Strength Of Brittle Materials Research Articles

Strength of brittle materials in tension

Strength of brittle materials in tension

An assessment of systematic errors in beam tests on brittle materials

In deriving the unit volume strength of brittle materials from beam bend test data, the shear and compressive stresses in the beam specimens are usually ignored. Depending on the span-to-depth ratio of the beam, these omissions may give rise to significant errors in the unit volume strength value, and in component failure probabilities derived from this strength value. In this paper, the effects of these systematic errors are considered for the 3-point beam as a function of span-to-depth ratio and for different values of the Weibull modulus. The relative errors are found to be small and conservative provided a sufficiently large span-to-depth ratio is used and the compressive/tensile strength ratio of the material is relatively high.

Note on the use of the diametral compression test for the strength measurement of ceramics

The strength of brittle materials is usually measured by a bend test, but when the material is of tubular form the method is troublesome. An apparently better way to measure the strength in such cases is to test rings cut from the material. The most convenient method of testing the rings is the so-called diametral compression test in which a compressive load is applied by two pressure plates parallel to the ring axis. In order to check the consistency of this test various types of tubes were tested. Four different diameters of tube (A to D) were chosen from commercially available alumina. Details of the different geometries and materials are given in the Table I. For each type of tube, 19 rings of three different lengths were used. Throughout the series the three different ratios of length to average radius were kept constant at 1.1, 2.2 and 3.3, respectively. The shortest (longest) ring of each type of tube is denoted by 1 (3) and the intermediate length by 2. The surface condition of the rings used was as-fired. According to an analysis by Sharman [1] the strength, of, of eccentric rings can be written as:

Effect of sliding friction forces on the strength of brittle materials

A model is developed for the strength degradation of brittle surfaces in sliding contact with spherical indenters. The loss of strength is associated with the propagation of partial cone cracks in the wake of the indenter. Detailed fracture mechanics calculations are circumvented by working in the limit of ideal point-load contacts, with the key proposition that the crack dimensions remain insensitive to rotations of the cone axis relative to the specimen free surface. In this way the simple Roesler solution for classical, well-developed cone cracks may be retained as a convenient “reference state” for a more general theoretical description, whereby the superposition of a tangential friction force onto the normal loading is accommodated via a straightforward coordinate transformation operation. The major predictions of the model are tested by measuring the strengths of glass surfaces after contact with a sliding steel sphere. In particular, the degraded strengths are not strongly influenced by the coefficient of friction, contrary to expectations from some earlier indentation analyses.

Inertia as a Factor in the Dynamic Strength of Brittle Materials

Previous strength determinations of ceramics subject to impulsive loads were interpreted in terms of a theory based on material inertia. Recent experiments are described, which show (1) that the dynamic strengthening mechanism is athermal, as required by the inertial theory, and (2) that microcrack growth, rather than initiation, is suppressed by the inertial effect.

The Effect of Stress Nonuniformity and Size on the Strength of Composite Materials

It has long been known that the strength of brittle materials like ceramics depends on the volume of stressed material and the nature of the stress distribution. Both of these effects arise because brittle materials are flaw-sensitive, and flaw severity is generally statistical in nature. As the probability of finding a serious flaw increases with increasing material volume, large brittle bodies tend to fail at lower stress levels than do smaller ones when both are subjected to the same kind of uniform stress field, such as pure tension. The dependence of strength on stress distribution arises because the stress in the region of at least one flaw must equal its critical value for failure to occur. In this paper, we refer to this phenomenon as a “nonuniformity effect.”

Thermal fatigue strength of brittle materials and friction-pair components of power-generation equipment

1. The long-term thermal-fatigue strength of hard materials (brittle and semibrittle) of different structural classes together with their level of brittleness and macroductility, obtained with a view to time effects, the scale factor, the physicochemical effects of the contacting medium, are also determined by the characteristics of structural inhomogeneity. 2. The time effects of long-term thermal-fatigue strength of hard materials are associated with the development of processes of thermal loss of strength in them at the maximum temperature of the thermal cycling and of retarded fracture at the mean temperature of the thermal cycles. 3. An analysis of the results of bench tests with actual structural elements made of brittle materials and subjected to thermal cycling in a medium of sodium for up to 9000 h with the aid of the newly worked-out relationship of thermal fatigue showed that they correspond to the calculated thermal fatigue strength with a safety factor equal to 2–3.

An improved strength-measurement technique for brittle materials

An improved apparatus for determining the fracture strength of brittle materials by a hydraulic bursting technique is described. The new design greatly reduces the number of specimens which fail at their edge and reduces the scatter in the results. To complement this, a more detailed theory is developed to analyse results. An investigation of the strength of silicon nitride as a function of the impact velocity of a water jet illustrates the use of the apparatus. A method for converting fracture stress data to equivalent flaw size data is given which allows a more physically meaningful and useful presentation of results.

