David L. Shelleman

Prediction of the Strength of Ceramic Tubular Components: Part I—Analysis

The objective of this paper is to develop the analytical background for test methodologies that will enable accurate prediction of the strength distribution of ceramic tubular components from the strength distributions of simple specimens. Four simple specimen configurations and two tubular configurations were selected for this purpose. The simple specimen configurations were (1) four-point bend, (2) C-ring tested in compression, (3) C-ring tested in tension, and (4) O-ring tested in diametral compression. In addition, a short tube tested by axially compressing rubber inside the tube and a long tube subjected to internal pressure were analyzed. These specimen configurations were for the most part selected in a tubular shape in order to simulate the shape of tubular structural components. The prediction of the strength distribution of one specimen from that of another was based on Weibull statistical theory. Effective volume and area expressions, necessary for failure prediction, were derived for these specimen configurations.

Stress relaxation of a soda lime silicate glass below the glass transition temperature

Stress relaxation is an important effect in the ion-exchange procedure of glasses, as it controls the stress profile and the strength. Creep and stress relaxation tests have been performed to study the viscoelastic behavior of soda-lime silicate glass at typical ion-exchange temperatures. The experimental data of these tests can be fitted well by the Burger model and a comparison between the viscosity data from both tests was made. The strain and temperature dependences of the stress relaxation process were studied and the glass exhibited a non-linear viscoelastic behavior and an anomalous temperature dependence. In addition, it was found there is a relationship between the glass density and the stress relaxation behavior.

Prediction of the Strength of Ceramic Tubular Components: Part II—Experimental Verification

The strength distribution of reaction-bonded silicon carbide tubes that failed by internal pressurization was predicted from strength distributions obtained from simple laboratory test specimens at room temperature. The strength distributions of flexure bars, C-rings tested in tension, C-rings tested in compression, diametrally compressed O-rings, and internally pressurized short tubes were compared with the strength distribution of internally pressurized long tubes. The methodology involved application of Weibull statistics using elasticity theory to define the stress distributions in the simple specimens. The flexural specimens did not yield acceptable results, since they were ground before testing, thereby altering their flaw population in comparison with the processing-induced flaw populations of the tubular specimens. However, the short tube internal pressure test, the C-ring tested in tension, and the diametrally compressed O-ring test configurations yielded accurate strength predictions of full-scale tubular components, since these specimens more accurately represent the strength-limiting flaw population in the long tubes.

High temperature, tube burst test apparatus

A testing apparatus is described that enables both single and double-ended tubular members to be tested under pressure and at elevated temperatures. For double-ended tubular members, the apparatus comprises first and second pressure seals at either end of the tubular member under test, both seals including annular compliant members that bear upon the internal surface of the tubular member. A heater is positioned within the tubular member and one of the pressure seals has an orifice through which the heater is connected to a power source. Pressurization occurs through an orifice in the other pressure seal and cooling apparatus surrounds the first and second ends of the tubular member to cool the pressure seals, thereby enabling the annular compliant members to retain their compliancy when the tubular member is heated to test temperature. For single-ended tubular members, a single pressure seal is used having pathways for both electrical and pressurization connections to the interior of the tubular member.

A Critical Review of the Diametral Compression Method for Determining the Tensile Strength of Spherical Aggregates

The validity of diametral compression as an effective means of determining the tensile strength of spherical ceramic bodies has often been questioned. In this paper, a comprehensive review of the original work, as well as alternative studies that suggest shortcomings of the original method, is made. For comparative purposes, data recently collected via diametral compression on aluminosilicate aggregates is presented in the context of these latter works and compared with the original methodology. Overall, results indicate that the diametral compression test can indeed provide an accurate measure of tensile strength when several important test criteria are met.

Test Methodology for Strength Testing of Soda-Lime-Silica Float Glass Before and After Enameling

Different biaxial flexure test geometries were investigated to determine the most reliable test for evaluating the strength of float glass specimens before and after enameling. The enameled and unenameled samples were tested using the ring-on-ring (ROR) and ball-on-ring (BOR) strength tests. The strengths of each sample set were analyzed using a conventional two-parameter Weibull analysis. For direct comparison of the data, combined Weibull moduli were calculated for the unenameled tin side, unenameled air side, and enameled tin side data sets. The principle of independent action (PIA) was assumed to be the appropriate fracture criterion and the data were scaled to determine if discrepancies existed between the different testing methodologies. The scale parameters (σo) were also calculated for the different test geometries. The results showed that there were no statistical differences between the scaled data. Based on the results it was concluded that the ROR test geometry was the better choice compared to the BOR test geometry because of the larger stressed area. The use of a concentric support ring was also found to be more desirable than a ring on equally spaced balls because of the stress concentrations at the support balls, which can lead to problems.