How do you choose the best load and force vectors for FEA?

A Finite Element Analyst (FEA) conducting a quality structural analysis has at least the following: -Test data -FEA data -Hand calculated F&M & stress/strain Spend time making a Free Body Diagram (FBD) of the structure to start this type of analysis. The Load & Force vectors in a FE Analysis are determined directly from the model's FBD. I do the following: -Use quadrille paper to make a (rough) drawing of the object with all forces contacting it also drawn -Make assumptions for areas that are structurally indeterminant -Divide & Conquer: Make sub-models in the FBD where possible -Solve the system using Newton's Laws of Mechanics Mimic the the FBD sub-models in the FEA software to maximize execution efficiency. #FreeBodyDiagram ☺️

Before applying loads in FEA, define your analysis goals. What are you testing - stress, strain, displacement, vibration, fatigue? What are the performance criteria and constraints? By clarifying objectives, you can determine the relevant load types and magnitudes for your model. For example, if evaluating fatigue, cyclic loads are key. If assessing deformation, static loads are critical. Defining objectives upfront guides the selection of realistic loads for your specific FEA study.

Objectives: - Ensuring applied load and force accurately simulate the real world environmental and operational conditions. - Balancing the model's complexity with computational efficiency by selecting appropriate load and force that captures essential behaviors in accurate form. - Minimize the errors by choosing load and force vectors that are consistent with material properties, boundary conditions and analysis outcome. - Optimizing the analysis by selecting load and force vectors that focus on specific design criteria. - Consider various operating conditions including extreme to potential failure modes. - Validate the results to correlate with physical or established benchmarks. - Document the details explaining the assumptions made.

Identify all sources of loads acting on your structure. These can be external, like gravity, pressure, wind, impact, or internal, such as thermal effects, friction, prestress. Gather data on their magnitudes, directions, and distributions. Use measurements, calculations, standards, or assumptions to quantify these loads. For example, pressure vessel FEA requires internal pressure loads, while bridge FEA needs vehicle, wind, and seismic loads. Comprehensive load source identification ensures your FEA represents real-world conditions.

Along with load identification process, it is really vital to consider how the whole system is reacting against each type of load. As some examples, regular quasi-static forces acting as vectors will be counteracted by the total stiffness of the system, and loads in form of acceleration, are balanced with mass and inertia. Recognising this can help you define loads more accurately.

Choose the appropriate load types in your FEA software to represent the identified load sources. Common types include nodal forces, distributed loads, body forces, boundary conditions, initial conditions, and load steps. Match the type to the load's nature. For example, use distributed loads for pressure, nodal forces for point loads, and body forces for gravity. Selecting suitable load types ensures accurate load application in the model. Consider the load's variation over time and space, using tables or functions if needed.

Pemilihan tipe beban ditentukan berdasarkan fokus analisis yang kita inginkan. contoh ketika kita ingin mengurangi jumlah elemen, gunakan remote load untuk mendefinisikan gaya dititik tertentu, dimana pada aktualnya gaya tersebut berada pada sebuah komponen yang bukan menjadi fokus analisis. Sehingga kita bisa hilangkan komponen tersebut dan menggantikannya dengan remote load atau remote mass.

Assign the load vectors to the chosen load types in your model. Specify the numerical values for magnitude and direction, ensuring consistent units and sign conventions. Use the appropriate coordinate system - global or local. For example, a nodal force of (100, 0, -50) N means 100 N in X, 0 in Y, and -50 in Z global directions. Double-check the load orientation and distribution. Concentrated loads at nodes can cause singularities, so apply small distributed loads instead for accuracy. Verify that the total applied loads match your expected values.

While applying loads, some complications might occur, that one should consider during the analysis. The most important problem, is reaching singularity (i.e. next to infinity stress) while dealing with point loads. A simple solution for this matter is to employ distributed loads acting on small surfaces instead of vectors on points, specifically if these points are not included in the node set of the whole meshed system.

• "Stress singularity" is an important concept, one should keep in mind during FEA-modelling. Applying 'point-loads' to your model usually cause this issue (other possible reasons being sharp re-entrant corners, point contacts, etc.) • Moreover, one should also consider Load's 'rigidity' as well, to ensure the applied loads depict real-life scenario. For example, if a very stiff machinery is placed on some surface let's say. Then, the load would be better modeled as its weight applied on just two ends, instead of a distributed load across the whole surface.

"How do you choose the best load and force vectors for FEA?" it's a bad posed question. FEA is a tool to help the structural analyst. The environment a specific structure has to survive it's a matter of field data, standards and local regulations. We have to know what to do and as engineers we take the responsibility of the project, and its safety! We can't go for "best load and force vectors" it's not a matter of personal judgment, we must use the right ones. I would change this title into "How do you model at best load and force for FEA". This makes sense because we have to represent properly what's going on.

Validate your FEA results against test data, hand calculations, or known solutions to verify the load application. Refine the loads and model iteratively to reconcile differences. Document all load assumptions, sources, and application details for traceability and future reference. Consider load combinations and sequences, such as applying bolt preload before external forces. Perform sensitivity studies by perturbing load magnitudes to assess their impact on the results. Remember that incorrect loading can undermine even the most detailed FEA model, so invest effort in the loading strategy. Collaborate with test engineers and designers to ensure loading realism.

It might be complicated at times to define certain types of loads, for example, prestressing fields in cables. Although there are standard ways to address this problem, you can use your creativity to come up with a solution as well. In the aforementioned example, the standard approach would include a definition based on stress fields, however, you can define the prestressing forces by applying temperature changes as well.