Learning Activities

In-Class Problem Solving

Example problems that can be worked through during class later in the week closer to the quiz. Each of these problems can be given out ahead of time so that students can prepare answers or given class time to discuss with their classmates. Additionally, providing visuals and tables is helpful in answering these questions so student providing answers can illustrate their thought processes by writing their answers on a blackboard. All four questions are comparisons of some sort and so the classroom assessment techniques of misconception/preconception check and approximate analogies can be especially useful in explaining the solutions. Scoring for in-person problem solving can be binary with participation (discussing with other students/providing answers)

Two worksheets with the in-class practice problems such as the ones below and are planned to be worked through at the end of the two class sessions following the lecture. The focus of the first worksheet is to cover the first two learning objectives, and the latter learning objectives for the second. These two worksheets should be sufficient preparation for the weekly quizzes as the questions for the quiz will be adapted from these questions.

Regarding inclusivity, all the activities were selected such that the students can have individual or group time to work through the problem or activity while being low stakes. The problems and handouts can be posted online and accessible to the students beforehand.

1. Identify 3 types of crystal defects in solids (one point, one linear and one planar) and suggest for each of these defects, 1 material property that is adversely affected by its presence and one that is improved. Also state what to look for in a crystal that possesses each of these defects.

2. (a) List four different defects in crystalline solids. (b) What evidence is available supporting the actual existence of the listed defects?

3. Attempt to account for the fact that polycrystalline aluminum (Al) has a higher tensile strength than single crystalline Al. Support your answer with an appropriate sketch.

4. Sketch the stress strain curve for three aluminum bars pulled in tension. The samples are annealed single crystal aluminum, poly-crystalline aluminum, and cold-worked aluminum.

Concept Demonstrations

Understanding the theory for the learning objectives is easier with visual aids so two learning activities will be used to help with the first three learning objectives. Bubble rafts help visualize dislocations in crystalline lattices and folds in carpets are useful in describing dislocation motion. Both together can be used to describe the effects of defects and grain boundaries on mechanical properties (objective 3).

These demonstrations would be conducted during lecture right before the concepts are formally defined allowing for students to make observations and start formulating thoughts on the learning objectives. The demonstrations can then be redone, but with the students describing the mechanisms and how they relate to crystalline systems.

Bubble Raft Demonstration

A bubble raft can be made with a soap-glycerin solution so a set of students can share a raft. See MRSEC UW-Madison demonstration for more details where the following questions were adapted.

Guiding Questions:

• Can you see different orientations of these hexagonal arrangements in the raft? If the bubbles were particles of a material, what would we call these areas? What would we call the areas in between these areas?
• Try popping some bubbles in the middle of the raft. then take two popsicle sicks or tongue depressors and use them to squeeze the raft together. This is like applying a compressive load to a material. What do you observe?
• Repeat the last step and then immediately after compressing the raft, try moving the popsicle sticks away from each other to model a tensile load. What do you observe? How does it compare to what you observed in the last step?
• Now, try popping many bubbles by running a glass rod (or your fingers) across the bubble raft. You should see bubbles in a highly irregular arrangement. What does this mimic in metals? Watch what happens for a few seconds of gently blowing on the raft. What do you see happening? How is the arrangement changing as you wait?

Carpet fold demonstrations

Introducing folds in carpets can mimic slip planes in crystals, and their motion can be seen as the fold is pushed across the carpet. More detail for the demonstration can be found in 'Introduction to Materials Science, McGraw Hill' (1972).

Guiding Questions:

• How is this analogous to crystals? If the carpet were a crystal, would you be able to identify the distance between slip planes?
• Where is the stress the greatest? Identify portions of the carpet and think back to the crystal analogy? What does the edge of the carpet represent? What does the fold mean?
• Explain how this affects mechanical properties? Restate this with slip planes in a crystalline material? Are there any examples you can think of? Grading should be done on participation with a similar scale to the in-class problem solving. A binary scoring system can also work here, but to encourage more depth of thought a sliding scale rewarding inquisitive thought can be implemented.