Effect Of Crack Orientation Research Articles

Effect of Multiple Location Defects on the Dynamics of Draft Gear used in Freight Railway Wagon

The present work investigates the effect of crack location on the modal frequency of draft gear used in autocouplers of freight railway wagon for various orientations. First seven mode shapes of a healthy draft gear have been determined using finite element approach. Defect of semi-elliptical shape is modelled in the lateral as well as longitudinal direction of the draft pad which is a component of draft gear. Various damage scenarios have been simulated by considering multiple locations of the crack in the draft gear for different orientations. Effect of crack orientation and defective pads location on the natural frequency of draft gear is analysed. It is seen that for single defective pad as well as multiple defective pads, the natural frequency of draft gear is dependent on the dynamics of draft pad. It is also observed that defect in consecutive pads causes more change in frequency as compared to single defective pad. As far as the location of defective pad is concerned, it is seen that the draft gear frequency is more sensitive to defective pads located either near the housing base plate or top follower. This study provides a tool to diagnose crack defect in draft gear based on vibration characteristics.

마찰교반용접된 7075-T651 알루미늄 합금 용접부의 피로균열전파율의 공간적 변동성에 미치는 균열 방향의 영향

Abstract: In this investigation, the effect of crack orientation on spatial randomness of fatigue crack growth rate (FCGR) in friction stir welded (FSWed) 7075-T651 aluminum alloy joints has been statistically analyzed by Weibull distribution. The fatigue crack growth tests are conducted under three different constant stress intensity factor range (SIFR) control at room temperature with R = 0.1 and frequency 10Hz on compact tension (CT) specimen machined at base metal (BM) and weld metal (WM). The experimental fatigue crack growth rate data were obtained for two types of specimens having LT and TL orientations. LT specimens both base metal and weld metal showed higher fatigue crack growth rate as compared to TL specimens. In the lower SIFR region, FCGR were found to be almost 3 times higher in higher SIFR region. The shape parameter of Weibull both LT and TL orientation for FCGR was increased with increasing SIFR, the scale parameter was also increased with increasing SIFR. The smallest value of the shape parameter was shown in weld metal specimens having LT orientation at lower SIFR region.

Pore–crack orientation effects on fracture behavior of brittle porous materials

Mechanical behavior of two-dimensional microstructures containing circular pores were simulated under uniaxial and biaxial loading using the finite element method. Resulting stress distributions were combined with classical fracture mechanics to investigate fracture behavior of brittle porous materials assuming that randomly oriented cracks are present along pore surfaces. Multiple crack orientations were found to introduce a variability in Weibull modulus even for the same set of microstructures containing equal number and size of cracks. Also, the variability increases with increasing crack size to pore size ratio. Under uniaxial loading, angular distribution of fracture origin widens with increasing porosity.

The mixed-mode fracture mechanics analysis of an embedded arbitrary oriented crack in a two-dimensional functionally graded material plate

Mixed-mode fracture mechanics analysis of an embedded arbitrarily oriented crack in a two-dimensional functionally graded material using plane elasticity theory is considered. The material properties are assumed to vary exponentially in two planar directions. Then, employing Fourier integral transforms with singular integral equation technique, the problem is solved. The stress intensity factors (SIFs) at the crack tips are calculated under in-plane mechanical loads. Finally, the effects of crack orientation, material non-homogeneity, and other parameters are discussed on the value of SIF in mode I and mode II fracture.

The fracture characteristic of three collinear cracks under true triaxial compression.

The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses.

Stress Intensity Factors for Cracked Finite Plates with Mixed Boundary Condition

The mixed boundary problems for finite plates with one crack or two collinear cracks are studied. Complex stress functions that satisfy the equilibrium equations and compatibility conditions in the cracked plate as well as the stress condition on crack surfaces are presented. Four models, that is, a square plate with one crack or with two collinear cracks and an airfoil-shaped plate with one crack or with two collinear cracks, are established. The unknown coefficients of the complex stress functions are determined by using boundary collocation method (BCM). The effects of crack orientation, crack distance, and boundary condition on SIFs are investigated by combining with BCM, and the corresponding photoelastic experiments are conducted. The test results generally agree with the BCM calculation results.

