MSE220 Lab Session #6
LAB: Charpy Impact Test
Charpy Impact Test Demonstration
A number of different standardized tests have been devised to measure the fracture toughness
values for structural materials. In the United States these standard test methods are developed by
ASTM. In brief, for each test type, the specimen (of specified geometry and size) contains a
preexisting defect, usually a sharp crack that has been introduced. The test apparatus loads the
specimen at a specified rate, and also measures load and crack displacement values. Most tests are
for metals, but some have also been developed for ceramics, polymers, and composites.
Two standardized tests, the Charpy and Izod, were designed and are still used to measure the
impact energy (sometimes also termed notch toughness). The Charpy V-notch (CVN) technique
is most commonly used in the United States.
The apparatus for making V-notch impact tests is illustrated schematically in Figure 1.
General Information on the Charpy Test
The deformability of a material can differs under different conditions of stress. For this reason,
knowledge of the deformation behavior of a material is an important criterion for evaluating and
selection a material. In numerous cases, it has been shown that cubic body centered (cbc)
materials can fail at low temperatures by brittle fracture.
A brittle material is incapable under certain circumstances of compensating for arising stress by
deforming. When a critical load is exceeded, dangerous, almost explosion-like brittle fractures
occur. With ductile materials, other specific phenomena arise. In a Charpy test, a notched
specimen whose two ends lie on a support is broken or bent by hammer impact and drawn
through the supports. The notched bar impact work is measured in Newton meters
(Nm) and represented in Joules (J). (1Nm = 1J)
The load is applied as an impact blow from a weighted pendulum hammer that is released from a
cocked position at a fixed height h. The specimen is positioned at the base as shown. Upon
release, a knife edge mounted on the pendulum strikes and fractures the specimen at the notch,
which acts as a point of stress concentration for this high-velocity impact blow. Any air friction
and bearing friction which may occur are negligible. The pendulum continues its swing, rising to
a maximum heightℎ′, which is lower than h. The energy absorption, computed from the
difference between h andℎ′, is a measure of the impact energy.
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Fig 1. Charpy impact test
In the pendulum-Impact tester, the hammer provides an impact of 25 Nm.
Objectives of this lab demo are as the following:
1)
2)
3)
Understand influence of the specimen material on the notched bar impact work
Understand influence of the notch shape on the notched bar impact work
Influence of the notch angle on the notched bar impact work
To be prepared for the experiments and able to answer the questions it is desirable to read
section 8.6 – Fracture Toughness testing (Chapter 6) of the text book. (Material Science and
Engineering; an Introduction – Callister and Rethwisch)
Here are the six specimens in three categories to compare the influences of shape, material and
angle of notched bar to fulfill this experiment:
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For objective #1
For objective #2
For objective #3
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To-do for the lab report:
1) Explain thoroughly the procedure to perform Charpy test for these specimens and how to
get comparable results
2) Answer the following questions thoroughly
A. Compare the impact energy absorption between brass and construction steel. Which
material exhibited higher toughness, and why do you think that is the case?
B. Analyze the results for the different notch shapes (U-shape vs. R5). How did the shape of
the notch influence the impact energy absorption?
C. Compare the impact energy absorption for the 45-degree notch versus the 90-degree
notch. How does the notch angle affect the toughness of the material?
D. Discuss the microstructural properties of brass and construction steel that might
contribute to their behavior in the Charpy test. How do these properties influence
toughness?
E. Explain how different notch shapes and angles affect the stress concentration at the notch
tip. How does this relate to the observed impact energy absorption?
F. Describe the failure modes observed in each specimen (e.g., brittle fracture vs. ductile
fracture). How did the material, notch shape, and notch angle influence these failure
modes?
G. If the tests were conducted at different temperatures, discuss how temperature influenced
the impact energy absorption. What trends did you observe?
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