PSI - Issue 14

Sudheer Patri et al. / Procedia Structural Integrity 14 (2019) 688–695

693

6

Sudheer patri et. al./ Structural Integrity Procedia 00 (2018) 000–000

Fig. 5. SEM fracturographs and EDS spectrum at location 1 showing traces of oxide inclusion

Table 1. Chemical composition of screw material and its comparison with the standard Elements Cr Ni Mo V

Si

Fe

Screw material IS 1367 standard

19.62

7.11

0.19

0.18

0.63

72.27

0.30 max

0.30 max

0.20 max

0.10 max

Not specified

Balance

4.2. Loading events As mentioned earlier, the main loading on the screws during normal operation is only the screw preload. Three possible loading events that may induce tensile load on the joint were postulated and analysed in this section. The postulated scenarios are (i) packing errors, (ii) loading during transportation and (iii) operational malfunction. Assembly errors and accidental scenarios are ruled out as the mechanism performed as per design intent during shop floor testing and no other damage was observed in the mechanism, respectively. External load applied on any screw joint is distributed between the screws and the joint members according to the ratio of their stiffness (Richard G. Budynas et. al. (2008)). However, once the screw started elongating under the external load separating the joint members, the total external load is transmitted to screws. Such a condition is considered in this case and accordingly, the axial load carrying capacity of the present joint is calculated as follows: The ultimate tensile load for the given screw size and material is 17300 N (IS: 1367 (Part-3)-1979) since the screws were as per standard IS 1367-3 with property class 12.9. In the previous section, it was found that the strength of the screws is 40 % lesser than the specified value. Thus, the strength of the joint = 0.6*6*17300 = 62280 N