Servo Hydraulic Software FAQ

Yes, you can. Before loading MAX, add the following lines to AXIS.INI (located in the C:\Program Files\Instron\MAX\Group0 folder): [FilterSystem] FilterProcess=RESAMPLING FilterType=BUTTERWORTH FilterPole=2 FilterFreq=25 The entries are described in the README.TXT file supplied with the program and installed in the C:\Program Files\Instron\MAX folder. Be careful to set the filter frequency higher than the test frequency (at least twice the test frequency is recommended to avoid the filter affecting the data).

Yes, you can. WaveMaker has a user interface for the filter. The System dialogue in WaveRunner allows the filter to be switched on or off. The filter frequency is always set to 1/5th of the data logging frequency. For example, if the data logging frequency is 200Hz, the filter will be set to 40Hz. The filter type and pole can still be selected in the WAVEMAKE.INI file (located in the C:Program FilesInstronWavemaker 32Group0 folder), as explained in the README.TXT file. The entries are: [FilterSystem] FilterProcess=RESAMPLING FilterType=BUTTERWORTH FilterPole=2

In order to measure energy accurately, the load-line displacement (LLD) needs to be measured accurately. Both ASTM E813 (Section 8.5.2) and E1820 (Section 8.7.2) require that any other measurement used to infer load-line displacement values is accurate to within +/-1%. Load line displacement can be corrected by entering a series of coefficients into the frame compliance dialogue. This is available if you choose a corrected LLD channel (e.g. choose 'Corrected Position' for actuator displacement). The formula used for correction is: LLD'=LLD -(E0+E1*L+E2*(L**2)+E3*(L**3)+E4*(L**4)+E5*(L**5)) LLD' is the corrected load-line displacement LLD is the measured load-line displacement from the selected channel E0...E5 are the coefficients entered in the Frame Compliance correction dialogue box. You will have to calculate these yourself from measurements made on an unnotched specimen. You need to use Hooke's law to determine the elastic displacement and subtract this from the measured displacement to give the displacement due to grips, load string, crosshead and frame columns. If this measurement is repeated at 10 or 20 loads, a 5th order polynomial fit to the load-frame displacement will give the coefficients E0...E5. L is the load You can change the coefficients of the equation used to calculate crack length from compliance measured using a COD gauge mounted on the front face.

Yes you can. You will have to purchase a second GPIB card and plug this into the computer (you do not need to install the software). Connect the Sefram to this card, not the one connected to the controller. The GPIB address in the JIC.INI file now becomes 1:20. The full entries should be as follows: [temperature] device=Sefram 8800 channel=4 GPIB address=1:20 type=5 range=4 center=0.1 filter=0 auto offset=off init string= [DCPD Active] device=Sefram 8800 GPIB address=1:20 channel=5 type=0 range=2 center=0 filter=5 auto offset=off init string= See manual M22-10019-EN or M22-10019-FR for more details.

Yes, it can. The compliance coefficient page allows you to choose an upper and lower limit for the fit, as well as a choice of either the loading or unloading section of the data. These values can be set before the test starts (compliance coefficient page) and adjusted while the test is running. If the correlation factor for the best fit is below a user settable figure (scroll run time screen to see these values), then a warning message appears after 3 of these poor fits. The test can be stopped or continued at this point.

The program has a 'delta K decreasing' control mode which allows ∆K to be decreased or increased as the crack grows. The formula we use for changing ∆K is as recommended in ASTM E647 and is of the form: ∆K=∆Koexp[Cg(a-ao)] where ∆Ko - initial required stress intensity ao - initial crack length ∆K - new stress intensity a - current crack length (measured by any of the selected methods, including DCPD) Cg - normalised K gradient Cg can be either negative for threshold or stress decreasing tests or positive for stress increasing tests. Cg can be changed by the operator while the test is running, as can ∆Ko.

Initially the crack length measured by the program will not be that of the notch. When the crack reaches the end of the chevron, the measured crack should be close to that of the notch.

The COD gauge is not zeroed (balanced) at the start. It is not necessary to do this because compliance measurements are all relative. The program calculates compliance by measuring the slope of either the unloading or loading section. Slope is a difference in COD readings. The absolute value of the COD reading is therefore not important. Nevertheless, it is wise to balance the COD gauge just after you have mounted it on the specimen.

