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The thermal durability of a large frontal area cordierite ceramic wall-flow filter for light-duty diesel engine is examined under various regeneration conditions. The radial temperature distribution during burner regeneration, obtained by eight different thermocouples at six different axial sections of a 75″ diameter x 8″ long filter, is used together with physical properties of the filter to compute thermal stresses via finite element analysis. The stress-time history of the filter is then compared with the strength and fatigue characteristics of extruded cordierite ceramic monolith. The successful performance of the filter over as many as 1000 regenerations is attributed to three important design parameters, namely unique filter properties, controlled regeneration conditions, and optimum packaging design. The latter induces significant radial and axial compression in the filter thereby enhancing its strength and reducing the operating stresses.

The isostatic strength of porous cordierite ceramic monoliths plays an important role during canning and subsequent operation of automotive catalysts. Its value depends on wall porosity, cell geometry, skin thickness and morphology, monolith size and contour, and substrate/washcoat interaction. If the stresses induced by canning loads and closure speeds exceed the isostatic strength, the monolith may exhibit either crushing or shear type failure. This paper presents the room temperature isostatic strength data for coated and uncoated ceramic monoliths of different contour, size, and cell geometry. The applied isostatic load on the monolith is translated into stresses in the porous cell wall using both an analytical model and finite element analysis. It is found that the failure criteria are governed by the fundamental tensile and compressive strengths of the cell wall.

This paper addresses the packaging design for monolithic cordierite ceramic converters to meet the new, stringent durability requirements of the 1990's, while minimizing warranty cost for the automaker. These objectives are best met by using a systems approach during the early phases of packaging design, i.e. by examining design interactions between the ceramic monolith, alumina coating, ceramic mat or wiremesh mounting material with seals, stainless steel can, heatshields, and associated peripheral components. Failure of any one of these components can prove detrimental to converter durability. In this paper we take advantage of overall understanding of the observed failure modes and individual component behavior, and present new data for optimizing the total converter durability through initial design. In particular, the impact of symmetric gas entry, monolith contour, clamshell anisotropy, mount density, stiffener ribs, and heatshield insulation on total durability is highlighted.

The physical properties, including modulus of rupture, structural modulus and thermal expansion coefficient of segmented, large frontal area, ceramic wall-flow diesel filters are presented. The effect of cement composition, its coverage and segmentation pattern on these properties and on the failure modes during strength testing is discussed. Using these properties the mechanical and thermal integrities of LFA filter are computed and compared with those of monolithic filter,. The paper discusses both the high efficiency (EX-47, 100/17) and low efficiency (EX-66, 100/25) filter compositions.

Ceramic honeycomb structures have been used successfully as catalyst supports in gasoline-powered vehicles for the past ten years. They are currently the leading candidate for trapping and oxidizing the carbonaceous particulate emissions in diesel-powered vehicles. In both of these applications the long term durability of the ceramic substrate is of prime importance. This, in turn, depends on the physical properties of cellular structure, cyclic nature of service loads and design of the mounting assembly. This paper examines the nature and dependence of both the mechanical and thermal stresses in the substrate on its geometry, properties, mounting parameters, and the operating conditions. It also compares the observed failure modes with those predicted by the theory. The paper concludes with a set of recommendations for optimal systems design and acceptable operating conditions which will promote the long term durability of the ceramic substrate.

An approximate analytical solution for stress distribution in the rectangular lens of a glass headlamp due to static and impact loading is presented. Both low mass/high velocity and high mass/low velocity impact data and the resulting failure modes are discussed. Generally, glass headlamp lenses break either due to Hertz stress (front surface under high localized tension), or due to flexural stress (back surface under tension due to bending), or the combination of two. Failure due to flexural stress is illustrated by a star-crack, while that due to Hertz stress is illustrated by a Hertzian cone or “bullet hole” in the lens. The failure mode during low mass/high velocity impact is predominantly Hertzian while that during high mass/low velocity impact is flexural for lenses 0.120″ to 0.150′ thick. No significant differences are observed in the impact resistance of standard and light-weight lenses in this thickness range.