FRACTURE SIMULATION IN POLYMER NANOCOMPOSITES USING MOLECULAR DYNAMICS

2021 ◽  
Author(s):  
SAMIT ROY ◽  
TANVIR SOHAIL
Keyword(s):  
Molecular Dynamics ◽  
Size Effect ◽  
Epoxy Polymer ◽  
Crack Tip ◽  
Far Field ◽  
J Integral ◽  
Critical Crack Length ◽  
Fracture Simulation ◽  
Platelet Size ◽  
Polymer Block

The objective of this paper is to (a) investigate the validity of application of continuum-based linear elastic fracture mechanics (LEFM) methodology, which is often employed by researchers to model fracture processes at the “discrete” atomic scale, and (b) to study the effect of nanographene platelet size on the rupture strength of an edge-cracked polymer block. The material selected for this study is EPON 862 epoxy polymer with 85% cross-link density. Further, an atomistic J-integral is implemented as a nano-scale fracture metric to investigate flaw-tolerance at the nanoscale reported by many researchers, and to develop a methodology to predict the initiation fracture toughness of the material. For this purpose, a bond-order based potential (ReaxFF) available in LAMMPS , a molecular dynamics (MD) software, is utilized. Predictions obtained using the atomistic J-integral are compared with LEFM predictions for the case of a cross-linked epoxy polymer block with a center-crack under uniform far-field loading. Significant deviations from LEFM for crack-lengths below a certain critical crack-length threshold are observed. Further, far-field stress vs. strain plots are obtained for an edge-cracked epoxy polymer block with a single 14 nm graphene nanoplatelet embedded ahead of the crack tip and it is compared with stress vs. strain plot obtained for the same epoxy block with two 7 nm graphene nanoplatelets embedded ahead of the crack tip to study platelet size effect. Significant size effect was observed as shown in the results.

Fracture Energy Evaluation Using J-Integral in Orthogonal Microcutting

2015 ◽  
Vol 4 (1) ◽  
Author(s):  
Dattatraya Parle ◽  
Ramesh K. Singh ◽  
Suhas S. Joshi
Keyword(s):  
Size Effect ◽  
Fracture Energy ◽  
Cutting Speed ◽  
Chip Thickness ◽  
Crack Tip ◽  
Nonlinear Behavior ◽  
Rake Angle ◽  
J Integral ◽  
Explicit Integration ◽  
Energy Evaluation

Fracture in cutting of ductile as well as brittle materials can be characterized using parameters such as K, G, R, and J-integral; of these, R has been widely used. To accurately evaluate the contribution of fracture energy in total cutting energy, J-integral would provide a more comprehensive basis as it encompasses several fracture modes, material plasticity, and nonlinear behavior. Therefore, this work adopts J-integral to evaluate the contribution of fracture energy to the size effect during microcutting of AISI 1215 steel. The work uses explicit integration method within ansys/ls-dyna to simulate two-dimensional (2D) orthogonal microcutting. U- and V-shaped cutting edges were used to represent a sharp crack-tip and a blunt crack-tip, respectively. Considering several alternative contours around crack-tip, covering the plastic zone, J-integral was calculated. Upon benchmarking J-integral values with other simulations in the literature, the approach was adopted for microcutting simulations in this work. It is observed that J-integral increases with uncut chip thickness, whereas it decreases with cutting speed, rake angle, and tool edge radius. The term (J/t0) defines contribution of fracture to the size effect in terms of J-integral, which is in the range of 4–24% under various parametric conditions. The corresponding values of R were always found to lie above those of the J-integral indicating that J-integral is relatively more appropriate parameter to quantify the fracture energy during microcutting.

