Effect Of Crack Depth Research Articles

Creep crack growth analysis using C t -parameter for internal circumferential and external axial surface cracks in a pressurized cylinder

Creep crack growth at elevated temperatures is a critical consideration in estimating the remaining life of high temperature structural components and in deciding their inspection interval. In this study, creep crack growth analyses for external radial-axial and internal radial-circumferential surface cracks in a pressurized cylinder were conducted by an analytical method. The effect of crack depth and crack length on the variations in C t and remaining life predictions were investigated for surface cracks with various initial aspect ratios. It was observed that the remaining life of an internal radial-circumferential surface crack was approximately 53 times longer than that of an external radial-axial surface crack for the same crack size and loading conditions with 316 stainless steel material. It was also observed that the variations in remaining life, crack propagations, and the C t values were considerably sensitive to the crack location and crack depth. Convergence of crack aspect ratio was not observed when the crack depth ratio was increased. Since the method is independent of material properties and location of the crack geometries, it can be extended to various material properties and various locations of the surface crack geometries.

Nanoscale Sensors: Dramatically Enhanced Mechanosensitivity and Signal‐to‐Noise Ratio of Nanoscale Crack‐Based Sensors: Effect of Crack Depth (Adv. Mater. 37/2016)

Nanoscale Sensors: Dramatically Enhanced Mechanosensitivity and Signal‐to‐Noise Ratio of Nanoscale Crack‐Based Sensors: Effect of Crack Depth (Adv. Mater. 37/2016)

Nonlinear dynamics of an asymmetric rotor-bearing system with coupling faults of crack and rub-impact under oil-film forces

The parametric instability of a rotor-bearing system with coupling faults of crack and rub-impact under nonlinear oil-film force is studied in this paper. A model considering time-varying crack stiffness, rub-impact force and nonlinear oil-film force is put forward to analyze the complicated nonlinear behaviors of the rotor-bearing system. The numerical simulation focuses on the effects of crack depth and the stator stiffness on the onset of instability and nonlinear responses of the rotor-bearing system by using bifurcation diagrams, Poincare maps, largest Lyapunov exponent and frequency spectrum. The multiple periodic, quasiperiodic and chaotic motions are observed in this study. The results indicate that crack depth and stator stiffness have influences on the vibration and instability of the rotor-bearing system with varied rotating speed. The motion of the system with coupling faults shows strong nonlinearity and instability in high speed region. Moreover, crack depth and stator stiffness interfere with the formation of oil whirl, thus, making the oil whirl appear later. There also exists interaction among coupling multiple faults. The research discloses the worthy energy exchange phenomenon of multi-fault system and is helpful for fault diagnosis and vibration control of real rotor-bearing systems.

Dramatically Enhanced Mechanosensitivity and Signal-to-Noise Ratio of Nanoscale Crack-Based Sensors: Effect of Crack Depth.

The sensitivity of a nanoscale crack-based sensor is enhanced markedly by modulating the crack depth. The crack-depth-propagated sensor exhibits ≈16 000 gauge factor at 2% strain and a superior signal-to-noise ratio of ≈35, which facilitates detection of target signals for voice-pattern recognition.

Vibration Analysis of a Cracked Beam on an Elastic Foundation

The transverse vibrations of cracked beams with rectangular cross sections resting on Pasternak and generalized elastic foundations are considered. Both the Euler–Bernoulli (EB) and Timoshenko beam (TB) theories are used. The open edge crack is represented as a rotational spring whose compliance is obtained by the fracture mechanics. By applying the compatibility conditions between the beam segments at the crack location and the boundary conditions, the characteristic equations are derived, from which the nondimensional natural frequencies are solved as the roots. Sample numerical results showing the effects of crack depth, crack location, foundation type and foundation parameters on the natural frequencies of the beam are presented. It is observed that the existence of crack reduces the natural frequencies, whereas the elasticity of the foundation increases the stiffness of the system and thus the natural frequencies. It is also observed that the type of elastic foundation has a significant effect on the natural frequencies of the cracked beam.

Dependence of Thermal Shock Crack on Specimen Width for Ceramic Materials

Knowledge of size effect of thermal shock properties of ceramics is a prerequisite in engineering applications. In the present study, the size effect of the cracking in the ceramic materials subjected to water quenching has been experimentally conducted. Based on the Rizk model, the equivalent specimen width of the elastic strip with cracks is introduced and modified to describe the effect of cracks on the deformation of the elastic strip underwater quenching. It is found that the simulation obtained from the proposed modified model is in good agreement with the experimental results. And the reasons for the size effect of crack depth and crack growth into the compressive region are well analyzed by theoretical results. The proposed model is expected to provide a powerful tool to characterize and predict the size effect on thermal shock crack of ceramic materials.

