Simulation of anisotropic crack tip deformation processes and particle interactions in toughened polymers

2019 ◽  
Vol 28 (1) ◽  
pp. 3-13
Author(s):  
Garrett Nygren ◽  
Ryan L Karkkainen
Keyword(s):  
Polymer Chain ◽  
Process Zone ◽  
Crack Tip ◽  
Local Stress ◽  
Material Design ◽  
Initial Study ◽  
Yield Zone ◽  
Particle Spacing ◽  
Deformation Processes ◽  
Local Yielding

This study develops a finite element-based simulation of submicrometer crack tip deformation processes in polymers to investigate local toughening effects. An initial study of how these processes interact with stiff inclusions is presented to enable further investigation of particulate toughening. Crack tip and process zone mechanisms, including polymer chain disentanglement, directional chain realignment with consequent anisotropy, and crack propagation, are considered in a dedicated user-defined material law. Such processes are generally homogenized on higher scale continuum levels analyses, but direct simulation can provide insight into toughening mechanisms that have been widely observed but not fully explained. The user material law herein was employed in a parametric study to investigate the relative importance of (1) the extent of local inelastic polymer chain realignment and (2) consequent anisotropic hardening of the realigned polymer chains. In order to explore the interaction of fracture processes with nanometer-scale inclusions, silica particles with varied spacing were also included in the simulations. The interaction between local stress concentration and energy dissipation mechanisms has been quantified. It is shown that in neat polymers, local yielding is the dominant toughening effect accounting for over 90% of the local energy absorption, whereas local stiffening alone would decrease toughness. Stiff inclusions were shown to generally decrease toughness, except in cases where local yielding greatly outweighs local stiffening effects. Roughly 45% increase in toughness was shown for a 250-nm particle spacing that balances the acceleration of elastic failure with the formation of a larger local yield zone size. This demonstrates the utility of employing dedicated material laws to microstructural scale analyses in providing design targets in material design.

scholarly journals The effect of a crack-tip radius on the validity of the singular solution

2004 ◽  
Vol 218 (7) ◽  
pp. 693-701 ◽  
Author(s):  
D Dini ◽  
D A Hills
Keyword(s):  
Singular Solution ◽  
Edge Crack ◽  
Process Zone ◽  
Crack Tip ◽  
Local Stress ◽  
Scaling Factor ◽  
Root Radius ◽  
Finite Crack ◽  
Tip Radius ◽  
Local Stress Field

The influence of the finite crack-root radius on the local stress field at the root of a crack is found explicitly. This is then applied as an inner asymptotic solution, embedded with the conventional crack-tip singular solution, to quantify the possible influence of local rounding on the ability of the singular solution to capture the characteristics of the crack-tip process zone. The scaling factor employed is the conventional crack-tip stress intensity, and the example of a simple edge crack in a tension field is used to illustrate the method.

Investigation of Constraint Effects on Fracture Toughness for CC(T) Specimens

2004 ◽  
Author(s):  
Dieter Siegele ◽  
Igor Varfolomeyev ◽  
Kim Wallin ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Crack Tip ◽  
Temperature Shift ◽  
Local Stress ◽  
Significant Loss ◽  
Reference Temperature ◽  
T Stress ◽  
Local Stress State ◽  
Constraint Effects ◽  
Crack Tip Constraint

Within the framework of the European research project VOCALIST, centre cracked tension, CC(T), specimens made of an RPV steel were tested and analysed to quantify the influence of local stress state on fracture toughness. The CC(T) specimens demonstrate a significant loss of crack tip constraint resulting in a considerable increase in fracture toughness as compared to standard fracture mechanics specimens. So, the master curve reference temperature, To, determined on the basis of CC(T) tests performed in this study is about 43°C lower than To obtained on standard C(T) specimens. Finite element analyses of the tests revealed that the above experimental finding is in a good agreement with the empirical correlations between the reference temperature shift and the crack tip constraint as characterised by the T-stress or Q parameter (Wallin, 2001; Wallin, 2004). The results of this work are consistent with a number of other tests performed within the VOCALIST project and contribute to the validation of engineering methods for the crack assessment in components taking account of constraint.

