Mechanical Engineering

Engineering Student at the University of Nottingham, attempting to aid revision, and maybe help a few others!

[trolleo-chileno]

[frigidhearts]

                                                     the first one though

[demaglia]

jfc

[thenewblackuk-blog-blog]

This morning we went to check out Poke Presents. A free event put together by the awe inspiring Poke, hosted at cooler now temporary event space Hackney House. 200 or so people took advantage of the free ticket offer and made their way over there with us to check out ‘The Internet Industrialist’ panel session. Fronted by some of Hackney’s coolest start-ups the session involved hearing first hand accounts from people who had recently reaped the benefits of using the internet to take a physical product to market.  One start-up that particularly caught our eye was Sugru. Sugru is a kind of self-setting rubber that makes fixing everyday objects, or modifying them a doddle. Its customer base varies from those using the product to fix cars and washing machines etc, to those who simply want to use it to create cool craft based objects, keyrings, ornaments and so on.

It was interesting to hear how the team at Sugru endorsed the idea of how embracing your online consumer community ads significant vaule to a brand, by using your website as a platform for supporters of the product to showcase their creative uses. 

By doing so they initially had fears about how those visiting the website may disregard the product’s potentially practical uses (fixing seals, cables or even shoes etc) when presented with a homepage that made the product look like children modelling clay, and visa versa.

However, they’ve created a fantastic (fully responsive) website that, by clicking keywords, or arriving at the site by particular search terms, quicly reinterprets the homepage by presenting the user with content and visuals more suited to their need. 

A fantastic example of a how to use a single website dynamically to talk to multiple consumer types. 

[nottinghamengineeringstude-blog1]

I cannot wait to get my hands on this stuff, my order has been placed!

[nottinghamengineeringstude-blog1]

HSF 1

Blood Vessels

Mass equivalent to length cubed

Strength equivalent to length ^2

As size increases skeleton must become more robust

Capillary size limited by size of red blood cells - diameter approx 10 (mew)m

Capillary spacing spcified by max diffusion path from capillary to tissue

Most flow laminar - ^4

Blood is non-Newtonian

Vessel walls contain muscle under active control - this are very complicated

Temperature Control

Internal heat transport

Heat loss depends on surface area - which is equivalent to length ^2

Heat production depends on volume of tissue - Length^3

Core temp of mammals approximately equal

Heat generation variable - implications for diet, locomotion, etc

Hibernation?

Control Systems

Nerve conduction velocities:

 - Type A, 12-130m/s

 - Type B, 15m/s

 - Type C, 0.5-2m/s

Nerve Type A

Large diameter

High conduction velocity

Myelinated fibres

Consists of 4 types of nerve fibres

- Alpha (afferent or efferent fibres)

- Beta (afferent or efferent fibres)

- Gamma (efferent fibres)

- Delta (afferent fibres)

Nerve Type B

Myelinated fibres

Small diameter

Generally preganglionic fibres of autonomic nervous system (ANS)

Low conduction velocity

Nerve Type C

Unmyelinated

Small diameter

low conduction velocity

Fibres include:

- Postganglionic fibres in ANS

- Nerve fibres at dorsal roots which carry sensory information: pain, temperature, touch, pressure, itch.

Dictionary Time!

ANS - Autonomic Nervous System. Acts as a control system functioning largly below level of consciousness, and controlls visceral functions

Postganglionic - In the ANS fibres from ganglion to effector organ are postganglionic

Myelinated - Myelin is a material that forms a layer around the axon of a neuron

Capillary - The smallest of a bodys blood vessels

Non-Newtonian - A fluid that differs from the properties of Newtonian fluids Big Bang Theory: Non-Newtonian Fluid

[nottinghamengineeringstude-blog1]

Ok, so I have been completely and utterly terrible at updating this blog! I'm now in my third year of my degree, which means I'm able to pick modules that I want to do. A lot of my friends decided to go down a certain route - for example, automotive, aeronautical, bio mechanical, etc - however I couldn't decide what I wanted to do, so chose to do a mixture of bio, materials, and sustainability!

