Diametrical compression

Omitting atypical high and low values of 10 and 100 MPa " Measured by the diametral compression method, omitting an atypical low value of 1-5 MPa... 

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. 

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. 

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). 

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

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...

In a recent attempt to bring an engineering approach to multiaxial failure in solid propellants, Siron and Duerr (92) tested two composite double-base formulations under nine distinct states of stress. The tests included triaxial poker chip, biaxial strip, uniaxial extension, shear, diametral compression, uniaxial compression, and pressurized uniaxial extension at several temperatures and strain rates. The data were reduced in terms of an empirically defined constraint parameter which ranged from —1.0 (hydrostatic compression) to +1.0 (hydrostatic tension). The parameter () is defined in terms of principal stresses and indicates the tensile or compressive nature of the stress field at any point in a structure —i.e.,... 

Optical trapping (also known as laser tweezers) 2.5 Diametrical compression (also called compression 35... 

A Models to describe microparticles with a core/shell structure. Diametrical compression has been used to measure the mechanical response of many biological materials. A particular application has been cells, which may be considered to have a core/shell structure. However, until recently testing did not fully integrate experimental results and appropriate numerical models. Initial attempts to extract elastic modulus data from compression testing were based on measuring the contact area between the surface and the cell, the applied force and the principal radii of curvature at the point of contact (Cole, 1932 Hiramoto, 1963). From this it was possible to obtain elastic modulus and surface tension data. The major difficulty with this method was obtaining accurate measurements of the contact area. 

Figure 16 Comparison of the dimensionless force Y and fractional deformation of a single 163 pm diameter ion-exchange resin particle (DOWEX 1X8-200, Sigma-Aldrich, UK) obtained by diametrical compression and by numerical simulation using the Tatara non-linear elastic model. E0n represents the initial Young s modulus at zero strain (data provided by Dr T. Liu).

Figure 19 Environmental SEM image of (a) Eudragit LlOO-55 and (b) Advantose 100 tablet in the fracture region after diametrical compression (reproduced from Yap et al., 2006). Permitted by Elsevier.

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

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. 

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.

Rees JE, Rue PJ. Work required to cause failure of tablets in diametral compression. Drug Dev Ind Pharm 1978 4 131-156. 

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 ... 

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