Meaning
Standardized testing protocols for the long-term mechanical characterization of thermoplastics are defined in a specific global document. Iso 899-1 provides a rigorous framework for determining the tensile creep of plastics under constant load and temperature. This document governs the testing geometry, the application of stress and the recording of strain data.
It ensures that creep modulus values reported by different resin manufacturers are comparable and reliable for engineering design.
Conditioning Requirement
Environmental control during the test is strictly mandated to prevent moisture or temperature fluctuations from skewing the results. Many polymers, especially polyamides, are sensitive to humidity which can act as a plasticizer and artificially increase the creep rate. The standard requires specimens to be conditioned at specific relative humidity levels before the load is applied.
Data Application
Engineering calculations for load-bearing plastic parts rely on the isochronous stress-strain curves generated by this method. These curves allow a designer to estimate the deformation of a part after five or ten years of service. A common mistake is using the short-term elastic modulus for a part that will be under permanent load, which leads to failure through excessive deformation.
Test Duration
Recommended intervals for data collection ensure that the initial rapid creep phase and the later steady-state phase are both captured.
