Engo Trial Study

Stress/Strain Graph Overview

The stress/strain graph provides engineers with a list of details which are needed for application design. The stress/strain graph gives many mechanical properties such as strength, toughness, elesticity, yield point and elongation during load.

True Stress

Stress calculated as the area of the material changes

Engineering Stress:

Stress calculated using the base area of the material

Yield Stress

The level of stress that marks the tranisition from elastic to permanent plastic deformation

Proof stress:

The amount of stress a material can endure until it undergoes plastic deformation (used when no yield point is visible)

Toughness:

Measure by the area under a stress-strain graph, is a measurement of how much energy a material can absorb.

Young’s modulus:

A measure of elasticity and is found by dividing stress by strain

Hookes Law:

Hookes Law states that stress is proportional to strain

Factor of Safety:

The allowable amount of stress that a material can safely hold.

 High Young’s Modulus

examples are metals

Low Young’s Modulus

examples are polymers

Destructive Testing

All destruvtive tests mean that the test piece IS DAMAGED in some way so that its beyond further use

Tensile Testing

A test that applies tension to a material and measures mechanical properties such as stiffness, toughness, resilience and elasticity as it generates a stress/strain graph.

Tensile Testing process

1. A material is securely clamped between 2 grips in a testing machine

2. A uniaxal tensile force is gradually applies at a constant rate, stretching the material

3. Force and elongation are calculated, generating a stress/strain graph

4. Yield Strength and UTS are calculated

5. Material eventually fails, properties of ductility and brittleness are recorded

Compression Testing

SImilar to tensile testing however it is the reverse where the load or force is directed inwards as if squashing the material

Compression Testing Process

1. Material placed between 2 compression plates

2. A steadily compressed force is applied to the material

3. Sensors from machine record deformation and load generating stress/strain graph

4. Yield point and UTS are calculated

5. Material fails/deforms

Non-Destructive Testing

Non-Destructive tests DO NOT PERMANENTLY DAMAGE the test piece and so it is therefore possible for the material to be put back into service.

X-Ray

1. Machine detects discontinuities in metals, polymers and composites

2. Material is tested through X-Ray machine

3. Variation in density of material

4. Printed onto film/screen

5. Image is examined, identifying any internal voids like cracks or flaws

Brinell Hardness Test

The Brinell Test is an indentation hardness test which uses a verified machine to force a spherical ball indenter into the surface of the material under test

Brinell Hardness Test Process

1. Push hard spherical ball into material with a set force

2. Analyse the size of the indentation with microscope

3. Measure the diameter 

4. Results

Rockwell Hardness Test

The rockwell hardness test measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load) using diamond indentor

Rockewell Hardness Test Process

1. Diamon indentor cone is pressed onto test piece surface with 10KP minor force

2. Test force is increased by 140KP acting as the major force

3. Forces held on material for a period of time

4. Major force then removed while minor force is still acting

5. The permanent increase in depth of indentation is measured

Vickers Hardness Test

In the vickers hardness test, an optical method, the size of indentation (the diagonals) left by the indentor is measured 

Vickers Hardness Test Process

1. Diamond pyramid pans down and carefully touches test piece surface

2. Test force slowly increases to specified value

3. Then indentor lifts again after being held down for a period of time

4. Microscope lens then resumes to its former position

1. Using control knob, tester uses 4 measuring lines to find length of 2 diagonals

SLUMP TEST

Measures viscosity and its workability of concrete

Slump Test process

1. Tampered pot is filled with concrete

2. Pot is inverted placed down onto a metal pan, before being lifted

3. Worker measures height, or the slump of the concrete and looks at the way it flows out to determine its viscosity

Concrete Mix:

• 1 part Cement

• 2 part Sand

• 4 part aggregate

• Water

Ceramics

Ceramics are formed when both metals and non-metals combine to create a new material

They can be crystalline or non-crystalline (amorphous)

Ceramics are formed through primary bonding such as ionic or covalent bonding

Ceramics Properties

• High melting points

• Good insulators

• Resistant to chemical attack

• Good resistance to weathering

Production of Ceramics Stage 1: Drying

Up to 150 degrees / Dries to surface water

Production of Ceramics Stage 2: Dehydration

150-650 degrees / Internal water is dried out

Production of Ceramics Stage 3: Oxidation

550-900 degrees / Creates oxides

Production of Ceramics Stage 4: Vitrification

900 degrees upwards / “Glassy Phase”

Glass

Glass is primarily made from Silica (Sand) and is melted in a furnace at 1700 degrees. Oxides of alumium, zinc, lead, titanium and cadmium are added to increase bond strength of the glass

Glass FLOAT PROCESS

1. Molten glass rolled from a furnace into a bed of molten tin

2. As glass ribbon rolls around tin bed, it cools preventing warping or loss of shape

3. Solidifed glass transfered to annealing lehr for slow cooling to release internal stress and prevent cracking/breaking

4. Finally cooled glass is cut into sections and shipped

Tempering Glass

• Heat the surface of the glass

• Rapidly cool the glass → which puts the outside of the glass in compression, while the interior stays in tension

