History
MAT201 is a sophomore course taught to most engineering students at N. C. State University. For many of these students Materials Science is not their intended major field of study, and this is their first engineering course. So it is important to make the course interesting and accessible to them while effectively communicating the basic principles which we expect them to retain. Conventional lecture presentations have difficulty in dealing with the rich graphics needed to convey complex and unfamiliar idea.
We began by creating improved graphics for several topics which were projected in class, found that they were helpful to the students (and also benefited faculty who could concentrate on the studentsÕ responses rather than the blackboard). This still did not solve the problem of how students could take notes from these graphics, so we turned to multimedia capabilities and created a web site and CD-ROMs. With funding from Project Succeed we created additional graphics and linked them with explanatory text.
The present site is about 2 Gigabytes in size and comprises about 1000 quicktime movies, including digitized video clips, animations, diagrams and cartoons. There are also more than 300 worked problems that use interactive math packages (Theorist and Matlab), a variety of self-paced quizzes, and cross-index links to the specific pages of the textbook we use (Askeland "The Science and Engineering of Materials", PWS Boston) and to five other textbooks that are commonly used for this type of course. The CD-ROM (published in both Mac and Windows versions by PWS) is particularly useful to students studying in locations where high-bandwidth access to the internet (required to effectively access the large graphics files) is not available.
The CD has been adopted either in conjunction with a textbook or by itself at more than 30 universities worldwide, ranging from Univ. of Florida (another Succeed campus), to Vanderbilt University, and even to the University of Queensland in Australia. The materials were also used in the Fall of 1997 as the sole text for an experimental distance learning version of the MAT201 course taught as part of NCSU's Project 25 (students followed the course materials entirely at their own pace, attended no class sessions and interacted with faculty and each other via e-mail, including taking tests). Information on this course is available at on-line. The course notes (representing the lecture notes that would be taken by a student who was able to select all of the important ideas and combine them into a 20 page summary of the entire course) supplied there are thoroughly linked to both the web site and CD-ROMs.
Extensive evaluation of the use of these materials was conducted both to refine and develop the most effective materials and to determine their effect on student performance. The results are summarized in a published paper (the text and figures are provided here as "pdf" or acrobat files).
A brief sample of the course contents follows. It emphasizes the various types of multimedia graphics used, with a few representative examples from those available. Most of these are Quicktime© movies; some of these should be run as movies while others are intended to be stepped through frame by frame. The example problems are shown as "pdf" files that lose the interaction of the math package; normally any numeric values can be changed with live updating of answers.
Introduction to Materials Science
1. Atoms, bonds and crystallography
Basic chemistry courses give students some understanding of atoms and bonds, but deal only slightly with solids in which 3D arrays of atoms are connected by metallic, ionic, covalent and van der Waals bonds. Diagrams illustrating the filling of electron orbitals graphically provide a different organization of information than tables of quantum numbers. Animations of bond forces as atoms are pushed together or pulled apart, color coding of the periodic table to show electronegativity, and other similar tools, help students to organize and recall knowledge they should already have.
Static drawings of crystal structure in books are very difficult for many students. Showing the various unit cells of crystallographically using computer graphics to rotate the view while showing space-filling atoms as well as the central points that define the basic geometry is an important aid to help students understand both the actual structures (and bonds) and the simplified drawings of the unit cells commonly encountered in texts. Showing just the portion of atoms within the unit cell is important to help students correctly count atom density. Worked problems with detailed explanations help students solidify their understanding.
A sequence of images can be used to effectively communicate difficult concepts such as the relationship between the stacking of hexagonal planes of atoms to create a structure that has the face-centered cubic structure. Partial transparency and color coding help to show the underlying unit cell. As discussed in the evaluation paper, we performed considerable testing of these graphics to find the best parameters to communicate the information to the greatest number of students, with particular emphasis on reaching women and minorities.
2. Defects and dislocations
The properties of real materials are largely controlled by imperfections in the crystal structure. These consist of points (extra or missing atoms), lines (dislocations), and planes (surfaces and grain boundaries). Several animations are provided to show in different ways how a dislocation moves in a lattice. A simple two-dimensional diagram duplicates the drawing in most textbooks (but with motion). In three dimensions, the dislocation is a line whose motion causes bulk deformation. Textbooks often use the analogy of a caterpillar to describe this process, but a video clip makes this connection more obvious.
3. Diffusion and solidification
Atomic diffusion is fully described by analytic equations which students can manipulate in example problems. But animations are very helpful to provide visualizations and a deeper understanding of the process. For several different common geometries, simulations are provided. The case of a diffusion couple is shown here as an a sequence of stored images, but the program is also provided in both Mac and Windows versions (NOTE - these are compressed executable files, select the proper one for your platform). Similar simulations are provided for a variety of physical processes ranging from crack propagation to alignment of electron spins in a ferromagnet.
