Artificial Crack Formation Theories And Methods

From the viewpoint of material science and fracture mechanics, crack means disaster. Itleads to abrupt failure of components, which may result in enormous accidents. But to theview of developing the utilities of crack, its spreading can be used to stress blanking.When thecrack technique is raised and intercross with the machining technique, a new field is cut. Withthe development of application and various stresses blanking, new demands are puttedforward. Under the subsidy of academic step and characteristic study in Lanzhou Universityof Technology, this paper is a crack technology research which applied to stress blanking.Arm at realizing the rules and high efficient fracture of solid materials provide efficient andconvenient artificial crack manufacturing methods for the engineering application of stressblanking.Based on the existing achievements of the theory of plane V-shaped notches inhomogeneous material and the theory of a crack perpendicular to bi-material interface, as wellas the basic equations of the plane problems and stress functions provided by Williams, stresssingularity Eigen-equation for artificial crack in bi-material models is deduced. This equationcan be considered as a generalization to that artificial crack in bi-material. The stress intensityfactor at the crack tip solving calculation methods is introduced. A new definition for thestress intensity factor of bi-material artificial crack is provided, and then is extended to theproblem of single material and bi-material crack. Taking single edge crack in finite plateloaded by uniaxial uniform tension and three-point bending specimen as objects investigated,the crack tip element size and the element discrete angle is studied in detail, and thenavailability of stress extrapolation method applied in bi-material models is verified. Under thesame boundary condition, a comparative analysis of the stress intensity factor in singlematerial and bi-material is done, the results verify feasibility of stress blanking by usingbi-material artificial crack．The influences of crack depth and crack angle and material’sPoisson ratio on singular stress fields near the bi-material artificial crack tip are analyzedsystematically, some useful conclusions are acquired. Ensure that under the premise ofstrength and toughness, the match materials of artificial crack should try to select big poissonratio ν1/ν2as soon as possible. And crack angle2α should be less than30°, or formation linearartificial crack, in order to enhance tip-crack stress field strength. The artificial crack used inthe process of stress blanking, in mechanical equipment allows conditions, crack tip fieldsintensity can be greatly enhanced by selecting a large artificial crack depth. Thus more efficient for stress blanking, this is a unique advantage of artificial crack for the blankingmaterial.