Welded joints are critical in structural engineering, bearing immense loads and enduring harsh conditions. Assessing their durability is no small feat. Traditional methods to evaluate the durability of welds can be time-consuming. This is where Durability Simulation Roles on 3DEXPERIENCE platform step in, offering a cutting-edge solution that combines advanced simulation capabilities with user-friendly workflows. Designers and engineers can evaluate the strength of the welds subjected to multiple loading scenarios.
The FKM Guideline is used for calculating the strength of mechanical components made from steel, cast iron, and aluminum, and is applicable to components that are machined or welded. The guideline assesses both static and fatigue strength. It is also used to assess the strength of weld seams, and base materials.
The Durability and Structural Performance Role or Durability and Mechanics Engineer Role allows for durability simulation and FKM assessment. The apps in these roles base their FKM assessments for the welded components on the FKM Guideline Analytical Strength Assessment of Components, 6th and 7th editions, chapters 3 and 4 [1]. For the non-welded components, the assessment is based on only the 7th edition of the Analytical Strength Assessment of Components. Also, the criteria used in the app applies fatigue assessments where the number of cycles is greater than 10,000.
The durability analysis cases for FKM assessment are based on an existing structural simulation analysis case. The structural simulation can include geometric and contact nonlinearity. Nonlinear material behavior can be assigned for components of the model not included in the FKM assessment. However, any nonlinearity in the structural behavior indicates stresses should not be scaled when setting up the FKM assessments. When it comes to creating the finite element model for use in FKM assessments, the weld fillet and interface between the weld fillet and plates must have compatible mesh. Element types can be either all solids or shells, however, a mixed mesh of solid and shell elements together cannot be used. The only supported weld failure mode is the toe failure.
The software provides material databases suited for FKM assessment of components per 6th and 7th editions. Users can also custom define materials providing values for Yield (proof) stress, Ultimate stress, FKM material, and Elongation. Material property should also include linear isotropic elasticity for structural analysis case that precedes the FMK assessment.
In the example illustrated in this article, the durability of the welds on the bucket of an excavator is evaluated. This is a two-step process consisting of two analysis types. First, a structural analysis is performed by defining three load cases that represent a maximum load applied at three different locations of the bucket – left side, right side, and middle of the bucket. This simulation calculates stresses on the bucket’s welds.
The second step to evaluate durability involves creating an FKM analysis case that configures the FKM fatigue assessment step. This uses the stress results from the preceding structural analysis. The durability analysis consists of a fatigue assessment and a fatigue loading history. The solver uses the stress results and loading history to calculate the expected lifetime of the welds in actual working conditions.
The Weld Fillet set allows the selection of fillets that represent the welds.
Parameters can be set as desired to characterize the weld fillet. The structural stress methods used to provide stresses for FKM assessment of welded components are surface stress extrapolation (SSE) for solid or shell models, and through thickness stress linearization (TTSL) for solid models only.
The fatigue loading event of type Superposition is used in this example to superimpose all three loading scenarios, i.e. the left, middle, and right load cases. The signal used is a pulse or on-off type where stress alternates between the maximum (on) and off. The durability analysis is run to simulate the effect of repeated load cycles on the integrity of the welds. In this case, 12,000 cycles for each loading scenario,
The combined utilization plot shows how well the welds withstand the load history. It enables identification of the weld location where failure is most likely to occur.
The plot shows utilization contours at the edges of the weld bead. The minimum value of the utilization factor can be useful in predicting the onset of weld failure.
By leveraging the Durability and Performance Engineer or Durability and Mechanics Engineer roles on 3DEXPERIENCE, engineers, and designers can simulate realistic load and operating environment conditions that welds will face. Useful insights can be drawn from such simulations to refine or optimize welded joints ensuring compliance of the design per the FKM guidelines.