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six materials that engineers have to work with:

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1. metals

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2. polymers

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3. ceramics

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4. glass

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5. fiberglass

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6. semiconductors

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in each case there is a difference at a very low level

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e.g. in the case of fiberglass, the microscopic architecture of the fiber-reinforced composite

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underlying principle

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a mantra of material science: structure leads to properties

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differences at the atomic or microscope level lead to differences at the macroscopic or engineering level

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stress-strained curve

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early concept of atomic bonding led to characteristic of stiffness

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bonding force curve is the first derivative of the bonding energy curve

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two carbon atoms in a polymer

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two aluminum atoms in a aluminum alloy

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the difference between an aluminum and oxygen ion in an aluminum oxide

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at the atomic scale, we are trying to tear atoms apart

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a macroscopic scale manifestations of atomic bonding

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production of materials

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make them fast or slow to affect desired properties

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how a crystal-structure deformation is the basis of plastic deformation

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edge dislocation

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metallic crystal structure

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a cubic arrangement of atoms

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in the middle, we have squeezed in an extra half-plane of atoms

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compare to perfect crystal

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contrast it with the dislocation area

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if you draw a loop around it, you don't come back to the same place: Burgers vector

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Burgers vector

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named after Dutch physicist Jan Burgers, is a vector, that represents the magnitude and direction of the lattice distortion resulting from a dislocation in a crystal lattice.

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this is the basis of quantifying this structure in a mathematical way

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the movement of those linear defects is the basis of plastic deformation

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an object in the plastic deformation range will first have undergone elastic deformation, which is reversible, so the object will return part way to its original shape

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deformation

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deformation refers to any changes in the shape or size of an object due to:

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1. an applied force

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2. a change in temperature

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as deformation occurs, internal inter-molecular forces arise that oppose the applied force

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if the applied force is not too great, these forces may be sufficient to completely resist the applied force and allow the object to assume a new equilibrium state and to return to its original state when the load is removed

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elastic deformation

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reversible

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elastomers and shape memory metals

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plastic deformation

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irreversible

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metal fatigue

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occurs primarily in ductile metals

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was originally thought that a material deformed only within the elastic range returned completely to its original state once the forces were removed

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however, faults are introduced at the molecular level with each deformation

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after many deformations, cracks will begin to appear, followed soon after by a fracture, with no apparent plastic deformation in between