue properties of materials will vary with the material quality, material source, types of stress, and duration of stress. Paper clips are usually made from cheap steel which has little strength and variability in quality is not important. Some paper clips have serrations that will accelerate failure as they provide locations for the crack to start. In the experiment, we can experience fatigue by comparing twenty different paper clips and can develop the relationship between metal failure and the factors behind that. Introduction: The purpose of this experiment is to understand the fatigue failure that occurs in our daily life by the use of paper clips. Fatigue failure occurs when the material is loaded and unloaded repeatedly. Each paper is bent repeatedly in cycles until they brake. The number of cycles that it takes the paper clip to break is recorded and illustrated with the help of a bar graph and histogram. The graph is also analyzed to determine why the result is not the same in every case of the paper clip. There are many factors that occur which cause fatigue failure in the paper clip because of which it breaks.

Theory: The purpose of this experiment is to understand the fatigue failure that occurs in our daily life by the use of paper clips. Fatigue failure occurs when the material is loaded and unloaded repeatedly. Each paper is bent repeatedly in cycles until they brake. The number of cycles that it takes the paper clip to break is recorded and illustrated with the help of a bar graph and histogram. The graph is also analyzed to determine why the result is not the same in every case of the paper clip. There are many factors that occur which cause fatigue failure in the paper clip because of which it breaks. When the materials are loaded and unloaded, they become weak, and they become unable to carry loads like they use to do before. This kind of failure is called fatigue failure. A simple example of this failure is the bending paper clip. A metal paperclip can be bent past its yield points but the repeated bending in the same section of wire will cause the material to fail and break. The stress at which material breaks is a measure of strength. Experimental Procedure and setup: Apparatus: Twenty paper clips 1) At first, we got twenty paper clips and straighten them fully. 2) Then we had selected the point which was not already bent as an experimental point. We started bending that point left and right or back and forth gently and slowly to approximately 30 degrees in both directions 3) We started bending that point left, right, and back and forth. It was done gently and slowly to approximately 30 degrees in both directions.

4) This process was repeated until the paper clip broke. 5) The complete period of the recurring motions from starting +30 to -30 degrees was considered as a complete cycle. 6) Steps 2-5 were repeated for the remaining 19 paper clips. 7) Then we rearranged the data in the table which shows the frequency of pins that broke and plotted in the histogram. Results: The results are shown with the help of bar graph and histogram. Chart 1 It is a table showing no. of cycle when different clips are twisted back and forth.

Clip 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

No. of Cycles 9 10 14 12 13 14 13 11 11 15 14 9 9 9 10 9 12 11

19 20

13 13

No.of Cycles 16 14 12 10 8 6 4 2 0

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3

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5

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7

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9

10 11 12 13 14 15 16 17 18 19 20

Graph showing no. of cycle vs clips

Chart 2 Number of cycles 9 10 11 12 13 14 15

Number of Clips 5 2 3 2 4 3 1

Histogram 6 5 4 3 2 1 0

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10

11

12

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14

15

Histogram showing no. of pins vs no. of cycles Discussion: Bending a wire back and forth to break is a great choice of an example of fatigue failure. It is an example of repeatedly exceeding yield stress and repeated permanent deformation in a ductile material. When making a structure or device out of ductile or malleable materials the designer should almost always keep cyclic stresses lower than the yield stress. Breaking this design rule usually results in a uselessly short lifespan. In this experiment, we used a simple object paper clip to understand the concept of fatigue. We know that the constant use of material causes fatigue. When we constantly bent material over and over it wore out and fails because of fatigue. By the data we received by counting the number of cycles it took to break a clip, we analyzed that most of the pins broke between 9 to 14 cycles. There is one break in 15 cycles as well. This might have happened because clips do not have the same diameter and the strength of an object is directly proportional to the thickness compare to another object made of similar material. Also, there is an experimental error since we did not rotate the paper pin in a perfectly

30-degree position. Also, we are not precise at applying force, we might have applied some extra force which detaches the clip from the weaker point. Conclusion: The purpose of this experiment is to understand the fatigue failure that occurs in our daily life by the use of paper clips. So, we should check for the fatigue failure in every possible machine to avoid any machine failure. Thus, we made a clear understanding about fatigue failure with the help of this experiment. References: Internet, book, handouts...