Analysis of Crack Growth in a 3D Voronoi Structure: A Model for Fatigue in Low Density Trabecular Bone

2002 ◽  
Vol 124 (5) ◽  
pp. 512-520 ◽  
Author(s):  
A. M. Makiyama ◽  
S. Vajjhala ◽  
L. J. Gibson
Keyword(s):  
Fatigue Life ◽  
Relative Density ◽  
Trabecular Bone ◽  
Crack Growth ◽  
Three Dimensional ◽  
Crack Size ◽  
Initial Crack ◽  
Low Density ◽  
Cycle Fatigue ◽  
Crack Growth Model

Both creep and crack growth contribute to the reduction in modulus associated with fatigue loading in bone. Here we simulate crack growth and subsequent strut failure in fatigue in an open-cell, three-dimensional Voronoi structure which is similar to that of low density, osteoporotic bone. The model indicates that sequential failure of struts leads to a precipitous drop in modulus: the failure of 1% of the struts leads to about a 10% decrease in modulus. A parametric study is performed to assess the influence of normalized stress range, relative density, initial crack size, crack shape and cell geometry on the fatigue life. The fatigue life is most sensitive to the relative density and the initial crack length. The results lead to a quantitative expression for the fatigue life associated with crack growth. Data for the fatigue life of trabecular bone are compared with the crack growth model described in this paper, as well as with a previous model for creep of a three-dimensional Voronoi structure. In our models, creep dominates the fatigue behavior in low cycle fatigue while crack growth dominates in high cycle fatigue, consistent with previous observations on cortical bone. The large scatter in the trabecular bone fatigue data make it impossible to identify a transition between creep dominated fatigue and crack growth dominated fatigue. The parametric study of the crack growth model indicates that variations in relative density among specimens, initial crack size within trabeculae and crack shape could easily produce such variability in the test results.

An Equivalent Creep Crack Growth Model for Probabilistic Life Prediction of Plastic Pipe Materials

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Yuhao Wang ◽  
Tishun Peng ◽  
Ernest Lever ◽  
Yongming Liu
Keyword(s):  
Experimental Data ◽  
Crack Growth ◽  
Growth Model ◽  
Life Prediction ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Crack Size ◽  
Initial Crack ◽  
Local Geometry ◽  
Crack Growth Model

Abstract Life prediction in energy infrastructure such as gas pipelines is important to maintain the integrity of such systems. This paper explores a life prediction model for polyethylene materials in natural gas distribution pipelines under creep damage. The model uses a power law equation to describe the crack growth rate and an asymptotic solution for the stress intensity factor (SIF) calculation considering local geometry variations. The SIF solution considers the effect of stress concentration introduced by common damages in pipes such as rock impingement and slit. An effective initial crack size model is proposed for the life prediction of plastic pipes considering the intrinsic initial defect. Large loading-induced plastic deformation is included by a correction factor in the crack growth model. The model is calibrated and validated using experimental data on Aldyl-A pipes with different types of damage. Due to the stochastic nature of the crack growth process, uncertainty quantification is performed, and Monte Carlo (MC) simulation is used to estimate the failure probability. The predicted probabilistic life distributions under different loading conditions are compared with the experimental data. Some conclusions and future work are drawn based on the proposed study and experimental validation.

Proof-Test-Based Life Prediction of High-Toughness Pressure Vessels

1996 ◽  
Vol 118 (1) ◽  
pp. 86-94 ◽  
Author(s):  
T. L. Panontin ◽  
M. R. Hill
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Life Prediction ◽  
Crack Size ◽  
Initial Crack ◽  
Pressure Vessels ◽  
Operating Pressure ◽  
High Toughness

The paper examines the problems associated with applying proof-test-based life prediction to vessels made of high-toughness metals. Two A106 Gr B pipe specimens containing long, through-wall, circumferential flaws were tested. One failed during hydrostatic testing and the other during tension-tension cycling following a hydrostatic test. Quantitative fractography was used to verify experimentally obtained fatigue crack growth rates and a variety of LEFM and EPFM techniques were used to analyze the experimental results. The results show that: plastic collapse analysis provides accurate predictions of screened (initial) crack size when the flow stress is determined experimentally; LEFM analysis underestimates the crack size screened by the proof test and overpredicts the subsequent fatigue life of the vessel when retardation effects are small (i.e., low proof levels); and, at a high proof-test level 2.4 × operating pressure), the large retardation effect on fatigue crack growth due to the overload overwhelmed the deleterious effect on fatigue life from stable tearing during the proof test and alleviated the problem of screening only long cracks due to the high toughness of the metal.

