Upgrade of the DRDC Atlantic Instrumented Drop …cradpdf.drdc-rddc.gc.ca/PDFS/unc160/p800696_A1b.pdf · Upgrade of the DRDC Atlantic Instrumented ... W7707-115135/001/PV CSA: Ian

DEFENCE DÉFENSE&

Defence R&D Canada – Atlantic

Copy No. _____

Defence Research andDevelopment Canada

Recherche et développementpour la défense Canada

Upgrade of the DRDC Atlantic Instrumented

Drop Tower Impact System

K.J. KarisAllenFACTS Engineering Inc.

Prepared by:FACTS Engineering Inc.PO Box 20039Halifax, NS B3R 2K9

Contractor’s Document Number: FR-DT310311Contract Project Manager: K.J. KarisAllen, 902-477-4062Contract Number: W7707-115135/001/PVCSA: Ian Thompson, Defence Scientist, 902-427-3444

Contract Report

DRDC Atlantic CR 2011-059

December 2011

The scientific or technical validity of this Contract Report is entirely the responsibility of the contractor and the contents do not necessarily have the approval or endorsement of Defence R&D Canada.

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Upgrade of the DRDC Atlantic Instrumented Drop Tower Impact System

K.J. KarisAllen FACTS Engineering Inc. Prepared By: FACTS Engineering Inc. PO Box 20039 Halifax, NS B3R 2K9 Contractor's Document Number: FR-DT310311 Contract Project Manager: K.J. KarisAllen, 902-477-4062 PWGSC Contract Number: W7707-115135/001/PV CSA: Ian Thompson, Defence Scientist, 902-427-3444

The scientific or technical validity of this Contract Report is entirely the responsibility of the Contractor and the contents do not necessarily have the approval or endorsement of Defence R&D Canada.

Defence R&D Canada – Atlantic Contract Report DRDC Atlantic CR 2011-059 December 2011

Contract Scientific Authority

Original signed by Ian Thompson

Ian Thompson

Defence Scientist

Approved by

Original signed by Leon Cheng

Leon Cheng

Head/Dockyard Laboratory (Atlantic)

Approved for release by

Original signed by Leon Cheng

Leon Cheng

Chair/Document Review Panel

© Her Majesty the Queen in Right of Canada, as represented by the Minister of National Defence, 2011

© Sa Majesté la Reine (en droit du Canada), telle que représentée par le ministre de la Défense nationale, 2011

DRDC Atlantic CR 2011-059 i

Abstract

The instrumented drop tower at the Dockyard Laboratory (Atlantic) has been used to determine dynamic fracture parameters of metallic materials. The impact system was upgraded through a contractual activity. The upgrades include: a new data acquisition system, custom software for converting load-time data into load point displacement data, a new computer, and a new tup. This Contract Report contains a description of the upgraded equipment, instructions for its operation, a description of a method for correction of load-displacement to account for machine compliance, and the results of the calibration.

Résumé

Le système d’essai de chute instrumenté du Laboratoire du chantier naval (Atlantique) a été utilisé pour déterminer les paramètres de la mécanique de rupture de divers matériaux métalliques. Le système d’impact a été mis à niveau dans le cadre d’une activité contractuelle. Les mises à niveau comprennent : un nouveau système d’acquisition de données, un logiciel sur mesure pour convertir les données sur le temps de chargement en données sur le point de déplacement du chargement, un nouvel ordinateur et un nouveau marteau. Le présent rapport prévu au contrat décrit l’équipement mis à niveau, contient un manuel de l’utilisateur, décrit une méthode de correction des données de déplacement de charge pour tenir compte de la conformité de la machine et explique les résultats de l’étalonnage.

ii DRDC Atlantic CR 2011-059


DRDC Atlantic CR 2011-059 iii

Executive summary


K.J. KarisAllen; DRDC Atlantic CR 2011-059; Defence R&D Canada – Atlantic; December 2011.

Introduction: The Dockyard Laboratory (Atlantic) instrumented drop tower has been updated by FACTS Engineering to take advantage of improvements in computing power and data acquisition systems. This Contract Report describes the upgraded equipment, provides an operating manual, describes a method for correction of load-displacement data to account for machine compliance, and explains the results of the calibration.

Results: The upgrades to the instrumented impact system include: a new data acquisition system, custom software for converting load-time data into load point displacement data, a new computer, and a new tup. A method of correcting load-displacement data for machine compliance is described. The system was calibrated and several tests were conducted that verified the accuracy of the calibration.

