ENGR45, FALL 2011, SRJC
Aaron Schuler, Bret Clark, Vikram Kalidas, Riley Yaylian
Abstract:
The Ductile-Brittle Temperature represents a point at which a
fracture in metal changes from :
Ductile - High energy plastic bending or deformation
to
Brittle – Low energy shatter
Impact tests:
• Charpy
• Izod
Calculations:
𝐸𝐸𝐸𝐸𝐸𝐸 = 𝑀𝑀ℎ𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 − 𝑀𝑀ℎ𝑓𝑓𝑓𝑓𝑓
= 𝑀𝑀𝑀𝑀𝑀 90 − 𝑀𝑀𝑀𝑀𝑀 𝜃
= 𝑀𝑀 1 − sin 𝜃
final height
initial height
Design:
Copper
Steel
Aluminum
Temperature Curves:
Temperature of Samples as a function of Time
50
0
0
20
40
60
80
100
120
140
Temperature, C
-50
Copper
-100
Aluminium
Steel
-150
-200
-250
Time, seconds
Results:
Low Carbon Steel
Low Carbon Steel Impact Test Results
50
45
40
Impact Energy, Joules
35
30
25
Steel
20
15
10
5
0
-160
-140
-120
-100
Temperature, C
-80
-60
-40
Results:
Aluminum
Aluminum Impact Test Results
0.6
0.5
Impact Energy, Joules
0.4
0.3
Aluminum
0.2
0.1
0
-160
-140
-120
-100
-80
-60
Temperature, C
-40
-20
0
20
40
Results:
Copper
Copper Impact Test Results
0.9
0.8
0.7
Impact Energy, Joules
0.6
0.5
0.4
Copper
0.3
0.2
0.1
0
-200
-180
-160
-140
-120
-100
Temperature, C
-80
-60
-40
-20
0
Ductile - Brittle
Transition
Temperatures
Bret Clark
Aaron Schuler
Riley Yaylian
Vikram Kalidas
Engineering 45 Materials
Santa Rosa Junior College
Fall 2011
Abstract
Ductile – Brittle transition testing is done on varies materials to view the behavior of metals when
temperature is varied. These types of transitions have been found more prominently in materials with
BCC and HCP crystal structures. Knowing the properties of ductility and brittleness for materials provides
manufacturers with information when they are trying to develop projects. The transition from ductile to
brittle can be very rapid and often times it could be very disastrous since there is almost no warning.
There are two different types of impacting testing, the Charpy and Izod impact tests. The Charpy impact
test is a standardized high strain test which determines the amount of energy absorbed by different
materials. The amount of energy absorbed gives the material’s toughness and this property is used to
study the ductile-brittle transition. The sample piece is loaded horizontally into the apparatus and the
pendulum hammer strikes the notched sample. The notch is put in the sample to initiate the crack
propagation. After the impact the sample is removed and examined. If the material breaks on a flat
surface then it is classified as brittle, if it is a jagged surface then it is classified as ductile. The Izod test is
very similar to the Charpy except that the sample is loaded vertically and then struck with the pendulum
hammer. Same types of classifications are used after impact results. For both tests the sample
dimensions have to be consistent and any variant of the samples can greatly affect the fracture and the
data.
Introduction
•
•
•
•
Finding the ductile – brittle transition temperature of various metals.
Designing and building an Izod impact testing apparatus.
Gathering materials to perform the impact test.
o Aluminum, Copper and low carbon steel.
o Liquid nitrogen.
o Thermo coupler to measure temperatures from liquid nitrogen to room temperature.
Performing the test and gathering results to determine the transition temperature for the three
materials.
