cve221 chapter 1 materials eng. concepts in color

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CVE221 Construction Materials &Quality Control

CHAPTER 1 Page (19-69)

Materials Engineering Concepts

Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc.


Objectives of Chapter 1:

1. Understand how to select and specify variableconstruction materials.

2. Know different types of loading and the constructionmaterials behavior.

2

Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc. 3

INTRODUCTION

Common civilengineering materials:

steel

mineral aggregates concrete

masonry

asphalt

wood

soil for geotechnicalengineers

Less common materials

aluminum

glass

plastic

Fiber-reinforcedcomposites




New Materials

Advances in

polymers adhesives

composites

geotextiles

coatings

synthetics

High performance

materials higher strength to

weight ratio

improved durability

lower costs


Material Selection Considerations

Economic factors

Mechanical properties

Non-mechanicalproperties

Production/construction

Aesthetic properties

Sustainableconsiderations

Emphasis

client’s needs

facility’s function


1.1 Economic Factors (0)

Factors to be considered

availability and cost of raw materials

manufacturing costs transportation

placing

maintenance

6




1.2 Mechanical Properties

Response of material to external loads

All materials deform under load depending on: material properties

magnitude and type of load

geometry of the material element


1.2.1 Loading Conditions Static (Dead) Loads – long term

applied and removed slowly so no vibrations

usually due to gravity

Dynamic (Live) Loads – short term shock or vibration

periodic – repeating wave form (rotatingequipment)

transient – quick impulse that decays back toresting (vehicles)

random – never repeats (earthquake)


1.2.2 Stress-Strain Relations

All solid materials deform under load

stress is like force (or load) with the size factored outso that we can directly compare different sizes

stress = force / area = F / A (psi, ksi, kPa, MPa, GPa)

strain is like deformation with the size factored out

strain = deformation / original length

= L / L0 (%, in/in, mm/mm)




Typical Stress-Strain Diagrams

– is usually linear in the low stress range but

transforms into non-linear

Glass and

chalk

Steel Aluminum

alloys

Concrete Soft

rubber


1.2.3 Elastic Behavior

Instantaneous response to load

Returns to its original shape upon unloading stretches bonds between atoms without rearranging

them


Linear & Non-Linear Behavior

A linear material has a straight line stress-straingraph

An elastic material returns to its original shape

12

Linear elastic

Non-linear elastic

Non-linearinelastic




Properties of an Elastic Material

Modulus of Elasticity or Young’s Modulus

E = / slope (rise over run) of the linear portion of stress-strain

curve

Poisson’s Ratio

= - l / a

relates lateral strain, l, to axial strain, a

as material is stretched the cross section shrinks and viceversa for compression

Range = 0 to 0.5 (practically 0.1 to 0.45)


Generalized Hooke's Law

For three directions (3D = triaxial)

E

z y x

x

E

x z y

y

E

y x z

z

yx

z

E E

E

AF

z z

y

z z

y x

z

00

00

0

For axially loadedmembers, nostresses in the xand y directions


What if response is not linear?

How do we find the slope (Modulus of Elasticity)?

Strain

S t r e s s

Initial

Tangent

Modulus

Secant

Modulus

Chord

Modulus

Tangent

Modulus




Typical Moduli and Poisson’s Ratios

Material Modulus

(psi x 106

)

Poisson’s

RatioAluminum 10-11 0.33

Brick 1.5-2.5 0.23-0.40

Concrete 2-6 0.11-0.21

Limestone 8.4

Steel 29 0.27

Wood 0.9-2.2

16


1.2.4 Elastoplastic Behavior (Page-26)Most materials are linear elastic in small stress range

and then plastic

the transition point is elastic limit

Elastic

stretches bonds between atoms withoutrearranging them

recoverable deformations (springs back)

Plastic

atomic bonds slip past each other and rearrange

permanent deformations (doesn’t spring all the wayback)


when unloaded, rebound parallel to the linear portion with someremaining plastic deformation

stretched bonds return, rearranged ones don’t

when reloaded, follows the rebound line and then original curve

strain hardening

stress increases during plastic deformation

reloading returns to previous peak stress

Elastic-perfectly plastic Strain hardening




S t r e s s

Total Strain

Elastic

Strain

Plastic

Strain

Force is applied resulting in

stress and strain

Strain

When force is removed,

stress returns to zero.

Path is parallel to the

initial slope of the curve.

Part of the strain is

“recovered,” this is

elastic behavior.

Part of the strain is

permanent, this is

plastic behavior.

Elastic Limit

New elastic limit

Reloading will resume to the highest

previous stress level.

Elastic limit is “reset to the previous

highest stress level.”

Response to further

loading follows

original stress-strain

behavior


What if there’s no clear transition point?

Extension methodOffset method


Elements of Stress-Strain Diagram




Definitions

Proportional Limit

transition between linear and non-linear behavior

Elastic Limit (Yield Point)

transition between elastic and plastic behavior – maximum stress with full recovery

Yielding

strain continues with little or no increase in stress(after elastic limit)

Ultimate Stress

maximum stress on the curve (tensile orcompressive strength)


Definitions (Cont.)

