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Mechanical Behavior, Testing, and Manufacturing Properties of Materials


Types of tests for determining the mechanical behavior of materials. ... Durometer. Used to test hardness of plastics, rubbers, and other soft materials. ... – PowerPoint PPT presentation

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Title: Mechanical Behavior, Testing, and Manufacturing Properties of Materials

Mechanical Behavior, Testing, and Manufacturing
Properties of Materials
  • Group 4 Brenton Elisberg, Michael Snider,
    Michael Anderson, and Jacob Hunner

  • Metals can be processed into various shapes by
    deforming them plastically under the application
    of external forces. The effects of these forces
    on material behavior are described in this
    chapter, including

  • Types of tests for determining the mechanical
    behavior of materials.
  • Elastic and plastic features of stress-strain
    curves and their significance.
  • Relationships between stress and strain and their
    significance, as influenced by temperature and
    deformation rate.
  • Characteristics of hardness, fatigue, creep,
    impact, and residual stresses, and their role in
    materials processing.
  • Effects of inclusions and defects in the brittle
    and ductile behavior of metals.
  • Why and how materials fail when subjected to
    external forces.

Section 2.1 2.2.6
  • Tension Test
  • Strength
  • Ductility
  • Toughness
  • Elastic Modulus
  • Strain-hardening capability
  • Test Specimen
  • Usually solid and round
  • Original Gauge length lo
  • Cross-sectional area Ao

  • Stress-strain curves
  • Linear elastic elongation in the specimen that
    is proportional to the applied load.
  • Engineering stress the ratio of the applied load
    P, to the original cross-sectional area, Ao, of
    the specimen.
  • Engineering stress equation s P/Ao
  • Engineering strain equation e (l-lo)/lo

  • Yield Stress the stress at which permanent
    (plastic) deformation occurs.
  • Permanent (plastic) deformation stress and
    strain are no longer proportional.
  • Ultimate tensile strength (UTS) the maximum
    engineering stress.

  • If the specimen is loaded beyond its UTS it
    begins to neck.
  • Fracture stress the engineering stress at

  • Modulus of elasticity ration of stress to strain
    in the elastic region.
  • Modulus of elasticity equation E s/e
  • This linear relationship is known as Hookes Law.
  • Poisons Ratio the ratio of the lateral strain to
    the longitudinal strain.

  • Ductility extent of plastic deformation that the
    material undergoes before fracture.
  • Two measures of ductility
  • Total elongation (lf-lo)/lo x 100
  • Reduction of Area (Ao-Af)/Ao x 100

True-Stress and True-Strain
  • True-stress ratio of the load, P, to the
    instantaneous cross-sectional area, A, of the
  • True-strain the sum of all the instantaneous
    engineering strains.
  • True-stress equation s P/A
  • True-strain equation e ln(l/lo)

Construction of Stress-Strain Curves
  • The stress-strain curve can be represented by the
    equation s Ken
  • K strength coefficient
  • n strain hardening exponent
  • Specific energy energy-per-unit volume of the
    material deformed.

Construction of Stress-Strain Curves
Strain at Necking in a Tension Test
  • True-strain at necking is equal numerically to
    the strain-hardening exponent, n, of the

Temperature Effects
  • As temperature increases
  • Ductility and toughness increase.
  • Yield stress and the modulus of elasticity
  • Temperature also affects the strain-hardening
    exponent of most metals, in that n decreases as
    temperature increases.

Section 2.2.7 2.7
  • Rate of Deformation
  • Superplasticity
  • Effects of Compression, Torsion, and Bending
  • Hardness, Toughness, and Strength

Rate of Deformation Effects
  • Some machines form materials at low speeds.
  • Hydraulic Presses
  • Some Machines form materials at high speeds.
  • Mechanical Presses

Rate of Deformation Effects
  • Deformation rate the speed at which a tension
    test is being carried out, in units of m/s or
  • Strain rate a function of the specimen length.
  • Short specimens stretch more during the same time
    period than a long specimen would.

