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This paper employs a systematic approach to packaging design and testing of a system and its components in order to determine the long term durability of light duty diesel filters. This effort has utilized a relatively new aluminum titanate filter technology as well as an advanced support mat technology engineered to provide superior holding force at lower temperatures while maintaining its high temperature performance. Together, these two new technologies form a system that addresses the unique operating conditions of diesel engines. Key physical properties of both the filter and the mat are demonstrated through laboratory testing. The system behavior is characterized by various laboratory techniques and validation procedures.

This paper provides elastic analysis of compressive stresses in the matrix and skin regions of automotive substrates during 3D- and 2D-isostatic strength testing. The matrix region is treated as transversely isotropic material and the skin region as isotropic material, each with their independent elastic properties. Such a solution helps quantify load sharing by the matrix and skin regions which, in turn, affect compressive stresses in each region. The analysis shows that the tangential compressive stresses in the skin and matrix differ significantly at the interface due to high stiffness ratio of skin versus matrix. The resulting strain in the skin is more severe for thin and ultrathin wall substrates and may lead to localized bending of interfacial cells thereby inducing premature failure. Methods to reduce compressive strain in both the matrix and skin without affecting performance-related advantages are discussed.

The oven shock test is an accelerated test which is often used to quantify the thermal durability of both coated and uncoated ceramic substrates. The test calls for heating the substrate for 30 minutes in an oven, which is preheated to specified temperature, and then cooling it in ambient environment for 30 minutes. Such a cycle induces axial and tangential stresses, during cooling, in the skin region whose magnitude depends on physical properties, oven temperature, radial temperature gradient and the aspect ratio of substrate. In addition, these stresses vary with time; their maximum values occur as soon as the substrate is taken out of the oven. This paper evaluates the severity of thermal stresses as function of above factors and estimates the probability and mode of failure during cooling using thermocouple data. Methods to reduce these stresses are discussed.

This paper focuses on the effect of temperature on biaxial strength of curved, symmetrically laminated, automotive windshields. In view of their aspheric curvature, the measurement of biaxial strength requires a special ring-on-ring test fixture with compliant loading and support rings. The key factors that affect strength are (i) fatigue behavior of surface flaws, (ii) expansion mismatch between glass and PVB interlayer, and (iii) interfacial bond integrity. These, in turn, depend on the operating temperature which for automotive windshields can range from −40°C in winter to +50°C in summer. The data show that the biaxial strength is 21% higher at −40°C and 28% lower at +50°C than that at room temperature. An assessment of fatigue and interfacial bond integrity shows that strength changes of these magnitudes are predominantly caused by residual stresses arising from expansion mismatch between glass and PVB interlayer.

This paper presents the strength data for conventional automotive windshields in both the new and used conditions. More specifically, the biaxial strength of outer surface of curved and symmetrically laminated windshield, measured in biaxial flexure, is reported. The relative contributions of inplane membrane stress, which can be significant for new windshields, and bending stress are quantified with the aid of strain gauge rosettes mounted on both the outer and inner surfaces of windshield. The strength distribution for new and used windshields, based on Weibull distribution function, is found to be multimodal indicating more than one family of surface flaws. Depending on handling damage during manufacturing, assembly and installation processes, the low strength region of new windshields can approach that of used windshields with 50,000+ road miles!

Thin wall ceramic catalysts offer improved performance by way of faster light-off, lower back pressure and higher FTP efficiency than standard ceramic catalysts. These advantages are attributed to their lower thermal mass, larger open frontal area and higher geometric surface area. This paper will focus on their physical durability, notably their thermal shock resistance. The critical physical properties which influence thermal shock resistance - namely modulus of rupture, elastic modulus and coefficient of thermal expansion - will be examined over a wide range of operating temperatures for both standard (400/6.5) and thin wall catalyst supports (600/4.3 and 400/4.5) with stable high temperature washcoat systems. These data help evaluate the thermal shock capability of each system via computation of thermal shock parameter. The validity of such computations is tested against the thermal shock data from oven test.

With stricter emissions standards, low back pressure requirements, and 100,000 mile durability specifications, ceramic catalysts have undergone significant developments over the past few years. The thrust in the ceramics area has centered on thin-wall structures to minimize back pressure and on high cell density for rapid light-off in close-coupled applications. The thin-wall structures are extruded from low expansion cordierite ceramic with adequate strength and thermal shock resistance equivalent to those of standard cordierite substrate. Examples of thin-wall substrate include 350XT which is extruded from a very low expansion dense cordierite ceramic, and 400/4 and 600/4 cell structures extruded from a low expansion modified cordierite ceramic. This paper will focus on the high fatigue resistance, excellent conversion efficiency, and low back pressure of 350 XT substrates with advanced washcoat system.

