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KISSsoft Tutorial: Shaft analysis __________________________________________________________________________________________

For release 10/2008 kisssoft-tut-005-E-shaftanalysis.doc

Last modification 27.10.2008 15:45:00 __________________________________________________________________________________________

1 Starting KISSsoft

1.1 Starting KISSsoft Start KISSsoft using Start/Program Files/KISSsoft 10-2008/KISSsoft. The following window will appear:

Figure 1.1-1: KISSsoft start window.

KISS

soft

Tuto

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05: S

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anal

ysis

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1.2 Starting the Shaft Calculation Module Choose the Shaft Calculation from the Modules tree window.

Figure 1.2-1: Modules tree window including the Shaft calculation module.

2 Analysing a Shaft

2.1 Example Problem, Starting the Example An example shaft, see Figure 2.1-1, shall be analysed. The following criteria are relevant:

- Deformation of the shaft - Critical speed (bending frequency) - Static and fatigue strength

Figure 2.1-1: Shaft to be analysed.

Pinion (helical gear with helix angle)

Roller bearings, supported on the left or right side

Key (notched shaft section)

Shaft

Coupling to motor

The shaft is driven by a motor attached via the coupling. The nominal power is 75kW at a speed of 980 rpm. This power is taken from the system at the helical gear, meaning that this pinion drives an application or a second shaft.

This example shaft is included in KISSsoft as an example file. Open it via the menu File-> Open and selection of Shafts 1.w10 followed by Open (see Figure 2.1-2).

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Figure 2.1-2: Opening the example file.

Upon opening the file the shaft (for a detailed description of shaft modelling see tutorials 03-006) is displayed in the tab Shaft editor (see Figure 2.1-1Figure 2.1-1) and calculated with the given parameters. By clicking the -icons from the tool bar (or by pressing F5) a new calculation is carried out. Results are given numerically and graphically (see following sections).

2.2 Results The Results window lists the most important magnitudes obtained from the calculation. Undock and resize this window either by double-clicking the title bar or by clicking the button in the upper right corner of the window.

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Figure 2.2-1: Results window in the shaft module main window.

2.3 Shaft Deformation The deformation of the shaft can be obtained via the menu Graphics ->Shaft->Displacement (bending curves etc.), or by choosing the option Displacement (bending curves etc.) from the dropdown-list in the Graphics window. Note that the shaft modules standard configuration provides a Graphics window in the lower right corner of the main window (see Figure 2.3-1).

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Figure 2.3-1: Graphics window in the shaft module main window.

As a first step, the user must define in which way the gears are to be considered in the analysis. To do so, activate the input window Basic data by clicking the appropriate tab in the main window (see Figure 2.3-2). Choose the desired option from the dropdown-list Gears (see Figure 2.3-3): Gears as load applications only: Mass and stiffness of gears are not considered. Consider gears as masses: Gears are to be considered as masses only. The gear is attached to

the shaft such that it transfers the external loads and its own mass onto the shaft but does not stiffen the shaft.

Consider gears as mass and as stiffness: Gears are considered as a mass and also to increase the stiffness of the shaft. The gear is rigidly fixed to the shaft and forms a single unit with the shaft.

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Figure 2.3-2: Input window active tab Basic data in the shaft module main window.

Figure 2.3-3: Options in the dropdown-list Gears.

The maximum deflection is given in the Results window and accounts for ux=18.55m. The Graphics window also shows the plane which this value refers to: =-63.53. Where is the angle enclosed by the planes normal and the z-axis. Note that by convention the positive sense of rotation is counter-clockwise with respect to the y-axis.

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Figure 2.3-4: Property browser options in the Graphics window.

Additionally, a list of the strain/stress results can be obtained via the menu Reports ->Diagrams of bending.

2.4 Natural Frequencies In the following, the first three critical frequencies are determined (chose the option consider gears as masses). Enter the value into the input field Number of eigenfrequencies. You can find it in the input window tab Basic data, as depicted in Figure 2.4-1. Carry out the calculation once more (either by pressing from the tool bar or by pressing F5) and choose the option Natural frequencies from the dropdown-list in the Graphics window.

Figure 2.4-1: Evaluation of natural frequencies.

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Clicking the button in the Graphics window opens the property browser which enables you to show/hide curves in the diagram. Figure 2.4-2 shows a sequence of Eigenmodes evaluated by KISSsoft. For a better understanding of the solutions the Eigenfrequencies are listed in the Results window with their physical interpretations (Figure 2.4-3).

Additional help can be found in the KISSsoft help by pressing F1 while the cursor is in the input field Number of Eigenfrequencies.

Figure 2.4-2: Graphical results of the natural frequencies calculation.

Figure 2.4-3: Physical interpretations of the first three Eigenfrequencies in the Results window.

2.5 Strength Analysis of Shafts KISSsoft comes with three different strength calculation methods:

1. Hnchen & Decker 2. FKM-Guideline, Edition 2002 3. DIN 743 (2000)

They are available via the tab Strength in the shaft module main window (see Figure 2.5-1). Throughout this tutorial we will limit ourselves to the use of the strength calculation method DIN 743 (2000). The strength calculation requires the definition of cross-sections. Right-clicking the Cross sections element in the Elements-tree opens a context menu. Left-click the option Sizing to have KISSsoft automatically choose another four critical cross-sections (see Figure 2.5-2).

