The Effect Of Seawater Corrosion On Mechanical Properties Of Macro-meso Crack Resistance Of Carbon Steel

The corrosion damage fracture of carbon steel is one of the main forms ofstructural failure for the metal materials being widely used in maritime infrastructure.Fracture mechanics and damage mechanics are important analysis tools for defectivematerials and the structural failure problems. Fracture behaviors of notched specimensduring three-point bending test and uniaxial tensile test were investigated by fracturemechanics in this dissertation. Different influences that shapes and sizes of presetincision have on fracture parameters in the fracture process were analyzed. The fracturelaw or mechanical properties of Q235specimen was compared between specimens withand without seawater corrosion. The theoretical basis and experiment data wereprovided for selecting material and safe designing on marine infrastructure. The mainresearch contents are as following.1. The investigation information of steel corrosion and fracture mechanics andmicromechanics development were introduced in the paper. The tensile specimens ofQ235steel with notch of different sizes were observed by Scanning ElectronMicroscopy (SEM) to study the carbon steel specimens’ fracture behavior andmicro-fracture morphology before and after the seawater corrosion.2. The influence of marine immersion on steel Q235mechanical properties wasanalyzed, and the change law of macroscopic mechanical properties was obtained indifferent cases in this dissertation such as the variation of stress intensity factor withcracking near the pre-crack, the size effect of fracture parameters, change law of thestress concentration factor and other parameters with the variation of specimen load andcrack length.3. The estimate approach of specimen maximum bear capacity with notch ofdifferent sizes was explored by using fracture mechanics parameters. First, the bearingcapacity of notched specimens was calculated by plastic slip line field theory. Second,the carrying capacity of notched specimens was estimated by double-K fracture criteriaand crack resistance model, which then was compared with the experimental data.4. According to the electronic tracking test on the specimen of three-point bendingbeam, the unloading law and the elastic-plastic crack deformation of carbon specimenswere further investigated. The effect of marine corrosion on the bearing capacityor fracture toughness was analyzed based on the experimental data. 5. The stress-strain diagram under different loads was obtained by using theABAQUS finite element analysis software to simulate the specimen and thecorresponding results were discussed.