New test methods were developed to characterize the high temperature durability of intumescent mats that are used to mount ceramic catalyst supports in stainless steel cans. The key attribute of these tests is the use of an electric resistance heating method to maintain a temperature gradient through the thickness of the mat when a cyclic or constant shear stress is applied to the mat interface. These tests are simple to perform and do not require expensive equipment or highly skilled operators. Using these new test methods, the durability of ceramic preconverters mounted with 4070 gm/m2 intumescent mat was studied. The results of these tests indicate that a preconverter package with 4070 gm/m2 intumescent mat can perform satisfactorily in the close-coupled application where temperatures exceed 900°C. The mat performance can be quantified in terms of applied stress and test temperature by utilizing the experimental methods described in the present study.

The preconverter is an essential element of exhaust gas treatment to help meet the tighter emission standards of TLEV and LEV levels. Its design must be chosen so as to meet the simultaneous requirements of compactness, faster light-off, low back pressure, high temperature durability and low cost. This paper presents design options for a ceramic substrate and durable package which lead to an optimum and cost-effective preconverter system. Preliminary data for high temperature physical durability of selected converter systems are presented. Performance parameters for light-off activity and back pressure are also computed and compared with those of standard substrates used in underbody application. Laboratory tests comprising of axial push-out test, high temperature vibration test, exhaust gas simulation test and the engine dynamometer test demonstrate the viability of ceramic preconverters for automotive application.

The design, performance and optimization of the extruded electrically heated metal converter have recently been published(1,2). The present paper focuses on the physical durability of extruded metal EHC support at high temperature representative of operating conditions. The mechanical, thermal, creep and fatigue properties of Fe-Cr-Al honeycomb structure over 25°-1000°C temperature range are reported. In addition, the stresses arising from mounting and thermal loads are computed via finite element analysis and compared with the high temperature strength of extruded metal EHC support. A safe design stress which predicts 192,000 kilometer durability is estimated from high temperature fatigue behavior of extruded Fe-Cr-Al honeycomb structure.

Since their introduction to automotive industry in 1975, ceramic substrates have successfully met the strength requirements for canning, engine and chassis vibrations, and thermal shock. This paper will focus on canning loads and techniques, and how they influence the stress distribution in ceramic substrates. The strength data, most relevant to canning stresses, will be presented for porous cordierite ceramic substrates as function of their contour, size and cell structure. Recent improvements in measuring the biaxial compressive strength will also be reviewed.

The use of a Calrod type electrical faceheater, powered by two 12V heavy duty batteries in series, as a regeneration initiator for a 12 in (30.5 cm) diameter × 12 in (30.5 cm) long segmented honeycomb ceramic filter is described. Recent test data, obtained on Deutz mining engines during the regeneration process, is presented. The effects of various regeneration parameters on the reliability and long-term durability of the filter is discussed together with the effect of fuel additives. The test data include both the measured temperature profiles and calculated thermal stresses in the filter with and without fuel additives.

The effects of cell geometry and dimensions on the thermal shock resistance of catalytic monoliths is examined analytically. Two cell geometries, namely square and equilateral triangle, are considered. Thermal gradients predicted by theory compare well with the experimental results. It is found that for equivalent thermal shock resistance the triangular cell requires lower coefficient of thermal expansion than the square cell. Also, as the cell density is increased for higher geometric surface area, both geometries require a reduction in thermal expansion coefficient to preserve their thermal shock resistance. The above comparison does not take into account some of the other considerations which affect the overall performance, such as manufacturing advantage and the conversion efficiency. Also, the triangular cell examined has a cell density of 236/in2 with 20% greater geometric surface area than the square cell with a cell density of 200/in2.

The paper describes the factors which must be considered when assessing the suitability of a material for a rotary regenerator disc which runs at 1850°F. Mechanical and thermal stressing, thermal stability, and corrosion resistance are analyzed, using the properties of type CPD-5 material. This is a new lithium-alumino-silicate glass ceramic developed by Corning Glass Works. The environmental conditions assumed are those found in the 2500°F turbine inlet temperature engine which is being developed by the Ford Motor Company.