Why do the specimens behave better when there is no transverse weld?

To answer this question, we must remember that the center of the beam is more restrained, and therefore less ductile. The edges are more likely to experience a uniaxial stress state, where biaxial stresses are expected in the center due to transverse constraint.

Multiaxial stresses inhibit the ductility of the material.

A transverse weld requires the placement of a portion of that weld in the more restrained center of the beam. When the weld is left off at this location (i.e., when there are only longitudinal welds) performance is consistently enhanced, as can be seen in the behavior of specimens 4 and 5.

Why is the performance of specimen 3 at 2,000,000 cycles better than all the others?

The arrows in Table 1 will help us answer this question. Notice that the ends of the longitudinal weld, and the transverse welds (if present) for all the specimens are located in regions of high stress — that is, in every case but specimen 3.

With the “concave” configuration, the transverse weld, in the region of reduced ductility, is placed in a region of reduced stress. The center of the beam still has reduced ductility, but due to the reduced stress, the weld placed in this area that is less critical.

Figure 2
Click to enlarge

Figure 2 represents what might be the best configuration, even though this was not tested: A long, inverted taper.

The critical portion of the transverse weld, the portion in the center of the beam flange, is in an area of low stress. This detail, of course, is what is often applied to construction and agricultural equipment where extra plates are added to strengthen a member.

Because we asked “Why?” we now understand why the inverted taper works.

Omer W. Blodgett, Sc.D., P.E., senior design consultant with The Lincoln Electric Co., struck his first arc on his grandfather's welder at the age of ten. He is the author of Design of Welded Structures and Design of Weldments, and an internationally recognized expert in the field of weld design. In 1999, Blodgett was named one of the “Top 125 People of the Past 125 Years” by Engineering News Record. Blodgett may be reached at (216) 383-2225.