improving-student-learning-of-materials-fundamentals

HCP crystal structure developed using I-DEAS in Crystals and Crystallography Lab Experiment 2: Tensile Properties of Metals The objective of this experiment is to learn how metals respo

2006-36: IMPROVING STUDENT LEARNING OF MATERIALS FUNDAMENTALS

Robert LeMaster, University of Tennessee-Martin

Robert LeMaster is an Associate Professor at the University of Tennesee at Martin He has over

20 years of research, development, and management experience on NASA and Air Force projects

Dr LeMaster received a B.S degree in Mechanical Engineering from the University of Akron in

1976, an M.S degree in Engineering Mechanics from the Ohio State University in 1978, and a

Ph.D degree from the University of Tennessee in 1983

Ray Witmer, University of Tennessee-Martin

Assistant Professor University of Tennessee at Martin, Registered Professional Engineer

© American Society for Engineering Education, 2006

Improving Student Learning of Materials Fundamentals

Introduction

All engineering students at the University of Tennessee at Martin (UT Martin) are required to

take an introductory course in materials science and engineering This is a common requirement

for most engineering programs At UT Martin this introductory course consists of two lecture

hours and one three-hour lab per week Additional exposure to materials concepts and

applications are obtained through courses such as Strength of Materials, and depending on the

area of concentration courses in Reinforced Concrete, Soils, Manufacturing Processes,

Electronics, and Machine Design An examination of student performance on the Materials and

Structure of Matter section of the Fundamentals of Engineering (FE) examination showed that

UT Martin students consistently scored below the national average and that the trend was

constant to slightly negative

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60

Sep-01 Apr-02 Oct-02 May-03 Dec-03

End Date

A.M.

P.M.

Figure 1 Comparison of UT Martin test results with national average

Figure 1 shows data that compares UT Martin

test results to the national average UT Martin

students take the General Engineering Exam

which includes a materials section in both the

A.M and P.M test sessions Results are shown

for both test sessions The results shown in the

figure are based on a four-point running average

that is used to dampen the oscillations

associated with individual test sessions

Removing the oscillations enables trends to be

more easily seen As seen in the figure, UT

Martin scores were consistently 5-10% below

the national average with slight negative trend

UT Martin’s goal is to have students

consistently score at or above the national

average on this exam This goal was not being

met in this subject area

UT Martin uses data from the FE to assess whether or not some program outcomes are being

met Core Curriculum Committees are responsible for reviewing the assessment data for groups

of courses and determining whether or not changes in course content is needed The Core

Curriculum Committee responsible for the materials course determined that the textbook,

prerequisites, and content covered in the course was similar to those at other universities

Therefore, reasons other than content had to exist that would explain the lower than expected

performance During the course of this review a number of potential contributing factors were

identified First, not all students had completed the materials course at the time of the

examination Depending on the area of concentration, materials may not be a prerequisite for

another course and in some cases students put off taking the course until their last semester of

enrollment It was decided that this problem was best addressed through advising in which

faculty made sure that students took the junior level course in their junior year instead of

deferring it until their last semester Second, it was determined that only the laboratory portion

of the course contained only a few experiments and it was decided that the laboratory portion of

the course needed to be strengthened The strengthening of the laboratory portion of the course

is the emphasis of this paper

Experiment Enhancement

A review of experiments used at other universities in conjunction with a first course in materials

was performed As part of this review, lab report requirements were also examined Information

was obtained from: 1) a visit to another campus (University of Tennessee – Knoxville) to

observe laboratory sessions and equipments, 2) discussions with colleagues from other

universities, and 3) experiments published in both the literature and on the web As a result of

this review a set of ten experiments were selected for implementation at UT Martin These

experiments were selected based on their correlation with lecture content, their ability to

demonstrate fundamental concepts, and the practicality of implementing them from the

standpoint of laboratory time and equipment In most cases the experiments were modified to

better fit within the equipment and lab time constraints at UT Martin These experiments are

listed in Table 1 along with the major topics covered by the experiment The following sections

provide a brief summary of each experiment

Table 1 List of Experiments and Major Concepts Covered

1 Crystals and Crystallography Crystal structures and interstitial sites

2 Tensile Properties of Metals Stress-strain curves and fracture

3 Ductile to Brittle Transition Fracture energy versus temperature

4 Cold Work and Recrystallization Annealing and recrystallization

5 Phase Diagrams Cooling curves and phase transformations

6 Hardenability of Steels Jominy bar end quench

7 Quench and Temper Heat Treatment Tempering curves

8 Galvanic Corrosion Electrical potentials and corrosion

9 Fracture of Glass Brittle fracture and Weibull Statistics

10 Hyperelastic Response of Elastomers Nonlinear response and Mooney-Rivlin equations

Experiment 1: Crystals and Crystallography

The objective of this laboratory is to learn the basic types of crystal structures and to develop a

sense for the relationships between them The exercises included in this laboratory familiarize

the student with the face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal

close-packed (HCP) crystal structures The structures are studied to determine the important

crystallographic parameters relating to crystal symmetry, density of atomic packing, and the

location and size of open spaces within the crystal

This type of laboratory is fairly common and a variety of methods are used by universities to

construct the unit cells For example, the University of Delaware uses Solid-State Model Kits

that are designed to allow models of many types of crystal structures to quickly be assembled 1

