Glass Products Under Mechanical and Thermal Loads

Airbag igniters are small assemblies consisting of a sealing component with specified electrical properties and an explosive. Robust igniters must guarantee the reliability of the electrical properties and of the explosive for many years. Thus, the compon

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Thermal Loads

8.1 Strength Optimization of Airbag Igniters Kurt Nattermann, Harald Krummel, Ludwig Frank Introduction Airbag igniters are small assemblies consisting of a sealing component with specified electrical properties and an explosive. Robust igniters must guarantee the reliability of the electrical properties and of the explosive for many years. Thus, the components must not exhibit any form of corrosion and the assembly must be air-tight. Otherwise, the explosive could degrade by moisture, for example. The necessary sealing properties of the igniters can be achieved with glassto-metal seals. These vacuum-tight assemblies of glasses with metals are used to feed electrical conductors through the walls of hermetically sealed packages. A typical glass-to-metal seal consists of an external metal part (in the following called the "ring"), in which a glass element is sealed [8.1, 2]. The glass element, in turn, encloses one or more leads (in the following called the "pins"), which are sealed into it. Glass-to-metal seals are successfully used in electric engineering and cover a wide range of applications in which the sealing glass serves as an excellent insulator. A special feature of airbag igniters is that their "normal operation" is an "explosion" in close proximity to a person. Therefore, the strength of the igniters must be sufficiently high in order to avoid personal injury by components splitting off. We have investigated the functionality and reliability of air bag igniters with two-step finite-element analysis (FEA), using the general-purpose FEA program ANSYS.

8.1.1 FEA for Axial-Symmetric Models We first consider a simplified axial-symmetric FEA model. The material parameters and the size (Table 8.1) of this model are close to those of the final device. H. Loch et al. (eds.), Mathematical Simulation in Glass Technology © Springer-Verlag Berlin Heidelberg 2002

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8. Glass Products Under Mcchanical and Thermal Loads

Table 8.1. Material parameters and geometrical data of axial-symmetric models

M ateTial parameters CTE Young's modulus Poisson's ratio Yield strength

Unit

Pin

Sealing glass

Ring

10- 6 K- 1 GPa

9 150 0.28 300

lOA 70 0.22

18 200 0.3 300

MPa

Geometrical data Radius Inner radius Outer radius Height after grinding Height before grinding Hcight after grinding

00

0.5mm l.355mm 3.52 mm 2.22mm 5.2 mm 4.99 mm

Figure S.la shows the ring, sealing glass, and pin of an igniter. The sealing glass does not completely fill the ring's bore. The dotted horizontal line indicates the grinding face, and the dashed line the rotational axis. The ring-glass and pin-glass interfaces are modeled by "doubled nodes", i.e., we assign at an interface separate nodes to each material, all exactly in the same position as in the adjacent material. Normally the nodes are coupled, but the coua)

Ro axi

l.

Grinding

face

~~ ~

~

~

§§~ ..

Glass

b)

E -

1= lIl-

Pin

Ring

\ Fig. 8.1. (a) FEM mesh, (b) von-Mises stress for elastic model

------

ovM/MPa 0 110 220 330

440

550 Cl

= Cl

660 770

880