Research On Quantification Evaluation Method For Damage Of Steel Structure Building Based On Metal Magnetic Memory Testing

The domestic and foreign ordinary damage detection methods based onferromagnetic materials are summarized in the thesis，how to use the Metal magneticmemory testing technology(MMMT) to evaluate the damage are analyzed．Thegeomagnetic effect， magnetostriction and the magneto-mechanical effect onferromagnetism members were analyzed based on the theory of ferromagnetism．Thereason why the MMMT can find the hidden damage and stress concentration zone wasexplained．The investigation shows that the MMMT is the only effective method whichcan give the early diagnostic of the ferromagnetism members．This dissertation concentrates on the key problem that the quantitative evaluationof the crack of steel structure, The relation of stress concentration and MMMT signalbased on theoretical analysis and experiments is researched and the MMMT signalfeature of crack is extracted at the same time．The main achievements of thisdissertation are as follows:The most widely used in industrial and civil construction of Q345B steel smoothspecimens and artificial prefabricated crack specimen under static load tensile wasmeasured by high accuracy WT10B type handheld digital Stella meter. By conductingstatic load tensile test, the relationship between magnetic memory signal and workingstress and their regular were analyzed.The material hidden damage evaluation parameters of metal magnetic memorywere established. The theory of professor Doubov that using the passing zero position of normalcomponent of leakage magnetic field to determine the stress concentration positionalso applies to steel structure building.We can quantitative evaluate the stress concentration that caused by cracking ofthe steel material speciments by gradient of magnetic. Using gradient method todetermine the stress concentration and hidden damage location is more accurate andeffective.In terms of quantitative evaluation, establish the quantitative evaluation method ofspecimen damage status in different deformation phases.The average intensity of magnetic field gradient method is adopted forquantitative evaluation of steel structure building crack specimen damage status. thevalue of m can be used to judge danger level of early damage of steel structurebuilding.