Significance: The instrumented impact system will enable the determination of dynamic fracture parameters of metallic materials relevant to the Canadian Forces. The upgraded drop tower impact system will be able to facilitate sophisticated dynamic fracture mechanics assessments.

iv DRDC Atlantic CR 2011-059

Sommaire


K.J. KarisAllen; DRDC Atlantic CR 2011-059; R & D pour la défense Canada – Atlantique; décembre 2011.

Introduction : Le système d’essai de chute instrumenté du Laboratoire du chantier naval (Atlantique) a été mis à jour par FACTS Engineering afin de tirer parti des améliorations de la puissance de calcul et des systèmes d’acquisition de données. Le présent rapport prévu au contrat décrit l’équipement mis à niveau, contient un manuel de l’utilisateur, décrit une méthode de correction des données de déplacement de charge pour tenir compte de la conformité de la machine et explique les résultats de l’étalonnage.

Résultats : Les mises à niveau du système d’essai de chute instrumenté comprennent un nouveau système d’acquisition de données, un logiciel sur mesure pour convertir les données sur le temps de chargement en données sur le point de déplacement du chargement, un nouvel ordinateur et un nouveau marteau. Une méthode de correction des données de déplacement de la charge pour la conformité de la machine est décrite. Le système a été étalonné et plusieurs essais ont été réalisés pour vérifier l’exactitude de l’étalonnage.

Portée : Le système d’essai de chute permettra de déterminer les paramètres de fissuration de matériaux métalliques pertinents pour les Forces canadiennes. Le système d’essai de chute mis à niveau permettra de réaliser des évaluations de la mécanique de rupture dynamique élaborées.

DRDC Atlantic CR 2011-059 v

Table of contents

Abstract …….. ................................................................................................................................. iRésumé …..... ................................................................................................................................... iExecutive summary ....................................................................................................................... iiiSommaire ..... .................................................................................................................................. ivTable of contents ............................................................................................................................ vList of figures ................................................................................................................................ viList of tables ................................................................................................................................. vii1 INTRODUCTION .................................................................................................................... 1

1.1 General .......................................................................................................................... 11.2 Dynamic Testing ........................................................................................................... 1

1.2.1 Determination of Impact Velocity .................................................................. 11.2.2 Conversion of Load-time to Load-Displacement ............................................ 11.2.3 Machine Compliance Determination .............................................................. 2

2 DESCRIPTION OF THE HARDWARE ELECTRONICS AND SOFTWARE DATA ACQUISITION SYSTEMS ...................................................................................................... 32.1 General Overview of the Impact Test System ............................................................... 32.2 General Description of the Electronic Hardware Components ..................................... 4

2.2.1 Description of Instrumented Force Transducer ............................................... 42.2.2 Description of Force Transducer Signal Conditioner ..................................... 52.2.3 Description of High-Speed Digitizing Electronics .......................................... 62.2.4 Microprocessor Based Interface Electronics ................................................... 7

2.3 General Overview of the System Software Algorithms ................................................ 73 SYSTEM CALIBRATION AND VERIFICATION .............................................................. 11

3.1 Static Calibration ......................................................................................................... 113.2 Calibration Verification ............................................................................................... 11

3.2.1 Low Blow Calibration Verification Procedure ............................................. 113.2.2 Determination of Machine Compliance ........................................................ 12

4 SYSTEM OPERATION ......................................................................................................... 145 SUMMARY ............................................................................................................................ 16References ..... ............................................................................................................................... 17Annex A Description of the LPD Output File Format ................................................................. 19List of symbols/abbreviations/acronyms/initialisms .................................................................... 20Distribution list ............................................................................................................................. 21

vi DRDC Atlantic CR 2011-059

List of figures

Figure 1: Photograph of the main components associated with the DRDC instrumented impact test system. ........................................................................................................ 3

Figure 2: Photograph of a specimen positioned on the anvil supports. ........................................... 4

Figure 3: Photograph of the Instron Model 8189 dynamic force transducer. .................................. 5

Figure 4: Photograph of the Vishay Model 2311 dynamic signal conditioner. ............................... 6

Figure 5: Photograph showing the back panel connections to the CS8222-1GS high speed digitizer. ........................................................................................................................ 7

Figure 6: Bitmap showing the main GUI associated with the instrumented impact test software. ........................................................................................................................ 9

Figure 7: Bitmap showing the command options available with the <File> selection located on the main menu bar. ................................................................................................... 9

Figure 8: Bitmap showing the pop-up window associated with the <Calibrate> command located on the main menu bar. .................................................................................... 10

