Diametral compression test

The diametral compression test is performed by compressing a thick disc along a diameter of the specimen. A diameter-to-thickness ratio of approximately 3 is preferred. Figure 17 shows this test, including grid lines and gages for measuring the strains developed as the sample is compressed between the tester platens. 

Figure 17. Diametral compression test. Deformations are followed by compression gages, cross head travel, and grid markings on the sample surface...

Diametral compression test, 34 Disc agglomerators capacity, 69... 

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 ... 

Figure 14.7 Diametral compression test on pipe (a) Without side support (b) smooth rigid side wall support. (c) half pipe under three point bending.

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 ... 

Hulled, brown rice grains were cut at the two ends leaving samples that had approximately the shape of cylinders. Diametral-compression tests were carried out with an Instron type of machine, applying cross-head speeds of 0.1 and 0.01 mmmin , at 20°C, with controlled RH. In these conditions, it has been checked that the failure took place along the diametral plane, dividing the grain into two equal half cylinders, which indicates that the fracture was only caused by a tensile stress (Fig. 2.15b). 

Rudnick, A., Hunter, A. R., Holden, F. C., 1963. An analysis of the diametral-compression test. Mater. Res. Stand. 

Fig. 8. Tensile strength estimated by diametral compression test versus open pores content in ceramics.

Fig. 10. Tensile strength estimated by diametral compression test of HA/gelatin composite materials using ceramics obtained at (a) 50 and (b) 100 MPa pressure, as a function of concentration of solution ( I—vacuum 1.33 Pa for 30 min, — vacuum 1.33 Pa for 10 min, andD— without vacuum for 30 min).

We can also resort to a diametric compression test, also known as the Brazilian test, for evaluating the tensile stress [CLA 70]. This test, which is particularly suitable for raw materials or for bars (non-sintered products), consists of compressing a pellet monoaxially (diameter D , thickness t) following a diametric direction. The breaking stress is then deduced from the mpture load using the following relationship ... 

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