The program calculates compliance for you and stores the normalised compliance (EvB/P) in the DAT file. v/P can be calculated by dividing the normalised compliance by modulus*thickness (E*B). If you want to use the LOP file to do an independent measurement, then use either the unloading or loading part of the data (load either falling towards zero or rising towards zero). On the ASTM standard 1820 it gives an equation for Pf, the precracking Load. Is this the delta load or the maximum load? Pf is a calculated load (section A1.3.2 in E1820). This section refers to 7.4.5 which states that 'The initial value of the maximum fatigue load should be less than Pf'. Pf therefore refers to maximum values, not delta (range) values.

The KIC standard E399 does not mention pop-ins and gives no guidance on dealing with them. If you look at Fig. 8 in the standard, the Type II test record shows a pop-in large enough to be considered for analysis. The software looks for the intercept of the offset slope (5%) with the test record so that where it crosses the test record, the value of force P5 can be calculated. This technique will ensure that smaller pop-ins are ignored. The software checks for any force higher than P5 that comes before P5 and will use that for the value of Pq used in the calculation of Kq and hence KIC. The standard also requires that Pmax/Pq<=1.1. This will invalidate a test where a large pop-in occurred well before the maximum load (Type II in Fig.8 will fall into this a category if it is drawn to scale).

DAX aims to collect a maximum of 3.072 seconds worth of data, whatever the data collection rate. This is done to ensure the user does not have to wait too long for the on-screen graph to update. For example, if 2 channels are being collected at 1kHz (sample interval=1ms), then a buffer size of 3072 rows is used. If the data collection rate is 0.1kHz (sample interval=10ms), then a buffer size of 307 rows is used. For a data collection rate of 5kHz, a buffer size of 4096 rows will be used (a maximum determined by memory constraints in DAX). A new buffer will therefore be ready for collection every 0.819s.

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If you are running the program in stress intensity control, the initial value of the crack length is used to calculate the initial value of stress intensity. The stress intensity will be incorrect if: 

1. The initial crack length is too small. 
2. Any of the specimen dimensions are incorrect. 
3. The elastic modulus is incorrect. Check these parameters before running the test again. As soon as the crack length is measured (unless the visual method has been selected), a more accurate value of stress intensity should be calculated. The program's control algorithm will then smoothly change the load amplitude and mean level to achieve the target stress intensity.

This value is not used in the crack length or stress intensity calculations. It is passed to the KIC program where it is used in CTOD calculations.

Yes, you can enter your own formula for both crack length and stress intensity for a tension and compression specimen. These formulae can be based on existing formulae or can be new types.

If the test is running in either total strain or stress control the elastic modulus (E) is calculated as an average of the first 20 measurements of both tensile and compressive modulii. This value of 20 can be changed in the LCF.INI file: [Modulus Limits] Average E over cycles = 20 The modulus and stress (σ) is used to calculate the elastic strain (σ/E) which is then subtracted from the total strain to give the plastic strain (εp). This is done for each row of values in the logged data. In mathematical terms: εp = εt - σ/E Elastic modulus is calculated on both unloading and loading slopes of the hysteresis loop. The unloading and loading slopes are measured using a least squares fit algorithm between limits set in the LCF.INI file: [Modulus Limits] Upper = 90 Lower = 65 The values are as a % of the stress range. The slope calculation is then repeated by adding further points to the least square fit, one at a time, until the mean square error (MSE) exceeds the value set in the data logging set-up section. MSE = (Σ (x i - yi )2)/n where x is σi/σmax and y is εi/εmax. This normalization of the values allows MSE to be used independently of the actual values of stress and strain. If the test is running in plastic strain control, the value of modulus entered in the specimen information section is used. As plastic strain is logged, the elastic strain is calculated from: εt = εp + σ/E

You should be able to communicate with the Eurotherm from Eurotherm.exe, even if only errors come back. If no communication is possible (it is always querying the temperature), then check on the 2408 that: 1. the communication protocol is set as 'Func=EI bi (EI-BISYNCH)' on the 'id=cm5' configuration menu 2. the baud rate is 9600 3. the correct cable is fitted to the correct com port (labelled on the back of the computer) 4. Make sure the com port is enabled in the BIOS of the computer (start-up setting) and has a 'normal' interrupt level and I/O address for the selected com port.

