Reviewerlec Matl.docx

Fracture Toughness and Fatigue in Engineering The main factors those affect the fracture of a material are: • Stress concentration • Speed of loading • Temperature • Thermal shock. TYPES OF TOUGHNESS Static Toughness Impact toughness Fracture toughnessIMPACT TESTING Is a method for evaluating the toughness, impact strength and notch sensitivity of engineering materials. TYPES OF IMPACT TESTING 1. Charpy Impact Test 2. Izod Impact Test Factors Affecting Charpy And Izod Impact Energy • Yield strength and ductility • Notches • Temperature and strain rate • Fracture mechanism DESTRUCTIVE TESTING Is a testing technique in which the application is made to fail in an uncontrolled manner to test the robustness of the application and also to find the point of failure. Endurance testing under severe conditions until the product fails

PURPOSE OF DESTRUCTIVE TESTING • To determine the service life of the product. • To find the point of failure. • And to detect design weaknesses that may not show up under normal working conditions. TYPES OF DESTRUCTIVE TESTING Tensile Testing Compressive Testing Bend Testing Hardness Testing Impact Testing Two Types of Bend Testing • 3-point Bend Testing • 4-point Bend Testing Most Common Hardness Testing I. The Rockwell hardness test II. The Vickers hardness test III. The Knoop hardness test IV. The Brinell hardness test Fatigue Testing Fatigue is the effect on metal of repeated cycles of stress Types Of Fatigue Tests: High Cycle Fatigue (HCF) of Metals Low-Cycle Fatigue Testing Purpose Of Fatigue Testing: The purpose of a fatigue test is to determine the lifespan that may be expected from a material subjected to cyclic

loading, however fatigue strength and crack resistance are commonly sought values as well

Corrosion Prevention and Control Corrosion is defined as the destructive and unintentional degradation of a material caused by its environment. Corrosion Control Cathodic protection (CP) Linings and coatings Corrosion inhibitors How to Prevent Corrosion Protective Coatings Environmental Measures Sacrificial Coatings Cathodic Protection Anodic Protection Significance and Purposes 1. Safety 2. Health 3. Environment 4. Economy 5. Structural Integrity 6. Energy Infrastucture

7. Conservation 8. Machineries \ Aqueous Corrosion Aqueous corrosion is an electrochemical reaction of materials due to a wet environment, resulting in the deterioration of the material and its vital properties. In order for aqueous corrosion to occur, the following must be present: •Oxygen •Electrolyte of moisture •Material with corrosion potential immersed in the electrolyte A.C. Appears as: •Pitting •Crevice corrosion •Intergranular corrosion •Stress corrosion • General corrosion

Pitting Corrosion Pitting corrosion is a localized form of corrosion by which cavities or "holes" are produced in the material. Crevice Corrosion Crevice Corrosion refers to the localized attack on a metal surface at, or immediately adjacent to, the gap or crevice between two joining surfaces. Intergranular Corrosion

This is a corrosion type that attacks the boundaries of the metal crystallites, as opposed to attacking the surface of the metal Stress Corrosion Stress corrosion refers to the degradation and/or rust formation of a given metal surface in an electrochemical fluid environment due to the metal being subjected to tensile forces in residual or direct form. General Corrosion general attack corrosion proceeds more or less uniformly over an exposed surface without appreciable localization The Rate of Corrosion The rate of corrosion is the speed at which any given metal deteriorates in a specific environment. Factors that affect the rate of corrosion: Oxygen, Temperature, Chemical Salts, Humidity, Pollutants GALVANIC CORROSION (Also called bimetallic corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. Three conditions must exist for galvanic corrosion to occur:

•

Electrochemically dissimilar metals must be present • The metals must be in electrical contact, and • The metals must be exposed to an electrolyte There are four elements necessary for corrosion to occur in a galvanic cell Anode ,Cathode, Electrolyte, Return Current Path

CREVISE CORROSION Refers to corrosion in confined spaces to which the access of the working fluid from the environment is limited. 3 MAIN TYPES: Metal ion concentration cells Oxygen concentration cells Active-passive cells PREVENTION: 1. Select the right materials for an appropriate surrounding. 2. Apply coating on the materials to block the compound that would take part in the reactions. 3. Add an insulating layer between the two metals so that the electron cannot pass through it.



Ultrasonic Testing (UT)

Why NDT?



