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RE: Lamellar Tearing

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The little I know about lamellar tearing is as follows:

1/ It is a concern because sulfides, silicates and aluminum oxide inclusions
can be "locked" in between "layers" of steel during the rolling process.
This results in reduced ductility and strength in the "through thickness"
plane of the structural element.

2/ It is of particular concern where fabrications generate through thickness
stresses during weld cooling of the large connections. This can result in
formation of voids at inclusions, cracks or a shear failure. It is also of
concern where transfer of tensile stresses through the thickness of a
section is required as is the case of web to cord connections in HSS trusses
or in some rigid beam to column connections.

3/ It is not normally a concern for typical flexible beam to column
connections such as the standard double angle because this connection allows
some rotation of the beam at the connection, however if you're ever tempted
to weld beam web directly to column, think again. Without proper detailing
this could result in lamellar tearing. The direct welded connection does not
allow any flexibility and designers mistakenly consider this to be a
flexible connection.

4/ There are several ways to minimize the risk of lamellar tearing including
contracting a fabricator who is familiar with the phenomenon and can
generate procedures minimizing tearing during the fabrication process. But
the best way is to detail connections that do not rely on transfer of
tensile stresses in the "through thickness" plane. This can be done fairly
simply by being aware of the orientation of beam components and direction of
stresses transferred.

5/ When you just can't avoid it, other more costly measures can be employed
such as 

a) specifying a steel with improved through thickness ductility
b) gouging out the base metal and rewelding or buttering.
c) complete radiographic testing of the plates prior to assembly and after
assembly  

That's my 2 bits. There is, no doubt, an expert out there who can write
volumes on the subject. Hope I was some help.     
   

> -----Original Message-----
> From:	Mark K Gilligan [SMTP:MarkKGilligan(--nospam--at)compuserve.com]
> Sent:	Thursday, March 25, 1999 10:20 PM
> To:	INTERNET:seaint(--nospam--at)seaint.org
> Subject:	Lamellar Tearing
> 
> Glauco
> 
> >Do you concern about Lamellar Tearing in your Structural Projects?
> Yes
> 
> >In a frame connection between a girder and the column do you concern
> about
> it?
> Yes
> 
> >Does AISC recommend something about it?
> Refer to the recommendations by SAC.  A good starting point is their web
> site at -
> http://quiver.eerc.berkeley.edu:8080/
> 
> >Do you know any rule of the thumb about Lamellar Tearing?
> >(In plates less than 19 mm it doesn't occur?)
> >(What kinds of ASTM steel it doesn't occurs)
> >(Does it occur in rolled shapes?)
> Keep the stresses low.
> Specify low sulfer steel.
> Specify steel with good ductility and toughness.
> Use welding electrodes that have good toughness properties.
> Follow low hydrogen welding procedures.
> Welding procedures should minimize restraint and weld shrinkage.
> Use non destructive testing procedures to find defects in the base
> material
> in the region of the weld prior to welding.
> Make sure the welders follow the welding procedures!!!!
> 
> >What kind of test I can do to know if a plate is resistent to Lamellar
> Tearing?
> See comments above.
> 
> Mark Gilligan
> 
> 
>