T357 Structural Integrity
TMA 03
Copyright © 2019 The Open University
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, transmitted
or utilised in any form or by any means, electronic, mechanical, photocopying, recording or otherwise,
without written permission from the publisher.
Contents
• TMA 03
• Question 1 (Block 2 Learning Outcomes 2.6, 2.7, 3.1 and 3.2)
• Question 2 (Block 2 Learning Outcomes 2.2, 2.4)
• Question 3 (Block 2 Learning Outcomes 4.1, 4.2, 4.3, 4.9)
• Question 4 (Block 2 Learning Outcomes 4.1, 4.2, 4.8, 4.13)
• Presentation
TMA 03
This tutor-marked assignment (T357 TMA 03) must be submitted by 12 noon (UK local time) on 16 April
2020.
This module uses the electronic TMA (eTMA) system for submission of TMAs. To submit your TMA,
4/6/2020 54352 – T357 Structural IntegrityTMA 03Copyright © 2019
https://www.australiabesttutors.com/Recent_Question/54352/T357-Structural-IntegrityTMA-03Copyright–169-2019 3/6
please go to your StudentHome page and follow the link(s) provided.
If you foresee any difficulty with submitting your assignment on time then 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 Handbook, which can also be accessed via your StudentHome page.
TMA 03 covers your learning in Block 2 Parts 1-4.
Question 1 (Block 2 Learning Outcomes 2.6, 2.7, 3.1 and 3.2)
This question carries 33% of the marks for this assignment
i. Figure 1 shows four distinct fracture surface micrographs taken at different magnifications. Discuss the
most likely failure mechanism in each case.
ii. Suggest, with justification, which fracture surface among those shown in Figure 1 would most likely be
observed in the failure of a ceramic material.
(8 + 2 = 10 marks)
b.
c.
d. Figure 1 Scanning electron micrographs of fracture surfaces for question 1
e.
i. Figure 2 (reproduced from Figure 2.40 in Block 2 Part 2) shows the fatigue-crack growth rate for a
metallic material. From the graph, estimate the number of cycles it would take to propagate a crack from
2.0 mm to 2.8 mm in length for a stress intensity range ?K of 20 MPa vm.
Figure 2 Fatigue-crack growth rate for a metallic material for Question 1(b)
ii. When collecting data to construct a graph such as the one shown in Figure 2, explain why it is
important to accurately measure the length of the growing crack.
(4 + 4 = 8 marks)
f. A thin walled steel cylindrical pressure vessel with a radius of 800 mm and a wall thickness of 38 mm is
designed to carry an internal pressure of 8 MPa. The steel has a fracture toughness of 95 MPa vm and a
yield strength of 520 MPa. For this material take the exponent in Paris relation, m = 3 and the coefficient,
C = 10-11.
Answer the following questions, stating clearly how you obtained each answer. You will need to use the
‘K calculator’ and ‘Fatigue calculator’ spreadsheets on the module DVD or module website. You may
wish to consider including copies of the completed spreadsheet calculations in your answers.
i. What is the maximum crack length through the wall that the vessel can tolerate when operating at the
maximum internal pressure to give a reserve factor of 2.5 on the load? (You will need to use the K
calculator; as in Block 2 Part 1, modeling the crack using the Plate in tension – through-thickness edge
crack geometry.)
ii. On inspecting the vessel, a welding defect in the shape of a through-thickness edge crack is discovered
and is measured to be 4 mm long. Determine how many pressurising cycles will it take for the crack to
grow to the size determined in part (i) if the vessel is regularly cycled to 90% of its maximum internal
pressure? (You will need to use the Fatigue calculator. Use a crack-growth increment of 0.01.)
iii. When the crack has grown to 6.0 mm the vessel is accidently subjected to 100 overload cycles equal to
436 MPa. Again using the fatigue calculator, determine what length the crack will grow to during these
overload cycles? What is the percentage reduction in life as found in part (ii) due to these overload cycles?
(5 + 5 + 5 = 15 marks)
Question 2 (Block 2 Learning Outcomes 2.2, 2.4)
This question carries 20% of the marks for this assignment
a. The S-N curve is used to graphically present the fatigue behaviour of a material:
i. With the aid of a sketch, explain what a S-N diagram is. How would a S-N diagram be generated in a
laboratory?
ii. Explain the terms: fatigue limit and endurance limit.
4/6/2020 54352 – T357 Structural IntegrityTMA 03Copyright © 2019
https://www.australiabesttutors.com/Recent_Question/54352/T357-Structural-IntegrityTMA-03Copyright–169-2019 4/6
iii. What is meant by the term R-ratio?
