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MPM Instrumented Data Acquisition (DAQ) System |
Introduction
MPM manufactures several impact test systems that can perform a wide
variety of impact tests including:
- Charpy impact testing (ASTM E23)
- Miniature Charpy impact testing
- Drop tower impact testing (ASTM E208, E436, and E 604)
- Plastic impact testing (ASTM D256, D1709, D2582, D3763, D5420,
D5628, D5941, and D5942)
- Dynamic Tear (ASTM E604 and E436)
- Beverage can impact testing
Most of the test machines can be provided with strain gage
or accelerometer instrumentation. Instrumented test systems enable measurement of the
force applied to the test specimen during an impact event. Then,
the instrumented test data can be used to calculate the energy absorbed by the
test specimen. In addition, the crack initiation and arrest loads can
be used in fracture mechanics models.
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DAQ System Showing Strain Gage Signal Conditioner Inside
Locked Case |
System Features
The MPM instrumented system is very accurate and versatile. Some important
system features are listed below:
- Up to 1,000,000 data points per test
- Data acquisition time ranges from microseconds up to 100
milliseconds (longer acquisition times available)
- User friendly software controls acquisition and data
analysis
- Optical encoder data can be read and stored
automatically
- Full system
includes:
-computer
-high speed 12 bit acquisition board
-strain gage amplifier
-instrumented striker
-flat panel monitor, optical mouse and keyboard
-hardware/software manual
-software
Sample Instrumented
Striker Data
The nature of the instrumented signal response depends on
the material being tested (metal, plastic, ceramic, composite, etc.), the test
temperature, and other key test parameters such as impact velocity. Shown
below is a typical instrumented striker voltage response for a Charpy test on
a metal test specimen at a test temperature in the transition region.
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Click below to enlarge and enhance
photo |
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| Instrumented Striker Voltage Response |
The voltage-time curve is converted to a force-time
curve through the load cell calibration. During the testing, the MPM system
measures the impact velocity directly using an optical encoder (see
Pendulum Machines page) or an infrared device (see
Drop Tower page). This velocity is then used in the
numerical integration of the measured force to determine the velocity-time
curve. A second numerical integration is performed to obtain the
displacement-time curve. These data are then used to construct the
force-displacement curve, and the total energy absorbed by the test specimen
is calculated by integration of this curve. These analysis steps are shown
graphically below.
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Click below to enlarge and
enhance photo |
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| Integration Plots |
Another analysis option is to determine characteristic
loads, deflections, and energies. The general yield load (for metal
specimens) is determined from the intersection of the elastic loading line and
a fit of the data during load up. The peak load is determined by least
squares regression of the data. Finally, for tests conducted in the
transition region, the brittle fracture load and crack arrest load are
determined from a robust data analysis algorithm. An example of the
characteristic load report is given below.
| Click below to enlarge and enhance
photo |
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| Characteristic Load Report |
System Upgrades
New test machines can be provided with an instrumented system or existing test machines can be upgraded
by the addition of the MPM state-of-the-art system. MPM will assemble the
system and provide a field installation and calibration if desired. The MPM
system can provide all of your laboratory impact data acquisition needs since
the system can be configured for pendulum machines and for drop towers.
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