Crack Orientation Angle Research Articles

Orientation characterisation of branched crack-like defects in curved components using ultrasonic array vector total focusing method

ABSTRACT Crack orientation is an important characteristic in crack evaluation such as predicting crack growth and measuring crack size. However, the curved surface of a component makes the ultrasonic ray path complicated and seriously affects the crack orientation characterisation in ultrasonic detection. To compensate for the effect of curved surfaces, this paper proposes a vector total focusing method (VTFM) for curved components using an immersion ultrasonic array. In this method, the curved surface profile is extracted from the image of the total focusing method (TFM) and combined with the VTFM to construct the vector fields containing defect orientation information. Then, the crack orientation angles are calculated from the vector fields. In simulation, a V-shaped crack-like defect is characterised under curved surfaces of different curvature, and excellent agreement is achieved between the calculated angles and the actual values. Experimentally, two curved samples with branched crack-like defects are manufactured and detected. The orientation angles of the inclined branches are measured to within 5° for large defects, and within 12° for small defects close to one wavelength. For branches perpendicular or parallel to the array, the errors would be larger due to the influence of sound waves reflected from the tip or the junction region of the branches. Through simulation and experiments, this curved surface VTFM algorithm is validated.

Crack deflection and crack paths in anisotropic aluminum alloy AA7010-T7452: Uncertainties and stochastic aspects

Crack deflection and crack paths in anisotropic aluminum alloy AA7010-T7452: Uncertainties and stochastic aspects

Method of understanding for investigation of crack propagation trajectory and fracture aspects in dental cracks on view of fracture mechanics theories.

Current research introduces understanding of dental-cracks mechanistic with fundamental fracture behavior in natural-teeth and orthodontics including mode I crack under both tension and compression, mode II crack under both clockwise-shear and anticlockwise-shear and mixed-mode cracks under both compression-shear and tension-shear. It depends on experimental models of transparent-Plexiglas including pre-cracks of different orientations angle (b) based on fundamental theoretical fracture analysis with comparison. Problem-concept, cracking aspects of fracture-initiation, propagation-direction, fracture-increment length, critical external-load and fracture path are predicted experimentally and theoretically using directional fracture approach and directional strain-energy density theory. Tests are carried out for (36) samples for compression and tension in LEFM. Friction-resistance between crack-surfaces is considered with derivation of equations and charts. Negative stress-intensity factor (-KI) is developed for solving complicated problems of cracks under occlusal compression loads. The occlusal loads are compression and shear producing lateral tensile mixed mode cracks. The critical propagation angle (qc), critical propagation load (sc) and critical propagation envelope of stress intensity factors (KI-KII) are developed with respect to crack orientation angle (b) with comparisons. They are necessary to predict the fracture propagation early before teeth-failure. It helps for prevention and control of dental-cracks, correct-restoration, prosthodontics, orthodontics, and development of new dental-materials and technologies.

Surface crack effect on frequency and vibration mode switching of solar-powered aerospace structures

Surface crack effect on frequency and vibration mode switching of solar-powered aerospace structures

A comparative study of several life prediction models based on the critical plane approach for fretting fatigue crack initiation

AbstractTo reasonably forecast the crack initiation characteristics of fretting fatigue, this study evaluates the accuracy of several damage models. The existing experimental and simulation investigations are compared, noting the similarities and differences in the crack initiation location, crack orientation angle, and crack initiation life predicted by various damage models. It is crucial to employ a reasonable and reasonable damage prediction model of fretting crack initiation life, as fretting fatigue, a phenomenon of mechanically fastened connecting parts, can considerably reduce the fretting fatigue life of the components. This paper compares the fatigue damage prediction models of fretting fatigue specimens under partial slip conditions, and it will help researchers understand the benefits and drawbacks of various damage models and give them the knowledge and foundation to select the more reasonable fretting fatigue damage model.

An experimental analysis of crack terminating perpendicular to the bimaterial interface under varying mode mixities

An experimental analysis of crack terminating perpendicular to the bimaterial interface under varying mode mixities

A peridynamic model based on generalized thermoelastic theory in a plate with oblique cracks

A peridynamic model based on generalized thermoelastic theory in a plate with oblique cracks

Fracture analysis of interfacial crack in piezoelectric bimaterial by XIGA approach using Bézier extraction of NURBS

This work presents analyses of interfacial crack in piezoelectrics bimaterial plate under electromechanical loading environment by extended isogeometric analysis (XIGA) approach using Bézier extraction of NURBS. Asymptotic crack–tip branch functions and discontinuous Heaviside function are implemented for local enrichment in the approximation of isogeometric analysis for capturing singularity at cracktip and discontinuity across surfaces of a crack. Bézier extraction of NURBS–based basis functions are implemented in discretization of domain for approximating both unknown field solution and geometries. The Bézier extraction operation decomposes the NURBS basis functions into a set of linear combination of Bernstein polynomials and a set of C 0 –continuity Bézier elements. Domain–form interaction integral is implemented to obtain generalized fracture parameters. To assess the robustness and accuracy in results obtained from XIGA, numerical results are first validated from analytical ones and then additionally, few numerical problems are solved for calculating the fracture parameters in terms of normalized intensity factors with respect to shear loads, electrical loads, crack orientation angle and angle of polarization.

