winLIFE BASIC 3.3
This
module is needed for the following additional programs
winLIFE MULTIAXIAL
and
winLIFE GEAR WHEELS AND BEARINGS
winLIFE Project-Management-System
A typical
task for industry will consist not only of one single fatigue life calculation.
In general, several load cases and variants will need to be calculated.
For this
purpose winLIFE offers a highly capable system for project tasks. Up to 1000
projects can be worked on simultaneously. The diagram below shows the user
desktop in which 9 projects are defined. The projects can be worked on one at a time or
started together and superimposed.
winLIFE user desktop
The
project generator makes it possible to create projects where the individual
parameters can be systematically varied.
Since a
lot of calculations lead to a longer calculation time, it is important that
this occurs automatically. Therefore,
the possibility of batch jobs is particularly important. The project files are saved in XML-Format and
can also be started from the desktop as a batch.
Obtaining Fatigue Material
Data
winLIFE offers several
possibilities of obtaining material data for fatigue life calculations. As well as generating based on
static material data, the program package also includes a large material data
base.
Creating a S-N-Curve based
on component propoerties and static material data
Since
there are many winLIFE customers in the fields of wind energy, ship building
and general engineering, special entry generators have been created which can
generate fatigue life data based on static material characteristics.
These
are:
·
S-N
curve generator for welded joints according to Germanischer Lloyd for ship
building
·
S-N
curve generator for welded joints according to Germanischer Lloyd for wind energy
·
S-N
curve generator for welded joints according to the FKM-guidelines
·
S-N
curve generator according to Hück, Trainer, Schütz
·
Generator
according to Uniform Material Law
The
following diagram shows an example of an entry mask for a generator according
to the FKM guidelines. This has been extensively tried and tested and is
established in many fields. An S-N curve can be estimated using static material
data such as yield stress and tensile strength together with component
information such as surface, notch factor, stress gradient etc.
Mask to create the S-N-curve
The
figure above shows the mask to create such a S-N-curve. The material data can
be partially modified by the user. In
many cases the user knows only some data from test results and he wants to create
the unknown data. So he can use winLIFE to generate the data and then overwrite
the values he knows.
As well
as the S-N-curve, winLIFE uses the presentation in Haigh-diagram, because the
influence of mean stress can be seen more evidently (see next figure).
Haigh
diagram showing the relation between stress amplitude, mean stress and fatigue
life
If the
failure rate for an analysis is of importance, the user can derive from a 50%
S-N-curve other failure rates. winLIFE considers different scatter rates in the
endurance range and the range of finite life fatigue
strength.
Creating a S-N-curve for
welded structures
You can calculate welded structures as
suggested in the FKM-Guidelines. The analysis is carried out in a similar way
to the Nominal Stress Method. You need to classify the welded structure and
according to the class a catalogue of S-N-curves exists.
|
|
|
|
Figure 4:
Types of welded components the user has to allocate
The
winLIFE S-N-curve generator helps you to establish such a curve.
This is a
relatively approximate procedure for a first step. To improve the results you can calculate
the welded structure according to the elastic stress or local stress approach
using a FEA analysis, where the geometry of the weld has to be modelled in
detail.
For the
use of the structural concept interfaces respective macros for the data
transfer are available in connection with ANSYS and FEMAP.
Creating e-N Curve
If you wish to use the Local Strain Approach, the program provides various
possibilities for creating cyclic material data (Uniform Material Law
etc.). The next figure shows the mask
for entering input data. Only static material data is entered and based on this
an estimation of the e-N-curve is created. The surface and – if no FEA is used
– the notch effect factor are used.
Figure 5:
Input form to create fatigue life data according to different laws
Using strain life curves
If you
wish to work according to the local strain concept, the necessary material data
can be obtained by generating based on static material characteristics (Uniform
Material Law) or by using the material data base.
The next
figure shows an example calculation where the cyclic data was obtained by
generating from static characteristics. For this component the diametral
quotient and the surface roughness in the notch was given. The
stress-strain-path of the component in the notch was calculated from the rainflow-matrix.
It is also possible to calculate the path without the rainflow, but using the
material memory.
Graphic
presentation of the fatigue life data and a calculated stress-strain path.
Material Data Bases
The data
base has been greatly improved in winLIFE 3.3. The complete FKM guidelines
material data base has been integrated and is available on the winLIFE CD.
Furthermore, the material data base according to the local concept with more
than 1400 material data sets has been added to the winLIFE CD. Until now, this
was only partly available on the internet. The user now has immediate access to
all material data.
Mask
including a record of the Internet Material Data Base (One additional site show
details such as name and chemical composition, another site the source and
author)
Getting Loadings
To
perform a fatigue calculation a loading is needed. This can be a measured load
versus time or a load spectrum.
Defining a load spectrum
A load
spectrum consist of cycles, which must be defined by
mean load,
load amplitude
and number of cycles.