Fatigue Life Analyses and Tests for Thick-Wall Cylinders Including Effects of Overstrain and Axial Grooves

1995 ◽  
Vol 117 (3) ◽  
pp. 222-226 ◽  
Author(s):  
J. H. Underwood ◽  
A. P. Parker
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Good Description ◽  
Crack Size ◽  
Initial Crack ◽  
Thick Wall ◽  
Inner Diameter ◽  
Life Analysis ◽  
Fatigue Life Analysis ◽  
Laboratory Life

A fracture mechanics-based fatigue life analysis was developed for overstrained, pressurized thick-wall cylinders with one or several semi-elliptical-shaped axial grooves at the inner diameter. The fatigue life for a crack initiating at the root of the groove was calculated for various cylinder, groove, and crack configurations and for different material yielding conditions. Comparisons were made with fatigue crack growth and laboratory life results from A723 thick-wall cylinders, in which cannon firing tests were first performed to produce axial erosion grooves, followed by cyclic hydraulic pressurization to failure in the laboratory. The life analysis, with an initial crack size based on the expected preexisting defects, gave a good description of the crack growth and fatigue life of the tests for cylinders with and without grooves. General fatigue life calculations summarized important material and configurational effects on the fatigue life design of overstrained cylinders, including effects of material yield strength, cylinder diameter ratio, stress concentration factor, and initial crack size.

Fatigue Damage Analysis on Crack Growth and Fatigue Life of Welded Bridge Members with Initial Crack

2006 ◽  
Vol 324-325 ◽  
pp. 251-254 ◽  
Author(s):  
Tai Quan Zhou ◽  
Tommy Hung Tin Chan ◽  
Yuan Hua
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Initial Crack ◽  
Traffic Loading

The behavior of crack growth with a view to fatigue damage accumulation on the tip of cracks is discussed. Fatigue life of welded components with initial crack in bridges under traffic loading is investigated. The study is presented in two parts. Firstly, a new model of fatigue crack growth for welded bridge member under traffic loading is presented. And the calculate method of the stress intensity factor necessary for evaluation of the fatigue life of welded bridge members with cracks is discussed. Based on the concept of continuum damage accumulated on the tip of fatigue cracks, the fatigue damage law suitable for steel bridge member under traffic loading is modified to consider the crack growth. The proposed fatigue crack growth can describe the relationship between the cracking count rate and the effective stress intensity factor. The proposed fatigue crack growth model is then applied to calculate the crack growth and the fatigue life of two types of welded components with fatigue experimental results. The stress intensity factors are modified by the factor of geometric shape for the welded components in order to reflect the influence of the welding type and geometry on the stress intensity factor. The calculated and measured fatigue lives are generally in good agreement, at some of the initial conditions of cracking, for a welded component widely used in steel bridges.

Mode-II Fatigue Crack Growth Model from Shear-Type Low Cycle Fatigue Properties

2016 ◽  
Vol 853 ◽  
pp. 15-21
Author(s):  
Kai Kai Shi ◽  
Li Xun Cai ◽  
Shuang Qi ◽  
Chen Bao
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Model Verification ◽  
Fatigue Properties ◽  
Mode Ii ◽  
Cycle Fatigue ◽  
Shear Type ◽  
Crack Growth Model

The inherent law between fatigue behaviors of shear-type representative volume element and mode-II fatigue crack growth is found in the range of cycle plastic zone near the crack tip. Prediction model for mode-II fatigue crack growth rate is then proposed by utilizing shear-type low cycle fatigue properties, plastic strain energy criterion, and effective cycle stress-strain field. Experimental data of two Aluminum alloys, 2024-T351 and 7075-T6, are used for the model verification. Good agreement between experimental and theoretical results is obtained.

Analysis on Low Cycle Fatigue Life and Fatigue Fracture Surface Morphology of TC25 Titanium Alloy

2016 ◽  
Vol 697 ◽  
pp. 652-657
Author(s):  
Rong Guo Zhao ◽  
Yi Yan ◽  
Yong Zhou Jiang ◽  
Xi Yan Luo ◽  
Qi Bang Li ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Fracture Surface ◽  
Crack Growth ◽  
Fatigue Fracture ◽  
Low Cycle Fatigue ◽  
Observation System ◽  
Cycle Fatigue ◽  
Stress Strain

