Analyzing failure modes using RBDs in Weibull++

ReliaSoft Weibull++ provides the ability to use a reliability block diagram (RBD) to model series, parallel and k-out-of-n configurations. In this article, we will give an example of how to use an RBD to conduct failure modes analysis.

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ReliaSoft Weibull++
Experiment and data
Analysis
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An electronic device can fail due to six independent primary failure modes: A, B, C, D, E and F. The component fails if mode A, mode B or mode F occurs. If mode C, mode D or mode E occurs alone, the component does not fail; however, the component will fail if any two (or more) of these modes occur (i.e., C and D; D and E; E and C; or C, D and E). The objective is to analyze each data set using the 2-parameter Weibull distribution with MLE and to determine the lower 1-sided 90% confidence interval on the reliability of this component at 100 hours.

Experiment and data

The following tables present the time-to-failure data for these modes (in hours).

Mode A			Mode B			Mode C
Number	State	Time	Number	State	Time	Number	State	Time
in Group	State	Time	in Group	State	Time	in Group	State	Time
1	F	1144	1	F	2221	1	F	19
1	F	1719	1	F	2257	1	F	140
1	F	2129	1	F	2569	1	F	292
1	F	2803	1	F	3029	1	F	432
1	F	3020	1	F	3805	1	F	528
1	F	3082	10	S	5000	1	F	552
1	F	3589				1	F	605
1	F	3973				1	F	734
1	F	4337				1	F	779
1	F	5011				1	F	874
1	F	5029
18	S	5500

Mode D			Mode E			Mode F
Number	State	Time	Number	State	Time	Number	State	Time
in Group	State	Time	in Group	State	Time	in Group	State	Time
1	F	1063	1	F	1290	1	F	605
1	F	1085	1	F	2261	1	F	760
1	F	1399	1	F	2355	1	F	773
1	F	1445	1	F	3209	1	F	854
1	F	1550	1	F	3284	1	F	890
1	F	2056	1	F	3394	1	F	1165
1	F	4384	1	F	3596	1	F	1220
1	F	4863	1	F	4203	1	F	1320
8	S	5000	1	F	4254	1	F	1967
			1	F	4294	1	F	2606
			1	F	4420	1	F	2834
			10	S	5000	15	S	3000

Analysis

Step 1: Using Weibull++, the first step is to create a new data sheet for grouped times-to-failure data with suspensions.

Step 2: Rename the folio to "Component" and the data sheet to "Mode A." Enter the data given for Mode A and use the 2-parameter Weibull distribution with MLE to calculate the parameters, as shown next.

Step 3: Insert another data sheet of the same type named "Mode B," enter the data given for Mode B and calculate the parameters. Repeat for the remaining failure modes.

Step 4: Choose Home > Insert > Diagram.

Step 5: Build the RBD that describes the reliability-wise configuration of the failure modes, as shown next.

Note that the node in the diagram requires 2 of the 3 paths to succeed.

Step 6: Click Calculate to analyze the diagram.

Then use the Quick Calculation Pad (QCP) to calculate the reliability at 100 hours with the lower 1-sided 90% confidence bound, as shown next.

The lower bound is estimated to be 96.71%.

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