study topics Flashcards
Q1: What are crystal imperfections (or defects)?
A: Crystal imperfections are irregularities in the atomic or ionic arrangement in a crystal lattice, disrupting the periodicity of the structure.
Q2: What are the types of imperfections in metals? Name and define them.
Point defects - Localized disruptions in the crystal lattice. Examples: Vacancy, Self-interstitial.
Line defects - One-dimensional defects disrupting the lattice along a line. Examples: Edge dislocation, Screw dislocation.
Area defects - Two-dimensional defects, also known as planar defects. Examples: Grain boundaries, Twin boundaries.
Q3: Describe vacancy and self-interstitial crystalline defects.
A:
Point defects - Localized disruptions in the crystal lattice. Examples: Vacancy, Self-interstitial.
Line defects - One-dimensional defects disrupting the lattice along a line. Examples: Edge dislocation, Screw dislocation.
Area defects - Two-dimensional defects, also known as planar defects. Examples: Grain boundaries, Twin boundaries.
Q3: Describe vacancy and self-interstitial crystalline defects.
A:
Vacancy: A lattice site that would be occupied by an atom is vacant, creating a “hole” in the crystal.
Self-interstitial: An extra atom is located at a position between regular lattice sites, distorting the structure.
Q4: What are the two types of solid solutions? Define and provide a drawing.
A:
Substitutional solid solution: Solute atoms replace host atoms in the lattice.
Interstitial solid solution: Solute atoms occupy the interstices (spaces between the host atoms).
Q5: What are the rules for forming substitutional solid solutions?
A:
Atomic size factor: Solute and solvent atoms must have a size difference of less than 15%.
Crystal structure: Solute and solvent must have the same crystal structure.
Electronegativity: The solute and solvent must have similar electronegativities.
Valency: Solvent atoms generally dissolve more of solute atoms with similar valency.
Q6: What are the characteristics of interstitial solid solutions?
A:
Solute atoms must be much smaller than solvent atoms.
They occupy the interstitial sites within the crystal structure, distorting the lattice.
Q7: Describe edge and screw dislocations.
A:
Edge dislocation: A line defect where an extra half-plane of atoms is inserted into a crystal.
Screw dislocation: A defect where a crystal is distorted in a helical shape due to shear stress.
Q8: Define single crystal and polycrystalline materials.
A:
Single crystal: A material where the crystal lattice is continuous and unbroken to the edges without grain boundaries.
Polycrystalline: A material composed of many small crystals or grains separated by grain boundaries.
Q9: Describe the atomic structure within the vicinity of a grain boundary.
A: Atoms near a grain boundary are less ordered and have higher energy than those within the grains. Grain boundaries act as barriers to dislocation motion, affecting material strength.
Q10: What is ASTM grain size number?
A: It is a standard that describes the average grain size in a material. Higher ASTM numbers indicate smaller grain sizes.
Q11: Does the grain size-number increase or decrease with decreasing grain size? Why?
A: The ASTM grain size-number increases with decreasing grain size because smaller grains mean more grain boundaries, corresponding to higher ASTM numbers.
Q12: Define stress, strain, and working stress.
A:
Stress (σ): The force per unit area applied on a material. σ=F/A
Strain (ε): The deformation per unit length due to stress. Formula:
ε=(E*σ)=(ΔL/L0)
Working stress: The maximum stress that a material can safely withstand under normal conditions.
Q13: What is safety factor and why is it needed?
A: The safety factor is a measure of how much stronger a system is than it needs to be for an intended load. It is necessary to account for uncertainties in load and material behavior.
Q14: What is Hooke’s law? Under what conditions is it valid?
A: Hooke’s law states that stress is directly proportional to strain within the elastic limit of a material. Valid for elastic deformations where the material returns to its original shape after removing the load.
Q15: Define and differentiate elastic and plastic deformation.
A:
Elastic deformation: Temporary deformation where the material returns to its original shape after the load is removed.
Plastic deformation: Permanent deformation where the material does not return to its original shape after the load is removed.
Q16: What is ASTM grain size number?
A: ASTM grain size number is a measure used to quantify the average size of grains in a material, with a higher number corresponding to smaller grains.
Q17: Define tensile stress and shear stress.
A:
Tensile stress: Stress that stretches material. Formula: σ=F/A
.
Shear stress: Stress that causes layers of material to slide past each other. Formula:
T=F/A
Q18: Define engineering stress and engineering strain.
A:
Engineering stress: The applied load divided by the original cross-sectional area of a material.
Engineering strain: The ratio of the change in length to the original length of a material under load.
Q19: Define true stress and true strain.
A:
True stress: The applied load divided by the instantaneous cross-sectional area.
True strain: The natural logarithm of the ratio of instantaneous length to original length.
Q20: Define tensile strain, lateral strain, and Poisson’s ratio.
A:
Tensile strain: The elongation per unit length in the direction of applied tensile stress.
Lateral strain: The contraction per unit length perpendicular to the applied load.
Poisson’s ratio (ν): Lateral strain to tensile strain. Formula:
