Mechanical and Environmental Factors in the Cyclic and Static Fatigue of Silicon Nitride

Abstract

The effects of environment on cyclic and static fatigue behavior were investigated with hot-pressed silicon nitride materials. Tests were conducted at ambient temperature on standard compact tension specimens, and a dc electric potential technique was used to monitor crack lengths in situ. The results indicate that the environmental sensitivity of our materials under both cyclic and static loading mirrors that of durable glasses in static fatigue. The materials were most sensitive to water in the environment, while changes in pH had no significant effect in the range tested. In addition, NH, was much less reactive with our materials than with vitreous SO,. In some cases, the intergranular glass appears to be the site of environmental interaction. Evidence was also found that cyclic fatigue is not simply a manifestation of static fatigue. Cyclic fatigue was seen to occur in the absence of measurable static fatigue, and the data indicate that the mechanism of cyclic fatigue involves damage to the crack wake shielding zone.

Ceramics and ceramic coatings in orthopaedics

“…Results obviously vary by material, but can also differ due to test conditions and applied stress ratios. Furthermore, the data shown in the Table are inclusive of various environmental conditionsparticularly the presence of moisture [211,212,[343][344][345][346][347][348][349][350][351][352][353][354][355]. Stress corrosion cracking is a common problem for all polycrystalline ceramics due in part to the presence of grain boundary impurities.…”

“…10(b) is a representative microstructure of these types of Al 2 O 3 -ZrO 2 nano-composites. For reference purposes, fatigue testing has been conducted for most of the biomaterials of Table 1a, and the reader is referred to selected publications for Al 2 O 3 [357][358][359][360][361][362], Mg-PSZ [363][364][365], Ce-TZP [366,367], Y-TZP [346,[368][369][370], Ce-and Y-ZTA [212,348,355,371,372], ATZ [211], Si 3 N 4 [344,354,373,374], CoCr [375], Ti6Al4V [376,377], PEEK [378][379][380], and cortical bone [381][382][383].…”

A model for complex aftershock sequences

“…Static fatigue, also known as stress, creep, or delayed fracture is the basic way of time-dependent failure under a constant load of a broad variety of materials, including textile fibers [Coleman, 1957], fiber composites [Phoenix, 1977], wood [Garcimart(n et at., 1997], microcrystals [Pauchard and Meunier, 1993], gels [Bonn et al, 1998], policrystalline ceramics [Jacobs and Chen, 1994], metals [$chleinkofer et al, 1996], silicate glasses [Charles, 1958], minerals [$cholz, 1968a;Barnett and Kerrich, 1980], and rocks [Atkinson, 1984]. In all these cases, the signature of static fatigue is the observation of a failure strength that is a function of the load history of the material.…”

Cerâmicas dentárias à base de ZrO2, aditivadas com biovidro: processamento, caracterização estrutural e mecânica

“…Um material frágil estará sujeito a falha mecânica para valores de solicitação cada vez menor, à medida que for submetido a trabalho (ANUSAVICE, 2005 (FREI, 1991;WEDDIGEN, 1992;KAWAKUBO, 1987;UENO;JACOBS, 1994). As relações entre os mecanismos que aumentam a tenacidade à fratura e mecanismos de fadiga cíclica vêm sendo discutidas, desde os anos 90.…”

“…Em oposição às outras técnicas, o método usado aqui também é baseado na propagação de ocorrência de defeitos intrínsecos no material, que é semelhante à condição encontrada na prótese de cerâmica real submetidos à fadiga. Crescimentos subcríticos das trincas, em materiais policristalinos submetidos a tensões cíclicas, podem resultar de rompimento de ligações na ponta da trinca em cerâmicas submetidas à degradação dos mecanismos tenacificantes, envolvendo ponteamento de grãos ou transformações de fase (CHEVALIER; OLAGNON;FANTOZZI, 1999;DAUSKARDT;RITCHIE, 1987;JACOBS;CHEN, 1995;TSAI;SHETTY, 1995). No caso do material em estudo, a presença da fase intergranular vítrea pode facilitar os fenômenos citados.…”