How SODIMEC verified a 198 t ladle lifting beam with SDC for Ansys
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Analysis of the cylinder system of grab unloader
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AS 4100:2020 Fatigue in SDC Verifier – How Section 11 Is Implemented
Read Full ArticleHow SODIMEC verified a 198 t ladle lifting beam with SDC for Ansys
Read Full StoryAnalysis of the cylinder system of grab unloader
All ProjectsAS 4100:2020 Fatigue in SDC Verifier – How Section 11 Is Implemented
Read Full Article
Last updated: 23 Apr 2026
Most fatigue verification workflows do not fail on theory. They fail in the handoff between results and verification.
You run the FEA model, extract stress histories, export data, process cycles in a separate tool, then try to carry the results back into the fatigue check. That adds time, extra validation work, and plenty of room for mistakes.
The Rainflow Counting Tool in SDC Verifier removes that detour. It extracts fatigue cycles directly from variable-amplitude stress histories and keeps the results inside the same verification workflow as the model, the standards, and the checks.
This article explains what the tool does, how the counting workflow is structured, and how the results are used in fatigue verification.
Fatigue damage depends mainly on three things:
Mean stress also matters because each counted cycle can carry a different mean value, and that directly affects fatigue assessment. In variable-amplitude loading, a reliable cycle-counting workflow must preserve not only the range and count of cycles, but also the mean stress associated with each cycle.
Under constant-amplitude loading, these are easy to define. Real structures almost never work that way.
Cranes, offshore equipment, railway structures, wind turbines, and heavy machinery operate under irregular load histories. Stress values rise and fall unpredictably across many time steps or load events. Before these histories can be used in fatigue verification, they must be reduced to counted cycles.
That is the role of rainflow counting.
A typical workflow looks like this:
Without cycle counting, the raw history is not directly usable for fatigue life assessment.
The Rainflow Counting Tool processes stress histories and converts them into fatigue cycles defined by:
The tool has been available in SDC Verifier since version 2021 R2 and is opened from:
Tools → Main → Rainflow Counting
The Rainflow Counting Tool interface in SDC Verifier, showing the calculation settings, result tables, half-cycle data, residue graph, and rainflow matrix in one workspace.
Because the tool works inside the same environment as the model and the verification setup, the rainflow results can be used directly in fatigue workflows without exporting data to external scripts or spreadsheets.
In practice, the tool is used after structural results are already available.
Perform the analysis in a supported solver such as Ansys, Femap, or Simcenter 3D. This produces stress results for the selected load history, time steps, or load cases.
Select the relevant Load Group and the result category to be processed. At this stage, the history that will be used for rainflow counting is defined.
The tool preprocesses the signal, extracts cycles using the selected method, and generates the corresponding outputs such as the rainflow matrix, half-cycle data, or residual stress history.
The counted cycles can then be used directly in custom checks or in fatigue verification workflows aligned with the selected standard.
The rainflow workflow in SDC Verifier consists of four main steps.
The first step removes intermediate data points between successive peaks and valleys. Only the local minima and maxima relevant for fatigue counting are kept.
Peak–valley filtering in SDC Verifier: the initial stress history is reduced to turning points by removing intermediate values that do not affect fatigue cycle counting.
This produces a turning-point sequence that preserves the damage-relevant shape of the stress history while eliminating data that does not affect cycle counting.
After peak–valley filtering, the tool removes very small stress ranges that have negligible influence on fatigue damage.
Hysteresis filtering in SDC Verifier: small stress ranges are removed from the peak–valley filtered history so negligible fluctuations do not distort fatigue cycle counting.
The hysteresis gate can be defined in two ways:
This helps suppress numerical noise and prevents insignificant micro-cycles from inflating the count.
The filtered history is then mapped to a fixed number of bins. Each stress value is moved to the center of the corresponding bin.
Discretization (binning) in SDC Verifier: the hysteresis-filtered stress history is mapped to bin centers so cycle counting can be performed on a consistent set of stress levels.
This makes the cycle-counting process consistent and produces a manageable output matrix. In practice, more bins improve resolution, while fewer bins reduce calculation time.
After preprocessing, the tool applies the selected counting method and generates the cycle data used in the next stages of fatigue verification.
The tool supports two counting methods.
This is the standard software-style implementation used in many fatigue workflows.
The algorithm evaluates each set of four points (A), (B), (C), and (D) in the binned history and checks whether the inner range is bounded by the outer range.
Four-point counting in SDC Verifier: the binned turning-point sequence is evaluated in successive groups, and inner points are removed when they form a closed cycle.
When that condition is met, a closed cycle is counted and stored.
Four-point method output in SDC Verifier: closed cycles are stored in the rainflow matrix, while the remaining unclosed turning points are shown in the residue graph.
The four-point method produces:
Residual output in SDC Verifier: after closed cycles are extracted by the four-point method, the remaining unclosed turning points are stored as the residual stress history.
This is the method most users will choose when they want matrix-based output and direct use in fatigue checks.
The half-cycle method, also known as the Pagoda Roof method, traces the flow path from peaks and valleys and counts half-cycles first. Matching ranges are then combined in the results.
Half-cycle counting in SDC Verifier: the binned stress history is traced in upper and lower directions to identify half-cycles before they are accumulated in the results.
The direction of counting can be set as:
The output is a Half Cycle Data table with counted stress ranges and their accumulated occurrences.