In the past UT Martin required students to construct

the three crystal structures from ping-pong balls and

hot glue Currently they are required to build

3-dimensional models of the crystal structures using the

I-DEAS CAD software (Figure 2) Using I-DEAS

requires that the students calculate the lattice size

parameters and the location of the atoms They also

learn to calculate the size of interstitial spaces and the

size of atoms that will fit within them These

calculations are important and having students make

them as part of the lab helps to ensure that they know

how to do them Lattice size parameters and atom

location calculations were not required when

constructing the unit cells from ping-pong balls The

instructors have found that having ping-pong models

of the crystal structures available during the lab

sessions helps explain and answer questions raised by students

Figure 2 HCP crystal structure developed using I-DEAS in Crystals and Crystallography Lab

Experiment 2: Tensile Properties of Metals

The objective of this experiment is to learn how metals respond to axial loads, understand the

terminology and parameters used to describe this response, gain familiarity with ASTM

standards, and gain experience using tension and hardness test equipment Tensile tests,

particularly of metallic materials, are fundamental tests that are performed at many universities

At UT Martin five different materials are used in this lab – AISI 1018, 4140, and 8620 cold

drawn steel, 6061-T6 aluminum, 360 brass, and ASTM A36 hot rolled steel The 1018, 4140,

and 8620 steels are used to show the effect of alloying on the tensile properties of steel – all

demonstrate a smooth transition from the elastic to work hardening portions of the stress-strain

curves Aluminum and brass are used to provide a comparison of the strength and toughness of

different materials They also demonstrate a smooth transition form the elastic to work

hardening portions of the stress-strain curves The hot rolled A36 specimen is used to

demonstrate high and low yield point phenomena exhibited by some materials Hardness

measurements are made on all samples prior to the performing the tensile tests The pre-test

hardness values are compared to post-test hardness data taken from the fracture zone to show the

increase in hardness associated with work hardening

Experiment 3: Ductile to Brittle Transition

The objective of this experiment is to learn how the ductility of metals is affected by

temperature, how this dependency can be determined using Charpy V-notch tests, learn the

terminology and parameters used in Charpy V-notch tests, gain familiarity with ASTM

standards, and gain experience using an impact test machine Charpy impact testing is also

commonly used in conjunction with first courses in materials science 2,3,4 At UT Martin,

fracture energy data is measured for three materials – Grade 40 gray cast iron, 1018 low carbon

steel, and 6061-T6 aluminum – at six temperatures (Table 1) The six temperatures do not

provide sufficient data to locate the ductile-brittle transition temperature, but do allow the

presence of an upper and lower fracture energy plateau to be identified if one exists Typically, P

the cast iron is brittle at all temperatures, the low carbon steel demonstrates an upper and lower

fracture energy plateau, and the aluminum does not become brittle at the lower temperatures

Table 1: Temperatures used in Charpy V-notch Experiements Temperature ( o F) Method used to Obtain Temperatures

500 Furnace

-109 Ethylene glycol and dry ice bath

Experiment 4: Cold Work and Recrystallization

The objective of this experiment is to determine the relationship between percent cold work,

%CW, and recrystallization temperature, demonstrate the effects of cold work and

recrystallization on the hardness of the alloy, learn the terminology and parameters associated

with cold work and recrystallization, gain experience using ASTM standards, and gain

experience using hardness testing and furnace equipment In this experiment ½ inch by 1/8 inch

by 4 inch samples of 360 cartridge brass are reduced in thickness by rolling Typically 10%,

20%, 30%, 40% and 50% thickness reductions are used After rolling, the samples are cut into

half inch lengths The various samples are placed in annealing furnaces having temperatures of

275 oC to 475 oC in increments of 50 oC After being annealed for one hour, the hardness of each

sample is plotted as a function of annealing temperature Experiments similar to this one that are

used at other universities can be found in references 4 and 6

Experiment 5: Phase Diagrams

The objective of this experiment is to learn how phase diagrams are constructed from a set of

cooling curves obtained for various alloy compositions, learn the terminology associated with

phase diagrams, and gain experience with measuring and mixing alloying components Several

similar experiments are reported in the literature 1,4,5 This particular experiment is modeled after

one developed by the Material Science Department at the University of Tennessee – Knoxville