Effects of Temp and Strain
  • Typical effects that temperature and strain rate
    have together on the strength of metals
  • Sensitivity of strength-to-strain rate increases
    with temperature.
  • Increasing the strain rate increases the strength
    of the material (strain-rate hardening).
  • The slope of these curves is called the
    strain-rate sensitivity exponent.
  • The relationship between strength and strain is
    represented by ? Cem
  • C is the strength coefficient and e is the true
    strain rate. m is the slope of the graph.

Rate of Deformation Effects
  • Ex You have 2 rubber bands, one 20 mm and the
    other 100mm in length. You elongate them both by
    10mm in a period of 1 sec. The engineering strain
    in the shorter one is 10/20.5 while the longer
    one is 10/100.1, thus the strain rates are .5
    s-1 and .1 s-1

  • Refers to the capability of some materials to
    undergo large, uniform elongation prior to
    necking and fracture.
  • This elongation can be as long as 200 to 2000
    of the original length.
  • Common items that demonstrate this bubble gum,
    glass (at high temp) and thermo plastics.
  • Because of this capability, some materials can be
    formed into complex shapes such as beverage
    bottles and even neon advertisement signs.

Other Deformation Effects
  • Hydrostatic Pressure pressure due to weight of a
  • Exposing some types of metals to high radiation
    is known to increase yield stress, tensile
    strength, and hardness. However it decreases
    ductility and toughness.
  • Increasing hydrostatic pressure can increase the
    strain at fracture of materials.
  • Billet A semi-finished form of steel that is
    used for long products such as bars and channels.
  • Creating hydrostatic pressure on a billet can
    turn 1 m of billet into 14 km of wire.

hydraulic press.htm
  • Many operations in manufacturing, especially with
    forging, rolling, and extrusion, are performed
    with the material being subjected to compressive

Compression Test
  • A specimen is subjected to a compressive load.
  • Carried out by compressing a solid cylindrical
    specimen between two well-lubricated flat dies.
  • The cylindrical specimens surface begins to
    bulge, known as barreling.

Disk Test
  • Compression test developed for brittle materials
    such as ceramics and glass.
  • A disk shaped specimen is loaded between to solid
    platens. Tensile stresses build up perpendicular
    to the centerline along the disk, fracture
    begins, and the disk will split vertically.
  • Tensile stress from this test can be calculated
    with the following equation ? 2P/?dt P is
    load at fracture, d is diameter of disk, t is

Torsion Test
  • In addition to tension and compression, a
    work-piece may be subjected to shear strains.
  • Punching holes in sheet metal.
  • Metal cutting.
  • Torsion test used for determination of properties
    in shear. Usually performed on a thin tubular
  • Shear stress can be calculated with formula
  • T is torque, r is average radius of tube, t is
    thickness of tube.
  • Shear strain is calculated with formula r?/l
  • r is radius of tube, ? is angle of twist in
    radians, and l is length of tube.

Torsion Test
  • The ratio of the shear stress to the shear strain
    in the elastic range is known as the shear
    modulus or modulus of rigidity.
  • The angle of twist, ?, to fracture in the torsion
    of solid round bars and elevated temp can help
    estimate forge-ability of metals.

  • Preparing specimens from brittle materials, such
    as ceramics and carbides, is difficult because of
    problems in shaping and machining them to certain
  • The most common test for brittle materials is the
    bend or flexure test.

Bend / Flexure Test
  • Rectangular specimen supported at its ends.
  • Load is applied vertically at 1 or 2 pts.
  • The stress at fracture in bending is known as the
    modulus of rupture, flexural strength, or
    transverse rupture strength.

  • Commonly used property which gives indication of
    the strength and resistance to scratch and wear
    of a material/specimen.
  • Resistance to permanent indentation.
  • Hardness is not a fundamental property because
    indentation depends on shape of indenter and load

Brinell Test
  • J. A. Brinell 1900
  • Involves pressing a steel or carbide ball of 10mm
    against a surface with various loads.
  • 500, 1500, or 3000 kg
  • Measures diameter of indentation.
  • Harder surfaces have small indentation while
    softer surfaces have larger indentation.

Rockwell Test
  • S. P. Rockwell 1922
  • Test measures depth rather than diameter of
  • Diamond indenter presses against surface with
    minor load and then major load.
  • The difference in depths of penetration is a
    measure of the hardness of material.

