When it comes to engineering and design, precision and accuracy are paramount. Design calculations and Finite Element Analysis (FEA) are two methods that engineers commonly use to ensure that their designs meet safety, performance, and efficiency criteria. However, there are situations where using design calculations alone is not feasible or efficient. In this blog post, we’ll explore when it’s possible to rely solely on design calculations and when FEA analysis becomes a more suitable approach. 

Design Calculations: 

1. Deterministic Approach: 

Design calculations are a deterministic approach to engineering analysis. They involve using established equations, formulas, and engineering standards to predict the behaviour of a component or system. These calculations are based on simplifications and assumptions that make them suitable for routine, well-understood situations. 

2. Static and Simplified Cases: 

Design calculations are often used for relatively simple and static cases, where the loads, materials, and geometries are well-defined and do not change significantly during operation. For example, calculating the required thickness of a steel beam to support a static load is a typical design calculation. 

3. Hand Calculations: 

In many cases, engineers can perform these calculations by hand or using spreadsheet software. These calculations are precise when done correctly, but they can be time-consuming and prone to errors, especially in complex scenarios. 

4. Validation and Verification: 

Design calculations require thorough validation and verification processes to ensure their accuracy. This involves comparing the calculated results with real-world tests or benchmark data to confirm that the design meets safety and performance criteria. 

Finite Element Analysis (FEA): 

1. Numerical Simulation: 

FEA is a numerical simulation technique that divides complex structures or systems into finite elements, such as triangles or tetrahedra. These elements represent discrete portions of the geometry, and mathematical equations govern their behaviour. 

2. Complex Geometries: 

FEA excels when dealing with intricate geometries that cannot be easily represented by simple equations. It can model complex shapes and analyse how stresses, strains, and deformations interact throughout the entire structure. 

3. Dynamic Analysis: 

FEA is well-suited for dynamic analyses where loads vary with time, such as vibrations, impact forces, and transient thermal effects. It can predict how a structure will respond to these dynamic inputs accurately. 

4. Material Variability: 

FEA can account for material properties that vary significantly within a structure. For instance, composite materials often have non-uniform properties, and FEA can model these variations precisely. 

5. Optimization: 

FEA enables engineers to optimize designs by iteratively adjusting parameters and running simulations to find the best configuration for specific goals, such as minimizing weight while ensuring structural integrity. 

6. Stress Concentrations: 

It is particularly useful in identifying stress concentrations and weak points within a design, helping engineers make informed decisions to strengthen those areas. 

When to Choose FEA over Design Calculations: 

• Use FEA when dealing with complex geometries, non-linear material behavior, and dynamic loads. 
• Opt for FEA when precision is critical, especially in safety-critical applications like aerospace or medical devices. 
• When you need to optimize a design or analyze its response to changing conditions, FEA is a valuable tool. 
• FEA is often the choice for research and development projects, where predicting exact behaviours or exploring multiple design iterations is essential. 

When Design Calculations Suffice: 

• Design calculations are suitable for routine, well-understood scenarios with simple geometries and static loads. 
• In cases where FEA may be overkill, such as sizing basic structural components or routine HVAC system designs. 
• For situations where time and resources are limited, and quick, reasonably accurate results are sufficient. 

The choice between design calculations and FEA depends on the specific engineering problem, the level of complexity, the availability of resources, and the desired level of precision. Engineers often use both methods in conjunction, relying on design calculations for initial sizing and FEA for detailed analysis and optimization.