After the characterization of the fibers, both types are subjected to creep tests in a climate chamber at constant temperature (20 °C) and relative humidity (60 %). Uncut fibers were clamped on both sides using the same clamping system as used in the characterization tests. The fiber is then placed in a creep frame, and subjected to a sustained load until failure. The time-dependent fiber elongation is contactlessly measured by a laser sensor at a rate of 1 Hz in the first week, and at 0.1 Hz afterwards. The maximum measurable elongation is 125 mm. The creep setup is schematically shown in Fig. 2a and a photo of the actual frame is presented in Fig. 2b.
Fig. 2 a Simplified creep frame, not shown is the supporting base b photo of the creep frame
In total, 26 creep samples have been tested, 14 of fiber A and 12 of fiber B. Every sample had an initial length of 200 mm and 5 different load levels were considered: 22, 36, 43, 53 and 63 %. The load level is defined as the applied creep load with respect to the average tensile strength. The number of specimens per load level and fiber type are summarized in Table 2.