Effect Of Crack Orientation Research Articles

Finite element analysis of macro-crack behavior in the cortical bone of a human tibia

The bone is a biological tissue that possesses a highly complicated hierarchical structure; hence, the tissue components of the bone exhibit variable mechanical proper-ties and a complex bone geometry. This is why the creation of a three-dimensional mod-el through CAD software facilitates the study of the mechanical behavior of bones. Com-bining the concepts of linear elastic fracture mechanics and finite element analysis pro-vides a practical solution to study the fracture behavior of the tibial bone. The objective of this study is to analyze the behavior of cracks in the cortical bone of the human tibia us-ing stress intensity factors in mode I, II, and III as rupture criteria to assess the bone damage response. The tibial bone is one of the most common sites for lower limb stress fractures, which pose problematic injuries. The results investigating the effect of the crack position in the bone demonstrate that the risk of crack propagation is mainly due to mode I opening and is highly favored in the distal zone compared to the middle and proximal regions, regardless of bone density. For the second case study, it is observed that regardless of the crack size, the maximum values of stress intensity factors KI are obtained in the distal zone. Regarding the effect of crack orientation, the results indicate the dominance of mode II for angles α = – 45°, 30°, 45°, leading to high values of stress intensity factors KII.

The effect of crack orientation on the mode I fracture resistance of pinewood

AbstractThe fracture resistance of pinewood under mode I loading is investigated experimentally for different crack plane orientations and the crack propagation direction parallel to longitudinal cells. Experiments are conducted on double cantilever beams using a digital image correlation system to evaluate the crack tip opening displacement. The compliance based beam method is used to determine the energy release rate at various crack lengths. The decomposition of crack propagation into the pre-peak and post-peak propagations is proposed to find the fracture energy contributions from individual toughening mechanisms in pinewood. The cohesive strengths measured in the experiments are confirmed by comparison with the tensile strengths obtained from separate tests performed on pinewood. An analytical model for evaluating the fracture process zone is used to validate the experimental results. The difference between the fracture energy values in different crack propagation systems is explained by using X-ray microtomography images of the fracture surfaces.

The method for the estimation of fracture toughness of thin-walled metallic tube considering the effect of crack orientation

Thin-walled metallic tubes are very susceptible to axial or circumferential cracks in harsh environments such as high temperature, high pressure, and severe corrosion, which seriously endangers the service safety of thin-walled tubes. Fracture toughness is an essential mechanical property index for evaluating the service safety of thin-walled metallic tubes, and its special thin-walled structure cannot be tested by using the specimens with standard configuration. In this work, based on the principle of energy density equivalence, the load–displacement and J-integral expressions of thin-walled metallic tubes with axial and circumferential cracks are proposed, and the fracture toughness test method of thin-walled metallic tubes with axial and circumferential cracks is established. Typical zircaloy cladding tubes were selected to complete the fracture test, and the influence of crack orientation on their fracture properties was investigated. The results show that the fracture toughness of circumferential cracks is lower than that of axial cracks, the circumferential cracks also face the risk of fracture failure, and the estimation of fracture properties of the cladding tubes with circumferential cracks cannot be simply replaced by axial cracks.

Effect of crack orientation on bacterial self-healing of bio-mortar in marine environment

The impact of crack orientation on healing in conventional mortar and bacteria-based bio-mortars was assessed under submerged marine conditions. The bacteria-based bio-mortar was prepared using Halobacillus Halophilus bacteria, expanded perlite aggregates and calcium lactate. Cracks were divided into five groups based on their orientation. Upward-faced and side-faced horizontal cracks in conventional mortar showed maximum overall healing of 77 %–90 % for the analysed crack range. Downward-faced and side-faced vertical cracks had three and four times less autogenous healing than upward-faced cracks, respectively; however, their healing doubled with the addition of bacteria. The variation in healing performance with orientation was explained by differences in the deposition of healing products under gravity. Additionally, healing products were also found within the cross-section of cracks in horizontally-placed bacteria-based specimens. Although their formation initiated away from the centre, after 35 days of exposure, the maximum healing was observed close to the centre spreading to the top surface of these bio-mortar specimens. These outcomes imply that results in literature must be carefully interpreted. This phenomenon of healing dependency on crack orientation is rarely studied and might have unknowingly affected the interpretation of the results in previous studies.

