Time of Flight Ultrasonic Determination of 3D Elastic Constants
Encyclopedia
The three dimensional elastic constants of materials can be measured using the ultrasonic
immersion method. This was pioneered by xx and xx from the National Physical Laboratory in the 19xxs. It has mainly been used for polymer
composite
materials. Knowledge of the elastic constants can be used to feed back into models of the material's behaviour or that of the composite manufacturing process used.
which has a pair of ultrasonic transducers located on either side of the sample which can be rotated using a stepper motor
.
The time of flight of an ultrasonic pulse
that has been transmitted through the material is measured using an electronic timer that determines the start of the transmitted pulse and the start of the received pulse using threshold detection. This timer is typically accurate to microsecond
or better resolution.
By rotating the sample, time of flight measurements can be obtained a range of angles of incidence, typically up to 40 degrees. From the time of flight, the phase velocity can be determined as a function of the angle of incidence of the ultrasonic pulse.
Using Christoffel's equations, the measured data can be fitted using a least squares numeric method to determine six of the nine elastic constants.
By slicing the composite material and re-arranging the slices, the method can be re-applied to obtain the remaining three constants not found from the original measurements.
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
immersion method. This was pioneered by xx and xx from the National Physical Laboratory in the 19xxs. It has mainly been used for polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
composite
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
materials. Knowledge of the elastic constants can be used to feed back into models of the material's behaviour or that of the composite manufacturing process used.
Immersion technique
The ultrasonic immersion method makes use of a temperature stabilised water bathWater bath
A water bath can refer to:* A Bain-marie* A heated bath* A Laboratory water bath...
which has a pair of ultrasonic transducers located on either side of the sample which can be rotated using a stepper motor
Stepper motor
A stepper motor is a brushless, electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any feedback mechanism , as long as the motor is carefully sized to the application...
.
The time of flight of an ultrasonic pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
that has been transmitted through the material is measured using an electronic timer that determines the start of the transmitted pulse and the start of the received pulse using threshold detection. This timer is typically accurate to microsecond
Microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
or better resolution.
By rotating the sample, time of flight measurements can be obtained a range of angles of incidence, typically up to 40 degrees. From the time of flight, the phase velocity can be determined as a function of the angle of incidence of the ultrasonic pulse.
Using Christoffel's equations, the measured data can be fitted using a least squares numeric method to determine six of the nine elastic constants.
By slicing the composite material and re-arranging the slices, the method can be re-applied to obtain the remaining three constants not found from the original measurements.