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time. A change in the load signal equivalent to 1 to 2 N (threshold load) shall be used to<br />
mark the point in time where zero reading of the extensometer is obtained. The point in time<br />
where the peak load is obtained will be captured by the data acquisition system and the<br />
accumulated elongation from the zero reading to the elongation corresponding to the peak<br />
load shall be used to calculate the failure strain. Once the test is complete, the device shall<br />
display the strain at failure. Peak load typically ranges from 10 to 100 N depending on the<br />
test temperature, grade, aging, and source of the binder. Stress and strain shall be displayed<br />
to the nearest 0.1 N.<br />
6.1.5 Elongation Measuring and Recording Devices--Specimen elongation shall be<br />
measured with a laser light transmitter and receiver. The non-contact laser extensometer shall<br />
be calibrated at least annually according to ASTM E83, MIL-STD 45662 and MIL-STD<br />
45662A. The transmitter shall produce a vertical plane of laser light that is monitored by the<br />
receiver and shall be arranged so that the test specimen interrupts the plane of laser light<br />
except for the slots in the insert. Thus, two spots of laser light are transmitted to the<br />
receiver. The receiver shall constantly monitor the relative position of the two spots of laser<br />
light to produce a voltage proportional to the distance between the two nearest edges of the<br />
spots of light. This voltage shall be converted to elongation by a controller attached to the<br />
receiver using a calibration factor determined by the manufacturer and verified when the<br />
extensometer is calibrated. The laser measurement range shall be 30 to 60 mm with an<br />
accuracy _< 0.005 mm. Elongations shall be recorded to the nearest 0.005 ram.<br />
6.1.6 Temperature Detection Device--The temperature detection device shall be a<br />
calibrated resistance thermal detector (RTD) readable and accurate to 0.1°C (note 3). The<br />
RTD shall be mounted inside the environmental chamber in the immediate vicinity of the test<br />
specimen. Cabling to the RTD shall be of sufficient length that the bulb of a total immersion<br />
mercury-in-glass thermometer can be held adjacent to the RTD for standardization purposes<br />
(See section 9.1.3).<br />
NOTE3.--Required temperature measurement can be accomplished with an appropriately calibrated<br />
platinum resistance thermometer (RTD) or thermistor. Platinum resistance thermometers meeting DIN Standard<br />
43760 (Class A) are recommended for this purpose. The required precision and accuracy cannot be obtained unless<br />
each RTD or thermistor is calibrated as a system with its respective meter or electronic circuitry (See section 9.1.3).<br />
6.1.7 Data Acquisition and Display Device--The data acquisition and display device<br />
shall display the load and elongation selected by the operator (stress and strain) on an LED<br />
(or other appropriate computer controlled display) during the time the test specimen is<br />
loaded. It shall detect the peak load and capture the elongation associated with the peak load.<br />
The maximum skew time between the load and corresponding elongation shall be 0.015 s.<br />
6.1.7.1 The data acquisition component shall consist of an IBM-compatible computer<br />
with three A/D channels; one for load (the load cell), one for elongation (the laser), and one<br />
for temperature (the RTD). Data shall be stored in ASCII format.<br />
6.1.7.2 Display of Stress-Strain Curve--The data acquisition and display system shall<br />
be capable of displaying a stress-strain curve in units of stress (MPa) versus strain (percent).<br />
This may be accomplished using the video screen of the data acquisition computer or with an<br />
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