Layered design analysis

By working the differences between the computed structural numbers required over each layer, the maximum allowable thickness of any given layer can be computed. For example, the maximum allowable structural number of the sub-base material would be equal to the structural number required over the sub-base subtracted from the structural number required over the subgrade (roadbed soil). In a similar manner, the structural numbers of other layers may be computed. 

The minimum thickness of the first layer (bituminous layers) is determined by the following equation  

In case the thickness of the first layer is rounded up to the nearest 1/2 inch, say Df, then the structural number is modified as 

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The determination of the thickness of a new pavement and effectively the thickness of each layer may be carried out by two alternative ways (a) by selection of layer thickness or (b) by layered design analysis. 

The scheme of experimental unit is presented in Figure 1. Biomass layer under analysis is placed in the cylindrical container 2OOmm0. The layer is enclosed from the top and the bottom by the specially designed grates whose hydraulic resistance is extremely low in comparison with the layer hydraulic resistance, the fact that was taken into account in the processing of experimental data. 

FEM analysis will establish the approximate thickness of carbon-fibre panelling required to meet overall stress requirements (expressed in g/m ). It will also establish the quality of carbon fibres required (expressed typically in terms of HT(A/S), UM, etc.) as well as their orientation (e.g. single-or multi-directional layer). Further analysis will identify in which areas the carbon-fibre thickness can be reduced to 50% if required, with local reinforcements applied to meet stress levels. This analysis can also help establish where carbon-fibre composites can be replaced by basalt-fibre composite components. As an example, FEM analysis would reveal that, based on the chosen wall design concept, a 4 x 400 g/m multi-layer carbon HT-fibre would achieve the required strength. It would also highlight those areas which would need... 

The thickness of the individual layer is determined from appropriate design charts, developed with the aid of the multi-layered elastic analysis software called DAMA. 

The subscript Bscs here refers to the value of the damage which is obtained as a resnlt of the base case fatigne design analysis for a given layer and for a given internal condition. 

This is the simplest and most straightforward solution when there is insufficient room on existing layers to place all the necessary interconnecting paths, add a layer. This approach has been widely practiced in the past, but when cost effectiveness of the substrates is of paramount importance, a very careful design analysis must be made to minimize layer counts in MLBs, because there is a significant cost increase with every additional layer in the board. As seen from Table 2.6, calculated for 6- x 8-in MLBs produced in large quantity with yields and conductor density kept constant, there is almost a linear relationship between board costs and layer count. 

Fitting analysis. For this to be possible, an assembly sequence plan must be constructed and the difficulty of assembling each part in the sequence rated using the design for assembly analysis tables. Difficult assembly tasks and non-value added processes are revealed as candidates for correction by redesign. Simple concepts such as the ability to assemble in a layer fashion can result in major cost savings. 

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