Vickers Test
  • Developed in 1922.
  • Comparable to Brinell Test except using a pyramid
    shaped diamond to make indentation.
  • Lighter loads than Brinell Test
  • From 1 to 120 kg

Knoop Test
  • Developed in 1939.
  • Comparable to Brinell and Vickers test.
  • Uses an elongated pyramid shaped diamond to make
  • Uses very light loads.
  • From 25 g to 5 kg.
  • Known as a micro-hardness test because of the
    lights loads.
  • Suitable for very small or very thin specimens.
  • Test also used for measuring the hardness of
    individual grains and components in a metal

Mohs Hardness Test
  • Developed by F. Mohs in 1822.
  • Test based on capability of one material to
    scratch another.
  • Each material can scratch all materials below it
    with a lesser hardness.
  • Based on a scale of 1 to 10.

  • Instrument with diamond-tipped hammer.
  • Hammer is dropped from a certain height.
  • Hardness is related to the rebound of the
  • Small and portable.

  • Used to test hardness of plastics, rubbers, and
    other soft materials.
  • An indenter is pressed against the surface and
    then a constant load is applied rapidly.
  • Hardness is measured based on depth of indent
    after 1 second.

Section 2.7 2.12
  • Fatigue Components in manufacturing equipment
    are subjected to fluctuating cyclic (periodic)
    loads and static loads.
  • Cyclic Stress on gear teeth
  • Thermal Stress -- cool die in repeated contact
    with hot work pieces
  • Both stresses may cause part failure at stress
    levels below normal static stress loading

  • Fatigue Failure -- Failure associated with every
    stress cycle, propagated through the material
    until critical crack is reached and material
  • Fatigue Testing -- Various stresses, tension
    then bending to a maximum load limit (total

  • S-N Curves
  • Stress Amplitude (S) -- Maximum stress specimen
    is subjected
  • Number of Cycles (N)
  • Level of stress a material tolerates decreases
    with an increase in cycles.

  • Endurance (Fatigue Limit) -- Maximum stress
    material may be subjected without fatigue
  • Aluminum Alloys and similar materials exhibit an
    indefinite endurance limit.
  • Fatigue strength is specified at a certain number
    of cycles (107.)
  • Carbon Steels have a proportional endurance limit
    and tensile strength, usually 0.4 to 0.5.

  • Permanent elongation of a component under a
    static load maintained for a period of time.
  • Grain-Boundary Sliding -- Mechanism of creep at
    an elevated temperature in metals.
  • In high-temperature applications, gas-turbine
    blades, jet engines, and rocket motors.
  • May occur in tools and dies subjected to constant
    elevated temperatures (forging and extrusion.)

  • Creep Testing -- Subjecting a specimen to a
    constant tensile load (engineering stress) at a
    certain temperature, measuring the length changes
    at various time increments.
  • Primary, secondary, and tertiary stages

  • Rupture (Creep Rupture) -- Failure by necking
    and fractures
  • Creep rate increases with specimen temperature
    and the applied load.
  • Secondary Linear ranges and slopes aid to
    determine reliable design.
  • A higher melting point generally is related to an
    increase in creep resistance.
  • Stainless Steels, Super-alloys and Refractory
    metals and alloys

  • Stress Relaxation -- The stresses resulting from
    loading of a structural component decrease in
    magnitude over a period of time, while the
    dimensions of the component remain constant.
  • Thermoplastics

  • Testing consists of placing a notched specimen in
    an impact tester and breaking it with a swinging
  • Impact or Dynamic Loading
  • CharpyTest -- Specimen supported at both ends.
  • Izod Test -- Specimen supported at one end.

  • Impact Toughness -- The energy dissipated in
    breaking the specimen may be obtained from the
    amount of swing in the pendulum.
  • Useful in determining the ductile-brittle
    transition temperature of materials.
  • High Impact Resistance High Strength High
    Ductility High Toughness

  • Notch Sensitivity -- Sensitivities to surface
    defects, lowers impact toughness.
  • Heat-treated metals, Ceramics, and Glasses

Failure and Fracture of Material
  • Failure -- One of the most important aspects of
    material behavior. It directly influences the
    selection of a material for a particular
    application, the methods of manufacturing, and
    the service life of the component.

