To:
Dr. Michael Jenkins
Director, Test Engineering
From: Atish Maman
Junior Test Engineer
Re:
Impact Testing
Summary:
This memo is a report on the Charpy V-notch impact test. This experiment tested 6061T6 Aluminum and A36 Steel using a Charpy testing machine with a 32-in long pendulum and
60-lb impact head. Tests were performed with a variable in temperature for each material using
water baths or acetone solutions to change temperatures. The temperatures tested against were:
200-212 °F for boiling water, 100-120 °F for warm water, 65-75 °F for room temperature water,
32-38 °F for ice water, 0-15 °F for salted ice water, -45 to -55 °F for Acetone with a small
amount of dry ice, and -90 to -109 °F for Acetone with a large amount of dry ice. The results
from the lab showcased a drastic change in impact energy for the A36 steel while the 6061-T6
Aluminum had an unchanged impact energy when compared across the different temperatures.
Introduction:
The Charpy impact test is designed to test for ductility of a material across different
temperatures as well as fracture toughness. This test is performed following the ASTM
International E23-18 Standard. The test applies a load in a swift motion which will cause the
material to fracture. The variation in temperature will affect the pattern of fracture and can vary
between completely brittle and completely ductile. The test is conducted across multiple
temperatures to study the different deformations that can happen when applied in engineering
situations. This assists in finding the material best suited for environments of application as well
as loads and stress in real world applications.
Procedure:
Before testing the materials, roles within a lab group were designated. After group
designation, five water baths were created. The boiling water bath was prepared by boiling water
to around 200 °F; the warm water bath was created by pouring some boiling water into room
temperature water to have it around 100 °F. The room temperature water bath was kept as is to
make its own water bath (65 °F). Ice was added to water to create a water bath around 32 °F; and
salt was added to a separate ice-water bath to make a colder water bath around 0 °F. An acetone
bath was created with a small amount of dry ice measuring about -50 °F; another bath was
created with more dry ice mixed in with a temperature of about -100 °F (See Appendix Figures
1&2).
Aluminum test specimens were placed in each water bath for five minutes to allow for
equilibrium in heat transfer and the temperature is recorded. Each one is loaded onto the Charpy
test machine by the test specimen loader. The pendulum is cocked and released, impacting the
test specimen (See Appendix Figures 3&4). The pendulum is locked in the rest position and the
fractured pieces of the specimen are retrieved. The impact energy is recorded from the dial on
the testing apparatus. The same process was performed with the Steel specimens.
Results and Discussion:
The impact energy of both the Aluminum and Steel specimens were graphed as a
function of temperature. It was found that the impact energy of Aluminum stayed generally the
same as temperature varied. Due to a global pandemic, test results from a previous semester were
used. The highest impact energy for Aluminum was 27.0 lbf-ft, this was the specimen recorded
with a temperature of -53.0 °F. From the NBS Monograph 63, the impact energy at a temperature
of 195 K was 16 lbf-ft. This is similar to lab findings and could be representative of Aluminum’s
small variation of impact energy with temperature changes. The lowest impact energy was 19.0
lbf-ft at a temperature of 67.0 °F. When compared to the values across multiple tests spanning 3
years, the lower temperatures resulted in a higher impact energy and the higher temperatures
resulted in a lower impact energy. The impact energies remained roughly the same and the test
specimens had small, if any, shear lips denoting a brittle fracture across the temperatures tested.
This is most likely due to the FCC structure in Aluminum.
Steel had more defined variation in impact energy compared to Aluminum. The highest
impact energy of 145 lbf-ft was recorded at a temperature of 124 °F. At higher temperatures,
shear lips on the test specimens were more prominent and denoted a ductile fracture. The lowest
impact energy of 4 lbf-ft was recorded at a temperature of -100 °F. At lower temperatures, the
specimens resembled the Aluminum specimens with small shear lips and brittle fractures. This
change in fracture is due to A36 Steel having a BCC structure. Referencing the NBS Monograph
63 showed that at a similar low temperature of 195 K, the average impact energy was 24 lbf-ft.
This is larger than the experimental values obtained from the lab and could have been due to
testing errors. When compared with the collection of previous values, higher impact energies
occurred when temperature was highest and lower impact energies were present with lower
temperatures.
When graphed, Steel had an extremely prominent “S” shape with a clearly defined
transition temperature while Aluminum resembled a linear function (See Appendix Figure 5).
The Aluminum tests specimens had a low ductility across all the temperatures tested whereas
Steel was brittle at lower temperatures and almost 100% ductile at high temperatures.
