## FEA Engineering White Papers

Here you will find an assortment of FEA white papers and presentations produced by the Predictive Engineering staff on topics such as Fracture Mechanics & FEA, Small Connection Elements, Linear & Nonlinear Buckling Analysis, RBE and Modeling Composites.

White Papers

# High-Cycle Fatigue Analysis - Stress-Life Made Easy

A brief walk-through is given on how a fatigue analysis works and a bit of foundation knowledge to guide a new user through this process.  It should be mentioned that we are focusing on the high-cycle fatigue of metals.

# Response Spectrum Analysis - Shock and Seismic in FEMAP & NX Nastran

Response spectrum analysis is widely used for the design and assessment of structures that are subject to earthquakes or shock events.

The reason we want to use a response spectrum is that it allows us to analyze transient events (time based events) without having to review hundreds or thousands of results sets. In essence, it allows us to assess the maximum dynamic response (stress, acceleration, velocity or displacement) of a structure using a very simple analysis technique (normal modes). Moreover all of this goodness can be had by only having to interrogate one (1) output set.

This tutorial will walk you through the theoretical background of response spectrum analysis and how to actually implement it within FEMAP & NX Nastran.

MODEL FILES

# Random Vibration Analysis in FEMAP

Random vibration is vibration which can only be described in a statistical sense.  The magnitude at any given moment is not known, but is instead described in a statistical sense via mean values and standard deviations.

Random vibration problems arise due to earthquakes, tsunamis, acoustic excitation (e.g., rocket launches), wind fluctuations, or any loading which is inherently random.  Often random noise due to operating or transporting conditions can also be considered.  These random vibrations are usually described in terms of a power spectral density (PSD) function.

In this white paper we will cover steps to create a PSD analysis in Femap, and compare the results to an analytical solution.

MODEL FILES

# Thermal-Stress Analysis: Theory and Practices

Thermal-Stress and Thermal-Deflection analyses are an important subset of general finite element analysis (FEA) modeling. Such analyses are common in the development of rocket motors, ASME pressure vessels, electronics (PCB), electronic systems (automotive lamp systems), composite curing mandrels, generators, satellites and etc.

# LS-DYNA Analysis: Improving the Precision of Discrete element Simulations through Calibration Models

##### Introduction

This Predictive Engineering white paper was delivered at the 13th International LS-DYNA User's Conference and was developed to support our LS-DYNA consulting services work.

##### Abstract of White Paper

The Discrete Element Method (DEM) is fast becoming the numerical method of choice for modelling the flow of granular material. Mining, agriculture and food handling industries, among many others, have been turning their attention towards this powerful analysis technique. In this paper, we present three simple calibration modeling tactics that should be the starting point for every DEM simulation of dry and semi-dry granular material. The three tests are designed to be as simple as possible in order to minimize the run time of the test simulations. The tests are developed to be run in a specific order, providing a sequential calibration procedure that does not involve multiple unknown variables in each test.

# Linear Dynamics for Everyone: Part 1

##### Why natural frequency analysis is good for you and your design

This article, reproduced from a three-part series in Desktop Engineering magazine, is a great introduction to the power of Finite Element Analysis to solve problems relating to vibration that often drives early product failure due to fatigue damage or just outright failure.

Introduction: Analysis work is rarely done because we have spare time or are just curious about the mechanical behavior of a part or system. It’s typically performed because we are worried that the design might fail in a costly or dangerous manner. Depending on the potential failure mode our anxiety might not be too high, but given today’s demanding OEMs and litigious public, the task could involve high drama with your name written all over it.

# Linear Dynamics part 2

In Part 2 of the Desktop Engineering magazine article, we explore vibration analysis and how it can show detailed structural behavior under dynamic loading. This article shows how we leverage Part I to indicate how the structure might respond to a vibrating load without having to do any type of more complex analysis. In short, this article shows how to interpret your normal modes results like a “pro”.

The Dominators: Modes with Mass: An interesting fact about normal modes analysis is that we can associate a percentage of the structure’s mass to each mode. With enough modes, you get 100 percent of the mass of the structure, though for complex structures this can mean hundreds of modes. The common thought is that if you capture 90 percent of the mass of the structure that will be good enough. For now, we’ll start classically and then show what this concept means in a real-world engineering situation.

# Linear Dynamics part 3

##### Extracting real quantitative data to anticipate everything from earthquakes to rocket launches

In Part 3 of the Desktop Engineering magazine article, we look into extracting real quantitative data to anticipate everything from earthquakes to rocket launches.

Introduction: If you’ve kept up with this series of articles, you now know more about the dynamic behavior of structures than 95 percent of your peer group within the design and engineering world. And after reading about how vibration analysis reveals key information about structural behavior (see DE, April and May 2008), the terms “natural frequencies, normal mode shapes, mass participation factors, and strain energy” have become integral to your vocabulary. Up to this point the discussion has centered on qualitative terms about the mechanical response of structures due to dynamic loading. In this last part, we'll show how to extract real quantitative data (i.e., displacements and stresses) from a simple normal-modes analysis.

# Bolt Preload with Femap and NX Nastran

Bolt preload adds quite a bit of complexity to any model since the analysis procedure is nonlinear (geometrically nonlinear) and that two sequential nonlinear runs are required to arrive at the final “bolt preload solution”. The utility of this approach lies in its ability to quantitatively calculate the bolt axial and shear forces for any type of bolted connection. Additionally, if bolt fatigue is important, then a bolt preload approach is invaluable.

