The XVI-th INTERNATIONAL SCIENTIFIC CONFERENCE „TEHNOMUS”
“Stefan cel Mare” University of Suceava - ROMANIA, May 13-14, 2011
WEIBULL ANALYSIS USING R, IN A NUTSHELL
Jurgen Symynck
1
, Filip De Bal
2
1
KaHo Sint-Lieven, jurgen.symynck@kahosl.be
2
KaHo Sint-Lieven, filip.debal@kahosl.be
Abstract: This article gives a very short introduction to fatigue and reliability analysis using
the two-parameter Weibull model. To gain expert insight in the inner workings of commercial
analysis packages such as Reliasoft’s Weibull++ and superSMITH Weibull, the authors created an
open source alternative with a subset of analysis tools and made it freely available as an Open
Source package for the R statistical software. This article explains briefly how to use the software,
how Weibull plots are generated and how conclusions can be drawn. For the complete and most
recent version of this document, check ref. [1]. For more in-depth treatment of the subject, check
ref. [2].
Keywords: Weibull, R, open source software, fatigue, reliability, analysis
1 Introduction
1.1 The FATIMAT project
FATIMAT (FATigue In MATerials) (ref.
[3]) is a PWO project (ref. [4]) supported by
KaHo Sint-Lieven (ref. [5]).
Because there is an ever increasing need
for lighter, stronger and cheaper products,
designers need to be more and more concerned
about the fatigue and reliability properties of
their products. With the arrival of high
precision electromechanical actuators and
servopneumatic valves, it is possible for small
and medium-sized companies to conduct
fatigue and durability testing using these
cheaper alternatives to servohydraulic fatigue
testing machines. The FATIMAT project
studies these alternatives.
For example an engine mount, used to fix
car engines to a car chassis, can be tested by
cyclically compressing it between 10 [mm] and
20 [mm] on a Zwick/Roell EZ020 high speed
electromechanical spindle actuator. The load
frequency is 3 [Hz]. After some time, the
specimen will show signs of wear-out (in this
case oil leakage) that are detected by the
machine software. The test is then halted and
the failure time is recorded. This test is
repeated (under identical loads and
circumstances!) for a number of specimens.
One of the subprojects of FATIMAT is to
analyze these failure data to allow conclusions
on the general reliability of the specimens to be
made. This is where Weibull analysis comes
in.
1.2 Commercial software packages.
Software packages like Reliasoft’s
Weibull++ (ref. [6]) or SuperSMITH Weibull
(ref. [7]) offer the reliability engineer very
powerful tools for analyzing and predicting
failure behaviour. Without extensive
background knowledge and proper software
training however, it is not difficult to draw
faulty, expensive and often disastrous
conclusions. Next to this are some features
missing in one software package while others
have different default settings. Finding a
reason for these differences is not always
straightforward.
1.3 Open Source alternative
FATIMAT has a tradition of combining
‘modules’ of functionality from different
manufacturers and vendors to create flexible
and cost effective test systems. For example, a
servopneumatic dynamic test system can be
built with off-the-shelf pneumatic components,
a standard PC and readily available Open
Source software (ref. [8]). For the post-test
analyzing of the lifetime data, a similar
approach was taken. By using and creating
open source software, maximum transparency,
portability and connectivity is guaranteed.