Things you should expect to see this year:

Actual updates! And on a regular basis.

Only hints about my group design project, because we want to market it and sell it!

Bio modules - I'm doing Human Structure and Function for Engineers, and Biomechanical Engineering.

Energy efficiency things, because really, that's where the world needs to be heading!

Sustainable Manufacturing - I am so excited about this module, there's hardly anyone taking it, which I'm really shocked by, but it looks so goooooooood.

Computer Modelling Techniques - This is core, and I am scared it's gonna be lots of Matlab =[ I studied Matlab last year, and it made me want to curl up in a ball and pretend the world didn't exist. Might have to post some of the work I did for that last year too, as I'm sure Tumblr is interested in computer programming, right?!

Fibre Reinforced Composites - I am a massive composites nerd. End of story.

Stress Analysis Techniques is another module that has been forced upon me. It doesn't sound too exciting, but if I enjoyed everything I don't think it would be a worthwhile degree.

I also have to study Management Studies, which is a load of crap. I hated it last year, and I don't want to do it again =[ It might get slipped in there somewhere though.

Hopefully someone somewhere will benefit from my blog, and if not, it's very good revision for me =]

[materialsgirlny]

Instantly become a polymer expert! Just memorize this chart. 

[materialsgirlny]

I just can’t get those tempting polymer bubbles off my mind, so it’s back to EPS we go. First let’s start with the chemistry, Polystyrene is made by the polymerization of styrene, which occurs via free radical vinyl polymerization. (If that’s not the makings of a nerd rock band name then I don’t...

[nottinghamengineeringstude-blog1]

Hi there! I found your tumblr on Google. Thank you so much for your posting about these engineering things, especially the strengthening mechanism posts. They really help me to finish my assignment on Physical Metallurgy subject. Thank you :)

Glad it was useful for you! Just wish I had more time to keep updating things =]

[nottinghamengineeringstude-blog1]

Hey... could you tell me why Tensile Strength is measured in N/m2?? thanks x

Well, you can also have it measured in Pa, it just depends on what you're doing.

I normally think of it as being the maximum stress that a material can withstand [which will be measured in Newtons], divided by the cross sectional area [which will be measured in m^2].

With Engineering there are lots of different units, and I find it hard to keep track a lot, so I tend to just write out the same equation saying whether it's a Mass, Distance, Force or Time that makes it up. Off the top of my head can't think of anything else that you'd need in there...

So in this case I'd write Force/(Distance X Distance) alongside Stress/Cross Sectional Area.

Hope that kind of makes sense!

[materialsgirlny]

[nottinghamengineeringstude-blog1]

materialsgirlny:

Looks like I’m inappropriately dressed for this occasion, but this Hog’s exhaust pipe would never be caught dead in the same situation. Wrapped around the VERY hot exhaust pipe is a woven wrap, preventing heat transfer and subsequent nasty burns. It also helps to keep heat inside the system, allowing for improved exhaust fluidics which in turn increase horsepower. Oddly enough this “Titatnium” exhaust wrap is made of lava rocks! I can’t find a definitive answer about the means of processing the rocks into a viable thread, but I have a theory. Melt processing, it is sillica after all.

This would be suitable for extrusion and could go directly into use in weaving looms, without sliver processing. (so convenient!)

If anyone knows the real answer, please enlighten us all. 

[nottinghamengineeringstude-blog1]

[nottinghamengineeringstude-blog1]

Manufacturing Processes 1 - Casting: Part II

Sand Casting

Sand bound with clay and water, or other additives

Green sand -  partially combusts when molten metal hits, leaving a better finish

Sand is packed around the pattern, which is traditionally made of metal or plastic, placed in a drag - diagram is in Manufacturing Processes 1 - Casting: Part I

Pattern is removed, and mould is reassembled

Molten metal is poured into the cavity

Mould is broken after solidification

Wide range of metals can be cast - steel, cast iron, stainless steel, aluminium, copper, nickel

No real limit to size and shape - minimum thickness is 2.5mm

Poorer tolerances than other processes, course surface texture

Takes a long time

Economical for a low number of castings

Used for cylinder blocks and large pipe fittings

Investment Casting

Make a master pattern out of wood/plastic/metal, then make a master die from a low melting point metal/rubber. Fill the master die with wax to produce a wax pattern.

