2 60mm, thickness 60mm, the length of prefabricated crack 18mm, the loading span 240mm and so on. The square point indicates the data of specimen without seawater immersion, and the triangle is for the specimen in seawater 60d. The hollow dots is for the specimen (H60B40A18) of dimension high 60mm, thickness 40mm, prefabricated crack length 18mm, and it is a load-displacement curve of initial loading, unloading and reloading continuously. Obviously, unloading and reloading curves are basically coincident. But the slope of curve is larger compare to the curve slope from zero load, and the results shows the material having harden characteristics. The solid circular point indicates the load-displacement curve of specimen that the 'H60B40A18' were loaded into the plastic phase, and unloaded to zero, then it immersed in seawater for 30d, and reloading on the same equipment. However, the displacement had been added the original plastic residual displacement after unloading. It can be seen that the curve slope of plastic seawater loading is lower than the unloading curve. And the curve segment become shorter over linear loading part. It shows the material performance having deterioration. For two kinds of thickness of specimen, the thicker specimen is increased significantly for the bearing capacity and deformation resistance ability of it Load-Displacement of Steel on Three Point Bending Beam with crack 0 50 100 150 200 250 300 0 2 4 6 8 10 12 Displacement (mm) Load (KN) H60B60A18 SISW h60b60a18 Befor soakinsea H60B40A18 Soaked in-sea after plastic deformation 3. The influence of seawater immersion on specimen toughness For the specimen of three point bending beam with incision, its stress intensity factor near incision root can be expressed as follows[6] 3/ 2 2 2 1 2 1 1 2.15 3.93 2.7 1.99 1.5 ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ − ⎠ ⎞ ⎜ ⎝ ⎛ + ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⎟ − ⎠ ⎞ ⎜ ⎝ ⎛ − − = h a h a bh h a h a h a h a PS a KI （1） Fig 1. The curve of load-displacement for three point bending steel beam with crack
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