In this investigation the nature of the plastic zone ahead of a crack-tip in centrecracked tension, double-edge-notched tension, single-edge-notched tension, compact tension, extended compact tension, and single-edge-notched bend specimens have been assessed by elastic-plastic finite element analyses at different applied load levels (J integral). The magnitudes of the plastic zone size (PZS) in the investigated specimens have been compared using a new reference standard J/as y where a is crack length and s y is yield stress of the material. The results demonstrate that the PZS is almost invariant with respect to specimen geometry up to a critical value of J/as y at a specific a/W ratio. However, beyond this critical value, the magnitudes of the PZS are found to depend on the specimen geometry, which has been attributed to the varying in-plane constraints at the crack tip in various specimens.

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The paper describes test specimen thickness effect on stress intensity factor (KI), and T-stresses stresses (T11 and T33) for a Compact Tension specimen. Formulations to estimate 3D KI, T11 and T33 stresses are proposed based on extensive 3D Finite element analyses. These formulations help to estimate magnitudes of 3D KI and T11 and T33 which are helpful to quantify in-plane and out-of- plane constraint effect of the crack tip. The proposed formulations are validated with the similar results available in literature and found to be within acceptable error.

Mode-I fracture behavior of glass-carbon fiber reinforced hybrid polymer composite was investigated based on experimental and finite element analysis. The compact tension (CT) specimen was employed to conduct mode-I fracture test using special loading fixtures as per ASTM standards. Fracture toughness was determined experimentally for along and across the fiber orientation of the specimen. Results indicated that the cracked specimens are tougher along the fiber orientations as compared with across the fiber orientations. A similar fracture test was simulated using finite element analysis software ANSYS. Critical stress intensity factor (K) was calculated at fracture/failure using displacement extrapolation method, for both along and across the fiber orientations. The fractured surfaces of the glasscarbon epoxy composite under mode-I loading condition was examined by electron microscope.

In this investigation the extent of the plastic zone size ahead of a crack-tip in single edge notched tension (SENT), compact tension (CT) specimens has been examined experimentally by micro-hardness technique and by elastic-plastic finite element analyses at different applied load levels. The magnitudes of the plastic zone size (PZS), r p ahead of crack-tip in the investigated specimens have been compared using normalized J-integral (J/aσ y , where, a-crack length and σ y-yield stress of the material). The results show the dependence of PZS on specimen geometry due to varied in-plane crack-tip constraint. The results also demonstrate that the existing analytical models do not explain the experimental results of PZS satisfactorily.