Effective elastic properties and S-wave anisotropy for rocks containing any oriented penny-shaped cracks in transversely isotropic background

Fractures have a significant influence on rock elastic properties. The existing elastic models for cracked medium mainly consider the crack dip angle. In this work, based on the previous transversely isotropic (TI) background and arbitrary dip crack model, a theoretical model is derived using the Bond transform matrix to quantify the effects of any oriented penny-shaped cracks on the elastic properties of rocks with a TI background. Based on this model, the effects of crack orientation on rock elastic properties are studied. Particularly, a special case with random crack orientation is investigated by using the spherical averaging of the crack compliance matrix with any orientations. Furthermore, the S-wave anisotropy for rocks containing multiple crack sets also is analyzed. The results indicate that the crack orientation has a great influence on rock elastic properties. Especially, the rock elastic properties indicate nonlinear changes with crack azimuth angles when cracks are inclined with respect to the TI background isotropic plane. The randomly oriented cracks decrease the overall rock elastic moduli but have little effect on rock anisotropy. For rocks containing multiple crack sets, parallel crack sets have great effects on the S-wave anisotropy, whereas the effects of orthogonal crack sets are negligible. Using this model, a complete workflow for the inversion of fracture properties using field data measured by acoustic logging is introduced. To explain the effect of crack azimuth angle, the crack density is inverted without considering crack orientation, only considering crack dip angle, and considering both crack dip and azimuth angles. The results indicate that the inversion results considering the crack dip and azimuth angles are in good agreement with the resistivity imaging results. This work provides the theoretical basis for fracture properties inversion for rocks with a TI background.

Effect of Crack Orientation on Laminated CFRP Composites Using Vibration and Numerical Analysis

Crack orientation, a critical parameter, significantly affects the dynamic properties of composite structures. Experimental free vibration tests were conducted on carbon fiber–reinforced polymer (CFRP) composite plates at room temperature with different crack orientations. Dynamic properties such as damping ratio, natural frequency, and storage modulus were measured using a four-channel dynamic pulse analyzer. Multi-sensors were mounted on the test plate to pick up the vibration signals. Experimental modal analysis was performed to identify the first three mode shapes of the defective plates. A numerical model using ANSYS software was developed via parametric investigation to predict the correlation between crack orientation and resonant frequencies with corresponding mode shapes. The orientation of the introduced cracks had a significant effect on the dynamic properties of CFRP composites. Vertical cracks had the most significant influence on the eigenvalues of the mode shape frequencies. Furthermore, the damping ratio was an effective method to detect the cracks in CFRP composites.

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.

Influence of Different Crack Factors on Acoustic Wave Signals Using Orthogonal Analysis

The existence of cracks in key components of engineering equipment is a huge threat to the safe operation of the equipment. The influence of four factors (length, location, orientation, and width of the crack) on the attenuation characteristic of signal propagation is studied through simulation and experiment. The orthogonal experimental design is applied to design the simulation scheme, and the signal affected by the four factors is simulated by the finite-difference time-domain method. The degree of influence of the different factors is evaluated by conducting an analysis of range and an analysis of variance. The results show that the influence of crack length and location on signal relative attenuation is more remarkable according to the significance level α = 0.05, followed by crack orientation and crack width. The attenuation trend in the experimental results is similar to the simulation. Therefore, the longer the crack length is, the easier it is to be detected by the acoustic wave technique, while the effect of crack orientation and crack width on identifying cracks is limited. The study successfully establishes the relationship between signal parameters and crack factors and offers a theoretical foundation for evaluating the status of cracks in key components.