On the Path-Dependence of the J-Integral Near a Stationary Crack in an Elastic-Plastic Material

2010 ◽  
Vol 78 (1) ◽  
Author(s):  
Dorinamaria Carka ◽  
Chad M. Landis
Keyword(s):  
Finite Element ◽  
Plastic Zone ◽  
Boundary Conditions ◽  
Path Dependence ◽  
Crack Tip ◽  
Mode I ◽  
Far Field ◽  
J Integral ◽  
Mode I Loading ◽  
Poisson's Ratios

The path-dependence of the J-integral is investigated numerically via the finite-element method, for a range of loadings, Poisson’s ratios, and hardening exponents within the context of J2-flow plasticity. Small-scale yielding assumptions are employed using Dirichlet-to-Neumann map boundary conditions on a circular boundary that encloses the plastic zone. This construct allows for a dense finite-element mesh within the plastic zone and accurate far-field boundary conditions. Details of the crack tip field that have been computed previously by others, including the existence of an elastic sector in mode I loading, are confirmed. The somewhat unexpected result is that J for a contour approaching zero radius around the crack tip is approximately 18% lower than the far-field value for mode I loading for Poisson’s ratios characteristic of metals. In contrast, practically no path-dependence is found for mode II. The applications of T- or S-stress, whether applied proportionally with the K-field or prior to K, have only a modest effect on the path-dependence.

scholarly journals Fracture Mechanical Analysis of Thin-Walled Cylindrical Shells with Cracks

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 592
Author(s):  
Feng Yue ◽  
Ziyan Wu
Keyword(s):  
Fracture Mechanics ◽  
Tensile Stress ◽  
Failure Modes ◽  
Cylindrical Shells ◽  
Crack Tip ◽  
Mechanical Analysis ◽  
J Integral ◽  
Thin Walled Structures ◽  
Circumferential Tensile Stress ◽  
Thin Walled

The fracture mechanical behaviour of thin-walled structures with cracks is highly significant for structural strength design, safety and reliability analysis, and defect evaluation. In this study, the effects of various factors on the fracture parameters, crack initiation angles and plastic zones of thin-walled cylindrical shells with cracks are investigated. First, based on the J-integral and displacement extrapolation methods, the stress intensity factors of thin-walled cylindrical shells with circumferential cracks and compound cracks are studied using linear elastic fracture mechanics, respectively. Second, based on the theory of maximum circumferential tensile stress of compound cracks, the number of singular elements at a crack tip is varied to determine the node of the element corresponding to the maximum circumferential tensile stress, and the initiation angle for a compound crack is predicted. Third, based on the J-integral theory, the size of the plastic zone and J-integral of a thin-walled cylindrical shell with a circumferential crack are analysed, using elastic-plastic fracture mechanics. The results show that the stress in front of a crack tip does not increase after reaching the yield strength and enters the stage of plastic development, and the predicted initiation angle of an oblique crack mainly depends on its original inclination angle. The conclusions have theoretical and engineering significance for the selection of the fracture criteria and determination of the failure modes of thin-walled structures with cracks.

Fracture Toughness of PVC/NBR Blends Evaluated by the J-Integral

1993 ◽  
Vol 66 (4) ◽  
pp. 634-645
Author(s):  
N. Nakajima ◽  
J. L. Liu
Keyword(s):  
Fracture Toughness ◽  
Energy Dissipation ◽  
Crack Initiation ◽  
Crack Tip ◽  
J Integral ◽  
Integral Methods ◽  
Locus Method ◽  
Two Phases ◽  
Fracture Processes

Abstract The effect of gel on the fracture toughness of four PVC/NBR (50/50) blends was characterized by two different J- integral methods. Three of these blends are compatible blends with 33% acrylonitrile in NBRs, and the fourth with 21% acrylonitrile content, is an incompatible blend. Two types of gel are involved in this study microgels and macrogels. The J-integral methods are (1) conventional method proposed by Bagley and Landes and (2) crack initiation locus method proposed by Kim and Joe. The same load-displacement curves are used in both methods. However, the latter eliminates the energy dissipation away from the crack tip in the determination of Jc, while the former does not. Both methods produced almost the same results indicating that the energy dissipation away from the crack tip is negligible in these samples. The fracture toughness of a macrogel-containing blend is much greater than that of a microgel-containing blend, which, in turn, is only slightly greater than that of a gel-free blend. This implies that the two gel-containing blends have different fracture processes. The incompatible blend has the lowest fracture toughness due to weak interaction at the boundaries of the two phases.

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