Diametral compressive strength

The diametral compressive strength has been used to estimate the tensile strength of certain AB cements (Smith, 1968). In this test, the load is applied diametrically across a cylinder of cement. Theoretical consideration of the test geometry shows that for a perfectly brittle material the failure that occurs is tensile in character. The difficulty in applying this test to AB cements is that they are not sufficiently brittle for this to hold true. In particular, the zinc polycarboxylate and glass-ionomer cements show sufficient plastic character to make the relationship between diametral compressive and tensile strength vary between AB cements of different types like the compressive strength test, this test is valid only as a means of comparison between similar materials (Darvell, 1990). 

Flexural strength is determined using beam-shaped specimens that are supported longways between two rollers. The load is then applied by either one or two rollers. These variants are called the three-point bend test and the four-point bend test, respectively. The stresses set up in the beam are complex and include compressive, shear and tensile forces. However, at the convex surface of the beam, where maximum tension exists, the material is in a state of pure tension (Berenbaum Brodie, 1959). The disadvantage of the method appears to be one of sensitivity to the condition of the surface, which is not surprising since the maximum tensile forces occur in the convex surface layer. 

Of all the methods of determining strength, the flexural test appears to be the most satisfactory. While not ideal, it does have the advantage of 

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Williams, P. D. Smith, D. C. (1971). Measurement of the tensile strength of dental restorative materials by use of a diametral compressive strength test. Journal of Dental Research, 50, 436-42. 

Diametric compressive strength (Bresilien test). Speed = 1 mm/sec. Test immediately after 7 days dry and after 7 days of immersion. 

The compressive strength of polycarboxylate cements at cementing consistency is 55—85 MPa (8,000—12,000 psi). Typical diametral tensile strength ranges from 8—12 MPa (1160 1740 psi). The solubiHty and disintegration in distilled water after 7 days at 37°C is 0.04—0.08 wt %, and is not reflected in clinical performance. 

Very recently, Williams, Billington Pearson (1992) have examined the effect of reinforcement by silver or silver-tin alloy on the mechanical properties of three glass-ionomer cements. Measurements of compressive, flexural, tensile (measured by the diametral compressive procedure) and shell strength are given in Table 5.17. These results show that the effect of reinforcement varies from cement to cement but, in general, increases it. 

Fig. 26 Effect of loading rate on the diametrical breaking strength of tablets compressed at different levels. (From Ref. 123.)...

Fig. 27 Methods of evaluating tablet crushing strength (a) bending or flexure strength (b) diametrical compression. (From Ref. 145.)...

Paradoxically, diametric compression, in which a disc-shaped sample is compressed diametrically between the crosshead plate and the base-plate, can be used to measure tensile strength (Gunasekaran and Ak, 2002). It is a simpler option than tensile testing because of the difficulty in the latter of satisfactorily gripping food material samples, which are relatively weak. 

L. C. Chow, S. Hirayama, S. Takagi, and E. Perry, Diametral tensile strength and compressive strength of a calcium phosphate cement effect of applied pressure, J. Biomed. Mater., S3 [5] (2000) 511-517. 

Tablet machine Manesty F speed 50 per min weight 490-510 mg. Strength test Diametral compression between flat-faced rams. Upper ram stationary, lower movi ng at 66 pm/s.

Pharmaceutical tablets are made from a number of components, and each component contributes to the tablet s final properties. Therefore, it is important to study the physical properties of the individual components and their mixture rules in order to predict the mechanical properties of the final tablet. Tensile strength is one of the crucial properties that assess mechanical strength the most common method for measuring tensile strength is the diametrical compression test discussed above (110). In this section the application of the Ryshkewitch-Duckworth equation to the analysis of tensile strength of mixtures will be discussed (151,152). 

The strength of tablets has traditionally been determined in terms of the force required to fracture a specimen across its diameter, the diametral compression test. The fracture load obtained is usually reported as a hardness value, an unfortunate use of a term that has a specific meaning in materials science, associated with indentation. The use of the fracture load does not allow for compacts of different shapes, diameters or thicknesses to be directly compared. For flat-faced circular tablets, a complete analytical solution exists for the stress state induced during the test (Barcellos and Carneiro 1953), allowing the tensile strength to be determined from the fracture load ... 

The stresses developed in convex tablets tested undergoing the diametral compression test have been examined by Pitt et al. (1989), who proposed the following equation for the calculation of the tensile strength ... 

A. A. Wereszczak, T. P, Kirkland, and O. M. Jadaan, "Strength Measurement of Ceramic Spheres Using a Diametrally Compressed "C-Sphere" Specimen", Journal of the American Ceramic Society, vol. 90, pp. 1843-1849, 2007. 

Delaying the light-initiation step in this way has been shown to affect a number of physical properties of resin-modified glass-ionomers. These include diametral tensile and compressive strength [20,21], both of which are reduced, and wear rates, which are increased [22]. Chemical properties, namely fluoride release [23], water uptake... 

The mechanical properties of concrete evaluated were the compressive and tensile strengths, at 7 and 28 days. Each result represents an average of 3 specimens. The compressive strength tests where performed according to the NP EN 12390-3 [16], where as the tensile strength test adopted was the Brazilian method, according to NBR 7222 [17], which determines the tensile strength by diametrical compression of specimens. 

Mellor, M., Hawkes, I. (1971). Measurementof tensile strength by diametral compression of discs and annuli. Engineering Geology, 5, 173-225. doi 10.1016/0013-7952(71)90001-9... 

Research on crack propagation in diametrical compression tests for intact and notched Brazilian disk specimens is conducted in the following cases. In the first case, experiments are aimed at determining the indirect tensile strength (Zhigalkin V.M. et ah, 2005). In the second case, the crack tip stress intensity factor is determined (Chaoshui Xu, 1993). The previous one was originally used for the ceramic samples (Shetty D.K. et al., 1985), but since the early 90 s began to be used for rocks (Zhao X.L. et al., 1993). 

J.T. Fell, J.M. Newton, Determination of tablet strength by the diametral-compression test. Journal of Pharmaceutical Sciences, 59,688-691,1970. 

Kamst et al. (1999) transposed to rice grains a diametral-compression test (Peltier, 1954 Rudnick et al., 1963) for measuring tensile strength. In this method, a horizontally placed cylinder is pressed between two flat plates. If proper load is applied, equally distributed along the cylinder (Fig. 2.15a), the maximum tensile stress becomes independent of the z-position between the two plates, and can be calculated as ... 

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