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Material Models Blog Posts

Computing and Controlling the Volume of a Cavity

February 3, 2014

There are various ways of handling interactions between fluids and solids in COMSOL. You can, for example, explicitly model the fluid using the full Navier-Stokes equations for the pressure and fluid velocity fields. Although that can be a very accurate approach, it’s much more expensive than is needed for certain types of Fluid-Structure Interaction (FSI) problems. Here, we’ll introduce a method for modeling enclosed volumes containing incompressible fluids, under the additional assumption that the momentum and energy transfer via the […]

Submodeling: How to Analyze Local Effects in Large Models

January 1, 2014

Computer aided engineering (CAE) helps us understand how mechanical systems work before they are physically realized. In order to properly reflect the reality, we continuously increase the modeling complexity when we simulate, validate, or optimize our applications. A simple technique to improve a model is to increase the number of finite elements that in turn create more evaluation points. The hardware and simulation time, however, may limit the size of the model, and other solutions are necessary — such as […]

Why All These Stresses and Strains?

November 21, 2013

In structural mechanics you will come across a plethora of stress and strain definitions. It may be a Second Piola-Kirchhoff Stress or a Logarithmic Strain. In this blog post we will investigate these quantities, discuss why there is a need for so many variations of stresses and strains, and illuminate the consequences for you as a finite element analyst. The defining tensor expressions and transformations can be found in many textbooks, as well as through some web links at the […]

Fatigue Prediction Using Critical Plane Methods

July 22, 2013

Research on fatigue started in the 19th century, initiated following failing railroad axles that caused train accidents. In a rotating axle, stress varies from tension to compression and back to tension in one revolution. The load history is simple because it is uniaxial and proportional. Fatigue can then be evaluated with the S-N curve, also known as the Wöhler curve, which relates stress amplitude to a component’s life. In many applications we deal with multiaxiality and non-proportional loading. In this […]

Fatigue — When Cyclic Stress Produces Fractures

September 26, 2012

Many of the products that engineers design experience cyclic stresses during use that are below the material’s yield stress; unfortunately, these stresses can still be the primary reason for failure. Thus, engineers and designers must find ways of including the effects of cyclic stresses when designing products for long-term use.


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