TMA 02
This module requires all assignments to be submitted electronically. To submit an assignment, please follow
the link(s) from your StudentHome page to the online TMA/EMA service.
There are restrictions on the size and format of any files you submit for TMA 02 via the online TMA/EMA
service. The maximum file size permitted for TMA 02 is 10 MB. Guidance on reducing the size of images is
available on the Resources page of the module website. You can only submit .doc, .docx, .xls, .xlsx or .rtf
documents, or zipped files containing only .doc, .docx, .xls, .xlsx or .rtf documents.
If you foresee any difficulty with submitting your assignment on time, you should contact your tutor well in
advance of the cut-off date.
For further information about policy, procedure and general submission of assignments please refer to the
Assessment Policies, which can also be accessed via your StudentHome page.
Note also the University's policy on plagiarism in the Assessment Policies.
TMA advice
This assignment covers Blocks 1 and 2. It consists of just one question or activity comprising 100% of the
marks available for this assignment. Read through the question and all the accompanying notes, particularly
the Further guidance on your TMA section, before starting work.
Make sure you read the question carefully. Look for key words that will clarify how you are to approach the
answer. For this assignment a report is required of the form expected for an engineering analysis project -
more detailed guidance as to the contents is given in the question instructions below. Other general advice is
available in Skills for OU Study: Assignments.
It is important to recognise the TMA as more than just part of the means by which the University awards your
module grade. It is a vital part of your learning process, which is why you receive feedback on it. You should
contact your tutor in advance to discuss any aspect of the TMA about which you are unsure, and then again
after you receive your script back, if there is any aspect of the marking that you would like to follow up. Question 1
This question carries 100% of the marks for this assignment.
A simplified three-dimensional approximation of an aluminium bicycle frame and schematic dimensions are
given in Figure 1. Your objectives are to model the frame and conduct analyses to investigate its strength and
stiffness under two given load conditions, and write an engineering style report on your analysis and
interpretation of the results. This report is actually the TMA that will be marked.
420
7
14
LIO
50
LII
www
L9
1.2
SEAT
PEDAL
CRANK
17
60 Figure 1. A simplified three-dimensional bicycle frame
Table 1
Material Type
Material Property.
Young's Modulus (E)
Poisson's Ratio
Density
Yield Stress
Outer Diameter
Thickness
Aluminium Al (6061-T6)
Value
75 GPa
0.30
2725 kg m-3
276 MPa
26 mm
2 mm
From the geometric information given in Figure 1 and the material data in Table 1, construct the base ANSYS
model. The joints labelled 1, 2, 3 etc. are effectively the key points KP1, KP2, KP3 etc. for establishing the
geometry of the frame with reference to the X,Y,Z axis set. Some of the coordinate values you'll have to work
out from the dimensions. The frame tube members or link lengths are labelled L1, L2, L3 etc.
When constructing the model, use SI units and adhere to the key-point and line numbering scheme given in
Figure 1. Initially, the cross-sectional dimensions to be used for the hollow aluminium tube are those given in
Table 1.
For meshing the model, use an appropriate PIPE element, e.g. PIPE288 elements.
Although the bike is under dynamic loads, we consider only two static cases in this analysis:
Load Case 1: Vertical Bending Test
Load case 1 is a 760 N vertically oriented down load (-Y) at the seat position (KP3) and a total vertically
oriented down load (-Y) of 500 N split equally at the pedal crank positions (KP7 and KP8). To account for
some of the dynamic effects in this static analysis, multiply all the loads by a factor of 2.
Use a ball-joint boundary condition for the front dropout (KP1) and a sliding boundary condition for the rear
dropouts (KP5 and KP6). You should carefully consider how these conditions are modelled as constraints in
displacement and/or rotation in each boundary.
Load Case 2: Horizontal Impact Test
Load case 2 is a horizontal (+X) load of 700 N applied to the front dropout (KP1). The rear dropouts (KP5 and
KP6) are fully restrained in all translations. Multiply load by a factor of 2. Required outputs from the analysis
The outputs required for these two load cases are:
●
●
Maximum von Mises (SEQV) stress
Maximum x-displacement
Maximum y-displacement
Plots of the von Mises and axial stresses
Bending moment and shear force diagrams.
Some of this data may be extracted directly in ANSYS. Other items may need to be obtained using element
table data. To do this, you should read about the element of your choice in the ANSYS manual, in particular,
input and output options. An example of an element table extraction for axial stresses at angle 0 from the
PIPE288 element is as follows:
ETABLE,AXIIO, SMISC,31
ETABLE, AXIJO, SMISC, 36
PLLS,AXII0, AXIJO
AXII0 and AXIJO are names you assign to the required data
SMISC 31 and 36 are the required data items for the I and J nodes, respectively
PLLS displays element table data as contoured areas along elements.
Your report should be written so that a person reasonably familiar with FEA (but not necessarily with ANSYS)
will understand it.
Further analysis
When you are happy that your model is producing sensible results, use it to do some design and optimisation.
Do this by carrying out further analysis runs to try different design options using your engineering judgement
and your ANSYS model.
Use Load Case 1 for this activity and suggest or try modifications to your model to make the design more
efficient in terms of the loads and stresses carried by the members - i.e. are some of them overloaded or could
they even be reduced in size? Keep the overall design the same as regards the number and layout of the
members but create new models with different diameters and thicknesses as you think fit.
Based on your initial analysis, which structural members look like they may be too large or too small, with
respect to their outer diameter? Modify these and compare the effects on resulting stresses. For design limits
and choices assume that the outer diameter can be changed in steps of 1.0 mm, leave the thickness at 2 mm
and do not allow any displacement (Ux, Uy, U₂) greater than 0.8 mm. The TMA report
Your TMA should be an engineering type report on your analysis and investigations. Ten pages should suffice
to include a verification section, explicit statements of all assumptions, log or input files (in an appendix), and a
compare and contrast (discussion) section.
Your report should also include some displacement values at key points, especially the highest ones and plots
from the relevant element tables including:
axial stress
shear force and bending moment diagrams
equivalent (von Mises) stress.
Further guidance on your TMA
The following table gives guidance on what you need to think about and include in your TMA, and the
breakdown of the marks for the various aspects of the analysis:
Aspect
Loading conditions
Boundary
conditions
Assumptions
Elements
Results
Verification
Guidance
Ensure that the loads have been applied correctly to take provisional
account of dynamic factors as suggested.
Think about what the loading conditions might represent in reality. Can these
be considered as worst cases?
We are looking for appropriate choice and applications and any comments
on what the boundary conditions might represent.
Assumptions could include discussion of the load conditions in a bit more
depth. Are there any other loads that might need to be included, separately
or together in your opinion, in designing a bike frame like this? Have you
made any assumptions in modelling the structural joints in the frame?
The choice of elements is given, but are they appropriate and would you try
any other types if you were given a free hand? In particular, advantages and
disadvantages of using shells or solids instead of pipes.
Note that there are two lots of results required; the initial main results being
the maximum von Mises stress values, maximum x and y displacements.
Also required are direct stresses, shear force and bending moment
diagrams. What are the results and what do they mean in relation to the
applied loads? What about long-term effects such as fatigue life etc.?
We'd expect to see some verification calculations and checks, for example
ballpark types of calculations on member loads and stresses.
Marks
5
5
10
10
20
20/n
