WPI MS4SSA Modules: What and How. Nima Rahbar and Wole Soboyejo Worcester Polytechnic Institute (WPI)

Transcription

1 WPI Modules: What and How Nima Rahbar and Wole Soboyejo Worcester Polytechnic Institute (WPI)

2 Initial WPI Modules: Building a Culture of S&T in Africa WPI s modules focus on complementary curricula for the inspiration of a STEM culture at the primary and secondary school levels This builds on WPI s rich culture of STEM outreach and project-based learning The modules have been developed for training the trainers and training the students The WPI modules focus on building a culture of S&T and digital content/pedagogy that can be scaled Materials science and engineering modules Robotics modules Project-Based Learning (PBL) Assistments and K-12 STEM training/strategies

3 WPI Approach to Theory and Practice WPI s approach to learning involves a combination of theory and practice This is relevant to the development of a pipeline of Africans in STEM fields Need strong foundation in math and science necessary but not sufficient condition However we also need a strong culture of problem solving, creativity, tinkering and team work informed by global best practices African Governments Gambia, Ghana, Ethiopia, Zanzibar, Lesotho, Malawi, Mauritius, Mozambique, Nigeria, Rwanda, Burkina Faso, Benin, Guinea, Senegal, Togo, Niger, Mauritania Participating Institutions and Collaborators From Africa, Japan, India, China and the United States

4 Background and Introduction to Materials Science and Engineering Modules Africa is rich in mineral and materials resources However most students in Africa have never heard about materials science and engineering Hence most of their knowledge of math and science is abstract and not connected to the materials opportunities around them Furthermore most students do not know much about how to add value to natural resources through materials processing There is therefore a need to introduce students to materials science and engineering modules Such modules could increase the pipeline of future materials scientists and engineers or applied scientists and engineers

5 From Artisanal Mining to Wealth Africa has a rich array of minerals and materials resources Artisanal Mining (Small-Scale) Difficult conditions Limited profits Industry (Mid- to Large-Scale) Africa s richest man (Aliko Dangote) manufactures cement from African raw materials Value addition to people, minerals and natural products

6 Optical Fibers The Silent Revolution Step-index optical fiber design. (a) Fiber cross section. (b) Fiber radial index of refraction profile. (c) Input light pulse. (d) Internal reflection of light rays. (e) Output light pulse. 6 (Adapted from Callister, William D., and David G. Rethwisch. "Materials science and engineering: an introduction. " Vol. 7. New York: Wiley, 2007.)

7 The Evolution of Engineering Materials What is in the future? 7

8 WPI Materials and Project- Based Modules Work with the WPI Team, ASM International, Pete Gange and the World Bank Team to develop modules for the teaching of materials science and engineering in African secondary schools The modules are presented at a level that can be taught to students in the final year of secondary school The modules include lecture materials, homework questions, quizzes, answer keys and project-based modules Lecture materials (structure, properties, processing, materials selection and design) Interdisciplinary project-based approach to solving African problems (clean water, clean energy)

9 Outline of Lecture Modules Introduction to materials science and engineering Crystal structure and crystallography Materials processing and characterization Introduction to mechanical properties Plasticity and deformation Fracture and fatigue Phases and phase diagrams Materials and their mechanical properties Electrical properties of materials Biomaterials and bio-inspired design Materials selection and design Project-based modules renewable energy/clean water

10 Materials Science and Engineering Science: Knowledge-driven exploration of materials Engineering: Application-driven development of materials 10

11 Common States of Stress Simple tension Simple compression Biaxial tension: Tensile testing in which the sample is stretched in two distinct directions. 11 Pure shear Hydrostatic stress: Identical stress that is given by the weight of material in water above a certain point

12 Definition of Strain Strain: Relative displacement between particles in a material body as a result of deformation σ u 2 Tensile Strain The ratio of extension to original length. No unit Shear Strain w w σ v 2 Lateral Strain Lateral/transverse Strain: the ratio of the change in length of material due to deformation in the longitudinal direction 12 θ τ τ

13 Mechanical Testing and Experimentation Measures instantaneous change in length of an object Create an electrical signal whose magnitude is directly proportional to the force being measured Clip gage: Attached to the extensometer use for strain measure 13

14 Elastic Properties of Materials Hooke s Law: Force (F) needed to extend or compress a material/body by some distance x is proportional to that distance. F=kx Observed that a Linear Relationship exists between Stress and Strain Stress Hooke s Law holds for elastic deformation Slope= Elastic Modulus Strain Young's modulus (E) is equal to the longitudinal stress (σ) divided by the strain (ε) 14 σ=eε, E= Young s Modulus τ= Gγ, τ = Shear stress G= Shear Modulus ratio of the change in pressure to the fractional volume compression

15 Young s Modulus Thomas Young ( ) 15

16 Poisson s Ratio Lateral contract generally associated with axial deformation and vice-versa This was first recognized by Poisson in 18th century Poisson s ratio is defined as: u = - e xx e yy Simeon Dennis Poisson ( ) 16