Temperature distribution and heat flow around a crack of arbitrary orientation in a functionally graded medium

This paper investigates the heat transfer problem of an infinite functionally graded medium containing an arbitrarily oriented crack under uniform remote heat flux. In the mathematical treatment the crack is approximated as a perfectly insulating cut. By using Fourier transformation, the mixed boundary value problem is reduced to a Cauchy-type singular integral equation for an unknown density function. The singular integral equation is then solved by representing the density function with a Chebyshev polynomial-based series and solving the resulting linear equation using a collocation technique. The temperature field in the vicinity of the crack and the crack-tip heat flux intensity factor are presented to quantify the effect of crack orientation and grading inhomogeneity on the heat flow around the crack.

The effects of crack orientation on the twin formation from the crack tip in γ′-Ni3Al

The effect of crack's orientation on the twin formation from the crack tip in γ′-Ni3Al has been studied by fabricating three types of mode I crack. The simulation results show that (001)<110> type crack produces two slip bands at the crack tip; however, (1̄10)<110> and (11̄1̄)<110> type cracks produce twins rather than slip bands at the crack tip. The formation mechanism of the twin is the slipping of 1/6[112] type Shockley partial dislocations on consecutive {111} planes. The underlying reasons of the twin and slip band formation have been studied in term of the generalized stacking fault energy and shear stress, and the study results show that it can be attributed to the asymmetry of shear stress associated with (111)<112> slip system.

Three-Dimensional Study of Fatigue Crack Growth in a Rotating Disc

The problem of fatigue-crack-growth in a rotating disc at different crack orientation angles is studied by using an automated numerical technique, which calculates the stress intensity factors on the crack front through the three-dimensional finite element method. Paris law is used to develop the fatigue shape of initially semi-elliptical surface crack. Because of needs for the higher mesh density and accuracy near the crack, the sub-modeling technique is used in the analysis. The distribution of SIF’s along the crack front at each step of growth is studied and the effect of crack orientation on the rate of crack-growth is investigated. The calculated SIF’s are reasonable and could be used to predict the probable crack growth rates in fracture mechanics analysis and can help engineers to consider in their designing and to prevent any unwanted failure of such components.

PARAMETER AND INTERACTION STUDY OF EDGE CRACK PROBLEM USING MESHFREE METHOD

In this work, element free Galerkin method (EFGM) has been used to obtain the solution of edge crack problem under mechanical loads as it provides a versatile technique to model static as well as moving crack problems without any requirement of remeshing. At first, some techniques are presented for enriching the EFG approximations near the crack tip such as extrinsic and intrinsic enrichment. Extrinsic enrichment involves the addition of solution form to the trial function, whereas the EFG basis is expanded to include few terms from crack tip solution in intrinsic enrichment. Apart from enrichment techniques, four basic techniques of smoothing meshless approximations near nonconvex boundaries are also presented such as diffraction, transparency, see through and wedge model. These techniques are then used for the parameteric analysis of an edge crack problem under mode-1 loading and results obtained using different approaches are compared with each other as well as with exact solution. Among these techniques, the extrinsic PU enrichment technique was found to be more accurate as compared to other approaches. Extrinsic PU enrichment technique has also been used for the analysis of a shear edge crack problem. In all these techniques, the value of mode-1 stress intensity factor and mode-2 stress intensity factor has been evaluated by interaction integral approach. Effect of crack orientation is also studied for different cases.

Dynamic Stress Intensity Factor Computation by Using Xfem Formulation

In this paper, we present a modeling of planar structures under dynamic loading containing stationary cracks in order to determine the dynamic stress intensity factor (DSIF). This parameter will be evaluated by using the eXtended Finite Element Method (XFEM) coupled with two different techniques, namely the technique of displacement jump and that of interaction integral. A comparison between the two approaches is discussed. Moreover, the effects of crack orientation and damping material on the DSIF variation are tested. The good correlation of the obtained results for the treated examples with the literature ones demonstrates the effectiveness, accuracy and robustness of the computer software developed in this study.

