Material properties & testing Flashcards
Mechanical properties can be split into two groups, what are their names?
‘Dynamic’ and ‘Static’
What are ‘Static’ properties?
“Static Properties - Properties that are largely independent of the rate of loading.” This category includes:
- Strength (Tensile, Compression and Shear)
- Elasticity
- Plasticity
- Ductility
- Hardness
- Malleability
What are ‘Dynamic’ properties?
“Dynamic Properties - Properties where the rate of loading is significant” This category includes:
- Creep
- Fatigue
- Toughness
- Resilience
- Brittleness
What happens during a tensile strength test?
During tensile testing a specimen is loaded to destruction. In order to avoid areas of high stress the sample must have a uniform cross sectional area and central gauge length. For round specimens the gauge length should be 5 times the diameter.
Extension and loads are then recorded and plotted on a ‘load extension’ graph. Alternatively a ‘Stress Strain’ graph can be used.
What is the limit of proportionality?
The point after which stress applied to a material is no longer proportional to the material’s strain.
What is the elastic limit?
The point after which the material will undergo permanant deformation if stress continues to increase.
What is the ultimate tensile strenth?
The point at which the material will break. During a tensile strength test the material will neck at this point.
Define ‘Toughness’
Toughness - (when a force/Stress is applied) A materials ability to absorb energy without fracturing.
What is the difference between tensile, compressive, torsion and shear strength?
Tensile strength - A material or structure’s ability to withstand forces/loads that act in opposite dirctions (pulling).
Compressive strength - A materials ability to withstand forces/loads that act to reduce its size (pushing).
Torsion strength - A materials ability to withstand turning/twisting forces (Twisting).
Shear strength - A materials ability to withstand forces/loads that would cause the material to shear.
Define ‘Creep’
“Creep (sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yieldstrength of the material. Creep is more severe in materials that are subjected to heat for long periods, and generally increases as they near their melting point.”
Define ‘Fatigue’
“Fatigue is the weakening of a material caused by repeatedly applied loads.”
Define ‘Brittleness’
The opposite of tougness, a material is brittle if, when subjected to stress, it breaks without significant deformation. A material that is brittle will have a very small elastic region and will undergo very little plastic deformaion before breaking.
brittle materials are often relitivly hard.
Define ‘Hardness’
A materials ability to resist surface indentation whan a force is applied perpendicular to the surface of the material.
Describe one test that can be preformed in order to determine a materials tougness.
The Charpy test:
There are two main test that can be done to determine a materials hardness. What are their names and how do they differ?
Brinell and Vicker’s hardness tests.
Brinell’s test uses a spherical indenter with a load of either 3000kg of 500kg.
Vicker’s hardness test uses a pyramid shaped indenter with a load of 10kg.