Dynamic stability of cracked multi-bay frame structures

ABSTRACTThe effects of crack depth and crack location on the in-plane static and dynamic stability of cracked multi-bay frame structures subjected to periodic loading have been investigated numerically by using the finite element method. For the rectangular cross-section beam, a crack element is developed by using the principles of fracture mechanics. In addition, the effect of the number of spans and static and dynamic load parameters on static and dynamic stability analysis are also investigated. For buckling and dynamic stability analyses, the results obtained by using the present model are presented in three-dimensional graphical forms and tables.

Variation of Local Flexibility Coefficients of Functionally Graded Cracked Shaft

The present paper deals with the analytical determination of local flexibility coefficients (LFCs) for a functionally graded (FG) cracked shaft. Finite element (FE) analysis has been performed using two nodded beam element having six degrees of freedom (DOF) at each node and Timoshenko beam theory (TBT) has been used. Material properties are assumed to be graded in radial direction following linear, power law and exponential law gradation respectively. In the present analysis, the mixture of Aluminum Oxide (Al2O3) and Stainless Steel (SUS304) is considered as FG material where metal content is considered decreasing towards the outer diameter of shaft. The LFCs of a cracked shaft is derived using Castigliano's theorem and Paris's equations in conjunction with the expression for stress intensity factors. A complete code has been developed using MATLAB program and validated with the existing results available in literatures. The LFCs are calculated for different crack depths and for different crack closer lines for a cracked shaft and the effect of crack depth and crack closer line position on the LFCs has been studied. Numerical results reveal that for a given crack configuration, LFCs values are maximum for metallic, minimum for ceramic shaft and the LFCs for FG shaft in between, and also the LFCs values increase with the increasing power law gradient indices.

Dynamic Analysis of Elastically Supported Cracked Beam Subjected to a Concentrated Moving Load

This study deals with the dynamic behavior of a cracked beam subjected to a concentrated force traveling at a constant velocity. Dynamic analyses for a hinged-hinged cracked beam resting on elastic supports under the action of a moving load are carried out by the finite element method. For the beam having rectangular cross-section, element formulation for crack element is developed by using the principles of fracture mechanics. In the numerical analysis, Newmark integration method is employed in order to calculate the dynamic response of the beam. The effects of crack depth, crack location, elastic support and load velocity on the dynamic displacements calculated for different locations on the beam are investigated. The results related to the dynamic response of the beam are presented in 3D graphs.

Experimental Investigation of Vibration Analysis of Multi-Crack Rotor Shaft

In recent years, the dynamic behaviour and diagnostic of cracked rotor have been gained momentum. In literature, several studies are available for cracked rotor systems, however very few authors have addressed the issue of multi-cracked rotor system. This paper deals with the nonlinear dynamic behaviour of multi cracked rotor system, which is analyzed experimentally and analytically with the considerations of the effects of the crack depth, crack location and the shaft's rotational speed. A new extension of Lagrangian method is used for analyzing the dynamic behaviour of a multi-cracked rotor system through Umbra Lagrangian formalism. The effects of crack depth on the shaft's stiffness and natural frequencies are analyzed experimentally. Natural frequencies have been obtained through vibration analyzer using impact hammer test under static conditions. This analysis also includes the dynamic response of rotor with breathing crack by using data acquisition system called OROS. It has been noticed that the stress concentration on the first crack has increased due to the presence of the second crack. Another interesting phenomenon is the influence of one crack over the other crack for mode shapes and for threshold speed limits. All such analysis has been carried out on experimental test rig consist of a symmetrical system, which has mild steel shaft between a pair of identical self-aligned double groove high speed bearings. The experimental results can be further validated with the analytical results.

The Effect of Crack Geometry on the Nondestructive Fault Detection in a Composite Beam

Defects in structures may be inherited from materials and manufacturing or they develop during service. Defects may cause catastrophic failure, which is why their detection and classification are important issues. Many aspects of defects have already been dealt with, but with wider applications of non-destructive testing methods to composite materials. However, the effect of arbitrary and random defect geometry on the applicability of these methods has been overlooked. In order to investigate this issue, this study carries out a free vibration analysis of a specially orthotropic cracked cantilever beam that was manufactured by Pultrusion. A new crack model, unlike the widely known V-shaped crack, is introduced and the effect of crack depth on the natural frequency is investigated, both experimentally and numerically. The results obtained from both the newand the V-shaped models are compared with each other, and it is revealed that the results are not sensitive to the geometry change.

