# MDM Practice Exam by Hart & Klein



## SacMe24 (Mar 20, 2018)

Hello everyone,

I've been preparing for the MDM exam  in April for quite some time now and came across a pratice exam by Scott Hart and Kevin Klein. I find that these problems are much more difficult than those from the NCEES practice exams. Have any of you had a similar experience? The material is good, but I don't think it did much to boost my confidence level even after practicing with material from PPI, 6-min. solutions, both NCEES practice exams (2011 and 2016), EngProGuides and Dr. Tom.

I just want to make sure I'm not off base here. Still practicing like mad for the exam....

Thanks for the read and comments.


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## Kloeb222 (Mar 20, 2018)

I have taken the engrproguides, NCEES, and this practice exam so far. I would definitely agree that this its the most difficult of the three. My scores have been 83%, 74%, and 70% on the three exams respectively. Although i got unusually lucky on a few problems on this exam with guessing.

The lack of solutions does not help either. I understand the idea behind giving "hints" instead of the solutions but even with the hints a few of the problems don't make sense to me. I suspect there are some errors also. The wording of some of the problems is pretty confusing as well. Then there are the assumptions that you are expected to make based on information that isn't given to you. Recall the spinning wheel with a braking torque applied problem.

I do still believe this is a good purchase for anyone taking the MDM exam. At this point i am working any problems i can get my hands on.


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## Engineer_562 (Mar 20, 2018)

jvanoye said:


> Hello everyone,
> 
> I've been preparing for the MDM exam  in April for quite some time now and came across a pratice exam by Scott Hart and Kevin Klein. I find that these problems are much more difficult than those from the NCEES practice exams. Have any of you had a similar experience? The material is good, but I don't think it did much to boost my confidence level even after practicing with material from PPI, 6-min. solutions, both NCEES practice exams (2011 and 2016), EngProGuides and Dr. Tom.
> 
> ...


Jvanoye

do you have this exam in PDF or physical book? If electronic, can I have a copy of it? Willing to pay of course.


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## SacMe24 (Mar 20, 2018)

Engineer_562 said:


> Jvanoye
> 
> do you have this exam in PDF or physical book? If electronic, can I have a copy of it? Willing to pay of course.


You can get it from Amazon.... https://www.amazon.com/gp/product/1976188172/ref=oh_aui_detailpage_o08_s00?ie=UTF8&amp;psc=1


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## SacMe24 (Mar 20, 2018)

Kloeb222 said:


> I have taken the engrproguides, NCEES, and this practice exam so far. I would definitely agree that this its the most difficult of the three. My scores have been 83%, 74%, and 70% on the three exams respectively. Although i got unusually lucky on a few problems on this exam with guessing.
> 
> The lack of solutions does not help either. I understand the idea behind giving "hints" instead of the solutions but even with the hints a few of the problems don't make sense to me. I suspect there are some errors also. The wording of some of the problems is pretty confusing as well. Then there are the assumptions that you are expected to make based on information that isn't given to you. Recall the spinning wheel with a braking torque applied problem.
> 
> I do still believe this is a good purchase for anyone taking the MDM exam. At this point i am working any problems i can get my hands on.


Kloeb222..... were those scores your first pass scores for all 3 exams? If so.. WOW... you're ready to pass this exam....my most recent one was the one from EngProGuides and I scored 62/80 on the first pass....


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## Kloeb222 (Mar 20, 2018)

Yes those we my first pass scores for all 3. I still want to go through them all once or twice more. I'm only taking this exam once!

I tried to pm you regarding this practice exam, but it says you are not able to receive messages.


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## Kloeb222 (Mar 27, 2018)

Here's one that doesn't make sense to me. (I am assuming there is a typo and they are looking for the max moment). I don't get a value close enough to any of the possible answers.


