Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Lamellar Tearing

[Subject Prev][Subject Next][Thread Prev][Thread Next]
The following text on lamellar tearing is from the AISC Manual (LRFD 2nd 
Edition). There are several references in the text below that can be found 
in the reference list at the end of each of the parts given below. Hope 
this helps you.

Charlie




>From Volume I-Structural Members, Specifications and Codes, Part 1 (page 
1-8):

"The information on strength and ductility presented in the previous 
sections generally pertains to loadings applied in the planar direction 
(longitudinal or transverse orientation) of the steel plate or shape. It 
should be noted that elongation and area reduction values may well be 
significantly lower in the through-thickness direction than in the planar 
direction. This inherent directionality is of small consequence in many 
applications, but does become important in the design and fabrication of 
structures containing massive members with highly restrained welded joints.

With the increasing trend toward heavy welded-plate construction, there has 
been a broader recognition of the occurrence of lamellar tearing in some 
highly restrained joints of welded structures, especially those using thick 
plates and heavy structural shapes. The restraint induced by some joint 
designs in resisting weld deposit shrinkage can impose tensile strain 
sufficiently high to cause separation or tearing on planes parallel to the 
rolled surface of the structural member being joined. The incidence of this 
phenomenon can be reduced or eliminated through greater understanding by 
designers, detailers, and fabricators of (1) the inherent directionality of 
construction forms of steel, (2) the high restraint developed in certain 
types of connections, and (3) the need to adopt appropriate weld details 
and welding procedures with proper weld metal for through-thickness 
connections. Further, steels can be specified to be produced by special 
practices and/or processes to enhance through-thickness ductility and thus 
assist in reducing the incidence of lamellar tearing. Steels produced by 
such practices are available from several producers. However, unless 
precautions are taken in both design and fabrication, lamellar tearing may 
still occur in thick plates and heavy shapes of such steels at restrained 
through-thickness connections. Some guidelines in minimizing potential 
problems have been developed (AISC, 1973). See also Part 8 in Volume II of 
this LRFD Manual and ASTM A770, Standard Specification for 
Through-Thickness Tension Testing of Steel Plates for Special 
Applications."

>From Volume II--Connections, Part 8 (page 8-113):

"A lamellar tear is a separation or crack in the base metal caused by 
through-thickness weld shrinkage strains. When steel is hot-rolled, 
sulphides or other inclusions are elongated to form microscopic platelets 
in the plane of the steel plate. These inclusions reduce the strength of 
the steel in the through-thickness direction below that in the longitudinal 
or transverse direction.

While special practices are available to produce low-sulphur steel which is 
resistant to lamellar tearing and ASTM A770 provides a testing method by 
which the through-thickness strength of the base metal may be measured, it 
is difficult to assure freedom from the possibility of lamellar tearing. 
Lamellar tearing is a phenomenon which can occur even in material with 
superior mechanical properties. Instead, the joint detail is most important 
in preventing lamellar tearing.

Some joint designs are inherently susceptible to lamellar tearing (AISC, 
1973). For example, the complete-joint-penetration groove-welded tee joints 
in thick sections shown in Figure 8-30 can develop lamellar tears in the 
crossbar of the tee flange. Such tears can be detected with UT. Other 
susceptible joints are shown with improved details in Figures 8-31 and 
8-32.

The probability of lamellar tearing may be minimized through good joint 
design and proper welding procedures. The joint design should minimize the 
weld size and, therefore, the resulting shrinkage strains. Additionally, 
the design should reduce the restraint which intensifies the local strains. 
The welding procedure should then establish a sequence to minimize 
component and internal restraint. Welding with low-hydrogen processes and 
effective pre-heat has also been shown to minimize lamellar tearing 
(Kaufmann, Pense, and Stout, 1981)."

-----Original Message-----
From:	Glauco [SMTP:glauco(--nospam--at)cenpes.petrobras.com.br]
Sent:	Thursday, March 25, 1999 11:35 AM
To:	seaint(--nospam--at)seaint.org
Subject:	Lamellar Tearing

Dear Sirs;


Do you concern about Lamellar Tearing in your Structural Projects?

In a frame connection between a girder and the column do you concern about 
it?

Does AISC recommend something about it?

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?)

What kind of test I can do to know if a plate is resistent to Lamellar 
Tearing?


Tks,

Glauco de Deus Ribeiro
Civil Engineer