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Many thanks for your response Wil. I intend to argue against the use of this material and will use your response as additional ammunition!

Thanks for the replies. To err on the safe side I probably need to stick with the 10,000-hour curve

I have a question regarding the degradation in mechanical properties of 6061-T6 aluminium alloy at elevated temperatures. The application involves operation at 250degC which creates quite a severe reduction in the strength properties. If I review published data (ESDU, MMPDS-4 etc) there are...

Thanks for that - there's some useful stuff there

I have an empirical formula developed by the RAE for calculating the equivalent static loading from a birdstrike. The report details are: The Design of Leading Edge and Intake Wall Structures to Resist Bird Impact Report No. RAE TR72056 I have not been able to obtain a copy of this report and...

Thanks for the response, but if the shaker table is being controlled such that the positive and negative accelerations are identical does it matter which way up the UUT is mounted? I would have thought that the modes and frequencies of the UUT would be the same either way.

If I am designing a vibration fixture for testing in the vertical axis, does it matter if the test item is mounted upside down? Some opinions say yes, since gravity is adding a 1g downward acceleration. My opinion is that the feedback loop in the vibration controller will neutralise this and...

Thanks for the response Greg. However, rainflow counting is used to reduce a complex set of periodic loadings to a simple set of stress reversals. I'm not sure if or how this can be applied to a random input spectrum.

If I run a stress analysis with a random vibration input spectrum, the output stresses will be in Grms (1-sigma), and therefore for a fatigue analysis I can also determine the 2-sigma and 3-sigma stresses. However, the thing I'm uncertain about is how to determine the number of cycles at each...

We wouldn't use Al. for those temperatures, it's strength would be non-existant. Our application is about 95degC.

Many thanks for the replies, and I appreciate that in any complex system there will be many resonances on the many separate components. However, this is a Qualification test and not a development test, so I am trying to understand what the specific requirements of DO-160 are. My belif is that...

Yes, I was also a bit confused by the expression, particularly as our operating temperature is >90degC. I've not seen fatigue temperature factors defined in MMPDS, can you provide a reference for the Ct=0.95 that you quoted? Many thanks, Peter

The procedure states "..select the most severe frequencies (maximum of 4). Perform sinusoidal dwells at each of these frequencies for 30 minutes". The most severe are those with the highest responses, and the reason I would suggest that it says 'maximum of 4' is that there are 4 sinusoidal bands.

I have a query related to the DO-160 Helicopter Vibration test procedure. A sine sweep has been conducted on a piece of equipment that has identified several closely spaced resonances within the 1st sinusoidal test band. The test house is conducting 4 separate sine dwells at the 4 highest...

Can I ask a couple of questions about Fatigue Modifying factors when performing a fatigue analysis of an aluminium component: 1. Temperature Factor - I have seen it recommended that a temperature factor of 1 is applied for temperatures up to 450degC. Whereas I have also seen it proposed that the...

The failures are occurring within a thread root. This is the predicted high stress region but the analysis also indicates that the stress levels are well below the fatigue limit.

Many thanks for your response Denial, which goes a long way to explaining the issue. I've made some rough (pessimistic) assumptions to some of the variables and the response is an order of magnitude above the pressure loading natural frequency. It therefore seems that the advice I received from...

I'm doing some stress analysis for a filter system that is subjected to 1,500,000 pressure cycles from 0 to 260bar, with a pulse rise rate of 100,000 to 200,000psi/sec. Previous analyses have been carried out assuming a steadily applied load repeated for the required number of cycles. However...