Materials and shape selection in design

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Expt 1: Deflection of Cantilever Beam Aim: To investigate effect of young’s modulus on

the deflection of cantilever beam.

Experiment Objectives:

To measure the deflection of different beam using liner potentiometric transducer( LPDT).

To present the values in terms of statistical value.

To become acquainted with various items of structural testing equipment.

To compare the analytical and experimental values of young modulus of elasticity (GPA)

Four test specimen from different material of same length and same circular cross section. Specimen include:

Steel

Brass

Aluminum

Hardwood

Experiment set up (Fig 1)

Procedure Set up the experiment as shown in fig 1.

Using appropriate instruments, measure the length and diameter of the beams

Load the beams one at time and add a load of 10 N at the end of rigidly held beam.

Measure and record the deflection of each beam on the table 1below

Material L(mm) R(mm) I() (mm)

Steel 400 9.525 6464.72 0.275 119.9986 210 42.8578

Brass 400 9.525 6464.72 0.409 80.68368 100 19.3

Aluminium 400 9.525 6464.72 0.630 52.38 70 25.17

Hardwood 400 9.525 6464.72 2.573 12.825 14 8.4

Key Results and discussion

Comparing the theoretical and experimental value the following can be deduced

For steel and Aluminium, large value error for the predicted ‘E’ are registered for small deflection.

Similarly for brass and hardwood significant and relatively small error of predicted value of ‘E’ are registered.

Steel has the smallest deflection while hardwood has the largest deflection.

Therefore, for same length and cross section, steel can withstand high forces compared to hardwood.

Factors Affecting Accuracy of the Test and potential Improvement

Factors affecting accuracy

Temperature; different material are affected by temperature thus ability to deflect.

Improper location of the hanger, location of the load may affect deflection of the beam.

Another factor may affect the accuracy may include improper calibration of the measuring instruments.

Potential improvement

Use of different load say 10N, 15N, 20N, 25N and 30N then calculate the average deflection.

Re-calibration of measuring instrument

Expt 2: Effect of Second Moment of inertial on Deflection of Cantilever Beam

Aims of the experiment

1) To isolate and investigate the influence of the geometry of beam cross-section on the beam stiffness.

2) Estimate the material properties fro nonstandard test and compare the cross results.

Experimental Objectives

1) Understand how geometry influence the stiffness of beams.

2) To discover the relationship with deflection of different PMMA geometry beams and how this affects the moment of inertia of an object.

Experiment Set-up Test specimen

Three test specimen of same cross section area include;

Circular

I-section

Square

Experiment set-up (fig 2)

Procedure Set up the apparatus as shown in figure 2.

Construct beams to be tested from the data table.

Place the beam to be tested on the clamp on meter stick.

Add 5 N mass on beam and take deflection reading. Record the value on the data table.

Repeat the same for the other two beams and fill the data table.

Table 2Beam section I (second

moments of area)Deflection(

circular 6464.72 4.465 3695.3667

I-section 22385.03697 1.5 3176.725203

square 6638.2848 4.57 3516.062956

=3462.7183

Key Results and discussion

A circular beam and square beam section has a large deflection.

I-section beam has a small deflection.

I-section beam is much stiff compared to circular and square beam section.

Second moment of area depends on shape of the beam as it can be seen, circular and square section has a relatively large moment of inertia compare to the I-section beam.

Beam with lower deflection is much stiffer than beams with large deflection.

Factors Affecting Accuracy of the Test and potential Improvement

Factors affecting accuracy

Shape of the beam

Temperature- Poly(methyl methacrylate) PMMA, thermal plastic is heavily affected by temperature values.

Potential improvement

Use of different load say 5N, 10N, 15N, 20N and 25N then calculate the average deflection

Importance of shapes and material Materials has grown into distinct and important

technology.

Behaviour and selection of material is area that requires decision to be made before they are made part of machine or complex structure

Material and shape play important role in design and manufacturing of engineering structure to achieve optimal performance.

Selection of material is the most paramount part of manufacturing after design process is complete.

To arrive at the best design for a product, wide variety of metal, plastic, woods, and ceramic material must be used.

Specific material properties that influence choice of material in design and manufacture of engineering structure are;

Strength

Ductility

Resistance to fracture

Fatigue and

Corrosion

Every mechanical engineer focusses on the properties of material and their effect on design, fabrication, quality, and performance.

Factors that influence choice of material

Material properties

The expected level of performance from the material

Material cost and availability

Right material must be priced appropriately

Material must be available

Processing-the process of machining the part must be considered, for example casting, machining or welding.

Effect of the material to the environment.

For example, choice of material to manufacture a wooden airplane and metal-framed airplanes, material must be stiff but light in weight in both cases.

Then factors involving cost, performance, safety, risk and aesthetics and environmental impacts are considered.

Material grain structure also play influence the use of a given material.

For example;

Steel-is strong, stiff, heavy but cheap

Aluminium-weaker, lighter, more expensive than steel

Composite- strong, stiff, very light, but expansive to buy and fabricate.

Material selection chart

Latest Development In Material Engineering Advancement in technology has led to development

of new process of manufacturing.

Product development and material knowledge has taken new dimension with 3D printing of complex structures.

Traditional manufacturing process such as machining has greater limitation when it comes to complex shape/structures.

Discovery in the field of material engineering continue to present new dimension every day.

Case 1: Shaft with Block bearing

Consider a solid work sketch of shaft with block bearing

Carbon steel is metal alloy that combines iron and carbon.

Two major steel alloy include;

Carbon steel

Stainless steel

The carbon in carbon steel make it harder and increase resistance to torsion and resist bending.

On the other hand, bearing are made of chrome steel.

Chrome steel is a high carbon steel with 1.5% chromium steel content.

Thus bearing have high strength to resist cracking and hard surface to resist subsurface rolling contact fatigue

Case 2: Turbine Turbine is a mechanical drive in which kinetic energy

of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with series of buckets or blades.

Test and Application My idea came from aerospace and defense industry

that uses additive manufacturing (3D printing) to;

Reduce material cost

Decrease labour content

Increase availability of parts.

Ways of Test

Subjecting the shaft to loading to test torsion and stiffness (resistance to bending).

Heating to test its ability to withstand high temperature under load.

Targeted application

Target application may include the following;

Modelling and prototyping

Complex engine part of aero plane

Reference Ashby, M. F., & Johnson, K. (2002). Materials and

design: The art and science of material selection in product design. Oxford: Butterworth-Heinemann.

Ashby, M. F. (1999). Materials selection in mechanical design. Oxford, OX: Butterworth-Heinemann.

International Conference on Material Engineering and Mechanical Engineering, & Gao, L. (2011). Advances in material engineering and mechanical engineering: Selected, peer reviewed papers from the International Conference on Material Engineering and Mechanical Engineering, August 20-21, 2011, Wuhan, China.