The Simulation Essentials for SOLIDWORKS Professionals
What do you really need to know to use SOLIDWORKS Simulation like a pro? The answer may surprise you. Even those fresh out of college with a mechanical engineering degree in hand will be pleasantly surprised to see how little they have to learn to use SOLIDWORKS Simulation—and we’ll review it all here. Think of this as your crash course in engineering for using SOLIDWORKS Simulation.
Is This Crash Course in Simulation For You?
Do you use SOLIDWORKS? Then, yes, this crash course is most likely for you. Over recent years, Simulation has transitioned from being the final step in the design process to becoming the tool guiding you every step of the way throughout the entire design process. It’s not just a validation tool; rather, simulation is a design guide—your “GPS navigation” for CAD, providing step-by-step insight into your design.
Material Science Essentials: Knowing the Material Input and Understanding the Results of your Simulation.
Material Science is the one topic that gives you a good foundation for your simulation setup and how to understand the results. We will introduce the key topics needed so you’ll be ready to run SOLIDWORKS Simulation like a pro.
Please note that for the purposes of this article, when we say Simulation, we are referring specifically to linear static analysis in SOLIDWORKS Simulation. This means that the materials are linear, elastic and isotropic (but those are topics for another article). This article serves as an introduction to the engineering background needed to understand Simulation.
Materials define exactly how the CAD model behaves in Simulation. Setting this up in Simulation is incredibly easy. You simply make your selection from the database to apply the material, just like you would at the CAD level. This is shown in the image below. It’s even easier If you apply your materials at the CAD level, because they’ll automatically be populated in Simulation.
Although the database is the same, it will look slightly different. Notice that from within Simulation you’ll see properties that are black, red and blue. These colors indicate what’s required for the study (red) and what might be required (blue) depending on the set up. As you can see in the image below, the line items are the same, but there is that added visual color cue indicating the required values for Simulation.
In my opinion, the three most important numbers for Simulation from the material library are:
- Modulus of elasticity (Young’s modulus)
- Yield strength
- Poisson’s ratio
These are the three properties that you really need to run a Simulation. Here’s what they mean.
Modulus of Elasticity
The modulus of elasticity, also known as Young’s modulus, or E, defines a material’s inherent strength. What you would call a stronger material would have a higher modulus of elasticity. For example, steel has a higher modulus of elasticity than aluminum, which has a higher modulus of elasticity than rubber.
This number, or property, is important because it defines exactly how much stress a material undergoes after it is loaded in Simulation, just like in the real world. Stress is what most designers look to as an indicator of failure in their model. Too much stress is bad. How much stress is okay? We answer this question later. (Spoiler Alert! It has to do with the yield strength.)
When you consider this at the atomic level, this is the strength of the bonds between atoms. In the context of the modulus of elasticity, a material is stronger because the atoms hold on to each other better. It takes more force to separate the atoms from one another. This separation, or space between atoms, is what we see as deformation or the change in shape. In other words, when you pull on something, it stretches because the atoms are being separated.
You can think of the modulus of elasticity as the “spring” between the atoms, as illustrated in the image below. The larger the modulus of elasticity, the stronger the “spring,” which means a greater force is needed to stretch the spring or move the material.
Stress & Strain
Before we can continue with the modulus of elasticity, we need to introduce the concepts of stress and strain. Every material has a map that defines its behavior when loaded. This map is called the stress strain curve. We know exactly how much stress a material will see when it is “strained” or loaded.
In static Simulation the stress strain curve is linear. This line can be defined entirely by the modulus of elasticity. In other words, a material’s behavior in Simulation can be defined in large part by the modulus of elasticity. See the image showing a stress strain curve for a material. This outlines the material’s reaction to loadings through the relationship of stress and strain via the modulus of elasticity.
- Stress (σ) is what you, as a designer, want to know to determine part failure. It describes the intensity of the load on an object. It is literally the force over an area.
- Strain (ε) is what you can measure. It’s defined as the ratio of the change in shape of an object.
- Modulus of elasticity (E) is used to determine stress from strain. It’s the slope of the stress strain curve for a material (in a linear static analysis, especially in this article). The higher the slope, the stronger the material. This is shown in the graph below.
- Hooke’s Law is the equation relating it all together.
The yield strength is used by designers as a measure of pass or fail for the design. Technically, the yield strength is a material property which marks the transition from the elastic deformation to plastic deformation. The difference between elastic and plastic is just temporary or permanent. Elastic deformation means it will go back to its original shape. Plastic deformation means its shape has been deformed too much and it will not go back to its original shape.
For a designer (in most circumstances), elastic deformation is okay, but plastic deformation is not—it’s considered a failure. Since the yield strength marks this transition, we use it to quantify pass or failure in terms of a value called the factor of safety.
The factor of safety is a number which relates the maximum stress to the yield strength. If this number is larger than 1 it passes; if it is less than 1 it is a failure.
A factor of safety plot can be easily shown in Simulation. The easiest way to use this plot is to have it indicate areas below a factor of safety of 1. This makes it obvious where there could be a failure. If you see any red, that’s where you need to focus your attention.
In Simulation, a stress result could be higher than the yield strength. However, it is important to note that this result is not accurate because beyond the yield strength the stress-Strain curve is no longer linear—meaning you need more than just the modulus of elasticity to get an accurate result. This is where a more advanced nonlinear simulation needs to be used. This is illustrated in the image below.
Poisson’s ratio describes how a material changes shape. As the material is stretched in one direction, it needs to contract in another; this is known as Poisson’s effect. When a material deforms, you aren’t adding or reducing the mass, just changing its shape. Poisson’s ratio describes this change of shape. This is illustrated in the image below. As you apply a force to a material it will expand in the direction of the force, and contract perpendicular to the force.
The checkerboard started out as perfect squares. When it deformed from the force, it changed its shape to a rectangle. The edges in the direction of the force (longitudinal) are now longer, while the edges perpendicular to the force (transverse) are now smaller. The ratio of the change of shape, or strain, in the transverse direction to the longitudinal direction is the Poisson’s ratio.
Putting it All Together in Simulation
Now that you understand what these important terms mean, let’s take a simplified look at the steps for how they are used by Simulation to get results.
- Step 1: Run Simulation and see how the applied forces change the material shape based on its stiffness from the modulus of elasticity.
- Step 2: Determine the change in shape to then calculate strain.
- Step 3: Use Hooke’s Law and the calculated strain to calculate stress.
- Step 4: Check the factor of safety to see if the part will fail or not.
With a combination of these essential material properties, you can paint the picture of your model’s performance. Is your design strong enough? Will it break? These are all questions you can now answer with Simulation.
This article was just an introduction, meant to build a foundation of understanding for using Simulation. There are even more advanced foundational topics worth exploring such as meshing. But when it comes to materials in Simulation, there are many more advanced topics covering more advanced materials such as composites, hyperelastic and viscoelastic. There are even other material failure modes beyond yield, such as resonance and fatigue. But at the end of the day, you don’t need to know this to be successful with using Simulation to guide you through the design process.
People spend their entire careers and devote their life’s work to studying these topics. But that is not necessary to use and benefit from Simulation. Behind all the complexity of the numerical methods and engineering concepts in FEA lies a level of elegance and intuitiveness that make SOLIDWORKS Simulation a powerful tool in the hands of SOLIDWORKS designers.