A biomedical engineer investigates the tensile behavior of a new biodegradable polymer suture fiber. During a destructive test, they record the relationship between the applied force and the extension of the suture fiber until it ruptures. The results are shown in the table below.
| Extension / mm | Applied force / N |
|---|---|
| 0 | 0 |
| 4 | 20 |
| 8 | 32 |
| 12 | 36 |
| 16 | 30 |
Describe the non-linear stretching behavior of the polymer suture fiber shown by the data.