At room temperature, the low cycle fatigue tests for smooth specimens of TC25 titanium alloy under various stress ranges are operated at a CSS280I-20w Electro Hydraulic Servo Universal Testing Machine with a microscopic observation system, and the low cycle fatigue lifetimes are measured. Based upon the analysis of stress-strain hysteresis loop of low cycle fatigue of TC25 titanium alloy, a simplified Manson-Coffin formula is derived according to both the experimental characteristics and the stress-strain constitutive model, the fatigue lifetimes are plotted against stress ranges, and a stress-fatigue life curve for TC25 titanium alloy is obtained by the linear regression analysis method. Finally, the fracture surface morphologies of TC25 specimens are investigated using a JSM-6360 Scanning Electron Microscopy, and the fatigue fracture mechanisms of low cycle fatigue are studied. It shows that the plastic deformations are mainly formed at the accelerated fracture stage, and various shear lips can be observed on the fracture surfaces, which demonstrates that the shear stress results in the final rupture of TC25 titanium alloy. During the fracture of low cycle fatigue, the cleavage nucleation leads to the formation of fatigue crack initiation region, the fatigue crack growth exhibits a mixed transgranular and intergranular crack growth mode, and in the final rupture region, the fracture surface of low cycle fatigue of TC25 titanium alloy appears as a typical semi-brittle fracture mode.

Life Prediction of Solder Joints by Damage and Fracture Mechanics

1996 ◽  
Vol 118 (4) ◽  
pp. 193-200 ◽  
Author(s):  
S. H. Ju ◽  
B. I. Sandor ◽  
M. E. Plesha
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Damage Mechanics ◽  
Solder Joints ◽  
Continuum Damage Mechanics ◽  
Computer Time ◽  
Initial Crack ◽  
Continuum Damage ◽  
Growth Path

Much research has been done on Surface Mount Technology (SMT) using the Finite Element Method (FEM). Little of this, however, has employed fracture mechanics and/or continuum damage mechanics. In this study, we propose two finite element approaches incorporating fracture mechanics and continuum damage mechanics to predict time-dependent and temperature-dependent fatigue life of solder joints. For fracture mechanics, the J-integral fatigue formula, da/dN = C(δJ)m, is used to quantify fatigue crack growth and the fatigue life of J-leaded solder joints. For continuum damage mechanics, the anisotropic creep-fatigue damage formula with partially reversible damage effects is used to find the initial crack, crack growth path, and fatigue life of solder joints. The concept of partially reversible damage is especially novel and, based on laboratory tests we have conducted, appears to be necessary for solder joints undergoing cyclic loading. Both of these methods are adequate to predict the fatigue life of solder joints. The advantage of the fracture mechanics approach is that little computer time is required. The disadvantage is that assumptions must be made on the initial crack position and the crack growth path. The advantage of continuum damage mechanics is that the initial crack and its growth path are automatically evaluated, with the temporary disadvantage of requiring a lot of computer time.

3D Crack Growth Analysis and Its Correlation With Experiments for Critical Turbine Components Under an International Collaborative Program

2008 ◽  
Author(s):  
J. Hou ◽  
J. Dubke ◽  
K. Barlow ◽  
S. Slater ◽  
L. Harris ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Operating Conditions ◽  
Cycle Fatigue ◽  
3D Crack Growth ◽  
International Collaborative ◽  
2D And 3D ◽  
Growth Analyses ◽  
Stress Analyses

Following a reanalysis of the original material data plus supplementary Low Cycle Fatigue (LCF) specimen testing, an Original Equipment Manufacturer (OEM) reduced the low cycle fatigue life limits for a number of turbine components. To ascertain the validity of the new life limits, an international collaborative spin rig test program was initiated to provide more accurate low cycle fatigue life limits. The program covered a broad range of activities including, Finite Element (FE) stress analyses, cyclic spin rig testing, fractographic assessment and fatigue crack growth (FCG) analyses. This paper describes the 2D and 3D crack growth analyses of critical turbine components in a turboprop gas turbine engine, comparison of predicted results obtained using different software and also correlations with spin test results from the program. First, FE stress analyses of selected turbine components were carried out under both engine operating conditions and spin-rig test configurations in order to determine the maximum and minimum operating speeds required to match the stress ranges at the critical location specified by the OEM under engine operating conditions. Second, 2D and 3D crack growth analyses were performed independently by three organisations for a disk bolthole using the state-of-the-art software. Third, the predictions from different software were compared, and the relative technical merits of each software were evaluated. Finally, the predicted results were correlated against the striation counts determined by the OEM from the results of spin rig tests.

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