Creep to Rupture of Short Fiber Reinforced PA
Our customer needed the creep to rupture behavior of some short fiber reinforced polyamides at elevated temperatures (100°C to 200°C). So, he asked us to perform and evaluate tests. He provided ISO standard test samples in the “dry as molded” condition.
Testing Strategy: We used our electro-mechanical test frame with temperature chamber and video extensometer for these tests. At each temperature, we started with tensile tests (Figure 1, Figure 2). Then we added creep tests. We always started with a creep stress lightly below the ultimate stress. Then, for each consecutive test, we reduced the creep stress. Thus, we started tracking a logarithmic rupture stress versus time relation (Figure 3, Figure 4). This helped us with the time, cost and quality critical task of planning the next creep test of each series. For test durations up to 10 hours we used the very well instrumented test frame. However, for test durations beyond 10 hours we used creep test frames. Thus, we kept cost under control.
PA water content (humidity) has a strong influence on creep behavior. And these test campaigns take weeks and months during which the material can take up water. Therefore, we monitored and documented specimen humidity carefully. And, if necessary, calibrated specimen humidity and uniformity before testing. By re-testing material over time, we tracked and documented the potential influence of physical and chemical aging during storage and conditioning.