Figure 9: Force versus voltage relationship generated during the transducer static calibration procedure with a signal conditioner excitation voltage and gain of 2.7 Vdc and 10, respectively. ................................................................................................................ 11

Figure 10: Machine compliance relationship for the drop tower assembly. .................................. 13

Figure 11: Load-displacement record for a notched ASTM E-604 specimen impacted at a velocity of 5.4 m/s (total absorbed energy 2065 J). .................................................... 15

Figure 12: Load-displacement record for a second notched ASTM E-604 specimen impacted at a velocity of 5.4 m/s (total absorbed energy 2242 J). .............................................. 15

DRDC Atlantic CR 2011-059 vii

List of tables

Table 1: Drop tower assembly force transducer calibration energy comparison with a hammer mass of 275 kg. ........................................................................................................... 12

viii DRDC Atlantic CR 2011-059


DRDC Atlantic CR 2011-059 1

1 INTRODUCTION

1.1 General

Impact tests are usually high-strain-rate, three-point bend tests of notched or precracked specimens for determination of fracture parameters for materials under dynamic conditions. The extension of fracture mechanics technology into the dynamic regime is critically dependent on accurate load/load point displacement (LPD) records [1,2]. This report is a comprehensive review of the method which the DRDC Atlantic instrumented impact system uses to convert load/time to load/load point displacement (load/LPD). It also describes the calibration and verification of the DRDC Atlantic drop tower force transducer.

1.2 Dynamic Testing

The information recorded during an instrumented impact test is the signal produced by a calibrated force transducer (within the tup, or striker) with respect to time. To convert the force/time data to force/displacement, the velocity at each moment must be known.

1.2.1 Determination of Impact Velocity

If system friction is assumed to be negligible, the impact velocity may be calculated from the initial height of the hammer assembly as:

It should be noted that since the accuracy of the relationship is predicated on negligible frictional losses, the hammer guide columns should be cleaned prior to testing to minimize frictional losses from this source.

1.2.2 Conversion of Load-time to Load-Displacement

As the specimen is contacted, there is a loss of energy and an associated loss of velocity, as follows:

The energy absorbed by the specimen (represented by the third term) is approximated by the area from time i to i+1 under the force time curve multiplied by the average velocity from i to i+1. The second term calculates the potential energy converted to kinetic energy due to vertical displacement of the striker assembly. In this manner, the velocity can be calculated for all times and the time can be converted to displacement by continually dividing time increments by the average calculated velocity during these periods. The initial velocity, Va, at t0, is the impact velocity, V0. A finite difference algorithm is used to balance dh and Vi+1 for all digitising steps after impact.

2/10 2 hgV (1)

0111 i

i

i

i

i

i

t

taa

h

h

V

V

dtVPdhgmdVVm (2)

2 DRDC Atlantic CR 2011-059

1.2.3 Machine Compliance Determination

When load/LPD is derived in the above manner, the area under the curve defines the energy absorbed by the entire impact system. Inclusion of work absorbed by the impact system during testing where brittle fracture occurs is vital for accurate results. The components of this energy are split into components absorbed by the machine, Um, and the sample, Us, given by:

where the final term can be split into the elastic portion, Ues, and the plastic portion, Ups:

Plastic deformation under dynamic conditions is difficult to quantify and is, therefore, undesirable. It has been shown [3] that the unloading portion of a load/LPD record from an impact where the specimen yields but does not fracture can be considered as an elastic occurrence. For uncracked rectangular, three-point bend specimens, the elastic load-line deflection is given by [4]:

Analytical expressions for these components are [5]:

and

Thus, substituting equations (6) and (7) into (5) gives an expression relating specimen deflection to material constants and instantaneous load. This relationship may be used to define the limits for the final term in equation (3). Substituting equation (3) into equation (2), integrating, and simplifying results in an equation relating changes in machine deflection to striker and specimen constants, changes in loading, and changes in hammer velocity. For a drop weight assembly, this relationship is given by:

111 si

si

mi

mi

i

i

sama

t

ta dPdPdtVP (3)

psess UUU (4)

shearbendtotal (5)

EWBSP

bend 3

3

4(6)

WEBSP

shear161.0 (7)

14.225.05.022

2

11

21

2

1 WSSPP

PPhgVVm

iiii

iimm ii (8)


