Patent Document ID: 20080010031
Application ID: 11667229
Patent Status: 0

Claim One:
1. A method of evaluating the fracture toughness of a material using a continuous indentation technique for continuously measuring an indentation load and an indentation depth while repeatedly applying the load to and removing the load from the material, the method comprising the steps of: measuring a stress coefficient, a strain hardening modulus and a yield stress using the continuous indentation technique and calculating a reduced elastic modulus (E r ) of the material; calculating an effective elastic modulus (E eff ) from the reduced elastic modulus; determining an initial elastic modulus (E 0 ) from an elastic modulus in a first range of the effective elastic modulus, which was determined using a plurality of unloading curves obtained using the continuous indentation technique; setting a void volume fraction (f) to a specific value within a range from 0.13 to 0.17 when a fracture type of the material is a I-type fracture type, and setting the void volume fraction (f) to a specific value within a range from 0.23 to 0.27 when the fracture type of the material is a II-type fracture type; calculating a damage parameter (D) from the void volume fraction using an equation D = π ( 4 3 ⁢ π ) 2 3 ⁢ f 2 3 ; calculating a critical elastic modulus (E*) using the damage parameter; calculating a characteristic fracture initiation point (h*) of the indentation depth using the critical elastic modulus; and calculating the fracture toughness (K JC ) of the material using the characteristic fracture initiation point of the indentation depth using an equation K JC = 2 ⁢ ⁢ E 0 ⁢ ω f = E 0 ⁢ lim h -> h * ⁢ ∫ 0 h ⁢ F A C ⁢ ⅆ h = E 0 π ⁢ k ′ ⁢ ln ⁡ ( 2 ⁢ ⁢ R 2 ⁢ R - h * ) , wherein k′ represents a slope (L max /h max ) between a maximum indentation load and a maximum indentation depth in an unloading curve.