Here you will find an assortment of FEA white papers and presentations produced by the Predictive Engineering staff.
Fracture Mechanics and Finite Element Analysis
Determining the basic parameters for a fracture mechanics analysis is easily accomplished using finite element modeling techniques. Nonetheless, the engineer must be cognizant of the limitations of both technologies for their rational use.
Analytical results are only as good as the experimentally measured fracture toughness data. Furthermore, fracture toughness of a material is not single-valued but may vary significantly due to environmental or fatigue effects.
This white paper, written in 1992, explores the rational use of FEA modeling techniques in fracture mechanics.
- Click to view (3.91 MB PDF)
Fracture Mechanics of Glass
Glass is a fantastic material for subsea use. It’s incredibly strong in compression, transparent, and also relatively light.
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.
This white paper explores the fracture mechanics of glass using FEA to simulate both static and dynamic stresses in a glass hydropshere.
- Click to view (135 KB PDF)
Small 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.
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.
The thermal CTE capability of the RBE2 connection will also be covered for completeness.
Lastly, the CBUSH element will be introduced and applications given on how to use this replacement for the CELAS element. The downfalls on using this element will be discussed and also why this element is a useful as a companion to the RBE2 and RBE3 elements.
Linear and Nonlinear Buckling Analysis and Flange Crippling
This white paper will walk you through the NX Nastran Buckling Analysis techniques and 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 an eight-passenger, deep-diving luxury submarine.
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.
Springs (CELAS) versus CBUSH Elements
There is no "versus", the only spring element that I use is the CBUSH. Why? If you use the standard NX Nastran spring element between non-coincident nodes, you have the potential to suck force out of your model; that is, your OLOAD won't match your SPCFORCE in the F06 file and your model is thus garbage. I made this mistake once and was schooled by senior analyst at Navistar when she noticed that my model had some strange stresses. This technical note provides the necessary foundation to easily use CBUSH spring elements in all types of FE models.
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.
See Analysis Data's True Colors
This article printed in Desktop Engineering's March 2011 edition is helpful when it's time to convince upper management to trust 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.
- Click to view (2 MB PDF)
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.
- Click to view (6 MB PDF)
Modeling Composites with Femap: An Introduction to The How and Why
Three methods for analyzing composites are explored. Each method has its good points, and some are more generally effective than others. Each has its own set of assumptions and limitations.
Using classical plate theory to model honeycomb panels can be effective, but it certainly has limitations and it should not be construed to be capable of handling all of the general cases that the more expansive laminate theory can.
As is true with all area of Finite Element Analysis, nothing can compensate for a lack of theoretical understanding and good judgment. The forgoing explanations represent a very small piece of the world of composite analysis and is meant only as a brief introduction.
- Click to view (1.6 MB PDF)
Linear Dynamics for Everyone: Part 1
This article, reproduced from a three-part series in Desktop Engineering magazine, is a great introduction to the power of Finite Element Analysis.
- Click to view (0.6 MB PDF)
Linear Dynamics for Everyone: Part 2
In Part 2 of the Desktop Engineering magazine article, we explore vibration analysis and how it can show detailed structrual behavior under dynamic loading.
- Click to view (0.3 MB PDF)
Linear Dynamics for Everyone: Part 3
In Part 3 of the Desktop Engineering magazine article, we look into extracting real quantitative data to anticipate everything from earthquakes to rocket launches.
- Click to view (0.5 MB PDF)