2 DESCRIPTION OF THE HARDWARE ELECTRONICS AND SOFTWARE DATA ACQUISITION SYSTEMS

2.1 General Overview of the Impact Test System

Figure 1 shows a photograph of the main components associated with the DRDC Atlantic instrumented impact test system. The impact system is comprised of two main components. The first component is a DynaTup Model 8100 vertical drop tower. The tower consists of a 275 kg hammer which is guided during the test sequence by a pair of precision slide rails. An Instron Model 8189 instrumented force transducer (tup) is mechanically fastened to the bottom of the hammer which applies a dynamic deflection transient to the test specimen which is positioned on a set of anvil supports located on the base attachment plate (Figure 2). The initial height of the hammer may be adjusted using the chain pulley lift mechanism provided with the system. The second main component of the system is the electronic instrumentation suite which captures the transient signal from the force transducer and post processes the signal into a load versus load point displacement relationship for evaluation. The instrumentation suite consists of a Vishay 2311 dynamic signal conditioner, a Gauge CS8222-1GS high speed digitizer, and a PC compatible microprocessor combined with a custom software suite. The following sections provide general descriptions of the specifications associated with the electronic hardware as well as a functional description of the software suite.

Figure 1: Photograph of the main components associated with the

DRDC instrumented impact test system.


Figure 2: Photograph of a specimen positioned on the anvil supports.

2.2 General Description of the Electronic Hardware Components

2.2.1 Description of Instrumented Force Transducer

The force transducer included with the system was an Instron Model 8189 tup designed to apply deflections to specimens configured in a three-point bend arrangement (Figure 3). The transducer was instrumented with precision semiconductor strain gauges arranged in a full-bridge configuration to convert sustained deflections into a proportional output signal. The general specifications associated with the transducer are given as: Full Scale Range: 135 ksi (600 kN) Nominal Bridge Resistance: 883 ohms


Figure 3: Photograph of the Instron Model 8189 dynamic force transducer.

2.2.2 Description of Force Transducer Signal Conditioner

The dynamic signal conditioner supplied by DRDC Atlantic as part of the project was a Vishay Model 2311(Figure 4). The conditioner was used to supply a selectable excitation voltage to the force transducer strain gauges and apply predetermined degrees of amplification and filtering to the signal generated by the full-bridge sensor arrangement. The general specifications associated with the signal conditioner are given as: Transducer Excitation Voltage Range: 1.4-15 Vdc Signal Amplification Range: 1-1000 Available Signal Filters: 10 Hz – Wide Band

A more detailed description of the functionality is provided by the user manual associated with the signal conditioner hardware [6].


Figure 4: Photograph of the Vishay Model 2311 dynamic signal conditioner.

2.2.3 Description of High-Speed Digitizing Electronics

A Gauge Model CS8222-1GS high speed digitizer was utilized to capture the signal generated by the Vishay Model 2311 conditioner. The function of the digitizer was the conversion of the analog signal into a digital format compatible with PC compatible microprocessor architectures. The digitizer was configured to function through a full length PCI interface slot available in most PC compatible microprocessors (Figure 5). The general specification associated with the digitizer is given by: Full Scale Digitizer Signal Range Selection: ±100mV to ±5 V Digitizer Sampling Rate Range: 1 kS/s to 10MS/s Digital Signal Resolution: 12 bits Maximum Onboard Sampling Capacity: 1x109 samples.

A more detailed description of the functionality is provided by the user manual associated with the digitizer hardware [7].


Figure 5: Photograph showing the back panel connections to the

CS8222-1GS high speed digitizer.

2.2.4 Microprocessor Based Interface Electronics

A commercial microprocessor (PC compatible) was included with the hardware suite to acquire, display, and store the digital data generated by the high-speed digitizer integrated into the system. A custom designed software suite was developed to display the converted data acquired from the force sensor using a series of virtual instruments. The general specification for the PC included: Monitor: 20 inch Flat Panel CPU: Intel Core I5-2500 Quad Core 3.3 GHz RAM: 4 GB DDR2 DRAM Non-Volatile Storage: 500 GB Hard Drive – 7200 rpm Operating System: Windows 7 Professional Enclosure: Standard Desktop Mini-Tower Configuration.

2.3 General Overview of the System Software Algorithms The DRDC Atlantic instrumented impact test acquisition and display software is an R&D oriented software package designed for gathering and analysing dynamic force-time data. Once the system has been configured, data base generation and maintenance is self-supervising. Using


this system requires no previous experience with computers. The system has a single control display which allows the operator complete access to the program functions if required. To initiate the program and generate the control display, choose the DT2011 shortcut from the Windows™ desktop.

