Thermal Testing
Typical Damage Causes and Failure Modes
Thermal testing of a component serves to assess its temperature resistance and analyze material properties under thermal influences. The investigation includes standardized procedures for determining temperature limits and flow behavior, which are crucial for practical application and quality assurance.
Melting Temperature, Glass Transition Temperature
The melting temperature of a thermoplastic polymer serves for material identification and provides indications of possible material mix-ups or polymer degradation due to unsuitable process conditions. The melting temperature is measured according to DIN EN ISO 11357 using Differential Scanning Calorimetry (DSC). This method measures the heat released or absorbed by a material as a function of temperature. In addition to the melting temperature, DSC can also measure the enthalpy required for melting. For amorphous polymers, the glass transition temperature is an important characteristic.
Vicat Softening Temperature
The Vicat softening temperature according to DIN EN ISO 306 is a measure of heat deflection temperature and thus the temperature resistance of plastics. To measure the Vicat Softening Temperature (VST), a defined indenter is pressed onto the surface with constant pressure while the temperature of the specimen is simultaneously increased. The Vicat softening temperature is defined as the temperature at which the indenter penetrates 1 mm deep into the surface. The softening temperature provides indications of the practical continuous service temperature limit for thermoplastic plastics.HDT Heat Deflection Temperature
The HDT heat deflection temperature is measured according to DIN EN ISO 75-2. Similar to the Vicat softening temperature, the HDT heat deflection temperature serves to determine the practical continuous service temperature of plastics. In this test, the specimen is placed on supports at its ends and loaded in the middle with a punch applying constant flexural stress, according to the three-point bending principle. The specimen is heated until a specified standard deflection is reached. The standard deflection corresponds to an outer fiber strain of 0.2%.Melt Flow Index
The melt flow index is often also referred to by the English abbreviations MFI (melt flow index) or MI (melt index). It serves to characterize the flow behavior of a thermoplastic polymer and thus its degree of polymerization. Through comparative measurements, the MFI is suitable for detecting material impurities and processing errors. A distinction is made between the melt volume-flow rate (MVR) and the melt mass-flow rate (MFR). Both are linked via the melt density; the measurement method is described in DIN EN ISO 1133 and is a routine procedure in plastics analysis.Adhesion and Peel Strength
Peel strength, i.e., the resistance of a sheet-like material to detachment, is particularly relevant for films, nonwovens, carpets, upholstery fabrics, and adhesive tapes. Depending on the application and test standard, the adhesive force can be peeled off at a peel angle of 180°, 90°, or a freely selectable angle. Similarly, roller devices can be used to maintain defined peel angles, for example, in the roller peel test according to DIN EN 1372 with a 90° peel angle or DIN EN 1464 with an approximately 60° peel angle.