Chapter 6 Flashcards
Destructive testing
render the test material useless for services - loaded to failure
Strength
the ability to of a material to withstand an applied load
Tensile Strength
two types
the ability of a metal to resist failure when subject to tensile or pulling load.
Ultimate tensile strength (UTS) and yield strength
Shear
a ductile mode of failure
Torsional Strength
a twisting or rotation force (strength)
impact Strength
same as Notch toughness - dependent on geometry
Fatigue Strength
Cyclic or repeated mechanical action on a member till failure
Ultimate tensile strength (UTS)
The maximum load-carrying capacity of that metal at the exact point when failure occurs
Elasticity
the deformation os a metal under load which causes no permanent deformation when the load is removed
- no permanent defamation or “set”
Plastic
when a metal is stressed beyond its elastic limit
-permanent defamation or “set”
Yield point / yield strength
the point at which a material’s behavior changes from elastic to plastic is referred to as its yield point.
- used for the maximum load for structures
As temp increases strength ?
decreases
The harder a metal the tensile strength
increases and vice versa
Tensile testing
must have the following 3 features
Two common shapes of specimen
Uses a reduced section that is intended to localize failure
- uniform cross section
- Easily measured to a cross sectional area can be calculated
- Free from surface irregularities
two most common type are CIRCULAR & RECTANGULAR
Toughness
a measure of a metal’s ability to absorb energy
usually as slow rate
toughness properties values only have meaning with temperature information.
Ductility
Temp change?
opposite of ductile is?
Expressed in two ways?
the ability of a material to deform, or stretch, under load without failing.
Directly related to temperature
ductility increases at higher temps and decrease at higher temps
opposite of ductile is brittle
Percent elongation and percent reduction of area
Rolling direction
Rolling direction = X
Transverse direction is = Y
Through thickness direction = Z
Hardness
ability of a metal to resist penetration o r indentation
Hardness Tests
Tests are performed using some type of penetrator which is forced against the surface of the test object
Brinell hardnes test
BHN?
Prepare test surface / apply test load, hold load for prescribed time, measure impression diameter, determine BHN from table
Covers a large area
reduces problems with surface irregularities and localized hardness
BHN = Brinell hardness number
10mm hardened steel ball & 3000 kg load
or 10mm tungsten carbide ball & 500kg load
Field testing uses a hamer blow
Rockwell Method Hardness test
smaller indentations than Brinell testing
Loader are also less @ 60kg to 150kg
Prepare test surface / place test in Rockwell tester, apply minor load using elevating screw / apply major load / release major load / release minor load and remove part
Microhardness test
hardnest test with impressions so small that high magnification os required . can be performed on a single gran if metal.
Vickers indicator has equal sides
& Knoop indicator has a long and short dimension
Prepare test surface / place specimen in holding fixture / locate area of interest using microscope / Make indention / Measure indention using microscope / Determine hardness using tables and calculations
BHN?
= Brinell hardness number
this number X 500 is about the same as the metals tensile strength
Notch toughness
materials energy absorbing ability when there are surface flaws present
toughness usually defines the materials behavior when loaded slowly / Notch toughness values reflect the energy absorption which occurs at high rate of loading
also referred to as impact strength
notch toughness decrease as its hardness increases and its tempura rue is reduced
Toughness test
Determine the temperature at which fracture behavior changes from ductile to brittle - Ductile and brittle transition temperature
Chirpy V notch test
Consist of pendulum with striker head, an anvil, release lever, a pointer and a scale
Endurance limit
maximum stress at which no failure will occur, no matter how many cycles the load is applied
(fatigue strength of carbon steels is roughly equal to half its tensile strength)
Soundness Testing
Metals soundness referee to its freedom from imperfections - its to see if the weld metal contained any imperfections or defects
3 types of sound ness test
Bend, Nick-break, fillet break
Bend test
3 types of bends
Face, root, & side bend
3 types of bends
- Guided bend, roller equipped guided bend , Wrap around guided bend.
Nick-break test
Used by pipeline energy
- Judges soundness of the weld by fracturing the specimen through the weld so the fracture surface can be examined for the presence of discontinuities
Fillet break test
soundness test used primarily for welders certification
Stress Relief
a controlled heat treatment which relieves residual stress in metal
Tempering
a heat treatment, usually of a quenched steel, that reduces sadness and restores ductility and toughness
Silicon
Small amounts .20% (up to 50%)
Deoxidizer
strengthens Iron
Manganese
Small amounts 30%
Deoxidizer, prevent inclusion, increased strength and hardness
Chromium
powerful alloying element in steel,
Increases harden ability
improves corrosion resistance
Molybdenum
Less than 1%
improves toughness and ductility (at low temps)
Aluminum
Added to steel in very small amounts as deoxidizer
improved toughness
“fine Grain practice”
Vanadium
Harden ability of steel
only .05%`
Niobium (Columbium)
Considered to increase harden-ability
stabilizer and improves weldability
Dissolved gases
Hydrogen, Oxygen and nitrogen
not good for steel
causes embrittle steel and cause porosity
