Download Mechanical Principles

Unit 5:
Learning hours:
NQF level 4:
Mechanical Principles
60
BTEC Higher National - H2
Description of unit
This unit covers an extended range of mechanical principles which underpin the
design and operation of mechanical engineering systems. It includes strengths of
materials and mechanics of machines. The aim of the unit is to provide a firm
foundation for work in engineering design and a basis for more advanced study.
Summary of learning outcomes
To achieve this unit a learner must:
1
Analyse complex loading systems
2
Investigate the behaviour of loaded beams and cylinders
3
Analyse power transmission system elements
4
Investigate the dynamics of rotating systems.
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Content
1
Complex loading systems
Relationship: definition of Poisson's Ratio; typical values of Poisson's Ratio for
common engineering materials
Two and three-dimensional loading: expressions for strain in the x, y and zdirections; calculation of changes in dimensions
Volumetric strain: expression for volumetric strain; calculation of volume
change
Elastic constants: definition of Bulk Modulus; relationship between Modulus of
Elasticity; Shear Modulus; Bulk Modulus and Poisson's Ratio for an elastic material
2 Loaded beams and cylinders
Relationships: slope: i 
deflection y 
1
 Mdx
E1
1
 Mdxdx
E1
Loaded beams: slope and deflection for loaded beams (eg cantilever beams
carrying a concentrated load at the free end or a uniformly distributed load over
the entire length, simply supported beams carrying a central concentrated load or
a uniformly distributed load over the entire length)
Stresses in thin-walled pressure vessels: circumferential hoop stress and
longitudinal stress in cylindrical and spherical pressure vessels subjected to
internal and external pressure (eg compressed-air receivers, boiler steam drums,
submarine hulls, condenser casings); factor of safety; joint efficiency
Stresses in thick-walled cylinders: circumferential hoop stress, longitudinal stress
and radial stress in thick-walled cylinders subjected to pressure (eg hydraulic
cylinders, extrusion dies, gun barrels); Lame's theory; use of boundary conditions
and distribution of stress in the cylinder walls
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3 Power transmission
Belt drives: flat and v-section belts; limiting coefficient friction; limiting slack
and tight side tensions; initial tension requirements; maximum power
transmitted
Friction clutches: flat single and multi-plate clutches; conical clutches;
coefficient of friction; spring force requirements; maximum power
transmitted by constant wear and constant pressure theories; validity of
theories
Gear trains: simple, compound and epicycle gear trains; velocity ratios; torque,
speed and power relationships; efficiency; fixing torques
4 Dynamics of rotating systems
Single and multi-link mechanisms: slider crank and three/four bar mechanisms;
production of vector diagrams and determination of relationships between
velocity, acceleration, power and efficiency
Balancing: single plane and multi-plane rotating mass systems; Dalby's method
for determination of out-of-balance forces and couples and the required
balancing masses
Flywheels: angular momentum; kinetic energy; coefficient of fluctuation of
speed; coefficient of fluctuation of energy; calculation of flywheel
mass/dimensions to give required operating conditions
Effects of coupling: conservation of angular momentum; energy loss due to
coupling; final common rotational speed
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Outcomes and assessment criteria
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Guidance
Delivery
This unit may be delivered as a stand-alone package or integrated into other programme
units. If it is delivered in an integrated way, care must be taken in the tracking of evidence
for the outcomes. Wherever possible, a practical approach should be adopted. Effort should
be made to identify the relevance of the principles covered to engineering applications and
system design.
Assessment
Evidence of outcomes may be in the form of assignments, laboratory notes, solutions to
applied problems or the results of unseen, timed tests/examinations. Evidence is likely to be
at outcome level in order to provide maximum flexibility of delivery.
Evidence may be accumulated by learners building a portfolio of activities or by a tutor-led
combination of tests and assignments. In either case, the evidence must be authentic,
relevant and sufficient to justify the grade awarded.
Links
This unit can be linked with the mathematics and mechanical applications units in the
programme.
Entry requirements for this unit are at the discretion of the centre. However, it is advised
that learners should have completed the BTEC National unit in Mechanical Principles or
equivalent.
Resources
Sufficient laboratory/test equipment should be available to support a range of practical
investigations.
Appropriate software packages should also be used wherever possible to verify solutions to
problems and system behaviour (for example, stress analysis).
Support materials
Textbooks

Hannah J and Hillier M J -Applied Mechanics (Longman, 1995) ISBN 0582256321

Hannah J and Hillier M J - Mechanical Engineering Science (Pearson, 1999)
ISBN 0582326753

Tooley M and Dingle L - Higher National Engineering (Butterworth-Heinemann, 1999)
ISBN 0750646292
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