Evaluating J-integral and Q parameter in high-density polyethylene using a combined experimental finite element method M SAHLABADI 1 , A VALIOLLAHI 2 , B KONH 3 and N SOLTANI 2 1 Department of Mechanical Engineering, College of Engineering, Temple University, Philadelphia, PA 19122, USA, 2 Intelligent Based Experimental Mechanics Center, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran, 3 Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, HI 96822, USA Received Date: 10 June 2016; Accepted Date: 20 October 2016; Published Online: ABSTRACT This work introduces a combined experimental finite element method (FEM) to calcu- late J-integral and Q parameter for centre-crack tension of high-density polyethylene specimens. In the majority of the studies to date, mostly a pure FEM has been used. However, the several simplified assumptions that are included in such models could result in imperfect predictions. This study aims to overcome this issue by suggesting a novel method that privileges from the displacement fields on specimens’ surface that is provided for our finite element model. The method introduced in this work has a merit in presenting Q results for a softening material. The results of our proposed method were in a satisfactory agreement with the pure FEM results of similar models, and thereby validating our approach. Using this model, the effects of parameters like crack length and thickness were also investigated. This method could be utilized in health monitoring of structures. Keywords centre-crack tension; DIC; finite element method; J–Q parameter; polyethylene. NOMENCLATURE A 2 = Amplitude of the asymptotic solution C = Correlation coefficient E = Young’s modulus G, and G′ = Grey-scale matrices of the subsets at (x, y) in reference image, and at (x′,y′) in deformed image J-integral = Path-independent integral along a curve around the crack tip K I = Stress intensity factor (mode-I) L e = Effective length Q = Measurement of the level of hydrostatic stress near the crack tip T i = Traction vector along the curve W = Strain energy density per unit volume ds = Incremental length along integral contours r, and θ = Polar coordinates u i = Components of displacement vectors y = Direction perpendicular to the crack Γ = Clockwise path around the crack tip α, and n = Romberg–Osgood constants δ ij = Kronecker delta ϑ = Poisson ratio σ 0 = Yield stress σ ij = Stress tensor (σ ij ) diff = Hydrostatic stress difference (σ ij ) FE = Stress field predicted by FE analysis Correspondence: M. Sahlabadi. E-mail: tug11932@temple.edu © 2016 Wiley Publishing Ltd. Fatigue Fract Engng Mater Struct 00 1–15 1 ORIGINAL CONTRIBUTION doi: 10.1111/ffe.12552