Materials and Structural Characterization Test Support Instruments

 The majority of characterization testing requires that you measure any or all of the following parameters -- Force, Displacement, Strain and Specimen Dimensions.  MTI offers a full range of accessory instruments to accurately satisfy these requirements. 

Force Measurement

All MTI universal testing systems are provided with a minimum of one universal (Tension and Compression) load cell of a capacity selected by the customer.  Often only one load cell is required to accomplish the full spectrum of testing because of the high resolution and accuracy of our 24-bit analog input system.  On some occasion though an additional load cell may be required and we offer a full selection of cells to meet such requirements.  MTI does not manufacture load cells (after all Ford and GM don't make automobile tires) but we instead offer cells supplied to companies specializing in these sensors.  This means significantly lower prices to you than you would see from other companies which force you to utilize their own expensive cells.  Our primary load cell suppliers are Interface Inc. (www.interfaceforce.com)  and Transducer Techniques  (www.ttloadcells.com)  and you can inspect their full range of load cells at their web sites.  We offer any of their cells with our purchased systems, or you can acquire them directly and easily include them into your system. 

 Specimen Dimensions

Probably the most common source of error in materials characterization testing is incorrect measurement of specimen dimensions, or errors in placement of measured dimensions into data processing programs.  The simple transposition of two digits in a thickness measurement can have disastrous results.  MTI has minimized the chance of such errors by allowing you to attach digital electronic calipers with serial data output directly to the MTI C-DAS control and data acquisition computer.  All testing programs are configured to allow you to type in dimension measurements, but far more conveniently you can simply press a button on the micrometer and have width and thickness data transferred directly to the program with no chance of error - and far more rapidly than manual typing.  A wide range of micrometers and calipers and gage heads are available and can be adapted to your system.  We offer instruments by Starrett, Brown & Sharpe and Mitutoyo as your requirements dictate. 

 Strain Measurement 

Often additional specialized instruments are required to accurately perform even seemingly routine materials and structural characterization tests.  A tensile test performed on a high strength structural metal or composite material to accurately determine Young's Modulus will require accurate strain measurements which cannot be achieved by simply monitoring the motion of the load frame crosshead.  MTI created the DSST (Dual-Sensor Strain Transducer shown at left) to provide high-accuracy  strain measurements to greatly simplify testing requiring determination of Modulus, Secant Modulus, Yield Stress and Strain and accurate identification of the proportional elastic limit for low strain materials such as advanced composites.  The DSST incorporates two axial strain sensors, one on either side of the specimen, which provide a true measure of the average strain in the specimen during testing.  This feature is of critical importance in compression testing of coupon specimens such as the IITRI and Celanese tests for advanced composite materials.  The 0.3-inch gage length DSST-C (compression version of the DSST) totally eliminates the requirement of bonding strain gages to the specimen, thus reducing test preparation time from several hours to a matter of seconds -- the same time it would take you to clip a clothes pin to the coupon -- because that's exactly how all DSST transducers are attached to a test specimen.   The picture to the left shows a DSST-C attached after the specimen was placed in a modified Celanese compression test fixture.  The DSST handles are squeezed together, spreading the sensor attachment points, and the instrument is then positioned into the exposed test region with the points aligned on each side of the specimen.  When you release pressure on the handles the DSST is held in place by its self-holding spring. 

All DSST strain transducers function from below 0 ºF to over 300 °F.  Standard gage lengths are 0.3-, 0.5-, 1.0- and 2.0-inches but other sizes have been provided to satisfy special requirements.

\Displacement Transducers

Most displacement measurements required for routine testing can be derived from crosshead motion data which is automatically provided with all MTI testing programs.  However in some cases a direct measurement of local motion is a necessity, such as might be the case of a beam specimen under 4-point deflection loading.  The photographs here illustrate the MTI-Disp and MTI-Disp-AO displacement transducers which are designed to satisfy just such requirements..   

These deflectometers function on the very simple concept of a vertically moving rod which is coupled to a strain-gaged deflection beam element.  The rod has a convenient tapped hole in its end so that various adapting contact arrangements can be easily configured, and it freely rotates through 360° so that the vertical measurement can be performed along any side of the instrument.  The standard arrangement includes a projecting horizontal arm with contacting tip which allows the rod to track up and down motions with deflections of either 1-inch or 2-inches total travel depending upon the model chosen.  The MTI-Disp model is configured as a full strain gage bridge sensor and requires that the user furnish suitable signal conditioning for data recording.  The MTI-BAF-4-2K signal conditioner readily accommodates the instrument in this configuration and provides amplified and filtered high-level signals suitable for any recorder or data acquisition system.  The MTI-Disp can also be attached directly to the second 24-bit A/D input channel of all MTI universal testing systems for fully automatic interfacing and operation.  In cases where a direct high-level filtered analog output is desired ( 0 to ±10 Volts) then the model MTI-Disp-AO is the configuration of choice.  This self-contained unit allows for control of balance, calibration and scaling and includes a digital display for visually monitoring the motion measurement.  The output signal is a suitable input to any type of data acquisition system.

If your requirement is more specialized then many types of deflection gages, instruments or custom designed systems are available to satisfy you needs.  MTI will work with you to arrive at a device which accomplishes exactly what is required in your application