improving-student-learning-of-materials-fundamentals

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 Page 11.739.1 © 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 1.60 A.M 1.40 Running Average Figure 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 P.M 1.20 1.00 0.80 0.60 0.40 0.20 0.00 Sep-01 Apr-02 Oct-02 May-03 Dec-03 End Date Figure Comparison of UT Martin test results with national average Page 11.739.2 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 along with the major topics covered by the experiment The following sections provide a brief summary of each experiment Table List of Experiments and Major Concepts Covered Lab Title Concepts Covered Crystals and Crystallography Crystal structures and interstitial sites Tensile Properties of Metals Stress-strain curves and fracture Ductile to Brittle Transition Fracture energy versus temperature Cold Work and Recrystallization Annealing and recrystallization Phase Diagrams Cooling curves and phase transformations Hardenability of Steels Jominy bar end quench Quench and Temper Heat Treatment Tempering curves Galvanic Corrosion Electrical potentials and corrosion 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 Page 11.739.3 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 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 3dimensional 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 them Lattice size parameters and atom location calculations were not required when Figure HCP crystal structure constructing the unit cells from ping-pong balls The developed using I-DEAS in instructors have found that having ping-pong models Crystals and Crystallography Lab of the crystal structures available during the lab sessions helps explain and answer questions raised by students 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 Page 11.739.4 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 not provide sufficient data to locate the ductile-brittle transition temperature, but allow the presence of an upper and lower fracture energy plateau to be identified if one exists Typically, 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 (oF) Method used to Obtain Temperatures 500 Furnace 212 Boiling water 70 Room temperature 32 Ice water bath -109 Ethylene glycol and dry ice bath -321 Liquid nitrogen 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 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 and 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 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 Page 11.739.5 Figure Jeweler’s melting furnace used in phase-diagram experiment Figure – LABVIEW GUI used during phase diagram experiment Page 11.739.6 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 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 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 Page 11.739.7 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 In this experiment precision dial indicators are used to measure the mid-span deflection of glass specimens loaded in three-point bending, Figure The glass specimens are standard microscope glass slides (1in x 3in x 0.4in) used in biological labs The loaddeflection 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 NeoHookian, Mooney-Rivlin and Mooney-Rivlin (augmented with an exponential term) equations This experiment is modeled after experiments found in References but has been expanded to include more hyperelastic type constitutive equations (i.e Mooney-Rivlin) In this Figure Small three-point load experiment digital dial calipers are used to measure the frame developed by R Witmer for distance between gage marks on a rubber band as it is Fracture of Glass experiment 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 shows comparisons of the three constitutive equations to the test data Constitutive Equation Comparison 450.00 400.00 350.00 Test Data Stress 300.00 Mooney-Rivlin 250.00 200.00 Mooney-Rivlin Augmented 150.00 Neo-Hookian 100.00 50.00 0.00 0.00 1.00 2.00 3.00 4.00 5.00 Stretch Page 11.739.8 Figure 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 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 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 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 Table 2: Example of questions answered in lab journal Lab Question 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 Determine the ASTM E8 specified load rate Determine the chemical composition of each specimen Review ASTM Standard E24 and provide a dimensioned sketch of the Charpy specimen 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 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 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 Create a graph that shows tensile strength versus tempering temperature Cite your reference for the conversion of RHB to tensile strength 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 Page 11.739.9 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 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 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 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 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 Page 11.739.10 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 the P.M sessions Figures through 11 contain plots of the data contained in Table Each plot shows fluctuating results along with a linear regression curve fit The slopes of the linear regression curves can be used to identify trends in the data The data for the A.M and P.M sessions prior to the laboratory changes (Figures and 9) show negative trends (i.e performance is getting worse) The data for the A.M and P.M sessions after the course changes (Figures 10 and 11) show a positive trend (i.e performance is getting better) for the A.M session, while the P.M session continues to show a slight negative trend The trend line slope shown in Figure 11 is -0.6x10-4 compared to -2x10-4 for Figure Therefore, although the trend for the P.M sessions is still slightly negative, it has been made less negative by 70% 1.20 1.20 1.10 1.10 1.00 1.00 0.90 0.90 0.80 0.80 y = -0.0002x + 8.9059 y = -0.0002x + 10.221 0.70 0.70 0.60 Oct-00 Apr-01 Nov-01 May-02 Dec-02 Jun-03 Figure Ratio for A.M Test Sessions Prior to Laboratory Changes 0.60 Oct-00 1.20 1.10 1.10 1.00 1.00 0.90 0.90 0.80 0.60 Jun-03 Jun-03 y = 4E-05x - 0.7618 y = -6E-05x + 3.3677 0.70 Nov-01 May-02 Dec-02 Figure Ratio for P.M Test Sessions After Laboratory Changes 1.20 0.80 Apr-01 0.70 Jan-04 Aug-04 Feb-05 Sep-05 Mar-06 Figure 10 Ratio for A.M Test Sessions After Laboratory Changes 0.60 Jun-03 Jan-04 A ug-04 Feb-05 Sep-05 Mar-06 Figure 11 Ratio for P.M Test Sessions After Laboratory Changes Page 11.739.11 Conclusions This paper describes efforts taken at the University of Tennessee at Martin to improve student understanding in the area of materials science and engineering The monitoring of test results from the Fundamentals of Engineering Exam in a particular subject area was used to determine the need for improvement and to assess whether efforts are leading to improvement Efforts to improve student understanding and retention focused on strengthening the laboratory portion of an introductory course in materials science and engineering Strengthening the laboratory experience required adding experiments and in some cases additional lab equipment It also required having students individually prepare handwritten lab journals that require the students to not only record and discuss data but to research ASTM standards, course material, and texts to answer questions relating to the material The laboratory portion of this course is now much more intensive than in previous offerings Data from the Fundamentals of Engineering Exam suggest that student understanding of materials science and engineering has improved as a result of the laboratory improvements Average test scores for the A.M session improved by 4% while the P.M session scores improved by 2% The negative trend in test scores for the A.M test sessions prior to the changes was made positive, while the negative trend in test scores for the P.M test sessions was made less negative by 70% Bibliography MASC 302 Materials Science for Engineers – Laboratory Notes for Mechanical Engineers, University of Delaware, 2000 Bates, S.P., Charpy V-Notch Impact Testing of Hot Rolled 1020 Steel to Explore Temperature ~ Impact Strength Relationships, 1990 National Educators Workshop: Standard Experiments in Material Science, Gaithersburg, Maryland, 1990 3445 Course Hardness Notes, MECE 3445—Materials Science Laboratory, University of Houston, 2002, http://www.egr.uh.edu/me/ceramics, observed 1/12/2006 MSE 201 Laboratory Notes, University of Tennessee-Knoxville, http://www.engr.utk.edu/mse/pages/courses.htm, observed 1/12/2006 Chen, K.C., How We Learned to Love the Phase Diagram with a Ti-Cr Alloy Characterization Lab, Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition, 2002, American Society for Engineering Education MIE 302 Handouts, Experiment – Property Modifications of Alloys, University of Massechusetts-Amherst, http://www.ecs.umass.edu/mie/faculty/nair/mie302/Lab%20Handouts/Lab3.doc, observed 1/12/2006 Galvanic Corrosion of Metals, University of New Brunswick, Department of Chemical Engineering, http://www.unb.ca/che/Undergrad/lab/2503.htm, observed 1/12/2006 Page 11.739.12