Operating Manual

LENGTH, LOAD, AND STRESS
The Ultrasonic Extensometer compares the time of ight measurement in a tiebar under load to that of the same tiebar in a
relaxed condition. This difference in time of ight appropriately factored for temperature and stress effects determines the
elongation of the tiebar under load and is the basis for all other data provided by the Ultrasonic Extensometer.
What separates Ultrasonic Extensometers from traditional ultrasonic thickness gauges is their ability to adjust to variations
in sound velocity caused by stress loading and temperature changes. As a tiebar is stretched the velocity of sound within
it decreases making the tiebar appear longer than the physical change in length. Temperature has a similar effect. As the
temperature of a tiebar increases, its ultrasonic length increases at a rate greater than its physical length. Not considering
these effects will introduce unacceptable error in the measurement result.
Stress and load data provided by the Ultrasonic Extensometer is calculated within the instrument based on simple physical
laws. When a mold closes, the hydraulic clamping pressure in the injection molding press stretches the tiebars – the greater
the clamping pressure the greater the elongation. In the elastic region of the tiebar material below the yield stress limit, the
relationship between tiebar elongation and applied stress is linear and described by Hooke’s law. The modulus of elasticity
of the material being tested is a constant and determines the ratio of stress to the change in length. Therefore by measuring
the time of ight of the acoustic wave and knowing the sound velocity of the tiebar material, the Ultrasonic Extensometer
calculates the change in length, the load and the stress applied to each tiebar.
2
APPLICATION OF THE ULTRASONIC EXTENSOMETER
While the theory behind the operation of the Ultrasonic Extensometer requires some knowledge of physical laws, the ap-
plication of these instruments is conversely simple. The user simply follows a specic setup procedure for each new test to
be performed and the instrument takes care of all the complex measurements and calculations. Once created, individual
setups are stored in the instrument and can be recalled at a later date to automatically set the instrument up for future tests.
A single Ultrasonic Extensometer will appropriately instrument an entire factory oor of injection molding presses. A trans-
ducer can be permanently afxed to each tiebar on each press if desired and a single instrument can be circulated through-
out the shop to perform a variety of set up and in process testing of multiple presses helping to ensure process quality and
machine up time.
Modulus of Elasticity, E = =
Where: P = Applied Load or Force
L = Relaxed Length of tiebar
A = Cross sectional area of tiebar
? L = Elongation of tiebar under load
Unit Stress PL
Unit Elongation A ?L
Contact Information
StressTel
50 Industrial Park Road
Lewistown, PA 17044
Tel: [phone]
Tel: [phone]
E-mail: [e-mail]