Brittle fracture index

Fig. 9 Effect of ambient relative humidity on the brittle fracture index of compact-made from Avicel PH 101 (0) and Emdex ( ). (Data adapted from Ref. 67.)...

Just as metals can be ductile or brittle, so can organic materials. The Brittle Fracture Index is a measure of the brittleness of a material. It is a measure of the ability of a compact of material to relieve stress by plastic deformation. The Brittle Fracture Index (BFI) is determined [29,31] by comparing the tensile strength of a compact, stress concentrator) in it, o-T0, using the tensile test we have described. A hole in the center of the compact generally weakens a tablet. If a material is very brittle, theoretical considerations show that the tensile strength of a tablet with a hole in it will be about one-third that of a solid tablet. If, however, the material can relieve stress by plastic deformation, then the strength of the compact with a hole in it will approach that of a compact with no hole. The Brittle Fracture... 

Material Bonding Index x 102 Brittle Fracture Index Strain Index x 102... 

Lot to lot variations of several drugs and excipients are shown in Table 9. Specially crystallized lots of ibuprofen, for example, show substantial changes in Brittle Fracture and Bonding Indices. Phenacetin shows a significant increase in brittleness at higher relative humidity. It was observed by Hiestand and Smith [31] that compacts of dried phenacetin did not fracture, while the lot equilibrated at 40% relative humidity did, consistent with the Brittle Fracture Index change. 

Hiestand has developed many indices that are useful for tablet formulations (16 18). These include the frequently cited brittle fracture index (BFI), the best-case bonding index (Bib), the worse-case bonding index (BI ), and the viscoelastic index (VI) (15,16). 

Brittle fracture index Calculated from crT and ctto 0.1-0.5... 

Compression stress (MPa) Dynamic indentation hardness (MPa) Tensile strength (MPa) Bonding index Brittle fracture index ... 

Brittle fracture index 0.26 Moderate 0.30 High 0.45 High... 

Brittle fracture index 0.12 Moderate 0.10 Moderate 0.19 Moderate... 

Generally, only powders that form hard compacts under an applied pressure without exhibiting any tendency to cap or chip can be considered as readily compactible. The compactibility of pharmaceutical powders can be characterized by its tensile strength and indentation hardness, which can be used to determine three dimensionless parameters strain index, bonding index, and brittle fracture index. 

A technique generally applied to characterize and prevent the capping and lamination of a material intended to be compacted is using the brittle fracture index (BFI). The BFI was designed by Hiestand et al. [31] and measures the ability of a material to relieve stress by plastic deformation around a defect. It is obtained by applying Equation (8) and compares the tensile strength of a tablet with a hole in its center (To), which acts as a built-in stress concentrator defect, with the tensile strength of a similar tablet without a hole (T), both at the same relative density ... 

Brittle fracture index 0.1671 for NF Lactose-315 (compression pressure 54.90 MPa) ... 

Pharmaceutical compacts are complex structures that present difficult challenges when measuring their mechanical properties. Hiestand was a pioneer who quantified the compaction properties of pharmaceutical powders and (105-109) the result of his work are indices known as the Hiestand Tableting Indices. These indices are dimensionless numbers used to describe the mechanical properties and consolidation behavior of materials under compression and decompression. The three main Hiestand Tableting Indices are the bonding index, brittle fracture index BFl), and strain index. 

Hiestand Tableting Indices Likelihood of failure during decompression depends on the ability of the material to relieve elastic stress by plastic deformation without undergoing brittle fracture, and this is time-dependent. Those which relieve stress rapidly are less likely to cap or delaminate. Hiestand and Smith [Powder Technol., 38, 145 (1984)] developed three pharmaceutical tableting indices, which are applicable for gener characterization of powder com-pactiability. The strain index (SI) is a measure of the elastic recovery following plastic deformation, the bonding index (BI) is a measure of plastic deFormation at contacts and bond survival, and the brittle fracture index (BFI) is a measure of compact brittleness. 

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