applied mechanics

2010-03-12T01:51:00.000-08:00

The main criteria of failure:

Tresca (The Maximum Shear Stress)
Von Mises (Shear Strain Energy)

These are used for ductile materials but for brittle materials;

Maximum Principal Stress (Rankine)
Mohr Fracture Criterion
are used.

(Reference: `Mechanics of Engineering Materials` by P.P. Benham andR.J. Crawford provide a good introduction.)

2009-06-01T07:41:00.000-07:00

Whitechapel Bell Foundry is Britain`s oldest manufacturing company. The company produced the Liberty Bell for the Philadelphia State House in 1752 and produced a replica of the Liberty Bell in 2001. A Bicentennial bell was also produced in 1976.
The Whitechapel business has been operating since 1570 and has produced some of the most famous bells in the world. Last year the firm cast in it`s foundry a new peal of twelve bells for the church of St Magnus the Martyr at London Bridge and if you are interested in this special company then look at the website www.whitechapelbellfoundry.co.uk

2008-02-22T07:34:00.000-08:00

Recycling! Can we do better?

My workplace decided to start a collection of plastic bottles, cans and paper in order to recycle this waste. A very good idea however I get the feeling that this enthusiasm to recycle does stop people thinking of other possibilities. Reuse of products is a preferable option that doesn`t require a huge infrastructure to make it work. the waste hierarchy looks like this:
Re-use
Recycle
Dispose

Recycling is often the best solution but if we take a moment to ask is a product`s life can be increased by re-use then perhaps we can do better.

2007-01-03T02:36:00.000-08:00

Bernoulli`s Equation

In Fluid Mechanics the energy equation is called Bernoulli`s but it is similar to the equation used in Thermodynamics. There are differences in Fluids when compared to Thermodynamics, Potential energy is important in fluids as is Kinetic energy.

1) What other energies are important in the Bernoulli equation?

2) State the equation when the units are:
(i) metres (ii) J/kg (iii) J

3) State the mass continuity equation.

2006-09-04T07:57:00.000-07:00

Thermofluids The Gas Laws

The combination Gas law of pV/T = C can be used to solve most problems because it combines Boyle`s, Charles` and the pressure law. It`s normally used in the form p1V1/T1=p2V2/T2.

A variation is one where the Characteristic Gas Constant `R` is used. For example, R for AIR is 0.287 kJ/kg K.

Question: What are the units for each component of the pV=mRT equation?

2006-09-04T07:46:00.001-07:00

The combined Gas Law allows us to do all calculations.

(p1V1)/ T1 = (p2V2)/T2

and pV =mRT where R is the characteristic gas constant.

For AIR, R= 0.287 kJ/kg K

Question: What are the units for all the components of the pV = mRT equation?
Also, prove the units for R = kJ/kg K.

2006-09-04T07:46:00.000-07:00

2006-05-12T13:08:00.000-07:00

KEVLAR is a modern material with many applications, particularly in the aerospace industry but an interesting fact about it is that is was invented by a woman.

1) What is the history of this material?

2) Find examples of successful applications of Kevlar.

3) State the important properties of Kevlar.

4) What is the origin of the name?

5) In which of the materials groups does Kevlar belong and how is it bonded?

2006-04-14T03:34:00.000-07:00

In Jesi

The Palio di San Floriano

29th and 30th April 2006 and 4th, 5th, 6th and 7th May 2006.

Look at www.paliodisanfloriano.com for the programme.

The Corteo Storico through the town begins at 16.30 on Sunday, 7th May.
Let`s hope for good weather.

2006-03-07T11:23:00.000-08:00

Introduction to Design: Guidelines

1)
Chose a product for your design study and complete a Design specification.
Select design factors, these may include: weight, size, cost, human interface, reliability, fixing arrangement, corrosion requirements, safety, quality, life cycle, other resources etc
Look at the factors and decide which are: crucial, non essential and consider if weighting of certain factors is useful.
Use a comparison chart to rate and rank the factors in order. Classify as essential, useful or desirable.

2)
Describe 4 approaches for generating ideas and proposals. These could include: brainstorming, experience, ideas from other products and applications, cause and effect diagrams and check lists.
Apply suitable approaches to the design requirements of the problem in your specificatio from part 1.
Prepare 3 proposals to satisfy the design requirements of your problem. It is important that the proposals are not variations of the same principle but should evolve from the use of techniques to provide ideas and solutions.
For each of the 3 proposals the Design activity should include:
* appropriate drawing/sketches should be produced
* appropriate manufacturing processes are selected and that selection justified.
* material selection is reasoned and justified.
* aesthetics of the product are described and illustrated.
* ergonomics of the product are described.