The effect of crack orientation on fracture behavior of tantalum by multiscale simulation

The quasicontinuum (QC) multiscale method is used to investigate anisotropic fracture behaviors of body-centered cubic (BCC) rare metal tantalum (Ta) loaded in Mode I and different fracture mechanisms are discussed from nanoscopic to continuum perspectives to have a deep understanding of brittle and ductile fracture. Initial crack deflection, brittle fracture by cleaving along low surface energy plane, ductile fracture as a result of dislocation emission and fracture accompanied by deformation twinning are all observed near crack tips of different crystal orientations. Particularly, some of these fracture mechanisms are found to be consistent with the latest experimental results. By examining different fracture behaviors, we find the surface energy and the available slip planes play a combined role in determining the fracture mechanisms near a crack tip. Both isotropic and anisotropic critical stress intensity factors are derived and compared for different crack orientations. A straightforward criterion that is proved to be applicable is used to distinguish brittle fracture from ductile fracture.

The influence of surface crack on the wear behavior of polyamide 66 under dry sliding condition

Abstract The effect of surface crack on the wear of polyamide66 sliding against steel counterface in dry condition was investigated in pin-on-plate reciprocating testing machine. The test rig was designed to perform wear tests under constant and fluctuating loading conditions at constant sliding speed for most of the stork. Effects of crack orientation, under different static and cyclic loading parameters, on wear behavior were examined. Relative change in wear rate due to surface crack existence, as well as crack orientation, was studied to provide understanding of surface fatigue wear. There was consistent evidence of the effect of surface crack on the wear rate under static and cyclic loading conditions. A single perpendicular crack on the rubbing surface results in high wear rate specially during running-in period. Polymer wear showed a higher sensitivity to surface crack under cyclic loads rather than static loads. The correlation between running-in wear and pre-existing surface cracks explained as a process of “ severe ” or “ progressive ” surface fatigue wear. Results of the present study provide a basis for assessing the fatigue wear resulting during the wearing-in period from pre-existing surface crack defect.

Mode III fracture of an arbitrary oriented crack in two dimensional functionally graded material

In this paper, a two dimensional functionally graded material (2D-FGM) under an anti-plane load with an internal crack is considered. The crack is oriented in an arbitrary direction. The material properties are assumed to vary exponentially in two planar directions. The problem is analyzed and solved by two different methods namely Fourier integral transforms with singular integral equation technique, and then by the finite element method. The effects of crack orientation, material non-homogeneity, and other parameters on the value of stress intensity factor (SIF) are studied. Finally, the obtained results for Mode III stress intensity factor of different methods are compared.

Mesh-Free Solution of Two-Dimensional Edge Crack Problems under Thermo-Mechanical Load

Abstract In this work, a mesh-free approach known as element free Galerkin method (EFGM) has been used to obtain the solution of two-dimensional edge crack problems in linear elastic fracture mechanics subjected to thermo-mechanical loads. The diffraction criterion has been modified with multiple crack weight technique to characterize the presence of all cracks in the domain of the influence of a node. The effect of crack orientation has been studied for two edge cracks lying on the same face as well as on opposite faces under plane stress conditions. The values of mode-I and mode-II stress intensity factors have been evaluated by domain based interaction integral approach. The results obtained by EFGM are compared with those obtained by finite element method.

Mode III arbitrarily oriented crack in an FGPM medium

This paper investigates the fracture behavior of an arbitrarily oriented crack in a functionally graded piezoelectric material subjected to antiplane mechanical and inplane electric loads. The material properties are assumed to vary exponentially. After applying the Fourier transform to the displacement and electrical potential, a system of singular integral equations is formulated and solved by applying the Gauss‐Chebyshev integration formula. The results show the effects of crack orientations and the nonhomogeneous material parameter on the stress and electrical displacement intensity factors.