Six small furnaces (Figure 3) are used to melt alloys of Pb and Sn – other alloys having a binary

eutectic phase diagram could be used Cooling curves are then obtained and simultaneously

displayed using the LABVIEW graphical user interface (GUI) shown in Figure 4 As the cooling

curves are developing the instructor is able to discuss them in real time using a projected image

of the GUI The raw data is saved in a file which is used by each student to determine the

liquidus, solidus, and transformation times

Figure 3 Jeweler’s melting furnace used in phase-diagram experiment

Figure 4 – LABVIEW GUI used during phase diagram experiment

Experiment 6: Hardenability of Steels

The objective of this experiment is to learn how cooling rate effects the hardness of quenched

steels, demonstrate the difference in the ability of alloys to harden (e.g hardenability of steels),

learn how the hardenability of steels is measured using the Jominy Test, gain familiarity with

ASTM standards, and learn the terminology associated with the Jominy hardenability test

(ASTM A225) This experiment is performed in accordance with the ASTM A225 standard

using an end-quench apparatus designed and fabricated at UT Martin (Figure 5a) Figure 5b

shows students removing a specimen from a furnace and loading it in the end-quench apparatus

Note the safety gear being worn by the students Three alloys are used in this experiment – AISI

1020, 4140, and 4340 – to demonstrate the effect of carbon and alloy content on hardenability

The 1020 alloy does not harden or demonstrate good hardenability due to the low carbon content

Both the 4140 and 4340 develop greater surface hardness than the 1020 alloy due to the higher

carbon content The 4340 alloy which has a higher chrome content demonstrates a much better

through thickness hardenability than does the 4140 alloy As with the other experiments, this

type of experiment is also performed at other universities 1,4

Figure 5 a) Jominy specimen during quench, and b) students loading specimen in quench

apparatus

Experiment 7: Quench and Temper Heat Treatment

The objective of this experiment is to learn how the properties of steels can be changed by heat

treatment processes involving the transformation of austenite to martensite, demonstrate the

effects of time and temperature on the properties of tempered martensite, and learn the

terminology associated with the heat treatment of steels The six furnaces used during the phase

diagram experiment are used to temper small samples of AISI 4140 that were previously

austenized and quenched The samples are tempered for one hour and a different tempering

temperature is obtained from each furnace Using six furnaces simultaneously enables the data

to be obtained in one lab session

Experiment 8: Galvanic Corrosion

The objectives for this experiment are to gain familiarity with the terminology used to describe

and measure corrosion, to learn about the electromechanical behavior of corrosion, to discover

which metal in a group is the most noble and which corrodes the most, and to study the concept

of sacrificial anodes and way to prevent corrosion by using them This lab is an adaptation of

corrosion experiment conducted at the University of New Brunswick and described in Reference

7 In this experiment the electrical potential between dissimilar metals in an electrolyte is

measured for several materials, which allow students to gain a hands-on understanding of the

galvanic series

Experiment 9: Fracture of Glass

The objectives of this experiment are to: 1) characterize the load-deflection curve for an

elastic/brittle solid, 2) calculate the fracture stress and quantify the variability of this property, 3)

observe delayed fracture when this brittle solid is loaded near the instantaneous breaking load,

and 4) gain familiarity with the terminology and testing methods associated with brittle fracture

This experiment is an adaptation of that found in Reference 1 In this experiment precision dial

indicators are used to measure the mid-span deflection of

glass specimens loaded in three-point bending, Figure 6

The glass specimens are standard microscope glass slides

(1in x 3in x 0.4in) used in biological labs The

load-deflection data is used to determine Young’s modulus for

each sample Statistical properties of Young’s modulus

are determined assuming a normal distribution The

fracture data is used to determine the parameters for a

two-parameter Weibull distribution

Experiment 10: Hyperelastic Response of Elastomers

The objectives of this experiment are to determine how

elastomers elongate under load and to experimentally

determine constitutive equation constants for the

Neo-Hookian, Mooney-Rivlin and Mooney-Rivlin (augmented

with an exponential term) equations This experiment is

modeled after experiments found in References 4 but has

been expanded to include more hyperelastic type

constitutive equations (i.e Mooney-Rivlin) In this

experiment digital dial calipers are used to measure the

distance between gage marks on a rubber band as it is

stretched The rubber bands are loaded with small

weights and both the load and unload response is examined Journal exercises require the

determination of the material constants for the various constitutive equations Excellent data is

obtained with a little care Figure 7 shows comparisons of the three constitutive equations to the

test data

Figure 6 Small three-point load frame developed by R Witmer for Fracture of Glass experiment