3)
Evaluate the design proposals generated in part 2.
Consider resources, costs, technology available and the technology capability,
Select the optimum design from the 3 proposals.
Use appropriate comparison selection procedures and justify the selection.

You are invited to add your own selection of product for this design study. Good luck!

2006-01-19T07:24:00.000-08:00

One of the HND2 students came in with a sample of a material that he is using as part of a project. we found that the material is called "kaylan" and information can be found at the website of the manufacturers. www.kaylan.co.uk
This elastomer is strong and flexible and is successfully used for wheel arches and mudflaps on high performance rally cars. It is fairly expensive, some prices can be seen on www.motorsportsuperstore.com

How would you describe the PROPERTIES of this material?

2006-01-10T06:30:00.000-08:00

Using tables in Thermodynamics.

Specific Enthalpy `h`(kJ/kg)
water hf,
Saturated Steam h= hf + x(hfg)

Note: hfg = (hg-hf)

Superheated Steam h= h @ Pressure & Temperature

Specific Volume `v`= x(vg) m3/kg

x = dryness fraction of saturated steam.

*Question
Produce a temperature v enthalpy for 0.85 dry saturated steam at 3 bar pressure.

*Question
What is the pressure 5.2 bar expressed in kN/m2?

Remember that Specific Volume is the inverse of the Density!

Units
Specific Volume= m3/kg
Density= kg/m3

Gas Laws
PV/T=C and PV=mRT

Specific gas constant `R`= 0.287 kJ/kg K.

2005-12-23T03:03:00.000-08:00

I received a book of "Porte e Portali in Fermo" written by Marco, whom I met last May, in cooperation with a photographer.
The photographs are superb and show the great variety of doors and portals in Fermo with the different architecturals styles down the ages. Fermo was an important city in Roman times in Marche. Marche from the "marks" were the boundary of the Roman Empire. The city occupies an obvious position of advantage in the ascoli piceno parte of Marche.
Anyway, Marco makes a serious point that the door portal is the basis of architecture of buidings and the design of the portal ensures that the door is supported. However the portal also hold the construction above the portal. Look at the number of balconies that were designed to be directly above the door.

In its simple form the force system is a simply supported beam supporting a UDL. Think about the reaction forces in the supports and how the cross beam is subjected to a combination of compressive and tensile stresses.
Also, consider the importance of a keystone in an arched portal and how this suited the materials chosen.

i think that it would be worth looking at local buildings, old and new and considering the force system about the doors and portals. remember that architects nowadays have a greater range of materials to select from.

2005-12-02T04:18:00.000-08:00

Reaction Forces, Shear Force and Bending Moment diagrams.

Reaction Forces
Applicable conditions of equilibrium.

Sum of the Forces Up = sum of the Forces Down

Sum of the Moments clockwise= Sum of the Moments anticlockwise
(take moments about one of the unknown reaction forces)

Shear Force Diagrams

Start and finish at zero.
Are measured in KN.
Show a sudden change for a concentrated load.
Show a gradual change for a Uniformly Distributed Force (UDL)
The place where the Shear Force crosses the origin will be the position of maximum bending on the beam.

Bending Moment Diagrams

Start and finish at zero.
Are measured in kNm.
Show a straight line for a concentrated load.
Show a curve for a UDL.
The value of the Bending Moment can be found by calculating the area under the Shear Force.
Always get a value for the place that the SF diagram passes through the origin.

A lot to remember but practice makes perfect!

2005-11-22T09:03:00.000-08:00

Traction
MEP Statics and Dynamics

Remember!
Tractive resistance will always oppose motion
The Inertia force is only active if there is acceleration or deceleration and it always opposes the direction of acceleration.
The "downhill component: mg sin(angle)"ALWAYS acts downhill.

2005-11-18T00:55:00.000-08:00

Transducers for 18/11/05

Using strain gauges we will measure the Modulus of Elasticity of the Aluminium beam.
Do you understand how the equipment works?
How does Hooke`s Law help?
Remember Poisson`s ratio? How is it relevant to this experiment?

