Transverse Shear Crack Research Articles

Acoustic Emission Measurements During a Four-Point Bending Test on a Reinforced Concrete Specimen

Acoustic emission (AE) measurements were carried out during a four-point bending test to in-vestigate the influence of the shear load-bearing capacity of reinforced concrete beams (so-called Leonhardt beam) with shear reinforcement. The results of AE measurements show that the AE activity begins immediately after starting loading. During the test approximately 3.500 AE events could be automatically located using longitudinal and transverse wave arrival times. Most AE events are in the central region of the specimen within the sensor network. Therefore, only the flexural tensile cracks are represented through AE locations. The transverse shear crack that occurred during the ultimate failure of the specimen is outside the sensor arrangement and has not been detected. Due to the localization error, the AE events are distributed in a cloud-like manner, and as a result, they do not sharply depict the macroscopic flexural tensile cracks. Ra-ther, acoustic emission indicates that a crack network of many small microscopic cracks formed in the tensile area, resulting in a very rough and fragmented crack morphology. Additional to the conventional source location, we applied the so-called collapsing method to highlight structures already inherent within the unfocused AE events clouds.

Mathematical modeling of rectilinear cohesive transverse shear cracks in a fiber-reinforced composite reinforced with unidirectional fibers

Mathematical modeling of rectilinear cohesive transverse shear cracks in a fiber-reinforced composite reinforced with unidirectional fibers

Experimental study on crack characteristics and acoustic emission characteristics in rock-like material with pre-existing cracks

Grain size composition, crack pattern, and crack length have a significant influence on the crack characteristics, mechanical characteristics, and acoustic emission characteristics of rock masses. In this paper, the crack characteristics, mechanical characteristics, and acoustic emission characteristics of rock masses with different grain size compositions, different crack patterns, and different crack lengths were investigated under uniaxial compression. The rock masses were made of rock-like materials. The crack initiation locations and crack propagation directions were different for a specimen comprised of one grain size range compared with specimens comprised of two or three grain size ranges. The specimens comprised of one and three grain size ranges crack progressively. The specimen comprised of two-grain size ranges brittle fracture. The highest peak axial load was found in the specimens comprised of one grain size range. The results showed that tensile wing crack, anti-tensile wing crack, transverse shear crack, compression induced tensile crack, and surface spalling were produced in specimens with different crack orientations. The rock mass with 2 cm long crack started to produce cracks from the tip of the crack extending to the top and bottom surface, soon forming through cracks. The rock was brittle fracture. The axial load reached the maximum and then fell rapidly. The acoustic emission energy reached a rapid maximum and then decreased rapidly. The rock mass with 3 cm long fissures started to produce cracks that only extended from the tip of the fissures to the top surface but not to the bottom surface. The rock mass was progressively fractured. The axial load was progressively decreasing. The acoustic emission energy also rose and fell rapidly several times as the rock mass was progressively fractured. Different rock crack lengths led to different crack processes and crack patterns, resulting in very different acoustic emission characteristics.

Influence of lateral impact on reinforced concrete piers under drying-wetting cycle and chloride ion corrosion environment

In order to study the influence of lateral impact on reinforced concrete piers in marine environment, drop hammer impact tests were carried out on piers with different corrosion rates obtained from drying-wetting cycle and chloride ion corrosion experiment to study the crack propagation process and failure modes of piers. Then by numerical simulation, the influences of impact velocity, impact mass, compressive strength of concrete and impact number on the performance of corroded piers were studied. The results showed that the failure modes of piers with different corrosion rates under lateral impact were different. The non-corrosive and low corrosion rate piers were destroyed by the bending shear which was jointly controlled by the transverse bending crack and oblique shear crack. The medium corrosion rate pier was the bending shear failure caused by oblique shear crack. The high corrosion rate pier was the joint action of bending shear crack and rust expansion crack. The increase of impact velocity, impact mass and impact number will increase the maximum deflection and the damage of the corroded piers, but the increase degrees were different. The increase was largest when the impact number was increased. Increasing impact number from 1 to 5, the maximum deflection increased by 26.3 times and the number of damage element increased by 4.3 times. Increasing the compressive strength of concrete will decrease the damage of pier, but with less degree. Increasing the compressive strength from 25 to 45 MPa, the maximum deflection and number of damage element were decreased by 10.7% and 9.4% respectively.

