Fatigue risks reduced by graphical glyphs

Tom Shelley reports on technology to investigate possible fatigue failures and a novel software approach to managing analyses generally



Design life estimates based on fatigue can now be produced using FEA in a process that the user can set up linking multiple graphical "Glyphs", each of which represents a window on an active software function.

Also built-in are data analysis algorithms to avoid the possibility of electronically generated garbage data producing garbage output, and this alone should make the software very worthwhile to use even if it does not yet totally solve the problem of preventing fatigue failures.

Fatigue, whereby repeated cyclic stresses cause failures at well below the apparent load bearing capacity of a structure, has been more or less understood for decades. It nonetheless remains a problem, potentially catastrophic in the case of aircraft and a major cause of warranty claims in other products.

Software to help design out many of the problems has been developed by Sheffield headquartered company nCode, which originally spun out of British Rail Research, later became part of AEA Technology and is now owned and being invested in by venture capitalists Coller Capital. The package is named, "DesignLife", and may be reduced to what the company calls its "Five box trick" in which loads, geometry and materials are input, a fatigue analysis is run and fatigue results are output. Each box exists as what the company calls a 'Glyph' which is an active process represented on screen. The glyphs may be linked together as required by the user. Processes can be developed with hundreds of steps, branches, and multiple analysis types but clicking on 'run' makes the data run automatically through each stage.

Loads may be derived from multiple transducers or simulated. Algorithms flag up gaps in data that may result from malfunctioning sensors and may also be used to remove electronic spikes. Geometry is imported directly from finite element model results files and the software presently works with NASTRAN, ANSYS and ABAQUS. DesignLife has its own post processor but will also output to other common post processors.

It can be used to automatically identify critical areas and perform stress-life and strain-life analyses. It includes spot weld analysis and will include seam weld analysis. A hotspot analysis facility automatically ranks results and sets the viewpoint so they can quickly be seen.

Its developers make no pretence that is does away with the need for expert engineers familiar with fatigue problems arising from residual gaps in load carrying fillet welds, failure to perform post welding stress relief annealing or complex interactions between residual stresses arising from forming and corrosion. It will, however, flag up quite a wide range of problems without having to discover them all in a prolonged prototype test, redesign and rebuild cycle and thus significantly reduce development time.

Marketing director Neil Kirtley told Eureka that most of the company's current revenue comes at the present time from in and around Detroit but offices have recently been opened in Japan and China where there is growing interest.

nCode
Pointers

* Software automates fatigue analyses

* It also identifies possible errors in electronically derived load data and may be used to eliminate same

* While it does not eliminate the possibility of fatigue failures, it highlights regions most at risk and does much to compress the design-build-test-redesign cycle

Author
Tom Shelley

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