What Every Engineer Should Know About FEA
What Every Engineer Should Know About FEA
A Guide for Engineers and Designers Who Commission Simulation Work
PART 1
Drop Simulation
The Ask, the Model, and Your Role as a Partner
Joseph P. McFadden, Sr.
The Holistic Analyst
2026
Why You Asked
You designed something. Or maybe you inherited something. Either way, it is yours now — and someone just asked the question that keeps engineers up at night.
What happens if it gets dropped?
That question is the beginning of a conversation between you and the physics of the real world. This series is built entirely around that conversation — not for the simulation engineer running the analysis, but for you. The engineer, the designer, the product owner who asked for the simulation in the first place, and who will eventually sit across a desk or a screen and try to make sense of what the results are telling you.
When engineers and designers reach out for simulation support, the request rarely arrives in technical language. It arrives as a need. We have a drop requirement and I need to understand how close we are. Something broke in testing and I need to understand why. I need to know if this design will survive before we build the next prototype.
All of those are the same ask underneath. You want to understand how your system behaves when the world treats it roughly. You want insight before a prototype breaks on a lab bench, or before a product fails in the field in a way you did not see coming. Finite element analysis — FEA — is one of the most powerful tools available to help answer that question. But like any powerful tool, it works best when both people in the conversation understand what it can and cannot do.
Your System
Before we go any further, it is worth pausing on a single word: your.
Whether you designed this product from the ground up, or you inherited a design that was already three generations old when it landed on your desk, you have a stake in it. You have an interest in understanding how it behaves. That stake is what brought you here. And it is what makes the work matter.
Your system has a nature. It has mass, stiffness, geometry, and material properties. When it is dropped — and things are always dropped, not as pessimism but as physics — all of those properties combine to determine what happens. The simulation does not change that nature. It tries to reveal it.
A key principle to carry through this entire series:
The simulation is a window into the nature of your system. How clearly it sees through that window depends on how faithfully the model represents the real design — and on the quality of the conversation between analyst and engineer.
What Actually Happens When Something Is Dropped
A drop event is short, violent, and full of information. To understand what the simulation is doing, it helps to first understand the event itself.
Consider dropping a smartphone — an object most engineers have held, and most have dropped at least once. The moment it leaves the hand, gravity accelerates it toward the floor. Impact occurs in a few milliseconds at most. In that window, the following happens simultaneously: the outer structure decelerates abruptly while internal components attempt to continue moving; the housing flexes, absorbs, and redirects energy; stress concentrates at corners, interfaces, and features with abrupt geometry changes; and energy that was kinetic motion converts into elastic deformation, plastic deformation, vibration, and heat.
The sound the phone makes when it hits the floor is physics announcing itself. The crack in the screen — or the absence of one — is the final verdict on how the structure managed that energy.
A drop event is over before you finish blinking. And yet everything that determines whether your design survives happens in that window. The simulation's role is to slow that window down, to observe it at every point in the structure and every moment in time, and to report what it finds.
What the Simulation Actually Does
At its core, a drop simulation is a virtual experiment. The analyst constructs a model of your product — not a perfect replica, but a carefully built representation that captures the physical attributes that matter most for the question being asked.
Building the Model
The geometry of your design is represented in the simulation. Features that are critical to load transfer and structural response are modeled with care. Details that have negligible influence on the answer may be simplified without meaningful loss of accuracy — a judgment call that requires engineering experience and knowledge of your product.
Materials are characterized by how they resist deformation, how strong they are, and how they behave under the high-speed loading conditions that a drop event produces. This last point matters more than most people realize: some materials behave differently when loaded quickly versus slowly, and a drop simulation must account for that.
The connections between components — how parts are fastened, bonded, or in contact with one another — are defined in the model. The way surfaces interact when they are forced together during impact has a significant influence on how loads transfer through the assembly.
Running the Analysis
Once the model is built, the analyst provides the starting conditions: the drop height (which determines the impact velocity), the surface the product lands on, and the orientation at the moment of impact. The simulation then steps through the event in time — thousands of tiny increments, each one a fraction of a millisecond long.
At each time step, the simulation asks: given where every piece of this structure was a moment ago, where is it now? What forces are acting? What is the stress at each location? What is deforming, and by how much? This process continues until the event is over and the structure has settled.
The result is not a single picture. It is a complete time history of the structural response — stress, displacement, and acceleration at every point in the model, from the first moment of contact to the point where the event has ended. Reading that time history is the work of the analyst. But understanding what it contains is the work of everyone at the table.
The Model Is Not the Truth
This is the most important concept in this series. Carry it with you through every simulation review you participate in.
The simulation is not the truth. It is an approximation — a carefully built, professionally executed, thoughtfully validated approximation of your design and the event it experiences.
Consider how a weather forecast works. A meteorologist does not show you the future. They show you what a very sophisticated model of the atmosphere believes the future will look like, given the best available input data and the best available physical models. You trust that forecast enough to bring an umbrella. You do not cancel the trip. Because you understand what it is: a useful approximation built with rigor and care, with acknowledged uncertainty at its edges.
