China 
Africa 
Explore chapters and articles related to this topic
Damage growth of laminated composite structures containing a hole
Published in Wojciech Pietraszkiewicz, Wojciech Witkowski, Shell Structures: Theory and Applications Volume 4, 2017
The stress intensity factor history is the primary information required for crack-growth calculations. In order to determine the stress intensity factors KI and KII and identify precisely the range of validity, Finite Element Analysis with NISA II Endure is performed. A fine meshing is used at the crack tip region, thus the convergence is checked. The number of elements and the outer dimensions Lx, Ly are chosen such that they do not affect the results. The continuum plane stress elements are applied. The stress intensity factors are calculated using the J-integral concept. The details of the numerical analysis are discussed in Ref. (Muc & Kędziora 2001, Kędziora et al. 2016)
Estimation of stress intensity factors of weld toe surface cracks in tubular K-joints
Published in M.A. Jaurrieta, A. Alonso, J.A. Chica, Tubular Structures X, 2017
S.T. Lie, S.P. Chiew, C.K. Lee, Y.B. Shao
To evaluate the stress intensity factors, several methods have been used by some researchers. In practice, the two commonly used methods are the J-integral and the displacement extrapolation. J-integral is a measure of the strain energy in the region of the crack tip. Shih and Asaro (1998) had proposed the relationship between the J-integral and the stress intensity factors as follow: () J=18πKT⋅B⋅K
Dynamic relaxation applied to continuum and discontinuum numerical models in geomechanics
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Peter Cundall, Christine Detournay
The representation of brittle material of given fracture toughness by the BPM can be used as a model for the fracture process in rock systems, provided that the particle size is chosen to satisfy Equation (56). For many rock types, this implies that the particle size should be of the order of 1 cm. Unfortunately, many rock systems encompass dimensions that are many orders of magnitude larger, and it would be computationally infeasible to model the entire system with small particles. Several strategies have been tried. One approach was the implementation of a J-integral-based criterion in the BPM. The J integral is a measure of energy release rate during a small fracture extension. It was originally formulated as a surface integral using classical continuum variables such as stress, displacement gradient and strain (Rice, 1968). For application to the BPM, the domain expression of the J integral was used, and the integral was reformulated in terms of variables of a discrete system. The J-integral-based criterion is non-local and requires time-consuming integration within a domain around a contact. The radius of the integration domain should be equal to at least a couple of particle diameters. Also, this criterion did not provide additional accuracy in resolution of fracture propagation mainly because of non-uniformity of forces (dispersion of local strain and stress) in contacts between particles in the BPM. The local, force-based criterion for fracture propagation is simpler and faster than non-local criteria such as one based on the J integral.
Fracture strength topology optimization of structural specific position using a bi-directional evolutionary structural optimization method
Published in Engineering Optimization, 2020
Jie Hu, Song Yao, Ning Gan, Yulin Xiong, Xing Chen
In this work, the XFEM is adopted to describe discontinuous fields such as cracks, voids and inclusions in the design domain by the enrichment shape function with discontinuous properties. The BESO method is used to carry out topology optimization by virtue of the algorithm’s discrete nature, resulting in a clear physical interpretation and naturally avoiding the definition of supplementing pseudo-relationships between fictitious materials and fracture toughness. The J integral is used to characterize the fracture strength as an indicator that assesses whether there is crack growth or not, and it is calculated by the interaction integral. The multi-objective design of the J integral criterion and the mean compliance C, which is used to guarantee the stiffness of the structure, is considered to prevent the crack propagation and enhance the fracture strength of the structure. A weighted average method is used to derive the Pareto front. The sensitivity of J and C is derived based on the adjoint method and the interaction integral.
Scaled boundary finite element method for calculating the J-integral based on LEFM
Published in Mechanics of Advanced Materials and Structures, 2023
The J-integral is known as one of the fundamental and vital concepts in fracture mechanics. Calculating the energy of a cracked domain, the SIF, and crack growth are some applications of the J-integral which can also be applied to some problems of nonlinear fracture mechanics. As an efficient numerical method, the SBFEM has been applied to fracture mechanics problems but it has not been used for calculation of J-integral directly yet. Therefore, this study proposed a formulation of the SBFEM for a direct calculation of J-integral in the LEFM. In summary, here the J-integral formulation based on the SBFEM was derived through defining a scaling center at the crack tip and defining the rectangular contour.
Investigation of the Inhomogeneous Mechanical and Crack Driving Force of Low Alloy Steel SA508 and Its Welded 309L/308L Stainless Steel Cladding
Published in Nuclear Science and Engineering, 2023
Shuai Wang, He Xue, Guiyi Wu, Zheng Wang, Kuan Zhao, Chenqiang Ni
The J integral, as the driving force of a crack, represents the potential or likelihood of crack growth.35,36Figure 8 shows the J-integral profile of cracks of different lengths, and the J values in the HAZ calculated by the continuous model are significantly higher than that in the sandwich model. Comparison between Figs. 7 and 8 shows similar changes in the crack driving force (i.e., Mises stress and J integral), which can be interpreted as the widely adopted sandwich model appearing to be on the nonconservative (unsafe) side compared with the continuous model, especially when the crack grows into the HAZ in the DMWJ.