Record all your readings, perform the calculations and draw the Stress-Strain graph.
Comment on the accuracy of your findings.

2005-11-08T08:21:00.000-08:00

Surface Texture for 11/11/05

Understand the meaning of the terms: roughness, waviness and errors of form.
What is the lay?
Use diagrams to aid your answer.

Explain these measures:
Root mean square deviation (Rq), max height of profile(Ry) and Mean height of profile (Rc)

It is important to do this work before the surface measurements are carried out in the workshop.

2005-10-24T08:30:00.000-07:00

The 2nd Law and Entropy for 27/10/05

Look for uncomplicated definitions and try not to stray. This can become complicated!

The Carnot cycle does provide an excellent example of reversible processes and can also be used to explain why an engine cannot achieve 100% efficiency.
Mechanical work can be completely converted to heat but why can`t heat be completely converted to work?

2005-10-24T08:23:00.000-07:00

The Second Law of Thermodynamics. 27/10/05

Look at the definitions of the 2nd law and select those which you feel are most meaningful. For example, look at Kelvin-Planck and Clausius.
When asked to define Entropy, it`s important that you stay on course and be content to give a definition that is sufficient and remains relevent to the work for this part of the course.
Think of the reversible adiabatic process and the significance of entropy in this context.
Use the Carnot cycle to give an example of a heat transfer processes that can be considered reversible.
What processes make up the Carnot cycle?
Can you explain how it is impossible for an engine to achieve 100% efficiency?

Heat energy and work energy are mutually convertible one into the other but there is an important difference. Mechanical work can be completely converted into heat energy but heat energy cannot be completely converted into work.
Therefore in the Carnot cycle, there is always a loss to a colder body and the efficiency of an engine can never be 100%.

The 2nd Law indicates the way in which heat can be converted to mechanical work.

2005-10-12T08:10:00.000-07:00

For Thursday 13 October 2005

Torsion:

The torsion equation.
Calculating `J` values

Torsion of a stepped shaft with common value of Torque.

Torque diagrams: show how the torue is distributed from a motor to a pulley system.

Thermodynamics:

The Gas Laws PV/T=C and PV=mRT

Non flow E E Q= (U2-U1) + W

Steady Flow E E :

H1 + KE1 + PE1 + Q = H2 + KE2 + PE2 + W + losses

Mass Continuity Equation

Refrigeration Cycle and the importance of (h2-h1) using chart and verifying with tables.

2005-10-07T05:40:00.000-07:00

For Monday 10/10/05
Criteria of Failure - Factors of Safety

1) Maximum Principal Stress (useful for brittle materials)

2) Maximum Principal Strain (useful for concrete)

3) Maximum Shear Stress (Tresca)

4) Maximum Strain Energy (values required may be obtained from experimentation)

5) Maximum Shear Strain Energy ( Von Mises)

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MEP Statics and Dynamics

Distance, Time, Velocity and Acceleration for linear and Angular motion.
The area under the Velocity- Time graph will give the distance travelled in metres.
The gradient of the diagonal line will give the acceleration.

Acceleration= (final velocity-initial velocity)/ time.

2005-10-06T00:49:00.000-07:00

For 6/10/05
Using the steady flow energy equation. Work and Heat transfer.
Refrigeration.

The basic cycle.
1-2 Compression:Increase in pressure (from 100% dry to Superheated vapour)
2-3 Condensing (from Superheated vapour to Liquid)
3-4 Expansion Valve: Decrease in pressure
4-1 Evaporation Liquid to dry saturated vapour.

The change in Enthalpy between 1 and 2 will be significant.

Processes:

Polytropic
Adiabatic
Isothermal
Know the formulae for Q and W and be able to manipulate the equations between Pressure, Volume and Temperature.

2005-10-04T06:54:00.000-07:00

Design for manufacture Wednesday 5/10/05

1) List and describe the elements of the design process.

2) List the factors which influence a design. describe how maintenance, ergonomices and materials influence the final decision.

3) List and describe the various stages of design documentation.

2005-10-03T00:42:00.000-07:00

Calculate the Direct Stress and the Strain at 2 suitable points on the graph.
The material is H C Copper (99.99% cu)
A= 20 mm2
l=25.25 mm

Typical values of Stress/ Extension
1) F= 1500N and x=0.5mm
20 F= 3000N and x= 1mm.

Also, give a definition of Hooke`s Law and comment on whether the law has been verified by the findings of the test.