African Fusion March 2016

Welding of tubular k-joints

construction, it was important to generate a model that is as realistic as possible and which is reliable. However, because computing power is limited, meaningful simplifications had to be made. To reduce computation time, a simplifiedoutline of a single K-joint of a tubular truss was created, as shown in Figure 6. This simplification consists of a bearing under the chord, two braces fixed by two rings and two clamps on the upper end of the braces. The clamps symbolise the welded joint to another chord. Some preliminary results of the simulations are covered in this section.

Figure 8: The maximum principle stress of the sample welded at 270 A (right) and 320 A (left) is due to the larger gap between braces.

Figure 6: A simplified 3D computer model of a tubular K-joint.

Themain points of interest in the evaluation are distortion and residual stresses. The residual stresses are comparedwith the results from the hole drilling method, but for detecting the distortion no measuring systemwas available. Due to the strong relationship between residual stresses and distortion, however, a comparison of the stresses gives information about the levels of distortion. Figure 7 shows an example of the variation of the gap be- tween the two braces. It is apparent that distortion becomes stronger with increasing distance between the two crown toes. Themain reason is the relationship between residual stresses and high heat input, because of the longer joint between the braces.

Figure 9: A principle stress minimum of the sample welded at 270 A (right) and 320 A (left) with different gaps.

Figure 10: The residual stress along a measuring line normal to the connecting line between the braces (welded at 270 A). To examine the calculated residual stresses, a measuring line with five measuring points at almost the same position as the hole drilling method (discussed in the next section) was inserted. The results are shown in Figure 10. Maximum principle stress ( σ 1 ) and principle stress minimum ( σ 2 ) are plotted against distance from the weld centre. Welding experiments A critical comparisonbetween calculatedandmeasuredvalues can be carried out after manufacturing real tubular K-joints with a robot welding system, as shown in Figure 11. A robot

Figure 7: The total distortion for different gaps between the braces.

The residual stresses are shown below. Figure 8 and Fig- ure 9 show the maximum principle stress and the principle stress minimum for two different welding procedures and a varying gap. Limiting both colour legends for a range of +500 MPa to -500 MPa in Figure 8, it is evident that the stress around the weld seams does not differ. Disregarding the area between the braces and only focusing on the crown toe, crown heels and saddler clearly shows that the different welding speeds and welding currents induce almost the same results. Similar to Figure 8, Figure 9 validates the finding that both welding procedures behave similarly.

welding system guaran- tees constant conditions for the whole test series. Figure 11: A tubular K-Joint after preparation for the hole drilling method.

17

March 2016

AFRICAN FUSION