Coat the wax pattern with an investment material - slurry of refracting oxides

Pack this into sandbox whilst the slurry dries, then heat mould to melt out wax. Bake and preheat mould prior to pouring casting metal

Allows for limitless intricacy

Gives an excellent surface finish

Can be used for a wide range of metals - Gold, Silver, Steels, Nickel, Copper, Magnesium, etc

Can be used with materials that have a high melting point

A high cost process, mostly for complex shapes - artwork, jewellery, gas turbine blades, etc

Gas turbine blades - Casting in thermal gradient promotes directional solidification, resulting in a single crystal being produced

[nottinghamengineeringstude-blog1]

Manufacturing Processes 1 - Casting: Part 1 Introduction

Casting

When a molten metal is poured into a solid mould, heat is then removed, leading to slight shrinking upon solidification

Usually used for complex shapes, large components, low ductility of alloy and when it's economical to

The main methods used are sand, die, investment and continuous

Large range of sizes that can be produced through casting

Expendable moulds are made of sand/plaster/ceramics, can be used for multiple patterns, or just single use - investment casting, lost foam

Multiple mould casting - die casting, pressure die casting, and gravity die casting

 - I've never put a gas vent in, but I can imagine it's a good idea with certain materials

During freezing, the latent heat of fusion is extracted, and the material is a mixture of both solid and liquid

Volume changes upon solidification

Ease of Casting

Low melting temperature = lower energy costs = longer mould life

Low viscosity and surface tension = finer details in complex shapes

Low solidification contractions = no cracks

Low thermal capacity and high conductivity = high production rates, die casting

Low solubility for gasses = avoids porosity

Not contaminated by air, no oxidation

Adequate strength

[nottinghamengineeringstude-blog1]

Properties of Materials: "The Rest" Part V Cost

Cost

Price to consumer per unit quantity

SI units = £/kg

London metal exchange for new and scrap prices

Many things affect cost:

Extraction of ore - ease, abundance, location in relation to where you are, quality

Processing to convert to pure metal, shape, and all energy costs, including transportation

Mark up from one supplier to the next needs to be taken into account

Prices fluctuate due to supply and demand, and the abundance of scrap

Highly relevant in the selection of materials

All design projects have a budget

If the material is in short supply, then it's going to cost more

Applications with high added value with enable expensive materials to be selected

Pretty much, all common sense.

[nottinghamengineeringstude-blog1]

Properties of Materials: "The Rest" Part IV Thermal Expansion

Thermal Expansion

The tendency to increase volume when heated

Depends on the thermal coefficient, alpha, measured in K^-1

Thermal strain produced due to the rice in temperature, E[thermal] = Thermal Coefficient x Change in Temperature

Measured by heating at a constant rate, and measuring the change in length using transducers or lasers

Coefficient of thermal expansion is the gradient of a Strain/Temperature graph

As a material is heated, the atoms vibrate, causing the bond length t o increase, resulting in the material expanding with heat and contracting with cooling

The stronger the bonds, the lower the thermal expansion

Heat induced expansion needs to be taken into account when deciding on a material for production, as this could lead to failure of the product

Expansion induced strains can cause yielding and distortion - these can occur during manufacturing, so when welding/hot forming/moulding/casting

Different thermal coefficients joined together and heated results in large stresses and severe distortion

[nottinghamengineeringstude-blog1]

Properties of Materials: "The Rest" Part III Density

Density

Mass/unit Volume

SI unis = kg/m^3

Most commonly considered for "lumps" of material, however powder and foam can be calculated for powder and foam - as you can take into account the air spaces between particles, or within the material

