Analysis of residual stress for mismatch metal–glass seals in solar evacuated tubes

The residual stress of mismatch seal between borosilicate glass 3.3 and stainless steel is analyzed for metal–glass solar evacuated tubes in this paper. As borosilicate glass has a much lower limit of stress than metal, a tube model with different sizes and shapes of metal and glass is simulated to determine the magnitude and profile of the residual stress in the glass region. The simulation results show that the maximum magnitude of the hazardous tensile stresses occurs at a few millimeters above the sealing area, not in the contact position; and the thickness of metal is the most important parameter of the seal which affects the stress level. The stress magnitude increases dramatically when the thickness of stainless steel increases from 10 to 60 µm. Therefore, to avoid breakage of the seal, the thickness of metal should be less than 40 µm. In addition, it is shown that both the cross-section shape of the metal ring and the contact length in the glass have a considerable impact on the stress. The stress level increases significantly with the increase of depth of the metal ring embedded in the glass. Comparison between a metal ring with trapezoidal cross-section and one with rectangular cross-section of equivalent mean thickness reveals that the former leads to smaller residual stress. Furthermore, the results show that variation in the glass tube dimensions, in compare to the metal ring parameters, has less effect on the residual stress level in the seal area. An increase in the thickness of the glass tube decreases the stress noticeably, whereas an increase in tube radius has a negligible impact. Finally, it is shown that the simulation results are in good accordance with results of experiments using samples of mismatch seal between borosilicate glass 3.3 and stainless steel successfully fabricated according to our proposed parameters.