The software package consists of a single executable (DT2011.exe) and several configuration files, which combine to generate a custom designed virtual instrument executing the data acquisition and control sequences. The programming language used to program the system was C++ using a Borland 32 bit compiler to assemble the C++ code into machine code. The system was designed for the 32 bit version of Windows 7 Professional and will not execute properly in 16 bit or 64 bit environments.

Figure 6 shows a bitmap of the main screen GUI associated with the software suite. The display is divided into four sections. The column of windows located on the left-hand side of the display is for the input of client, test apparatus, test specimen, and procedure descriptions. While the windows do not affect the acquisition of the data, several of the input parameters are used for post processing the force-time data. The variables associated with the windows may be up to 100 characters in length. The initial screen displays the data types associated with input for each window.

The bottom centre/right section of the screen contains the buttons, scroll bars and track bars used to configure and control the digitizer during data acquisition. The operator can set test parameters such as the transducer full scale range, digitizing rate, trigger level and the trigger delay. This section of the screen also contains the buttons to activate the data acquisition sequence.

The upper/right section of the screen contains the radio buttons and track bars used to control the post processing of the data displayed immediately below the controls. The operator can define the point of initial impact and final fracture. Selecting the <Calculate> button generates the load-load point displacement based on the current initial impact and final fracture points selected. An additional cursor button has been provided to determine the force, displacement, and absorbed energy for any point associated with the data record.

The final section of the display is the command menu located along the top of the display. The command menu allows the operator to input variables as well as output captured data to ASCII text files (Figure 7). There are two methods available for inputting digitizer configuration data to the system. Upon system initialization, the user can manually enter data into the description variables and digitizer control buttons. Alternatively, a variable/test file “ID.tim” (the file saved upon the successful capture of a test) can be recalled to automatically configure the system to the previous settings.

Figure 8 shows a bitmap of the pop-up window activated by the <Calibrate> option. This window consists of a series of edit boxes which facilitates user input of the calibration constants associated with a particular sensor signal range in kN/V. The system has been initially configured to take advantage of the precision range selections provided by the CS8222-1GS digitizer with Vishay signal conditioner excitation voltage and amplifier gain of 2.7 Vdc and 10, respectively. As such, a common calibration constant may be utilized to provide a decade of available range selections. The full scale voltage associated with each range is 100% - 2.0Vdc, 50% - 1.0Vdc, 25% - 0.5, and 10% - 0.2Vdc. The full scale force displayed by the GUI for each range is the product of the full scale voltage and the calibration constant.


Figure 6: Bitmap showing the main GUI associated with the instrumented impact test software.

Figure 7: Bitmap showing the command options available with the <File> selection located on the main menu bar.


Figure 8: Bitmap showing the pop-up window associated with the

<Calibrate> command located on the main menu bar.


3 SYSTEM CALIBRATION AND VERIFICATION

3.1 Static Calibration

A static calibration procedure was utilized to generate the calibration constants for the Instron Model 8189 force transducer associated with the instrumented impact system. A Satec Model 120HLV 500 kN load frame was used to ramp compressive loads on the drop tower load cell to predetermined levels. Voltages corresponding to specified load levels were recorded and fed into a linear regression routine for processing. The resulting relationship provides a means of converting the voltage signal generated during impact into force. The force verses voltage relationship corresponding to a bridge excitation voltage of 2.7 Vdc and amplifier gain of 10 is shown in Figure 9. The results of the linear regression of the data points indicated excellent linearity and a transducer calibration constant of 174.78 kN/V.

y = 174.7821xR² = 1.0000

0102030405060708090

100

0 0.1 0.2 0.3 0.4 0.5 0.6

Transducer

Force(kN)

Transducer Signal (V)

Figure 9: Force versus voltage relationship generated during the transducer static calibration procedure with a signal conditioner excitation voltage and gain of 2.7 Vdc and 10, respectively.

3.2 Calibration Verification

3.2.1 Low Blow Calibration Verification Procedure

To test the calibration of an impact system, it is necessary to provide a situation where the energy transfer to the specimen is known. One method of verifying calibration is by measuring the


energy of the hammer assembly subsequent to impact. A “low blow” test is one methodology which may be utilized to verify the calibration of a drop tower assembly. The procedure typically utilizes standard unnotched specimens in a three-point bend configuration. The specimen will deflect (bend) as long as the hammer assembly direction of motion is the same as the initial impact direction. The energy absorbed by the specimen when the velocity is zero (maximum load) is given by:

Since the load-LPD energy can be determined for any point during a “low blow” test, it provides an excellent method of verifying the calibration.