Another simulation illustrates the solidification of solid crystals from a liquid, to show how the grain structure observed in a microscope is formed. A video clip of the formation of spherulites in a polymer shows a real example that can be compared to the simulation to verify that the basic physical process is well understood.
4. Mechanical properties
The study of mechanical behavior of materials is best conducted in a hands-on laboratory, but this course does not include one. As the best substitute available, we include video clips of actual testing, for a variety of tests (tensile and compression testing, impact testing, as well as creep, fatigue, hardness, etc.). This has the advantage that it becomes possible to compare the macroscopic behavior of the sample with the behavior of the slip planes in the crystal structure that cause necking in the tensile test.
For the impact test that measures the energy absorbed when a swinging hammer breaks the specimen, the digitized video actually shows more than the student could see in a real lab, by slowing down the process as the hammer strikes the specimen.
To assist the student in understanding notch sensitivity (fracture toughness), common aids are used such as a sheet of paper in which notches of different root radius are cut, and then torn by hand. They can perform this type of test themselves to better understand the effects.
Such low-tech illustrations of basic principles using inexpensive everyday materials have encouraged another use of these multimedia tools. They form the backbone of a third-fourth grade science curriculum presently in use in the Wake County (Raleigh) Public Schools that teaches 9 year olds about science based on the properties of common materials (the unit is called "Stuff- how it's made and why it breaks"). The curriculum covers atoms, bonds, crystal structures, and the differences between metals, ceramics, glasses and polymers. Teachers use the CD-ROM in class and students can also access the web site. We plan to further develop this use of the materials in the future for middle and high schools by adding age-appropriate explanatory text and additional examples and hands-on experiments.
5. Phase diagrams and microstructure
Phase diagrams (especially for materials in the solid state) are not familiar to many engineering students, so cartoons are used to illustrate the concepts of unlimited solubility, limited solubility and insolubility.
Placing the phase diagram side by side with a cooling curve and a diagram of the evolution of microstructure is an effective way to communicate to students the meaning of the diagram and also its consequences for the microstructure of the material. For more complicated systems, the use of such generic diagrams introduces ones for real materials such as lead-tin solder. The microstructure of this material (as revealed in the light microscope) corresponds to that predicted by the phase diagram. Mechanical testing of these materials (viewed on videotape clips) makes the link between structure and properties.
Interactive worked problems assist students in understanding the use of the phase diagram and lever law to predict microstructures quantitatively. These examples show a simple isomorphous phase diagram and one with a eutectic.
6. Material processing
Most materials are heat treated to develop desired microstructures and properties. One type of treatment is age-hardening, whose three steps take the second element into solution, quench the material, and age it to form the desired fine precipitate. The aging temperature affects the time required and final properties. Similar sequences illustrate in cartoon form other solid state reactions including eutectoid and martensitic transformations.
Mechanical processing such as cold rolling is illustrated with diagrams as well as video clips using laboratory instruments. Representative microstructures show the effect on the grain structure.
In addition to the use of laboratory machines for processing, a wide-ranging series of video clips illustrate real-world materials processing. These range from the blacksmith to a modern steel mill.
7. Metals, ceramics, glass, polymers, composites, wood & concrete
The same tools (cartoons, diagrams, simulations) described above are used for other materials as well. For example, the formation of nylon by the reaction of two different molecules is better understood from a rendered diagram of the molecules that shows the necessary atom rearrangements than a simple chemical diagram in a textbook (the actual process of making nylon is also shown in another video). Worked problems for the same reaction and for other polymer formation reactions allow the student to solidify their understanding with quantitative calculations. A sequence of diagrams showing linear polymer chemistry communicates information more effectively that static tables.
Modern materials include a wide variety of types. Video clips include the manufacture and processing of ceramics, polymers, and glass, as well such practical metal-working operations as welding. Several materials suppliers have cooperated by allowing us to use short clips from their advertisements where appropriate.
8. Electrical and magnetic properties, corrosion
Topics such as electrical and magnetic properties and electrochemical corrosion are more abstract and more difficult for many students than mechanical properties and material processing. Simple animations showing forward and reverse bias help students understand device operation. Graphics that show several different factors side by side so that they can be related to each other are particularly helpful. In the example of the effect of temperature on conductivity of an n-type semiconductor, stepping forward and back through the frames allows comparing and relating the promotion of electrons across the conduction band, the shape of the Fermi function, and the conductivity. Most students find it helpful to go through this several times exploring and connecting the various pieces of information.