17 Plastic Deformation Deformation which is not recovered upon unloading Stress Elastic Slope= Elastic Modulus Strain Stress loading Elastic + Plastic unloading 17 Permanent deformation Strain

18 Yield Stress Associated with the transition from elastic to plastic deformation: Stress Elastic Plastic σ y Strain 18

19 Stress-Strain Curve During Materials Deformation 19

20 Tensile Strength Associated with the maximum of the stress-strain curve: Stress TS Strain Not used for design purposes since structures compromised after such large deformations 20

21 Brittle and Ductile Materials Energy absorbed by the material up to the point of failure: Brittle materials stretch uniformly up to a certain point and then rupture A brittle material does not have a plastic region Ductile materials will withstand large strains before the specimen ruptures Ductile materials often have relatively small Young s moduli and ultimate stresses Ductile materials exhibit large strains and yielding before they fail 21

22 True Stress Versus True Strain Important for large-strain deformation Cross-sectional area of samples change with strain (conservation of volume) Most notable in comparing tension with compression tests: 22

23 True Stress vs. True Strain Response equivalent in tension and compression: Actual hardening in tension is plotted: Stress True Engineering 23 Strain

24 Trues Stress and True Strain Account for the Instantaneous cross-sectional area of sample: Quantity Engineering True Stress Strain 24 Engineering stress (σ) is the applied load (F) divided by the original cross-sectional area (A o ) of a material True stress (σ T ) is the applied load (F) divided by the actual (instantaneous)cross-sectional area (A i ) Engineering strain (ε) is the amount that a material deforms per unit length (l 0 ) in a tensile test. True strain (ε T ) equals the natural log of the quotient of current length over the original length

25 Worked Example An aluminum alloy with a Young s modulus of 70 GPa and a Poisson s ratio of 0.3 is deformed under tensile loading. Then tensile specimen is deformed instantaneously from its original length of 5 cm to a length of cm. If the yield strain is 0.1%, determine The true strain associated with the deformation 25

26 Worked Example The engineering strain associated with the deformation Is the true strain enough to cause plastic deformation? Since yield strain is 0.1%, a strain of is enough to cause plasticity Is the engineering strain enough to cause plastic deformation? Since yield strain is 0.1%, a strain of is enough to cause plasticity 26

27 Worked Example Identify the regimes in which volume is conserved during the deformation Volume is conserved during plastic deformation Is the volume conserved in the elastic regime? Volume is not conserved during elastic deformation Identify the range of strain which volume conservation holds Volume is conserved during plastic deformation with strains larger than

28 Materials Selection and Design The main problem of materials selection in mechanical design is the interaction between function, material, shape and process. Function dictates the choice of both material and shape. Process is influenced by the material The process determines the shape, the size, the precision and, of course, the cost 28 Adapted from Ashby, Michael F. "Materials selection in mechanical design." Metallurgia Italiana 86 (1994):

29 Materials Property Charts 29 Adapted from Ashby, Michael F. "Materials selection in mechanical design." Metallurgia Italiana 86 (1994):

30 Proposed Implementation Strategy African countries and regional nodes work with team to implement materials science and engineering, project-based learning, assistments and robotics modules Work with selected nodes on the training of trainers in pedagogy + use of teaching modules and project-based approach to materials science and engineering in SSA 4 initial nodes in SSA (Rwanda, Nigeria, Niger and Gambia) Trainers will include experts from teacher training colleges, secondary school teachers, university lecturers/professors, government officials, development partners and African networks (Materials and Robotics) Work with interested nodes and countries to scale and test the impact of the modules on desired outcomes Assess the effectiveness of the training modules at the local and regional scales Refine the training modules for continuous improvement

31 Summary & Concluding Remarks This talk presents an introduction to WPI s modules on materials science and engineering, assistments, robotics and PBL modules that are part of the program The teaching modules presented here focus mostly on an introduction to materials science and engineering structure, properties, processing, materials selection & design They enable a more intuitive approach to learning how to use the materials around us for different functions The teaching modules can be complemented with projectbased learning, assistments and robotics approaches that teach problem solving and engineering within an African/global context We welcome your engagement in using human capacity in science and engineering as engines for African development...

32 Acknowledgments Nima Rahbar (WPI) Paula Quinn (WPI) Rick Vaz (WPI) Jessica Rosewitz (WPI) Habibeh Chosehali (WPI) Sina Askerinajad (WPI) Arvand Navabi (WPI) Jingjie Hu (Princeton) Vanessa Uzonwanne (WPI) John David Obayemi (WPI) Zebaze Kana (WPI) Ali Salifu (WPI) Ken Stafford (WPI) Brad Miller (WPI) Ken Mbanisi (WPI) Nick Bertozzi (WPI) Neil Heffernan (WPI) Christina Heffernan (WPI)

33 THANK YOU! THANK YOU!