Crack Growth In Compression Research Articles

Phase field modeling of frictional slip with slip weakening/strengthening under non-isothermal conditions

Cracks, veins, joints, faults, and ocean crusts are strong discontinuities of different length scales that can be found in many geological formations. While the constitutive laws for the frictional slip of these interfaces have been the focus of decades-long geophysical research, capturing the evolving geometry such as branching, coalescence, and the corresponding interplay between frictional slip and the mode II crack growth in compression remains a challenging task. This work employs a phase field framework for frictional contact originated in Fei and Choo (2020), s.t. these strong discontinuities are represented by implicit functions and the frictional responses of the transitional damage zone is approximated by a diffusive constitutive law that captures the coupling between the bulk and interfacial plasticity. To replicate the rate dependence and size effects commonly exhibited in frictional interfaces, we propose a regularized constitutive law for the slip weakening/strengthening at different loading rates and temperature regimes. Numerical examples are provided to show that the regularized model may converge into the strong-discontinuity counterpart and capture the frictional response along geometrically complex interfaces.

An Analysis Of Explicit Finite Element TypeSimulations Of Fracture Propagation InCompression

Direct modelling technique is used to study crack growth in compression from an inclined shear crack and a pore based on a finite difference code FLAC. In this modelling the microstructure is represented by finite elements. Fractures are treated as sequences of elements with largely reduced or zero moduli. Crack propagation is simulated by the removal of the element at which the failure criterion is satisfied by setting it to the null element. We used a natural crack propagation criterion: the crack propagates when the major principal stress at the element at the crack tip exceeds the local tensile strength. The numerical results are compared with analytical LEFM solutions in which the influence of free surface on crack propagation is accounted for by the method of dipole asymptotics.

Influence of shape and locations of initial 3-D cracks on their growth in uniaxial compression

Mechanisms of 3-D crack development in uniaxial compression have been studied. Several tests undertaken on different transparent casting resin, cement and mortar samples with single internal cracks of different shapes and sizes, produced by different techniques, demonstrated that 3-D crack growth in compression was qualitatively different from the two-dimensional case. Unlike 2-D cracking, there were intrinsic limits on 3-D growth of wing cracks produced by a single pre-existing crack. This limitation was related to the wrapping (curving) of emerging wings around the initial crack. On the other hand, in samples with few initial cracks, a special crack arrangement existed which could produce a large tensile fracture parallel to the direction of loading. Particularly, for two coplanar initial cracks, the tensile fracture was produced only when the inter-crack spacing was below a critical value. In samples where the initial cracks were present in high concentrations, the influence of interaction always generated a number of tensile fractures parallel to the direction of loading.

Analysis of compressive fracture in rock using statistical techniques: Part I. A non-linear rule-based model

Abstract A new non-linear rule-based model for the fracture in compression of heterogeneous brittle materials such as rock is presented and used to study crack nucleation and propagation at the grain scale. We have used the model to simulate uniaxial compression tests of rock samples and results underscore the importance of crack interaction in extensile cracking of rock in compression even at low crack densities. Moreover, the model produces non-linear stress–strain behavior similar to that observed in laboratory tests. We have analyzed the stress–strain behavior and found that in these simulations fracture occurs in the following way. First, initial damage occurs by random cracking. When approximately 15% of the sites are broken, cracks start to interact and coalesce to form larger cracks which then may propagate a significant fraction of the array length. Crack extension may be followed by crack arrest and subsequent formation of a damage zone ahead of a crack tip. Finally, a series of cracks will link and form a fracture that eventually causes failure. The model shows decreasing compressive strength with increasing size following a power-law relationship with an exponent that is similar to that determined from the study of laboratory and field-test results. The model can also incorporate heterogeneity in the strength and geometry of rock fabric; in part II, the model is used to investigate how microscale heterogeneity in these parameters affects extensile crack growth in compression.

The mechanism of 3D crack growth in compression: The role of non-singular terms

This paper presents results of a characterization procedure, based on back analysis, of a nonlinear deformation behavior of a discontinuous rock mass during excavation of a large underground power house cavern. The objective is to introduce the concept of isolating effects of nonlinear joint deformation to be back-analyzed from measured displacements and to demonstrate the effectiveness of this method for identifying strain distribution and deformational mechanism within a jointed rock mass.

Use of the shadow optical method of caustics to predict fatigue crack growth in compression: Leftheris, B. P. and Papazian, J. M. J. Eng. Mater. Technol. (Trans. ASME) (Oct. 1992) 114 (4) 399–405

Cyanovirin-N (CVN) is a novel cyanobacterial protein that selectively binds with nanomolar affinities the mammalian oligosaccharides Man8 and Man9. Consequently, CVN potently blocks HIV entry through highly avid carbohydrate-mediated interactions with the HIV-envelope glycoprotein gp120, and is under preclinical investigation as an anti-HIV microbicide. CVN contains two non-overlapping carbohydrate-binding sites that bind the disaccharide Manα(1-2)Manα (which represents the terminal disaccharide of all three arms of Man9) with low to sub-micromolar affinities. The solution structure of a 1:2 CVN:Manα(1-2)Manα complex revealed that CVN recognizes the stacked conformation of Manα(1-2)Manα through a deep hydrophilic-binding pocket on one side of the protein (site 2) and a semi-circular cleft on the other (site 1). With the prominent exception of the C1 hydroxyl group of the reducing mannopyranose ring, the bound disaccharide is positioned so that each hydroxyl group is involved in a direct or water-mediated hydrogen bond to the polar or charged side-chains comprising the binding pocket. Thus, to determine whether the next-most reducing mannopyranose ring will augment CVN affinity and selectivity, we have characterized by NMR and ITC the binding of CVN to three synthetic trisaccharides representing the full-length D1, D2 and D3 arms of mammalian oligomannosides. Our findings demonstrate that site 1 is able to discriminate between the three related trisaccharides methyl Manα(1-2)Manα(1-2)Man, methyl Manα(1-2)Manα(1-3)Man and methyl Manα(1-2)Manα(1-6)Man with remarkable selectivity, and binds these trisaccharides with KA values ranging from 8.1×103 M−1 to 6.6×106 M−1. Site 2 is less selective in that it binds all three trisaccharides with similar KA values ranging from 1.7 to 3.7(±0.3)×105 M−1, but overall binds these trimannosides with higher affinities than site 1. The diversity of pathogenic organisms that display α(1-2)-linked mannosides on their cell surfaces suggests a broad defensive role for CVN in its cyanobacterial source.