Low voltages



No poles to attract particles



Control of amperage



Test piece too precious to be destroyed



Test piece to be reuse after inspection

NONDESTRUCTIVE TESTING (NDT)



For quality control purpose



Danger of arcing

is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system



Test piece is in service



Danger of overheating



Heavy transformer required



Must have good electrical contact



Usually two-man operation

Disadvantages:

Visual Inspection 

Most

basic

method.

Tools

borescopes, Objectives of NDT

and

common include

magnifying

inspection fiberscopes,

glasses

and

mirrors.



To detect internal or surface flaws



To maintain uniform quality level

Nondestructive testing method used for defect



To control manufacturing processes

detection. Fast and relatively easy to apply



To aid in better product design

and part surface preparation is not as critical

Liquid Penetrant Testing



To ensure operational readiness.

as for some other NDT methods

This method employs a penetrating liquid, which is applied over the surface of the component and enters the discontinuity or crack. Steps for Performing a LPT

Detection of surface flaws

Magnetic Particle Inspection (MPI)

Electromagnetic Yoke - A magnet that



Visual Inspection

induces a magnetic field in the area of a part



Magnetic Particle Testing (MT)

that lies between the poles.



Liquid Penetrant Testing (PT)

Detection Of Internal flaws 

Radiographic Testing (RT)

Advantages and Disadvantages of MPI

1) Surface Preparation 2) Penetrant Application



AC or DC fields

3) Excess Penetrant Removal



Useful in confined spaces

4) Developer Application

5) Inspection

Ultrasonic methods of weld testing use beams of sound waves (vibrations) of short wavelength and high frequency, transmitted from a probe and detected by the same or other probes Test Techniques

6) Final Surface Cleaning

Advantages of PT as an NDT Method: 

High

sensitivity

to

small

surface

discontinuities 



Pulse-echo and Through Transmission



Normal Beam and Angle Beam



Contact and Immersion



Portable method

Inspection Applications



Relatively inexpensive

• Flaw detection (cracks, inclusions, porosity,



Can only detect discontinuities that are open to the surface



Can only inspect parts with nonporous surfaces



Must pre-clean/post-clean parts



Inspector must have direct access to the

etc.) • Erosion & corrosion thickness gauging • Assessment of bond integrity in adhesively joined and brazed components • Estimation of void content in composites and plastics • Measurement of case hardening depth in steels

Time-consuming

Ultrasonic Testing

to

both

surface

and

subsurface

discontinuities. • Depth of penetration for flaw detection or measurement is superior to other methods. • Only single-sided access is needed when pulse• High accuracy in determining reflector position and estimating size and shape. • Minimal part preparation required. • Electronic equipment provides instantaneous results. •

Detailed

images

can

be

produced

with

automated systems. •

Has

other

uses

such

as

thickness

measurements, in addition to flaw detection. Radiographic Testing

part surface 

Sensitive

echo technique is used.

Few material limitations

Disadvantages of PT as an NDT Method

Advantage of Ultrasonic Testing

Data Presentation A-scan B-scan C-scan

Radiography is used in a very wide range of applications including medicine, engineering, forensics, security, etc. Examples of application of radiographic



Pipeline welded joint inspection



Pressure vessel fabrication quality control



Welder qualification testing



Structural steel fabrication



Detect Discontinuities in weld

 

Very minimal or no part preparation is



Image viewed immediately on screen.

required.



Time consumption is less.

Permanent test record is obtained.

Types of Radiographic Testing

Demerits: Radiographic Testing 

Poor resolution



Film Or Paper Radiography



Low image contrast



Computed Radiography



Electronic image intensifier required for



Real Time Radiography

Both surface and internal discontinuities



Neutron Radiography

can be detected.



Stereo Radiography

Significant variations in composition can



X-ray Radiation

be detected.



Gamma Rays Radiation



It has a very few material limitations.



Neutron Radiation



Can be used for inspecting hidden areas

Advantages: Radiographic Testing  

(direct access to surface is not required) 

Very minimal or no part preparation is



Sand inclusions

required.



Blow holes



Shrinkage

Both surface and internal discontinuities



Cracks

can be detected.



Inclusions

Advantages: Radiographic Testing   

Flaws Detection : Radiographic Testing

Significant variations in composition can

Merits: Radiographic Testing

be detected.



No need of washing and developing films.

It has a very few material limitations.



Low cost.

increasing the contrast