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## PARSCORA (Mar 27, 2018)

Kloeb222 said:


> Here's one that doesn't make sense to me. (I am assuming there is a typo and they are looking for the max moment). I don't get a value close enough to any of the possible answers.
> 
> View attachment 10974


Attached I have how I would solve this problem on the test.  I don't think this is correct because this is intended for static loading.  Since this shaft is rotating, this would most likely fail due to fatigue, which is not considered in this equation.  But since we know it is less than B, C and D; A seems like a safe educated guess.

hopefully someone else is more help!


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## SacMe24 (Mar 28, 2018)

Kloeb222 said:


> Here's one that doesn't make sense to me. (I am assuming there is a typo and they are looking for the max moment). I don't get a value close enough to any of the possible answers.
> 
> View attachment 10974


I ran into the same problem as you... this problem doesn't make sense to me as stated....sorry I couldn't be of more help...I will be going over a select number of these problems a 2nd time this coming weekend... it's crunch time!


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## emmajuwa (Mar 28, 2018)

PARSCORA said:


> Attached I have how I would solve this problem on the test.  I don't think this is correct because this is intended for static loading.  Since this shaft is rotating, this would most likely fail due to fatigue, which is not considered in this equation.  But since we know it is less than B, C and D; A seems like a safe educated guess.
> 
> hopefully someone else is more help!
> 
> View attachment 10975


Your solution seems correct to me. I used exactly the same approach and got the same answer. I wont overthink it especially when the fatigue stress concentration is not provided and the shaft is not a stepped shaft. Why don't you email the authors. It is definitely a typo. The question should be "maximum bending moment".


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## Kloeb222 (Mar 28, 2018)

I get 643 in-lbf by using the principal stress eq due to a moment and torque from this link (also found in the MERM but i don't have it with me right now):

http://www.nptel.ac.in/courses/112107146/lects &amp; picts/image/lect34/lecture34.htm

I'm not gonna worry about this one too much though.


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## emmajuwa (Mar 28, 2018)

Kloeb222 said:


> I get 643 in-lbf by using the principal stress eq due to a moment and torque from this link (also found in the MERM but i don't have it with me right now):
> 
> http://www.nptel.ac.in/courses/112107146/lects &amp; picts/image/lect34/lecture34.htm
> 
> I'm not gonna worry about this one too much though.


Failure by principal stresses will be for brittle materials which wasn't specified. A similar problem in NCEES practice exam specified the failure criterion to use.


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## iMechanical (Mar 28, 2018)

Just passing through, saw this problem, and thought it was interesting...

First, the equation written above to solve for torque (i.e. Sig' = (16/(pi*d^3))*SQRT(4M^2+3T^2)) is based on Distortion Energy Theory which is a yield criterion. The problem specifies the "Tensile Strength," which tells you that you should use an equation derived using an ultimate criteria (i.e. maximum shear stress).

Next, if you wanted to solve this problem using a similar approach, you'd actually need the following equation:


Tau_Max = (16/(pi*d^3))*SQRT(M^2+T^2)

If I use this equation, I get ~_*516 in-lbf*_, which is close(r) to (A).

You can also solve it another way without using the cookie-cutter equation (but is a time sink):


T = 63025*P/n ~525.2 in-lbf

Calculate Tau = Tr/J

J = (pi/32)*d^4 ~0.0061 in^4

Tau = (525.2)(0.25)/0.0061 ~21525 psi


Ftu = 60 ksi; Fsu = 0.5*Ftu = 30 ksi

Tau_1,2 = +\- 0.5*SQRT((S_x - S_y)^2 + (2*Tau)^2)

Tau_1,2 = Fsu = 30 ksi (Max Principal Shear Stress)

S_x = ? (Need to solve for this)

S_y = 0

Tau = 21525 psi (Solved for above)


Solve for S_x

After some algebra, S_x ~41793 psi


Solve for M

S_x = My/I

I = J/2 ~0.00307 in^4

M = (S_x)*(I)/y = (41793)(0.00307)/0.25 ~_*513 in-lbf (A)*_


Eating dinner so excuse any slight miscalculations.

Hope this helps you guys.


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