Monday, April 18, 2011

CrazyEngineers Forum - Mechanical & Civil Engineering

CrazyEngineers Forum - Mechanical & Civil Engineering

Modal analysis with acceleration loading in patran/nastran

Posted: 18 Apr 2011 05:41 AM PDT

Hi,
I want to do modal analysis for a rocket that is subjected to various accelerations (like 9g, 18g). I want to wonder if the modal analysis results are different for unloaded and loaded (with acceleration) cases. If they are different how can I solve this problem with acceleration loading?
I have read "inertia relief" procedure for static analysis. But for the modal analysis I have not encountered any information.
Can you help me?
Thanks a lot...

Pattern making materials.

Posted: 06 Apr 2011 06:21 AM PDT

Hi friends, there are a few pattern making materials which are used widely in industry.
I will be telling you about them. Please correct me if I get wrong somewhere.

1.Wood: Wood has been a popular choice amongst foundry shops. It is very common and cheaply available. Mostly Burma, C.P.Teak is used. Wood has a tendency to warp.
Mostly nowadays compressed wood laminates and laminated wood impregnates are used. Laminated woods are nothing but resins.

2.Metal: This has an advantage that it does not have any storage problems.
Whenever any metal is used as a pattern, a shrinkage allowance is given to it.
The various metals commonly used are
cast iron: It is very brittle and is not used for applications involving shocks hence it is available cheap than other iron and steel varieties.
Brass: Heavier than cast iron but it does not rust. and also, it is restricted to smaller patterns.
Aluminium: Melts at a very low temperature, soft and easy to make pattern. Only draw back is that it can break hence has to be handled with care.
White metal. It is the best metal that can be thought of. It melts at 473 K and does not shrink much.

3.Plasters: Nowadays, gypsum is used as a pattern making material. It has a compressive strength of 275-300 kg/cm2. The various varieties of plasters in market are Hydrocal and Hydrostone etc.

Rubbers, waxes and plastics are nowadays used mostly because they are cheap. They have the exact properties for a pattern materials. Mostly thermoplastics and epoxy resins are used in plastic and wax varieties respectively.
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