A drop simulation works the same way. The model is built with rigor. The analyst applies professional judgment at every step. But there will always be a gap between the model and the physical world. The floor surface in the simulation may not match the one in the test lab. The material properties in the model are characterized from standard databases or coupon tests, not from every lot of plastic your supplier has ever produced. The boundary conditions — how the product is constrained, what the contact conditions are — involve assumptions that may be more or less representative of reality.
None of this is a failure. It is the nature of modeling. The analyst's job is to understand where those gaps exist, to minimize them where they matter, to quantify them where they can be quantified, and to communicate them clearly. Your job is to hear that communication, to bring your knowledge of the real product to the conversation, and to make design decisions with appropriate confidence — not false certainty.
What the simulation provides:
Insight into where stress concentrates and where load paths are established. Relative comparisons between design alternatives. An early warning system for structural vulnerabilities. A foundation for asking better questions before physical testing begins.
Understanding the Results
When results come back to you from a drop simulation, you will typically encounter several types of output. You do not need to be an expert in finite element analysis to engage with these intelligently. You need to understand what each type of result is telling you and what questions it should prompt.
Stress
Stress is a measure of how hard the material is being pushed or pulled at any given location. Think of it as the internal pressure the structure is under. Every material has a threshold — a level of stress beyond which it will yield, crack, or fail. The simulation shows you the distribution of stress across your structure at the worst moment of the impact event.
High stress in a location that is hidden inside the assembly, near a weld, at a sharp corner, or at a transition between wall thicknesses is particularly important to identify early. These are the locations where failures tend to originate. The simulation will find them whether they are visible in the design drawings or not.
Displacement
Displacement tells you how much parts of the structure moved during the impact. This matters in two ways. Permanent displacement — deformation that does not spring back — is a direct measure of whether your product has been structurally damaged even if it has not fractured. Temporary displacement during the event matters when you have clearances to maintain between components, or when you need to know whether internal parts will contact one another in ways the design did not intend.
Acceleration
If your product contains sensitive internal components — printed circuit boards, displays, hard drives, sensors, or any mechanism that must survive the event and continue functioning — then the accelerations those components experience during the drop are as important as the stress in the housing. The housing may survive without a visible crack while the board inside it has experienced forces well beyond what its components were qualified for. Acceleration results bring those internal loads into view.
Time History
All of the above results exist as a function of time, not just as a single worst-case snapshot. The stress builds, peaks, and dissipates. Waves of energy travel through the structure. Some components experience their peak loading early in the event; others are loaded by the rebounding structure after the initial contact has ended. Understanding when the worst case occurs — not just how severe it is — gives you and the analyst important context for interpreting what the model is showing.
Your Role as a Partner
The most important role in a simulation review does not belong to the analyst. It belongs to you.
You are not a customer picking up a finished package. You are a partner in an investigation. The analyst brings the method — the knowledge of how to build the model, run the analysis, and interpret the mathematics. You bring the product knowledge: the design intent, the manufacturing realities, the field failure history, the use cases that do not appear in any formal requirement document.
That knowledge is not optional context. It is essential input that shapes what the model is built to represent, what results are most important to examine, and what the findings actually mean for your design decisions.
The best simulation work happens in conversation — in the space between the model and the real product, where human judgment on both sides of the table is the only tool that bridges the gap.
Consider the questions that only you can answer. Is there a knit line from the injection molding process at the location where the simulation is showing peak stress? Are the internal components mounted differently in production than in the CAD model? Has this design been through a previous revision that addressed a known failure mode, and does the model reflect that revision? These are not simulation questions. They are product questions. And they profoundly affect what the simulation results mean.
Consider also the questions you should be asking. Where exactly is the worst-case stress? What is the margin between that peak stress and the material's yield strength? What orientation of impact produced this result — is that the most likely real-world drop scenario? What would change if the wall thickness were increased in that region? If the material were changed? If a rib were added?
An analyst who receives those questions will give you a richer, more useful analysis. An analyst who does not receive them will give you an accurate answer to the question they assumed you were asking — which may or may not be the question you actually needed answered.
The questions that make you a better partner:
What assumptions did the model make that I should be aware of? Where does the model agree with test results, and where does it not? What design change would most improve the structural response? What would you want to know about the real product that you do not know now?
Looking Forward
In the sections that follow, we will go deeper into the specific elements of a drop simulation that you, as a design partner, need to understand. We will examine the inputs that shape the model — and how your knowledge of the real product affects the choices made there. We will look at the results in more detail, and at the common places where the gap between the model and reality is widest. And we will talk about how to use what the simulation tells you to drive better design decisions.
The goal of this series is not to turn you into a simulation engineer. The goal is to make you a better partner in the work — someone who can sit across from a set of results, understand what they are showing, ask the right questions, and carry the findings back into your design process with confidence.
Your system has a nature. The simulation is a window into that nature. The quality of what you see through that window depends on the model, the method, and the conversation between everyone at the table.
That conversation starts now.
— End of Part 1 —
© 2026 Joseph P. McFadden, Sr. | The Holistic Analyst | McFaddenCAE.com
Freely shared for the engineering community. Not for resale.
