FEA FAQ's

FEA FAQ's
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What is the role of a Consulting Engineer?

By consulting engineer I'm referring to an individual who is independently employed and has academic training in a specific field or fields of engineering plus professional experience in those fields plus a professional license to practice engineering in a specific state. If your company builds civil types of structures such as: public buildings, bridges, dams, roads, etc. your designs most likely are required to be evaluated by a registered professional engineer and if deemed satisfactory will put his or her stamp on the design. This could be one of your existing employees or an independent consulting engineer.

If your company designs commercial products you probably do not need to have your designs approved by a professional engineer but you do have an obligation to do a diligent job on the design, fabrication, and testing (the engineering) of your products. It also is far cheaper to find problems before you go into production of a new product or a modification of an existing product. Engineers, whether on your staff already, or an independent consultant can help with this.

Independent consulting engineers allow you to hire the specific expertise you need when you need it without retaining someone on staff permanently. Independent consultants usually have a high level of academic training and professional experience, frequently higher than experienced employees or contractors. While we normally work at a higher hourly rate than direct employees, you are only paying for our services when you need them. We also have a business to run with all of the expenses associated with that so it's not reasonable to expect us to work at the same hourly rate as a direct employee, even one with the same level of qualifications. Although if you compare hourly costs for a direct employee including indirect costs, with a contract engineer, and with an independent consulting engineer you will find that the total costs are comparable assuming comparable qualifications.

Clients are under no obligation to follow our recommendations although it is usually unwise not to. It's a little like a visit to the doctor, who can tell you what you need to do, it's up to you to do it.

If we say that a design is satisfactory it will be for a very specific set of quantitative criteria such as: specific geometry, loads, boundary conditions, and material properties. It will also apply to a very specific type of analysis: linear, non-linear, static, dynamic, etc. For a registered professional engineer to put his or her stamp on a design he or she must either do the design and/or analysis themselves or directly supervise those that do. Normally an independent consulting engineer is not supervising the clients employees, he or she is doing the design and/or analysis themselves. If we are only hired to do a linear static analysis we will provide the results of that analysis and make our recommendations based solely on that type of load. If a dynamic analysis is called for we would have to do a dynamic analysis in order to determine if the product or structure is acceptable under specific dynamic loading.

What is Finite Element Analysis (FEA) ?

FEA is typically used to model or simulate the behavior of complex mechanical parts to external stimuli. It is most useful on complex parts or assemblies that would be very difficult or impossible to solve in a mathematically closed form manually. It is frequently used to minimize or possibly eliminate building physical prototypes for testing.

FEA involves building an accurate 2D or 3D geometry model of the component to be analyzed. The model is broken up into discrete elements with nodes at their corners. Material properties are assigned for all materials used in the part. Boundary conditions are used to model physical connections to the part by setting the appropriate degrees of freedom (DOF) for all boundary nodes. Each node has up to six DOF comprised of three for translation, and three for rotation. Boundary conditions can also be used to model: dynamic, thermal, fluidic, and electrostatic connections. This part of the modeling process is done with a CAD like preprocessor to the FEA software, or geometry data can be imported from your existing CAD or solid modeling software which may be an easier way for people to work.

Once the geometry, materials, and boundary conditions are set, the next step is for the engineer to decide on the element type(s) and analysis type and then run the FEA solver to solve thousands (or hundreds of thousands) of simultaneous differential equations to obtain a physical displacement at each node. This strain data is then used to compute stress data at each node. A graphical postprocessor is used to digest all of this data and display it superimposed over the geometry model of the part with color coded stress (or other parameters) contour lines. Models can also be sliced to display stress contours inside the part.

What are Elements and Nodes ?

Elements are the discrete geometric subdivisions of the model. A 2D FEA model will normally have either triangular and/or quadrilateral elements. A 3D FEA model will normally have either 3D bricks and/or 3D tetrahedra as elements. Nodes are at the intersection points of the lines that make up an element.

What are Boundary Conditions (BC) ?

Boundary conditions are the way that a specific node in a FEA model is attached to the ground or some other node in the model. A variety of BC's are available including: rigid or fixed, elastic spring, etc. BC's can be specified to be fixed in any or all of the six DOF.

How do you build a FEA model ?

You must create 2D or 3D geometry which matches the real object that you want to analyze. It can be created within the preprocessor of the FEA software or previously created geometry can be imported from a CAD system or a solid modeler.

What do the terms Linear, Non-Linear, Static, and Dynamic refer to ?

In engineering analysis, whether FEA is used or not, linear refers to an analysis or FEA model where linear behavior of the item being analyzed and its materials are assumed to occur. That is the object being analyzed will not be loaded beyond the elastic limits of its materials.

Non-linear refers to a model deflection, its materials, and/or boundary conditions which will be subjected to non-linear behavior. Some materials exhibit non-linear stress-strain behavior and this is referred to as material non-linearity. If large deflections are present they result in geometric non-linearity. Finally if boundary conditions change for different load levels this is referred to as boundary non-linearity.

Static refers to a model which is loaded statically or is loaded dynamically so slowly that it can be assumed to be loaded statically. That is the applied load is fixed in amplitude with respect to time or changes with time so slowly that it can be treated as a static load.

Dynamic refers to a model which is loaded dynamically or in a time dependent fashion. Examples would be shock, vibration, and seismic loading where the load amplitudes vary significantly with respect to time.

How much computer hardware do I need?

At least as much as is required for CAD work - see the answer to this question for CAD/CAE FAQ's. FEA, 3D solid modeling, and graphics image processing are three disciplines that require enormous amounts of computing horsepower. The fastest and most powerful microcomputer systems will be slow for very large models, possibly too slow. But they work very well for small to medium sized models.

How long does it take to become proficient with Algor, or any other powerful FEA software?

In spite of what the sales and marketing people say, for any FEA company, it takes a while to become proficient with FEA software - months to years is typical. And months is very optimistic. With effective training it takes less time, without training it takes much longer. Utilizing FEA software correctly relies heavily on engineering judgment and experience. Practitioners should have a significant amount of academic training and professional experience in: mechanical design, statics, dynamics, materials, and stress analysis or other related analytical techniques.

What are efficient FEA work habits?

Take the Introduction to Algor FEA course and find out. If you don’t learn to work efficiently, you probably won’t.