Toughened Glass

Blowing cool air over the outer surfaces of heated glass

Laminating Glass

• Lay out a base layer of glass, place resin on top

• Add a second layer of glass

• Repeat as necessary, put in vacuum oven to laminate

Soda Lime Glasses: Most common type of glass

→ Softens at 850 degrees

→ Low cost, wont recrystallise, water resistant

→ Used For: Window and plate glass, bottles, tableware and light bulbs

Borosilicate Glasses: Contains up to 20% boron oxide and has low thermal expansion

→ Good resistance to fracture at elevated temperatures 

→ Known as PYREX

→ Used For: Electrical insulation, ovenware and laboratory ware

High Silica Glasses: Formed to required product shape then reheated to 1200 degrees removing most of the boron Oxide

→ Excellent resistance to thermal shock

→ Used For: Where high temperatures are experienced

Lead Glasses: Contains high proportion of lead, lowering the softening temperature well below 850 degrees of Soda Lime

→ High refractive index

→ Used For: Optical glass, neon sign tubes and thermometer tubes

Cemente manufacturing method

1. Combining limestone and shale (a type of clay), mixing them up and blasting them in a furnace

2. Once clicker is formed, its crushed into fine powder and used to make cement

Cement properties and uses

Properties: Strong in Compression, Weak in tension, low toughness, Castable

Uses: Binder in concrete

Bricks

Bricks are manufactured from clay after being formed into the desired shape via pressing or extrusion.

Bricks Manufacturing Process

1. Clay is crushed up, broken down into finer particles and screened to remove debris

2. Water is added to create paste & forced through the rectangle dye with 3 pins to make a slug

3. Bricks are cut to length, stacked, then dried for 2 days, then fired in a kiln at 1040 degrees

Bricks Properties and Uses

Properties: Strong in Compression, Weak in tension, low toughness

Uses: Rectangular building blocks, used to make walls of buildings

Composites

A composite material is defined by its combination of two or more distinct materials, that create a new material with enhanced properties

Timber

• Is a natural composite consisting of two main components: cellulose (provides strength) and lignin (provides rigidity)

• Used for various applications like furniture, tools and structural uses like bridges

• Its workability and apadptibility make timber a versatile construction material

Timber properties and uses

Properties: Corrosion-prone, good specific strength, decent bending performance, high Young's modulus

Uses: Beams, Trusses, Interior Fit Outs

Concrete

• Made of 4 main ingredients: Sand, aggregate, cemente and water

• Good under compression but weak in tension

Concrete properties and uses

Properties: Strong Compression, Weak Tension, Resistant to Corrosion, Durable

Uses: Building walls, foundations, bridges 

Ashphalt

• Main component Bitumen gives asphalt its black colour and adhesive properties

• Used on roads to minimse tire rumble and improve drainage

• Water resistant properties

• In Civil structures it is coated on metals and fabrics as a waterproofing membrane

• Excellent adhesive to surfaces

Asphalt Properties and Uses

Properties: Tough & Crack resistant, hard wearing

Uses: Roads

Geotextiles

Are engineered textiles made from polymers that assist in drainage, filtration, reinforcement and soil separation

Geotextile uses

→ Reinforce and stabalise slopes and earth walls

→ Rutting on roads, railways and subrages on construction sites

→ Often laid in large sheets directly onto the subsoil over a road, railway or paved surface

Geotextiles Materials:

→ High density polyethylene and polyester

→ Polypropylene

→ PVC

Geotextiles properties

→ Provides toughness

→ Corrosion resistance

→ Tensile strength

Geotextiles manufacturing method

Polymer extruded or slitted into fibres that are rolled into a mat or mesh like fabric

Crack Formation and Growth

Cracks are formed in the creation of a material and are tiny imperfections within the material, and grow when external forces act on it

Failure due to cracking

Materials fail due to cracking because the external load is too great, spreading the crack further

Repair or Elimination of failure due to cracking

Repair	Elimination
Drill a hole at the end of a crack so forces within the crack are more evenly distributed Welding a plate over the crack	No Sharp corners/Stress concentration points Choosing a more appropriate material  Choosing a more suitable manufacturing method

Laminated VS Tempered Glass

Laminated Glass	Tempered Glass
Sandwich 2 layers of glass together, with a PVB resin layer in between. Put through a vacuum oven to set. Doesn't shatter on impact Only one side of the glass shatters Blocks more UV radiation More soundproof Vechile windshield, shopfronts, windows of buildings	Heated to 600+ degrees, then hit with cold blasts of air, forcing exterior into compression, exterior into tension High Tensile Strength Still Shatters Can't be repaired Breaks into small pieces Used where breakage is a risk, vehicle windows, shower doors, glass furniture

Softwoods VS Hardwoods

Softwood		Hardwoods
Structure: No Vessels, only pores More flexible Lightweight		Structure: Has Vessels and pores Denser Sturdier Weather Resist

