Preliminary study on the determination of the Weibull modulus of strength distribution in quasi-brittle materials

In this paper,how to determine the Weibull modulus of a fracture strength distribution is discussed with its physical implications for quasi-brittle materials.Based on the Markov chain assumption,it is shown that the lifetime(i.e.,the time taken for formation of a critical defect)in a quasi-brittle material can be described by a gamma probabilistic distribution function.Prior to macroscopic failure,the effective number of energy barriers to be overcome is determined by the slope of the energy barrier spectrum,which is equivalent to the Weibull modulus.Based on a fracture mechanics model,the fracture energy barrier spectral slope and Weibull modulus can be calculated theoretically.Furthermore,such a model can be extended to take into account the crack interactions and defect-induced degradation.The predicted Weibull modulus is good agreement with that derived from available experimental results.

SIZE EFFECTS OF WINDOW GLASSES IN TALL BUILDINGS

A certain strength is required for the window glasses in tall buildings due to the high wind pressure. The strength for large size glasses is generally deduced from the testing results of specimens with samll sizes by the Weibull statistics theory. By a great deal of experiments the authors have studied the thickness , span and width effects of flat glasses of on bending strength under biaxial stresses. Compared with the Weibull theory, the accuracy of strength is determined and a modification is made for the volume effect proposed by Weibull. The size effect of Weibull modulus is investigated as well and the reasonable specification for flat glass strength is suggested.

Interaction between Weibull parameters and mechanical strength reliability of industrial-scale water gas shift catalysts

A fundamental step in the production of an industrial catalyst is its crushing strength assessment. Limited literature exists in which the strength reliability of supported catalysts is investigated from production to their application in a reactor. In this work, cylindrical supports were prepared by pelletizing high poros- ity γ-alumina powder, and Cu-Znf/γ-Al2O3 catalysts were prepared by impregnation of the pelletized γ-alumina supports with an aqueous solution of copper and zinc nitrates. The support-forming variables, such as binder concentration, compaction pressure, calcination temperature, and drying procedure were investigated. The Weibull method was used to analyze the crushing strength data of the supports, and the fresh and used catalysts before and after the low-temperature water gas shift reaction. Support formation at a 50 wt% binder concentration, 1148 MPa compaction pressure, 500 ℃ calcination temperature, and rapid drying （100 ℃, 8 h） led to the maximum support mechanical reliability. The most reliable catalyst with respect to simultaneous appropriate catalytic performance and mechanical strength was prepared from a support with the lowest mean crushing strength （26.25 MPa）. This work illustrates the impor- tance of the Weibull modulus as a useful mechanical reliability index in manufacturing a supported solid catalyst.

Effect of pyrolytic carbon interphase on mechanical properties of mini T800-C/SiC composites

The effect of pyrolytic carbon(PyC) thickness on the tensile property of mini T800 carbon fiber reinforced SiC matrix composites(C/SiC) was studied. PyC interphase was prepared by chemical vapor infiltration(CVI) process using C3H6–Ar as gas source, the PyC thickness was adjusted from 0 to 400 nm, and then the SiC matrix was prepared by CVI process using methyltrichlorosilane(MTS)–H2–Ar as precursor and gas source. The results showed that the tensile strength of mini T800-C/SiC increased first and then decreased with the increase of the PyC thickness. When the thickness of PyC was 100 nm, the average strength reached the maximum value of 393 ± 70 MPa. The Weibull modulus increased from 2.0 to 8.06 with the increase of PyC thickness, and the larger the Weibull modulus, the smaller the dispersion, which indicated that the regulation of PyC thickness was conducive to improve tensile properties.

Experimental and statistical assessments of the mechanical strength reliability of gamma alumina catalyst supports

The mechanical strength of solid catalysts is considered an important factor in terms of ensuring the reliable performance of industrial reactors. In this work, a pelletizing method was used to form gamma alumina support for catalysts. Response surface methodology （RSM） was employed to analyze and model the effects of various manufacturing parameters on the crushing strength of the supports. These parameters were binder concentration, compaction pressure, calcination temperature, and drying mode. The suggested model was verified by applying an analysis of variance to assess its validity with regard to crushing strength. The mechanical reliability of various supports was also determined by calculating their Weibull modulus values through linear regression of the Weibull equation. The material with the highest mechanical strength reliability will have both a high mean crushing strength and a high Weibull modulus, and the best values obtained for a support in this work were 70.7 MPa and 6.63, respectively. The conditions used to form this sample were： 20mass% binder concentration, 861 MPa compaction pressure, 466 ℃ calcination temperature, and gentle drying.

Effect of Al powder and silica sol on the structure and mechanical properties of Al_2O_3-ZrO_2 foams

Polymeric sponge replication method is one of the common ways for ceramic foam production. The existence of central triangular voids in the struts results in a decrease of mechanical properties limiting their applications. To remove this defect, some additives consisting of Al powder particles and silica sol are added to ceramic slurries consisting of Al2O3 and ZrO2 （partially stabilized zirconia）. With increasing temperature for pyrolyzing and sintering of raw materials, first the Al powder and then the glass phase which consisted of melted Al2O3, ZrO2 and SiO2 was soaked into hollow struts. SEM investigations showed that the center of foam struts were free of hollows. XRD considerations depicted that a ZrO2 phase with tetragonal crystallographic structure is present in the produced foam which could be the reason of improved toughness and mechanical properties. Compressive strength of foams increased significantly due to the decrease of closed porosity. The Weibull statistical study showed remarkable increasing of the Weibull module and its value for foams with 10, 20 and 30 ppi was 5.91, 6.06 and 6.53 respectively.