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In engineering plastic selection, test data are often regarded as the most objective and reliable basis for decision-making. Yet in real projects, rework and field failures caused by “correct data but wrong material choice” are far from rare. The issue does not lie in the tests themselves, but in misunderstandings of test conditions, data boundaries, and engineering relevance.
Tensile and flexural strength values are among the most frequently misinterpreted data points. Standard tests are conducted at 23°C and 50% relative humidity, while nylon materials are highly sensitive to temperature and moisture. Under high humidity or elevated temperature, mechanical strength can decrease by more than 30 percent. Many failure cases show that using dry-as-tested data directly for structural calculations leads to unexpected deformation or fracture in service.
Heat deflection temperature is another parameter often taken out of context. HDT values are measured under specific loads and heating rates and are intended for comparative purposes. In real applications, components are typically subjected to long-term static loads or cyclic stress. When operating near the HDT, nylon materials may experience significant creep deformation, even if the temperature never exceeds the test value. Over time, this can result in dimensional instability and functional failure.
