Fracture Process In Solids Research Articles

Parameter identification of a phase-field fracture model using integrated digital image correlation

Phase-field fracture (PFF) modeling is a popular approach to model and simulate fracture processes in solids. Accurate material parameters and boundary conditions are of utmost importance to ensure a good prediction quality of numerical simulations. In this work, an Integrated Digital Image Correlation (IDIC) algorithm is proposed to calibrate boundary conditions, Poisson’s ratio, fracture energy and internal length, all at once, by using the phase-field model itself and images of a deforming sample. The presented approach is applied to virtual experiments mimicking a single edge notched shear test and implemented in the open-source deal.II-based software pfm-cracks and the digital image correlation library Correli 3.2. The reliability of the results is investigated for different levels of acquisition noise, thereby demonstrating high robustness and accuracy for a wide range of noise levels. The conditioning of the problem is analyzed via sensitivity fields for all parameters and the eigendecomposition of the Hessian matrix used in the IDIC algorithm.

A probabilistic model of acoustic emissions generated during compression test of cementitious materials for crack mode classification

This article presents a study on crack mode classification in cementitious materials under uniaxial compression usinggaussian mixture modeling (GMM) of acoustic emissions approach. To implement a retrofitting method to an in-serviceconcrete structure, a prior knowledge about the type of crack developed in the concrete structure is useful. Because,occurrence of AE events during fracture process in solids is random, a probabilsitc method has been required to classify theAE sources related to different types of cracks. In this study, a monotonically increasing unconfined uniaxial compressiveload has been applied on different cylindrical specimens of plain cement concrete cast with maximum coarse aggregate sizeof 20 mm, 12.5 mm and cement mortar to study crack classification. It has been observed that the slope of the line separatingthe AE data clusters belonging to tensile and shear cracks is more steep for the concrete specimen containing 20 mm maximumcoarse aggregate when compared to the concrete specimen containing 12.5 mm maximum coarse aggregate and cementmortar. This indicated that as the coarse aggregate size in concrete increased, the generated AE events related to shearcracking decreased. Also, the AE based b-value has reached minimum at the peak load. At the time of failure, AE related toshear cracking has increased sharply.

Acoustic emission signal ‘peak amplitude-distribution’ analysis related to concrete fracture under uniaxial compression

Acoustic emissions (AE) released during the compressive fracture of cementitious materials have been subjected to analysis using ‘AE based b-value’ to study the fracture process. Identification of the ‘AE sources locations’ in three dimension is not always possible. With a minimum number of AE sensors mounted on the test specimen and by using the AE based b-value analysis, it is possible to study fracture process and the damage status in solids. The b-value of AE is calculated using the Gutenberg–Richter empirical relationship (G-R law), which is available in seismology. The details related to original G-R relation and it’s suitability for AE testing were discussed. In this article it has been tried to look into the variations of the AE based b-value in cementitious test specimens prepared with different cementitious mixture proportions. Effect of (i) coarse aggregate size in cementitious materials (ii) loading rate during compressive fracture process (iii) age of concrete on b-value variation were discussed. The trend of variation in AE based b-value during fracture process in concrete and mortar was different. It was observed that when the compression toughness of the cementitious material increases, higher b-values were observed. When the loading rate was high, quick cracking occurred and lower b-values were observed. As the coarse aggregate size in the cementitious material increases, the cumulative AE energy was higher. The reason may be due to the compression toughness of the cementitious material. The AE based b-value is useful to identify the different stages of compressive fracture process in solids.

Release-Rebound Processes: Vector Motions

The tensor relations describing the shear deviatoric strains and rotation strains may be presented as vector relations in a special coordinate system, e.g., in the diagonal or off-diagonal one. However, these fields can be also presented in the 4D invariant forms by means of invariant Dirac tensors. We present 4D relativistic relations for the invariant shear deviatoric strain and rotation strain vectors closely related to a fracture process in solids and to the molecular strains (shear and rotational) in fluids. These shear and rotation strains may interact with the radial derivatives of pressure along the propagation directions.

