Question 4.1: In the spider lift shown in Fig. 4.17a, a few of the highlig...
In the spider lift shown in Fig. 4.17a, a few of the highlighted components
are made of composite materials. These components are adopted to avoid a direct circuit flow from a power line to ground. The parts are prototyped and tested in the real-world application environment. However, a failure occurred to one prototyped component as shown in Fig. 4.17b, and the user wanted to find out the cause of failure in the product design (Bi and Mueller 2016). The CAD model of the failed part is shown in Fig. 4.7c; establish the modeling procedure of FEA for the analysis of composite parts.
The Solidwork Simulation is used to analyze a composite part as follows.
Firstly, the properties of the composites are defined. Figure 4.18 shows the interface to define newmaterial properties. ‘Linear elastic orthotropic’ is selected as themodel type to specify the attributes of composite materials.
Secondly, the laminates of the composite material are configured. Figure 4.19a shows the interface to define a surface which is made of composites. Figure 4.19b shows its main attributes,which include the number, the thicknesses, and thematerials of plies; the attributes also include the directions of plies in each layer.
Thirdly, the failure criteria are specified for each solid body.As shown in Fig. 4.20, the Solidworks Simulation supports all three options of failure criteria in Table 4.1 to define the factor of safety for composite materials. In addition, the software supports the automatic selection of failure criteria based on the assigned material properties.
Fourthly, the steps in FEA modeling are followed to (1) create part geometry, (2) assign material properties, (3) create meshes, (4) define boundary conditions and loads, (5) run the model, and (6) post-process the simulation results. Figure 4.21a–c shows the outcome examples for the distributions of displacement, stress, and the factor of safety in the first ply of the part surface.
Table 4.1 Commonly used failure criteria of composite materials
| Failure criterion | Formula | Strengths and stresses |
|
Maximum stress failure criterion |
\left.\begin{matrix}-\sigma ^{fC}_{11} < \sigma _{11} < \sigma ^{fT}_{11} \\\\\ -\sigma ^{fC}_{22} < \sigma _{22} < \sigma ^{fT}_{22} \\\\ \left|\tau _{12} \right| < \tau ^{f}_{12} \end{matrix} \right\} |
\sigma ^{fT}_{11} and \sigma ^{fC}_{11} are tensile and compression strengths along longitude direction |
|
Tsai-Hill failure criterion |
\frac{(\sigma _{11} )^{2} }{(\sigma ^{fT}_{11} )^{2} } + \frac{(\sigma _{22} )^{2} }{(\sigma ^{fT}_{22} )^{2} } + \frac{(\tau _{12} )^{2} }{(\tau ^{f}_{12} )^{2} } – \frac{\sigma _{11} \sigma _{22} }{(\sigma ^{fT}_{11} )^{2} } < 1 | |
|
Tsai-Wu failure criterion |
X_{1}\sigma _{11} + X_{2}\sigma _{22} + X_{11}{\sigma _{11}}^{2} + X_{22}{\sigma _{22}}^{2} + X_{66}{\tau _{12}}^{2} + 2X_{12}{\sigma _{11}}\sigma _{22} < 1 |
