1,063 research outputs found
A nonlinear high temperature fracture mechanics basis for strainrange partitioning
A direct link was established between Strainrange Partitioning (SRP) and high temperature fracture mechanics by deriving the general SRP inelastic strain range versus cyclic life relationships from high temperature, nonlinear, fracture mechanics considerations. The derived SRP life relationships are in reasonable agreement based on the experience of the SRP behavior of many high temperature alloys. In addition, fracture mechanics has served as a basis for derivation of the Ductility-Normalized SRP life equations, as well as for examination of SRP relations that are applicable to thermal fatigue life prediction. Areas of additional links between nonlinear fracture mechanics and SRP were identified for future exploration. These include effects of multiaxiality as well as low strain, nominally elastic, long life creep fatigue interaction
The 1/r singularity in weakly nonlinear fracture mechanics
Material failure by crack propagation essentially involves a concentration of
large displacement-gradients near a crack's tip, even at scales where no
irreversible deformation and energy dissipation occurs. This physical situation
provides the motivation for a systematic gradient expansion of general
nonlinear elastic constitutive laws that goes beyond the first order
displacement-gradient expansion that is the basis for linear elastic fracture
mechanics (LEFM). A weakly nonlinear fracture mechanics theory was recently
developed by considering displacement-gradients up to second order. The theory
predicts that, at scales within a dynamic lengthscale from a crack's
tip, significant displacements and displacement-gradient
contributions arise. Whereas in LEFM the singularity generates an
unbalanced force and must be discarded, we show that this singularity not only
exists but is {\em necessary} in the weakly nonlinear theory. The theory
generates no spurious forces and is consistent with the notion of the autonomy
of the near-tip nonlinear region. The J-integral in the weakly nonlinear theory
is also shown to be path-independent, taking the same value as the linear
elastic J-integral. Thus, the weakly nonlinear theory retains the key tenets of
fracture mechanics, while providing excellent quantitative agreement with
measurements near the tip of single propagating cracks. As is consistent
with lengthscales that appear in crack tip instabilities, we suggest that this
theory may serve as a promising starting point for resolving open questions in
fracture dynamics.Comment: 12 pages, 2 figure
Crack propagation in honeycomb cellular materials: a computational approach
Computational models based on the finite element method and linear or nonlinear fracture mechanics are herein proposed to study the mechanical response of functionally designed cellular components. It is demonstrated that, via a suitable tailoring of the properties of interfaces present in the meso- and micro-structures, the tensile strength can be substantially increased as compared to that of a standard polycrystalline material. Moreover, numerical examples regarding the structural response of these components when subjected to loading conditions typical of cutting operations are provided. As a general trend, the occurrence of tortuous crack paths is highly favorable: stable crack propagation can be achieved in case of critical crack growth, whereas an increased fatigue life can be obtained for a sub-critical crack propagation
3D-Mesomechanical analysis of external sulfate attack in concrete
The present study focuses on degradation of concrete by external sulfate attack. The numerical model developed by the MECMAT/UPC group, incorporates coupled C-M analysis using a meso-mechanical approach with discrete cracking, using the MEF and zero thickness interface elements with a constitutive law based on nonlinear fracture mechanics concepts. Examples of application are run on 2D and 3D samples, with geometries and FE meshes generated with a code developed also in-house. The numerical analysis is carried out using two independent codes and a “staggered” procedure. The first code performs the mechanical analysis and the second the diffusive/reaction chemical problem. 2D uncoupled and coupled analysis are presented and discussed. Preliminary coupled 3D results are also presented and compared with equivalent 2D results, and the differences are detected and analyzed
Elevated temperature crack growth
The objective of the Elevated Temperature Crack Growth Project is to evaluate proposed nonlinear fracture mechanics methods for application to combustor liners of aircraft gas turbine engines. During the first year of this program, proposed path-independent (P-I) integrals were reviewed for such applications. Several P-I integrals were implemented into a finite-element postprocessor which was developed and verified as part of the work. Alloy 718 was selected as the analog material for use in the forthcoming experimental work. A buttonhead, single-edge notch specimen was designed and verified for use in elevated-temperature strain control testing with significant inelastic strains. A crack mouth opening displacement measurement device was developed for further use
Analysis of the microbond test using nonlinear fracture mechanics
Microbond tests composed of single fibre and matrix droplet are often used to
determine the properties of fibre reinforced composites. Interfacial shear
strength is quantified by the maximum pull-out force assuming a uniform stress
distribution along the fibre. Here, nonlinear finite element analyses are
performed to investigate the validity of this assumption.Comment: Submitted to 17th international conference on composite materials
(ICCM-17
Cohesive zone models in history dependent materials
Copyright @ 2013 ACMECohesive zone model is a well known concept in nonlinear fracture mechanics of elasto-plastic materials. In contrast to that, we discuss a development of the cohesive zone model to linear, but time and history dependent, materials. The stress distribution over the cohesive zone satisfies a history dependent rupture criterion for the normalised equivalent stress, represented by a nonlinear Abel-type integral operator. The cohesive zone length at each time step is determined from the condition of zero stress intensity factor at the cohesive zone tip. It appeared that the crack starts propagating after some delay time elapses since a constant load is applied to the body. This happens when the crack tip opening displacement reaches a prescribed critical value. A numerical algorithm to compute the cohesive zone and crack length with respect to time is discussed and graphs showing the results are give
Nonlinear fracture mechanics-based analysis of thin wall cylinders
This paper presents a simple analysis technique to predict the crack initiation, growth, and rupture of large-radius, R, to thickness, t, ratio (thin wall) cylinders. The method is formulated to deal both with stable tearing as well as fatigue mechanisms in applications to both surface and through-wall axial cracks, including interacting surface cracks. The method can also account for time-dependent effects. Validation of the model is provided by comparisons of predictions to more than forty full scale experiments of thin wall cylinders pressurized to failure
Докритичний розвиток тріщини поздовжнього зсуву у в'язкопружному композиті
В рамках нелінійної механіки руйнування отримано рівняння розвитку тріщини поздовжнього зсуву в композитному матеріалі, компоненти якого мають лінійно в'язкопружні властивості. Дослідження виконано на основі двох моделей механізму розвитку тріщини: моделі сталості довжини зони передруйнування та моделі сталості напружень у цій зоні. Запропоновану схему розв'язання застосовано для побудови числового розв'язку задачі у формі кінетичних кривих розвитку тріщини.In the frame of nonlinear fracture mechanics, the equations for the growth of a longitudinal shear crack in a composite, whose components possess linearly viscoelastic properties, are constructed and numerically solved
Surface waves in deformed Bell materials
Small amplitude inhomogeneous plane waves are studied as they propagate on
the free surface of a predeformed semi-infinite body made of Bell constrained
material. The predeformation corresponds to a finite static pure homogeneous
strain. The surface wave propagates in a principal direction of strain and is
attenuated in another principal direction, orthogonal to the free surface. For
these waves, the secular equation giving the speed of propagation is
established by the method of first integrals. This equation is not the same as
the secular equation for incompressible half-spaces, even though the Bell
constraint and the incompressibility constraint coincide in the isotropic
infinitesimal limit
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