Failure and Fracture of Material
  • In selecting and processing materials
  • Fracture -- Either internal or external.
    Sub-classified into Ductile or Brittle.
  • Buckling -- Longitudinal deformation under
    compression, similar to barreling.
  • Some products are designed with failure essential
    for their function
  • Food and Beverage containers with tear tabs
  • Shear pins on shafts to prevent damage if
  • Perforated paper or metal (packaging)
  • Metal or plastic screw caps for bottles

Failure and Fracture of Materials
  • Ductile Fracture -- Plastic deformation proceeds
  • Highly ductile materials neck down to a point
    before failing.
  • Most metals and alloys will neck down to a finite
    area and then fail.
  • Generally ductile fractures take place along
    planes which shear stress is a maximum.

Failure and Fracture in Materials
  • Ductile Fracture -- Plastic deformation proceeds
  • Close examination of ductile fracture surface
    shows a fibrous pattern with dimples.
  • Failure is initiated with formation of tiny voids
    which grow and coalesce, developing micro-cracks
    leading to fracture.
  • In tension-test, fracture begins at the center of
    the necked region as a result of the growth and
    coalescences of cavities.

Failure and Fracture in Material
  • Cup-and-Cone Fracture -- Due to appearance, the
    fracture surface of a tension-test specimen.

Failure and Fracture in Materials
  • Effects of Inclusions -- May consist of
    impurities of various kinds and of second-phase
    particles, such as oxides, carbides, and
  • Extent of influence depends on their shape,
    hardness, distribution, and fraction of total
  • Higher Volume fraction of inclusions, the lower
    the ductility of the material.

Failure and Fracture in Materials
  • Effects of Inclusion contd
  • Two factors affect void formation
  • The strength of the bond at the interface between
    an inclusion and the matrix.
  • The hardness of the inclusion a soft inclusion
    will conform to the overall shape change of the
  • Mechanical Fibering from the alignment of
    inclusions during plastic deformation.
  • Subsequent processing of material must involve
    considerations of the proper direction of working
    for maximum ductility and strength.

Failure and Fracture in Material
  • Transition Temperature -- Across a narrow
    temperature range many metals undergo a sharp
    change in ductility and toughness.
  • The phenomenon occurs mostly in body-centered
    cubic and in some hexagonal close-packed metals,
    rarely exhibited by face-centered metals.
  • Transition Temperature depends on composition,
    microstructure, grain size, surface finish and
    shape of the specimen, and deformation rate.
  • Transition Temperature raises with high rates of
    deformation, abrupt changes in work-piece shape,
    and the presence of surface notches.

Failure and Fracture in Material
  • Strain Aging -- Phenomenon in which carbon atoms
    in steels segregate to dislocations thereby
    pinning them and increasing the resistance to
    dislocation movement. Resulting in increased
    strength and reduces ductility.
  • Accelerated Strain Aging Phenomenon occurs in a
    few hours at a temperature higher than room

Failure and Fracture in Material
  • Blue Brittleness -- Occurs in the blue-heat
    range where steel develops a bluish oxide film.
  • Blue Fracture -- Occurs with little or no gross
    plastic deformation.
  • In tension, fracture takes place along the
    cleavage plane (crystallographic plane), where
    the normal tensile stress is a maximum.
  • Low temperature and a high rate of deformation
    promote brittle fracture.
  • The fracture surface of polycrystalline metal
    under tension has a bright granular appearance.

Failure and Fracture in Material
  • Tensile stresses normal to the cleavage plane,
    initiate and control the propagation of fracture.
  • Chalk, Gray Cast Iron, and Concrete

Failure and Fracture in Material
  • Defects -- Scratches, flaws, and pre-existing
    external or internal cracks.
  • The high tensile stresses subject the tip of the
    crack to propagate the crack rapidly due to the
    materials inability to dissipate energy.
  • Catastrophic failure occurs under tensile
    stresses when compared to their strength in
  • Trans-granular -- Crack propagates through the

Failure and Fatigue in Material
  • Inter-granular -- Crack propagates along the
    grain boundaries, generally when the grain
    boundaries are soft, contain a brittle phase, or
    have been weakened by liquid- or solid-metal

Failure and Fracture in Material
  • Fatigue Failure -- Minute external or internal
    cracks develop at pre-existing flaws or defects
    in the material. The cracks propagate over a
    period of time and leads to total and sudden
    failure of the part.