A peridynamic model for non-Fourier heat transfer in orthotropic plate with uninsulated cracks

• A non-Fourier heat transfer analysis method of orthotropic plate with uninsulated cracks is established. • A peridynamic model considering the non-Fourier effect, orthotropy of medium and crack thermal resistance is developed. • Multi-cracks in brittle metal bismuth are analyzed by the non-Fourier theory. • The crack thermal resistance is positively related to the maximum temperature difference at the crack. • The thermal relaxation has the greatest influence on the cracks parallel to the heating boundary. In this paper, the transient temperature response of a cracked plate under thermal shock is investigated. To eliminate the problems caused by the assumption of infinite heat propagation speed, the non-Fourier heat transfer theory is adopted. A peridynamic model is developed to consider the non-Fourier effect, the orthotropy of thermal conductivity, and the crack thermal resistance. This model avoids the spatial derivative and is efficient to analyze the problems with discontinuities. Based on the Kapitza thermal resistance model, a thermal resistance bond is proposed to deal with the uninsulated crack. The explicit and implicit discrete schemes of peridynamic formulation are presented to solve the temperature field. The model is verified by the analytical solution and excellent agreements are obtained. For the non-Fourier phenomenon observed in bismuth, numerical examples are presented for analyzing the effects of crack thermal resistance, crack orientation angle, and multi-crack distribution on non-Fourier heat transfer.

Transient heat transfer analysis of an orthotropic composite plate with oblique cracks using dual-phase-lagging model

Cracks have a significant effect on heat transfer in composites, yet the influence of oblique cracks on the temperature response of composites has not been fully investigated under strong transient thermal shock, in which the heat propagation velocity cannot be assumed to be infinite. In this work, the dual-phase-lagging heat transfer model is employed to capture the transient temperature response. By imposing different boundary conditions on the crack surface, an extended boundary correction algorithm has been derived to avoid the problem of non-convergence when dealing with large and small angle cracks. The effects of crack orientation angle and interaction between cracks on dual-phase-lagging heat conduction in orthotropic materials are analyzed at the macroscale. For the two-dimensional representative volume element (RVE) of fiber reinforced composite material, the influence of the multi-crack distribution on dual-phase-lagging heat conduction at the mesoscale is further discussed in detail.

Damage tolerance in engineering components: Implementation to anchor heads

• In civil engineering structural safety often relies on safety coefficients. • Damage tolerance may help to improve structural safety. • Damage tolerance is presented for designing prestressing anchorages (PA). • 2D and 3D FE models are used for assessing damage tolerance of PA. • A specific anchorage geometry is analysed to show the effectiveness of this approach. Damage tolerance is commonly used as a design criterion in some engineering fields, such as aerospace engineering, but is not usual in civil engineering, where structural safety often relies on safety coefficients. This work presents a study on how using damage tolerance for designing post-tensioning anchor heads, usual mechanisms in many civil engineering works, can be useful for building safer structures. Damage is simulated using 2D and 3D finite element models, considering axisymmetric damage and single damage, respectively. The influence of several aspects, such as the crack depth, the crack orientation angle or the shape of the anchorage, is studied. Lastly, a specific anchorage geometry is analysed using the damage tolerance concept to show that this approach may help in the design of this type of elements.

Dynamic Characteristics Analysis of a Coupled Multi-crack Rotor System

Abstract This paper establishes a coupled model for multi-crack rotor using Timoshenko beam element with six degrees of freedom, and derives the stiffness matrix in the equations of motion accounting for the coupling between multiple cracks (the interaction between cracks). Then the effects of crack orientation angles (the relative angle between cracks, γ) on dynamic characteristics of the coupled multi- crack rotor near 1/3 and 1/2 subcritical speeds are analysed. The coupling between cracks induces more complex nonlinear dynamic characteristics such as large magnitudes of the super-harmonic components, which can be used as the indicators of early crack and for multi-crack identification. This work has a promotive significance for the application of the model-based method in the field of multi-crack detection of actual rotors.

