Assessment 5
Fall
2020
MET 180
Structure and Properties of Materials
Assignment #5
Impact Testing: Influence of Notch Shape on the Notched Bar Impact Work
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1. Introduction
In this experiment, students will perform Impact Toughness Testing using impact tester equipment. They will find out how the Notch Shape will influence notched bar impact work. They will also learn how the force and stress distribution will propagate inside the specimen during the hammer impact.
2. Objectives
· Performing Charpy impact test using the
Pendulum Impact Tester
to measure the impact toughness of materials.
· It is to be determined in this experiment how different notch shapes influence the notched bar impact work and therefore also the notched bar impact strength.
3. Equipment/Components/Software:
Equipment
Specimen
GUNT- R5 specimen
Instrument
Vernier Caliper
4. Theory
Ao
:Cross-sectional Area of the specimens in the Notch Root in cm2
Ao = a x b
5. Experimental Procedure
Pendulum Impact Tester will be used to measure the impact toughness properties of test specimens (Figure 1).
Figure 1. Pendulum Impact Tester.
Figure 2 illustrates in a diagram how the specimen is mounted and how the hammer impacts on the specimen in the support.
(a)
(b)
Figure 2. (a) Top view of notched bar specimen (b) Unit base with support and specimen
The task of the trailing pointer is to indicate the energy expended for the impact on a scale (Fig. 3). When the hammer swings through the lowest possible point (zero point), the trailing pointer is carried with it.
· Pos. 1: Position of the trailing pointer before the release of the hammer.
· Pos. 2: Attained position of the trailing pointer after the hammer has swung. The energy absorbed by the specimen can then be read out directly.
Figure 3. Trailing pointer and scale
In order to record the influence of the notch shape alone on the notched bar impact work to be expended, specimens must be selected which are made from the same material and have the same remaining cross-section in the notch root.
The following specimens are selected from the specimen range for this experiment:
· GUNT R5 specimen
· ISO-U specimen
Both specimens are provided in the material Steel 11SMn30.
Experimental procedure to break the specimens at room temperature with the pendulum impact tester.
1. Lock the hammer
· Lift the hammer lock upwards and move the hammer against the direction of impact as far as the stop of the axis until the safety hook of the lower hand lever locks into place.
· Let go of the hammer lock and ensure that the hammer lock holds the hammer in place.
2. Set the trailing pointer to Pos.1 (see Fig. 3).
3. Insert the notch specimen into the support. The specimen is positioned with the notch facing the impact and affixed to the mandrel.
4. Release the hammer
· The lower hand lever must remain pushed in during the experiment, so that the swinging pendulum does not come into contact with the brake.
· Lift the hammer lock upwards and push the lower hand lever to release the pendulum.
5. Read the value shown by the trailing pointer for the expended notched bar impact work on the scale of the unit and enter this into the table on the worksheet.
6. Experimental Work
Watch the video link below to observe how Charpy impact test is being performed. Answer the experimental questions accordingly. (50 Pts: Each 10 pts)
Charpy Impact Test:
(Write down your answers in blue color)
Question 1:
What does the test engineer do to make sure the Pendulum impact tester measures toughness accurately and friction is correctly compensated?
Question 2:
What type of materials are suitable for low temperature impact toughness applications and why?
Question 3:
What type of materials show ductile to brittle transition in the impact energy versus temperature graphical test results?
Question 4:
Main principal of the impact toughness measurement:
Initial potential energy of the pendulum at the start position: Ei = m g H
Final potential energy of the pendulum after the impact: Ef = m g h
What is the notch impact energy (KV) in terms of Ei and Ef ?
Question 5:
How does the test engineer place the specimen on a support in the lower part of the machine (Notch is facing the hammer or Notch is not facing the hammer) and which device does he use to adjust the specimen position?
7. Report
Charpy Impact tests are carried out for two specimens of which the material type and specimen dimensions are provided below.
Answer the questions in tasks 1, 2, 3 and 4:
(Use blue color in your answers)
Task 1: (10 points)
What is the notch root cross sectional area A0 in cm2 for the specimens?
Task 2: (15 points)
Impact Test results for two specimens are provided in Table 1.
Notched Bar Impact Work Wnbi (J) results are tabulated in the second column of Table 1.
Calculate Notched Bar Impact Strength Snbi (Nm/cm2) for each specimen.
Table 1
Specimen
Notched Bar
Impact Work
Wnbi (Nm)
Impact
Strength Snbi (Nm/cm2)
GUNT- R5 specimen
6.4
ISO-U specimen
9.6
Task 3: (10 points)
It can be concluded that in this experiment, the same materials with different notch shapes deliver scattered results. Compare the notched bar impact work and impact strengths of specimens with each other:
Task 4: (15 points)
Plot Notched Bar Impact Work,
Wnbi and Notched Bar Impact Strength Snbi versus materials column diagrams. Show the experimental results and specimen materials on the diagram. Label your chart, x and y axes. Provide dimension (unit) for the y-axis.
Use MS Excel – 2D Column chart to plot your diagram and copy your chart here.
8. Analysis
Question 1: (Bonus: 5 points: each 2.5 pts)
A steel wire is loaded with 1000 kg as shown in the figure.
Considering the following mechanical properties of the wire:
· Initial diameter of the wire,
do
is 42 mm
· Initial length of the wire
lo is 8000 mm
· Young’s Modulus of steel alloy,
E
is 190 GPa
· Yield Strength,
Y
of steel alloy is 280 MPa.
a) What is the engineering stress,
σ
, on the wire?
b) Calculate the final length,
lfinal
of the wire
References
Callister, Jr., W. D., & Rethwisch, D. G. (2015). Materials Science and Engineering (Ninth ed.). Wiley.
Charpy Impact Test. (2020, 07 18). Retrieved from YouTube: https://www.youtube.com/watch?v=tpGhqQvftAo
Copyright © American College of the Middle East. 2020. Page 1 of 11
Copyright © American College of the Middle East. 2020. Page 11 of 11