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Indentation induced failure - poster

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Indentation induced failure - poster

  1. 1. Indentation-Induced Failure of Hard Coatings Adnan Abdul-Baqi & Erik van der Giessen Koiter Institute Delft FIntroduction ) max O R r (τIndentation-induced failure of hard coatings is modelled by means of h a Film (elastic) t max normal σcohesive surfaces. Interfacial delamination (normal & shear) and Interfacecoating cracking are the failure events being under consideration. z shear Symmetry axisFor the cohesive surface, the constitutive behaviour is given in terms Substrate (elastic-plastic) ∆ (∆ ) n tof a traction versus separation law, where we have adopted the uni-versal binding law used by Xu and Needleman [1]. It is characterizedmainly by the peak traction and the separation energy (Fig. 2).Results Figure 1. Geometry. Figure 2. Cohesive zone tractions. The energy for normal or shear separation is the area under the corresponding curve. Interfacial delamination: 0 σe/σy 0 1 σzz/σmax 1.40 1.00 1.20 shear delamination 0.75 0.8 normal delamination 1.00 0.50 50 0.80 20 0.25 0.60 0.6 F/Fmax 0.00 z (µm) z (µm) 0.40 -0.25 0.20 -0.50 0.4 100 40 0.2 (b) 0 150 (a) 60 0 0.5 1 1.5 2 0 50 100 150 0 20 40 60 h/t r (µm) r (µm) Figure 3. (a) Shear delamination . t = 5 µm, τ max = 1.2 GPa . Arrows show the shear direction, line Figure 4. Load versus displacement (F-h) curves for shows the location of the delaminated area. (b) Normal delamination. t = 2.5 µm, σ max = 1.5 GPa . Fig. 3. Coating cracking: 0 0 σrr/σmax σrr/σmax 1 e 2.00 2.00 1.56 1.56 d 5 0.8 1.11 5 1.11 0.67 0.67 0.22 0.22 0.6 F/Fmax z (µm) z (µm) 10 -0.22 10 -0.22 b c -0.67 -0.67 0.4 -1.11 -1.11 a 15 -1.56 15 -1.56 -2.00 -2.00 0.2 20 (a) 20 (b) 0 0 5 10 15 20 0 5 10 15 20 0 0.5 1 1.5 r (µm) r (µm) h/t Figure 5. Coating cracking. t = 2 µm, σ max = 11 GPa . (a) First crack at r 1 = 7.0 µm . (b) Second Figure 6. Load versus displacement curve for Fig. 5. crack at r 2 = 9.4 µm . Labelled points correspond to specific failure types. a and b on the curve correspond to mode I cracks at loca- tions r 1 and r 2 , respectively. At c the first crack growsConclusions until the interface and at d it shears of f. Point e corre- sponds to some limited interfacial delamination in the1. Shear delamination may occur in the loading stage. It is imprinted on the load vs displacement curve by a kink. vicinity of the coating cracks.2. Normal delamination may occur during the unloading stage, where a circular part of the coating is lifted offfrom the substrate. It is imprinted on the load vs displacement curve by a hump.3. Coating cracking may occur during the loading stage. The first circumferential crack occurs outside the con-tact area. The crack is imprinted on the F-h curve as a kink.4. On further loading, subsequent cracking occurs with crack spacing of about 1.25 times the coating thickness. [1] X.-P. Xu, A. Needleman, Model. Simul. Mater. Sci. Eng. 1 (1993) 111.

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