Effects of crack orientation and heat treatment on fatigue-crack-growth behavior of AM 17-4 PH stainless steel

The effects of heat treatment and crack orientation on fatigue-crack-growth (FCG) behavior of 17-4 precipitation hardening (PH) stainless steel (SS) fabricated via a laser powder bed fusion (LPBF) additive manufacturing (AM) system were investigated. Accurate representation of FCG thresholds, the region defining crack growth as either very slow or nonexistent, is extremely important in adoption of AM for structural applications. In this study, new methods called compression pre-cracking constant-amplitude (CPCA) and load-reduction (CPLR) were used to generate FCG rate data in the near-threshold (low-rate) regime using non-standard or modified compact specimens. For comparison, the current ASTM load-reduction (LR) method was also used. Results indicate that FCG behavior of AM 17-4 PH SS in the Paris regime was comparable to that of wrought 17-4 PH SS in the peak-age condition. Although the post-manufacturing heat treatment was found to be necessary in order to improve tensile strength of this alloy, the results of this study indicate that this particular heat treatment process had no influence on FCG behavior of LPBF 17-4 PH SS. The effect of crack orientation with respect to the build direction however was evident. FCG rates were slightly lower for specimens with a crack parallel to the build direction (i.e. longitudinal crack) in the Paris regime as compared to that of specimens with a perpendicular crack (i.e. transverse crack). The near-threshold FCG behavior for specimens with a longitudinal crack did not show the usual stress ratio (R)-shift from low to high R. The low-R data was vastly different than the data generated using the specimens with a transverse crack. Our results also imply that both the current ASTM standard LR method and the new CPLR method induce remote closure, which prematurely slows down crack growth and produces an abnormally high threshold.

A Study of the Automated Eddy Current Detection of Cracks in Steel Plates

Applying life estimation approaches to determine in-service life of structures and plan the inspection schedules accordingly are becoming acceptable safety design procedures in aerospace. However, these design systems shall be fed with reliable parameters related to material properties, loading conditions and defect characteristics. In this context, the role of non-destructive (NDT) testing reliability is of high importance in detecting and sizing defects. Eddy current test (ECT) is an electromagnetic NDT method frequently used to inspect tiny surface fatigue cracks in sensitive industries. Owing to the new advances in robotic technologies, there is a trend to integrate the ECT into automated systems to perform NDT inspections more efficiently. In fact, ECT can be effectively automated as to increase the coverage, repeatability and scanning speed. The reliability of ECT scanning, however, should be thoroughly investigated and compared to conventional modes of applications to obtain a better understanding of the advantages and shortcomings related to this technique. In this contribution, a series of manual and automated ECT tests are carried out on a set of samples using a split-D reflection differential surface probe. The study investigates the level of noise recorded in each technique and discuss its dependency on different parameters, such as surface roughness and frequency. Afterwards, a description of the effect of crack orientation on ECT signal amplitude is provided through experimental tests and finite element simulations. Finally, the reliability of each ECT technique is investigated by means of probability of detection (POD) curves. POD parameters are then extracted and compared to examine the effect of scanning index, frequency and automation on detection reliability.

P.406 Intrinsically disordered regions of synapsin hold together synaptic vesicles of the reserve pool in a living synapse

A novel computational methodology is proposed in this work to simulate the nonlinear hydro-mechanical process in saturated porous media containing crossing fractures. Specifically, the weak form of mechanical coupling and mass transfer equations is derived based on Biot’s theory and lubrication theory, respectively. The weak discontinuity for pressure field around T-shaped crack is described by a new junction enrichment function. The nonlinear hydro-mechanical coupled equations are obtained by Extended Finite Element Method (XFEM) discretization and solved by Newton-Raphson method. This proposed computational model is verified by comparing numerical results with analytical solution. The robustness of this numerical method is demonstrated by several examples. The effects of crack orientation, matrix stiffness, and confining stress on the equivalent permeability of fractured porous medium are investigated. Numerical results indicate that the interaction of cracks plays a critical role on the hydro-mechanical behavior of the saturated porous media containing crossing fractures.