Table 1 contains the low blow available energy (Equation 9) and load/LPD energy results of six unnotched steel specimens with an anvil span of 203.2 mm. The specimen height and width dimensions were 42.30 mm and 28.65 mm, respectively. Triplicate impact tests with drop heights of 15.80 mm and 25.64 mm with a hammer mass of 275 kg were conducted. The results show an excellent correlation between available potential energy and post-processed load/LPD energy value results.

Table 1: Drop tower assembly force transducer calibration energy comparison with a hammer mass of 275 kg.

Drop Height (mm) 15.80 15.80 15.80 25.64 25.64 25.64

Energy From Eq 9 (Joules)

45.141 45.141 45.141 72.259 72.259 72.259

Load/LPD Energy (Joules)

45.14 45.09 45.10 72.23 72.21 72.10

Difference (%) -0.006 -0.031 -0.010 -0.043 -0.099 -0.190

3.2.2 Determination of Machine Compliance

The controlled deflection of unnotched specimens also provides the requisite data for the determination of machine compliance as characterized by equation 8. By way of example, Figure 10 represents the machine force/displacement relationship for tup model 8189 used with the drop tower assembly for the 42.30 mm wide specimen utilized for the low blow calibration verification. Sources of non-linearity exhibited by the curve are the deflection of complex beams and localized brinelling of the tup over the contact surfaces. The contribution from localized brinelling of the tup over the contact surfaces suggests that the compliance may be dependent of specimen width and, as such, a generated relationship should only be utilized to modify load-LPD records from specimens with a similar width.

igmVmENERGY 202

1 (9)


0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 30 60 90 120 150

Displacemen

t(m

m)

Force (kN)

Machine + Specimen

Machine

Figure 10: Machine compliance relationship for the drop tower assembly.


4 SYSTEM OPERATION

Once the system has been configured using one of the two options provided in Section 2.3, the digitizer can be activated by clicking on the “SET TRIGGER” button. The software will configure the CS8222-1GS digitizer and check for configuration errors. If no errors are encountered, a message box with the caption “Click OK to Activate Capture” will be displayed. Clicking “OK” arms the trigger for approximately 20 seconds at which point the system times out and disarms the trigger. If the trigger level conditions are met during the 20 second interval, the system will capture up to eight load-time traces and display the first trace on the terminal. The user may scroll through the traces captured and select the trace associated with the impact event using the scroll box button provided to the left of the graph box. Once the impact event of interest is displayed in the graph box, immediately save the record as a “ID.tim” file to avoid the possible modification of the data set during subsequent post processing.

Post processing of the impact data is achieved using the “Zero”, “End”, and “Calculate” buttons combined with the graph track bar located at the top of the graph. The point of impact can be selected by clicking on the “Zero” button. Pulling the track bar pointer in combination with the keyboard arrow keys is used to isolate the point of initial impact. Accurately defining the point of initial impact is necessary in order to define the initial velocity conditions for the numerical algorithm which converts load-time to load-displacement using conservation of energy principles. The point of final fracture can be similarly defined by clicking on the “End” button and using the track bar and keyboard arrow keys. Data boxes have been provided to display the force values associated with the zero and end positions. Once defined, clicking the “Calculate” button recalculates the load-displacement relationship and displays the selected interval in the graph box.

There are two different types of files which the operator can save to disk storage. The first file type is the load-time data file. Saving the load-time file is executed immediately after the successful capture and display of a new instrumented impact record. The file is saved using the “ID.tim” descriptor (the “*.tim” file type is the default setting for the system). If the operator requires a data file containing load-displacement couplets for the displayed data, this can be achieved by saving the file using the “*.lpd” file descriptor in the <SAVE AS> popup window. The load-displacement couplets are saved in a comma delimited format which is a compatible import format for most commercially available spreadsheet and graphing packages (see Appendix A for output file format). The basic procedure for saving a file is the same regardless of the file type. The procedure is given as:

a) Choose the <File/Save As> option from the command menu.

b) Set the file type using the file type menu.

c) Input the name of the file to be saved (include the file descriptor).

d) Click on the “SAVE” box in the Save File window box.

To highlight the system capabilities, duplicate specimens were machined and notched in accordance with the dimensional requirements of ASTM E-604 [8]. The specimens were subjected to an impact loading event with a hammer mass of 275 kg and an impact velocity of 5.4


m/s. Figure 11 and Figure 12 show the load-displacement data together with the absorbed energy associated with the impact tests. The morphology of the test records is typical of an intermediate impact testing rate where the initial portion is dominated by the load spikes associated with the transfer of inertial energy from the tup to the specimen. The subsequent plasticity sustained by the specimen dampens the inertially generated oscillations and as such the data subsequent to maximum load is dominated by the monotonic deflection characteristics of the specimen in three-point bending.

