Table 1.

Comparison of Fracture Toughness Measurements of Articular Cartilage

Method type	Modified single edge notch test	Single edge notch test	Trouser tear test	Micro-penetration test
Sample sources	Cartilage with bone from the patella of adult mongrel dogs* and cows**	Bovine patellae	Cartilage with bone from the patella of adult mongrel canines	Bovine articular cartilage from patellae
Geometry of samples	6 mm width, 0.2 mm thickness in a rectangular shape	7×25 mm in width×length, 1–4 mm thickness in a rectangular shape	3 mm width, 0.2 mm thickness in a rectangular shape	10×10×4 mm in a rectangular shape, including the articular cartilage (1–2 mm thick)
Model	From energy balance, a pseudoelastic model	The poroelastic fracture toughness model21	From energy balance, one-dimensional model	Modified standard protocols for Nanoindenter XP
Fracture toughness value	Toughness of canine cartilage range J=0.14–1.2 kN/m (Average 1070±870 Nm/m2)*; Average toughness of bovine cartilage 1030±1019 Nm/m2**	KpIc=1.83±0.8 MPa.mm½	Finding: T=J/1.7	Run #1: 1102±136 Nm/m2; Run #2: 825±133 Nm/m2
Crack opening mode	Mode I	Mode I	Mode III	Mode III
Advantages	Easily view the whole process and approximate the elastic modulus	The process is simple and fast. Easily view the whole process and approximate the elastic modulus	Straightforward calculation and fewer samples are needed	Significantly smaller standard deviations of toughness value are obtained.
Disadvantages	Complicated calculation and more samples are required.	Complicated calculation and sample preparation is difficult to some extent	Difficult to view the fracture process under a microscope. It simulates unrealistic failure mode.	The tip geometry affects the results.
References	*27; **28	21,11	27	39

K_pIc, Apparent fracture toughness; T, Apparent fracture toughness; J, J integral.