Stress testing thermal/humidity

Thermal/humidity stress testing involves exposing samples to various conditions of temperature and humidity. Once the conditions are chosen, the samples are placed in either ovens which control the conditions or saturated solutions of salts in desiccators. The physical appearance of the sample is important and should be monitored throughout the study. In addition, any loss or gain of water should be noted as well. 

According to the thermal/humidity stress testing conditions selected, samples are placed into appropriate ovens. If humidity ovens capable of 70°C/30% RH and 70°C/75% RH are not available, saturated salt solutions contained in desiccators can be used to control humidity accurately. These conditions are particularly useful for high-potency drug substance compounds for which samples must be contained. A saturated NaCl solution is used to obtain conditions of 75% RH at 70 °C and a saturated MgCl2 solution is used to obtain conditions of 30% RH at 70 °C. 

Abstract Coupled THM simulation of the FEBEX, which is the full-scale in-situ Engineered Barrier System Experiment performed in Grimsel Test Site in Switzerland, is one Task in the international cooperation project DECOVALEX III. In the Task, the simulation of the thermal, hydraulic and mechanical behaviour in the buffer during heating phase is required, e.g. the evolutions and the distributions of stress, relative humidity and temperature at the specified points in bentonite buffer material. 

Traditionally, environmental stress in test systems is simulated using an environmental chamber in a thermal cycling mode. Although this method has produced system failures, interpretation of the failure in terms of cause is very difficult since there are, at a minimum, three variables—(1) temperature, (2) humidity, and (3) mechanical stress, all of which may be operating simultaneously. 

---