Thermal shock parameter

The behaviour of particle- and whisker-reinforced CMCs under conditions of thermal shock can be modelled successfully using the fracture mechanics methods outlined in the previous paragraph (e.g. Aldridge and Yeomans, 2001) while the thermal shock parameters (figures-of-merit) can also be useful for initial material comparison. 

An alternate, simple technique for assessing thermal durability is to compute the thermal shock parameter from physical properties. This parameter, defined by Eqs. (38) and (39) is the ratio of mechanical strain tolerance to thermal strain imposed by the radial temperature gradient. The higher this parameter is, the better the thermal shock capability will be. 

Table 13 Companson of Strength and Thermal Shock Parameter of Standard and Thin-Wall Substrates...

Table 16 demonstrates good compatibility between either of the two substrates and the four washcoats. The increase in DES is rather maiginal relative to that of the substrate. The impact of these properties on thermal shock parameter is summarized in Table 17. The TSP values are reduced by only 5-10% for 5, and 10-20% for 52.

Table 18 Strain Tolerance and Thermal Shock Parameter Data for EX-32, 236/11.5A Substrate and Catalyst During High-Load Operation of a Heavy-Duty Truck Engine...

Table 11 Axial Thermal Shock Parameter for Cordieritc Ceramic Diesel Filters (for Tp = 400°C)...

W.L. Headrick, and R.E. Moore, Sample preparation, thermal expansion, and Hasselman s thermal shock parameters of self-flow refractory castables, Refract. Appl. News 7(1) 9-15 (2001). 

Table 13.1 Comparison of thermal shock parameters for a number of ceramics. Poisson s ratio was taken to be 0.25 for all materials...

TABLE 34.11 Comparison of Thermal Shock Parameters for a Number of Ceramics ... 

Tool material Density (mg/m) Hardness Transverse rupture strength (MPa) Fracture toughness (MNm- / ) Young s modulus (GPa) Poisson s ration Thermal expansion (10- /K) Thermal conductivity (W/mK) Thermal shock parameter... 

The well-known thermal shock parameter of the material is defined as... 

Rodrigues JA, Pandofelli VC. Thermal treatment temperature and its influence on the thermal shock parameters of refractory castables. Interceram. 2002 51(May) 186-189. 

Rogrigues JA, Pandolfelli VC, Rigaud M. Elevated temperature thermal shock parameters for refractories. Interceram 2002 51 (5) 322-326. 

It is therefore apparently futile, with regard to relationships [8.74] and [8.75], to try to optimize simultaneously the resistance to sudden mpture by thermal shocks (parameters R or R ) and the damage resistance (parameters R and R )- In other words, the optimization of the resistance to a severe shock leads to materials which are likely to be damaged rapidly by microcracking and vice versa. A choice has therefore to be made, according to the apphcation in view. 

A number of thermal stress fracture resistance parameters were defined to relate thermo-physical and mechanical properties of the materials with their TSR. Five thermal shock parameters (R, R , R , R and R ) are commonly used to describe TSR (Fahrenholtz, 2007). These parameters are divided into two categories i) based on criteria that relate to crack initiation (R, R and R ) and ii) based on necessary conditions for crack propagation (R and R ). The R parameter has been described in Equation (1), while R and R parameters are defined by the following relations... 

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