Observations on Sustained Load Environmental Crack Growth of a Titanium 8Al-lM0-lV Alloy

CORROSION ◽  
1971 ◽  
Vol 27 (12) ◽  
pp. 525-530 ◽  
Author(s):  
R. J. BUCCUI ◽  
P C PARIS
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Room Temperature ◽  
Crack Arrest ◽  
Sustained Load ◽  
Distilled Water ◽  
Time To Failure ◽  
Nacl Solution ◽  
Test Technique

Abstract Sustained load environmental cracking of a mill annealed titanium 8Al-1Mo-1V alloy was investigated by methods amenable to fracture mechanics. Two environments were considered: 3.5% NaCl solution and distilled water, both at room temperature. Varying amounts of crack propagation followed by subsequent crack arrest were detected at K levels considerably below an apparent KIscc (almost 2 to 1) that would be determined from a time to failure test technique. At crack arrest locations along the specimen surface, minute amounts of crack division were often observed under magnification.

Environment-Assisted Cracking of Zr-Based Bulk Metallic Glass

2007 ◽  
Vol 561-565 ◽  
pp. 1279-1282 ◽  
Author(s):  
Yoshikazu Nakai ◽  
Makoto Seki ◽  
Yasunori Yoshioka
Keyword(s):  
Cyclic Loading ◽  
Metallic Glass ◽  
Crack Propagation ◽  
Crack Growth ◽  
Bulk Metallic Glass ◽  
Stress Ratio ◽  
Deionized Water ◽  
Sustained Load ◽  
Loading Frequency ◽  
Nacl Solution

Crack propagation tests on a bulk metallic glass, Zr55Cu30Ni5Al10, were conducted either in aqueous sodium chloride (NaCl) solutions or deionized water. Crack growth experiments were conducted under cyclic loading at a stress ratio of 0.1 or 0.5 under a loading frequency of 20 or 1.0 Hz. The experiments were also conducted under a sustained load. Although the crack growth rate in deionized water was almost identical to that in air, the rate in NaCl solution was much higher than that in air even in a very low concentration of NaCl such as 0.01%. In 3.5% NaCl solution, the time-based crack propagation rate during cyclic loading, da/dt, was determined by the maximum stress intensity factor, Kmax, but was independent of the loading frequency and the stress ratio, and the rate was almost identical to that of environment-assisted cracking under a sustained load.

A Fracture Mechanics Approach to Thermal Fatigue Life Prediction of Solder Joints

1990 ◽  
Vol 203 ◽  
Author(s):  
Yi-Hsin Pao
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Thermal Fatigue ◽  
Solder Joints ◽  
Failure Process ◽  
Growth Equation ◽  
Thermal Fatigue Crack ◽  
Runge Kutta Method ◽  
Growth History

ABSTRACTThe approach developed is based on the assumption that thermal fatigue crack propagation in solder joints is primarily controlled by C* and J integrals. The effect of microstructural coarsening on crack propagation is discussed. A fracture criterion, J≥Jc, is used to define the failure of the joints. A crack growth governing equation has been formulated and can be numerically integrated to obtain the crack growth history given stress history as an input. The approach was applied to model the experiment by Wong and Helling [15]. In their experiment, surface-mounted electronic devices using eutectic Pb/Sn solder were tested in thermal cycles of −20 to 100°C and −55 to 125°C. A unified constitutive equation was assumed for the eutectic Pb/Sn solder. An equation for solving the shear stress in the joint was formulated and is coupled with the crack growth equation. Both equations were solved simultaneously by the Runge-Kutta method for the stress-time and crack growth history. The results of the prediction are in a good agreement with the experimental data, which indicates that fracture mechanics may be applied to describe the failure process of solder joints under cyclic thermal loadings.

