Dynamic crack propagation in composites

Theocaris, P. S.; Milios, John

doi:10.1007/bf00042384

Cited by 54 publications

(10 citation statements)

References 7 publications

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“…In homogeneous plates one of the significant factors for branching is the attained level of the crack velocity [1,2], while in nonhomogeneous plates, e.g., plates containing inclusions as happens with particulates and fibre composites, an additional main factor for branching is the existence of several types of interfaces [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

The variation of the dynamic modulus on crack propagation modes

Papadopoulos

Theocaris

1987

Int J Fract

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The variation of the elastic modulus due to the dynamic propagation of a crack and its influence on the instability of this dynamic process was studied, based on the theory of the T-criterion of failure of the material. Conditions for an eventual bifurcation of the moving crack were established according to this criterion. Furthermore, a comparison was undertaken between the results derived from the T-criterion and an improving modification of the S-criterion, called S 2-criterion, which Was based on the two-term expressions of the elastic stress field around the crack. While in the T-criterion the dilatational strain energy density, T~, was calculated on the respective Mises elastic plastic boundary where the distortional component of strain energy density was constant, in the S2-criterion the core region was defined by the respective initial curve of the dynamic caustic.It was shown that the changes of the dynamic modulus and Poisson's ratio, depending on the relative crack velocity, were the main factors creating these instability-and bifurcation-phenomena of the moving cracks. Nomograms of the critical relative velocities of bifurcation versus the dynamic modulus and Poisson's ratio were plotted and compared satisfactorily with experimental data. It was indicated that, while the T-criterion gave satisfactory results all over the range of velocities and moduli, the S 2-criterion gave comparable results only for brittle or semi-brittle cases. List of symbolsrl, 01, r:, 02, r, 0 = kl, ~ = E,, E, = Y, V i Cl~ C 2 t) = = zs,~ = dW/dV = ro = TD = (7 0 O=_ ~b = crack tip stresses referred to Cartesian coordinate system. polar coordinate system centered at crack tip. stress intensity factors. elastic moduli of the material. Poisson's ratios of the material. velocities of the longitudinal and the shear waves, respectively. crack velocity. the mass density of the material. parametric equations of caustics. elastic strain-energy density. dilatational strain-energy density. distortional strain-energy density. yield stress of the material. angle of birfucation.

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Section: Introductionmentioning

confidence: 99%

The variation of the dynamic modulus on crack propagation modes

Papadopoulos

Theocaris

1987

Int J Fract

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“…However, in non-homogeneous plates, e.g. specimens containing inclusions, or several other types of interfaces, mechanisms of crack bifurcation are not yet well understood (Theocaris and Milios [2], Theocaris and Pazis [3], Theocaris [4]). …”

Section: Introductionmentioning

confidence: 99%

Bifurcation predictions for moving cracks by the T-criterion

Theocaris

Georgiadis

1985

Int J Fract

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The directional instability of moving cracks was studied within the context of the maximum dilatational energy density, or T-criterion. To make bifurcation predictions according to the T-criterion theory it suffices to consider only the singular stress field. In this paper the stress field for a non-uniformly propagating crack under mode-I deformation was adopted. Predictions concerning both the critical crack velocity and the bifurcation angle was given. In this way, not only totally brittle fractures described previously by the S-criterion were correctly encountered, but also the results were extended to initially ductile materials where the T-criterion conserves its total efficiency.

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“…The certainty value c(w i ) given by Eqn. (21) is calculated for each node of the field defined in the previous step. 4.…”

Section: Moving Crack Trajectory Detectionmentioning

confidence: 99%

“…The method of caustics [21,22,19] is another approach that tracks the approximate position of the crack tip because of the light caustic formed from the light reflected (or diffracted) when a light beam impinges on the deformed surface of the specimen in the neighborhood of the crack tip. In addition, to the crack tip location this method can also be used to extract the dynamic stress intensity factors and therefore reconstruct the local form of the stress and strain fields, but it requires reflective and diffracting deformable media and therefore it is not general enough.…”

Section: Introductionmentioning

confidence: 99%

On the feasibility of crack propagation tracking and full field strain imaging via a strain compatibility functional and the Direct Strain Imaging method

Iliopoulos

Michopoulos

2016

International Journal of Impact Engineering

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a b s t r a c tThe simultaneous tracking of the trajectory of a moving crack along with the measurement of the corresponding full field strain fields associated with this motion due to quasi-static or dynamic impact loading, is a problem of high interest from both the perspectives of the engineering practice and engineering science alike. However, full field optical methodologies have not yet been able to address the issues arising in experiments with moving boundaries such as dynamically evolving cracks. Such a problem requires solving simultaneously the problem of identifying the dynamically evolving geometry of the cracks as well as the problem of introducing these cracks into the full-field representation of a relevant full field method. In the present work we are introducing a methodology that can solve this problem. Specifically, we describe an optical method that can be used to detect dynamically evolving discontinuities on the surface of a body even if they are invisible to the eye, by using a strain compatibility functional that makes no continuity assumptions about the underlying medium. The relevant data from this process are then introduced in a full field representation that leads to an acceptable estimation of the discontinuous strain field. The proposed method is based on the recently introduced Direct Strain Imaging method that can be used to visualize and quantify the full fields of the strain tensor components. Synthetic numerical experiments were performed to generate synthetic crack propagation data along with the associated strain fields in order to assess the feasibility of the proposed method. The approach employed for this purpose was that of applying the extended finite element method to solve the problem of a propagating crack in an elastic medium with inclusions and holes under quasi-static tension. Finally, we present the results of detecting the synthetically produced crack trajectory as well as the relevant strain fields.Published by Elsevier Ltd.

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Dynamic crack propagation in composites

Cited by 54 publications

References 7 publications

The variation of the dynamic modulus on crack propagation modes

The variation of the dynamic modulus on crack propagation modes

Bifurcation predictions for moving cracks by the T-criterion

On the feasibility of crack propagation tracking and full field strain imaging via a strain compatibility functional and the Direct Strain Imaging method

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