Imperfection In Solids.pptx

solid

1. Imperfection In Solids By: Eng. Ahmed Hegazy Khallaf

2. Crystalline Defects Zero dimensional: Point Defects One dimensional: Linear Defects (Dislocations) Two dimensional: Surface (Planar) Defects

3. Point Defects: Vacancies Self-interstitial Impurities

4. Linear Defects (Dislocations) Edge Dislocation Edge dislocation is a linear defect that centers around the line that is defined along the end of the extra half-plane of atoms. Which is perpendicular to the plane of the page. Within the region around the dislocation line there is some localized lattice distortion .

5. Linear Defects (Dislocations) Screw Dislocation It’s formed by a shear stress that is applied to produce the distortion. the upper front region of the crystal is shifted one atomic distance to the right relative to the bottom portion.

6. Linear Defects (Dislocations) Mixed Dislocation Most dislocations found in crystalline materials are probably neither pure edge nor pure screw, but exhibit components of both types; these are termed mixed dislocations.

7. Surface (Planar) Defects External Surfaces One of the most obvious boundaries is the external surface, along which the crystal structure terminates. Surface atoms are not bonded to the maximum number of nearest neighbors, and are therefore in a higher energy state than the atoms at interior positions. The bonds of these surface atoms that are not satisfied give rise to a surface energy. To reduce this energy , materials tend to minimize the total surface area.

8. Surface (Planar) Defects Grain Boundaries A grain boundary is the area of mismatch between volumes of material that have a common orientation of the crystallographic axes. The atoms at grain boundaries are not in their perfect crystal positions and hence the grain boundary is less dense. These atoms are at higher energies than the atoms inside the volume of a grain.

9. Surface (Planar) Defects Twin Boundaries Twin boundaries is a special type of grain boundary across which there exists a mirror image of the crystal lattice. It is produced by mechanical shear stresses and/or annealing of some materials.

10. Smart Materials The study of smart materials and smart material systems is a diverse discipline. Some of these materials exhibit a volume change when subjected to an external stimulus such as an electric potential; others shrink, expand, or move when heated or cooled. Still other types of smart materials produce electrical signals when bent or stretched.

11. Smart Materials These materials with one or more property can be significantly altered in a controlled fashion by external stimuli . Thus this material has built-in or intrinsic sensor (s) , actuator (s) and control mechanism (s)

12. Types of Smart Materials Piezoelectric Materials Shape Memory Alloys Magneto Restrictive Materials PH-Sensitive Materials Chromogenic systems others

13. Classifications of Smart Materials Active Smart Materials The materials which possess the capability to modify their geometric or material properties under the application of electric, thermal or magnetic fields, thereby acquiring an inherent capability to transduce energy . Ex: Shape Memory Alloys, Piezoelectric Materials Passive Smart Materials They lack the inherent capability to transduce energy. Ex: Fiber optic material

14. Applications of Smart Materials piezoelectric and shape memory alloy materials as actuation elements for a deformable aircraft control surface. Shape memory alloy actuators were utilized for large-deflection, low frequency shape control, while ultrasonic piezoelectric motors were used to control flexible surfaces on the trailing edge of the wing . vibration suppression motion control

15. References [1] William D. Callister , “Materials Science and Engineering: An Introduction 8e”, John Wiley & Sons, 2010. [2] Donald J. Leo, “Engineering Analysis of Smart Material Systems”, John Wiley & Sons, 2007. [3] Susmita Kamila, Jr. “Introduction, Classification, and Applications of Smart Materials: An Overview, American Journal of Applied Sciences, 2013.