Estimation of C* Integral for Mismatched Welded Compact Tension Specimen

The C* integral for the compact tension (CT) specimen is calculated using the estimation equation in ASTM E1457-15. This equation was developed based on the assumption of material homogeneity and is not applicable to a welded CT specimen. In this paper, a modified equation for estimating the C* integral for a welded compact tension (CT) specimen under creep conditions is proposed. The proposed equation is defined on the basis of systematically conducted extensive finite element (FE) analyses using the ABAQUS program. A crack in the welded CT specimen is located in the center of the heat-affected zone (HAZ), because the most severe type IV cracks are located in the HAZ. The results obtained by the analysis show that the equation for estimating the C* integral in ASTM E1457-15 can underestimate the value of the C* integral for creep-soft HAZ and overestimate for creep-hard HAZ. Therefore, the proposed modified equation is suitable for describing the creep crack growth (CCG) of welded specimens.

Lifetime Estimation Method of Polyethylene Pipe Based on the Full Notch Creep Test

The Creep Crack Growth (CCG) of polyethylene pipe directly limits its long-term lifetime. The long-term lifetime estimation of polyethylene pipe was proposed by combining the crack kinetics and Paris-Erdogan crack growth model. According the Full Notch Creep Test (FNCT) to measure the relationship between the crack opening displacement COD and the test time ti of the preformed PE ring notch specimens during creep tension, and the crack growth rate da/dt, stress intensity factor KI can be calculated, then the inherent parameters A, m of PE materials can be obtained through the Paris-Erdogan crack growth model. Finally, the relationship between the crack depth af and the crack growth time tCCG of polyethylene pipes in the long-term use process can be extrapolated. The test result shown that, when the specification of PE pipes were dn110-sdr11, if there was an initial crack with a depth of aini = 0.4mm on the outer wall of the pipe, and under the continuous action of pipe pressure with p = 0.4 MPa, when the depth crack of PE1 and PE2 pipes expanded to 0.8mm, it needed to maintain or replace the defective pipe section, and the lifetime of the pipes were 22.89 and 20.03 years. Respectively, if the pipes were not maintained and replaced in time, and it will exist medium leakage only takes 14.13 and 12.44 years.

A theoretical and computational investigation of mixed mode creep crack growth along an interface

In this paper, we propose a theoretical framework for studying mixed mode (I and II) creep crack growth under steady state creep conditions. In particular, we focus on the problem of creep crack growth along an interface, whose fracture properties are weaker than the bulk material, located either side of the interface. The theoretical framework of creep crack growth under mode I, previously proposed by the authors, is extended. The bulk behaviour is described by power-law creep, and damage zone models that account for mode mixity are proposed to model the fracture process ahead of a crack tip. The damage model is described by a traction-separation rate law that is defined in terms of an effective traction and separation which couple the different fracture modes. Different models are introduced, namely, a simple critical displacement model, empirical Kachanov type damage models and a micromechanical based model. Using the path independence of the C * -integral and dimensional analysis, analytical models are developed for mixed mode steady-state crack growth in a double cantilever beam specimen (DCB) subjected to combined bending moments and tangential forces. A computational framework is then implemented using the Finite Element method. The analytical models are calibrated against detailed Finite Element models and a scaling function (C k ) is determined in terms of a dimensionless quantity Φ 0 (which is the ratio of geometric and material length scales), mode mixity χ and the deformation and damage coupling parameters. We demonstrate that the form of the C k -function does not change with mode mixity; however, its value depends on the mode mixity, the deformation and damage coupling parameters and the detailed form of the damage zone. Finally, we demonstrate how parameters within the models can be obtained from creep deformation, creep rupture and crack growth experiments for mode I and II loading conditions.

A theoretical and computational investigation of mixed mode creep crack growth along an interface

In this paper, we propose a theoretical framework for studying mixed mode (I and II) creep crack growth under steady state creep conditions. In particular, we focus on the problem of creep crack growth along an interface, whose fracture properties are weaker than the bulk material, located either side of the interface. The theoretical framework of creep crack growth under mode I, previously proposed by the authors, is extended. The bulk behaviour is described by a power-law creep, and damage zone models that account for mode mixity are proposed to model the fracture process ahead of a crack tip. The damage model is described by a traction-separation rate law that is defined in terms of effective traction and separation rate which couple the different fracture modes. Different models are introduced, namely, a simple critical displacement model, empirical Kachanov type damage models and a micromechanical based model. Using the path independence of the $$C^{*}$$ C ∗ -integral and dimensional analysis, analytical models are developed for mixed mode steady-state crack growth in a double cantilever beam specimen (DCB) subjected to combined bending moments and tangential forces. A computational framework is then implemented using the Finite Element method. The analytical models are calibrated against detailed Finite Element models and a scaling function ($$C_{k}$$ C k ) is determined in terms of a dimensionless quantity $$\phi _{0}$$ ϕ 0 (which is the ratio of geometric and material length scales), mode mixity $$\chi $$ χ and the deformation and damage coupling parameters. We demonstrate that the form of the $$C_{k}$$ C k -function does not change with mode mixity; however, its value depends on the mode mixity, the deformation and damage coupling parameters and the detailed form of the damage zone. Finally, we demonstrate how parameters within the models can be obtained from creep deformation, creep rupture and crack growth experiments for mode I and II loading conditions.