Failure Stress and Apparent Elastic Modulus of Diesel Particulate Filter Ceramics 2012-01-1252
Three established mechanical test specimen geometries and test methods used to evaluate mechanical properties of brittle materials are adapted to the diesel particulate filter (DPF) architecture to evaluate failure initiation stress and apparent elastic modulus of the ceramics comprising DPFs. The three custom-designed test coupons are harvested out of DPFs to promote a particular combination of orientation of crack initiation and crack plane. The testing of the DPF biaxial flexure disk produces a radial tensile stress and a crack plane parallel with the DPF's longitudinal axis. The testing of the DPF sectored flexural specimen produces axial tension at the DPF's OD and a crack plane perpendicular to the DPF's longitudinal axis. The testing of the DPF o-ring specimen produces hoop tension at the DPF's original outer diameter (OD) and at the inner diameter of the test coupon, and a crack plane parallel to the DPF's longitudinal axis. The testing of these mechanical test coupons also enables the determination of an apparent elastic modulus of the DPF ceramic material. Results consistently show that the apparent elastic modulus of the DPF ceramics is much less (e.g., up to an order of magnitude less) than apparent elastic modulus estimated using sonic- or resonance-based test methods. These specimen geometries, produced stress states, and modes of consequential crack initiation are discussed in context to the DPF's symmetry along with the assessments of each specimen's ease of fabrication, testing, failure stress determination, ultimate viability, and prospects for test standardization. Lastly, an explanation is offered for why the apparent elastic modulus measured with these three mechanical test coupons is relatively low and why their low values are more accurate for predicting thermomechanical stresses in DPFs.