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80

Force(kN)

Displacement (mm)

Figure 11: Load-displacement record for a notched ASTM E-604 specimen

impacted at a velocity of 5.4 m/s (total absorbed energy 2065 J).

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80

Force(kN)

Displacement (mm)

Figure 12: Load-displacement record for a second notched ASTM E-604 specimen

impacted at a velocity of 5.4 m/s (total absorbed energy 2242 J).


5 SUMMARY

Instrumented drop tower impact tests are used for the determination of fracture parameters under dynamic conditions. Such tests require accurate load/load point displacement data. The report describes the upgrade and calibration of the DRDC Atlantic instrumented impact testing system. The upgrades included a PCI bus, large memory capacity, high-speed digitizing card together with a custom designed software executable for converting load-time data into load point displacement data. A method of correcting load-displacement data for machine compliance is described. A static calibration technique for generating instrumented load/LPD energies has been conducted. The results of several low blow tests conducted are in excellent agreement with the initial potential energy available, verifying the system calibration.


References

[1] Kobayashi, T., Yamamoto, I., and Niinomi, M., “Evaluation of Dynamic Fracture Toughness Paramaters by Instrumented Charpy Impact Tests”, Engineering Fracture Mechanics, Vol. 24, 773-782, 1986.

[2] Joyce, J.A., Hackett, E.M, “Dynamic J-R Curve Testing of a High Strength Steel Using the Key Curve and Multispecimen Techniques”, ASTM STP 905, 715-740, 1986.

[3] KarisAllen, K.J. and Morrison, J., “The Determination of Instrumented Impact Machine Compliance Using Unloading Displacement Analysis”, Experimental Mechanics, Vol. 29, No. 2, 152 – 156, 1989.

[4] Haggag, F.M. and Underwood, J.H., “Compliance of a Three Point Bend Specimen at Load Line”, International Journal of Fracture, Vol. 26, R63-R65, 1984.

[5] Roark, R.J., Formulas for Stress and Strain, McGraw-Hill (1965).

[6] Instruction Manual - Model 2311 Signal Conditioning Amplifier, Vishay Measurements Group.

[7] Compuscope Software Development Kit for Windows (User Guide), SKD Version 4.2, Gauge Applied Technologies, 2005.

[8] ASTM E-604, “Standard Test Method for Dynamic Tear Testing of Metallic Materials”, Annual Book of ASTM Standards, Vol. 3.01, ASTM International, 2005.




Annex A Annex A Description of the LPD Output File Format

The LPD output file is created with a file header with descriptive labels (including units if applicable) followed by the data record consisting of displacement-force couplets. The data entries are formatted in a comma delimited structure to be compatible with most commercially available spread sheet programs. The format is given by:

File Header Format File Name: <text> Specimen ID: <text> Total Energy: <float> J Cursor Energy: <float> J

Data Entry Format Displacement0 <float>,Force0 <float>

.

.

. Displacementn <float>,Forcen <float>

End of File


List of symbols/abbreviations/acronyms/initialisms

ACRONYMS

ASCII American Standard Code for Information Interchange

CPU Central Processing Unit

DRAM Dynamic Random Access Memory

DRDC Defence Research & Development Canada

GUI Graphical User Interface

GS Giga Sample

LPD Load Point Displacement

PC Personal Computer

PCI Personal Computer Interface

R&D Research and Development

NOMENCLATURE

m Mass of Striker Assembly

g Force Due to Gravitation

h0 Initial Hammer Assembly Height

hi, hi+1 Striker Deflection at Time i, i+1

i, i+1 Specimen Deflection at Time i, i+1

V0, Vf Hammer Assembly Initial and Final Velocity

Vi, Vi+1 Velocity of Striker at Time i, i+1

Va, Pa Average Striker Velocity, Average Force Between i, i+1

Uem Elastic Energy Absorbed by Machine

Ues, Ups, Us Elastic, Plastic, and Total Energy Absorbed by Specimen

mi, mi+1 Machine Deflection at Time i, i+1

si, si+1 Specimen Deflection at Time i, i+1

mtot Total Elastic Deflection

b, sh Elastic Deflection Contribution from Bending, Shear

Pi Force Recorded by Instrumented Load Cell at Time i

S, W, B, a, b Specimen Anvil Span, Width, Thickness, Crack Length, Remaining Ligament