(6 + 4 + 2 = 12 marks)
b. Commercially pure titanium alloy with an ultimate tensile strength of 550 MPa is tested at an R ratio of
0.1. The endurance limit at 107 cycles is found to be 200 MPa.
i. Calculate the mean stress in a fatigue test with a stress amplitude of 200 MPa and an R ratio of 0.1.
ii. Use the Goodman equation to calculate the endurance limit at a mean stress of 0 MPa for this alloy.
(Hint: if you combine equations 2.1–2.4 in Block 2 Part 2 the following equations can be derived:
and .
You might find them useful)
c. (4 + 4 = 8 marks)
Question 3 (Block 2 Learning Outcomes 4.1, 4.2, 4.3, 4.9)
This question carries 9% of the marks for this assignment
Explain the role played by each of corrosion, corrosion fatigue and stress corrosion cracking in the failure
of materials and structures. You can give examples as appropriate. Your answer should not exceed 500
words.
(9 marks)
Question 4 (Block 2 Learning Outcomes 4.1, 4.2, 4.8, 4.13)
This question carries 28% of the marks for this assignment
Read the following case study before answering the questions that follow.
Note that this question is designed to test how you utilise the evidence given to you to find a viable
solution to an engineering problem. You should only use the information given in the question and should
not seek additional information from other sources.
Case study
A building worker was seriously injured when he fell from scaffolding whilst installing air-conditioning
equipment in a shopping mall. He was working on a temporary tower erected by assembling together
frames and tubes (Figure 3). These are made from aluminium alloy, chosen for its light weight and hence
ease of use.
Figure 3 Modular scaffolding platform
The frames slot into one another vertically and are braced by diagonal members. The tubes have a springloaded claw at each end so that they can be snapped onto a cross-tube and so provide a balustrade (C in
Figure 3). Upright parts of the frame allow the horizontal tubes to be attached and remain secure without
slipping away. The claw fits over the tube from above. A typical claw is shown in Figure 4. The tubes are
extruded, while the fittings, including the claws, are cast from the alloy.
Figure 4 Claw locking mechanism
The mechanism includes a metal crescent (1) that rotates about a pivot (P), and whose position is
controlled by a metal finger (2) that rotates about a different pivot point. The finger exerts pressure on the
crescent by means of a helical steel spring (S) with two arms that are fitted to the same pivot as that of the
finger.
An investigation into the accident was carried out. On retrieving the fallen tube, it was found that the claw
at one end was fractured (Figure 5), while that at the other end was intact (Figure 6).
Figure 5 Broken claw
Figure 6 Intact claw
The broken claw showed a brittle fracture surface, with numerous pinholes that indicated porosity in the
original material. A sample that included the origin of the fracture was taken for metallurgical analysis, as
shown by the rectangular flat part in the upper left-hand corner of the claw arm (Figure 7). The analysis
showed that the alloy was within specification. The fracture surface was fresh and unoxidized, and there
were no signs of fatigue striations when it was examined under the microscope. The appearance of the
fracture suggested that it had been broken by lateral bending. It was also established that the claw had
broken during the accident and not from impact with the ground after it had failed, although the matching
4/6/2020 54352 – T357 Structural IntegrityTMA 03Copyright © 2019
https://www.australiabesttutors.com/Recent_Question/54352/T357-Structural-IntegrityTMA-03Copyright–169-2019 5/6
ends were lost in the shopping mall. The tube had been used without prior problems until the accident.
Figure 7 Fracture surface of claw at top
Examination of the intact claw from the other end of the fallen tube showed that the spring was badly
rusted, with both arms having been destroyed. The spring on the broken end was also rusted, although the
arms were intact.
The injured worker sued his employers, claiming that the broken claw had been badly made, had
excessive porosity, and was thus too weak to support his weight during normal usage.
Questions
a. By referring to the two diagrams of Figure 4, describe briefly the action of the claw in holding a tube in
a locked position. Start by considering how a tube is pushed into the claw, and the sequence of events that
produces a locking force. You may want to sketch the forces acting on the crescent and finger when the
tube is locked in place.
Indicate which parts are safety-critical, and explain why.
(12 marks)
i. Outline two possible theories to explain the failure of the balustrade tube, using the evidence revealed by
the analysis.
ii. Based on the evidence, which is the most likely explanation for the failure?
iii. Would the worker be likely to succeed in his claim as stated? Explain your answer.
(8 + 4 + 4 = 16 marks)
Presentation
The final 10% of marks for the assignment are awarded for presentation (see ‘Presentation of TMA
answers’ on the Assessment tab for guidance). These will be scored as Question 5
The post T357 Structural Integrity appeared first on Versed Writers.