Thermal stress resistance

Hasselman, D.P.H. (1970), Thermal stress resistance parameters for brittle refractory ceramics a compendium , Am. Ceram. Soc. Bull, 49, 1033-1037. 

For material initially undamaged, the appropriate parameter expressing the tendency for cracks to be developed, and therefore strength to be lost, can be considered to be that for crack initiation. This has been expressed in terms of thermal stress resistance parameters.25,30,52,86-88 Kingery used the infinite slab symmetrically heated or cooled with a constant heat transfer coefficient to derive thermal shock fracture resistance parameters R, R and fusing the equations ... 

The parameter R is applicable for the case of instantaneous change in surface temperature (infinite h) for conditions of rapid heat transfer R is for a relatively low Biot modulus ( jl< 2) for conditions of slow heat transfer R" is for a constant heating or cooling rate.88 defines the minimum temperature difference to produce fracture under conditions of infinite heat-transfer coefficient, i.e. A = 1. The parameter Ris inversely proportional to a. Alow value of a is therefore essential for good thermal stress resistance. The coefficient of thermal expansion normally increases with increasing temperature however, thermal conductivity decreases. 

Kingery, W.D., Factors affecting thermal stress resistance of ceramic materials , J. Am. Ceram. Soc., 1955 38(1) 3-15. 

Hasselman, D.P.H. (1978), Figures-of-merit for the thermal stress resistance of high-temperature brittle materials a review , Ceramurgia, 4(4), 147-150. 

Stresses caused by steady-state thermal gradients may or may not cause failure, depending on the degree of constraint imposed by some parts of the item upon others or by external mounting. Thermal stress resistance (face-to-face temperature differentials) that causes tensile stress is observed in some types of glasses. When glass is suddenly cooled, as by the removal from a hot oven, tensile stresses are introduced in the surfaces and... 

Thermal Stress Resistance. Epoxy-glass printed circuit boards, containing various electronic components were dip-coated and cured as described above and then cycled from -65°C to +125°C in forced air chambers according to the following schedule 1 hr at -65°C, 2 min at room temperature, 1 hr at +125°C, 2 min at room temperature, 1 hr at -65°C, etc. Such boards survived 20 to >50 cycles without cracking and/or delamination of the coating. 

We have described a new type of conformal coating which is shelf-stable, solventless, one-component, and rapidly cured by a combination of UV and heat. Once cured, this coating has very good electrical properties, thermal stress resistance, and hydrolytic stability. With the proper choice of solvents, all or a portion of the cured coating can be removed from a circuit board to repair the electronic parts. 

Tedlar is moderate in cost and has known long-term performance out-of-doors. It has excellent toughness, good weather resistance, and moderately good electrical and optical performance. Its thermal stress resistance is marginal but adequate (2-6> shrinkage at 150°C) for most needs. Its cost is higher than optimum, but can be used as a thin film, especially when coupled with less expensive polyethylene terephthalate film for better electrical properties at a lower cost. 

The thermal stress resistance parameter 31 is based on the maximum stress that arises during a thermal transient. The stresses are usually less... 

Because most development work has been done on non-oxide materials, particularly SiC fiber-reinforced SiC CMCs (SiC/SiC) with fiber interfacial coatings of either carbon or boron nitride, non-oxide CMCs are more advanced than oxide CMCs. Non-oxide CMCs have attractive high temperature properties, sueh as creep resistance and microstructural stability. They also have high thermal conductivity and low thermal expansion, leading to good thermal stress resistance. Therefore, non-oxide CMCs are attractive for thermally loaded components, such as combustor liners (see Figure 1-4), vanes, blades, and heat exchangers. 

To achieve fracture in UHTC materials, ManLabs researchers decided to notch all subsequent test specimens. Notches were 6 mm deep x 1.6 mm wide and parallel to the axis of the cylinder, extending inward from the outer surface along the entire length of the specimen. The main disadvantage of using notched specimens was the lack of adequate experimental and analytical data on the shape factor required to compare the experimental results with predicted properties as well as the inability to compare these results with those of previous evaluations. Their results showed that materials with SiC and carbon additions displayed somewhat higher steady state thermal stress resistance than the other compositions. Nonetheless, all the diboride compositions tested showed a level of thermal stress resistance considerably above any other ceramics they had tested. ... 

Clougherty, E. V., Niesz, D. E. and Mistretta, A. L. Research and Development of Refractory Oxidation-Resistant Dihorides, Thermal Stress Resistance, Part n Vol.VI, AFML-TR-68-190, ManLabs Inc., Cambridge, MA, (1968). 

Hasselman, D. P. H. Singh, J. P. Analysis of Thermal Stress Resistance of Microcracked Brittle Ceramics. CeramicBulietinBR, 856-860 (1979). 

Name Material Laser wavelength A (nm) Upper level lifetime, r(/4S) Thermal stress resistance Rt (W/m /2) Type of pumping"... 

W, D, Kingery, "Factors Affecting Thermal Stress Resistance of Ceramic Materials," Journal of the American Ceramic Society, 38 3-15 (1955). 

D. P. H. Hasselman, "Figures of Merit for the Thermal Stress Resistance of High-Temperature Brittle Materials," Ceramurgia Int. 4[4] 147-50 (1978). 

In the 1980s, in an effort to develop thermal stress-resistant materials for aerospace applications, a new concept of materials was proposed to deal with the boundary problem [1, 2]. That is, a ceramic coating on metal or a ceramic/metal joined material with continuous texture was developed in order to increase the adhesion strength and minimize the thermal stress near the... 

---