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Desktop Engineering Blog

Composite Zoning Optimisation

Posted by Andy Woodward on 15-Jun-2017 16:58:33

It is for good reasons that designing laminated composite structures is sometimes known as a ‘black art’.  It is not easy to intuit from the topology of and loads applied to a component what a good ply layup should be.  Many companies rely on the wisdom of veteran engineers’ hard won experience, but sometimes it is necessary to take a step back and ask “what else could we try?”.

Often the design of a composite layup starts with the definition of zones within a part.  The layup on each of these zones can then be fettled using FEA to arrive at a stacking sequence which can then be used to define plies. 

But how do you choose the zones? Is it arbitrary based on the topology of the part? Do you just chequer-board your panel into regular squares?  You could use a technique developed with MSC Nastran for one of the F1 companies.

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Topics: Various - MSC, MSC Software, FEA, Analysis, MSC Nastran, Composites

Fracture Mechanics

Posted by Andy Woodward on 30-May-2017 11:30:00

Modelling Cracks the Easy Way

In my previous blog I talked about the advantages of automatic re-meshing in the analysis of rubbers in improving accuracy and stability of a simulation.  One advanced application of this capability that was not touched upon was in the field of crack propagation.

In many industries it is sufficient to use your analysis to predict that a crack could initiate and redesign the part to avoid this occurrence.  In others though it is possible that a crack may be identified from an in-service inspection whereupon it becomes necessary to understand if it will propagate under the loads applied and how quickly so that a replacement can be introduced in a timely manner.

Predicting crack growth in materials with finite elements can seem more art than science. 

As an example, in some codes you may need to construct a very precise ‘rosette’ mesh at the crack tip.

A series of angular perturbations to the crack tip node are then simulated to look at the energy release resulting from extending the tip with the assumption being it moves in the direction of the greatest energy release.

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Topics: Various - MSC, MSC Software, FEA, Analysis

Random Vibration Fatigue

Posted by Andy Woodward on 05-May-2017 14:09:58

In a previous article I discussed using random analysis to predict failure of components in a vibration environment.  Random analysis is a quick way of ensuring that statistically the maximum stress due to a vibration loading will not exceed a set level, but the most common mode of failure in such an environment is not due to one single load spike but due to the summation of damage from all the load cycles – known as fatigue failure.

Classically fatigue failure due to a transient load was performed quasi-statically.  A known load history was combined with stresses from a unit load in the FEA model to create a stress time history.  Rainflow cycle counting was used to evaluate the stress cycles and then damage calculated from these using classical theories like Goodman and summed using Miner’s rule.  There were problems with this method though.

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Topics: Various - MSC, FEA, Analysis

Welding Simulation

Posted by Andy Woodward on 20-Mar-2017 10:49:55

In an earlier article I talked in general terms about the benefits of using CAE tools to model the physics of manufacturing processes.  In this article I will show a case study example using welding simulation to decide on the best strategy for welding a two-part swing arm together.

The objective is to compare two different clamping schemes with third iteration that uses tack welds to hold the parts together.

The two parts were made of carbon steel, welded along an ~80mm length using arc welding with an estimate energy input of around 2000J per centimetre. 

The simulation tool used for this analysis uses a state-of-the-art multi-physics finite element programme as the underlying solver, but has a custom user interface that speaks to the manufacturing engineer about his process flow and not about the minutia of an FEA job set up.

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Topics: Various - MSC, FEA, Analysis