Al~traet--Fracture Mechanics of Ductile Metals (FMDM) theory is used to obtain the plane strain fracture toughness, K~, for different materials. The traditional approach for obtaining the K~ value is to conduct several standard tests on cracked plates that are costly and time consuming. The fracture toughness value provided by the FMDM theory depends on the stress-strain curve for the material in question, and this is readily available in MIL-HDBK-5 and other reliable sources. The results of the plane strain fracture toughness (Kt0 values provided by the FMDM theory were compared with the experimental data and it was concluded that the two are in excellent agreement. It is proposed that, in the interest of economy and convenience, K~c testing could be replaced by the FMDM theory. NOMENCLATURE a: depth of semi-elliptic part-through crack (in.) c: half critical crack length (in.) E: Young's modulus in tension (ksi) h: effective height of slip band (0.00056 in.) hF: effective height of strained region at crack tip (in.) h~: effective height of strained region near crack tip (in.) k: thickness parameter K: stress intensity factor Kc: plane stress fracture toughness K~: plane strain fracture toughness n: exponent in Ramberg-Osgood relation for ErP P: plastic energy absorption rate per unit thickness (kips/in.) T: energy consumed in creating unit area of new crack surface (kips/in.) t: plate thickness (in.) Ur: energy consumed per unit thickness in plastic straining at crack tip (kips) Up: energy consumed per unit thickness in plastic straining (kips) Uu: energy consumed per unit thickness in plastic straining near crack tip (kips) W: width of test specimen (in.) WE: density of plastic energy under stress-strain curve from the strain at which necking begins, to the strain at trF (ksi) Wo: density of plastic energy under stress-strain curve from the strain at ~r, to the strain at which necking begins (ksi) 0: angular coordinate in stress field 2: crack shape factor #: thickness parameter; also 10 6 m (0.0000394in.) v: Poisson's ratio fl: thickness parameter tr: gross area stress perpendicular to plane of crack, uniaxial tensile stress (ksi) trr: uniaxial true tensile stress (ksi) O'TL: uniaxial true elastic limit tensile stress (ksi) trrr: true tensile stress in stress field in the direction of the radius r (ksi) aru: uniaxial true ultimate tensile stress (ksi) O'TV: uniaxial true yield tensile stress (ksi) at:: true tensile stress in stress field in z-direction (ksi) aro: true tensile stress in stress field in the direction perpendicular to the radius r (ksi) trrr0: true shear stress in stress field in r 0-plane (ksi) au: uniaxial ultimate tensile stress (ksi) 6u~-: average uniaxial tensile stress from 0.998 tru to trr, ksi av: uniaxial yield tensile stress (ksi) Eps: corrected neck uniaxial plastic tensile strain (corrected for gage length) Er: uniaxial true tensile strain ErL: uniaxial true tensile strain at a = trL Eru: uniaxial true tensile strain at start of necking.