You should be able to communicate with the Eurotherm from Eurotherm.exe, even if only errors come back. If no communication is possible (it is always querying the temperature), then check on the 2408 that: · the communication protocol is set as 'Func=EI bi (EI-BISYNCH)' on the 'id=cm5' configuration menu · the baud rate is 9600 · the correct cable is fitted to the correct com port (labelled on the back of the computer) · Make sure the com port is enabled in the BIOS of the computer (start-up setting) and has a 'normal' interrupt level and I/O address for the selected com port.

The program uses the 7-point regression method, as per ASTM E647, Appendix X1 to calculate da/dN. The crack length calculated from the regression method is stored in the DAT file as 'Crack Length (reg)'. The stress intensity (Delta K) is calculated from this crack length. Note that the first 3 and last 3 entries in the DAT file will be zero for da/dN, Crack Length (reg) and Delta K.

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The crack length is calculated from the standard 5th order polynomial. The default coefficients are those for a CT specimen. If you use this method, you will have to calculate your own set of coefficients. The stress intensity is calculated from the following formula K=deltaP*Mg*Mb*Ms*((1/W^2)*2*(a/3.1415)^0.5) where a - crack length W - specimen width If a/W>0.2: Mg=0.1*a/W^2+0.29*a/W+1.081 Mb=0.75*a/W^2-0.185*a/W+1.019 Ms=0.9*a/W^2-0.21*a/W+1.02 If a/W<=0.2 Mg=1.143 Mb=1+0.06*a/W Ms=1+0.07*a/W

The formulae used for calculating crack length 'a' are: a=Z/(0.8-1.7*a/W+2.4*(a/W)^2+0.66/(1-a/W)^2) Z=E*B*W^2*v/P/(3*Span) W - Width E - modulus v/P - compliance (COD/force) As the formulae require a value of 'a' to start, the software keeps re-calculating until the error between successive iterations is less than 0.0005. The seed (first) value of a is W.

A VI is like a function, subroutine, subprogram or procedure in other programming languages. You can describe what the VI does just as you can include comments in conventional programming languages. This is the way we describe each driver or VI in the Instron 8800 drivers. Unlike other programming languages, every VI has it's own window for the inputs and outputs which appear as controls and indicators. The 'code' is in a second window called the diagram. For a demonstration, try this link: http://sine.ni.com/apps/we/nioc.vp?cid=1381&lang=US

This is a facility for changing the value of the compliance determined from crack opening and load. The pop-up help for the formula given on the specimen parameters screen gives more information. The coefficients B0 and B1 need to be determined by a series of trials. The program does not provide a facility for calculating them.

Most communication errors can be solved by powering down all equipment, including machine frame, control tower and computer. They should then be powered back on in the following sequence: machine frame, control tower and computer. This should result in communication being re-established. If not, check all cables and connections and perform the restart that was described above. If this does not fix your problem, then please call Instron Tech Support at 1-800-473-7838. Please make sure that you have all relevant serial and model numbers at hand when calling.

Da/dN is calculated whenever the logging criterion is satisfied. The data storage criterion of crack length results in smoother values of da/dN.

DAX has an internal buffer for displaying real-time data which can hold a maximum of 4096 points. At 5kHz this buffer is filled in under a second. DAX collects a buffer of data from the controller lasting about 0.4s (2048 points), saves it to disk and displays it on the screen. In the Data Points display on the screen it shows >4096 and >2048, warning you that the graph can only show a buffer of data at a time instead of a whole cycle. The correct number of data points is written to the file, if you are logging the data to disk.

You first of all need to make sure that the maximum value is set to a realistic number. If this is the case, then the decimal separator in the PRN (sequence file) file may not match the program setting. This is usually the same as the operating system (e.g. ',' for German Windows). Comma separated files are supplied with the standard sequences. You have to choose 'Custom' during the installation of the files to install the comma separated files.

Software supplied by National Instruments maybe continuously checking the GPIB bus. Find VISACONF.INI. Open it and find DisableAutoFind in the section [GPIB-VXI-CONFIG]. Change the 0 to 1 to disable the feature. Save the file and reboot the PC.

