TRANSIENT AND RESIDUAL-STRESS IN A PORCELAIN-METAL STRIP

被引:34
作者
ASAOKA, K [1 ]
TESK, JA [1 ]
机构
[1] NATL INST STAND & TECHNOL,DIV DENT & MED MAT POLYMERS,GAITHERSBURG,MD 20899
关键词
D O I
10.1177/00220345900690020901
中图分类号
R78 [口腔科学];
学科分类号
1003 ;
摘要
Porcelain-fused-to-metal (PFM) restorations may develop cracks during processing or in-mouth service if the relative physico-mechanical properties of the porcelain and metal are highly mismatched. Precise conditions when this might occur are not known. Many processing and property variations can affect the stresses developed throughout a porcelain-metal system. To understand this, we conducted a computer simulation of stress developed in a PFM beam. The simulation considers cooling from temperatures higher than the porcelain sag-point. The following temperature-dependent factors were incorporated: the elastic modulus, shear viscosity (porcelain), and coefficients of thermal expansion. The cooling rate dependencies of the glass transition temperature, (Tg), and the temperature distribution during cooling were also included. The results suggest that transient tensile stress at the porcelain alloy interface may result in cracks in the porcelain during cooling. Occlusal forces may set up stresses to cause cracking at the surface of the porcelain if the compressive residual stress is not high enough. PFM restorations with an alloy of high thermal expansion coefficient require rapid cooling; on the contrary, PFM restorations with the alloys of lower coefficients require slow cooling. A high cooling rate can make up for thermal expansion mismatches between the alloy and the porcelain up to 2 × 10-6/°C. Finally, the results indicated that curvature was not a sensitive indication of stress for a multimaterial beam when visco-elastic relaxation and high cooling rates are involved. For the case modeled here, curvature varied inversely with a 1/2 to 1/7th power of the stress. © 1990, SAGE Publications. All rights reserved.
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页码:463 / 469
页数:7
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