脆性材料の時間に依存する変形と強度に関する研究

脆性材料の時間に依存する変形と強度に関する研究

A New Load-Transmitting Medium to Measure Strength of Brittle Materials

Abstract A testing apparatus based on the principle of a new load-transmitting medium developed by the author is presented in this paper. Instead of solid bearing platens, “Lamina Pack” bearing platens are used in a compression test to overcome the shortcomings of current testing techniques. Data obtained in past investigations of nonmetallic brittle materials demonstrated that machines using solid bearing platens in contact with the specimen cause significant lateral restraint to the specimen and severe disturbances to the specified stress state, resulting in misleading apparent strength measurements. Previous attempts to replace testing machines with solid bearing platens have failed as the machines proposed do not have sufficient load capacity to measure the compressive strength under combined stresses of most of the brittle materials of engineering use. The apparatus exerts no appreciable lateral restraint to the specimen and has a high load-transmitting capacity. Strain measurements on specimens subjected to uniaxial compression applied by lamina platens show uniform deformation and indicate that the specified stress state (purely normal stresses applied to the boundaries of the specimen) has been closely approached.

Specimen for determining the strength of brittle materials

Specimen for determining the strength of brittle materials

Further Comments on “Strain‐Rate‐Dependent Effect of Specimen Volume on the Strength of Brittle Materials”

Further Comments on “Strain‐Rate‐Dependent Effect of Specimen Volume on the Strength of Brittle Materials”

A Statistical, Micromechanical Theory of the Compressive Strength of Brittle Materials

A general theory of the compressive strength of brittle materials is presented. This theory proposes that failure is brought about by structural weakening from accumulated crack damage which increases with the stress level. The statistics of the flaw distribution and the mechanism of crack initiation and extension are important. A sample calculation using the theory is given to demonstrate its application.

On the effect of crack growth on the scatter of strength of brittle materials

On the effect of crack growth on the scatter of strength of brittle materials

Comments on “Strain‐Rate‐Dependent Effect of Specimen Volume on the Strength of Brittle Materials”

Comments on “Strain‐Rate‐Dependent Effect of Specimen Volume on the Strength of Brittle Materials”

Methods for Determining the Strength of Brittle Materials in Compressive Stress States

Abstract Testing techniques capable of stressing brittle materials in any biaxial compressive stress state have been developed. The design of the specimen, the test devices, and the testing procedures are described in detail. Test results obtained with these techniques, which define the compressive biaxial failure envelope for WESGO AL-995 alumina, are presented. The general problems inherent in the compression testing of very strong brittle materials are discussed.

Compressive strength of brittle materials

Compressive strength of brittle materials

Strain‐Rate‐Dependent Effect of Specimen Volume on the Strength of Brittle Materials

Journal of the American Ceramic SocietyVolume 58, Issue 9-10 p. 452-454 Strain-Rate-Dependent Effect of Specimen Volume on the Strength of Brittle Materials D. P. H. HASSELMAN, D. P. H. HASSELMAN Member, the American Ceramic Society.Search for more papers by this authorG. B. KENNEY, G. B. KENNEYSearch for more papers by this authorKARL R. McKINNEY, KARL R. McKINNEY Member, the American Ceramic Society.Search for more papers by this author D. P. H. HASSELMAN, D. P. H. HASSELMAN Member, the American Ceramic Society.Search for more papers by this authorG. B. KENNEY, G. B. KENNEYSearch for more papers by this authorKARL R. McKINNEY, KARL R. McKINNEY Member, the American Ceramic Society.Search for more papers by this author First published: September 1975 https://doi.org/10.1111/j.1151-2916.1975.tb19021.xCitations: 8 Supponed in part by the Army Research Office—Durham, under Grant No. DA–ARO–D–31–124–73–G45 and by the National Science Foundation under Undergraduate Research Participation Grant No. GY-10084. At the time this work was done, the writers were with the Ceramics Research Laboratory, Lehigh University, Bethlehem, PA 18015. Karl R. McKinney ison Leave from the Naval Research Laboratory, Washington, DC. G. B. Kenney is now with the Department of Materials Science, Massachusetts Institute of Technology, Cambridge, MA 02139. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume58, Issue9-10September 1975Pages 452-454 RelatedInformation

Determining the strength of brittle materials by means of fracture-surface studies

Determining the strength of brittle materials by means of fracture-surface studies

Method of testing brittle materials such as glasses and sitals under conditions of biaxial compression

1. We have created a new method of studying the deformation and rupture resistance of commercial glasses and sitals under conditions of biaxial compression (largely eliminating the effect of high contact stresses on the resultant strength and elasticity characteristics) by gluing the ends of the samples into depressions in the metallic bearings with self-hardening compositions; this procedure also enables us to make a valid estimate of the effects of other factors, such as various boundary conditions, the presence of apertures, glued joints, sharp edges and chamfers, mechanical damage, and the etching (pickling) of the lateral surface on the technical strength of brittle materials. 2. We have found that reliable data regarding the strength of glasses and sitals may be obtained more consistently by using fairly rigid loading devices, preserving the initial contour conditions over the whole range of sample loading, and eliminating possible damage attributable to loss of stability. 3. We have established that elastic compressive strains in glasses and sitals amounting to at least 2.5% may be measured reliably by means of paper-based strain-gage sensors glued to the fire-polished lateral surface by means of epoxy resin heat-treated at 150°C for 7 h and containing (wt. %): epoxy resin ED-6 74, dibutylphthalate 14.8, and polyethylene polyamine 11.2. 4. Using the method so developed, we have obtained fresh data regarding the strength of sheet glass subject to linear and plane compression, which, being comparable quantities, may correspond to the first theory of strength or the Mohr criterion. 5. Under conditions of axial and biaxial compression over the whole range of loads studied (right up to the rupture point), sheet glass constitutes an elastic material with a rectilinear stress-strain diagram.