Effect of Crack Orientation on Fatigue Life of Reinforced Concrete Bridge Decks

In visual inspection of bridges at sites, much attention is given to the density and width of cracks of concrete, but little attention is paid to crack orientation for the diagnosis of bridge performance. In this research, the effect of crack orientation on the remaining fatigue life of reinforced concrete (RC) bridge decks is investigated for crack patterns with a wide range of possible crack orientations. The data assimilation technology of multi-scale simulation and the pseudo-cracking method, which are widely validated for fatigue-lifetime simulation, are utilized in this study. The impact of the crack direction on fatigue life is found to be associated with the coupled flexure-shear mode of failure, and the mechanism to arrest shear cracking by preceding cracks is quantitatively estimated. This mechanism is similar to the stop-hole to prevent fatigue cracks in steel structures, and it enables us to enhance the fatigue life of RC decks. It is demonstrated that the crack orientations that approximate the longitudinal and transverse directions of RC decks are the ones that most extend remaining fatigue life. Finally, the higher risk cracking locations on the bottom surface of RC decks are discussed, presenting information of use to site inspectors.

Extended finite element modeling nonlinear hydro-mechanical process in saturated porous media containing crossing fractures

A novel computational methodology is proposed in this work to simulate the nonlinear hydro-mechanical process in saturated porous media containing crossing fractures. Specifically, the weak form of mechanical coupling and mass transfer equations is derived based on Biot’s theory and lubrication theory, respectively. The weak discontinuity for pressure field around T-shaped crack is described by a new junction enrichment function. The nonlinear hydro-mechanical coupled equations are obtained by Extended Finite Element Method (XFEM) discretization and solved by Newton-Raphson method. This proposed computational model is verified by comparing numerical results with analytical solution. The robustness of this numerical method is demonstrated by several examples. The effects of crack orientation, matrix stiffness, and confining stress on the equivalent permeability of fractured porous medium are investigated. Numerical results indicate that the interaction of cracks plays a critical role on the hydro-mechanical behavior of the saturated porous media containing crossing fractures.

A simple finite element method for elliptic bulk problems with embedded surfaces

In this paper, we develop a simple finite element method for simulation of embedded layers of high permeability in a matrix of lower permeability using a basic model of Darcy flow in embedded cracks. The cracks are allowed to cut through the mesh in arbitrary fashion and we take the flow in the crack into account by superposition. The fact that we use continuous elements leads to suboptimal convergence due to the loss of regularity across the crack. We therefore refine the mesh in the vicinity of the crack in order to recover optimal order convergence in terms of the global mesh parameter. The proper degree of refinement is determined based on an a priori error estimate and can thus be performed before the actual finite element computation is started. Numerical examples showing this effect and confirming the theoretical results are provided. The approach is easy to implement and beneficial for rapid assessment of the effect of crack orientation and may for example be used in an optimization loop.

Effects of crack orientation on the fatigue crack growth rate and fracture toughness of AA6063 alloy deformed by ECAP

In this study, effects of crack plane orientation on the fatigue crack growth rate and fracture toughness of 6063 aluminum alloy deformed by equal channel angular pressing (ECAP) were investigated. The ECAP process continued up to five passes without failure. Grain refinement was obvious after five passes of the ECAP process. Textural studies showed aligning the grains in known directions. After four passes, yield and ultimate strengths increase respectively from 90 MPa and 209 MPa to 300MPa and 375 MPa and also reduction in elongation was observed. The roughness decreased after the process. The fatigue crack growth rate was investigated at different load ranges with the same load ratio for different orientations. The crack growth rate increased after one pass of the ECAP process. After five passes, the AA6063 shows a lower crack growth rate in compared with as-received material. The fracture toughness of mode I and mixed-mode for different orientations were measured. The results showed that the orientation has a significant effect on the fatigue crack growth and fracture toughness of the ECAPed samples. The fracture surfaces were studied using scanning electron microscope (SEM) and refined equiaxed dimples were observed after the ECAP process.

The Propagation Behavior of Collinear Cracks under Compression

In this paper, brittle materials with three collinear discrete cracks under compression have been studied, and a corresponding fracture condition has been proposed. In order to exam the effectiveness of the fracture condition and investigate the factors that control crack initiation and propagation, experiment study by using cement mortar and sandstone specimens with three collinear cracks has been implemented, and the effects of crack orientations, the distance between two cracks and the confining stresses have been investigated. The test results agree well with the fracture condition proposed in this paper.

