Modeling of composite interfaces subjected to thermal stresses and physical aging

Author(s):  
D.-A. Mendels ◽  
Y. Leterrier ◽  
J.-A.E. Månson
2009 ◽  
Vol 131 (1) ◽  
Author(s):  
M. A. Neidigk ◽  
Y.-L. Shen

The generation of thermal stresses is a major cause for mechanical failure in encapsulated electronic components. In this study numerical modeling is employed to analyze thermal stresses in a high-voltage transformer encapsulated with filled epoxy. The transformer assembly consists of materials with an extremely disparate range of thermomechanical properties. The thermal histories considered mimic those in the operational condition. It is found that, upon thermal cooling from elevated temperature, the ceramic core can be under local tensile stress although it is entirely surrounded by materials with much greater coefficients of thermal expansion. The unique aspect of this paper originates from the fact that the volume shrinkage of the viscoelastic encapsulant during physical aging contributes to an increase in stress over time, thus increasing the tendency of fracture. This counter intuitive result (stress increase due to nonlinear viscoelastic physical aging) can now be predicted using constitutive models recently developed at Sandia National Laboratories. When a silicone coating between the core and the encapsulation is included, the stress is significantly reduced. The modeling result is shown to corroborate with the actual performance of the transformer.


Author(s):  
Warren J. Moberly ◽  
Daniel B. Miracle ◽  
S. Krishnamurthy

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.


1999 ◽  
Vol 30 (4-6) ◽  
pp. 296-302
Author(s):  
F. V. Nedopekin ◽  
Victor K. Tolstykh ◽  
N. A. Volodin ◽  
V. V. Belousov ◽  
S. V. Gridin

AIAA Journal ◽  
2002 ◽  
Vol 40 ◽  
pp. 1228-1232 ◽  
Author(s):  
B. V. Sankar ◽  
J. T. Tzeng

1996 ◽  
Vol 11 (2) ◽  
pp. 179-187 ◽  
Author(s):  
M. Akay ◽  
S. Ozden
Keyword(s):  

2017 ◽  
Vol 27 (6) ◽  
pp. 1249-1265 ◽  
Author(s):  
Yijun Liu ◽  
Guiyong Zhang ◽  
Huan Lu ◽  
Zhi Zong

Purpose Due to the strong reliance on element quality, there exist some inherent shortcomings of the traditional finite element method (FEM). The model of FEM behaves overly stiff, and the solutions of automated generated linear elements are generally of poor accuracy about especially gradient results. The proposed cell-based smoothed point interpolation method (CS-PIM) aims to improve the results accuracy of the thermoelastic problems via properly softening the overly-stiff stiffness. Design/methodology/approach This novel approach is based on the newly developed G space and weakened weak (w2) formulation, and of which shape functions are created using the point interpolation method and the cell-based gradient smoothing operation is conducted based on the linear triangular background cells. Findings Owing to the property of softened stiffness, the present method can generally achieve better accuracy and higher convergence results (especially for the temperature gradient and thermal stress solutions) than the FEM does by using the simplest linear triangular background cells, which has been examined by extensive numerical studies. Practical implications The CS-PIM is capable of producing more accurate results of temperature gradients as well as thermal stresses with the automated generated and unstructured background cells, which make it a better candidate for solving practical thermoelastic problems. Originality/value It is the first time that the novel CS-PIM was further developed for solving thermoelastic problems, which shows its tremendous potential for practical implications.


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