Creep Time Limits and Yield Stress

The time-dependent deformation which occurs in a plastic material under constant stress is called creep. Creep at a given time is the difference between the total strain at that time and the initial instantaneous strain experienced on loading. The time-dependent decrease in stress needed to maintain a constant strain is called stress relaxation.

Figure 9 shows creep time limit curves for different nylons. PA12GC's yield stress point lies in a region far above the reach of other nylons. For example, at the load level of 2,300 PSI, PA12GC would yield to the stress only after about 1,000 hours, while the next best nylon, PA 6.6, would yield after less than 10 hours.

Fig. 9a shows tensile stress over time curve comparison between PA 12GC and PA 6.

Due to the combination of its superior properties Intech Power-Core™ (PA12GC) outperforms and outlasts other polyamids in most conventional applications. Its gravity casting technique allows it to be used effectively in areas where the production technology of other plastics is limited, for example, by a maximum diameter of 6 inches, and expands Power-Core's domain into traditional steel, bronze or ceramics applications.

Fig 9. Creep vs. Time Curves for Intech Power-Core plastic material

Fig 9a. Tensile Stress - Time Curves PA126 and PAG