Bolt preload is used to clamp together two plates or two structures and create a frictional lock between the members and reduce the effects of cycling loading on the bolt. With respect to the laWer (i.e., bolt fatigue), bolt preload can make all the difference between a safe, long-­‐lasting structure or catastrophic failure.

# Fracture Mechanics and Finite Element Analysis

This white paper was done to provide an easy to understand approach to the use of finite element analysis (FEA) toward fracture mechanics. It starts off with a review of fracture mechanics and boils it down to a simple principle of energy in (loading) equals energy out (fracture).

# Fracture Mechanics of Glass

Glass is a fantastic material for subsea use. It’s incredibly strong in compression, transparent, and also relatively light. This white paper explores the fracture mechanics of glass using FEA to simulate both static and dynamic stresses in a glass hydrosphere.

Introduction: Research on the use of glass for submersible applications mostly ended in the 1970’s as world interest in the deep parts of the ocean shifted elsewhere. While glass had some early successes, research halted with the rise in acceptance of acrylics for shallow submersible ports and the realization by Naval research that glass is not a good material to resist nearby explosive detonations. Since that time considerable advances in fracture mechanics, reliability analysis, coatings, and manufacturing techniques have occurred.

# Linear and Nonlinear Buckling Analysis and Flange Crippling

This white paper will walk you through the use of NX Nastran and LS-DYNA to do classical Eulerian Buckling, geometric nonlinear buckling and complete, full-physics nonlinear buckling (LS-DYNA). We will also show you how to validate your linear buckling analysis with a non-liner static analysis. Additional examples are presented on flange crippling and then finally the application of these techniques to the buckling analysis of a beer can and then an eight-passenger, deep-diving luxury submarine.

Everybodys’ First Buckling Analysis Model: The cross-section properties and equations given above provide all the necessary ingredients to calculate the buckling load of the column.  The factor “K” shown above is used to classify the beam’s end conditions (Manual of Steel Construction, 8th edition, American Institute of Steel Construction).  The buckling load depends upon whether the beam’s end points are fixed, pinned or partially constrained.

# Mastering RBE Elements

This set of notes taken from one of our technical web seminars, condenses down in a logical fashion the very complex behavior of multi-point constraints which form the numerical foundation of RBE2 and RBE3 elements. Examples are presented to illustrate good and bad modeling practices.

# Modeling Composites Handbook: An Introduction to the How and Why with Femap, NX Nastran and LS-DYNA

This 100+ page Handbook is intended to be the starting point for engineers that are interested in simulating the mechanical response of composite materials using Femap and then analyzing their models using NX Nastran or LS-DYNA. Basic laminate modeling theory is introduced and then tied back to how it is implemented within Femap. We also provide some easy to use rules such that one can create their own composite mechanical properties based on the rule-of-mixtures and cover the limitations of this method.

Important Chapters in this Handbook are: Composite Micromechanics, Laminate Modeling in Femap, Creating a 2D Laminate Model in Femap, Creating a 3D Laminate Model in Femap, Modeling a Sandwich Composite, Laminate Failure Theories in Femap, Modeling the Failure Behavior of Composite Laminates, Four-Point Bending of a Sandwich Composite Using Femap and NX Nastran and a very useful Addendum.

# NX Nastran Connection Elements (RBE2, RBE3 and CBUSH) and How Amazingly Useful They Are for FEA Modeling

This white paper assumes that the reader has the basics of FEA down pat and an inkling of how R-elements work. The objective is to describe in detail how to use R-connections and CBUSH elements correctly and with confidence.  If you make it through this note, you’ll most likely know more about these little connections than 99% of your peers.

Introduction: We’ll cover the basics of MPC terminology which is the foundation of the RBE2 and RBE3 connections.  A keen understanding will be provided on how to think in terms of independent and dependent nodes.  It’ll be obvious after this discussion that it is not logical to apply SPC’s to dependent nodes or to connect other dependent nodes between different R-elements.  Best practices will be covered and some recommendations given (e.g., be careful when using MPC’s in a nonlinear analysis and especially so when large displacements are involved).

The thermal CTE capability of the RBE2 connection will also be covered for completeness.

# Principles of Vibration Analysis

Vibration analysis is a huge topic and is easily the second most common type of FEA analysis after the basic static stress analysis. Within the field of vibration analysis, the most common type of analysis is that based on the linear behavior of the structure or system during its operation. That is, its stress/strain response is linear and when a load is removed, the structure returns to its original position in a stress/strain free condition.

What’s Covered: Foundation of Frequency Analysis, Standard Normal Modes Analysis, Modal Frequency Analysis, PSD Analysis, Direct Transient Analysis, Model Checkout (mass and constraints) and Additional Reading

An Excerpt From the White Paper: Standard Normal Modes Analysis: To see how this is applied in practice, we will run through an analysis project from start to finish (Normal Modes, Modal Frequency, PSD and Direct Transient). The model has been tweaked to protect the innocent.

# See Analysis Data's True Colors Image

This article printed in Desktop Engineering's March 2011 edition is helpful when it's time to convince your engineering lead to trust your finite element stress data results. The paper explains why you don't always get what you want—and how to get what you need when analyzing data's true colors.

Introduction: Whenever you see a stress contour plot, just assume that it is wrong,” says Mark Sherman, head of the Femap Development Team for Siemens PLM Software Solutions. Although Sherman’s comment sounds a bit dramatic, it’s par for the course in computer modeling, where a common saying is “garbage in, gospel out (GIGO).”

White Paper Outline: How Stresses are Calculated in FEA, De-Bugging Jagged Stress Contours, Judging Good and Bad FE Shapes, Saint-Venant’s Principle of Decreasing Load Effects, Interpreting Stress Results and Visualizing Beyond FEA