Plywood Vs Laminated Wood

Plywood	Laminated Veneer Wood
Veneers at 90 degrees to the last Moderate Strength Lightweight Used for Panelling	Parallel grain runnings High Strength Higher Density/Heavier Used for beams

Precast Concrete VS Onsite Concrete

Precast Concrete	Onsite
Manufactured offsite in a controlled environment Faster construction times Enhanced Quality Reduced on sight labor	Poured and cured onsight Slower construction speed for need for framework Depends on onsight conditions Minimal transport required

Reinforced Concrete

Uses steel rebar to enhance tensile capacity

Concrete is cast over steel rebars

Pre Tensioning Concrete

Techniques to place cables under tension before concrete hardens

Concrete is cast over pre-tensioned cables

Post Tensioning

Tension is applied using steel cables after concrete has set

Concrete is cast over tubes, where the concrete sets, wires are pulled through the slab, and anchored to plates

Chemical Corrosion

• Happens without water, through direct chemical reactions

• EG: Aluminium, Chromium or Nickel reacts with oxygen to form a protective oxide layer

• Oxide Layer: Prevents further corrosion

• EG: Green colour of the statue of liberty comes from oxidation of copper alloy panels

• Pipes carrying gases can corrode from reactions between the metal and the gas

Prevention: Lining pipes with nert materials like elastomers or polymers to block chemical

Electrolytic Corrosion

• Occurs in wet environments

• Involves two dissimilar metals connected by a conductor

• Both metals are in contact with the electrolyte (moisture)

• The more reactive metal = anode, less reactive = cathode

• Ions move from the anode to the cathode

• Continous electron flow causes the anode to corrode

Galvanic Corrosion

Is a form of Electroyltic corrosion and happens when an anode and cathode is produced within a structure through a vatiety of ways

Stress Corrosion

• Distortion or Deformation of metal grains occurs during drilling, bending or fabrication

• Creates dissimilar grains/crystals within same metal structure

• Distorted grains act as anodes (more reactive)

• Undistorted (unstressed) grains act as cathodes

• This difference sets up a galvanic cell

Dry Corrosion

Chemical reaction with gases at higher temperatures. An example is fire tubes in steam boilers.

Wet Corrosion

Wet corrosion is when a fluid is placed in an electrolyte (a solution with ions that carry an electric charge)

Issue with Corrosion

• Economic Cost

• Structural failure

• Aesthetic Issues

• Safety Hazards

Painting

• Requires constant maintenance and upkeep

• Creates a protective barrier that blocks moisture, oxygen and corrosive substances from reaching metal surface

Metallic Coatings

• Includes electroplating, cladding, spraying of molten metal like zinc or hot dip galvanising

• Prevent corrosion by acting as a protective barrier

• Can provide sacrificial protection, where a more reactive metal corrodes instead of the underlying metal

Galvanic Protection

• Reffered to as “sacrifical anode”, Blocks of zinc are placed on the structure

• This is to prevent corrosion of a more valuable metal, such as steel or iron.

Impressed Voltage Protection 

• A low level current is passed through the structure

• This current replaces the electrons that are lost during the process of corrosion

Lift

Upward force that counteracts weight

Perpendicular to wing

Wing shape, speed, air density, angle of attack

Weight

The gravitational force pulls the aircraft down

Toward Earth

Mass × gravity

Thrust

Forward force that propels aircraft

In direction of travel

Engine power, propeller/jet type

Drag

Resistance force acting opposite to motion

Opposes thrust

Shape, speed, air viscosity

Angle of Attack

The greater the angle of attack, the more lift is generated. Too much angle of attack will result in the plane's stalling.

Bernoulli's principle lift

An increase in velocity means a decrease in pressure. 

As wind flows underneath a wing, it creates a slower, higher pressure below and a faster, lower pressure above. Due to the pressure difference, the wing moves upwards. Creating Lift

Venturi Effect

If a fluid flows through a constricted gap, the pressure will decrease, but the speed through that area will increase

Flaps

Create more lift/drag. Located between the fuselage and ailerons.

Elevators

Controls the pitch of the Plane. Located at the rear of the plane

Rudder

Controls the Yaw of the Plane (Side to Side)

Ailerons

Located at the end of the wing and helps control roll.

Winglets

On the tip of the wing, help to reduce the pressure gradient, increasing lift and fuel efficiency. (Lightning Rods on the Ends)

Air brakes

Air brakes are a hydraulic system that creates drag and reduces lift, forcing more pressure onto the brakes.

Fuselage

Responsible for holding the passengers, crew and cargo.

Vertical Stabiliser

The vertical stabiliser sits on the top of the wing and prevents the yaw from swinging side to side.

Tail

The tail must have a downforce to maintain stability and prevent the aircraft from pitching uncontrollably.

Pitch:

Up or Down

Yaw

Left and Right

Roll

Aircraft rotating from side to side

Internal Combustion Engine:

The internal combustion engine mixes fuel and air, which is then ignited by a spark plug, forcing a piston down and another piston up