Use of the Shadow Optical Method of Caustics to Predict Fatigue Crack Growth in Compression

The shadow optical method of caustics has been applied to the measurement of the bulging out of the surface of aluminum alloy 7075-T6 in the vicinity of a blunt notch in a single edge notch tensile sample after a compression overload and during compression fatigue. The size and shape of the caustic were found to be sensitive functions of the amount of elastic and plastic strain in the vicinity of the notch. Examination of the caustic during application and after release of the overload shows the elastic zone to be larger and more circular than the plastic zone, as predicted. A crack was propagated through the plastic zone using only far-field cyclic compression loading: the crack was self-arresting at the edge of the elasticplastic boundary created by the initial compression overload. The size of the plastic zone as measured by the caustic was found to agree with the maximum length of the crack. The actual surface profile in the vicinity of the notch was measured and its shape was used along with geometrical arguments to develop a model for interpretation of the caustics results. These results indicate that the caustics technique can be used to detect the presence of a plastic zone at the tip of a notch after a compressive overload, and that the size of this zone as measured by caustics is approximately equal to the size as determined by subsequent fatigue crack propagation.

Effects from vibrations in wear testing of ceramics

AbstractIn unlubricated pin-on-disc tests on a 95% alumina, fluctuations were observed in the recorder traces for applied load, displacement, and friction. It was indicated by analysis of the fluctuations, together with consideration of the characteristics of a simple harmonic oscillator, that the frequencies were probably lower than the natural frequency of vibration of the test equipment. It is proposed that the resultant cyclic loading promotes fatigue crack growth in compression and causes wear by degrading the surface.MST/755

Using fatigue crack growth in compression for evaluating cyclic cracking resistance

hydrogen at high temperatures and pressures," Zh. Prikl. Khim., No. 12, 1894-1897 (1958)o 3. Yu. I. Archakov, Hydrogen Corrosion of Steel [in Russian], Metallurgiya, Moscow (1985). 4. I. G. Ovchinnikov and V. V. Petrov, "Calculations of cylindrical shells interacting with hydrogen at high temperatures and pressures," Stroit. Mekh. Raseh. Sooruzh., No. 2, 9-12 (1985). 5. I. G. Ovchinnikov and A. Yu. Salikhov, "Deformation and failure of a thick-wall cylindrical shell subjected to high-temperature hydrogen corrosion," in: Calculation of Structural Members Interacting with Corrosive Media [in Russian], Saratov Polytechnic Institute (1985), pp. 3-7.

Brittle failure in compression: splitting faulting and brittle-ductile transition

The micromechanics of brittle failure in compression and the transition from brittle to ductile failure, observed under increasing confining pressures, are examined in the light of existing experimental results and model studies. First, the micromechanics of axial splitting and faulting is briefly reviewed, certain mathematical models recently developed for analysing these failure modes are outlined, and some new, simple closed-form analytic solutions of crack growth in compression and some new quantitative model experimental results are presented. Then, a simple two-dimensional mathematical model is proposed for the analysis of the brittle—ductile transition process, the corresponding elasticity boundary-value problem is formulated in terms of singular integral equations, the solution method is given, and numerical results are obtained and their physical implications are discussed. In addition, a simple closed-form analytic solution is presented and, by comparing its results with those of the exact formulation, it is shown that the analytic estimates are reasonably accurate in the range of the brittle response of the material. Finally, the results of some laboratory model experiments are reported in an effort to support the mathematical models.

Compressive Stability of Delaminated Random Short-Fiber Composites, Part I—Modeling and Methods of Analysis

The compressive stability of delaminated random short-fiber composites is con sidered. A mechanistic model is introduced for the problem. Both buckling stability and crack stability (i.e., delamination growth) are investigated. Two analytical methods are developed for studying the buckling stability of the delaminated com posites. The first is formulated on the basis of the well-known Rayleigh-Ritz method, including transverse shear in the composite and distorsional deformation in the delaminated ligament. The second method employs a plane-elasticity, finite-element buckling analysis. Both local buckling and coupled global and local buckling are ex amined. A fracture mechanics approach is used to study the possible compressive crack growth at buckling. The validity of the model and the accuracy and efficiency of the methods of analysis are demonstrated and discussed.

A note on brittle crack growth in compression

The growth of cracks in photoelastic material and glass under compression is being studied as part of an investigation of brittle fracture of rock. In compression the most severely stressed crack is inclined at about 30° to the axis of compression. Such cracks, when either isolated or placed in an array, grow along a curved path which becomes parallel with the direction of compression. When this direction is attained, growth stops, unless applied compression is increased considerably. Cracks in certain en échelon arrays start to grow at much smaller applied stress than that required to enlarge an isolated crack.