These initial unload values are determined from the displacement-load characteristic measured during the bedding-in cycles. The program calculates the displacement necessary to achieve the load. At low loads, the displacement-load characteristic can be non-linear due to slack in the load string (C(T) specimens) or low loads (SEN specimens) on the rollers. Although the program uses the upper half of the bedding-in cycle for measuring the displacement-load characteristic, the bedding-in load and the minimum load must be large enough to ensure the displacement-load characteristic is linear in the upper half of the bedding-in cycles. It is also important to make sure that the loop shaping for the load channel and the specimen type is good.

You need to check that the frame compliance procedure was carried out correctly. This procedure determines how much of the displacement measured by the position transducer mounted in the actuator is due to movement in the grips, load string, crosshead and columns of the machine. If this procedure is done at too small a load or, for example, the specimen did have a machined notch in it, then the selected load-line displacement channel will be incorrectly adjusted for 'frame' compliance. When running the frame compliance procedure, check the following points: 

1. A non-notched specimen must be used for the frame compliance measurement. 
2. The maximum load must exceed the maximum load expected in the test with a notched specimen. 
3. Make sure that the minimum load value is sufficient to ensure that there is enough load on the bend specimen for satisfactory load control.

This message will occur if there are not enough data points within the various exclusion lines. The most likely reason for this is that the starting load-line displacement value is too large. If you examine the load-displacement data you should be able to estimate a more suitable starting value. Running the test in COD control (C(T) only) will enable the starting point to be estimated more accurately. The load-line increment value may be too large. This value can be changed while the test is running by clicking the 'Parameter Change' button. The dialogue box allowing changes to the parameters will appear at the end of the current unloading sequence.

There is a bug in windows 2000 that prevents it from updating the registry when the screensaver is turned off. To following is a fix for this: Go into the start menu, choose run and type "regedit". Go to HKEY_CURRENT_USER\Control Panel\Desktop. You will see a key called "ScreenSaverActive". This is probably set to 1 and it should be set to 0 if the screensaver is off. To Reset: Right click on "ScreensaverActive". Select "Modify". Change the 1 to 0 and select "OK". Warning: Modifying the registry incorrectly can cause serious problems and may require you to reinstall the operating system. Please back-up the registry before any modifications are carried out.

This error only applies to the compliance method for calculating crack length and can be caused by: 1.The COD and/or the load values are too small for the system in use. The error arises because of increased scatter in the least square fit. The correlation coefficient is smaller then the R^2 value (you can see these on the status screen). The R^2 value can be lowered to stop the error happening. You may need to use smaller travel COD gauge or a lower capacity load cell or testing system to solve the problem. 2. There could be a resonance of the COD gauge or testing frame. Lowering the test frequency may help to solve this problem. This can be done while the test is running by clicking the change control parameters button.

This is probably due to the numbers in the file not being formatted correctly. Each number must have the same number of characters. Positive numbers must be preceded by a space or + sign, e.g. ‘ 0.4563’ or ‘+0.4563’. Trailing zeroes must not be omitted, e.g. 0.4 must appear in the file as +0.4000 if other numbers have 4 digits after the decimal place. If you are using Excel to produce the file, define a custom number format of ‘+0.0000;-0.0000’and apply this to all the data. Save the file as a Text (tab delimited) format. Rename the extension to PRN after saving the file. Always keep a copy of the original file in XLS format. The numbers should range between +1.0 and –1.0. See the Random Loading manual (M22-10000-EN) for more details.

DAX waits for the waveform generator to start on the master axis. So if there is no waveform running on the master axis, then it will not start data acquisition. There is a simple workaround - set a waveform on the master axis with zero amplitude. The waveform generators will have to be started together, but the rotary axis can be set-up independently of the axial axis. The axial axis will not move.

The measured crack length is probably larger than the test end criterion crack length. This may have happened because the value is too small or there is a problem in calculating the crack length. See the question on errors in calculating crack for suggestions on correcting this problem.

The 'File is blank' message appears if the field 'Fatigue Crack Length:' is not found within the first 200 rows of the DAT file. The computer has been switched off or the power went off when the crack front entry screen in the run or results module was being accessed. Open the DAT file with Notepad. Open a known good DAT file in another copy of Notepad. Copy and paste the missing post test data from the known good data file to the end of his data string in the corrupted DAT file. This will eliminate the 'File is blank' message.

