Material Testing and Properties Flashcards
What does tensile testing avoid in order to perform an accurate test?
Avoids high or non uniform stress being generated.
What variables are measured during a tensile test?
Force and extension of test piece.
What is the formula and units for engineering stress?
Stress = Force/ Cross sectional area
Pascals
What is the formula for engineering strain?
Strain = Change in length/ Original length
What is the formula for young’s modulus? And what are the units?
Youngs modulus, E = Stress/ Strain
Pascals.
What affect does temperature have on youngs modulus?
Higher temp means lower youngs modulus.
What is the formula for poisson’s ratio?
Poissons ratio = Lateral strain/ longitudinal strain
Why is it difficult to tensile test ceramics?
They are very brittle.
What is the definition of hardness and what is it related to?
Ability to resist scratching/ surface indentation.
Related to a metals tensile and yield strength.
What type of hardness test leaves a circular indentation?
Brinell Test
What are the four hardness tests?
Brinell, Vickers, Knoop and rockwell.
What is the formula for brinell hardness?
Brinell hardness = applied load (kg) / surface area of impression
What is the definition of toughness?
The ability of a material to absorb energy.
High toughness generally means a material has high _____ and _____ ?
strength and ductility.
Low toughness usually means a material is ______ ?
Brittle.
What are 2 methods of testing toughness?
Izod and charpy impact tests.
Briefly describe the impact toughness test.
A pendulum swings and breaks a test sample. The height the pendulum reaches after it breaks the sample is measured.
Relationship between temp and E value?
high temp = low E value
Relationship between temp and yield/tensile strength?
high temp = reduced strength
Relationship between temp and hardness?
high temp = low hardness
Relationship between temp and ductility?
higher temp = higher ductility.
If a material is brittle will it fracture suddenly or slowly?
Suddenly.
If a fracture occurs within a ductile material, will the crack be sharp or blunt?
Blunt.
What manufacturing defects can cause fracture?
Porous casting, surface scratches.
What crystal defects can cause fracture?
Vacancies and dislocations.