Failure and Fatigue in Material
  • Beach Marks -- Term given the fracture surface
    in fatigue.
  • Striations -- On the fracture surface, several
    appearing on each beach mark.

Failure and Fatigue in Material
  • Improving Fatigue Strength -- Fatigue life is
    influenced greatly by the method of preparation
    to the surfaces of the part or specimen.
  • Fatigue Strength of manufactured products may be
    improved overall by
  • Inducing compressive residual stresses on
  • Shot Peening or Roller Burnishing
  • Case hardening (surface hardening) by various

Failure and Fatigue in Material
  • Fatigue Strength of manufactured products may be
    improved overall by
  • Providing a fine surface finish and thereby
    reducing the effects of notches and other surface
  • Selecting appropriate materials and ensuring that
    they are free from significant amounts of
    inclusions, voids, and impurities.

Failure and Fatigue in Material
  • Factors and processes that may reduce fatigue
    strength decarburization, surface pits
    (corrosive) acting as stress raisers, hydrogen
    embrittlement, galvanizing, and electroplating.
  • Stress-Corrosion Cracking -- Either over a
    period of time or soon after being manufactured,
    parts free from defects may develop cracks.

Failure and Fracture in Material
  • Stress-Corrosion Cracking -- contd
  • Crack propagation may be inter- or
  • Susceptibility of metals to stress-corrosion
    cracking depends mainly on the material, on the
    presence and magnitude of tensile residual
    stresses and on the environment (Salt water and
    other chemicals.)
  • To avoid Stress-Corrosion cracking stress relieve
    the part after it is formed. Full annealing may
    be done, but reduces the strength of cold worked

Failure and Fatigue in Material
  • Hydrogen Embrittlement -- The presence of
    hydrogen may reduce ductility and may cause
    severe embrittlement and premature failure in
    many metals, alloys, and nonmetallic materials.
  • Especially severe in high-strength steels.
  • Melting of Metal, Pickling (removal of surface
    oxides by chemical or electrochemical reaction,)
    Electrolysis in Electroplating, Water Vapor in
    the Atmosphere, Moist Electrodes, and fluxes in
  • In copper alloys, Oxygen may also cause

Residual Stresses
  • Work-pieces are subjected to plastic deformation
    that is not uniform throughout the part.
    Stresses remain within a part after it has been
    formed and all the external forces are removed.
  • The bending of a metal bar. The elastic and
    plastic deformation resulting in a permanent
  • The linear load reaches the yield stress,
    changing non-uniformly. The release of the
    external force is opposite the curvilinear load
    (elastic.) The difference in the two loads
    gives the residual stress pattern within the bar.
    Compressive residual stresses in ad and oe,
    tensile residual stresses in od and ef.

Residual Stresses
  • Warping -- Disturbances of residual stresses
    acquire a new radius of curvature to balance the
    internal forces.
  • Temperature Gradients within a body may also
    cause residual stresses (cooling or forging.)
  • Contractions and Expansions within a material
    produce non-uniform deformation (beam or lumber.)
  • Tensile residual stresses on a surface are
    undesirable due to the reduction in strength when
    an external force is applied to the part
    (brittle, less ductile.)

Failure and Fatigue in Material
  • Compressive residual stresses on a surface are
  • Shot Peening and Surface Rolling
  • Reduction and Elimination of Residual Stresses --
    Either by stress relief annealing or by further
    deformation of the work-piece.
  • Stress Relaxation may occur over time, and may
    increase greatly by raising the temperature of
    the work-piece.

Work, Heat, and Temperature
  • Almost all of the mechanical work of deformation
    in plastic working is converted into heat.
  • Stored Energy -- A portion of work stored within
    the deformed material as elastic energy.
  • 5 to 10 of total energy input, in some alloys
    may be as high as 30

Work, Heat, and Temperature
  • Change of Temperature is the ratio of specific
    energy to the density and specific heat of
  • Higher Temperatures are associated with large
    areas under the stress-strain curve and with
    smaller values of specific heat.
  • Physical properties as specific heat and thermal
    conductivity depend on temperature and must be
    taken in account during calculations.
  • If deformation process is performed rapidly, the
    heat losses will be relatively small over that
    brief period.
  • If the process is carried out slowly, the actual
    temperature rise will be only a fraction of the
    calculated value.

