Table 3.

Material parameters used in the screening experiment with two levels (low and high) and 14 factors (X_screen) and the Box–Behnken surface design with three levels (low, baseline and high) and 7 factors (X_BB)

Material parameter	Microstructure	Abbreviations	Factor levels			X screen	X BB
			Low (− 20%)	Baseline	High (+ 20%)
Young’s modulus (GPa)	Matrix	E mat	12	15	18	1	–
	Osteon	E ost	9.6	12	14.4	2	1
	Cement line	E cl	14.4	18	21.6	3	2
Poisson’s ratio	Matrix	ν mat	0.24	0.3	0.36	4	–
	Osteon	ν ost	0.24	0.3	0.36	5	–
	Cement line	ν cl	0.24	0.3	0.36	6	–
Critical damage initiation strain (MAXPE criterion)	Matrix	${\epsilon }_{\text{max},\text{mat}}^0$	0.0032	0.004	0.0048	7	–
	Osteon	${\epsilon }_{\text{max},\text{ost}}^0$	0.0032	0.004	0.0048	8	–
	Cement line	${\epsilon }_{\text{max},\text{cl}}^0$	0.0032	0.004	0.0048	9	3
Critical interface strain (QUADE criterion)	Cement line	${\epsilon }_{n,\text{cl}}^0$	0.00084L	0.00105L	0.00126L	10	4
			0.0012R	0.0015R	0.0018R
			0.0028T	0.0035T	0.0042T
	Cement line	${\epsilon }_{s,\text{cl}}^0$	0.00084L	0.00105L	0.00126L	11	4
			0.0012R	0.0015R	0.0018R
			0.0028T	0.0035T	0.0042T
Strain energy release rate (kJ/m2)	Matrix	G mat	0.16	0.2	0.24	12	5
	Osteon	G ost	0.16	0.2	0.24	13	6
	Cement line	G cl	0.16	0.2	0.24	14	7

Critical interface strains are specified for each osteon direction: ^Llongitudinal, ^Rradial, ^Ttransversal. Baseline values are based on values from the literature (Table 1) and introduced in a previous study (Gustafsson et al. 2018a)