Ex 1. Materiales Ing. Civil Ch.1

Criteria for Material Selection

Economic Factors
Mechanical Properties
Nonmechanical Properties
Production/Construction Considerations
Aesthetic Properties
Sustainable Considerations
Material Variability

Economic Factors

Availability and Cost of Raw material
Manufacturing Cost
Transportation
Placing
Maintenance

Mechanical Properties

Response of the material to loads

Failure types

Catastrophic and Functional

Example of catastrophic failure

material failure

Examples of functional failure

Excessive roughness, excessive displacement, excessive vibrations

Static (Dead) loads

long term forces applied and removed slowly, therefore vibrations dont occur.

What are static loads a result of ?

gravity

Dynamic (Live) Loads

short term forces that cause shock or vibration

types of dynamic loads

periodic (repeating wave form), transient (quick impulse that decays back to resting) and random (never repeats)

Which material has this stress-strain response

Glass and Chalk

Which material has this stress-strain response

Steel

Which material has this stress-strain response

Aluminum

Which material has this stress-strain response

Concrete

Which material has this stress-strain response

Rubber

Elastic Behavior

Instantaneous response to load
Returns to its original shape upon unloading

Characteristic of linear behavior

a linear material has a straight line stress-strain graph

What approximating modulus is used in the graph?

Secant modulus

What approximating modulus is used in the graph?

Chord modulus

What approximating modulus is used in the graph?

Initial tangent modulus

What approximating modulus is used in the graph?

Tangent modulus

Definition of yield point when not well defined

0.2% offset method and 0.5% extension method

Viscosity

resistance to flow/shear force

Viscoelastic Materials

Have both elastic and viscous response and have a delayed response

On what depends the deformation on viscoelastic materials

duration of load
rate of loading
temperature

Creep

long-term deformation under constant load

Rheological models

combination of elements used to model mechanically the time-dependent behavior of materials

Types of failure

fracture, fatigue, buckling, yielding, excessive deformation

Safety Factor

Base on how well certain values are known

Example of nonmechanical properties

unit weight, density, specific gravity, surface roughness, absorption, permeability, porosity

Surface Characteristics

Corrosion and Degradation
Abrasion and Wear resistance
Surface texture

Corrosion and degradation

Deterioration over time
Depends on the material characteristics

Abrasion and Wear Resistance

Important in moving parts
Mostly for pavements (aggregates)

Surface texture

Smooth or rough textures

Fatigue

Ocurre en siglos dependiendo la densidad de la carga

Buckling

Ocurre por debajo del esfuerzo de ruptura. Depende de la rigidez de la seccion

Yielding

Articulacion plastica

Excessive deformation

hay mucho desplazamiento

Three sources of variance:

material, sampling, testing

Error vs Blunder

error means something donde incorrectly and blunder is a careless mistake often unnecessarily

Precision

measure many times and get same result

Bias

Tendency to deviate in one direction from true value

Accuracy

close to true value; absence of bias