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Materials

Properties of Materials- Chapter 1

QuestionAnswer
Material Engineering Understanding the behavior and performance of materials
Why we need this knowledge For the design, construction & maintenance of civil structures
Advancements in Material Technology Objectives • Better quality • More economical • Safer materials
Material Engineer Involved in: • Selection • Specifications • QC/QA
Economic considerations Cost of material include: • Direct cost (raw material & availability) • Manufacturing • Transportation • Placing • Maintenance Example: Bituminous mixtures
“Response to external load” depends on: • Properties of materials • Magnitude, location, and type of load • Element geometry Example: Steel beam in a building
Types of material or element failure: –Collapse failure –Functional failure Example: Structural beam or column in a building
Loading conditions: • Static loading:“Remain in place (sustained or dead load) or removed slowly” Ex: Load of the structure, furniture, occupants, etc. • Dynamic loading: “cause vibration of structure” Ex: “Earthquakes”, Vehicles on roads or bridges”.
Elastic behavior Deforms under load with perfect recovery after load removal of the load (Ideal condition)
Modulus of elasticity (E)= Normal stress / Normal Strain
Poisson’s ratio = Lateral strain/ Axial strain (Range: 0.0‐0.5)
Elastoplastic behavior Types: Brittle material: No deformation (very little) prior to failure (Concrete). Ductile material: Appreciable plastic deformation prior to failure (Steel).
Toughness: Amount of energy required to fracture a specimen or sample or the area under the stress strain curve.
Creep Long term deformation caused by sustained loads (example: concrete).
Viscous flow Short Term deformation caused by sustained load (example: asphalt mixtures)
Temperature Generally, higher temperature increases toughness and visa versa (changes material from brittle to ductile)
Fracture mode of failure Fails when loads exceeds the maximum stress (Ex: concrete column in building)
Fatigue mode of failure Though stress are below maximum stress, it will fail as a result of repeated loads (Ex: highway pavement)
Excessive deformation(deflection) mode of failure Makes people uncomfortable though the structure is sound
Factor of Safety (FS) Stress at Failure/Allowable Stress
Density Mass/Volume
Unit Weight Weight/Volume
Specific Gravity Mass of Material/Mass of water of equal volume at specified temp
Density and Unit Weight of Aggregates Needs other terms to assess based on degree of compaction, voids, etc.
Thermal expansion Rate of material expansion with temperature; expressed as coefficient of thermal expansion
Surface characteristics Surface texture, abrasion resistance and wear, forms of surface deterioration
Corrosion form of surface deterioration surface disintegration by dissolution (example: metals)
Degradation form of surface deterioration loss of solvent (example: asphalt)
Wear form of surface deterioration External abrasion action (example: rigid and flexible pavements/studded tires)
Aesthetic characteristics Appearance of material, requires the collaboration between the architect and material engineer
Material Variability Changing properties of certain material as a result of natural, production, environmental and human factor
Precision Variability of repeated measurement under carefully controlled conditions
Accuracy conformity of results to the true value or the absent of bias
Bias Tendency of an estimate to deviate in one direction from the true value or systematic error between a test value and the true value
AMRL (American Materials Reference Laboratory) a certification agency for engineering laboratory
Sampling A true representation of a population (material)
Random Sampling requires all elements of the population to have an equal chance to be chosen for selection
Representative Sampling Taken from the population and representative of the entire lot
True sampling depends on: •Number of samples •Nature of material •Rate of production •Production period •Production equipments
Control charts A graphical presentation to verify a process's in control
Experimental Errors are caused by: • Human errors • Machine errors
Created by: smh02