Effect of crack orientation on vibration characteristics of partially cracked FGM plate: An analytical approach

A nonlinear analytical model for vibration analysis of partially cracked thin FGM plate as affected by the crack orientation, crack length and plate aspect ratio is presented. The proposed analytical model is based on the Kirchhoff’s classical plate theory. A single partial crack located at the centre and at an arbitrary orientation is considered in a FGM plate. The crack is in the form of a continuous line and the line spring model is used to incorporate it’s effect in the form of moment and in-plane forces. Berger’s formulation is used to introduce the non linearity in the model while the Galerkin’s method is used for obtaining the solution of the governing differential equation. Results for the fundamental frequencies as affected by the plate aspect ratio, gradient index, crack orientation and crack length is presented for all edges simply supported boundary condition. It is found that the crack orientation affects the fundamental frequencies of the partially cracked FGM plates.

The effect of crack orientation on the nonlinear interaction of a P wave with an S wave

AbstractCracks, joints, fluids, and other pore‐scale structures have long been hypothesized to be the cause of the large elastic nonlinearity observed in rocks. It is difficult to definitively say which pore‐scale features are most important, however, because of the difficulty in isolating the source of the nonlinear interaction. In this work, we focus on the influence of cracks on the recorded nonlinear signal and in particular on how the orientation of microcracks changes the strength of the nonlinear interaction. We do this by studying the effect of orientation on the measurements in a rock with anisotropy correlated with the presence and alignment of microcracks. We measure the nonlinear response via the traveltime delay induced in a low‐amplitude P wave probe by a high‐amplitude S wave pump. We find evidence that crack orientation has a significant effect on the nonlinear signal.

Effect of crack orientation on fatigue behavior of CFRP-strengthened steel plates

The introduction of carbon fiber reinforced polymer (CFRP) with higher Young’s modulus has broadened its application to the strengthening of steel structures, especially under fatigue loading. Most research on CFRP strengthening of steel under fatigue loading has focused on tension fatigue testing, assuming that cracks or crack-like defects propagate in pure tension mode. However, the complex details and welded connections in aging metallic structures may contain cracks orientated randomly with respect to the loading direction. This paper aims to extend the current knowledge of CFRP strengthening of steel elements in tensile fatigue loading to the case of mixed tension and shear loading. Steel plates were artificially cracked from a central hole at six different angles (10°–90°) with respect to the loading axis. Each crack angle represents a certain degree of mode mixity. Ultra-high modulus CFRP was used for strengthening in this study. Twelve specimens were strengthened with two CFRP patching configurations. Six unrepaired specimens were tested to act as control specimens. A shifting phenomenon was identified to describe the influence of mixed mode in terms of crack propagation. A mixed mode modification factor was developed to estimate the fatigue life of CFRP-strengthened steel plates with inclined initial cracks.

Numerical modeling of two-phase fluid flow in deformable fractured porous media using the extended finite element method and an equivalent continuum model

In the present paper, a numerical model is developed based on a combination of the extended finite element method and an equivalent continuum model to simulate the two-phase fluid flow through fractured porous media containing fractures with multiple length scales. The governing equations involve the linear momentum balance equation and the flow continuity equation for each fluid phase. The extended finite element method allows for an explicit and accurate representation of cracks by enriching the standard finite element approximation of the field variables with appropriate enrichment functions, and captures the mass transfer between the fracture and the matrix. Due to the high computational cost of X-FEM, this technique is only used to model large fractures. The pre-existing short fractures, which are distributed randomly in the porous medium, contribute to the increase of the effective permeability tensor and are modeled with an equivalent continuum model. Finally, the robustness of the proposed computational model is demonstrated through several numerical examples, and the effects of crack orientation, capillary pressure function, solid skeleton deformation, and existence of short cracks on the pattern of fluid flow are investigated. It is shown that the developed model provides a correct prediction of flow pattern for different crack configurations.