Definition
of a cycle
The
experiences in various areas of science show that there are different types of
load spectra, which can be simply defined. Publications in automotive industry,
aerospace or wind energy systems show what kind of load spectrum is acting in a
problem such as this. If you have this information the winLIFE spectrum
generator allows you to create very fast load spectra. The figure below shows
three basic types of load spectra.
Examples
for different load spectra, generated by the built-in generator (top: normal
distribution, middle: linear distribution (n=1), bottom: p - spectrum)
Using Load histories
Another
way is to use a loading history (stress, moment, force) which is normally
obtained from a measurement, in special cases the user can type the data in
manually. A data-import from other programs is usually possible without any
problems. The length of time history is only limited by the disk space.
Loading manually entered
The load
– e.g. forces as a function of time – are entered in the entry mask and then
saved. Because of the time involved, you will only want to enter short load
sequences using this method.
Entry mask
with graph showing data and results
Force Generator (Sinus)
It is
often required to generate simple load time function paths quickly and easily. This is possible using the sinus generator
described below.
Entry of
sinus generator and graph showing resulting signal
Import of Measured Load Time
Functions
Generally
very detailed measured data is used and the length can be several
gigabytes.
Measured load history which is zoomed
Interactive
data input and data modification for load spectra, load histories and rainflow-matrix
is possible by marking the range in the graphic account and modifying
comfortably by use of mouse or keyboard.
The winLIFE
Program uses the Rainflow method as is usual when calculating fatigue
life. The rainflow matrix only contains
the signal parts relevant to the damage.
winLIFE
shows the results of the damage calculation in the rainflow matrix in colour.
The critical signal parts are therefore immediately obvious.
If the
local concept is used, the stress- strain paths from the rainflow matrix are
calculated and shown in a graph. The
total damage is obtained by adding together the damage proportions (linear
damage accumulation hypothesis).
Fatigue Life Calculation
Using FEA
winLIFE
can import data from FEA and use it for the fatigue calculation. In this case
the local stresses and further conditions of each node are considered.
Because,
generally speaking, not all the nodes of a structure are endangered - the
damage usually begins on the surface - the user can select nodes for the
fatigue life calculation according to various criteria. By doing this, the
number of nodes to be examined can be substantially reduced and the calculation
time shortened accordingly.
Macros are supplied with winLIFE so that data can be transferred from
FEA-Programs. The results from winLIFE,
i.e. the damage for each individual node, can be shown by the FEA-program in
colour. A separate colour is used for
each different range of damage. The FEMAP
user-interface is available for all data transactions between winLIFE and NASTRAN Users will therefore have no
difficulties using this program.
winLIFE is
used in collaboration with the following FEA-codes:
-
FEMAP-based
programs like MSC.NASTRAN, NEiNASTRAN and NX.NASTRAN, WTP2000
-
IDEAS
-
SAMCEF
The
interface to FEA is described in detail and many users wrote their own
interface. Successful links to
Short description of the
calculation procedure for an example
In a
short description the fatigue calculation procedure is shown. The following
figure shows a part of a truck suspension which is loaded dynamically by a
force (see overnext figure). Because of the symmetry only half of the part is
analysed.
Component
of a truck suspension, which was used to predict fatigue life
In the
fist step a static FEA calculation is used to ascertain the stress within the
component. For this purpose the state of
stress is calculated in a structure which is subjected to a standard load Fo.
The direction of the standard load must correspond to the acting force
F(t).
The
elastic stress for each load F(t) can then be calculated in a linear way
corresponding to the quotients F(t)/Fo. If, for example, a force F(t) exists as shown
in the next figure, then the stress within a component can be calculated for
any required moment. In the case of local concept, there is an actual
stress-strain curve. This means that the
actual stress path for each node, including plastic deformation can be
calculated using Neuber's rule.
Loading of
the component versus time
The
loading was got from measurement on a
test drive. winLIFE makes a rainflow count of the loading and the result is
shown in the next figure.
Rainflow
Matrix including damage results
The
Material data for fatigue analysis are the cyclic properties (see figure) and
the damage parameter life curve (see figure)
Cyclic
stabilized material properties
Stress-strain path calculated from the rainflow
matrix for the critical node
From the
rainflow count and the cyclic properties the stress-strain-path is calculated (see
figure). Based on the counting and the damage parameter life curve (see figure)
a damage sum is calculated for each node of the structure. The results are
shown as a map on the structure.
Damage Parameter
Life Curve according to Smith Watson and Topper
Beside
the Local Strain Approach shown here, it is possible to use stress based methods
using S-N curves.
As well
as the local concept, a stress based concept can also be used for calculation.
Here S-N curves can be used based on stresses.
