Crack growth analysis uses linear elastic fracture mechanics and related crack growth material properties to determine how fast a crack or crack-like defect will grow. The analysis can provide an estimate of the remaining safe life a structure that contains a crack. Fracture mechanics is based on the concept of a stress intensity, K, that describes the magnitude of both the stress and strain fields around a crack. It is computed from the stress range, Δσ, and crack size, a, and crack shape, f(a/b):
Thus, the rate of crack growth is determined by the loading, crack size and crack shape.
Enter as much data as you know. If it is not enough, you will be asked for more. Fields with a light blue/gray background represent the minimum required data to begin calculations. Other data may become necessary as calculation proceeds. Pressing the button provides help in the form of an equation or default information for a parameter.
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Loads can be entered as either the maximum and minimum values or as the stress range and R ratio. Stresses entered are assumed to be elastic. Fracture mechanics is based on the nominal stress in the uncracked structure.
Crack growth analysis requires a crack growth curve for the material. The linear portion of the curve represents stable crack growth and is characterized by an intercept, C, and slope, m. The threshold stress intensity, ΔKTH, represents a stress intensity below which cracks will not grow. This is analogous to the fatigue limit in traditional fatigue analysis.
You may load a material from the database by selecting it and clicking on "Load Material", or browse the database by clicking the "Material Property Finder" button, or specify individual properties directly. Clicking "Material Property Estimator" will show the default properties that are computed from the input values.
For registered users, the Material Property Estimator will display a plot of the data. Registered users may also save this material in their personal database by clicking the "Save Material" button.
public/A356-T6 public/Aluminum 2024-T3 public/Aluminum 2024-T3 public/Aluminum 2024-T351 public/Aluminum 2219-T851 public/Aluminum 7075-T6 public/Man-Ten public/RQC-100 public/Stainless Steel 316 public/Steel 1045, Normalized, BHN=153 public/Steel 3.5NCMV public/Steel 4340 public/Steel 4340 public/Steel 4340M public/Steel A27, Cast, BHN=135 public/Steel A514-B public/Steel A517 public/Steel A533-B public/Steel A533B public/Steel A542 public/Steel A588 public/Steel EN24 public/Steel EN30B
Stress intensity factors, K, describe the stresses and strain fields around a crack. Although they are quite different mathematically, they are used in a way that is similar to stress concentration factors in traditional fatigue analysis. Unlike stress concentration factors, stress intensity factors continuously change as the crack grows in the structure. Like stress concentration factors, they are a function of the ratio of the geometric variables and type of loading. For example they are a function of the ratio of the crack size and plate width. They are also a function of the crack shape as well. The general form of the stress intensity is given by:
The F term corrects for the different crack shapes and the f(a/b) term corrects for the geometric variables of the component. The stress intensity finder combines all of these into a single correction.
The fatigue life is not very sensitive to the final crack size. Any reasonable estimate may be used.
Enter the function F(a) as a tab or comma delimited text string or use the Stress Intensity Factor Finder. You may choose to cut and paste F(a) directly from Microsoft Excel. If you do not choose to use the Stress Intensity Factor Finder, make sure that the crack length, a, has units of meters and F(a) is dimensionless.
You may paste tab-delimited text (such as would be copied from a spreadsheet) into a box, and it will be expanded out automatically.
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