Materials and Procedure
Aluminum
Copper
♦ Cut equal samples of the material from the flat bars
Low Carbon Steel
♦ Acquiring liquid nitrogen
♦ Using the liquid nitrogen to calibrate the thermo coupler
♦ Getting one sample of each metal to -196 °C then using logger pro and the thermo coupler to
gather the temperature change while the sample is fastened in the apparatus
♦ After gathering the data for the temperature change from -196 °C to room temperature, it is
easier to find temperatures needed because they are now associated with time
♦ Putting all the samples in the liquid nitrogen to achieve the lowest temperature
♦ Loading one sample into the sample holder and waiting until the needed time to release the
hammer starts the process of data collection
♦ The hammer is released from an angle of 0 on the protractor
♦ A camera is used to record the value of initial and final angle measurements
♦ The equation for energy is put into an Excel spreadsheet and the value of the final angle is
inputted to give the energy absorbed
♦ This process is repeated for all samples and all metals
Raw Data
Copper
Sample
Temp
Angle
Energy
Time (s) (°C)
(°)
Absorbed (J)
8
-175
175
0.3729
15
-162
176
0.2387
17
-149
177
0.1343
20.5
-123
177
0.1343
22.75
-95
177
0.1343
25
-70
177
0.1343
27.25
-48
177
0.1343
30.5
-27
177
0.1343
34.25
-10
177
0.1343
Steel
Sample
Time (s)
5.5
10
16.5
27
37.5
Temp
Angle
Energy
(°C)
(°)
Absorbed (J)
-154
162
4.7965
-118
166
2.9110
-96
170
1.4888
-74
144
18.7163
-51
145
17.7231
Aluminum
Sample
Temp
Angle
Energy
Time (s)
(°C)
(°)
Absorbed (J)
4.5
-146
176
0.2387
7
-105
176
0.2387
9.25
-77.5
178
0.05970
11.25
-58
178
0.05970
13.25
-46
178
0.05970
17.5
-18
179
0.01493
20
-10
179
0.01493
RT
25
180
0
Discussion
We first created a Temperature vs. time graph by reducing test samples to the temperature of liquid
nitrogen -196 °C (77 K) and placing them into the clamp designed to secure the samples, for each sample
material with a specific cross sectional area. With this we could estimate the time necessary to elapse
before desired test temperature was reached. At desired temperatures (i.e. times) the pendulum was
released and a change in height was recorded to evaluate the energy lost due to the impact of the
pendulum with the sample. ΔU = mghf - mghi = energy lost = - energy absorbed by test sample.
Copper-- We observed a very small trend of increased energy absorption at lower temperatures. So
small in fact, that that to ascertain a DBTT from this data would be irresponsible. The DBTT of copper is
inconclusive.
Aluminum--Testing aluminum samples produced data that suggests that this material becomes more
brittle with increase temperature. A very narrow change in energy does not allow for a definitive DBTT.
This minute change may be the result of experimental error due to lack of sensitivity of equipment.
From our data the DBTT of aluminum is inconclusive.
Low-carbon steel-- Testing the DBTT of low-carbon steel resulted in large jump in energy absorption
between the temperatures -96°C and -74°C. The energy absorbed went from 1.49 J to 18.7 J. This large
ΔU is indicative that the DBTT of low-carbon steel is in this range. Because of this range and referenced
temperatures of: hot-rolled Dual-Phase 590 (DP590) DBTT= -95℃ and low-carbon steel 1018 DBTT= -5
℃. Our steel samples have lower carbon than .18%
Possible Error
The amount of energy absorbed by the material depends significantly on the size of the cross sectional
area, and inconsistencies in the cross-sectional area within one species of sample is a source of potential
error. The force of impact, coupled with the instability of the equipment, introduced potential energy
loses. Force on sample securing clamps position, relocated it, resulting in inconsistencies. When
corrected the data collected resembled theoretical. Sample insertion time variations from original
Temperature vs. time graph resulted in inconsistencies.
Conclusion
Experiment was a success. We were able to create an apparatus that works as an Izod impact test
mechanism. We were able to gather data that corresponds to existing data referenced from textbooks
and resources on the internet. Our group managed to accomplish these tasks and furthermore, was able
to put it to the test and perform a full experiment resembling the process of ductile – brittle transitions
used in the field. The lack of sensitivity of our equipment did not allow for conclusive results for
aluminum or copper species. We were able identify a temperature range for the DBTT for an unknown
carbon content of low carbon steel.
Sources
Charpy Impact Test: http://en.wikipedia.org/wiki/Charpy_impact_test
Izod Impact Test: http://en.wikipedia.org/wiki/Izod_impact_strength_test
Graphs, pictures and material properties: Materials Science and Engineering: An Introduction by William
D. Callister Jr.
Dr. Younes Ataiiyan