The application of fracture mechanics to engineering design has provided significant advances in understanding of the causes and mechanisms of failure and crackgrowth. Despite this, there are still some aspects that remain incompletely understood.such as the crack closure/crack shielding effect. The presence of crack closure/shield-ing acts to reduce Ak. The mechanisms of crack closure/shielding are complicated, andhave not been fully understood. This work focuses on the plasticity-induced crack tipshielding mechanism and presents a novel approach to characterising the elastic stressfields under the influence of the plastic enclave surrounding the crack tip. The model issuccessfully applied to determine the four stress parameters experimentally using full-field photoelastic stress analysis on polycarbonate CT specimens, following studiesof the effect of the (a priori unknown) crack tip position and the valid data collectionzone giving the best fit between the model predictions and the experimental data. Thepredicted values from the model demonstrate good data repeatability, and exhibit sensi-ble trends as a function of crack length and load ratio that are interpretable in terms ofphysically meaningful changes to the plastic enclave. In addition, the model is provento describe the stress feld around a crack more accurately than classic Wiiliams’ stresssolution. The model is also extended to AL 2024-T3 specimens using a full-feld dis-placement measurement technique, digital image correlation. Using the Sobel edgedetection method to identify the crack tip from the displacement feld with a rectangu-lar shaped data collection zone employed in the current study, reasonable trends wereagain demonstrated in the experimental results as a function of crack length.