Features of Dynamic Deformation of an Elastoviscoplastic Material in the Vicinity of a Moving Crack Tip

Some features of the behavior of ideal tips of transverse shear and tear cracks (“shear-tear” crack tips) propagating together with the shear wave fronts are investigated. It is shown that in the quasi-static approximation, the ideally plastic behavior of the material near the tear crack has a spatial character and has characteristic planes oriented at an angle of 45 degrees to the directions of the principal stresses. This makes it possible to interpret the flow of material at the tip of a tear crack as sliding along the faces of regular polygonal pyramids with bases in the tear plane. The leading edge of a “shear-tear” crack, on which both tear and transverse shear occur, in the process of propagation degenerates either into the tip of a tear crack or into the tip of a transverse shear crack. This is due to the fact that the shear or tear of a smaller magnitude reaches its limiting value earlier (stops) and then the tip of the remaining type of crack propagates.

Phase field modeling of fracture in fiber reinforced composite laminate

A new phase method for predicting crack propagation path and mechanical response of fiber reinforced composite laminate is proposed. A new three-dimensional (3D) crack surface density function considering material anisotropy is proposed for composite laminates. The explicit relationship between the model penalty parameter (MPP) in a standard anisotropic phase field method and the material properties is solved analytically. This relationship is then used to construct a new expression of driving force in phase field model to account for longitudinal, transverse normal and transverse shear cracks in composite laminates. The proposed method is implemented into the commercial software ABAQUS through user subroutine user defined element (UEL). Numerical methods on both two-dimensional (2D) lamina and 3D angle ply laminate are provided. The present predictions are in good agreement with the experimental and other numerical results.

Mathematical modeling of the propagation of precursors of the front edges of cracks as spatial curves on the fronts of waves of a strong discontinuity of rates and stresses

Crack propagation occurs at the macro level with finite elastic displacements, deformations and stresses far from the front edge of the crack. In the neighborhood of the front spatial edge of a crack during its development, the behavior of the material is really inelastic, when the changes take place at the micro and nano levels.In this paper with the use of the Bingham model of an elasto viscoplastic (EVP) material, a small δ-neighborhood is chosen around the front spatial edge of a crack. The neighborhood has the shape of a cylinder with a curvilinear axis. It is shown that the wave fronts of plastic deformation are waves of longitudinal or transverse deformation and bear the front edges of the precursors these are longitudinal shear cracks and transverse shear cracks or detachment cracks.Ordinary differential equations of transfer of the intensity of tangential shear stresses and normal detachment stresses behind the precursor of the crack edge depending on the path traveled by the front edge of the crack are constructed. Exact solutions are obtained in the case of a non-stressed material. The finiteness of the length of a growing crack in an EVP material has made it possible to clarify the classical criteria for brittle fracture.

Asymptotic Analysis of the Plane Strain State Generated by a Finite Longitudinal Shear Crack

In the linear theory of elasticity, an arbitrary crack is represented as a combination of three: longitudinal shear cracks, transverse shear cracks, and normal tear cracks that do not interact with each other. In the nonlinear theory, for some types of strain energy potentials, a finite longitudinal shear crack necessarily generates a strain in the transverse plane. This article proposes an asymptotic description of the deformed state of a crack in the transverse plane under the action of a finite longitudinal shear in an incompressible material with a Mooney–Rivlin potential, and an assessment is made of the effect of additional deformation on the condition of the start of a crack.

Conditions of Self-Similarity of Edge Transverse Shear Cracks in a Square Plate

We determine the stress-strain state of a rectangular plate with edge crack under the conditions of transverse shear. The conditions of self-similar crack propagation are established. We deduce a formula for the evaluation of the stress intensity factors KII via the shear stresses.

Free vibration analysis of stiffened and cracked laminated composite plate assemblies using shear-deformable dynamic stiffness elements

In the paper, the dynamic stiffness method based on the HSDT and FSDT plate theories is applied to study free vibration characteristics of composite stiffened and cracked plate assemblies. The dynamic stiffness matrices for transverse vibration of laminated composite plate based on the HSDT and FSDT previously derived by authors have been coupled with the dynamic stiffness matrix of laminated composite plate undergoing in-plane vibration. The numerical analysis has been carried out through several illustrative examples in order to check the applicability and accuracy of the proposed method in the free vibration analysis of stiffened plate assemblies. The effects of transverse shear deformation, boundary conditions, side-to-thickness ratios, crack length or reinforcement amount within the GFRP beam on the free vibration characteristics have been discussed, and the variety of new results has been provided as a benchmark for future investigations.

