Investigations into the tensile failure of doubly-convex cylindrical tablets under diametral loading using finite element methodology.
Investigations into the tensile failure of doubly-convex cylindrical tablets under diametral loading using finite element methodology.
复制标题
使用有限元方法研究径向载荷下双凸圆柱片的拉伸破坏。
DOI：
10.1016/j.ijpharm.2013.06.069
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发表时间：
2013
影响因子：
5.8
通讯作者：
J. Newton
中科院分区：
文献类型：
--
作者：
F. Podczeck;Kevin R. Drake;J. Newton
在文献中，存在用于计算双凸片的直径压缩拉伸强度的各种解决方案，并且每种方法仅基于从单一材料（石膏、微晶纤维素）获得的实验数据。这些解由复杂的方程表示，并且压坯的弹性和弹塑性行为也有所不同。这项工作的目的是开发一个通用方程，该方程独立于变形行为而适用，并且仅基于简单的片剂尺寸，例如直径和片剂总厚度。借助 3D-FEM 分析，评估了中心圆柱双凸片与总片厚度比 W/D 在 0.06 至 0.50 之间以及面曲率比 D/R 在 0.25 至 1.85 之间的拉伸破坏应力。弹性和弹塑性变形行为均被考虑。结合 80 个单独模拟的结果表明，双凸片的拉伸破坏应力 σt 可以通过以下公式计算：σt= (2P/πDW)(W/T)=2P/πDT，其中 P 为破坏载荷，D 为直径，W 为中心圆柱厚度，T 为片剂总厚度。当 WequalsT 时，该方程转换为标准巴西方程 (σt= 2P/πDW)，即对于扁平圆柱形片剂同样有效。在实践中，使用这个新方程无需复杂地测量片剂尺寸，因为它只需要直径和片剂总厚度的值。它还可以为双凸片剂的机械强度设定标准。新方程同时适用于片剂在负载下的弹性和弹塑性变形行为。它对于 0.06 和 0.50 之间的 W/D 比与 0.00 和 1.85 之间的 D/R 比的所有组合均有效，但 W/D= 0.50 与 1.85 和 1.43 的 D/R 比组合以及 0.40 和 0.30 的 W/D 比与 D/R= 1.85 组合除外。有限元分析表明，在这些特殊情况下，可能会出现上限失效甚至更复杂的失效模式。 FEM 结果进一步表明，当改变片剂的整体尺寸和形状以获得最大片剂拉伸强度时，一般来说，0.15 至 0.20 之间的 W/D 比是有利的。然而，双凸片的最大拉伸应力永远不会超过具有相似宽/深比的平面圆柱形片的最大拉伸应力。最低拉伸应力取决于 W/D 比。对于最薄的中心圆柱体厚度，该最小应力出现在 D/R= 0.50 处；对于 0.10 和 0.20 之间的 W/D 比，最小拉伸应力的 D/R 比增加到 0.67，对于所有其他中心圆柱厚度，最小拉伸应力为 D/R= 1.00。
In the literature various solutions exist for the calculation of the diametral compression tensile strength of doubly-convex tablets and each approach is based on experimental data obtained from single materials (gypsum, microcrystalline cellulose) only. The solutions are represented by complex equations and further differ for elastic and elasto-plastic behaviour of the compacts. The aim of this work was to develop a general equation that is applicable independently of deformation behaviour and which is based on simple tablet dimensions such as diameter and total tablet thickness only. With the help of 3D-FEM analysis the tensile failure stress of doubly-convex tables with central cylinder to total tablet thickness ratiosW/Dbetween 0.06 and 0.50 and face-curvature ratiosD/Rbetween 0.25 and 1.85 were evaluated. Both elastic and elasto-plastic deformation behaviour were considered. The results of 80 individual simulations were combined and showed that the tensile failure stressσtof doubly-convex tablets can be calculated fromσt= (2P/πDW)(W/T) = 2P/πDTwithPbeing the failure load,Dthe diameter,Wthe central cylinder thickness, andTthe total thickness of the tablet. This equation converts into the standard Brazilian equation (σt= 2P/πDW) whenWequalsT, i.e. is equally valid for flat cylindrical tablets. In practice, the use of this new equation removes the need for complex measurements of tablet dimensions, because it only requires values for diameter and total tablet thickness. It also allows setting of standards for the mechanical strength of doubly-convex tablets. The new equation holds both for elastic and elasto-plastic deformation behaviour of the tablets under load. It is valid for all combinations ofW/D-ratios between 0.06 and 0.50 withD/R-ratios between 0.00 and 1.85 except forW/D= 0.50 in combination withD/R-ratios of 1.85 and 1.43 and forW/D-ratios of 0.40 and 0.30 in combination withD/R= 1.85. FEM-analysis indicated a tendency to failure by capping or even more complex failure patterns in these exceptional cases. The FEM-results further indicated that in generalW/D-ratios between 0.15 and 0.20 are favourable when the overall size and shape of the tablets is modified to give maximum tablet tensile strength. However, the maximum tensile stress of doubly-convex tablets will never exceed that of a flat-face cylindrical tablet of similarW/D-ratio. The lowest tensile stress depends on theW/D-ratio. For the thinnest central cylinder thickness, this minimum stress occurs atD/R= 0.50; forW/D-ratios between 0.10 and 0.20 theD/R-ratio for the minimum tensile stress increases to 0.67, and for all other central cylinder thicknesses the minimum tensile stress is found atD/R= 1.00.