10-04-2017, 09:10 PM
THERMOMECHANICAL ANALYSIS
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INTRODUCTION
Thermomechanical Analysis (TMA) is the study of the relationships between a sample s length (volume) and its temperature
Thermal expansivity () is a useful engineering quantity
DEFINITION
A technique in which a deformation of the sample under non-oscillating stress is monitored against time or temperature while the temperature of the sample, in a specified atmosphere, is programmed.
PRINCIPLE
A cylindrical or oblong sample or specimen is subjected to load via a vertically adjustable quartz glass probe. The probe is integrated into an inductive position sensor.e system is heated at slow rate. If specimen expands or contracts, it moves the probe . A thermocouple close to the specimen measures the temperature.
TYPES OF PROBES
Compression probe -low load over a wide area of sample
Penetration probe - a high load over a small area for the purpose of measuring softening temperatures.
Tension probe used for measuring non-self supporting specimens - such as thin films and fibres under tension.
Volumetric probe - thermal volumetric expansion of irregularly shaped specimens
CALIBRATING THE LENGTH
The length is calibrated with metallic specimens that have a known, reversible coefficient of linear thermal expansion.
APPLICATIONS
TMA mainly used determination of
Glass transition temperature
Softening temperature
Melting temperature
Coefficient of thermal expansion
Percentage of shrinkages of samples