CALCULATION OF THERMAL STRESSES IN A SUBSTRATE-COATING SYSTEM

Thermal stresses induced during cooling from temperatures used for coating deposition were calculated for various fiber-coating systems. Systems under study include several types of carbon, alumina, and zirconia fibers. Coatings considered were TiB2, Si3N4, and SiC. Typical calculated stresses were on the order of 0 to 2 GPa. The results were used to analyze the effects of variable physical parameters such as coating thickness and crystallographic orientation on the stress levels. Each fiber-coating system was then compared using a nominal coating thickness of 5 μm in order to rank the various fiber-coating combinations. Among the results obtained, it was shown that orientation of deposited coatings usually leads to higher tensile stresses.

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Thermal Benefits of Low Solar Absorption Coating for Preventing Rail Buckling

2015 Joint Rail Conference ◽

10.1115/jrc2015-5669 ◽

2015 ◽

Author(s):

Hao Wang ◽

Jiaqi Chen ◽

P. N. Balaguru ◽

Leith Al-Nazer

Keyword(s):

Thermal Stresses ◽

Three Dimensional ◽

Surface Preparation ◽

Organic Content ◽

Coating System ◽

Solar Absorption ◽

Coating Application ◽

Dimensional Finite Element ◽

Hot Weather ◽

Three Dimensional Finite Element

A low solar absorption coating for rail application is developed to reduce the peak rail temperature and buckling risk in summer months. The proposed coating system provides a highly reflective surface through white or off-white color and has constituents to provide high abrasion resistance and self-cleaning properties. The zero volatile organic content (VOC) and one hundred percent inorganic coating system has excellent adhesion to steel surfaces with minimal surface preparation. This paper presented the outdoor temperature monitoring results of the coated rail segments under hot weather. The results show that the application of coating could significantly reduce the peak rail temperature up to 10.5°C. Three-dimensional finite element (FE) models were developed to predict temperature distributions and thermal stresses in the rail. The thermal stress simulation shows that, when the rail neutral temperature (RNT) is relatively low, rail coating decreases the compressive stress in the rail up to about 50% during the hottest hours. Although increasing the RNT decreases compressive thermal stresses in the rail, it could increase the risk of rail break due to the increased tensile stresses in the rail. The coating application could reduce the high RNT requirement during rail placement and prevent rail buckling as the effective RNT decreases after traffic and maintenance. Therefore, the low solar absorption coating could serve as a proactive way to control peak temperatures and thermal stresses in the rail.

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Deformation at interfaces of Ti-6Al-4V/SiC fiber composites

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121193 ◽

1992 ◽

Vol 50 (1) ◽

pp. 158-159

Author(s):

Warren J. Moberly ◽

Daniel B. Miracle ◽

S. Krishnamurthy

Keyword(s):

Thermal Stresses ◽

Load Transfer ◽

Coefficient Of Thermal Expansion ◽

Hot Isostatic Pressing ◽

Matrix Composites ◽

Ongoing Research ◽

Aerospace Applications ◽

Sic Fiber ◽

The Matrix ◽

Intermetallic Matrix Composites

Titanium-aluminum alloy metal matrix composites (MMC) and Ti-Al intermetallic matrix composites (IMC), reinforced with continuous SCS6 SiC fibers are leading candidates for high temperature aerospace applications such as the National Aerospace Plane (NASP). The nature of deformation at fiber / matrix interfaces is characterized in this ongoing research. One major concern is the mismatch in coefficient of thermal expansion (CTE) between the Ti-based matrix and the SiC fiber. This can lead to thermal stresses upon cooling down from the temperature incurred during hot isostatic pressing (HIP), which are sufficient to cause yielding in the matrix, and/or lead to fatigue from the thermal cycling that will be incurred during application, A second concern is the load transfer, from fiber to matrix, that is required if/when fiber fracture occurs. In both cases the stresses in the matrix are most severe at the interlace.

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