Mechanisms and characterization of impact damage in 2D and 3D woven fiber-reinforced composites

Low velocity impact damage of 2D and 3D woven glass/epoxy composites with the same areal density and material constituents were examined. Characterization of damage for both plate and beam sample geometries was investigated through the collection of high-resolution cross-sectional images after impact. Load and displacement data collected during impact testing reveals that the threshold load to introduce delamination damage is independent of the fabric architecture and is constant across a range of impact energies. Delamination length and opening of 3D woven composites was less than 2D composites impacted at the same energy as a result of suppression of delamination propagation and opening offered by the Z-tow reinforcement of the 3D fabric architecture. The formation of transverse shear cracks was independent of the fabric architecture.

Mode I and mode II fatigue crack growth resistance characteristics of high tempered 65G steel

Purpose: To investigate the fatigue crack growth at normal tension and transverse shear of 65G steel with the high tempered martensite microstructure and to build an appropriate fatigue crack growth rate curves. To determine the main and auxiliary fatigue crack growth resistance characteristics, which are necessary for machine parts life-time estimation at rolling contact fatigue conditions. Design/methodology/approach: For determination of fatigue crack growth resistance at normal tension a standard compact specimens with edge crack were tested using a hydraulic testing machine and fatigue testing at transverse shear were performed on the I-beam specimens with the edge longitudinal crack using the original testing setup. For crack growth measurement an optical cathetometer B-630 was used. The crack growth rate V was calculated as crack length increment during loading cycles. The stress intensity factor range K was determined by dependence "K = (1 – R)Kmax accordingly to the standard test methods. To establish crack faces friction factor at transverse shear fragments of fractured beam specimen containing crack faces were cut out and tested as a friction pair according to Amontons Coulomb's law. On the base of test results the fatigue crack growth rate curves in logarithmic coordinates "K vs. V were built. These graphical dependencies for normal tension and transverse shear were used for determination of fatigue crack growth resistance characteristics: fatigue threshold "Kth, fracture toughness "Kfc, "K1-2 and "K2-3 which indicates the beginning and the end of middle-amplitude region of curve, "K*, parameters C and n of Paris’s equation. Metallographic and fractographic analyses were performed on the scanning electronic microscope Zeiss EVO 40XVP. Findings: Empirical dependences of the stress intensity factor range on fatigue crack growth rate at normal tension and transverse shear of 65G steel with the high tempered martensite microstructure are obtained. Based on these graphical dependencies the fatigue thresholds and fracture toughness as well as the parameters of Paris’s equation are determined. Research limitations/implications: The fatigue crack growth on 65G steel under low-, medium- and high-amplitude cyclic loading at normal tension and transverse shear was investigated. The fatigue crack growth rate values for a wide range of stress intensity factor are estimated. On the base of fractographical analysis the features of fracture of high tempered martensite in 65G steel at transverse shear are studied. It is shown that the transverse shear crack faces friction factor for high tempered martensite structure is less than for low tempered martensite. Practical implications: Using the fatigue crack growth resistance characteristics of 65G steel at normal tension and transverse shear and related fatigue crack growth rate curves it is possible to predict the life-time of machine parts made of steels with high tempered martensite structure, working at rolling contact fatigue conditions. Originality/value: Complete fatigue crack growth rate curves of 65G steel with tempered martensite structure at normal tension and transverse shear are built and the fatigue crack growth resistance characteristics for both modes of fracture are determined for the first time.

Determination of the Stress Intensity Factor for a Transverse Shear Crack in a Beam Specimen

By the method of superposition of stressed states, we deduce a formula for the stress intensity factor KІІ under the conditions of transverse shear of an I-beam specimen. The comparison of the results of calculations with the theoretical data obtained earlier by the finite-element method reveals their satisfactory convergence within a broad range of relative crack lengths.

Fracture initiation in the contact region under shear

In the contact region between sliding elastic bodies, there are subregions where the interacting shores are bonded and subregions where they can slide along each other. It is convenient to interpret the latter as transverse shear cracks with slip resistance forces acting on their closed shores. In the end regions of such a crack, stress concentration may lead to fracture initiation in the contacting bodies. Experimental results and an analytic model of the phenomenon are given for a situation where the fracture intersects the contact plane tilted with respect to the direction of the loads.

Slip dynamics at a patterned rubber/glass interface during stick-slip motions

We report on an experimental study of heterogeneous slip instabilities generated during stick-slip motions at a contact interface between a smooth rubber substrate and a patterned glass lens. Using a sol-gel process, the glass lens is patterned with a lattice of parallel ridges (wavelength, 1.6 μm, amplitude 0.35 μm). Friction experiments using this patterned surface result in the systematic occurrence of stick-slip motions over three orders of magnitude in the imposed driving velocity while stable friction is achieved with a smooth surface. Using a contact imaging method, real-time displacement fields are measured at the surface of the rubber substrate. Stick-slip motions are found to involve the localized propagation of transverse interface shear cracks whose velocity is observed to be remarkably independent on the driving velocity.

