6 things all engineers should know before FEA

Engineers in every industry will do finite element analysis （FEA） Integration into the design cycle , To ensure the safety of its products , Cost effective and quick to market . however , Analysis is not like CAD Model into any FEA It's as simple as in the bag .

There are more software options today than ever before . Over the years , Engineers have only been able to use linear static stress analysis . lately , The finite element software package has been extended to include nonlinear static stresses , Dynamic stress （ Vibration ）, Fluid flow , conduct heat , Electrostatic and based on FEA Stress and motion analysis function of . These functions are usually combined to perform an analysis that considers a variety of physical phenomena , And tightly integrate them into CAD In the interface .

This article will briefly discuss some FEA Basic knowledge of , Then outline the engineer's decision to use FEA What you need to know when .

1.     FEA Basic knowledge of . The finite element model is a discrete representation of the continuous physical parts to be analyzed . The representation is created using nodes , These nodes are connected together to form form elements . Nodes are discrete points on physical parts , At this point , The analysis will predict the response of the part due to the applied load . According to the node degrees of freedom （DOF） Define this response . For stress analysis , According to the selected element type （ For example, beam , plate ,2D and 3D Elements ）, Each node can have up to six degrees of freedom （ Translate three components and rotate three components ）. The grid of connected elements on the common node includes the grid . When adjacent elements share nodes , The displacement field is continuous on the boundary of the shared element , And it can transfer loads between elements .

2.     Design criteria . In any analysis , The engineer first needs to determine the important physical phenomena and environmental conditions to which the parts will be exposed , And the desired design objectives . for example , One of the most common concerns of engineers is to maximize the durability of parts . The first step in the analysis is to determine whether the design is subject to static or dynamic conditions . In its practical application , Parts are fixed in space , Is it vibrated or moved relative to other parts in the assembly ？ When you run the entire product during the entire motion cycle , What's going to happen ？ these years , Engineers facing expensive computing resources use static FEA The software calculates the pressure in time at a single moment to simplify the problem . Only if the design has not been impacted for a period of time , When movement or applied load changes , This method works .

3.     3. Multiple physical fields . In addition to considering the ability of parts to withstand mechanical stress ,FEA Software also often enables engineers to predict other actual stresses , for example ： The effects of extreme temperatures or temperature changes （ Heat transfer analysis ）, The flow of fluid through and around an object （ Fluid flow analysis ）, Or the voltage distribution over the entire surface or volume of the object （ Electrostatic analysis ）. These effects usually work together , therefore ,FEA Procedures must consider their impact on each other , This is important . for example , Computer chips may heat up over time , Cooled by the air flow from the fan , Vibrate and live with other parts . A typical approach might be to isolate and compute each variable , Then enter the results into... At one time FEA In the program . however , Each variable also affects all other variables , Therefore, it is often necessary to use coupling analysis or tools for correlating results .

4.     Motion simulation . It's cheaper to use today , Faster computers ,FEA The growth trend is to use finite element models to simulate large-scale motion . In the past , The design process needs to be able to build for different purposes （ Design , Processing or analysis ） An expert on models . however , With more computing power at your fingertips , Engineers today can use the same model for all three requirements , You can even perform motion analysis from their desktops . There are three common methods ： Motion load transfer requires engineers to use two applications ： The kinematics software package is used to obtain approximate loads , Then input it into FEA Analysis in the program . This method does not simulate the motion of the finite element model , But only simulate many approximate static points . It is faster than the manual calculation of stress , But it uses the rigid body motion program , The engineer must therefore accept certain assumptions . for example , Parts such as washers are flexible , But the rigid body program cannot calculate . The explicit time step method uses a large number of short time intervals to simulate the actual motion of the model . It passes along time “ Forward ” To determine the solution , Extrapolate from the previous time step solution . Within a given time interval , This method is very fast , But for the whole scene , It may take too long . for example , If you want to simulate a car hitting a telegraph pole , It would be impractical to use this method to consider the actual impact moment . be based on FEA The implicit time step method and the automatic time step scheme for stress and motion analysis can be realized by running relatively inactive time periods in larger time steps （ For example, constant acceleration or deceleration ） To simulate the motion period of the model , Then automatically reduce the time step size to capture the cycle of key activities , For example, contact between surfaces , Local buckling or impact . therefore , For the motion of the part , Precise solutions for deformation and stress become practical . however , As usual , There are trade-offs in speed , Because this method will calculate the results at each time point .

5.     modeling . After determining the type of analysis required and the characteristics of the operating environment , The engineer must generate an appropriate analysis parameter （ For example, load , Constraints and appropriate meshes ） Finite element model of . CAD / FEA Three approaches to interoperability are available in ease of use , Accuracy and functionality can be very different ：CAD The common document format approach requires the engineer to CAD Export solid model to neutral file format （ for example IGES,ACIS or Parasolid）, Then import the neutral file FEA System for setup and analysis . Although this method usually enables engineers to make full use of FEA Program , But it may also lead to CAD Geometry data is missing . therefore , This is not the ideal method , Because it sometimes involves using a simplified version of the problem .“ One window ” CAD / FEA Method does not require file translation , because FEA The supplier has built analytics into CAD In the solid modeler . The user chose this option because it is easy to use , Because they can be accessed from a drop-down menu in a single application FEA function . however , Due to space and interface limitations ,FEA Providers often simplify their single window versions . in addition , because FEA The company must target each CAD The supplier's software can only integrate these two products by customizing its products , So it may also be limited . therefore , If CAD / FEA The interoperability approach is in many ways CAD Environment or with medium to advanced analysis functions , Then the Engineer may need to purchase and learn other software .“ Outside a window ” Of CAD / FEA Methods do not require file translation , But it has additional features , Can be in and CAD The solid modeler executes on different computers FEA analysis , And you can use a single interface to handle multiple CAD software package . The main difference is that FEA Run in a separate application , therefore FEA The supplier can provide a more complete version （ for example , Include more element types , Mesh and analysis options ）, Without other analysis software . One possible drawback of this approach is , Engineers must learn at the same time CAD and FEA Software .

6.     Interpretation of the results . After the engineer obtains the analysis results , He or she inevitably asks ：“ How do I know my answer is correct ？” therefore ,FEA The software must provide a result verification or validation tool . Ideally , These tools include not only displacement , Stress or other resulting profile , It also includes precise profiles that provide qualitative and quantitative validation . Usually , The analysis and modeling choices made by the engineer will determine how easy it is to interpret the results . for example , If a linear static stress analysis is performed , Then only the contour at a single point in time will be available . The indicated stresses need to be interpreted in some way , For example, compare the value with the yield stress of the material used in the analysis . Besides , The engineer also assumes that the moment of analysis in the linear static stress analysis represents the worst case . On the other hand , If you execute on a solid assembly based on FEA Stress and motion analysis , It will be much easier to interpret the results , Because you can see the model moving over time , bending , Bend or even break . These time-dependent results can be recorded in animation files , for example Windows .avi Format . In addition to the animation function , The Engineer shall expect FEA The software is fast , Easy to use visualization tools , To view and present the results of all analysis types and other integrated display options , For example, the automatic option for generating the resulting contour image file . And drawing ,VRML Document and HTML The report . These tools can be used to prepare to present results to other engineers, even managers and customers . Consider carefully the analysis discussed here , Modeling and interpretation of results , It will help engineers to understand their FEA The effectiveness of the results more confidently demonstrates its design .