**3. Finite element modeling**

A finite element (FE) model was created for the four-point bending specimen in an attempt to understand the stress distribution adjacent to the hand-holes. This model was constructed to be identical to the weld detail and geometry of the specimens. The model also included an initial imperfection in the detail along the line where cracking would first be observed. The purpose was to determine how a crack through the throat of the fillet weld would affect the stress distribution. Local stresses were mesh dependent for this study. Finer mesh sizes often increase the stresses local to important geometric details, whereas a coarse mesh often results in a reduction in local stress. The model as a whole consisted of 633,324 nodes with 346,747 elements. Each consisted of a mix of both hexahedral and tetrahedral element types. **Figure 11** depicts the mesh and model as a whole.

Stress "hot spots" indicate where fatigue cracking is likely to develop. **Figure 12** shows a longitudinal stress map along the "Z" axis. Under bending, longitudinal stress developed and the distribution, sense, and magnitude are affected by the presence of the hand-hole detail. This is shown in **Figure 12** with the shade of blue being a relatively low stress while elevated stress (**Figure 11**) is green. Hot spots appear alongside most of the hand-hole, maximum values between the 10:00 and 2:00 positions,

*Fatigue Behavior of Reinforced Welded Hand-Holes in Aluminum Light Poles with a Change… DOI: http://dx.doi.org/10.5772/intechopen.106342*

**Figure 11.** *Overall model.*

**Figure 12.** *Contours of longitudinal stresses around the hand-holes.*

**Figure 13.** *Stress concentration X direction.*

**Figure 14.** *Stress concentration Z direction.*

as well as between the 5:00 and 7:00, indicated by a lighter shade of blue. Elevated stresses are apparent on the inside edge of the reinforcement. Stresses are larger near the junction of the inside and outside legs of the reinforcement [9]. This makes sense because, as the tube bends, the cast reinforcement attempts to elongate on the tension side. This stretches the reinforcement insert and results in transverse bending.

**Figures 13** and **14** show how a crack within the detail effects the stress hot spots. In **Figure 13**, to be precise, the stress is along the "X" axis and shows that the highest concentration of stress is located at the "end" of the crack with a red color. **Figure 14** shows this exact same phenomenon along the "Z" axis.
