MODULE 4 Flashcards
is the separation of a body into two or more pieces in response to an
imposed stress that is static (i.e., constant or slowly changing with time) and at temperatures that
are low relative to the melting temperature of the material.
Simple fracture
is a respected and established technique which is used to ascertain both the physical and mechanical properties of raw materials and components.
Materials testing
Reasons of Conducting Material Testing
Ensure quality
* Test properties
* Prevent failure in use
* Make informed choices in using materials
also known as tension testing, is a fundamental materials science test in
which a sample is subjected to a controlled tension until failure.
Tensile testing
are used to
determine the mechanical behavior of materials under static, axial tensile, or stretch loading.
Tensile tests
is a strain measurement device used to measure the extension of a material under load.
extensometer
The most common testing machine used in tensile testing
universal testing machine.
is used to calculate the engineering
strain,
elongation measurement
is the opposite of tensile testing.
Compression testing
the compressive
strength is relatively easy to obtain, showing marked failure.
For brittle materials,
compressive strength is generally based on an arbitrary deformation value.
ductile materials,
There are four parts of a compression testing
Main machine part:
Hydraulic part:
Controller part:
Computer series(optional):
is used to determine the rate at which a material expands as a
function of temperature.
Linear Thermal Expansion
is the separation of a body into two or more pieces in response to an
imposed stress that is static (i.e., constant or slowly changing with time) and at temperatures that are low relative to the melting temperature of the material.
Simple fracture
Fracture can also occur from
Fatigue and creep
Types of Fracture Mode in Metal
Ductile Fracture
Brittle Fracture
characterized by extensive plastic deformation in the vicinity of an
advancing crack.
Ductile Fracture
cracks may spread extremely rapidly, with very little accompanying
plastic deformation. Such
Brittle Fracture
crack propagation corresponds to the successive and
repeated breaking of atomic bonds along specific crystallographic planes
cleavage.
is a property that is a measure of a material’s resistance to brittle
fracture when a crack is present.
Fracture toughness
purpose of impact testing
is to measure an object’s ability to resist high-rate loading.
can be one of the most difficult properties to quantify.
Impact resistance
factor of its ability to absorb energy during plastic deformation.
material’s toughness
have low
toughness as a result of the small amount of plastic deformation that they can endure.
Brittle materials
at lower temperatures, the
impact energy of a material is
decreased
notch configurations
V-Notch, U-Notch, Key-Hole
Notch, as well as Un-notched and ISO (DIN) V-Notch,
is an ASTM standard method of determining the impact resistance
of materials.
Izod Impact Test
Izod Impact Test position?
vertical position
Izod Impact Test Specimens of metals
square,
Izod Impact Test Specimens of polymers
rectangular
The Izod impact test, like the Charpy impact test, is also used to test materials at ______ to try to simulate conditions that may occur in the actual use of the material.
low
temperature
may be obtained by testing a number of
identical specimens at different temperatures, and then plotting the impact energy as a function
of temperature, the ductile-brittle transition becomes apparent as the resulting curve shows a
rapid decline in impact strength as the temperature increases.
Ductile to Brittle Transition Temperature
The Charpy Impact Test was invented in 1900 by?
Georges Augustin Albert Charpy (1865-
1945)
measures the energy absorbed by a standard notched specimen
while breaking under an impact load
Charpy impact test
Charpy Impact Test
energy absorbed by the specimen is determined
measuring the decrease
in motion of the pendulum arm.
is a form of failure that occurs in structures subjected to dynamic and fluctuating
stresses (e.g., bridges, aircraft, machine components).
Fatigue
this type of failure normally occurs after a lengthy period
of repeated stress or strain cycling.
fatigue
susceptible to this type of failure.
polymers
and ceramics
alternating from a maximum tensile stress (σmax) to a minimum compressive stress
(σmin) of equal magnitude.
Reversed Stress Cycle
the maxima and minima are asymmetrical relative to the zero-stress level.
Repeated Stress Cycle
the stress level may vary randomly in amplitude and frequency.
Fluctuating Stress Cycle
_______ id defined as the average of the maximum and minimum stresses in the
cycle
Mean Stress
______is the difference between maximum and minimum stress or can be
calculated using this formula
Range of Stress
is one-half of this range of stress.