WES 2808 for Brittle Fracture Assessment of Steel Components under Seismic Conditions – Part V: Equivalent CTOD ratio for correction of constraint loss in beam-to-column connections

Crack-tip plastic constraint in beam-to-column connections with a surface crack 1) at the bottom of a conventional type of weld access hole and 2) at weld start/end points of butt welds to connect beam flange and diaphragm subjected to bending moment were analyzed by FEM. The equivalent CTOD ratio β used for engineering toughness correction for constraint loss for the beam-to-column connections are compared with those for the wide plate components with the same size of a crack subjected to tension load. Then, the analyses of β by means of the wide plate component, CSCP and ESCP, are conducted, and the crack depth effect on β is formulated with focusing on crack depth ratio a/t.

A loss of constraint assessment using σ*-V* approach to describe the effect of crack depth on reference transition temperature T0

The assessment of fracture behaviour of ferritic/ferritic martensitic steels in Ductile to Brittle Transition (DBT) region iscrucial for shallower cracks. In this work the fracture behavior of In-RAFM steels isinvestigated with systematically varying a/W using Master Curve approach. This a/W effect is investigated using σ*-V* approach by calculating the active volume at simulated crack front. It is observed that the fitting parameter of σ*-V* approach is in direct correlation with changing constraint parameter ΔTstress. The constraint effect with varying crack depth is also captured by a novel constraint parameter referred as Weibull triaxiality.

Safe burst strength of a pipeline with dent–crack defect: Effect of crack depth and operating pressure

A defect that contains both dent and crack, often known as dent–crack defect, may lead to a failure due to rupture or leak in the pipe wall. Hence, the pipeline operator becomes concerned about the performance and safety of the pipeline when a dent–crack defect is diagnosed. A research was recently completed at the Centre for Engineering Research in Pipelines, University of Windsor to study the effect of the crack depth on the safe pressure capacity (burst strength) of 30-inch diameter and API 5L X70 grade linepipe. This study found that the dent–crack defect with crack depth of 70% of wall thickness can reduce the pressure capacity by 55%. This paper discusses the test specimens, test setup, test procedure, test results, and data obtained from finite element analyses.

Residual static strength of cracked concrete-filled circular steel tubular (CFCST) T-joint

Concrete-filled circular t steel tubular joints (CFSTJs) in practice are frequently subjected to fluctuated loadings caused by wind, earthquake and so on. As fatigue crack is sensitive to such cyclic loadings, assessment on performance of CFSTJs with crack-like defect attracts more concerns because both high stress concentration at the brace/chord intersection and welding residual stresses along weld toe cause the materials in the region around the intersection to be more brittle. Once crack initiates and propagates along the weld toe, tri-axial stresses in high gradient around the crack front exist, which may bring brittle fracture failure. Additionally, the stiffness and the load carrying capacity of the CFSTJs with crack may decrease due to the weakened connection at the intersection. To study the behaviour of CFSTJs with initial crack, experimental tests have been carried out on three full-scale CFCST T-joints with same configuration. The three specimens include one uncracked joint and two corresponding cracked joints. Load-displacement and load-deformation curves, failure mode and crack propagation are obtained from the experiment measurement. According to the experimental results, it can be found that he load carrying capacity of the cracked joints is decreased by more than 10% compared with the uncracked joint. The effect of crack depth on the load carrying capacity of CFCST T-joints seems to be slight. The failure mode of the cracked CFCST T-joints represents as plastic yielding rather than brittle fracture through experimental observation.

Numerical Simulation of Stress Intensity Factor for Socket Weld Toe Cracks in Small Branch Pipes

Vibration fatigue of small branch pipes usually induces weld toe cracks. Some cracks will cause advertently shutdown of the Nuclear Power Plants (NPPs). Moreover, to judge the vibration fatigue failure is the bottle neck in structure health monitoring of the small branch pipes in NPPs. In order to solve this problem, a socket weld pipe was simplified as the cantilever beam model, and the stress intensity factor (SIF) was calculated by the ABAQUS software and ZENCRACK software in this paper. The effects of crack depth, circumferential crack size and working load on SIF were discussed. The analysis results show that the SIF for outer surface circumferential crack distributes as an upside down “U” alphabet. And the maximum value of SIF is at the deepest point of the crack and is a linear increasing function of external load P. Basing on the plane strain fracture criterion, critical crack sizes bearing different external loads were calculated. With the increasing of loads, the critical crack size decreases. These critical values can be applied as the benchmark for evaluating the vibration fatigue failure in the structure health monitoring of small branch pipes in NPPs.

