×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Jobs

Solid Finite Element vs Through-thickness stress close to yield point

Solid Finite Element vs Through-thickness stress close to yield point

Solid Finite Element vs Through-thickness stress close to yield point

(OP)
Hi gents!

I would like to ask you about your engineering opinion on following FEA case.

Given is thick plate (40mm thickness) with dimensions in plan of 500x500mm. It is modelled by solid finite elements with edge of 10mm each.
At some small area of this plate, in effect of loading conditions, there is cubic area 40x40x40mm for which mean von Mises stress is equal to yield strength of the ductile steel material plate is made from. Other areas are well below yield strength.
Note, it is through-thickness phenomenon.

Question is, how would you interpret the results and why, will the plate take it or not?

RE: Solid Finite Element vs Through-thickness stress close to yield point

it sounds like your plate has yielded, and maybe needs a non-linear analysis.

another day in paradise, or is paradise one day closer ?

RE: Solid Finite Element vs Through-thickness stress close to yield point

(OP)
That is what I think too. Literature and various codes are giving following acceptance criteria for nonlinear problem, it is peak strain allowable value of 5% for bilinear stress-strain material curve. Now one may ask if this 5% value should be found at one FE node value or averaged among some cubic/area? If one value, how to exclude any singularities from this, perhaps it is true that in its definition - strain values cannot have singularities, do you agree, rb1957?

RE: Solid Finite Element vs Through-thickness stress close to yield point

if you exceed yield through the thickness for a sizeable area, you've probably yielded the plate. Results from a linear model aren't usable.

another day in paradise, or is paradise one day closer ?

RE: Solid Finite Element vs Through-thickness stress close to yield point

Keep in mind that the yield stress is traditionally set at 0.02% strain. This is not the elastic limit of the material. So, if you are at or above the YS of the material, you have probably already exceeded the elastic limit of the material.

Secondly, if you are above YS, the elastic model is still useful in that you can alter the design and compare the resulting stresses without having to go full nonlinear. Besides, if you are using common plate, the nonlinear characteristics of this material is quite complex making the analysis perhaps even less useful. I would work to reduce the stress by changing geometry if possible to get it below the YS point.

RE: Solid Finite Element vs Through-thickness stress close to yield point

Given that the plate is 40mm thick and the length of the long side of the material is 500mm you may consider running the FEA as a shell or thin plate. The general rule I've read indicates a plate can be considered "thin" when the thickness is 1/10 or less of the long dimension on the plate. I generally use 1/15 to 1/20 with the FEA software I use. The results will give you another data point to consider how accurate your brick analysis is. In addition, there should be a precision analysis feature in your software. Follow up on that tool to determine where 10% precision is. ANSYS published some documentation some time ago indicating they would recommend a stress precision of 10% or less for accurate results.

RE: Solid Finite Element vs Through-thickness stress close to yield point

As it is through thickness stress, the material will yield in shear. A hole will be punched.

Saco van Loon www 2st nl

RE: Solid Finite Element vs Through-thickness stress close to yield point

OP, what is the loading condition the plate is subjected to? If its transverse loading, are you applying a pointed load on a node? If so, as you have mentioned, the local peak stresses could be due to local high force concentration. Also what are the fixity or support conditions for the plate?

This is one check I can think of. Please see the variation of Von Mises stresses from loading point to some short distance. If the variation is huge, then the anomaly could be due to loading effect i.e. if the distance to which stresses are below yield is really short.

"At some small area of this plate, in effect of loading conditions, there is cubic area 40x40x40mm for which mean von Mises stress is equal to yield strength of the ductile steel material plate is made from."

"Note, it is through-thickness phenomenon."

You are quoting both Von Mises as well as Through-thickness. It is possible that major component in Von Mises is coming from Through Thickness (is the through thickness stress normal or shear components?)

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

White Paper - How to Capitalize on HVAC/R Trends to Drive Business Growth
According to Steve Yurek, CEO of the Air Conditioning, Heating and Refrigeration Institute, the HVAC/R industry is facing change on all fronts. This includes challenging trends on contractors and distributors like new refrigerants, growing automation, complex sensors and monitoring, green initiatives and a technician shortage. We look at these trends and outline actionable insights on how it all can be turned into a competitive advantage and business opportunity. Download Now
eBook - Manufacturing the Cars of Tomorrow
In this ebook, we'll explore how additive manufacturing is going to transform the way cars are made. This includes commentary from thought leaders such as Ford's CTO, Ken Washington, Customer case studies of ways 3D printing is being used today, and a variety of part examples where 3D printing is already impacting how automobiles are made. Download Now
White Paper - Smart Manufacturing for Semiconductor
New technologies and approaches present great opportunities for semiconductor manufacturers to achieve high levels of innovation, yield and improvement. This white paper explores some of these cutting-edge technologies and how they can be applied effectively in the semiconductor industry. Read about how Smart Manufacturing is transforming the semiconductor industry. 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