Irregular shapes can have the density calculated by submerging in a water or gas tank and measure the displacement

Arises from the mass, size and packing of atoms

The size of atoms doesn't vary very much, but the mass of them does

As you move down the periodic table, the mass and density increases

Closely packed structures, eg metals = high density

More open structures, eg ceramics = intermediate density

Open structures, eg polymers = low density

Very little can be done to change the bulk density of a material - via alloying, processing and heat treatments

Composites result in a higher density, as the volume is weighted at an average of the two components

metals > ceramics > polymers

Metals have close-packing due to metallic bonding, and have a large atomic mass

Ceramics are covalently bonded and so less dense, and often have lighter elements

Polymers are often amorphous, and made of lighter elements - eg C, H and O

Composites have intermediate values when it comes to density

Polyethylene < Water < PVC < Magnesium < Graphite < Aluminium < Diamond < Titanium < Iron and Steel < Copper < Gold

Important in design as it will derive the final mass

Often want to save on weight - cars, planes, etc

Youngs Modulus/Density and Stress/density often quoted and compared - Al often said to have high specific strength, or high strength to weight ratio

Low density = low mass = desirable 

[nottinghamengineeringstude-blog1]

Properties of Materials: "The Rest" Part II Hardness

Hardness

Resistance to indentation/plastic deformation

Harder the material, smaller the indent after an applied load

Determind by load/projected area of indent

non-SI units of Force/Area, kgf/mm^2 - can be converted to MPa by multiplying by g. Converted value is then appoximately 3x yield stress

Made on surface of material, non-destructive, and therefore ideal for quality control and measuring surface properties post treatments

Vickers test uses a diamond, pyramid shape. Hv = F/A

Resistance to permanently indenting the surface

Large resistance = resistant to plastic deformation, or cracking under compression/high strength

Large resistance = better wear properties

Polymers < Alluminium Alloys, Brass < Easy Machine Steels < File Hard < Cutting Tools < Nitrided Steels < Diamond

As deformation is compressive, can't test on ceramics

Lead < Annealed Alluminium < Annealed Copper < Steel < Tungston Carbide < Alumina < Diamond - Hardness and yield strength

Material selection isn't driven by hardness, but it is a good indication of yield strength and resistance to wear and indentation

Good for a rapid assessment of properties, used for quality inspections between batches, ensuring that processing and heat treatments have the desired effect

[nottinghamengineeringstude-blog1]

Properties of Materials: "The Rest" Part I

Ductility

Measure of plastic strain at point of failure

Larger the strain, more ductile the material

% Elongation, EL = (Lf-Lo)/Lo x100, where Lf is the length with fraction, and Lo is the original length

% Reduction in area at fracture, (Ao-Af)/Af x100, where Ao is the original cross-sectional area, and Af is the cross sectional area with fracture

Ability to undergo plastic deformation

Readily occurs in metals, as their dislocations make them very ductile

Limited in ceramics due to being brittle

If chains slide easily in polymers, then they're ductile.

Rarely a concern, as stresses stay below yield stress

Considered in material forming, so you know how much you can reduce the thickness of the material by before it will fracture.

Ductility decreases with cold working

Elastomers > Polymers > Metals > Ceramics

Toughness

Resistance to fracture when stressed

Energy needed to break a unit volume, J/m^3

Area under stress/strain curve

Dictated by the degree to which plastic flow will occur within the material

A good balance of ductility and strength leads to a high toughness

Important to think about during material selection

High toughness means increased resistance to impact

Can be used to intentionally deform and absorb energy - eg crash protection structures

Brittle

Opposite of toughness

Absorbs very little energy during fracture

Charpy Impact

Energy to fracture measured

Used to compare materials, and the effect of test temperature

Swinging pendulum, impacts notched sample. Energy absorbed is calculated by the reduced height to which the pendulum swings on the rebound - the PE loss. When we did this, things went flying!