Stress intensity factors for internally loaded crack in a composite plate subjected to arbitrary biaxial loading at infinity

The stress analysis of infinite anisotropic plate with openings is an interesting field of investigation. An attempt is made here to solve elastostatic problem of infinite laminated composite plate subjected to in-plane loading, with an arbitrarily oriented crack, using Muskhelishvili's complex variable formulation. The crack or part of it is subjected to internal pressure and/or internal shear. The stress intensity factors are obtained by evaluating Schwarz integral, for given boundary conditions. The generalised formulation is coded using MATLAB 6.5 and numerical results are obtained for graphite/epoxy and isotropic material. The plane-stress crack models are prepared in ANSYS for some of the cases and results are compared with the present method. The effect of crack orientation, crack length, loading pattern, fibre orientation and stacking sequence on stress intensity factors is studied.

Quantitative evaluation of crack orientation in aluminium plates based on Lambwaves

The forward- and back-scattering of Lamb waves by through-thickness cracks of varyinglength and orientation was studied by numerical simulation and experimental validation.Surface-bonded piezoelectric discs were arrayed as actuators and sensors to generate andcollect Lamb waves, respectively, and the effect of crack orientation on Lamb wavepropagation was evaluated. Lamb waves reflected and transmitted by cracks of finite sizewere assessed to obtain the reflection and transmission coefficients subject to crackorientation, with the aid of a Hilbert transform. Using this relationship, crack orientationwas quantitatively determined by evaluating the different amplitudes of energy peaks in theHilbert spectra. The distribution of scattered waves around a crack was further studied forthe circumstance of normal wave incidence. The limitation of the proposed technique foreffective damage identification based on forward analysis of wave scattering was alsodiscussed.

Impact initiation of explosives and propellants via statistical crack mechanics

A statistical approach has been developed for modeling the dynamic response of brittle materials by superimposing the effects of a myriad of microcracks, including opening, shear, growth and coalescence, taking as a starting point the well-established theory of penny-shaped cracks. This paper discusses the general approach, but in particular an application to the sensitivity of explosives and propellants, which often contain brittle constituents. We examine the hypothesis that the intense heating by frictional sliding between the faces of a closed crack during unstable growth can form a hot spot, causing localized melting, ignition, and fast burn of the reactive material adjacent to the crack. Opening and growth of a closed crack due to the pressure of burned gases inside the crack and interactions of adjacent cracks can lead to violent reaction, with detonation as a possible consequence. This approach was used to model a multiple-shock experiment by Mulford et al. [1993. Initiation of preshocked high explosives PBX-9404, PBX-9502, PBX-9501, monitored with in-material magnetic gauging. In: Proceedings of the 10th International Detonation Symposium, pp. 459–467] involving initiation and subsequent quenching of chemical reactions in a slab of PBX 9501 impacted by a two-material flyer plate. We examine the effects of crack orientation and temperature dependence of viscosity of the melt on the response. Numerical results confirm our theoretical finding [Zuo, Q.H., Dienes, J.K., 2005. On the stability of penny-shaped cracks with friction: the five types of brittle behavior. Int. J. Solids Struct. 42, 1309–1326] that crack orientation has a significant effect on brittle behavior, especially under compressive loading where interfacial friction plays an important role. With a reasonable choice of crack orientation and a temperature-dependent viscosity obtained from molecular dynamics calculations, the calculated particle velocities compare well with those measured using embedded velocity gauges.

Experimental Study on Fatigue Crack Growth in a Titanium Alloy

A series of test for the fatigue crack growth rate da/dN and the threshold ΔKth values were performed with CT specimens on a ship-condenser material titanium alloy plate and rolled ring. Base metal, welded joint and HAZ (heat affected zone) materials were used to make different test specimens. Specimens made from the titanium plate were cut along L-T direction, those made from rolled ring were obtained along C-R and L-R direction respectively. Results show that the fatigue crack growth rate value of welded joint is much higher than those of base metal and HAZ material. The da/dN values of C-R direction specimens are much higher than those of L-R direction specimens, whereas the ΔKth values are lower. It means that welding process may lead to a great reduction in the fatigue property for titanium alloy and the effect of crack orientation on fatigue property is not negligible for titanium alloy. To select a proper orientation of titanium material is therefore very important in engineering practice. Results also indicate that a simplified method can be used to calculate the ΔKth values for titanium material, that is, ΔKth values may be calculated directly from the da/dN expression in a zone near the threshold and the laborious measurements of ΔKth may therefore be saved.