Short Crack Growth Model in a Particulate Composite Using Nonlinear Elastic Fracture Mechanics

2003 ◽  
Author(s):  
Ying Zhang ◽  
Tsuchin Chu ◽  
Ajay Mahajan
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Particulate Composite ◽  
Initial Crack ◽  
Short Crack ◽  
Video Tape ◽  
J Integral ◽  
Elastic Fracture ◽  
Crack Growth Model

The fracture mechanics model for a long crack does not work very well with short-crack propagation when the initial crack length is less than 5.1 mm (0.2 inch). In order to investigate the short crack effect, a series of tests of particulate composite specimens with long and short cracks were performed and the results recorded on a video tape. This test data was analyzed to determine the fracture parameters. Two initial crack lengths, 2.5 mm (0.1 inches) and 7.6 mm (0.3 inches) were used in the crack propagation tests. Based on the principle of linear elastic fracture mechanics (LEFM), the stress intensity factor KI was obtained. The instantaneous time-dependent J-integral for 0.1 and 0.3 inch crack specimens was determined by the NEFM analytical approach. The crack growth behavior was also investigated in the form of J-integral resistance curves. The calculated J-integral was reversed to derive a new KI. The new KI was compared with the measured value obtained from LEFM analysis results to determine the feasibility of applying the linear fracture approach to the non-linear behavior of the material. The results showed that the KI computed from the J-integral increased by 24.5%, and was at the time prior to the peak load for the 0.1 inch crack. For the 0.3 inch crack, the acceptable range was from the onset of propagation to the 9% strain stage (yield strain for the material), where the increase of the new KI was within 15.6%.

Application of 3D Fracture Mechanics for Improved Crack Growth Predictions of Gas Turbine Components

2017 ◽  
Author(s):  
Kanwardeep S. Bhachu ◽  
Santosh B. Narasimhachary ◽  
Sachin R. Shinde ◽  
Phillip W. Gravett
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Gas Turbine ◽  
Crack Growth ◽  
Structural Integrity ◽  
Crack Arrest ◽  
3D Crack Growth ◽  
Mechanics Analysis

Fracture mechanics analysis is essential for demonstrating structural integrity of gas turbine components. Usually, analyses based on simpler 2D stress intensity solutions provide reasonable approximations of crack growth. However, in some cases, simpler 2D solutions are too-conservative and does not provide realistic crack growth predictions; often due to its inability to account for actual 3D geometry, and complex thermal-mechanical stress fields. In such cases, 3D fracture mechanics analysis provides extra fidelity to crack growth predictions due to increased accuracy of the stress intensity factor calculations. Improved fidelity often leads to benefits for gas turbine components by reducing design margins, improving engine efficiency, and decreasing life cycle costs. In this paper, the application of 3D fracture mechanics analysis on a gas turbine blade for predicting crack arrest is presented. A comparison of stress intensity factor values from 3D and 2D analysis is also shown. The 3D crack growth analysis was performed by using FRANC3D in conjunction with ANSYS.

Numerical simulation of fatigue crack propagation in mixed-mode (I+II) using the program BemCracker2D

2019 ◽  
Vol 10 (4) ◽  
pp. 497-514
Author(s):  
Pedro G.P. Leite ◽  
Gilberto Gomes
Keyword(s):  
Numerical Simulation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Mode I ◽  
Post Processing ◽  
Content Type

Purpose The purpose of this paper is to present the application of the boundary element method (BEM) in linear elastic fracture mechanics for analysis of fatigue crack propagation problems in mixed-mode (I+II) using a robust academic software named BemCracker2D and its graphical interface BemLab2D. Design/methodology/approach The methodology consists in calculating elastic stress by conventional BEM and to carry out an incremental analysis of the crack extension employing the dual BEM (DBEM). For each increment of the analysis, the stress intensity factors (SIFs) are computed by the J-Integral technique, the crack growth direction is evaluated by the maximum circumferential stress criterion and the crack growth rate is computed by a modified Paris equation, which takes into account an equivalent SIF to obtain the fracture Modes I and II. The numerical results are compared with the experimental and/or BEM values extracted from the open literature, aiming to demonstrate the accuracy and efficiency of the adopted methodology, as well as to validate the robustness of the programs. Findings The paper addresses the numerical simulation of fatigue crack growth. The main contribution of the paper is the introduction of a software for simulating two-dimensional fatigue crack growth problems in mixed-mode (I+II) via the DBEM. The software BemCracker2D coupled to the BemLab2D graphical user interface (GUI), for pre/post-processing, are very complete, efficient and versatile and its does make relevant contributions in the field of fracture mechanics. Originality/value The main contribution of the manuscript is the development of a GUI for pre/post-processing of 2D fracture mechanics problems, as well as the object oriented programming implementation. Finally, the main merit is of educational nature.