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Figure 2.5-1: Input window Strength in the shaft module main window.

Figure 2.5-2: Definition of additional cross-sections in the Elements-tree

2.5.1 General Data The group General data can be found in the Strength input window. Here, information on the type of load and the desired calculation (static proof only or also fatigue proof) is to be given. For shafts which are loaded with different frequency for bending and torsion (e.g. continuosly rotating shafts which are stopped and started once in a while), it must first be decided whether a constant load for torsion or a pulsating load is to be assumed. Alternatively, both combinations

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(alternating bending and constant torque or alternating bending and pulsating torque) can be analysed. The smaller resulting saftey factor is then to be used.

Figure 2.5-3: Group General data in the tab Strength.

The Maximal load factor is used for the static proof and scales the actual loads.

2.5.2 Information on Material The shaft material and surface roughness has already been defined and may be altered in the Elements-editor (see Figure 2.5-5). For the strength analysis however, further information is necessary to calculate certain factors (e.g. technological size coefficient). Figure 2.5-4 shows the group Material which can be found in the input window tab Strength.

Figure 2.5-4: Group Material in the tab Strength.

Figure 2.5-5: Shaft parameters in the Elements-editor.

Raw diameter Diameter of the raw material at which the last heat treatment occured which is responsible for the final material properties.

State during heat treatment Select the desired option from this dropdown-list for the calculation of the technological size coefficient and the part yield and ultimate strength: Pre-turned on actual diameter: No influence of the raw diameter, the technological size

coefficient K1,deff is calculated for each cross section based on the effective diameter. Raw diameter: The technological size coefficient is calculated for the whole shaft and is

used for all cross-sections.

Material characteristic values

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This dropdown-list offers a variety of options how KISSsoft is to determine the critical material characteristics: with reference diameter: Values are taken from database (at reference diameter) and

multiplied with K1 (technological size coefficient) Rm, Rp acc. database, W for reference diameter: Yield and ultimate strength are taken

from database (for respective diameter, without adding K1), alternating strength is taken for reference diameter and multiplied with K1.

Rm, Rp acc. database, W constant: As above, but alternating strength taken from database for respective diameter, without adding K1.

Rm, Rp acc. database, W calculated from Rm: Alternating strength is calculated from ultimate strength (according to formulas given in DIN/FKM), ultimate strength is taken from database for respective diameter.

2.5.3 Definition of Cross Sections for Analysis KISSsoft can analyse a total of 20 cross-sections. All the cross-sections listed in the Elements-tree will be evaluated. Besides having KISSsoft choose the critical cross-sections automatically (using the von Mises stress criterion and the notch factor) they can also be defined manually. Basically there are two kinds of cross-sections available:

Figure 2.5-6: Choosing a cross-section from the Cross sections context menu.

Limited cross section This cross-section enables you to choose the position (y-coordinate) freely. Any other data concerning the shaft will be taken from the model as seen in the active tab Shaft editor. If more than one notch factor is defined for a single cross-section you may choose it from the dropdown-list Effect of notch1.

1 KISSsoft considers only one notch factor per cross-section. Combined notch factors must be treated manually.

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Figure 2.5-7: Elements-editor for the Limited cross section.

Free cross section This cross-section empowers you to set any value concerning the strength calculation at a given y-position. Every pre-defined shaft parameter and calculated load can be ignored and newly defined.

Figure 2.5-8: Elements-editor for the Free cross section.

Effect of notch Choose the kind of notch factor from a list. If set to Own Input the notch factor has to be given explicitly, otherwise the parameters of the notch have to be defined (e.g. key).

Notch factor If Effect of notch is not set to Own Input the computed notch factors will be displayed in these fields upon calculation.

Bending moment, Torque, Place a checkmark in the checkbox next to the input fields to alter these values.

2.5.4 Analysis and Results Once all cross sections are defined, click in the tool bar or press F5 to execute the strength calculation. The results are shown in the Results window as a quick reference (see Figure 2.5-9). According to the german standard DIN 743 the minimal required safety factor is 1.20. However, this value is to be increased if the effect of a failure is high or if the load assumptions are uncertain.

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Figure 2.5-9: Quick referenced safety results for the given cross-sections.

2.6 Reports For a detailed description of the calculation results click in the tool bar or press F6 to obtain the report.

3 Further Calculations

3.1 Other Analysis Modules Critical speeds, torsion: included in the computation of natural frequencies, see section

2.4 Buckling: Calculation of buckling load (axial pressure) or safety factor Calculation of crowning: The analysis returns a proposal for the crowning of a pinion to

compensate the deformation of the shaft due to bending and torsion Calculation using load spectra: finite life analysis using load spectra and different

modifications of Miners rule can be performed

3.2 Calculation of Hydrodynamic Bearings and Roller Bearings Using KISSsoft, it is possible to calculate the lifetime of the bearings modelled on the shaft. The loads acting on the bearings are calculated automatically, even for statically overdetermined shafts. See Tutorial 007 on bearing analysis.