Fracture mechanical analysis of two commercial polyoxymethylene homopolymer resins

Abstract

This research addresses the fracture mechanical analysis of two commercially available polyoxymethylene homopolymer resins. Two types of experiments are used: monotonic fracture toughness tests and cyclic fatigue crack growth tests. The resulting total lifetimes in the fatigue crack growth tests are split up into the appropriate parts of crack growth initiation and fatigue crack propagation. Fracture surfaces of monotonic and cyclic tests are analyzed using light microscopy and scanning electron microscopy. Besides the mechanical tests, the morphology within the used compact tension specimens is examined in detail by using differential scanning calorimetry, small-and wide-angle X-ray scattering, and polarized light microscopy. The results are analyzed and discussed, considering observations in the previous studies published in the literature. It is shown that both materials can be well analyzed using linear elastic fracture mechanics and their fracture mechanical properties are presented in conjunction with a detailed documentation of the microstructure.

Cyclic tests on cracked round bars as a quick tool to assess the long term behaviour of thermoplastics and elastomers

“…Closer to the centre a dimple-like pattern was dominant, before changing to a flat surface. POM also showed fracture surfaces similar to literature [16] without signs of ductile deformation, such as stretched fibrils, at a magnification of 1000-times. H-NBR also exhibits a rather smooth fracture surface.…”

“…9). The area close to the notch is a rather plane surface with small flaky patterns, quite similar to fracture surfaces found in CT-specimen fatigue tests of the same material [16]. Following, is the transition area, where the surface is covered with small grooves, quite similar to the top right picture of Fig.…”

“…1. Frequency was chosen at 10 Hz for PE, PVC and POM according to findings or experience in literature (PE [15], POM [16], PVC [17]). For PP [7], PB, PA12 and H-NBR [13] testing frequency was reduced to 5 Hz to avoid excessive hysteretic heating.…”

Fatigue Fracture Properties and Morphology of Polyoxymethylene (POM) Plates Produced under Moderate Processing Conditions

“…For both resins, the molecular weight and the polydispersity index are given in Table 1. For Tenac, this data was already published previously [15]. The corresponding data for the Delrin resin used in this study was also determined at that time.…”

“…It is frequently used for components which are exposed to cyclic loading [1][2][3][4][5][6][7], and hence, its fatigue properties are of technical interest. Generally, this material shows only small crack tip plasticity in fatigue crack growth tests, and thus, it can be investigated quite well using linear elastic fracture mechanics [8][9][10][11][12][13][14][15][16].…”