Development of Efficient Crack Growth Simulator Based on Hot-Mix Asphalt Fracture Mechanics

2003 ◽  
Vol 1832 (1) ◽  
pp. 105-112 ◽  
Author(s):  
Boonchai Sangpetngam ◽  
Bjorn Birgisson ◽  
Reynaldo Roque
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Boundary Element ◽  
Crack Growth ◽  
Hot Mix Asphalt ◽  
Displacement Discontinuity ◽  
Successful Implementation ◽  
Loading Conditions ◽  
Premature Failure ◽  
Major Mode

It has long been accepted that cracking of hot-mix asphalt (HMA) pavements is a major mode of premature failure. Many state departments of transportation have verified that pavement cracking occurred not only in fatigue cracking in which a crack initiates from the bottom of the asphalt layer but also in other modes such as low-temperature cracking and the more recently identified top-down cracking. Recent work at the University of Florida has led to the development of a crack growth law based on viscoelastic fracture mechanics that is capable of fully describing both initiation and propagation of cracks in asphalt mixtures. The model requires the determination of only four fundamental mixture parameters, which can be obtained from less than 1 h of testing using the Superpave® indirect tensile test (IDT). These parameters can account for microdamage, crack propagation, and healing for stated loading conditions, temperatures, and rest periods. The generalization of the HMA crack growth law needed for its successful implementation into a displacement discontinuity boundary element method is described. The resulting HMA boundary element approach is shown to predict the crack propagation of two coarse-graded mixtures under cyclic IDT loading conditions.

Fatigue Crack Propagation in 8- and 22-Layer 7075-T6 Aluminum Alloy Laminates

1978 ◽  
Vol 100 (1) ◽  
pp. 32-38 ◽  
Author(s):  
N. J. Pfeiffer ◽  
J. A. Alic
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Crack Propagation Rate ◽  
Crack Arrest ◽  
Propagation Rate ◽  
Adhesively Bonded ◽  
Crack Divider ◽  
Crack Growth Rates

Rates of fatigue crack propagation have been determined for adhesively bonded 7075-T6 laminates having a crack divider geometry. Two lamina thicknesses were used, the resulting laminates having either 8 or 22 layers. Crack growth rates were generally within the same range as for monolithic 7076-T6 alloy, and were somewhat slower in the 22-layer laminates than in those with 8 layers. Instances of decreasing crack propagation rate with increasing stress intensity amplitude, as well as of crack arrest, were observed. These are interpreted in terms of interactions between the layers during the progressive transition from a flat mode of crack growth to a slant mode.

Augmenting Generic Fatigue Crack Growth Models Using 3D Finite Element Simulations and Gaussian Process Modeling

2019 ◽  
Author(s):  
Adrian Loghin ◽  
Shakhrukh Ismonov
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Gaussian Process ◽  
Crack Growth ◽  
Life Assessment ◽  
Growth Path ◽  
3D Fem

Abstract Assessing the crack propagation life of components is a critical aspect in evaluating the overall structural integrity of a mechanical structure that poses a risk of failure. Engineers often rely on industry standards and fatigue crack growth tools such as NASGRO [1] and AFGROW [2] to perform life assessment for different structural components. A good understanding of material damage tolerant capabilities, and the component’s loading mission during service conditions are required along with the availability of generic fracture mechanics models implemented in the lifing tools. Three-dimensional (3D) linear elastic fracture mechanics (LEFM) finite element modeling (FEM) is also a viable alternative to simulate crack propagation in a component. This method allows capturing detailed geometry of the component and representative loading conditions which can be crucial to accurately simulate the three dimensionality of the propagating crack shape and further determine the associated loading cycles. In comparison to a generic model, the disadvantage of the 3D FEM is the extended runtime. One feasible way to benefit from 3D modeling is to employ it to understand the crack front evolution and growth path for the representative loading condition. Mode I stress intensity factors (KI) along the predetermined crack growth path can be generated for use in fatigue crack growth tools such as NASGRO. In the current study, such a 3D FEM lifing process is presented using a classical bolt-nut assembly, components that are commonly used in engineering design. First, KI solutions for a fixed crack aspect ratio a/c = 1 are benchmarked against a similar solution available in NASGRO. Next, a predefined set of crack shapes and sizes are simulated using 3D FEA. A machine learning model Gaussian Process (GP) was trained to predict the KI solutions of the 3D model, which in turn was used in the crack propagation simulation to accelerate the life assessment process. Verification of the implemented procedure is done by correlating the crack growth curves predicted from GP to the results obtained directly from 3D FE crack propagation method.

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