×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Allowable for Thicknesses per MMPDS

Allowable for Thicknesses per MMPDS

Allowable for Thicknesses per MMPDS

(OP)
Hello,

I had a question on how to best properly apply material properties to a given piece of metal. As an example of the question: say that there is an aluminum 7075-T73 plate 4 inches thick that is machined down to form a pocket, so that all thicknesses are now 1 inch thick. Would one need to use mechanical properties for the 4 inch thickness range or could one use the 1 inch material properties for structural analysis?

RE: Allowable for Thicknesses per MMPDS

I think you are conflating strength and stress here. The material strength (tensile and yield) is the same no matter how thick or thin the geometry. As strength is thought of in terms of load/area, you would effectively have increased applied stress 4 times with the 1" plate in this example compared to the 4" plate. You have to compare this stress (as a starting point) to the material yield and tensile strengths to see if it might be acceptable.

RE: Allowable for Thicknesses per MMPDS

The material properties are related to the size that it was during the last thermo-mechanical process.
If there is a de-rate on 4" plate, then you stuck with that regardless of how thin you machine it.
The properties are related to heat treatment response usually.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Allowable for Thicknesses per MMPDS

The material strength (tensile and yield) is the same no matter how thick or thin the geometry. - nope, completely wrong. See MMPDS tables for strength vs plate thickness.

And agree, you must use properties for the starting plate or bar thickness prior to machining. And you must pay attention to L, LT, and ST direction strength differences.

RE: Allowable for Thicknesses per MMPDS

I'm acronym challenged: what is MMPDS?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Allowable for Thicknesses per MMPDS

MMPDS => Metallic Materials Properties Development and Standardization

MMPDS is an FAA/DoD authoritative source for aerospace-use metals [alloys/temper/spec] mechanical [and some physical] data. This manual was an evolution/replacement-for MIL-HDBK-5 Metallic Materials and Elements for Aerospace Vehicle Structures ... which was an evolution/replacement for ANC-5 Strength of Metal Aircraft Elements

ASMH => Aerospace Structural Metals Handbook is also an authoritative source for metal [alloys/temper/spec] mechanical and physical and [some] fabrication data.

DO NOT CONFUSE these FAA/DoD authoritative metals Handbooks with the informative ASM [American Society of Materials] Metals Handbooks

NOTE1. Another useful authoritative handbook for conventional [industrial] metal alloys, mechanical and physical properties, is...
CINDAS Structural Alloys Handbook.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

RE: Allowable for Thicknesses per MMPDS

The MMPDS is maintained by Battel Columbus.
The design properties are based on detailed statistical analysis.
This is why they are picky about starting size and orientation.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Allowable for Thicknesses per MMPDS

Thanks!
(I'm also aerospace deficient; my world is heavy metals)

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Allowable for Thicknesses per MMPDS

The strength of the machined part is a function of the original thickness of the plate. So if you machine a part from a 4 inch thick plate of 7075-T73 so that the walls are 1 inch thick or less, the strength of that wall is still that of the 4 inch thick plate you started with (accounting for the various debits due to machining method, notches, surface finish, etc.)

Doug

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close