MERM Conflicting information

[buick455]

I keep seeing conflicting information in the MERM that is not in an eratta that I can find. Note: I have the 12th edition 1st printing MERM and the 12th edition 2nd printing sample problem book.

As mentioned in one of my posts, is a wide beam 8 or 10 times the thickness? The MERM says 8 or 10 times. In a Lindeburg sample problem he used 10 times and it was not wide(in the problem 8 would have been wide). So is it 8 or 10??

Also, I was working a Lindeburg coil spring problem last night and in the MERM it states that the allowable stress is .45-.65 of the ultimate strength for steel springs. It gives specific guidlines when to use .45 and when to use .65. In the sample problem he used .75 x ultimate = the yield strength then .5 of that was the allowable stress (this is in the Shigley book but Shigley used .577 x the yield strength). Note: I understand where .5 and .577 comes from but it also seems unclear when to use .5 and when to use .577 in shear stress problems. Anyway, I used .45 x ultimate and got the wrong answer but it was close (.65 would have been furthur from the answer).

Anyone had some ideas??

 

[buick455]

I am getting the feeling that as I have not received any input on these question in three difference forums that either:

1. No one cares.

2. No one else is taking the MD depth.

3. I am asking too difficult a question.

4. Did I say no one cares?

I keep seeing conflicting information in the MERM that is not in an eratta that I can find. Note: I have the 12th edition 1st printing MERM and the 12th edition 2nd printing sample problem book.
As mentioned in one of my posts, is a wide beam 8 or 10 times the thickness? The MERM says 8 or 10 times. In a Lindeburg sample problem he used 10 times and it was not wide(in the problem 8 would have been wide). So is it 8 or 10??

Also, I was working a Lindeburg coil spring problem last night and in the MERM it states that the allowable stress is .45-.65 of the ultimate strength for steel springs. It gives specific guidlines when to use .45 and when to use .65. In the sample problem he used .75 x ultimate = the yield strength then .5 of that was the allowable stress (this is in the Shigley book but Shigley used .577 x the yield strength). Note: I understand where .5 and .577 comes from but it also seems unclear when to use .5 and when to use .577 in shear stress problems. Anyway, I used .45 x ultimate and got the wrong answer but it was close (.65 would have been furthur from the answer).

Anyone had some ideas??

 

[benbo]

I'm an EE but let me take a guess-

I think it's answers 1 and 4 - with the corollary explanation that you are talking about a few missing errata out of 100s of pages of information. The likelihood that this will have any real effect on the use of this reference for the exam, or whether one passes the exam or not, is probably miniscule.

They probably screwed up. Write to Lindeberg, or whoever, and tell him.

 

[buick455]

As I got a 68 on my last exam I think 2 problems are important, not that I am looking for a 70 but every point counts.

I did report this issue through PPI.

I'm an EE but let me take a guess-
I think it's answers 1 and 4 - with the corollary explanation that you are talking about a few missing errata out of 100s of pages of information. The likelihood that this will have any real effect on the use of this reference for the exam, or whether one passes the exam or not, is probably miniscule.

They probably screwed up. Write to Lindeberg, or whoever, and tell him.

 

[benbo]

As I got a 68 on my last exam I think 2 problems are important, not that I am looking for a 70 but every point counts.
I did report this issue through PPI.

Two problems may be important but the chances that this exact issue will come up on the actual exam are miniscule.

 

[Shaggy]

If you do run into this exact situation on the exam, calculate it both ways. The answers are in the format of "most closely matches". So if both of your solutions most closely match to two separate answers... then you have a problem. At that point flip a coin. Chances are, if there is a wide beam problem, the problem statement will say wide beam, or it will have a width that is much more than 10 times the thickness.

Also, regarding the springs, follow shigley.

 

[Sschell]

As usual, I agree with shaggy... and usually points 1 & 4 apply to me... I mainly like to post fluff and BS on this fourm.

 

[JoeysVee]

I'm going to use 10 but they wont have a problem that is close to 10 so you'll be ok there. I think it's accurate to about 10 but different authors define accurate differently.

0.45 to 0.65 is correct. It's based on statistics and most of the time .577 will do it....so for the exam use .577 and you'll be ok. They won't put an outlier on the exam so .577 is the number to use. Personally I think 0.75 was either a mistake or something really weird was going on. I don't have the Lindeburg sample exam so I can't look the problem up but don't let Lindeburg's hard ass exam with weird problems screw you up....use 10 and .577 and you'll be ok.

I would have answered sooner but I just saw this post.