If you are running the program in stress intensity control, the initial value of the crack length is used to calculate the initial value of stress intensity. The stress intensity will be incorrect if: 

• The initial crack length is too small. 
• Any of the specimen dimensions are incorrect. 
• The elastic modulus is incorrect. Check these parameters before running the test again. As soon as the crack length is measured (unless the visual method has been selected), a more accurate value of stress intensity should be calculated. The program’s control algorithm will then smoothly change the load amplitude and mean level to achieve the target stress intensity.

You need to check the following points: 

1. If you are saving data during the test to a network drive, make sure no back-up software could be slowing or stopping access to the file. 
2. Check that power management options (e.g. turning off the hard disk after a period of time) are switched off. 
3. Make sure the screen saver is not slowing the application program down (for example, some virus scanners scan all programs on the hard disk when the screen saver comes on).

If you are using the compliance method for calculating crack length, there could be several reasons for this: 

1. The elastic modulus is incorrect. A common mistake is to enter too many zeroes. If this and all the other reasons have been eliminated, click the 'Check Modulus' box on the specimen parameters screen. The program will assume the initial crack length is correct, and calculate the elastic modulus from the compliance measurement and the specimen dimensions. The program will warn you if the value is more than 10% of the value you have entered. 
2. One or more of the specimen dimensions are incorrect (width, thickness, net thickness, span (if applicable), half gauge length (if applicable)). 
3. Clevis grips and pins could be too tight. ASTM E813 and E1820 recommend flat bottomed holes in clevis grips. 
4. The crack length coefficients are not correct for the specimen type in use. Check the values in the crack coefficients dialogue. To use default values for the selected specimen type, re-select the specimen type in the specimen parameters page. If you are using a DCPD system to measure the crack length then check the DCPD coefficients are correct. Consult the operating instructions for the DCPD system for further suggestions.

If you are using the compliance method for calculating crack length, there could be several reasons for this: 1. The elastic modulus is incorrect. A common mistake is to enter too many zeroes. If this and all the other reasons have been eliminated, click the "Check Modulus" box on the specimen parameters screen. The program will assume the initial crack length is correct, and calculate the elastic modulus from the compliance measurement and the specimen dimensions. The program will warn you if the value is more than 10% of the value you have entered. 2. One or more of the specimen dimensions are incorrect (width, thickness, net thickness, span (if applicable), half gauge length (if applicable)). 3. Clevis grips and pins could be too tight. ASTM E647 recommends oversize holes, flat bottomed holes or roller bearings in clevis grips. 4. The crack length coefficients are not correct for the specimen type in use. Check the values in the crack coefficients dialogue. To use default values for the selected specimen type, re-select the specimen type in the specimen parameters page. 5. The test frequency is too high causing resonance of the frame and/or the COD gauge. The load versus COD graph can help diagnose this problem. Waviness to the plot or loops at either end can indicate a resonance problem. Lowering the test frequency may help to solve this problem. This can be done while the test is running by clicking the change control parameters button. 6. Front end filter is not set to the same frequency value for the load and COD channels. If you are using a DCPD system to measure the crack length then check the DCPD coefficients are correct. Consult the operating instructions for the DCPD system for further suggestions.

Check that the envelope time (attack) is set to a value of zero. You can change this to zero (0) in the Waveform (cyclic) generator screen available from the FT Console right click menu. Make this change before you start the test.

1. There could already be a fatigue crack in the specimen.
2. The loop shaping of the load channel is poor. 
3. The initial crack length is too large. 
4. Any of the specimen dimensions are incorrect. 
5. The elastic modulus is incorrect.

You have probably setting the logging criteria to cycles. When you do this, the program will log and therefore calculate da/dN at this interval, irrespective of whether the crack has grown or not. If you choose the logging criteria as crack increment, da/dN is only calculated when the crack grows and the scatter in da/dN is therefore much smaller.

Check that the global data sampling rate is at least 50Hz (0.05kHz) or higher. This restriction only applies to the 233 unit. Use Data Reduction and Maximum Time between points to lower the number of points collected. For example, a maximum time between points of 0.2s is equivalent to 5Hz. ‘Log point when feedback changes by’ may result in more points being collected than a row every 0.2s.