Module3-1

Module 3
Properties Characterization of Materials
3.1 Properties and Evironmental Variables 3.2 Mechanical 3.2 Mechanical Properties 3.2.1 Stress
3.2.2 Strain(unit deformation)Stress 323Stress-Properties
3.3 Electrochemistry 3.4 Thermal Properties 3.5 Determining Materials Structure
3.2.3 Stress 3.2.3 Stress--strain diagrams and Hooke’s law
3.2.4 Ultimate strength or tensile strength 3.2.5 Yield strength 3.2.6 Resilience 3.2.7 Shear stress
z Recall the vocabulary and fundamental concepts related to the mechanical and thermal properties of materials
z Use diagrams,explanations,and calculations to determine mechanical and thermal Objectives
properties of materials materials..
z Determine the names and types of standard mechanical tests for the properties they measure
z Familiar with the main characterization methods for materials
Q3.1
How does one tell the difference between the materials that are used to produce the many products in our daily lives?
A :The materials can be identified by properties or characteristics characteristics..
Structure
Subjecting Subjecting Material Material to external forces and/or conditions
change
properties
Service needs
affect
meet
Environments
Uses
determine
properties +
Properties Properties::
9Behavior of materials when subjected to some external force or condition condition..
9Those characteristics that help modify and
distinguish
one material from another another..3.1 Properties and environmental variables g Classification Classification::
Properties
Physical properties
Chemical properties
z
Physical properties
involve no change in the composition of the material
z Chemical properties
are associated with the transformation of one material into another
Subdivisions of physical properties
Mechanical 力学性质
metallurgical 冶金性质fabrication 加工性质General 一般性质M ti Magnetic 磁学性质Electrical 电学性质Thermal 热学性质Optical 光学性质thermonuclear 热核electro electro--optical 光电性质
physical properties
resulted from the response of the materials to some environmental variable
z Definition
9A measure of a material’s ability to carry or resist
mechanical forces or stresses
z Importance
9rank rank highest highest in in importance importance when selecting materials 3.2 Mechanical properties (力学性质)
for many applications
9affect how the material can be worked
¾Examples
9Durability 耐久性9Formability 可成形性9Rigidity 刚度9strength 强度9Toughness 韧性
Three mechanical tests
mechanical tests
Q4.2
What are the three mechanical tests that supply the most useful information for most applications?
tensile test 拉伸试验
impact test 冲击试验
hardness test 硬度试验
strength 强度rigidity 刚度durability 耐久性
4.2.1 Stress 应力
Definition
9the resistance offered by a material to external forces or loads
Measurement
Tension, compression, or shear
9Measured in terms of the force exerted per area
F σ=
A 9Customary Unit : psi (Customary Unit : psi (p p ounds per ounds per s s quare quare i i nch)SI unit: N/m 2or Pa （pascal pascal) )
1Pa=1N/m 2
Normal stress
正应力
the amount of force area over which it acts
4.2.2 Strain (unit deformation)
Definition
9The unit change in the size or shape of material as a result of force on the material 9Deformation: the change in a physical dimension 尺寸
Types
9Unit axial or longitudinal deformation 单位纵向形变
9Unit lateral deformation 单位横向形变
Dimensionless
Total deformation
z Total axial deformation Δl=δl =l
=l --l 0d 0
No load
z Total lateral deformation Δd=δd =d 0 -d
F
F
d l 0
l
Δl
Tensile load
拉伸载荷
z Axial or longitudinal unit
deformation (纵向单位形变)(axial strain 轴向应变)d 0
No load
Unit deformation
ε=
=
Δl mm δmm
F F
d l 0
l Δl
long.l 0 mm
l 0 mm
z Lateral unit deformation
(横向单位形变) (
) (lateral strain lateral strain 横向应变)
εlat.=
=
Δd mm d 0 mm
δmm d 0 mm
z The ratio of the lateral unit deformation or strain (εlat., 横向单位形变) to the longitudinal unit deformation or strain (εlong , 纵向单位形变)
εPoisson’s ratio (泊松比)
9εlong > εlat., μ<1;
9Tensile load: length increased, width decreased
Compressive load: Compressive load: length decreased, width increased length decreased, width increased
εlong.
lat.μ=
3.2.3 Stress 3.2.3 Stress--strain diagram and Hooke’s law
A stress A stress--strain diagram for low strain diagram for low--carbon steel
Elastic region (弹性区)
Plastic region (塑性区)
应力
应变
Abscissa 横坐标
Ordinate
纵坐标
z Elastic region (弹性区)
9Straight Straight--line portion of the diagram
9The material will return to its original dimensions once the load 载荷has been removed
Elastic region and Hooke’s law 9Elastic deformation 弹性形变: If the material : If the material reverts reverts back to its to its normal size normal size and and shape shape upon removal of the load 载荷
z Hooke’s law 虎克定律
9Each increase in stress will produce a proportionate increase in the strain
E ：elastic modulus 弹性模量
σ=E εElastic Modulus
z Young’s modulus, modulus of elasticity, tensile modulus, modulus of elasticity in tension, coefficient of elasticity
z The ratio of engineering stress to engineering strain in the linear or elastic region of the stress in the linear or elastic region of the stress--strain curve
∆ε
∆σ
E=
∆σ∆
ε
Elastic Modulus
z Obtained graphically by measuring
9the the tangent tangent 正切of the of the slope angle slope angle (倾角) in the elastic region of the stress of the stress--strain curve
9the the slope slope (斜率) of the straight ) of the straight--line portion.
