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Info Letter No. 100 - November/December 2006

by Fritz Ruoss

FED1+ : Load Spectrum for Dynamically High-stressed Compression Springs

If stroke and load cycles change periodically, a load spectrum can be defined in the newest version 20.0 of FED1+. The software calculates life expectation and number of strokes until damage from load spectrum. Input values for load items are spring length L1 and L2, number of strokes, then cycle duration of period.

FED1+ at first calculates number of strokes until failure for each component of the load spectrum (Nni) by means of the Goodman diagram. Next calculate fatigue life for the theoretical case, that load collective consists only of one component: tNi = Nni / ni * Tp. Life expectation of load spectrum can then be calculated in the way of parallel springs or electrical resistors:

1/tN = 1/tN1 + 1/tN2 .. + 1/tNi .. + 1/tNn

At "View->Load Spectrum", FED1+ shows tables of load spectrum and calculation results, graphics for percentage of strokes and damage share.

Shear stresses tauk1 and tauk2 of L1 and L2 are listed in the Goodman diagram, as usual. If a load spectrum is defined, number of strokes and life expectation for load spectrum is listed as well.

If number of load cycles are below the 10 Mio. line, spring is fatigue-resisting (infinite lifetime). But not for load spectrum: only if every member of the load spectrum N > 10 Mio., spring is fatigue-resistant.

FED1+ Consider Power-On Period for Fatigue Life Calculation

Load spectrum can also be used to calculate endurance for springs with power-off periods.

Example: spring load is 1500 strokes/minute (25 Hz), but only 5 minutes per hour. Duration of period is then 3600s, number of strokes is 1500 x 5 = 7500. Load spectrum consists of only one component.

Fatigue Life of Springs

Some users of HEXAGON spring software wondered that one time fatigue life and number of load cycles was printed, and another time not.

Fatigue life is calculated if:

1. type of stress: dynamic (at Edit->Application)

2. Goodman diagram available for material selected from database

3. permissible variation between loads overridden (< 10 Mio. load cycles)

Goodman diagram describes lines for 100,000, 1 million and 10 million load cycles. Beyond of the 10 million limit, spring is fatigue-resisting. If the spring was not damaged after 10 million load cycle, it will never fail. Life-time is infinite.

To make fatigue-resisting property more clear in the printout, for fatigue-resistant springs is printed now: "Load cycles N: > 10 Mio."

FED1+ Preview with Excel Interface

New preview function (at "File->Open Table") was improved again: file date and some more spring properties have been added to the table. When enlarging the window, table also is enlarged, hidden fields are shown. A menu was added to the preview window. Besides menu items Exit an Help, a new function "Export Excel" has been added that runs Microsoft Excel (if installed) and copies the table into an Excel worksheet.

Preview function like in FED1+ will be added to all HEXAGON programs next time.

ZAR1+ Preview

In 25 columns, essential dimensions and strength properties of gear 1 and gear 2 are listed in the preview table.

SR1 Preview

Preview function loads all files in the current folder. Preview function of SR1 takes more time than in FED1+ and ZAR1+, because many properties have to be loaded from database files.

FED6 Char.Line of Spring F, R L (Spring Force, Rate, Length)

For input of spring rate Ri, you can now use button "<" to calculate spring rate that generates turning point (change of spring rate) exactly in the center between current and previous position. If you click to "R min", turning point will hit the previously defined position point.

FED1+, 2+, 3+, 5, 6, 7: Select Surface Protection

For faster input, surface protection may be selected from a listbox (ph = phosphated, cu = copper-coated, ez = zinc-coated, za = zinc-aluminium-coated, tb = bright dry, nb = bright wet.

WN2, WN8 - Input Power, Speed, Torque

Instead of torque, you also can enter power and rotational speed now.

"Courier New" for Text Printout

It seems that fix font "Courier" is no longer supported from new laser printers. At printout, you may get black columns, or a proportional font (Arial) is used instead. Default text font for text printout was now changed from "Courier" to Courier New".

New Software WN9

Our new software WN9 calculates splined shaft connections to DIN ISO 14 and other standards. WN9 will be available soon.

Key Code Request with Computer Info

Request key code for WN20151-10247:34878 (HEXAGON-BER/5.0/1.6GHz/200MB/80.0GB)

Some users do not know how to describe their computer in license contract (need new key codes, because PC "Smith1" was replaced by "Smith2"), so computer details are sent together with key code request now.

New Update Prices 2007

From 1.1.2007, update price increases from 31 to 40 Euros. CD or email attachment now includes manual files in pdf format. Online manual is started by a mouse click into "index.htm" file (requires Internet Browser and Adobe Acrobat Reader). Or print all pdf files and replace in manual folder.

"Full-Update" with printed manual pages on paper is no longer available.

New price for "Deluxe-Update" (Program on CD and printed manual) is 70 Euros.

Shipping Cost 2007

New Shipping and handling charges from 1.1.2007: Germany 10 Euro, Europe 25 Euro, World: 60 Euro.

Delivery by email is free of charge.

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