Heat deflection temperatureHDT

The temperature region over which an amorphous or partly amorphous polymer changes from a rigid, glassy state to a softer, rubbery one. It sets a practical upper service temperature for resins and adhesives and can be reduced by absorbed moisture or incomplete cure.

Long-duration testing in which a constant load or stress is applied to a specimen, usually at controlled temperature, while the slow time-dependent deformation is recorded. It is particularly important for polymers, adhesives and membranes, where deformation under sustained load can govern long-term design.

A thermal analysis technique that applies a small oscillating deformation to a specimen while temperature or frequency is varied, measuring storage modulus, loss modulus and tan delta. It is a sensitive method for determining the glass transition temperature and degree of cure of resins, adhesives and composites, and is also used on bituminous and polymeric roofing materials.