Constitutive Equation Comparison

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00 400.00 450.00

0.00 1.00 2.00 3.00 4.00 5.00

Stretch

Test Data Mooney-Rivlin Mooney-Rivlin Augmented Neo-Hookian

Figure 7 Comparison of Constitutive Equations and Experimental Data for Hyperelastic Response of Elastomers Experiment

Lab Reports

A variety of lab report requirements were encountered during the review of experiments and

practices used at other universities These ranged from formal lab reports written by teams to

laboratory journals that were hand written by each student In some cases the lab

reports/journals reported and interpreted data only for the experiment under consideration, while

others required that students provide answers to additional questions The approach adopted at

UT Martin was to have students prepare individually hand written lab journals The adoption of

this approach was based on the time required by students, faculty grading time, and the assurance

that all students would do all of the work The journals contain information about the

experiment being conducted, data, data interpretation and analysis, and the answers to a series of

questions that require the students do research outside of the lab setting The additional

questions are similar to homework problems, and including the questions with the lab journals

ensures that all students do the homework and obtain feedback on it There are generally several

questions associated with each experiment and students will have to spend several hours

answering them Example questions are listed in Table 2

Table 2: Example of questions answered in lab journal Lab Question

1 Calculate the theoretical density of Ni at room temperature Perform research to

determine the atomic radius and crystal structure Compare your value to the

reported in the literature Cite your reference

2 Determine the ASTM E8 specified load rate Determine the chemical

composition of each specimen

3 Review ASTM Standard E24 and provide a dimensioned sketch of the Charpy

specimen

4 Review ASTM E18 and ASTM E140 to convert the Rockwell B hardness data to

Brinnell hardness Determine the chemical composition for 260 cartridge brass

Cite your reference

5 Show the temperatures associated with the start and end of solidification on a

published Pb-Sn phase diagram Discuss how these temperatures compare to the

liquidus and solidus lines on the phase diagram Citer your references

6 Review ASTM A255 and sketch the experimental setup for the Jominy Test

Make a sketch of a time-temperature transformation curve for a “typical”

hypoeutectoid plane carbon steel and sketch the cooling path for the

transformation of austenite to martensite by a water quench Cite your

references

7 Create a graph that shows tensile strength versus tempering temperature Cite

your reference for the conversion of RHB to tensile strength

8 Construct a galvanic series for the five metals listing the most cathodic to the

most anodic Compare these with a published list of ½ cell potentials Cite your

references Discuss any similarities or differences

Online Tools and Resources

The Blackboard web-based course management software is used in this course All lectures are

presented using Power Point and the lecture notes are made available to students online Web

access to common lab data that must be used by students to prepare lab journals is also facilitated

by the Blackboard This course also uses the online testing capability of Blackboard An

introductory course in materials science and engineering does not involve lengthy calculations

with lots of algebraic manipulation Calculations can be done quickly and many questions can

be asked during an examination This requires students to study all of the material associated

with a test because there is a good probability that there will be question on all areas Tests used

in this course typically contain approximately 40 questions This many questions allow the tests

to cover a lot of breath while still enabling students to have enough time to finish the exam It

also allows adoption of a no partial credit rule since each question is only worth a few points

Students are not given a copy of the exam after it has been taken They are allowed to come by

the instructor’s office and see which ones they missed, but they do not have a copy of the test

that can be passed along to future students

Data Analysis

The primary source of data used to determine if the

students were learning materials better was student

performance on the Materials and Structure of

Matter sections of the NCEES Fundamentals of

Engineering Exam (FE) The number of materials

related questions contained on either the A.M or

P.M section is relatively small – on the order of

eight Thus the FE exam data can provide only

limited insight into the depth and breadth to which a

student understands a subject area

Table 3: Ratio of UTM Correct /

National Correct Test Date A.M P.M

Before Course Changes

April 2001 1.07 0.89 October 2001 1.02 1.08 April 2002 0.84 1.02 October 2002 1.04 0.70 April 2003 0.86 0.85

Average 0.96 0.91

After Course Changes

October 2003 1.02 0.97 April 2004 1.00 0.78 October 2004 1.11 1.00 April 2005 0.78 0.98 October 2005 1.07 0.91

Average 1.00 0.93

The metric used in this study is the ratio of the

average number of questions answered correctly by

UT Martin students divided by the average number

of questions answered correctly by all students (i.e

national average) Table 3 shows this ratio for April

and October test offerings starting in April 2001

through October 2005 The table also shows the

average for both the A.M and P.M test sessions

before and after the course changes

The percent correct ratio prior to the laboratory changes was 0.96 and 0.91 for the A.M and P.M sessions respectively The percent correct ratio following the laboratory changes was 1.00 and 0.93

respectively This represents a 4.0% improvement in the A.M sessions and a 2.2% improvement in