Recommendations:
The experiment, although not directly performed, was effective in showcasing
temperature effects on the ductility of metals. This experiment tends to have inconsistencies and
that may be due entirely to human error. This can occur with students not being quick or careful
enough when loading the test specimen in the pendulum arm or not reading the temperature and
impact energy dial correctly. This could be remedied with a single group of laboratory test
engineers. However, this subtracts from the overall experience of performing the tests directly.
Appendix:
Figure 1: Test Specimens in High Temperature Baths
Figure 2: Test Specimens in Low Temperature Baths
Figure 2: Test Specimens in Low Temperature Baths
Figure 3: Test Specimen placed on Charpy Test Machine
Figure 4: Charpy Test Machine in Cocked Position
IMPACT ENERGY (lbf-ft)
250
200
Steel
150
100
50
-200
-100
0
0
100
TEMPERATURE (°F)
Aluminum
200
300
Figure 5: Graph of Impact Energy (lbf-ft) Vs. Temperature (°F)
ME 32
ENGINEERING MATERIALS LABORATORY
Spring 2020 (AY 2019-20)
Experiment #3: Impact Testing
Introduction and Background
Static or quasi-static properties and performance of materials are very much a function of
the processing of the material (heat treatments, cold working, etc.) in addition to design
and service factors such as stress raisers and cracks.
The behaviour of materials is also dependent on the rate at which the force is applied.
For example, a polycarbonate tensile specimen which might show a relatively low yield
point but up to 200% elongation at a low loading rate may show a much greater yield
point but at only 5% elongation at an order of magnitude faster loading rate. Low carbon
steels, such as 1018, may show considerable increases in yield strength and work
hardening at high strain rates.
In quasi-static tests, the amount of energy required to deform a material is determined
from the area under the tensile stress-strain curve and is know as the modulus of
toughness. Under dynamic loading, stress-strain response is typically not recorded.
Instead, the transfer of energy from a device such as a drop weight or a swinging
specimen to the deforming or breaking specimen is equated to the "impact energy."
The Charpy V-notch impact test uses a standard Charpy impact machine to evaluate this
impact energy. The machine consists of a rigid specimen holder and a swinging
pendulum hammer for striking the impact blow to a V-notched specimen as shown in
Figs. 1 and 2.
Unfortunately, while the test, including machine and specimen geometry, has been
standardized, the test results do not provide definitive information about material
properties and thus are not directly applicable to design (as for example might be a yield
strength). However, the test is useful for comparing variations in the metallurgical
structure of materials and in determining environmental effects, such as temperature on
the dynamic response of the material.
One of the most dramatic results of Charpy V-notch impact tests is in the form of plots of
impact energy versus temperature in which sigmoidally-shaped curves (see Fig. 3) show
substantial decreases in some materials' abilities to absorb energy below a certain
transition temperature. This ductile to brittle transition is most apparent in materials with
BCC and HCP crystalline structures as for example in steels and titanium. A classic and
dramatic example of this ductile to brittle behaviour is the low carbon steel Victory ships
of WWII cracking in half under even the mild conditions of sitting at anchor in a harbor.
1
mass, m
h1
h2
IZOD
IMPACT ENERGY=mg(h1-h2)
CHARPY
V-NOTCH
Figure 1 Schematic of Charpy Impact Testing including Izod and Charpy V-notch specimens
IMPACT ENERGY
Figure 2 Charpy V-notch specimen configuration from ASTM Test Method E23 used in this lab exercise
Ductile
Brittle
Ductile/Brittle
Transition
TEMPERATURE
Figure 3 Schematic of plot of impact energy versus temperature showing sigmoidal curve
Materials with FCC structures (e.g., aluminum and copper) have many slip systems and
are more resistant to brittle fracture at low temperatures.
In this laboratory exercise the primary outcome will be plots of impact energy versus
temperature for two materials 6061-T6 aluminum (FCC) and 1018 or A36 steel (BCC).
Note the effects of temperature and material type on the levels and shapes of the curves.
2
Standard Test Methods
In this laboratory experiment, one standard test method is used and referred to as follows:
ASTM International. E23-18 Standard Test Methods for Notched Bar Impact Testing of Metallic
Materials.
