ANSYS workbench 疲劳分析教程(英文)

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Figure 1: Editing SN curves
3. Analysis Fatigue results can be added before or after a stress solution has been performed. To create fatigue results, a fatigue tool must first be inserted into the tree. This can be done through the solution toolbar or through context menus. The details view of the fatigue tool is used to define the various aspects of a fatigue analysis such as loading type, handling of mean stress effects and more. As seen in Figure 2, a graphical representation of the loading and mean stress effects is displayed when a fatigue tool is selected by the user. This can be very useful to help a novice understand the fatigue loading and possible effects of a mean stress.
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3.1.1 Constant amplitude, proportional loading This is the classic, “back of the envelope” calculation. Loading is of constant amplitude because only 1 set of finite element stress results along with a loading ratio is required to calculate the alternating and mean stress. The loading ratio is defined as the ratio of the second load to the first load (LR = L2/L1). Loading is proportional since only 1 set of finite element stress results is needed (principal stress axes do not change over time). Common types of constant amplitude loading are fully reversed (apply a load then apply an equal and opposite load; a load ratio of –1) and zerobased (apply a load then remove it; a load ratio of 0). Since the loading is proportional, the critical fatigue location can be ascertained by looking a single set of FEM results. Likewise, since there are only 2 loadings, no cycle counting or cumulative damage calculations need to be done.
Fatigue Analysis in the Ansys Workbench Environment
D. Alfred Hancq, Ansys Inc., May 2003 Contents 1. Introduction 2. Materials 2.1. Stress-Life Data Options 3. Analysis 3.1. Loading 3.1.1. Constant Amplitude, Proportional Loading 3.1.2. Non-Constant Amplitude, Proportional Loading 3.1.3. Constant Amplitude, Non-Proportional Loading 3.1.4. Non-Constant Amplitude, Non-Proportional Loading 3.2. Load Effects 3.2.1. Mean Stress Correction 3.2.2. Multiaxial Stress Correction 3.3. Miscellaneous Analysis Options 4. Results 4.1. Fatigue Life 4.2. Fatigue Damage 4.3. Factor of Safety 4.4. Stress Biaxiality 4.5. Equivalent Alternating Stress 4.6. Fatigue Sensitivity Chart 4.7. Rainflow Matrix Chart 4.8. Damage Matrix Chart 5. Typical Use Cases 5.1. Connecting Rod Under Fully Reversed Loading 5.2. Connecting Rod Under Random Loading 5.3. Universal Joint Under Combined Torsion and Bending 6. Additional Fatigue Resources and Revision History 1. Introduction It is estimated that 50-90% of structural failure is due to fatigue, thus there is a need for quality fatigue design tools. However, the availability of commercial fatigue tools is limited while the ones that are available are usually quite expensive and difficult to use in the hands of a designer. It is hoped that these designers, given a proper library of fatigue tools, could
ｗｗｗ．ｂｚtigue tool information page
3.1 Loading Fatigue, by definition, is caused by changing the load on a component over time. Thus, unlike static stress safety tools, which perform calculations for a single stress state, fatigue damage occurs when the stress at a point changes over time. There are essentially 4 classes of fatigue loading with the fatigue tool currently supporting the first 3: • Constant amplitude, proportional loading • Non-constant amplitude, proportional loading • Constant Amplitude, non-proportional loading • Non-constant amplitude, non-proportional loading
quickly and accurately conduct a fatigue analysis suited to their needs in a friendly and well structured environment. Fatigue was initially introduced as a new capability at version 6.0. Its focus has been to provide useful information to the design engineer when fatigue failure may be a concern. Fatigue results can have a convergence attached. Currently, a stress-life approach has been adopted for conducting a fatigue analysis. Several options such as accounting for mean stress and loading conditions are available. A fatigue analysis can be separated into 3 areas: materials, analysis, and results evaluation. Each area will be discussed in more detail below: 2. Materials A large part of a fatigue analysis is getting an accurate description of the fatigue material properties. Since fatigue is so empirical, sample fatigue curves are included only for structural steel and aluminum materials. These properties are included as a guide only with intent for the user to provide his/her own fatigue data for more accurate analysis. In the case of assemblies with different materials, each part will use its own fatigue material properties just as it uses its own static properties (like modulus of elasticity). 2.1 Stress-life Data Options/Features • Fatigue material data stored as tabular alternating stress vs. life points. • The ability to define mean stress dependent or multiple r-ratio curves if the data is available. • Options to have log-log, semi-log, or linear interpolation. • Ability to graphically view the fatigue material data • The fatigue data is saved in XML format along with the other static material data. • Figure 1 is a screen shot showing a user editing fatigue data