∆ε
∆σ
E=
tan θ=θ
Elastic Modulus
z An indication of the stiffness of the material when subjected to a tensile load
z A measure of the interatomic bonding forces in a material
–The The higher higher the magnitude of the magnitude of elastic modulus,elastic modulus,the higher the magnitude of these bonding forces, the stiffer the the materials,materials,the higher the resistance of the material to being deformed.When a material is loaded with external forces the material with the highest modulus value experiences the _______amount of deformation or strain.a)greatest b)least
Q4.3
Stress Stress--strain diagram
Yield point
(屈服点)
Plastic region (塑性区)
应力
应变
Elastic region (弹性区)
•Dividing line •Transition from the elastic to the plastic region of the curve
9The dividing line or transition from elastic to the plastic region
9When a stress reaches the yield point, a large increase in in strain strain occurs with occurs with little little increase in in stress stress..
Yield point (屈服点)
Yield point Plastic region (塑性区)
p
(屈服点)
Elastic region (弹性区)
z Plastic deformation (塑性形变)
9Beyond the yield point, the material will continue to deform, but with continue to deform, but with less stress less stress than before
Pl ti d f ti h th l d i Plastic region (塑性区)
9Plastic deformation 塑性形变: when the load is removed the material will removed the material will not return not return to its original dimensions (or the material is permanently deformed 永久变形)
Yield point (屈服点)
•No pronounced yield point
Grey cast iron 灰铸铁
9No clear indication of the start of yielding as the load is increased
Modulus of elasticity: the slope of a Modulus of elasticity: the slope of a tangent tangent to the stress to the stress--strain curve at the origin 原点
3.2.4 Ultimate Strength or Tensile Strength
The maximum stress developed in a material during a tensile test tensile strength
g
Ultimate shear
strength ≅75% ultimate tensile strength Uniform strain (εu )
Application of ultimate strength or tensile strength
9A good indicator of the presence of defects in the crystal structure of a metal
9A valid criterion for tensile strength
brittle materials
9The amount of plastic deformation must be limited to much smaller values than that accompanying the maximum stress
4.2.5 Yield strength(屈服强度)
The The stress stress
corresponding to the the elastic limit elastic limit The lowest stress yield strength
at which plastic deformation occurs For most design, the yield strength is assumed to be the same in tension as in compression
elastic limit
Yield point strain
(εyp )
Stress Stress--strain diagram
Yield point (屈服点)
Ultimate strength （极限强度）
Yield strength
屈服强度
Elastic region (弹性区)
Plastic region (塑性区)
Fracture (断裂点)
应力
应变
Elastic modulus
Determining offset yield strength
The stress at which the offset line intersects the stress stress--strain curve
Offset line Intersection point
0.2% offset (as elastic limit),
also specified as 0.1% or 0.5%
Offset line, parallel to the straight the straight--line portion
A stress A stress--strain diagram for an aluminum alloy
z Steps for determining offset yield strength
1.
Offset 2.Offset line
3.Intersection point
4.
Include the values of offset & the stress
offset yield strength
z The yield strength of metals is much
higher than that of other materials z The difference The difference in the in the yield strength and
tensile strength tensile strength indicates the indicates the ductility ductility of of materials
z The difference between the The difference between the yield strength yield strength
and and tensile strength tensile strength
Brittle & Ductile materials
brittle materials: very little difference ductile materials: wide difference
3.2.6 Resilience (回弹)
Modulus of resilience (R)回弹模量
9The The area area under which under which the straight the straight--line portion l i i ) f h (elastic region elastic region) of the ) of the stress stress--strain curve 9A measure of the energy per unit volume that the material can absorb without plastic deformation
SI unit: MPa
z Symbol: τ
z A shearing force produces a shear stress (τ), resulting in a shearing deformation (δs )
3.2.7 Shear stress (shearing stress)
The shear force, F, produces an an angular deformation angular deformation (δs )
A0
δs
h
F
F Before a shear load is applied
z The The deformation deformation produced by the shear force F divided by the by the dimension h dimension h
Shear strain (γ)(剪切应变)
i δs
F h in.
δs in.γ=
h
F
γ
•The The tangent tangent 正切of
the angle labeled γin radians 弧度
z Shear modulus
of elasticity (G)
9The ratio of the
shearing stress to Modulus of rigidity (Modulus of rigidity (G) G) 刚性模量
the shearing strain in elastic region
γ
τG=
Shear stress stress--strain diagram
9SI Unit: psi or pascal。