Mechanical and electronic design of universal testing machines is fairly mature. The new developments are in control software. Modern PC software provides increased productivity and accuracy and is easier to use. Says Instrons Mc Manuis, The software capabilities add a level of reproducibility not previously attained.
Adds Art Nehr, marketing manager at Testing Machines Inc., Rather than rely on a single reading at the breaking point, designers and quality managers now can see what happens throughout a test. Did the material stretch or deform before breaking? Did it deform in proportion to the force? The answers can help them evaluate alternative materials, determine safety margins, and better simulate end-user applications.
The new software automates testing, data collection, analysis, report output, and data storage and retrieval. A user can tell the machine to run at a certain load rate and the system will automatically adjust the speed of the crosshead. New software also allows users to get true strain values during tests by means of position transducers that measure exactly how far the crosshead has moved. The change in length of the specimen is divided by its original length to give automatic strain calculations.
New software also allows for automatic load-cell identification and calibration when changing transducers. It reads the electronics of the load cells and sets up the parameters, eliminating the mechanical modifications previously performed by an operator.
Newer software with faster data acquisition provides more accurate capture of peak loads and allows more detailed examination of stress/strain curves when running tests at higher speeds or with fluctuating loads.
Typical data-acquisition rates are around 50 Hz (taking readings 50 times per second), though sampling rates up to 5 kHz are available.
The newest PC-driven universal testing machines are less expensive than machines with digital control panels that have been around for more than a decade. New PC models have simpler controls and often do away with the digital display that provides the graphical readout. Says Hayward from Tinius Olsen, The software of new PC-based universal testing machines now drives the whole operation, so that the cost can be knocked down by eliminating the digital display and some electronics.
Last year, Tinius Olsen launched the PC-based T-Series of single- and dual-column universal testing machines with capacities up to 22,250 lb. Hayward estimates that the machines in the T-Series, including the PC and Test Navigator software for data acquisition, cost about 10% less than the companys S-Series of bench top units, which have a digital control panel. Says Hayward, The user has to reprogram an S-Series machine to change the test routine. With the PC-driven T-Series, you can have a choice of user-selectable test routines that measure different parameters.
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