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XFEM simulation of radial-median crack formation in brittle medium underneath sharp indenters
Felix Rickhey,Minsoo Kim(김민수),Hyungyil Lee(이형일) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
The evolution of radial-median cracks occurring in sharp indentation of brittle materials is simulated using the extended finite element method (XFEM). Issues associated with XFEM are discussed for the particular problem. For the evaluation of fracture toughness, hardness is considered as dependent of indenter angle and Poisson’s ratio. Parameter studies are then carried out to assess the influence of indentation test, indenter and material parameters on fracture toughness. The results can be used to improve fracture toughness evaluation by indentation.
Indentation cracking of monocrystalline silicon considering fracture anisotropy
Rickhey, Felix,Marimuthu, Karuppasamy Pandian,Lee, Kwangmin,Lee, Hyungyil Elsevier 2019 Theoretical and applied fracture mechanics Vol.100 No.-
<P><B>Abstract</B></P> <P>Despite its inherent anisotropy, in indentation cracking monocrystalline silicon has often been treated as an isotropic material. An attempt at accounting for its anisotropy is made here. We propose a (simplified) material model that allows the simulation of anisotropic cracking in Vickers indentation of monocrystalline silicon. Anisotropy is confined to the elastic domain; the complex plastic deformation is considered through an effective yield strength, which irreversible deformations are merged into. Numerically obtained hardness values agree well with literature values. The well-known Lawn-Evans-Marshall equation is modified to account for the anisotropy of cubic materials. The variation of the crack size for diverse orientations on Si(0 0 1), Si(1 1 0) and Si(1 1 1) is analyzed. Numerical results are found to be in a generally good agreement with the experimental results by Ebrahimi and Kalwani (Mater Sci Eng A 1999;268:116–26), which shows that the simplifications regarding the material model are appropriate. The model can be applied also to other cubic materials such as germanium.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A simplified material model that allows investigation of fracture anisotropy is proposed. </LI> <LI> Lawn-Evans-Marshall equation is modified to account for the anisotropy of cubic materials. </LI> <LI> Material anisotropy must be considered when determining the residual field intensity. </LI> <LI> Numerically obtained crack lengths agree well with experimental data. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
An efficient way of extracting creep properties from short-time spherical indentation tests
Rickhey, Felix,Lee, Jin Haeng,Lee, Hyungyil Cambridge University Press (Materials Research Soc 2015 Journal of materials research Vol.30 No.22
<▼1><B>Abstract</B><P/></▼1><▼2><P>Indentation as a means to extract creep properties has the advantage that it can be applied directly to micro/nano-structures. Many studies on indentation creep reported at least partially poor agreement with creep parameters derived from uniaxial test. One important reason for the incompatibility is the neglect of transient creep. Another one is the choice of equivalent stress and strain measures to relate the different material responses. Applying a material model that accounts for transient creep effects we propose an efficient method for deriving creep properties from short-time spherical indentation tests. We first determine a subsurface point where the material response is very close to that observed in uniaxial tests. We then map the load-displacement data to the material response, expressed in terms of two dimensionless variables, at this point. Converting the dimensionless variables data to stress, strain, and strain rate data, we finally determine the material's creep coefficient and exponent.</P></▼2>
Numerical approach to the evaluation of forming limit curves for zircaloy-4 sheet
Kim, Minsoo,Rickhey, Felix,Lee, Hyungyil,Kim, Naksoo Published for the Materials Research Society by th 2015 Journal of materials research Vol.30 No.21
<P> The forming limit strains (FLSs) of zircaloy-4 sheets are studied. After having obtained the true stress-strain curve of zircaloy-4 using the weighted-average method, limit dome height (LDH) tests are performed to establish experimental FLSs. We summarize related theoretical forming limit curves (FLC) and discuss their limitations. Two finite element (FE) models are established for determining FLSs; an LDH test FE model for the negative minor strain sector, and a biaxial tensile FE model for the positive minor strain sector. The numerical FLSs are found to agree well with experimental data. Since the numerical FLC gives the strain at the onset of local thinning (whereas the experimental FLC provides the strain between local necking and ductile fracture), resulting FE FLS values are slightly lower than the experimental ones so that results can be regarded as conservative. Our FE approach substitutes the expensive and time-demanding experimental LDH tests. </P>
최영식(Youngsick Choi),Rickhey Felix,이진행(Jin Haeng Lee),이형일(Hyungyil Lee) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
In this paper, we extend the method of Lee et al. (2010) and evaluate material properties of high hardness materials with spherical indentation. Using regression equations considering 4 indentation variables, the load-displacement relation is converted into a stress-strain relation. To calculate properties of high hardness materials, we then write a program which converts loading / unloading data from the indentation test to the corresponding true stress-strain data. The error in material properties computed by the program lies within 0.3, 0.8 and 6.4 % for Youngs modulus, yield strength and hardening coefficient, respectively.
Spherical indentation for brittle fracture toughness evaluation by considering kinked-cone-crack
Marimuthu, Karuppasamy Pandian,Rickhey, Felix,Lee, Jin Haeng,Lee, Hyungyil Elsevier 2017 Journal of the European Ceramic Society Vol.37 No.1
<P><B>Abstract</B></P> <P>This work aims at evaluating the fracture toughness of brittle materials by spherical indentation. The cone-cracking is simulated by the extended finite element method (XFEM) in Abaqus. The formation of a kinked-cone-crack is observed when the indenter comes into (second) contact with the surface part outside the ring-crack. The effects of friction, Poisson’s ratio and cone-crack kinking on the Roesler’s constant <I>κ<SUB>c</SUB> </I> are analyzed. Based on numerical results, the Roesler’s method for evaluating the fracture toughness is enhanced by considering kinked-cone-crack. By performing systematic XFE analyses, a database for enhanced Roesler’s constant <I>κ<SUB>c</SUB> </I> | <SUB>kink</SUB> is provided for the fracture toughness evaluation of brittle materials. Finally, the proposed method is verified by conducting spherical indentation tests on soda-lime glass specimens.</P>