China
Africa
Explore chapters and articles related to this topic
Mechanical Properties of Materials in Microstructure Technology
Published in Bharat Bhushan, Handbook of Micro/Nano Tribology, 2020
Fredric Ericson, Jan-Åke Schweitz
Thermal fatigue is a special case of dynamic fatigue where the load cycling is caused by temperature changes and an associated variation in the thermal stress. The fatigue process is accelerated by the periodic temperature peaks, which causes thermal destabilization of the material, activates corrosion processes, speeds up diffusion processes, etc. Contrary to “normal” dynamic fatigue, which usually is of a high-cycle character, thermal fatigue often is of low-cycle character. Thermal chock is a well-known problem in brittle materials used for high-temperature applications. A rapid temperature change gives rise to a steep thermal gradient in the body, which fractures under the influence of the high local thermostress generated. Silicon and other conventional semiconductors are normally used in low-temperature applications and in chemically protected environments, and there is little reason to worry about thermal fatigue or thermal chock under these conditions. In the near future, however, materials like Si3N4 and SiC will be frequently used in micromachined structures for high-temperature applications, and phenomena such as thermal fatigue and thermal chock will have to be taken into consideration.
Digital Holography and Its Application in MEMS/MOEMS Inspection
Published in Wolfgang Osten, Optical Inspection of Microsystems, 2019
Wolfgang Osten, Pietro Ferraro
Recent trends in gas sensors involve use of miniaturized devices characterized by very low power consumption and by fabrication processes compatible with IC silicon technology, which offer many potential advantages compared to standard sensor fabrication processes. Following these trends, many efforts have been made to develop gas sensors on Si, and several different microstructures have been conceived. They rely on a thin sensing film deposited on a suspended membrane having low thermal conductivity and realized using the Si bulk micromachining technique. The gas sensor fabrication needs different materials, with different properties, and different technological processes, which involve high-temperature treatments. Consequently, the structure is affected by the presence of residual stresses, appearing in the form of undesired bending of the membrane. Moreover, when the temperature of the heating resistor increases, a further warpage of the structure is induced. High thermal stress gradients and induced deformations can lead to mechanical failure of the structure.
Numerical modelling of thermal stress in RCC dams using 2-D finite element method – case study
Published in L. Berga, J.M. Buil, C. Jofré, S. Chonggang, Roller Compacted Concrete Dams, 2018
J.L. Calmon, Juan Murcia, S. Botassi dos Santos, E. Gambale, C.J. da Silva
The thermal stress calculation depends on the following properties: Poisson ratio, modulus of elasticity and coefficient of thermal expansion. Based on the literature review when carrying out thermal studies, various authors used Poisson’s ratio in the range of 0.16 to 0.21. For purposes of this paper a constant value 0.21 was used. The value of the coefficient of thermal expansion of concrete depends, to a large extent, on its composition and moisture conditions. For purposes of this paper a constant value of 11.7 X 10−6/°C was used.
Influence of lithium carbonate and superplasticizer as admixtures on low calcium dialuminate cement castable submitted to thermal shock
Published in Journal of Asian Ceramic Societies, 2021
Arlin Bruno Tchamba, George Elambo Nkeng, Nangah Che Randy, Marcel Guidana, Ngouloure N M Zenabou, Yannick Tchedele Langollo, Daniel Ducho, Thomas A. Bier
Refractory concrete as structural material for high-temperature application has received significant attention during the last decade [4]. Ultra-high Performance Concrete (UHPC) requires an optimized granulometry for packing density, a very low water/cement ratio (below 0.25) and compressive strength higher than 150 MPa. During a rapid temperature change of a material, there occurs transient temperature distribution which induce thermal stress, resulting to thermal shock. The stress intensity is related to the difference in temperature between an ascending thermal shock and a descending one. The descending temperature is more destructive to brittle materials and tensile stress is generated on the surface. This circumstance may be sufficient to activate preexisting micro-cracks and to lead to body damage or fracture [8,9].
A criterion-selection diagram for the thermal shock resistance of a hollow circular cylinder
Published in Journal of Thermal Stresses, 2019
Hollow circular cylinders are widely used in many industrial applications, for example, in pressure vessels, nuclear power pipes, and gun barrels [1–3]. The thermally induced failure is of much concern in such components as thermal shock usually arises due to a sudden temperature change in external environments. Once the magnitude of the resulting thermal stress is high enough to rupture the wall material or to trigger the unstable growth of existing cracks, the so-called thermal shock failure occurs. The thermal shock resistance (TSR) is thus central to the integrity evaluation in severe thermal transients [1–6]. This necessitates the identification of appropriate material-ranking criteria in order to select the most desirable material for thermal shock application. Therefore, understanding the thermal failure mechanism and optimizing the TSR have received constant and considerable attention in both academic and industrial communities [1–8].
Interlaboratory study on low temperature asphalt binder testing using Dynamic Shear Rheometer with 4 mm diameter parallel plate geometry
Published in Road Materials and Pavement Design, 2022
Johannes Büchner, Michael P. Wistuba, Ondrej Dasek, Matthias Staschkiewicz, Hilde Soenen, Adam Zofka, Torsten Remmler
The asphalt materials’ susceptibility to low-temperature cracking is considered a fundamental performance property of asphalt pavements, which is significantly driven by the temperature-dependent asphalt binder properties (Wang et al., 2017). Asphalt binder is a viscoelastic material, capable of stress relaxation. As a consequence of temperature changes, thermal stresses can evolve in the asphalt pavement due to material shrinkage which are usually assimilated by the asphalt binder’s relaxation properties. However, at low-temperature condition the stress relaxation capability is reduced and the thermal stress might reach the strength limit which will damage the material in the form of a crack (Coufalík et al., 2015).