West
Conshohocken,
PA;
ASTM
International,
2018.
doi: https://doiorg.hmlproxy.lib.csufresno.edu/10.1520/E0023-18
Equipment
Charpy V-notch test specimens of 6061-T6 aluminum and 1018 (hot rolled) or A36
steel
• Charpy testing machine with 32-in long pendulum arm and 60-lb impact head
• Type K thermocouple and digital readout unit
• Beakers of room-temperature water, warm water and boiling water
• Beakers of plain iced water
• Cryo-beakers of salted iced water and super cold liquids
•
Objective
The purpose of this exercise is to examine the effects of temperature on the material’s
notched, impact resistance using the standard Charpy V-notch impact test. The Charpy
V-notch impact is a mechanical test for determining qualitative results for material
properties and performance which are useful in engineering design, analysis of structures,
and materials development.
The experimental principle for the Charpy V-notch impact test is quite simple. A large
pendulum device delivers an impact loading to a test specimen containing a standard Vnotch. After the impact and fracture of the specimen, there will be a loss in the energy of
the pendulum as measured by its reduction in maximum height. For this impact testing
machine, the fracture energy is measured (in lbf-ft or N-m) using a calibrated needle and
dial combination located on the side of the machine. In the absence of other mechanical
losses, the decrease in the pendulum energy is equal to the fracture energy of the test
specimen.
Procedure
CAUTION: When using the Charpy testing machine, stand well clear of the swinging area of the
pendulum both when the arm is cocked and for some time after the arm is released for a test
while it is still swinging. Serious injury will result from a swinging pendulum arm.
For each material repeat the following steps
• Designate a person as the "operator" of the Charpy test machine: all other persons
must stand clear during testing
• Designate a person as the "monitor and recorder" of temperatures and impact energies
• Designate a person as the "test specimen loader" who will remove test specimens
from the liquid bath, quickly placing them on the test fixture of the Charpy testing
machine
• Designate a person as the "test specimen retriever" who will retrieve the broken
halves of the test specimens, will bind the halves together and will mark the test
temperature on each pair of specimen halves for later examination and inspection.
3
• Use the following procedure to conduct tests in the order shown after exposure to the
pre-conditions to give the approximate test temperatures indicated:
Boiling water (200-212°F)
Warm water (100-120°F)
Room temperature water (65 to 75°F)
Ice water (32 to 38°F)
Salted ice water (0 to 15°F)
Acetone with some dry ice (-45 to -55°F)
Acetone with much dry ice (-90 to -109°F)
• Place the thermocouple probe in the appropriate liquid bath being sure to allow both
the test specimens and the thermocouple to equilibrate for at least five minutes prior
to testing.
• Record the indicated temperature
• "Cock" the pendulum by raising it to lock it into the release mechanism and stand
clear while the pendulum is held in the "cocked" position.
• Using the tongs, quickly remove the test specimen from the bath and place it on the
test fixture with the notch opening facing away from the direction of the cocked
pendulum. The goal is to limit the total transfer time to five seconds for less.
• Stand clear
• Release the pendulum
• Secure the pendulum in its rest position (i.e., hanging vertically) and retrieve the
fractured specimen halves. Label the test specimen piece(s) according to the testing
temperature.
• Record the impact energy (read directly from the dial on the Charpy test machine)
• Repeat these steps for the each temperature and each material.
• After all testing has been completed, be sure to examine the fracture surfaces of each
test specimen for clues as to the nature of the fracture (e.g., fibrous, cleavage).
Record digital images fracture surfaces.
Results and Discussion
At a minimum, address the following in your Results and Discussion section.
1. Use appropriate graphical methods to illustrate impact energy as a function of
temperature for all the materials on the same graph.
2. Compare the impact results for each materials to tabulated values from a literate
source such as the ASM Metals Handbook, NBS Monograph 63 “Tensile and
Impact Properties of Selected Materials from 20 to 300 K (1963), ASM
Aerospace Specifications. Comment on differences and similarities.
3. Examine the type and degree of deformation of each fracture surface. Correlate
this information with the corresponding impact energies. Comment on the
correlations and the relation to the microstructure of the material.
Appendices
At a minimum include raw data, this lab handout, sample calculations and a list of
references in the Appendix.
4
ME 32 Engineering Materials Laboratory
IMPACT TESTING
DATA SHEET
NAME______________________________________DATE____________
LABORATORY PARTNER NAMES____________________________________________
____________________________________________
EQUIPMENT IDENTIFICATION______________________________________
_______________________________________
Aluminium
Pretest Conditioning
Temperature (°F)
Impact Energy
(lbf-ft)
Temperature (°F)
Impact Energy
(lbf-ft)
Boiling water
Warm water
Room temperature water
Ice water
Salted ice water
Acetone with some dry ice
Acetone with much dry ice
Steel
Pretest Conditioning
Boiling water
Warm water
Room temperature water
Ice water
Salted ice water
Acetone with some dry ice
Acetone with much dry ice
5