Assessment of structural integrity of subsea wellhead system: analytical and numerical study

Subsea wellhead systems exposed to severe fatigue loading are becoming increasingly a significant problem in offshore drilling operations due to their applications in wells with higher levels of pressure and temperature, situated at larger depths and in harsher environments. This has led to a substantial increase in the weight and size of offshore equipment, which, in combination with different loading conditions related to the environmental factors acting on the vessel and riser, has greatly increased the loads acting on subsea well systems. In particular, severe fatigue loading acting on the subsea wellhead system was detected. For this reason, a combined analytical and numerical study investigating the critical effect of crack depth on the overall structural integrity of subsea wellhead systems under cyclic loading was carried out. The study is based on a Linear Elastic Fracture Mechanics (LEFM) approach.

The use of roving discs and orthogonal natural frequencies for crack identification and location in rotors

A variety of approaches that have been developed for the identification and localisation of cracks in a rotor system, which exploit natural frequencies, require a finite element model to obtain the natural frequencies of the intact rotor as baseline data. In fact, such approaches can give erroneous results about the location and depth of a crack if an inaccurate finite element model is used to represent an uncracked model. A new approach for the identification and localisation of cracks in rotor systems, which does not require the use of the natural frequencies of an intact rotor as a baseline data, is presented in this paper. The approach, named orthogonal natural frequencies (ONFs), is based only on the natural frequencies of the non-rotating cracked rotor in the two lateral bending vibration x–z and y–z planes. The approach uses the cracked natural frequencies in the horizontal x–z plane as the reference data instead of the intact natural frequencies. Also, a roving disc is traversed along the rotor in order to enhance the dynamics of the rotor at the cracked locations. At each spatial location of the roving disc, the two ONFs of the rotor–disc system are determined from which the corresponding ONF ratio is computed. The ONF ratios are normalised by the maximum ONF ratio to obtain normalised orthogonal natural frequency curves (NONFCs). The non-rotating cracked rotor is simulated by the finite element method using the Bernoulli–Euler beam theory. The unique characteristics of the proposed approach are the sharp, notched peaks at the crack locations but rounded peaks at non-cracked locations. These features facilitate the unambiguous identification and locations of cracks in rotors. The effects of crack depth, crack location, and mass of a roving disc are investigated. The results show that the proposed method has a great potential in the identification and localisation of cracks in a non-rotating cracked rotor.

Effect of Load Angle on Limit Load of Polyethylene Miter Pipe Bends1

The aim of this paper is to investigate the effect of crack depth a/W = 0–0.4 and load angle (30 deg, 45 deg, and 60 deg) on the limit load of miter pipe bends (MPB) under out-of-plane bending moment with a crosshead speed 500 mm/min. The geometry of cracked and un-cracked multi miter pipe bends are: bend angle, α = 90 deg, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene (HDPE), which is applied in natural gas piping systems. Butt-fusion welding is used to produce the welds in the miter pipe bends. An artificial crack is produced by a special cracking device. The crack is located at the crown side of the miter pipe bend, such that the crack is collinear with the direction of the applied load. The crack depth ratio, a/W = 0, 0.1, 0.2, 0.3, and 0.4 for out-of-plane bending moment “i.e., loading angle ϕ = 0 deg”. For each out-of-plane bending moment and all closing and opening load angles the limit load is obtained by the tangent intersection method (TI) from the load deflection curves produced by the specially designed and constructed testing machine at the laboratory (Mechanical Design Department, Faculty of Engineering, Mataria, Helwan University, Cairo/Egypt). For each out-of-plane bending moment case, the experimental results reveals that increasing crack depth leads to a decrease in the stiffness and limit load of MPB. In case of combined load (out-of-plane and in-plane opening; mode) higher load angles lead to an increase in the limit load. The highest limit load value appears at a loading angle equal, ϕ = 60 deg. In case of combined load (out-of-plane and in-plane closing; mode) the limit load decreases upon increasing the load angle. On the other hand, higher limit load values appear at a specific loading angle equal ϕ = 30 deg. For combined load opening case; higher values of limit load are obtained. Contrarily, lower values are obtained in the closing case.

Fault Feature Analysis of a Cracked Gear Coupled Rotor System

Considering the misalignment of gear root circle and base circle and accurate transition curve, an improved mesh stiffness model for healthy gear is proposed, and it is validated by comparison with the finite element method. On the basis of the improved method, a mesh stiffness model for a cracked gear pair is built. Then a finite element model of a cracked gear coupled rotor system in a one-stage reduction gear box is established. The effects of crack depth, width, initial position, and crack propagation direction on gear mesh stiffness, fault features in time domain and frequency domain, and statistical indicators are investigated. Moreover, fault features are also validated by experiment. The results show that the improved mesh stiffness model is more accurate than the traditional mesh stiffness model. When the tooth root crack appears, distinct impulses are found in time domain vibration responses, and sidebands appear in frequency domain. Amplitudes of all the statistical indicators ascend gradually with the growth of crack depth and width, decrease with the increasing crack initial position angle, and firstly increase and then decrease with the growth of propagation direction angle.