`Ultra'-fast fracture strength of advanced ceramics at elevated temperatures

Choi, Sung R.; Salem, Jonathan A.

doi:10.1016/s0921-5093(97)00525-x

Cited by 16 publications

(25 citation statements)

References 29 publications

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“…The validity of Eq. 5 is limited to a certain level of applied stress rates where the bending strength no longer increases with increasing stress rate [23,24]. In the current investigation, the loading rates appear to be too low to expect that the values get close to such an inert strength even at the highest used loading rates.…”

Section: Resultsmentioning

confidence: 58%

Micro- and macro-mechanical testing of transparent MgAl2O4 spinel

et al. 2012

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Advanced transparent ceramics with high chemical and thermal stability are gaining increasing interest as replacement of glass-based materials in technical window applications. The mechanical reliability and performance of transparent MgAl 2 O 4 with a grain size of 5 lm has been characterized at ambient temperature using micro-mechanical indentation and macroscopic bending tests. The measurements focused on elastic modulus, fracture toughness, crack kinetics, and strength, the latter analyzed with Weibull statistics. The effect of slow crack growth is assessed using a strength-probability-time plot. Complementary fractography by optical, confocal and scanning electron microscopy provided a correlation between failure origin and fracture stress. The results and reliability aspects are discussed in terms of linear elastic fracture mechanics.

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Section: Resultsmentioning

confidence: 58%

Micro- and macro-mechanical testing of transparent MgAl2O4 spinel

et al. 2012

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“…Thus, the fracture energy density has been found to be by an order of magnitude higher than the critical energy release rate in static tests with notched alumina specimens, [4]. This observation has been recently fully con®rmed in dynamic fragmentation tests of alumina spheres, [5], and can not be explained by strain-rate effects in the strength of ceramics, [6], applying to a much lower range of strain rates. Our simulations of energy losses based on the continuum damage model yield obviously a good estimate of the enhanced fracture energy density at spalling.…”

Section: Enhanced Energy Dissipation At Spallingmentioning

confidence: 93%

“…It has been established, on the other hand, that the speci®c energy needed for spalling fracture exceeds by almost an order of magnitude the values typical for static fracture of notched specimens of the same material, [4]. This phenomenon, con®rmed recently in dynamic fragmentation tests of alumina spheres, [5], can not be explained by strain-rate effects in the strength of ceramics, [6], which apply rather to the strain-rate range of below 10 )4 s )1 , i.e. some six orders of magnitude below the strain rates of some 500 s )1 in our tests; there were no indications of strain-rate effects in the dynamic spall experiments with regard to the tensile strength.…”

Section: Introductionmentioning

confidence: 93%

“…The drop in the strength has been observed already at temperatures substantially below the temperature of active degradation of alumina (1950°C). Since the dynamic loading blocks viscous grain sliding, [6], it seems obvious that neither mechanisms related to bulk phase transitions at melting nor ow phenomena at grain boundaries can be responsible for the effect. It is rather the microfracture from pre-existing intergranular¯aws with heavily constrained plastic¯ow, [11], which may be the dominating mechanism in spalling.…”

Section: Introductionmentioning

confidence: 99%

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Enhanced fracture energy and effects of temperature at spalling in ceramics: continuum damage modelling

Najar

Silberschmidt

Müller-Bechtel³

2000

Archive of Applied Mechanics (Ingenieur Archiv)

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Enhanced fracture energy losses at spalling and the temperature dependence of the spalling strength of alumina ceramic bars are analysed on the basis of the experimental tests conducted both in room temperature and within the temperature range up to 1500°C at strain rates of some 500 s )1 . The experimental method and the measurements are ®rst shortly outlined. The mechanical response of ceramic bars is modelled then as a heterogeneous distribution of brittle-elastic mesoelements undergoing continuum damage at the known strain history, corresponding to that registered in the experiments. The mesoelements are characterised by the values of initial damage randomly¯uctuating within a given band-width superposed on a deterministic distribution, which corresponds to the fabrication conditions of the ceramic bars. The model has been tested in the evaluation of room-temperature experiments, its parameters: the average value of the initial damage, Young's modulus of the undamaged material and the energy absorption capacity in continuum damage are taken from the calibration ®tting the experimental data. The registered energy losses at spalling, which exceed the static values of fracture energy by almost an order of magnitude, can be explained thus by the enhancement of the dissipation due to bulk damage, which is computed on the basis of the above parameters. The temperature change of the Young's modulus of the matrix material is taken as corresponding to the measured change of the uniaxial wave velocity in the bar, and corrected by the temperature change of the mass density. The analysis of the model shows that the drop in the spalling strength of the specimens with the increase of the temperature is phenomenologically related to the falling energy absorption capacity within the continuum damage mechanism. An explanation of this phenomenon is attempted, based on the grain-sizerelated mechanisms of the microfracture from pre-existing intergranular¯aws distributed over the bulk of ceramics.

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“…Hence, it would be possible to see material's response to fife and strength more clearly and accurately with even a small number (about 5 at each condition) of test specimens. Also note that the alumim was very susceptible to SCG at elevated temperatures _ 800°C with significantly low values of SCG parameter ofn = 7-12 [17], so that it would be much easier usingthe aluminato scrutinize the influence of SCG/damage-accumulation on thecombined loading seqtumcesmore accurately. The expedm_tal work for the Case IH loading was not conducted in this study, primarily due to limited availability oftest specimens.…”

Section: Methodsmentioning

confidence: 99%

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

Choi

Gyekenyesi

2000

Journal of Engineering for Gas Turbines and Power

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Slow crack growth a,-udysis was ped'onned with tJ_ee different loading histories including constant s_'css-mteJconstant slress-ratc testing (Case I loading), constant skess/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case ITI loading_ Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case H loading history. The numerical solutions were in reasonable agreement with the experimental data, indicafin 8 that notwithstandin 8 some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test materials.

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`Ultra'-fast fracture strength of advanced ceramics at elevated temperatures

Cited by 16 publications

References 29 publications

Micro- and macro-mechanical testing of transparent MgAl2O4 spinel

Micro- and macro-mechanical testing of transparent MgAl2O4 spinel

Enhanced fracture energy and effects of temperature at spalling in ceramics: continuum damage modelling

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

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