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

final height initial height

Calculations:

𝐸𝐸𝐸𝐸𝐸𝐸 = 𝑀𝐸ℎ𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 − 𝑀𝐸ℎ𝑓𝑖𝑖𝑖𝑖 = 𝑀𝐸𝑀𝑀𝐸 90 −𝑀𝐸𝑀𝑀𝐸 𝜃 = 𝑀𝐸 1 − sin 𝜃

Design:

Copper Steel

Aluminum

Temperature Curves:

-250

-200

-150

-100

-50

0

50

0 20 40 60 80 100 120 140

Tem

pera

ture

, C

Time, seconds

Temperature of Samples as a function of Time

Copper

Aluminium

Steel

Results: Low Carbon Steel

0

5

10

15

20

25

30

35

40

45

50

-160 -140 -120 -100 -80 -60 -40

Impa

ct E

nerg

y, Jo

ules

Temperature, C

Low Carbon Steel Impact Test Results

Steel

Results: Aluminum

0

0.1

0.2

0.3

0.4

0.5

0.6

-160 -140 -120 -100 -80 -60 -40 -20 0 20 40

Impa

ct E

nerg

y, Jo

ules

Temperature, C

Aluminum Impact Test Results

Aluminum

Results: Copper

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0

Impa

ct E

nerg

y, Jo

ules

Temperature, C

Copper Impact Test Results

Copper

Ductile - Brittle Transition Temperatures

E n g i n e e r i n g 4 5 M a t e r i a l s

S a n t a R o s a J u n i o r C o l l e g e

F a l l 2 0 1 1

B r e t C l a r k

A a r o n S c h u l e r

R i l e y Y a y l i a n

V i k r a m K a l i d a s

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 Low Carbon Steel

♦ Cut equal samples of the material from the flat bars

♦ 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

Time (s) Temp (°C)

Angle (°)

Energy 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

Aluminum Sample

Time (s) Temp (°C)

Angle (°)

Energy 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

Steel Sample

Time (s) Temp (°C)

Angle (°)

Energy Absorbed (J)

5.5 -154 162 4.7965 10 -118 166 2.9110

16.5 -96 170 1.4888 27 -74 144 18.7163

37.5 -51 145 17.7231

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