The
results of a fatigue life calculation, the damage sum, damage equivalent
amplitude. The number of load cycles until failure is available in an
Export-File where the FE-Program can access them and show as in the diagram
below. For FEMAP an interface is delivered which is automatically installed
onto the FEMAP user desktop.
Results of
the winLIFE damage sum in FEMAP
Without FEA
If no FEA
is used the calculation is done only for one point – typically the notch. The
information about the geometry and the relation between stress and load now
must come from the user. This means he has to enter the notch factor, stress
gradient, surface, etc.
A fatigue
life calculation without FEA can be carried out by the two classic methods - Nominal
Stress Method and Local Strain Approach.
With the
Nominal Stress Method, various hypotheses can be used to consider the fatigue
limit (original, modified according to Haibach, elementary, Liu and Zenner). The
following figure shows these possible hypotheses.
Possible
hypotheses available in winLIFE
If the
calculation is done according to the Local Strain Approach, this is done similarly
to the procedure using FEA.
Addition of different
calculation results
Assume
you are developing a car which runs on different road types. You have
measurements of each road and fatigue calculations for each road for the measured
length.
Customers
use on the road types will be different in length from that which you have
measured. You can now transform the fatigue results from your measured road
length to the other length of customers use and you can add the damage sum for
the total length of all road types.
By adding
a weight factor, winLIFE adds together the results of different calculations
for each node.
Superposition und
Extrapolation
Fatigue
Life Calculations are generally carried out for a specified loading. The
following test scenario of a test drive with a test vehicle on various types of
road surface is an example. Usually there is only one measurement for each part
of the route so that the results of the measured journey have to be
extrapolated for the required time or route and added together for all parts of
the route.
A factor
can be calculated from the target and actual values. The results of the test
route then have to be multiplied by this factor. This process is called extrapolation. The
user can calculate and set the factor or he can enter the target and actual
values and the program will calculate the factor automatically.
The
adding together of the results of the individual parts of the route is called
superposition.
Table:
Data of a test journey with target and actual values and the factor calculated
for the extrapolation.
|
|
Measured time trial route [s] |
Measured route test route [km] |
Target set |
Factor |
|
Main road |
1322 |
18 km |
2000 s |
2000/1322= 1,51 |
|
Motorway |
3122 |
74 km |
200 km |
200/74=2,7 |
|
Track road |
1017 |
6,3 km |
20 km |
20/6,3 = 3,17 |
|
Cross country |
2522 |
4,2 km |
3600 s |
3600/2522=1,42 |
Statistical
Analysis
The entry mask shown below enables you to ascertain
the statistical reliability. The results from the fatigue life calculation
previously carried out and the data from the S-N curve used are taken over.
Calculation
of statistical characteristics
Data Handling and
Correction
If
measured data is used in many cases a data correction is needed. A lot of
faults occur and in the first step the user has to check the data. winLIFE
enables to check and correct the data simply in an interactive manner.
You can modify
load histories and load spectra in the following way:
·
-
find and remove Spikes
·
-
select data and multiplying, adding or overwriting them
Additionally
you can modify the number of cycles in a rainflow matrix. This helps to check
the results too.
Presenting and analysing
the results
All common
graphics in result presenting are available, such as:
·
Rainflow-Matrix
·
Range
Mean Pair Count
·
Level
Crossings
·
S-N-Curve
together with the load spectrum and percentage damage
·
Haigh-diagram
including the loads as points
·
Protocol
file including the results for each node
Report Generator
The
report generator enables the user to print without individual steps such as
opening the graphics. The report generator makes it easier to document a
project using only a few work steps. For each method an individual collection
of graphics can be selected as shown in the following mask for the Nominal
Stress Method. Only one mouse click is needed to create a printout or a PDF-file.
Input mask
for the report generator
PDF-report
which is automatically created according the user-selections from figure 17.
Individual Scaling and
designing of Graphics
For each
diagram special settings of colour and line type are possible. Clicking on the
object shows a window with the properties which can be changed. An example of an
individual layout shows the next picture. For each graphic you an select the
·
Font
size
·
Line
colour
·
Line
type
·
range
of axis
User
modified graphic layout.
Units
Defining
units
The unit
for stresses can be defined in different ways. The internal calculation in
winLIFE is done in N/mm2. If another unit for the stress is wished
then you can select from the unit-list. Mostly PSI is used and therefore it is
prepared.
If you
want to define your own unit for stress you can create it by entering the name
of the unit and the multiply factor.
The other
sizes used in winLIFE have the following standard units which cannot be
changed.
strain [‰]
RPM [1/min]
Any unit
for the load can be used but it has to be done consequently !
winLIFE
is shipped with 3 default-definitions:
ISO-Units
as ‚Default’ [N/mm²] multiply
factor 1
‚PSI’ [lbf/in²] multiply factor 145,04
‚Double
Default’ (range) [N/mm²] multiply factor 2