Stress amplitude
_____ is the ratio of minimum and maximum stress
Stress Ratio (R)
is sometimes called the endurance limit.
Fatigue limit
represents the
largest value of fluctuating stress that will not cause failure for essentially an infinite number of
cycles.
fatigue limit
For many steels, fatigue limits range
between 35% and 60% of the tensile strength
is defined as the stress level at which failure will occur for some specified
number of cycles
Fatigue Strength
is the number of cycles to cause failure at a specified stress level
Fatigue life
helps determine a material’s ability to withstand cyclic fatigue loading
conditions.
Fatigue Testing
Cyclic fatigue tests produce repeated
loading and unloading in
tension, compression, bending, torsion or combinations of these stresses.
Fatigue tests are
commonly loaded in
tension, compression
Types of fatigue tests
Load Controlled High Cycle and low cycle fatigue testing (LCF),
the test is run in strain control with the load as a
dependent variable.
low cycle fatigue testing
are often conducted on smooth bar specimens in load,
force or stress control.
High-cycle fatigue (HCF)
can be particularly useful in industries that rely on materials in temperature-varying
and cyclic conditions including aerospace, architecture, automotive, oil and gas, and power
generation industries.
Low
cycle fatigue
three stages to low cycle fatigue testing.
The first stage is designed to detect crack initiation on a polished specimen.
* The second stage is propagation life, which occurs after initiation.
* The third stage is failure, which is usually determined by some percentage of load drop
from a stable condition.
The purpose of
destructive testing
is to determine service life and to detect design weaknesses that may not show
up under normal working conditions.
is most suitable, and economic, for objects which
will be mass-produced, as the cost of destroying a small number of
specimens is negligible
Destructive testing
Commonly used methods of destructive testing of material
- Tensile Test
- Hardness Tests
- Impact Tests
- Creep
- Fatigue
- Other Mechanical Tests
measures a material’s strength by determining resistance to penetration.
Hardness testing
constitute the most common method used to measure hardness
because they are so simple to perform and require no special skills.
Rockwell tests
Indenters in Rockwell tests
spherical and hardened steel balls having diameters of 1/16, 1/8, 1/4,
and 1/2 in. as well as a conical diamond (Brale) indenter, which is used for the hardest materials.
Two types of Rockwell Hardness Tests
Rockwell and Superficial Rockwell
minor load is 10 kg
Rockwell test,
Major loads in Rockwell test
major loads are 60, 100, and 150
kg.
What is the minor load of suoerficial test?
3 kg is the minor load
The two most common indenter
Rockwell B (ball) used for soft materials and Rockwell C (cone) uses diamond cone for hard materials.
What indenter is use in Brinell test?
Spherical Indenter
diameter of the hardened steel (or tungsten carbide of Brinell Test?
10mm or (0.394 in.
What indenter is used in the Vickers Hardness Test?
diamond
indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf.
advantages of the Vickers
are that extremely accurate readings can be taken, and just one type of indenter is used for all types of metals and surface treatments.
Disadvantages of Vicker Hardness Test
Much expensive than Brinell and Rockwell Machine
Diamond Pyramid is used?
Knoop and Vickers tests
Diamond Pyramid
Knoop and Vickers tests
Applied Loads are much smaller
Microindentation Hardness Tests
designated by HK and HV
Knoop and Vickers hardness numbers
referred to as micro indentation-testing methods
The Knoop and Vickers technique
ratio of the load applied to the indenter
Knoop hardness number HK
the applied load (kgf) divided by the
surface area of the indentation (mm2
Vickers Diamond pyramid Hardness
The standard Charpy Impact Test specimen consist of a bar of metal, or other material
55x10x10mm
CHARPY TEST
2mm deep, with 45° angle and 0.25mm radius along the base
V-notch:
CHARPY TEST
5mm deep notch with 1mm radius at base of notch
U-notch and keyhole notch
the maxima and minima are asymmetrical relative to the zero-stress level.
Repeated Stress Cycle
one-half of this range of stress.
Stress amplitude
sometimes called the endurance limit
Fatigue Limit
The goal of the test is to determine the number of cycles to fracture for each specimen.
Load Controlled High Cycle
characterized by high amplitude, low-frequency plastic strains
LCF
