Laboratory handout - Newcastle University

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Oct 30, 2013 (3 years and 7 months ago)

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UNIVERSITY OF NEWCASTLE UPON TYNE

SCHOOL OF MECHANICAL AND SYSTEMS ENGINEERING

Module ref.

MEC 2005

Module title:

MECHANICS OF SOLIDS


Sheet No:

1

Sheet description:

Strengths & Testing Laboratory

DOWNHILL SKI PROJECT


Skis are designed with a number
of criteria in mind. One of these is stiffness


skiers want skis that are
neither too stiff nor too flexible. Looked at from this point of view, a ski is a beam with a somewhat
more complex shape that is treated in standard textbooks on the strength of ma
terials. In this mini
-
project you are asked to investigate the stiffness of a ski of a construction that was regarded as a high
-
tech in 1998. Find out all you can about it in the three weeks you have available.


Things you need to know:


(1)

A good start
ing point for background detail is the case study described by Gibson and
Ashby (L.J. Gibson and M.F. Ashby,
Cellular Solids
, Pergamon Press 1988, Chapter 9.5:
Library reference 620.11


GIB, in the Undergraduate Reference Collection).

(2)

You can test th
e ski stiffness using very simple equipment. Do not load it with more than
about 10 kg mass. It is advisable to load the beam symmetrically, e.g. loading point half
way between the supports in three
-
point bend.

(3)

The thickness of the aluminium skin is 1
.8 mm (for black ski) and 1 mm (for purple ski).
The thickness of the polyethylene coating on the bottom surface is 1.2 mm. Young’s
modulus for aluminium and polyurethane foam are 70 and 0.4 GPa respectively; the shear
modulus of polyurethane is 0.2 GPa.

(4)

Useful expressions for sandwich beams are provided on an information sheet.




You should:

(a)

Determine what dimensions to measure and set out a method for calculating the stiffness.
Decide what features of the beam construction can be ignored in t
he calculation.

(b)

Discuss any interesting aspects of ski design that may have emerged in your investigation.

(c)

Report a figure for ski stiffness under clearly specified conditions.

(d)

Say why you think it is useful to be able to calculate the stif
fness rather than to rely only
on the experimental measurements?

Departmental Ref.JTE/LAB/2

Revise Date: 2.3.2007.

Lecturer: G.R. Johnson

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