How to pick the right type of steel.

Hi there.
I am (along with my projectgroup) currently working on our 3rd semester project of our industrial engineerin education af the University of
Aalborg, Denmark. Our project is to build a crane that can lift a certain type of boats and we've just reached the phase where we are to choose the type of steel the crane should be built in. Our problem with this is due to the problem, that we haven't been introduced to any 'algorithms' for choosing the right type of material nor the type of profile. We really don't want to pick a material without anyh argumentation (even though this is what we've been told to do). Therefore, we've been browsing around the web in hope of finding any recognized methods for choosing the right type of material, but without any luck, and that's where you guys come in :-)
So basically, is there any recognized methods of choosing the correct materials based on various factors. It doesn't need to be to complex, this is still only 3rd semester - but better complex than vague :-)
Thank you for your time. Christian Rasmussen, Denmark.
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snipped-for-privacy@gmail.com wrote:

Rule of thumb for beginners: Use what others use. In "Introduction to Materials", you should have learned what type of steel is used for what purpose.
After that, there's Stahlschlssel (Key to steels).
Michael Dahms
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Michael Dahms skrev:

Thank you, I will try to get hold of the "Introduction to materials". We've been introduced to segments of the Stahlschlssel, personally I love the german engineering books, but unfortunately it's not so popular here among the younger lectors. Though I was hoping there existed an 'selection of materials 101'-algorithm :-)
Thank you for your help. Christian
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snipped-for-privacy@gmail.com wrote:

Bookstores list books available on "Materials Selection".
(Amazon.com product link shortened)61177980/ref=sr_1_22/104-2861583-4407163?ie=UTF8&s=books Principles of Materials Selection for Engineering Design, The (Hardcover) by Pat L. Mangonon
(Amazon.com product link shortened)61177980/ref=sr_1_23/104-2861583-4407163?ie=UTF8&s=books Time-Saver Standards for Building Materials & Systems: Design Criteria and Selection Data (Hardcover) by Donald Watson "
(Amazon.com product link shortened)61178234/ref=sr_1_33/104-2861583-4407163?ie=UTF8&s=books Handbook of Materials Selection     Handbook of Materials Selection by Myer Kutz (Hardcover - Jul 22, 2002)
There are a number of older works as well.
Hit the library and the bookstores.
Good luck.
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snipped-for-privacy@gmail.com wrote:

Materials selection charts ( http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/ ) are a simple way of showing which class of material is good for what you want. If you've already decided on steels, you can still use this sort of approach to identify a grade if you have tabulated data about the properties. For a given problem, you can narrow down the range of acceptable materials using some absolute constraints on the properties of the material you want (e.g. corrosion rate, some derived mechanical parameters based on the maximum load you want to lift or hold). Then, decide on something to be maximised or minimised, such as the overall cost of the assembly, and derive a 'performance index' based on this. For example, if you use a weaker material you might need more of it to do the same job, so your performance index might be (strength / cost-per-unit-weight), which should be maximised. Depending on the geometry of your loading (especially if bending is involved), various terms in your performance index might need to be squared or cubed. For steels, strength and cost are the main variables, while stiffness and density tend to be similar. If you're using pre-formed sections, you can also incorporate some kind of 'shape factor' into your performance index, a scalar parameter that characterises things like resistance to bending of a certain profile shape, usually relative to a solid rod of circular cross section.
Joe
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