Failure Analysis Of Nickel Coated Metal Sheet During Deep Drawing

Coated metal sheet is a kind of composite materials, which a metal layer withresistant to corrosion and wear, high strength, and other special functions is depositedon metal substrates. Due to these excellent properties, it plays a very important role inbuilding industry, mechanical equipment, aeronautics and astronautics, instrument andvehicle manufacturing industry. However, in the process of deep drawing of coatedmetal sheet, it contains many multi-nonlinearity problems, such as geometricalnonlinearity (large displacement and large deformation), material nonlinearity(elastic-plastic deformation) and nonlinear boundary (contact and friction), whichresults in many kinds of failure modes such as wrinkling, fracture and spalling of thecoating. Nonlinear problems cause the complexion of deformation principles duringdeep drawing of coated metal sheet, and the variety of the failure modes. So thetraditional onefold Forming Limit Diagram(FLD) method can’t study the failuremacroscopically and comprehensively. It is necessary to develop other methods tosolve the problem. In the thesis, the failure problems of the coated metal sheet in thedeep drawing process were studied by theoretical analysis, finite element modelingand experiments, respectively. And the achieved main contents and results are asfollows:(1) The dimensional analysis was introduced into failure analysis of coated metalsheet in the deep drawing. When the failure happened in the process of deep drawing,the frame relation between the maximum punch displacement and process parameters,geometry parameters, and material parameters was established according to the Пtheorem of the dimensional analysis. The relationship between the maximum punchload and the mechanical properties of the coated metal sheets was also analyzed bythe П theorem of the dimensional analysis. And the relationship was verified by thetheoretical analysis, which provide theoretical guidance for establishing the failuremechanism map.(2) The failure of coated metal sheet in the deep drawing was converted into theplastic instability of coated metal sheet under simple stress state. The fracturephenomenon in the corner radius of punch was considered as the plastic instabilityunder the uniaxial tension. The relationship between the critical fracturing stress andstrain point of coated metal sheet and those of the component’s was obtained based onthe basic theory of composite sheet. The wrinkle problems of the flange part during deep drawing coated metal sheet was also studied according to the basic theory ofcomposite sheet and energy, the rules when wrinkles start emerging were formed withand without consideration the blank holder force.(3) The finite element modeling of failure behavior of the coated metal sheet inthe deep drawing process was built based on the continuum damage mechanics modelin Chapter3. The definite conditions for the simulation of the deep drawing withfinite element modeling were ensured. According to the finite element, there are maintwo failure modes in the deep drawing of coated metal sheet, i.e. fracture andwrinkling. A method of establishing failure mechanism map was suggested based onthe dimensional analysis and finite element modeling. The nickel coated metal sheetbeen treated as the research object, the failure mechanism map was built based onboth the process parameters and the geometry parameters.(4) Deep drawing experiments was made on the nickel coated metal sheet withself-designed drawing tools and the universal drawing machine. Two kinds of failuremodes occurred in the deep drawing process. These were the wrinkle of the flangepart and the fracture at the punch fillet. The experimental results were consistent withthe results of the finite element modeling by comparing the punch load displacementcurve, the shape of drawn parts and the distribution of strain, which demonstrated theaccuracy of the finite element modeling, and verified the effectiveness of failuremechanism map in the deep drawing process of the coated metal sheet via combinedthe finite element modeling with dimensional analysis.In general, the failure problem during deep drawing the coated metal sheet wasanalyzed theoretically in the thesis. The detailed contents were as following: themaximum load in the deep drawing process and the maximum drawing depth beforefailure were discussed via dimensional analysis; theoretical derivation on the fractureand wrinkle problems were carried according to the composite sheet theory; thefailure modes were predicted via the finite element modeling, and demonstrated theaccuracy of the finite element modeling by deep drawing experiment; the failuremechanism map was built based on the process parameters and geometry parametersin the deep drawing process of the coated metal sheet.