Mathematical study of an arbitrary-oriented crack crossing the interface of bonded functionally graded strips under thermo-mechanical loading

This article intends to explore the behavior of an arbitrary oriented crack that crosses the interface of bonded finitely thick functionally graded strips under thermo-mechanical loading. The angled crack is partially insulated. Application of the superposition technique and Fourier transformation on the governing equations of heat conduction and plane elasticity help to reduce the boundary-continuity conditions to Fredholm type singular integral equations. For solving these integral equations, the jump of the temperature and displacement across the crack surface are expressed as a series of Jacobi polynomials. Employing the residue theory and Schmidt method, the expressions of stress intensity factors (SIFs) are obtained which along with the local material parametric function determine strain energy release rates (SERRs). The novelty of the article is the investigation of the impact of thermo-mechanical loading on mode I and II crack tip SIFs and SERRs to study the behavior of arbitrary oriented partially insulated crack when it crosses the interface. The results of the present study are also validated. The key feature of the article is the graphical presentations of crack tip SIFs andSERRs for different values of crack insulation parameter, crack orientation angle, strips’ thickness, and non-homogeneity parameters. • An angled crack in a bonded functionally graded strips was studied. • Effect of thermo-mechanical loading when crack crosses the interface was examined. • The residue theory and Schmidt method are used for the computational purpose. • The expressions of mode I and mode II crack tip SIFs and SERRs are obtained. • Impact of thermo-mechanical and geometric parameters on SIFs and SERRs are studied.

A new integral equation method for calculating interacting stress-intensity factors of multiple holed-cracked anisotropic rock under both far-field and arbitrary surface stresses

Calculation of interacting stress-intensity factors (SIFs) of multiple holed-cracked anisotropic problem is of very importance not only for improving hydraulic fracturing technology in shale-gas exploitation, but also for optimizing crack-arrest holes in rock engineering. Current literatures are mainly focused on interacting SIFs of multiple holed-cracked anisotropic body under far-field stresses regardless of surface stresses on holes and cracks. In this paper, a new integral equation method, based on our derived exact fundamental stress solutions (with simple formulae and high-efficiency calculation process), is proposed to calculate interacting SIFs for multiple holed-cracked anisotropic rock under both far-field and arbitrary surface stresses, where the circular-holes and cracks are of any number, sizes, orientations, relative locations. The new method is proved to be valid by comparing our results of interacting SIFs with those obtained by Green function's method, hyper-singular integral equation method and finite element method. Several computational examples are given to investigate effect of loadings, holed-cracked geometries and orthotropic material properties of shale on interacting SIFs. Research results show that the far-field stress ratio (σx∞/σy∞) greatly affects the neutral crack orientation angle α0of KIA, KIIA and KIB (with null-effect of the circular-hole on the crack) but scarcely affects α0of KIIB (where A, B are inner, outer crack-tips). The surface compressive stresses acting alone on the hole (n) and alone on the crack (p) have little effect on α0. The circular-hole radius (r) is almost irrelative to α0, but relative to the amplifying or shielding degree of interacting SIFs. Young's modulus ratio (E2/E1) and bedding plane orientation angle (φ) of shale decide α0 of KIB but are nearly independent of α0 of KIA and KIIA. In addition, decreasing σx∞/σy∞ or increasing n, p can facilitate crack propagation, and decreasing E2/E1 and φ are helpful for crack arrest. The new method not only avoids the trouble in solving the singular integral equation (without any singularity), but also has high accuracy (exact fundamental stress solutions) and wider application (under both far-field uniform stresses and arbitrarily distributed surface stresses) than the common methods. It is proved to be effective for predicting the multi-crack initiation of rock under hydro-mechanical coupling stress in underground rock engineering for safety assessment and cracking-arrest design, and for optimizing the orientation angle of hydraulic-crack to form better fracturing network in shale-gas exploitation for improvement of shale-gas exploitation efficiency.

Non-Fourier heat conduction analysis of a 2-D plate with inner cracks at arbitrary direction angles

This paper investigates the problem of a 2-D plate containing internal cracks at arbitrary angles to the heating surface under thermal shock. The finite difference method is applied to solve the temperature distribution and a difference scheme of the oblique crack is developed. For the first time, a non-Fourier heat transfer analysis method of a 2-D plate with inner cracks at arbitrary direction angles is established. Specifically, for a strip with an inner crack paralleling to the surface, numerical results are compared with the analytical solutions by rotating the boundary, and perfect agreement is obtained. Numerical experiments are further presented to investigate the influence of crack orientation angle and multi-crack distribution on non-Fourier heat conduction.

