Weibull

The reliability of a product/component constitutes an important aspect of product quality. Of particular interest is the quantification of product reliability, so that one can derive estimates of the product expected useful life. Knowing the probability of product/ component failures at different stages of its life can be very useful to make a decision about when to replace or overhaul the component.

A useful general distribution for describing failure time data is the Weibull distribution named after the Swedish professor Waloddi Weibull (1887-1979), who demonstrated the appropriateness of this distribution for modeling a wide variety of different data sets.

It is often meaningful to consider the function that describes the probability of failure during a very small time increment (assuming that no failures have occurred prior to that time). This function is called the hazard function (or, sometimes, also the conditional failure, intensity, or force of mortality function), and is generally defined as:

h(t) = f(t)/(1-F(t))

where h(t) stands for the hazard function (of time t), and f(t) and F(t) are the probability density and cumulative distribution functions, respectively. The hazard (conditional failure) function for most components or devices can best be described in terms of the "bathtub" curve: Very early during the life of a device, the rate of failure is relatively high (so-called Infant Mortality Failures); after all components settle, and the electronic parts are burned in, the failure rate is relatively constant and low. Then, after some time of operation, the failure rate again begins to increase (Wear-out Failures), until all components or devices will have failed.

The Weibull distribution is flexible enough for modeling the key stages of this typical bathtub-shaped hazard function.

Weibull distribution is very useful in reliability because of its ability in modelling increasing and decreasing failure rate functions.

SoHaR solution fully supports Weibull analysis as part of its approach to failure analysis, understanding and prevention.

By utilizing Weibull distribution SoHaR team can understand the reasons for failure causes and establish a lasting preventive action.

RAM Commander Weibull Module

RAM Commander reliability software provides Weibull module allowing input/import of failure statistics (time to failure) and calculation of Weibull distribution parameters (Shape and Scale):


Weibull parameters calculation algorithm takes into consideration "censored" data too, e.g. not only failures but also times at which equipment was tested and appeared to be operational.

After the calulation user may generate Weibull reports and graphs like PDF (Probability Density Function), CDF (Cumulative Distribution Function), FR(t),  number of failures till time t etc. to predict failures, plan warranty times etc.:


Distribution parameters can be used in sustem reliability analysis using Reliability Block Diagrams module of RAM Commander.

Functional Packages:
PREDICTOR

• 5 Standard Operating Reliability Prediction Methods
• BOM Builder, Temperature Curves, Mission Profile, and Import Wizard
• Full set of ready-to-print Reliability Reports
• Enhanced Report Generator for user defined reports

RELIABILITY PRO

• 5 Standard Operating Reliability Prediction Methods
• BOM Builder, Temperature Curves, Mission Profile, and  Import Wizard
• User Defined Components Reliability Data Module
• Full set of ready-to-print Reliability Reports
• Enhanced Report Generator for user defined reports
• Components Library Module (over 400k components)
• RBD - Reliability Block Diagram

MAINTAINABILITY PRO

• Maintainability Module (according to MIL-STD-472 Procedure 5A)
• Built in libraries for Tasks, Times, STE, Skills, and Materials
• Maintenance Engineering Report (MEA Report)
• Maintenance Task Analysis Report
• Full set of ready-to-print Reliability Reports
• ILS Supprt Fields (user defined)
• BOM Builder, Temperature Curves, Mission Profile & Import Wizard
• Enhanced Report Generator for user defined reports
• RCM/MSG-3 Module
• FMECA Module

FAILURE ANALYSIS & ISOLATION

• BOM Builder, and Import Wizard
• FMECA (covering both Hardware & Functional) Module
• Customizable FMECA Worksheet
• FTA Module
• FMECA Import/Export
• Testability Module
• Full set of FMECA & FTA ready-to-print Reports
• Full set of ready-to-print Testability Reports including graphical trouble shooting, fault isolation, etc.
• FMD-97 Library
• Enhanced Report Generator for user defined reports

SAFETY ASSESSMENT

• SSA supporting IEC 61508 (Safety Standard for Safety Instrumented Systems) and MIL-STD-882D (SHA, O&SHA), SAE, ARP 4754A, and ARP4761
• Customizable FMECA Worksheet
• FTA Module
• RBD Module
• Markov Chains Module
• FMECA Import/Export
• Full set of ready-to-print Safety Reports
• Enhanced Report Generator for user defined reports

AVIATION SAFETY

• SSA & FHA according to SAE, ARP 4754A, ARP4761, and FAR 25 1309b
• FTA including ready-to print reports
• MSG-3 (System, Zonal, and Structural) including ready-to-print reports
• MMEL including ready-to-print 5-column report
• FMECA including ready-to-print FMECA reports, BOM Builder, and Import Wizard
• Enhanced Report Generator for user defined reports
• Report Template Utility for layout customization

See also:
SoHaR Reliability and Safety Software Overview
Reliability&Safety Analysis Software Download 
SoHaR Reliability, Safety and Quality Services