Careers

arrow_back_ios

Main Menu

arrow_back_ios

Main Menu

See All Software See All Strumenti See All Trasduttori See All Vibration Testing Equipment See All Electroacoustic See All Acoustic End-of-Line Test Systems
arrow_back_ios

Main Menu

See All Software di analisi e simulazione See All Software DAQ See All Driver e API See All Utilità See All Controllo delle vibrazioni See All Sistemi di alta precisione e calibrazione See All Sistemi DAQ See All Dispositivi portatili S&V See All Elettronica industriale See All Analizzatore di potenza See All Condizionatore di segnale S&V See All Trasduttori acustici See All Sensori di corrente e tensione See All Sensori di spostamento See All Sensori di forza See All Load Cells See All Multi Component Sensors See All Pressure Sensors See All Strain Sensors See All Estensimetri See All Temperature Sensors See All Tilt Sensors See All Torque Sensors See All Vibration Transducers See All Accessories for Vibration Testing Equipment See All Vibration Controllers See All Measurement Exciters See All Modal Exciters See All Power Amplifiers See All LDS Shaker Systems See All Test Solutions See All Actuators See All Combustion Engines See All Durability See All eDrive See All Production Testing Sensors See All Transmission & Gearboxes See All Turbo Charger
arrow_back_ios

Main Menu

See All nCode - Analisi della durata e della fatica See All ReliaSoft - Analisi e gestione dell'affidabilità See All API
img

expand_more
chevron_left
chevron_right

Weibull++ Crescita dell'affidabilità - Semplice determinazione MTBF

A new helicopter system is under development. System failure data are collected on five helicopters during the final test phase. The total number of flight hours is 500, accrued over a period of 12 weeks. The 500 flight hours are partitioned into six intervals, each covering a two-week period. Every two weeks, each helicopter undergoes a thorough inspection to uncover any failures that may have occurred since the last inspection. Therefore, although the actual failure times are unknown, the analysts have the cumulative total number of flight hours and the cumulative total number of failures for the five helicopters for each two-week period.
Interval #     Interval Length in Flight Hours     Failures in Interval
1 0 - 62 12
2 63-100 6
3 101 - 187 15
4 188 - 210 3
5 211 - 350 18
6 351 - 500 16

Analysis and discussion

 

A standard folio data sheet configured for grouped failure times data type is created by selecting Times-to-Failure Data > Grouped Failure Times on the first page of the Project Item Wizard window, as shown next.

Figure 1: Selecting the data type and units of measurement for the new folio

The data set is then entered and the Crow-AMSAA (NHPP) model is selected for analysis, as shown next.

Figure 2: Data set entered in the standard folio

After analyzing the data, the results summary shows that the demonstrated failure intensity (DFI) value at the end of the 28 hours of testing is 4.4947.

Figure 3: Summary of results showing that the failure intensity demonstrated at the end of the test

This can also be seen by using the Quick Calculation Pad (QCP). Since the test ended at 28 days, the DFI is equal to the instantaneous FI at 28 days, as shown next.

Figure 4: Quick calculation showing the DFI (i.e., failure intensity at the end of the test)

A plot of the MTBF vs. time is shown next. The plot shows the mean time between failures plotted against time. The horizontal lines represent the instantaneous MTBF over the marked interval. The points represent actual failures in the data set.

Figure 5: MTBF vs. time plot showing both instantaneous and cumulative MTBF

The cumulative MTBF line is then removed by right-clicking the plot.

Figure 6: Show/Hide Items window with cleared option for cumulative MTBF line

The plot now looks like this.

Figure 7: MTBF vs. time plot showing only instantaneous MTBF