Half-cycle results in SDC Verifier: individual upper and lower half-cycles are counted as 0.5 and then accumulated by stress range in the Half Cycle Data table.
The tool interface is built around a few practical settings.
Defines the load-time history used for calculations.
Defines which result type will be used for rainflow counting, such as stress or another selected result category.
Specifies the stress history used in the calculations. When a Load Group is selected, the corresponding history is applied automatically.
Ignores stress ranges smaller than or equal to the selected percentage of the maximum stress range.
Ignores stress ranges smaller than or equal to a fixed stress value.
Defines the bin resolution used during discretization. More bins increase accuracy and matrix resolution, but also increase processing time.
Defines whether half-cycle counting is performed Left-to-Right, Right-to-Left, or in both directions.
Used when one Load Group contains another Load Group. The tool can use the Minimum, Maximum, or Absolute Maximum result in those calculations.
Allows the user to limit the calculation to the relevant part of the model using the standard selector controls.
For the four-point method, the main output is the Rainflow Matrix.
This matrix stores cycles using two coordinates:
Each matrix cell contains the number of cycles that occur between those two stress levels.
This representation is useful because it preserves both cycle range and cycle mean. Large cycles, small repeated cycles, and dominant loading patterns become visible immediately in the matrix.
That distinction matters because two cycles with the same range may still have different fatigue impact if their mean stresses differ. The matrix therefore captures more than just amplitude distribution; it preserves the information needed for realistic fatigue damage evaluation.
The tool also stores the residual stress history, which represents unclosed excursions that remain after closed cycles are extracted.
Rainflow results are stored as named system variables. These are available directly in Custom Checks and in standard-based fatigue workflows inside SDC Verifier, which means you can write verification logic against the actual cycle data without any intermediate export step.
Custom Rainflow Summation Check in SDC Verifier: named rainflow variables are used directly in the fatigue formula, so cycle data can feed verification logic without external scripts or manual transfer.
Because the cycle data remains inside the same model environment, the engineer does not need to manually transfer stress ranges, mean stresses, or cycle counts into a separate verification tool.
These include:
These variables can be used directly in Custom Checks and in custom fatigue summation logic.
The counted cycles are not the final result. They are the input to fatigue verification.
In SDC Verifier, rainflow results can be used in workflows aligned with standards such as:
This is especially relevant in heavy lifting, crane, and related structural applications where variable-amplitude fatigue is part of the design check.
Because the counting is performed inside the same environment as the model and the verification logic, the workflow stays consistent from stress history to counted cycles to fatigue result.
In many standards, rainflow counting is not always named as an explicit mandatory method, but proper cycle counting under variable-amplitude loading is required in practice. That is why ASTM E1049 remains the core methodological reference for compliant implementation.
Consider a crane structure under variable operational loading.
A dynamic analysis is performed in the solver. Stress histories are extracted from critical weld locations and grouped in the relevant Load Group. The Rainflow Counting Tool is then applied to that history.
The tool filters the signal, bins it, and counts cycles using either the four-point or half-cycle method. The resulting ranges and cycle counts are then used in the fatigue evaluation, for example through the relevant standard-based workflow or through a custom rainflow summation check.
Instead of moving results through external tools, the engineer keeps the full sequence inside one model environment.
When rainflow counting is handled outside the verification environment, the usual costs are obvious:
| SDC Verifier | External tool (MATLAB / Python) | Manual (Excel) | |
|---|---|---|---|
| Integrated with FEA results | ✅ | ❌ Export required | ❌ Export required |
| ASTM E1049 compliant | ✅ | Depends on library | ❌ Impractical |
| Feeds fatigue standard checks directly | ✅ | ❌ Manual re-import | ❌ Manual re-import |
| Traceable in one model | ✅ | ❌ | ❌ |
| Supports EN 13001, EC3, DIN 15018 natively | ✅ | ❌ | ❌ |
An integrated rainflow workflow does not make the engineering easier in the sense of lowering rigor. It makes the workflow cleaner by keeping the counting logic, variables, and fatigue checks connected to the same model.
That is the main value of the tool.
The Rainflow Counting Tool is included in the full SDC Verifier package — no external scripts, no data handoffs, results connected directly to EN 13001, Eurocode 3, and DIN 15018 fatigue checks.
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The Rainflow Counting Tool in SDC Verifier extracts fatigue cycles from variable-amplitude stress histories and keeps the results inside the same verification workflow as the model and the checks.
It supports both four-point and half-cycle counting, includes preprocessing steps such as peak–valley filtering, hysteresis filtering, and binning, and provides outputs that can be used directly in fatigue verification.
For engineers working with irregular loading histories, the main advantage is simple: cycle counting, fatigue variables, and verification logic stay connected to the same model instead of being split across multiple tools.
Yes. The Selection block lets you define which elements or nodes are included.
The residual is displayed separately and stored alongside the rainflow results. These unclosed excursions can then be considered in the chosen fatigue workflow.
That depends on the required balance between accuracy and speed. More bins give better amplitude resolution, especially for steep S–N curves, but also increase processing time.
Yes. The rainflow variables can be used in Custom Checks, including custom summation logic.
The tool is used directly in SDC Verifier, or within SDC Verifier workflows connected to Ansys, Femap, and Simcenter 3D.
Yes. In workflows where hotspot stress is used for weld fatigue assessment, rainflow counting can still be applied to the resulting histories. This makes the tool relevant not only for nominal-stress workflows, but also for more detailed weld verification approaches.
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