Table 1.

Examples of strength and toughness of a fibrillar interface in the flaw insensitive and flaw sensitive regimes for two types of materials.

	soft materials, e.g. PDMS		stiff materials, e.g. keratin
E (MPa)	1	2000
ν	0.5	0.5
γs (mJ m−2)	50	50
Wad (mJ m−2)	50	50
σ0 (MPa)	0.1	20
	flaw insensitive	flaw sensitive	flaw insensitive	flaw sensitive
a (μm)	10	100	1	10
χ	0.24	2.4	0.48	4.8
h=10a (μm)	100	1000	10	100
ηmin	2.67	0.58	0.08	0.017
ωmax	0.14	0.47	0.73	0.77
condition for fibrillar interface to be stronger at ω=ωmax	A>3.35 mm	A>0.65 mm	A>3 μm	A>19 μm
a common value of A=4 mm is used to calculate Fs and Wf below	a common value of A=20 μm is used to calculate Fs and Wf below
σs (MPa)	0.1	0.06	20	8.88
Fs (N) at ω=ωmax	0.72	1.39	0.02	0.01
Wf (J) at ω=ωmax	3.98×10−6	4.21×10−5	9.6×10−10	1.96×10−9