MSE 5090: Case Studies in Material Selection

Week 6 - Material Selection Without Shape

1. Request for Student Feedback
2. Objectives
3. Reading assignment
4. Discussion questions
5. Example problem Ashby B3.4
6. Example problem  Ashby B3.1
7. Week 6 assignments:  Ashby Problems   CS External Contact(s)
8. Reference Material

 Request for student feedback:

 Professor Stringfellow and I have committed to resolving the issues related to this course. Based on some of the problems discussed below,  it seems that some midcourse adjustments are needed to keep the course on track. A key problem has arisen with the CMS software. More of this below:

A. CMS Software:

Some history:

What now?

I have also heard reports that the "software never worked," even last year.  This year we have a later version of the software, so it isn't the same as last years software. Even so, I didn't get reports last year that the software wasn't working. In fact almost all of the reports were that students liked the software and found it easy to use. A  number of students used the software for their homework and case studies. These case studies are available in the library. It is possible that some students couldn't make the software work, but I received no reports of that .  Similarly, in earlier years the software seemed to work well and , in fact , was on reserve in the library  and did not get damaged during use over a whole quarter. This year the software does  work, and I regret the inconvenience caused by factors beyond our control. I've never encountered this degree of difficulty with a program before. Yet software difficulties are part of the real world experience of most engineers.

B. Solving Ashby  problems and homework:

1. Setting up the problem - i.e. determining the nature of the problem- the design requirements and the constraints-30%
2. Using the standard solutions or other modeling techniques to obtain the equations incorporating 1 above-15%
3. Solving the model equations to determine performance indices to use for material selection-25%
4. Using the charts and software to narrow down the materials selection choices-20%
5. Selecting between the narrowed down materials choices using extrinsic and practical considerations-10%.

Thus the software is a convenience in part 4. It is an aid in narrowing down materials choices and is more specific than the charts. Almost all the problems in the Ashby book can be solved without them and were for the most part last year. Therefore, until we fully resolve the software issue, students have the option of submitting the homework in paper form or in software as that becomes readily available. Again, deadlines are perforce relaxed because of the software tools issues. It is important to note that the software yields more refined choices of materials and is faster for multistage selection, but adds no new concepts to the materials selection process.  In that regard , I will be going through how to solve problems without the final selection phase using the software beginning next week.

C. Technical Content of Case Study:

Yet the non technical content is necessary , even if not sufficient. Almost every time a professor writes a proposal the non technical considerations( what the sponsor needs) come into play. The culture of high technology will certainly affect your lives and careers, and this is the course we use to  explore it. It is assumed that students will be able to present the technical parts clearly, although I am prepared to review how that is done too. As the problems will show, the technical approach in a case study is complex and requires insight into materials. That is the point of doing the homework over the next few weeks. Yet , as discussed so often in class and these notes, understanding and framing the study in the company/market/economic etc. framework will add depth and awareness to your technical insights.

D. Student Support:

Online support request:  Online Course Support

 E. Course Organization Issues:

	Derive performance indices for more complex problems
	Analyze cases in materials selection without shape
	Utilize standard solutions to derive performance indices and design requirements
	Develop a methodology for obtaining  contacts with industry for the case study

This week we will study the way to derive design requirements and performance indices for materials selection where shape is unimportant. The cases can be analyzed using graphical techniques by hand or using the CMS software. However it is important to note that the key to the problem isn't the software, but the analysis that precedes its use.  It is useful to do at least a couple of the problems both ways (if possible). These techniques can be readily extended to apply to your case study. As you might imagine, software with a more comprehensive data base and more robust decision support computational engine are beginning to see wider application in industry.

	ASM pages 322 - 332- Failure analysis in materials selection (for case study and background);
	Ashby pages 70 - 130-Case studies in materials selection without shape:

	Do the solutions to standard problems and standard performance indices constitute real engineering?
	How do the results of failure analysis help determine design requirements?
	How can you get input from professionals in the field for your case study?

Sample problems that we will discuss this week (these are related to those on the homework):

Problem 3.4

Derive a performance index and use it to identify a subset of materials which should make good vaulting poles.  Does the result match with what you know about real vaulting poles? How is the selection changed if the criterion is that of storing the most energy per unit weight, instead of volume?

Solution for Problem 3.4

One can identify that a vaulting pole is a device of the type (b) in figure 6.11 on page 86 in Ashby.

1. The elastic energy stored per unit volume in a vaulting pole is given by equation 6.19 on page 87 of Ashby.

	so		which needs to be maximized.
			(One can pick up the right materials from Chart 4)

2.  As indicated in equation 6.21, the performance index for the elastic energy stored per unit weight is given as

which needs to be maximized. (One can pick up the right materials from Chart 5.)

An alternative approach will be given in class.

Problem 3.1

(a)	Show that the best material for a cantilever beam of a given length  and
	given (i.e. fixed) square section (t X t) which will deflect least under a given end load F
	("Useful Solutions", Appendix A, section 3) is that with the largest value of the index
	M = E, where E is young's modulus (neglect self-weight).
(b)	Show that the best material choice for a cantilever beam of a given length and with a
	given section (t X t) which will deflect least under its own weight is that with the largest value of M = E/p where p is the density.

Solution for Problem 3.1

The point of this problem is that the performance index depends on the mode of loading, on the geometric constraints and on the design goal.
(a) The beam is shown in Figure 3.1 (a). The end-load F produces a deflection d
 

("Useful Solutions", Section 3) of

where E is the modulus of the beam material and I is the second moment of the area,
 

which, for a square section of side t, is

so that the deflection becomes

The magnitude of the load F and the dimensions and t are given.

The deflection d is minimized by maximizing

M = E

Figure 3.1 Cantilever beams, loaded in various ways, with square sections which are fixed (a and b) and free (c and d).

The deflection is minimized by maximizing

Ashby B 3.10, B 3.11, B 3.13, B 3.14 and B 3.17 (Due 10/14/98)
Subject: Week 6 - Ashby B 3.10, 3.11, 3.13, 3.14 & 3.17

Case Study: Document Plan for External Contact(s) (Due 10/16/98)
Subject: Week 6 - Case Study External Contacts

The purpose of this assignment is to provide you with experience is arranging and conducting interviews to gain deeper insight into the case events beyond the documented materials.  Review the Collecting Case Content section of Writing Engineering Cases for guidelines on conducting an interview. Personal interviews with people involved in the area of your case study often provide some of the most valuable and interesting input to your study - to say nothing of  a networking opportunity and a chance for long term professional connections, even jobs.

Write a brief Contact Plan for each interviewee for your Case Study. Your contact plan should include the following information:
 

	Contact information: Name, Phone number(s), Address, Email
	Three introductory statements to persuade prospective interviewee to agree to the interview
	Contact log: Date, Time, Content of conversation, Appointment/call back times
	Professional information: Position, Role in Case, What make this individual a credible source?
	Ten questions to be used in the scheduled interview

Below is a link to a hyper linked compendium of references on failure analysis from the ASM
http://www.asm-intl.org/cgi-bin/webfind.exe?keywords=failure+analysis

For those of you who like to experiment with different software packages, the ESM is the ZDNET of materials software. From this site you can download shareware or demos of many programs in use in the field today.
http://www.esm-software.com./
 

Online Course Support