cranfield university mahadi abd murad an integrated structural ...

Hoop Stress (MPa)
95
93
91
89
87
85
83
81
79
77
75
0 1 2 3 4 5 6 7 8
Figure 3.30: Hoop Stress versus L/W Ratio (2 different materials)
From Figure 3.30, as the length of composite repair and ply thickness increase,
the hoop stress that is measured in the centre of the notch root of the steel pipe model
decreases until the minimum value is reached at 80.64 MPa (i.e. referring to carbon
epoxy with 18 plies). Most of the repaired pipes with variable plies have reached their
minimum stresses as the composite repair length is around 160 mm except for carbon
epoxy with four plies where, at this length, the maximum hoop stress occurs. However,
a further increase in length of the composite repair of each variable ply, gradually
increases the hoop stress. Hence, from the graph, the optimum length of repair for the
defect width of 40 mm is 160 mm.
L/W Ratio
Table 3.13 summarises the axial stress results against the ratio of repair length to
notch length. Likewise, the phenomenon of the hoop stress distribution, as shown in
Figure 3.30, occurs in the axial stress distribution but at a smaller magnitude, as referred
to in Figure 3.31. The minimum axial stress that has been recorded for 18 plies of
carbon epoxy composite at a length of 160 mm is 34.75 MPa.
110
4 Plies Glass/Epoxy
4 Plies Carbon/Epoxy
8 Plies Glass/Epoxy
8 Plies Carbon/Epoxy
12 Plies Glass/Epoxy
12 Plies Carbon/Epoxy
18 Plies Glass/Epoxy
18 Plies Carbon/Epoxy