Work, Heat, and Temperature
  • Specific Energy (u) -- Work of deformation per
    unit volume
  • Density (d)
  • Specific Heat of Material (c)

Chapter 3
Physical Properties of Materials
  • Engineers must make conscious function and
    performance decisions based on the physical
    properties of materials

Physical Properties of Materials Ch. 3
  • Overview
  • Density
  • Melting point
  • Specific heat
  • Thermal conductivity
  • Thermal expansion
  • Electrical, magnetic and optical properties
  • Corrosion resistance

  • Mass per Unit Volume
  • Typical units include
  • kg/m3
  • lb/ft3
  • Specific Gravity
  • Density with respect to water
  • No units

  • Strength-to-Weight ratio
  • Specific Strength
  • Tensile strength / density
  • Stiffness-to-Weight ratio
  • Specific Stiffness
  • Elastic modulus / density
  • Units of length

Melting Point
  • The energy required to separate the atoms of a
  • Units of temperature
  • Important consideration when the material will be
    subject to an operating temperature or a thermal
    cycle during manufacturing process
  • Annealing
  • Heat treating
  • Hot working

Specific Heat
  • The energy required to raise the temperature of a
    unit mass by one degree
  • Units of J/kg K
  • Important consideration in the forming or
    machining operations

Thermal Conductivity
  • The rate at which heat flows within and through a
  • Units of W/m K
  • Very low thermal conductivity of Titanium
  • Can result in excessive tool wear during machine

Thermal Expansion
  • The expansion or contraction of a material when
    exposed to a thermal cycle
  • Units of µM/m C
  • Hot rivets are installed through holes in steel
  • When the rivets cool they contract causing an
    extremely tight compressive stress on the joint

Electrical, Magnetic and Optical Properties
  • Electrical Properties
  • Conductivity
  • The ratio of the current density to the electric
    field strength
  • Dielectric Strength
  • A materials resistivity to direct electrical

Electrical, Magnetic and Optical Properties
  • Electrical Properties
  • Conductors
  • Superconductors
  • Semiconductors
  • Piezoelectric effect
  • A reversible interaction between an elastic
    strain and an electric field
  • Typical applications include pressure
    transducers, sensors, and strain gauges

Electrical, Magnetic and Optical Properties
  • Magnetic Properties
  • Ferromagnetism
  • Ferrimagnetism
  • Magnetostriction
  • The expansion or contraction of a material when
    subjected to a magnetic field
  • The principle behind ultrasonic machining

Electrical, Magnetic and Optical Properties
  • Optical Properties
  • Color
  • Opacity

Corrosion Resistance
  • Corrosion
  • Typically used to describe metal or ceramic
  • Similar phenomena occur in plastics
  • Often referred to as degradation

Corrosion Resistance
  • Types of corrosion
  • Pitting
  • Intergranular
  • Crevice
  • Galvanic cell
  • Stress-corrosion cracking
  • Selective Leaching
  • Oxidation
  • Passivation

Corrosion Resistance
  • Pitting
  • Can occur over the entire surface or be localized
  • Intergranular
  • Occurs along grain boundaries

Corrosion Resistance
  • Crevice
  • Occurs at the interface of bolted or riveted
  • Galvanic cell
  • Occurs between dissimilar metals when an
    electrolyte is present
  • Not as common in pure metals or single-phase

Corrosion Resistance
  • Stress-corrosion cracking
  • Cold worked metals are most susceptible
  • Selective leaching
  • Occurs when metalworking fluid attacks specific
    elements in tool and die materials

Corrosion Resistance
  • Oxidation
  • A chemical reaction which leaves a small layer of
    oxidized material on the surface
  • Resists further corrosion
  • Aluminum Titanium
  • Passivation
  • The development of a protective film by chemical
  • Stainless Steel

Physical Properties of Materials
  • Review
  • Density
  • Melting point
  • Specific heat
  • Thermal conductivity
  • Thermal expansion
  • Electrical, magnetic and optical properties
  • Corrosion resistance

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