Rupture Stress

point where specimen fractures or ruptures

Brittle Material

has little plastic deformation before failure (glass,concrete)

Ductile Material

has lots of plastic deformation before failure(structural steel, rubber)

23


1.2.5 Viscoelastic Behavior

Viscosity: Resistance to flow(i.e., to shear force)

for linear materials:

= shear stress/rate ofshear strain, unit Pa.s orcP

Viscoelastic materials

have both elastic andviscous response

have delayed response24




Viscoelastic materials

Deformation depends on

oDuration of load

oRate of loading

A quick shock or pulse may cause littledeformation, while a sustained load can causemuch deformation

o Temperature

Creep: Long-term deformation under constant load

Asphalt concrete creeps

Portland cement concrete creeps over decades

25


Rheological models page [33-35] not included !

used to model mechanically the time-dependent behavior ofmaterials

basic rheological elements

Rheological models are combinations of elements

Maxwell Kelvin

Prandtl

Burgers

Spring St. VenantDashpot

26Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc.


1.2.6 Temperature & Time Effects (Page -35)

Temperature affects mechanicalbehavior of all materials

high temp = ductile

low temp = brittle

Impact fracture test measures toughness at differenttemperatures

Viscoelastic materials like asphalt and polymers aregreatly influenced by a change of only a few degrees

Metals require a much greater temperature changebut are similarly affected




1.2.7 Work & Energy

Work (or Energy) = force x distance

Modulus of Resilience: energy required to reach yieldpoint

Toughness: energy required to fracture


1.2.8 Failure and Safety

Several ways to fail –

fracture or breakage

fatigue (repeated stress)

general yielding

buckling

excessive deformation

For safety, structures are designed to carry loadsgreater than anticipated


Endurance Limit




Factor of SafetyFS = (allowable stress / actual stress)

FS is proportional to cost and is chosen by:

o cost

o material variability

o accuracy in considering all loads

o possible misuse

o accuracy in measuring material response

(good testing?)

FS =allowable

failure

> 1


1.3 Non-Mechanical Properties

Other than load responses:

Density

Thermal Expansion

Surface Properties

Abrasion & Wear Resistance

Surface Texture


1.3.1 Density and Unit Weight

density = = m / V

unit weight = = W / V

specific gravity

w

G




1.5 Aesthetic Characteristics

The civil engineer is responsible for working with the

architect

The mix of artistic and technical design skills makesthe project acceptable to the community

Engineers should understand that there are manyfactors beyond the technical needs that must beconsidered

37


1.6 Sustainable Design

Sustainable design is the philosophy of designingphysical objects, the built environment and servicesto comply with the principles of economic, social, andecological sustainability.

The materials used for CE projects are important tothe sustainability of the project.

The Green Building Council developed theLeadership in Environment and Energy Design,LEED, building rating system to evaluate the

sustainability of the project.

38


Sustainable Design (Cont.)

For new construction and major renovations the ratingareas include:

Sustainable sites

Water efficiency

Energy and atmosphere

Materials and resources

Indoor environmental quality

Innovation in design

Regional priority

39




1.7 Material Variability

All materials have variability

Some materials are more uniform than others

oSteel vs. concrete vs. wood

Error vs. mistake

Three sources of variance:

Material

Sampling

Testing

Use good sampling and testing techniques tominimize those variabilities


Precision: measure many times and get same result

Bias: tendency to deviate in one direction from truevalue

Accuracy: close to true value; absence of bias


1.7.1 Sampling (Page-46 )

Proper sampling must ensure that a random andrepresentative sample is taken from the population (e.g.,stockpile, lot, etc.)

Random: have an equal chance of being selected

Representative: perfect average of the entire stockpile

Sample size:

depends on materials variability & tolerance level ofresults

more variability dictates a larger sample

Rigorous statistical evaluations required for specialapplications:

high quality asphalt and Portland cement concrete




Describes many populations that occur in nature,including material properties

Area under the curve between any two valuesrepresents the probability of occurrence

1.7.2

Normal

Distribution

43


Decrease inspection frequency

Early detection of troubles

Provide a record of quality

Basis of acceptance

1.7.3

Control

Charts


1.7.4 Experimental Error (Page-50)

Caused by 3 factors:

Procedural errors

Are often undiscovered

Machine errors (bias)

If known and constant can be easily corrected

Human errors

Minimize by repetition, double-checking, etc.o Always do more than one test




1.8 Laboratory Measuring Devices Direct

Ruler, dial gauge, calipers

Physical & material properties are usually measured(time, deformation, force, etc.)

Indirect

LVDT, strain gauge, load cell

measuring changes in electric voltage and relating todeformation, stress, or strain

must be calibrated

Electronic sensors can be easily connected to digitaldevices or computers:

CDAS (computerized data acquisition system)


Dial Gauge

LVDT

StrainGauge

47


ProvingRing

LoadCell

Extensometer

Non-ContactExtensometer

48




Important considerations:

Sensitivity

Accuracy

Calibration

Sensitivity of measuring devices:

the smallest value that can be read on the device’sscale

sensitivity is not accuracy or precision

accuracy cannot be better than the sensitivity

When choosing a device, sensitivity depends on therequired accuracy, which depends on the type oftest.

cve221 chapter 1 materials eng. concepts in color

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