Combination of Wedge Splitting and Bending Fracture Test-Crack Tip Stress Field and Nonlinear Zone Extent Analysis

2014 ◽  
Vol 969 ◽  
pp. 67-72 ◽  
Author(s):  
Jakub Sobek ◽  
Václav Veselý ◽  
Stanislav Seitl
Keyword(s):  
Numerical Study ◽  
Process Zone ◽  
Crack Tip ◽  
Stress Distributions ◽  
Fracture Test ◽  
Three Point Bending ◽  
Test Geometry ◽  
Configuration Changes ◽  
Bending Fracture ◽  
Wedge Splitting

The paper is focused on a numerical study of fracture test of quasi-brittle materials which is a combination of both the wedge splitting and the three-point bending configuration. Changes in some parameters of the test geometry lead to variations in constraint conditions at the crack tip, which affects the extent of the fracture process zone, i.e. the volume where the crucial processes, determining the possibility and extent of the failure take place. Differences indicated by the failure extents (expressed as the crack pattern) and stress distributions are plotted for several stages of loading for the proposed fracture test configurations.

Dynamical Fracture Instabilities Due to Local Hyperelasticity at Crack Tips

2006 ◽  
Vol 929 ◽  
Author(s):  
Markus J. Buehler ◽  
Huajian Gao
Keyword(s):  
Large Scale ◽  
Brittle Materials ◽  
Crack Tip ◽  
Local Stress ◽  
Nonlinear Material ◽  
Physical Reason ◽  
Shear Wave Speed ◽  
Linear Elastic ◽  
Strongly Nonlinear ◽  
Wide Range

ABSTRACTWhen materials break and cracks propagate, bonds between atoms are broken generating two new material surfaces. Most existing theories of fracture assume a linear elastic stress-strain law. However, the relation between stress and strain in real solids is strongly nonlinear due to large deformation near a moving crack tip, a phenomenon referred to as hyperelasticity or nonlinear elasticity. Cracks moving at low speeds create atomically flat mirror-like surfaces, whereas cracks at higher speeds leave misty and hackly fracture surfaces. This change in fracture surface morphology is a universal phenomenon found in a wide range of different brittle materials, but the underlying physical reason has been debated over an extensive period. Using massively parallel large-scale atomistic simulations employing a new, simple atomistic material model allowing a systematic transition from linear elastic to strongly nonlinear material behaviors, we show that hyperelasticity can play a governing role in dynamical crack tip instabilities in fracture of brittle materials. We report a generalized model that treats the instability problem as a competition between different mechanisms controlled by local stress field and local energy flow near the crack tip. Our results indicate that the fracture instabilities do not only appear in defected materials, but instead are an intrinsic phenomenon of dynamical fracture. Our findings help to explain controversial experimental and computational results, including experimental observation of crack propagation at speeds beyond the shear wave speed in rubber-like materials.

Effect of Welded Mechanical Heterogeneity on Local Stress and Strain Ahead of Growing Crack Tips in the Piping Welds

2011 ◽  
Author(s):  
Lingyan Zhao ◽  
He Xue ◽  
Wei Tang ◽  
Xiurong Fang
Keyword(s):  
Crack Tip ◽  
Local Stress ◽  
Stress And Strain ◽  
Strain Fields ◽  
Mechanical Heterogeneity ◽  
Constant Loading ◽  
Primary Loop ◽  
Weld Joints ◽  
Growing Crack ◽  
Crack Tips

Primary loop recirculation (PLR) piping weld joints are more susceptible to stress corrosion cracking (SCC). But it is difficult to accurately predict SCC growth rate in PLR piping weld joints because the material and mechanical properties in weld joints are quite complicated. Especially, it is provided that hardening in the weld heat-affected zone (HAZ) might play an important role in promoting SCC growth. Considering welded mechanical heterogeneity, the local stress and plastic strain fields ahead of growing crack tip in 316L PLR piping weld joints are analyzed, the effect of constant stress intensity factor (KI) and constant loading on SCC behaviors of PLR piping weld joints is investigated in this study. The results show that the mechanical fields of SCC tips behave quite differently under constant KI and constant loading because of welded mechanical heterogeneity and advanced crack length, which demonstrate that the effect of constant loading on the stress and strain ahead of the growing crack tip is bigger than that of constant KI.