E, Specimen Elastic Material Modulus, Material Poisson’s Ratio

DOCUMENT CONTROL DATA (Security classification of title, body of abstract and indexing annotation must be entered when the overall document is classified)

1. ORIGINATOR (The name and address of the organization preparing the document. Organizations for whom the document was prepared, e.g., Centre sponsoring a contractor's report, or tasking agency, are entered in section 8.) K.J. KarisAllen FACTS Engineering Inc. PO Box 20039 Halifax, NS B3R 2K9

2. SECURITY CLASSIFICATION (Overall security classification of the document including special warning terms if applicable.)

UNCLASSIFIED (NON-CONTROLLED GOODS) DMC A REVIEW: GCEC APRIL 2011

3. TITLE (The complete document title as indicated on the title page. Its classification should be indicated by the appropriate abbreviation (S, C or U) in parentheses after the title.) Upgrade of the DRDC Atlantic Instrumented Drop Tower Impact System

4. AUTHORS (last name, followed by initials – ranks, titles, etc. not to be used) K.J. KarisAllen

5. DATE OF PUBLICATION (Month and year of publication of document.) December 2011

6a. NO. OF PAGES (Total containing information, including Annexes, Appendices, etc.)

34

6b. NO. OF REFS (Total cited in document.)

8 7. DESCRIPTIVE NOTES (The category of the document, e.g., technical report, technical note or memorandum. If appropriate, enter the type of report, e.g.,

interim, progress, summary, annual or final. Give the inclusive dates when a specific reporting period is covered.) Contract Report

8. SPONSORING ACTIVITY (The name of the department project office or laboratory sponsoring the research and development – include address.) Defence R&D Canada – Atlantic 9 Grove Street P.O. Box 1012 Dartmouth, Nova Scotia B2Y 3Z7

9a. PROJECT OR GRANT NO. (If appropriate, the applicable research and development project or grant number under which the document was written. Please specify whether project or grant.)

9b. CONTRACT NO. (If appropriate, the applicable number under which the document was written.)

W7707-115135/001/PV

10a. ORIGINATOR'S DOCUMENT NUMBER (The official document number by which the document is identified by the originating activity. This number must be unique to this document.) FR-DT310311

10b. OTHER DOCUMENT NO(s). (Any other numbers which may be assigned this document either by the originator or by the sponsor.) DRDC Atlantic CR 2011-059

11. DOCUMENT AVAILABILITY (Any limitations on further dissemination of the document, other than those imposed by security classification.)

Unlimited

12. DOCUMENT ANNOUNCEMENT (Any limitation to the bibliographic announcement of this document. This will normally correspond to the Document Availability (11). However, where further distribution (beyond the audience specified in (11) is possible, a wider announcement audience may be selected.)) Unlimited

13. ABSTRACT (A brief and factual summary of the document. It may also appear elsewhere in the body of the document itself. It is highly desirable that the abstract of classified documents be unclassified. Each paragraph of the abstract shall begin with an indication of the security classification of the information in the paragraph (unless the document itself is unclassified) represented as (S), (C), (R), or (U). It is not necessary to include here abstracts in both official languages unless the text is bilingual.)

The instrumented drop tower at the Dockyard Laboratory (Atlantic) has been used to determinedynamic fracture parameters of metallic materials. The impact system was upgraded through a contractual activity. The upgrades include: a new data acquisition system, custom software forconverting load-time data into load point displacement data, a new computer, and a new tup.This contract report contains a description of the upgraded equipment, instructions for its operation, a description of a method for correction of load-displacement to account for machine compliance, and the results of the calibration.

14. KEYWORDS, DESCRIPTORS or IDENTIFIERS (Technically meaningful terms or short phrases that characterize a document and could be helpful in cataloguing the document. They should be selected so that no security classification is required. Identifiers, such as equipment model designation, trade name, military project code name, geographic location may also be included. If possible keywords should be selected from a published thesaurus, e.g., Thesaurus of Engineering and Scientific Terms (TEST) and that thesaurus identified. If it is not possible to select indexing terms which are Unclassified, the classification of each should be indicated as with the title.) Impact testing; drop tower


Documents

Upgrade of the DRDC Atlantic Instrumented Drop …cradpdf.drdc-rddc.gc.ca/PDFS/unc160/p800696_A1b.pdf · Upgrade of the DRDC Atlantic Instrumented ... W7707-115135/001/PV CSA: Ian