Nonlinear ultrasonic detection of partially closed cracks in metal plates using static component of lamb waves

This paper presents physical and experimental studies of the static component of Lamb waves (SCLWs) induced by partially closed cracks. The generation mechanism of SCLWs was investigated according to the nonlinear interaction between Lamb waves and partially closed cracks with various lengths, widths and orientation angles in finite element simulations. It was found that the SCLWs are more sensitive to the crack length, width and orientation angle as compared with the second harmonic Lamb waves. Fatigue crack evolution was further experimentally detected in aluminum alloy plates using SCLWs. Consistent with the simulation results, the acoustic nonlinearity parameter increases monotonically with increasing fatigue crack length. We show that the SCLWs are sensitive to partially closed cracks and can serve as a potential method to quantitatively evaluate the evolution of partially closed crack in metal plates. The findings of this study pave the way for the detection of partially closed crack using SCLWs in the field of nondestructive evaluation and structural health monitoring. • Partially closed cracks detection is proved using SCLWs. • Crack surfaces serve as excitation sources of SCLWs. • SCLWs increase with crack length and orientation angle, and decrease with crack width. • SCLWs are more sensitive to partially closed cracks as compared with second harmonics.

An EFGM approach for permeable, semi-permeable and impermeable crack interaction study in 2D piezoelectric domains

This paper presents the numerical simulation of permeable, semi-permeable and impermeable crack interaction study in 2D piezoelectric domains using an element-free Galerkin method (EFGM). The electric and displacement fields are described by introducing the singularity terms into an approximation function. This study is performed with respect to effects of electrical loading, crack surface boundary conditions, crack orientation angles, aspect ratio and number of cracks in order to examine these effects on fracture parameters. Multiple inclined equidistant cracks are considered in piezoelectric domain under different crack surface boundary conditions. The proposed enrichment criterion accurately estimates fracture parameters which shows the robustness, efficacy and applicability of EFGM approach.

Profile reconstruction and quantitative detection of planar defects with composite-mode total focusing method (CTFM)

The profile reconstruction of planar defects by ultrasonic imaging is helpful for obtaining the flaw type, size, orientation and other characteristics. In this paper, composite-mode total focusing method (CTFM) is proposed by selecting the strongest response from 21 views at every reconstructed point, realizing the profile reconstruction and quantitative detection of priori unknown planar defects except for the near-horizontal defects with a set of phased array (PA) probe and wedge. Subsequently, eight effective views corresponding to 45° longitudinal-wave wedge are determined considering Snell's law and beam directivity. The 64-element linear array probe with 5 MHz central frequency and 45° wedge were used to reconstruct a series of 5 mm length cracks with different orientations (0°, ±15°, ±30°, ±45°, ±60° and ±75°) by CTFM in simulation. The measurement errors of crack lengths, orientation angles and central depths with the 6 dB drop rule were within 0.42 mm, 1.87° and 0.58 mm, respectively. The experimental results showed that the characteristics of 5 mm length slots were presented with high accuracy, verifying the feasibility of CTFM. Meanwhile, the planar and volumetric defects can be distinguished qualitatively by CTFM. Finally, the reconstructed image by naive sum is compared with the CTFM image, and the effects of wedge angle and number of elements on profile reconstruction are discussed. • CTFM is proposed to realize the profile reconstruction and quantitative detection of priori unknown planar defects. • The whole profiles of −75°–75° cracks/slots are reconstructed with high accuracy by using a set of PA probe and wedge. • The detection capability of CTFM is related to the number of elements and wedge angle.

Crack growth angle prediction of an internal crack under mixed mode load for unfilled elastomer using the strain energy density factor

ABSTRACTThis article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second‐order Ogden model was used to describe the rubber‐like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles.

The Effect of Crack Orientation on the Propagation of Cracks in Graphene Nanoplatelet Carbon Fiber-reinforced Epoxy Composites Using Digital Image Correlation

This study experimentally investigated the fracture behaviors of graphene nanoplatelet (GNP) carbon fiber-reinforced polymer (CFRP) composites for varying amounts of GNP reinforcement, crack lengths and crack orientation angles. The specimens were subjected to tensile loading, and their fracture toughness values were determined with respect to maximum damage load and crack length. To compare the results obtained from experimental data, the fracture toughness values, strain distributions and crack tip opening displacements were determined by using a Digital Image Correlation (DIC) technique from images recorded during the tests. The results showed that increasing the amount of GNP increased the fracture toughness of specimens. On the other hand, increasing the crack orientation angle decreased the fracture toughness. Increasing the crack length increased the fracture toughness values for a crack orientation angle of 30° but decreased for a crack orientation angle of 90°. DIC results were found to be compatible with the calculated results using crack length and damage stress values.