Does the Process Zone Control Crack Growth?

1992 ◽  
Vol 45 (8) ◽  
pp. 367-376 ◽  
Author(s):  
H. Abe´ ◽  
M. Saka ◽  
S. Ohba ◽  
T. Hashida
Keyword(s):  
Crack Growth ◽  
Main Crack ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Crack Tip ◽  
Compact Tension ◽  
Initial Crack ◽  
Zone Control ◽  
Notch Length

Fracture toughness tests were carried out by using small compact tension specimens of Westerly granite. Relation between the load-line displacement and the initial crack-tip separation changed from linear to nonlinear and then to linear again with increasing loading. The onset of the main crack growth was found to occur in a loading level at which the relation was nonlinear. This result disclosed that the onset of main crack growth in granite occurred without experience of the complete area under the tension-softening curve. The critical value of the initial crack-tip separation for onset of the main crack growth was obtained independently of the initial notch length. Also monitoring of the growth of the fracture process zone by ultrasonic technique showed that its length related with the crack-tip separation independently of the initial notch length. By combining the results just mentioned, it was concluded that the fracture process zone controlled the onset of the main crack growth.

Fracture Toughness of Freshwater Ice—Part II: Analysis and Micrography

1996 ◽  
Vol 118 (2) ◽  
pp. 141-147 ◽  
Author(s):  
L. J. Weber ◽  
W. A. Nixon
Keyword(s):  
Fracture Toughness ◽  
Fracture Surface ◽  
Experimental Technique ◽  
Loading Rate ◽  
Process Zone ◽  
Crack Tip ◽  
Simple Method ◽  
Dislocation Activity ◽  
Freshwater Ice

Experiments have been performed to determine the effect of loading rate and temperature on the fracture toughness of freshwater ice. A first paper (Weber and Nixon, 1996) presents the experimental technique and results, while this paper focuses on discussion of the crack tip process zone and fracture surface micrography. A simple method to estimate the size of the process zone will be presented. Also, fracture surface micrography will be used to interpret the results of the temperature experiments by considering evidence of dislocation activity in preferentially oriented grains.

scholarly journals Study on the Fracture Process Zone near the Mode I Dynamic Crack Tip

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Chenmeng Ji ◽  
Chengzhi Qi
Keyword(s):  
Approximate Method ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Crack Problem ◽  
Crack Tip ◽  
Complex Stress ◽  
Mode I ◽  
Dynamic Crack ◽  
Stress Function Method

Evaluation of the shape and size of the fracture process zone near the mode I dynamic crack tip is still a problem unsolved completely at present. The research on the relationship between the fracture process zone and crack velocity near the mode I dynamic crack tip is quite limited, and some researchers have also developed experimental methods or numerical methods. In this research, based on the theory of elastodynamics and the complex stress function method, an approximate method for solving the mode I dynamic crack problem was proposed. The fracture process zone near the mode I dynamic crack tip was analyzed. The results showed that the areas of the fracture process zone determined based on the approximate method are nearly the same as the results obtained based on the well-known stress fields. The approximate method could provide a good reference for determining the fracture process zone near the mode I dynamic crack tip since no analytic methods had been found for evaluating the fracture process zone near the dynamic crack tip to the authors’ knowledge.

A Two-Parameter Description of the Behaviour of a Process Zone at a Crack Tip: Relation Between the Parameters

2005 ◽  
Author(s):  
E. Smith
Keyword(s):  
Process Zone ◽  
Crack Opening ◽  
Crack Tip ◽  
Relative Displacement ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Power Series Expansions ◽  
Elastic Crack ◽  
Crack Tip Opening ◽  
Crack Faces

The relative displacement of the crack faces and the tensile stress ahead of a Mode I elastic crack tip can be expressed, in the immediate vicinity of the tip, by two-term power series expansions, the two terms being associated with the stress intensity factor KI and a dimensionless parameter g0. These parameters feature prominently in cohesive process zone models of a crack tip with regard to the crack tip opening displacement vT, process zone size s, the crack opening area A and the effective opening area AD of the process zone. This paper shows that KI and g0 depend upon each other via a relation which is dependent upon the geometrical configuration but is independent of the configuration’s loading pattern.

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