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03 Sep 2022

# Implicit vs. Explicit FEA: What's the Difference?

Skill-Lync

Both implicit and explicit Finite Element Analysis is used to solve Partial Differential Equations (PDEs). Both techniques are valid methods for solving time-dependent problems, but there are differences between them that help explain why different kinds of problems are suited to each method. In this article, we’ll explore implicit vs explicit in FEA so you can better decide which technique would be best suited to your needs!

## What is Implicit FEA?

Implicit FEA is a numerical technique for solving differential equations by discretizing them into a system of algebraic equations that can be solved using matrix methods. In implicit FEA, the state of the component is defined as a function of the present and future states.

Implicit FEA is best suited for analyzing static or low-speed phenomena and the solution is calculated for large time steps.

## What is Explicit FEA?

In explicit FEA, also known as dynamic analysis, the analyst applies loads to the model and then lets the software compute deformation, stress, and strain. This method is best suited for highly nonlinear problems or problems with complex contact conditions. Explicit FEA calculation is done with a very small time step of 10^-6 seconds.

If an engineer needs to know how much force it would take for someone to break through a wall, they need to use explicit FEA software.

### The Pros and Cons of Implicit Analysis

Implicit analysis has four primary benefits.

•  Implicit simulations require less computational power than explicit analyses for performing static analysis.
• They produce more accurate results than explicit simulations when modelling deformable bodies such as polymer sheets or metal panels.
• Third, their computational efficiency means that they can be run on commercial CAD packages such as AutoCAD® without the need for expensive software licenses.

Finally, the implicit analysis doesn't take into account contact between objects in the model. For example, if there are no pins in a design, then there's no need to calculate contact pressure during simulation.

### The four drawbacks of implicit FEA include

1) It cannot handle problems where contact occurs

2) It needs to iterate through every possible deformation until the desired result is found

3) Calculations can become unstable when there are high-frequency modes present in the problem

4) Users need some expertise to know what inputs should be applied for successful results.

### The Pros and Cons of Explicit Analysis

There are several advantages to using explicit FEA

• First, it is very effective at simulating non-linear problems.
• Second, it can handle large deformations and large strains.
• Third, it is very efficient in terms of memory usage.

• There are also some disadvantages to using explicit FEA.
First, it can be difficult to obtain an accurate solution due to the large number of variables involved.
• Second, the analysis can be time-consuming.
• Finally, this type of simulation can only take one loading condition into account at a time.

### An Example Use Case - A Lightweight Car vs. A Heavy Truck

A car company is deciding to design their new car using implicit and explicit conversion in FEA. They want to keep the car lightweight, so it uses less fuel and emits fewer greenhouse gases. However, they also need to make sure the car can withstand crashes, especially when hit by a heavy truck. In this case, the car company would likely choose to use explicit FEA for its accuracy in simulating high-energy impact events.

That said, other factors could affect their decision: if they wanted to minimize costs, then they might opt for implicit FEA; if they wanted more accurate results but didn’t mind spending more money on calculations, then implicit FEA might be the way to go.

### Use Case 2: Load Heterogeneity

One major advantage that explicit solvers have over implicit is the ability to simulate load heterogeneity. This means that engineers can apply different loads to different parts of their model, which is perfect for creating realistic simulations. For example, they could simulate a car crash by applying a high load to one side of the car while keeping the other end at a normal load. The result would be an unequal distribution of stress throughout the vehicle.

### Use Case 3: Structural Damage Detection

In the case of structural damage detection, implicit analysis is commonly used in the aerospace industry to detect cracks and defects in aircraft components. It is also used to identify small cracks or deformation in a structure, while explicit analysis would be used to simulate a catastrophic event such as an earthquake or explosion.

### Use Case 4: Contact Fatigue

One use case for explicit analysis is contact fatigue. This type of failure occurs when there is repeated contact between two surfaces, causing small cracks to form. Over time, these cracks can grow and lead to failure. With explicit analysis, engineers can simulate this type of failure to help prevent it from happening in the real world.

### 5 Examples of When to Use Each Method

1. If you have a complex model with lots of moving parts, you'll want to use implicit FEA. This method can handle complex geometries and large deformations.
2. If you need to simulate a dynamic event, like an explosion or a car crash, explicit FEA is the way to go. This method is better at handling high rates of change.
3. If you're working with a large system, it's possible that implicit could run out of memory while explicit may not, so better use explicit.
4. If you're looking for detailed results, explicit FEA might be a better option. Implicit FEA often provides more accurate results when dealing with static loads.
5. The best choice for your needs will depend on what you're trying to simulate and how detailed your results need to be.

Author

Anup KumarH S

Author

Skill-Lync

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