This standard is Part 3 of the series "Plastics - Acquisition and Presentation of Comparable Multi-Point Data." It provides a standardized set of methods and procedures for systematically obtaining and presenting long-term performance data of plastics under various environmental conditions, with a focus on the influence of environmental factors on mechanical properties. The standard establishes a unified basis for the scientific evaluation and comparison of the long-term performance of plastic materials, helping to address difficulties in judgment caused by a lack of data comparability. The simulation of environmental conditions covered by the standard requires specific equipment, including ovens (for long-term thermal aging), chemical immersion containers (for chemical resistance testing), and artificial weathering chambers (for simulating combined environmental factors such as light, heat, and moisture). The quantitative assessment of final performance changes relies on a universal material testing machine to accurately measure key mechanical parameters such as tensile properties and stress-strain relationships of specimens before and after aging.