High-temperature tensile creep testing

Figure 6.2 High-temperature tensile creep testing apparatus. (Reproduced from Leaderman, H. (1962) Large longitudinal retarded elastic deformation of rubberlike network polymers. Trans. Soc. RheoL, 6, 361. Copyright (1962) Society of Rheology.)...

This superplastically deformed silicon nitride also showed substantially improved creep resistance at high temperatures, when the stress was applied along the extruding direction. For example, the creep rates of the deformed body in tensile creep tests conducted at 1200 °C was found to be about one order of magnitude lower... 

High temperature deformation is also an extremely important property of ceramic composites for many applications. The techniques required for measuring creep are very similar to testing techniques for determining tensile strength and flexural strength. These techniques, as well as creep properties and mechanisms, are covered in Chapter 4. 

The microstructures of the consolidated and deformed samples were characterized by X-ray diffraction, optical and electron microscopy (SEM and TEM). The samples for mechanical testing have been prepared by spark erosion. The linear thermal expansion was determined by using a thermomechanical system (TMA). The temperature-dependent elastic moduli have been measured by the resonance frequency and the pulse-echo method. The bulk moduli were determined by synchrotron radiation diffraction using a high-pressure diamond-die cell at HASYLAB. The compression and creep tests were performed with computer-controlled tensile testing and creep machines. 

Satisfactory behavior of Hastelloy XR material has been found with respect to weldability, tensile and creep properties through optical microscopy and corresponding tests in air at room temperature and at high temperatures up to 950 C, respectively [40]. 

Mechanical tests using bending, tensile and compressive load conditions including the determination of elastic constants of the orthotropic material were carried out under room and high temperature conditions. For creep tests in tension four testing devices were established and creep tests longer than 6,000 h were carried out with different CMC qualities. The WHIPOX CMCs show much better creep resistance compared to state-of-the-art metallic combustor materials. 

Fig. 4.144 Tensile-creep modulus of polyethylene, high density, at different stress levels and test temperatures [12Els],...

The most important goal for each NASA-developed CMC system was to be able to operate under potential component stress levels for long time at its selected upper use temperature (UUT). To evaluate this capability, tensile test specimens from the various CMC panels were subject to creep-rupture testing in ambient air at their goal UUT and at stresses of -60% of their room-temperature cracking stress. The primary performance objective was to demonstrate greater than 500-hour life without specimen rupture. Since high-temperature mpture of an initially uncracked CMC is typically controlled by CMC... 

High temperature crack growth behavior under creep conditions was studied in SiC whisker-reinforced mullite. Four-point flexumral specimens were prepared for crack growth experiments by introducing Vickers indentation-induced cracks on the tensile surface. Samples were tested in creep in air at a nominal smface tensile stress at 150 MPa and a temperature of 1400°C. Crack growth and nucleation, and extent of creep-strain were... 

Structural adhesives such as epoxy resins can be treated as any rigid polymer and samples can be machined from cast sheets to produce test-pieces. These can then be used to measure typical tensile properties such as failure stress and strain. Using accurate exten-sometry, it is possible to characterize completely the uniaxial properties of an adhesive. The Creep of adhesive joints is especially important for structural adhesives maintained at high temperature. It is possible to determine the creep resistance of such materials by applying suitable loads at an appropriate temperature to samples of the adhesive, and to record the deformation with time. From such data, it will soon be evident if the adhesive is suitable for use or if it will cause a joint to deform with time. It is important to remember that humidity is likely to affect the properties of the adhesive, and in a long-term creep experiment, the humidity could cause premature failure. 

Pd-containing alloys mentioned above are solid solution strengthened and their application temperatures are usually limited to below 500°C. In order to establish a base line data for the development of high temperature creep resistant braze alloys, mechanical properties of thin foils of these alloys were evaluated. 82Au-18Ni was annealed at 850°C for 5 hours before tensile tests, whereas all other foils were treated at 900°C. 

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