Cohesive Discontinuities Growth Analysis using a Nonlinear Boundary Element Formulation

The present work deals the development of a nonlinear numerical model for structural analysis of solids composed by multi-domains considering cohesive discontinuities along its interfaces. The numerical method adopted is the boundary element method (BEM), through its singular and hyper–singular integral equations. Due to the mesh dimensionality reduction provided by BEM, this numerical method is robust and accurate for analyzing the fracture process in solids, as well as physical nonlinearities that occurs along the body’s boundaries. Multi-domain structures are modelled considering the sub-region technique, in which both equilibrium of forces and compatibility of displacements are enforced along all interfaces. The crack propagation process is simulated by the fictitious crack model, in which the residual resistance of the region ahead the crack tip is represented by cohesive tractions. It leads to a nonlinear problem relating the tractions at cohesive interface cracks to its crack opening displacements. The implemented formulation is applied to analysis of three examples. The numerical responses achieved are compared to numerical and experimental solutions available in literature in order to show the robustness and accuracy of the formulation.

Introduction to asymmetric continuum: dislocations in solids and extreme phenomena in fluids

We present a new approach to the continuum theories: for solids, our version includes the asymmetric stresses, symmetric strains and antisymmetric rotations, while for fluids we take the similar assumptions but related to the respective time rates of these fields. We consider the constitutive relations and the balance laws: those related to the antisymmetric stresses are equivalent and substitute the required relations for the angular moment; a similar approach with rates of these fields is applied for fluids. The stress-dislocation relations are derived and the role of rotation motions in the fracture processes in solids is studied. A new theory of the extreme motion phenomena in fluids is developed.

Possible mechanisms for the nucleation of primary fracture zones during deformation-induced phase transformations in solids: III. Local melting at the prefracture stage

The mechanism and kinetics of the nucleation of primary damage in a crystal lattice are considered at the stage of its prefracture. The zones of local melting of a solid phase near stress concentrators are shown to be the most probable damages, whose accumulation significantly accelerates the development of fracture processes in solids during plastic deformation.

Possible mechanisms for the nucleation of primary fracture zones during deformation-induced phase transformations in solids: II. The role of phase transitions between the states of aggregation

The conditions of local phase transitions between the states of aggregation that occur in a solid phase during deformation are analyzed. A hypothesis is proposed that these transitions can play a key role in the nucleation of primary fracture zones in solids. The validities of this hypothesis and the traditional models used to describe the fracture processes in solids are compared using the available experimental data.

Microscopic treatment of the fracture process in solids

The process of brittle fracture in a solid is presented as the formation and evolution of an ensemble of elementary carriers (frustrons). The latter represent a mesoscopic region of localized strong shear deformations surrounded by an envelope of an elevated level of plastic flow. The conditions of fluctuation generation of frustrons, their characteristics, and the growth of the supercritical cluster are determined. The fracture time is derived.

Fracture kinetics of adhesion layers in composite systems

1. In preparing composites from materials of comparable strength, it is necessary to consider the possibility of the formation of a •three-dimensional• transitional layer in the contact plane. This layer may have strength characteristics different from those of the original components. 2. The kinetic process of fracture in such layers is similar to the fracture process in solids and is described by an equation similar to the Zhurkov equation. 3. The existence of the linear function log τad(1/T) for the adhesive layers makes it possible to use the given method to predict the long-term strength of loaded adhesive joints. Here, it is necessary to account for the specific character of stress distribution in the adhesive contact. 4. Study of the kinetic nature of the strength of adhesive contacts on models makes it possible to detail the process of the fracture of composite materials and find new ways of improving the mechanical strength of composites.

Three-dimensional fracture of unidirectional composites

i. Brief Review of Investigations in Three-Dimensional Fracture of Heterogeneous Materials. From the very start of investigations of fracture processes in solids, the attention of investigators has been focused on two basic conceptions. One of these treats fracture as an intergrowth of macrocracks from the most serious flaw through sound material and results in relationships of linear fracture mechanics [i, 2]. The other conception is associated with the idea of "damage accumulation" and most likely has its own origin in [3]. A more detailed bibliography of the problem is given in a book by Tamuzh and Kuksenko [4].

Nucleation of submicroscopic cracks in stressed solids

The study of very fine cracks formed in stressed solids was carried out using different types of solids, such as polymers, ionic crystals, and metals. Such methods as small-angle X-ray scattering, light scattering, and electron microscopy were used. Size, form, orientation and concentration of submicrocracks have been estimated. A study of the connection between submicrocracks and the structure of solids and of the kinetics of crack accumulation has been started. The development of the fracture process in solids on the basis of nucleation and successive coalescence of submicrocracks is discussed.