Fatigue Analysis and Defect Size Evaluation of Filled NBR including Temperature Influence

0558759 - ÚFM 2023 RIV CH eng J - Journal Article
Schieppati, J. - Schrittesser, B. - Tagliabue, S. - Andena, L. - Holzner, A. - Poduška, Jan - Pinter, G.
Fatigue Analysis and Defect Size Evaluation of Filled NBR including Temperature Influence.
Materials. Roč. 15, č. 11 (2022), č. článku 3745. E-ISSN 1996-1944
Institutional support: RVO:68081723
Keywords : vulcanized natural-rubber * lifetime prediction * crack-growth * probability-distribution * stress amplitude * behavior * initiation * propagation * dependence * failure * fatigue * fracture mechanics * filled rubber * X-ray microtomography * defect size * temperature * J-integral
OECD category: Materials engineering
Impact factor: 3.4, year: 2022
Method of publishing: Open access
https://www.mdpi.com/1996-1944/15/11/3745

The fatigue behavior of a filled non-crystallizing elastomer was investigated on axisymmetric dumbbell specimens. By plotting relevant Wohler curves, a power law behavior was found. In addition, temperature increases due to heat build-up were monitored. In order to distinguish between initiation and crack growth regimes, hysteresis curves, secant and dynamic moduli, dissipated and stored energies, and normalized minimum and maximum forces were analyzed. Even though indications related to material damaging were observed, a clear trend to recognize the initiation was not evident. Further details were revealed by considering a fracture mechanics. The analysis of the fracture surfaces evidenced the presence of three regions, associated to initiation, fatigue striation, and catastrophic failure. Additional fatigue tests were performed with samples in which a radial notch was introduced. This resulted in a reduction in lifetime by four orders of magnitude, nevertheless, the fracture surfaces revealed similar failure mechanisms. A fracture mechanics approach, which considered the effect of temperature, was adopted to calculate the critical defect size for fatigue, which was found to be approximately 9 mu m. This value was then compared with the particle size distribution obtained through X-ray microcomputed tomography (mu-CT) of undamaged samples and it was found that the majority of the initial defects were indeed smaller than the calculated one. Finally, the evaluation of J-integral for both unnotched and notched dumbbells enabled the assessment of a geometry-independent correlation with fatigue life.
Permanent Link: https://hdl.handle.net/11104/0333983