Destruction of a perforated body in transverse shear

We consider the problem of doubly periodic system interaction of circular holes and straight cracks with end zones emanating from the surface of the circular holes designed collinear with the axes of abscises and ordinate in transverse shear. The solution to the problem of equilibrium of a perforated body under transverse shear cracks with connections in the end zone is reduced to solving two infinite algebraic systems and two nonlinear singular integral equations. From the solutions of these equations we find converging efforts in the binders of end zones. The condition of crack growth is formulated taking into account the criterion of maximum extraction binders.

On subcritical development of a shear crack in a composite with viscoelastic components

We present results of an investigation of the development of a transverse shear crack in a composite material with linearly viscoelastic components under external shear load. The solution is divided into the following two main stages: determination of the time dependence of the crack tip opening displacement and determination of the crack-growth kinetics as a result of the solution of integral equations. In the first stage, we use the solution of the corresponding elastic problem of determination of the crack opening displacement and the problem of determination of the effective moduli of the composite reinforced with unidirectional discrete fibers. Using the theoretically proved principle of elasto-viscoelastic analogy and the method of Laplace inverse transformation, we obtain a solution in a time domain. In the second stage, using the criterion of critical crack opening displacement for a transverse shear crack and an equation for the viscoelastic crack opening displacement of this crack, we construct an equation of crack growth. We present results of the numerical solution, which illustrate the influence of relations between the relaxation parameters of the materials of the components on the durability of the body with a crack.

Revealing, identifying and assessing “non‐predictable flaws”, crack type IV, by quantitative acoustic emission non‐destructive inspection technology, photo‐elastic and metallurgical methods

AbstractQAE NDI technology has been adapted to revealing, identifying and assessing one type of previously non‐predictable failure of high energy equipment and piping, known as crack type IV. The research established the following: Cracks of type IV correspond to transverse shear crack mode II, according to the classification used in fracture mechanics and the physics of solids. The length of crack mode II jumps, the velocity of it propagation are significantly higher than in case crack mode I under the same loads. The earliest quantitative statistical Acoustic Emission (AE) indications and peculiarities necessary and sufficient to reveal cracks in specimens loaded by tension or shear loads, especially the differences in the AE power, median Energy, Average Frequency and Hit Rate of the AE signals flow. etc. Based on the findings described above have been formulated requirements and technological solutions for revealing, typifying and assessing crack IV.

Asymptotics of stresses and strain rates near the tip of a transverse shear crack in a material whose behavior is described by a fractional-linear law

An approximate solution of the problem of determining the fields of stresses and strain rates due to creep near the tip of a transverse shear crack in a material whose behavior is described by a fractional-linear law of the theory of steady-state creep is given. It is shown that the strain rates have a singularity of the type \( \dot \varepsilon \) ∼ r−α near the crack tip; the order of singularity α changes discretely, depending on the polar angle, and takes the values 1, 2/3, and 1/2.

The steady motion of a circular crack along the interface of a layer and a half-space

An exact analytical solution is given of the direct axisymmetric steady dynamic problem in the theory of elasticity of the motion, with an arbitrary constant subsonic velocity ν = c along the interface of a rigidly coupled layer 0 ≤ z ≤ H and a half-space z ≤ 0, of a circular transverse shear crack 0 ≤ r ≤ r0 + ct (r0 ≤ 0) with and without a cavity at its tip. Using Hankel transformation in terms of biwave potentials, a general solution of the fundamental equations of motion in the theory of elasticity and the basic solutions of the first fundamental boundary-value problem are separately constructed for the layer and the half-space for the case of arbitrary normal and shear stresses in the plane of separation z = 0 in a moving cylindrical system of coordinates r1 = r + ct, z1 = z. A special regularization of the main solution is carried out which ensures the convergence of the integrals for all stresses and displacements while preserving the high accuracy of the solution to whatever level may be desired [1, 2]. On the basis of the main solutions, a mathematical formulation is given of the mixed problem of the motion of a transverse shear crack with a cavity at the tip and its reduction to a system of three singular integral equations with Cauchy kernels which allows of regularization by the Carleman-Vekua method in terms of the closed solution of the corresponding characteristic system of singular integral equations. When the width of the cavity vanishes, one of the equations of the system solves the problem of a transverse shear crack without a cavity. Criteria are established for the existence of a cavity and its absence as a function of the elastic and velocity characteristics of the layer and half-space and the velocity of motion of the crack c.