236 Journal of Bionic Engineering(2008)Vol 5 No. 3 5. 2. 1 Nonlinear buckling analy Structural bionic design A nonlinear buckling analysis is a static analys with large deflection action, extended to a point where the structure reaches its limited load or maximum load Organism structure Mechanical structu Before a nonlinear buckling analysis, an eigenvalue buckling is needed to achieve the upper limit of the bearing load. Eigenvalue buckling analysis predicts the Similarity analysis theoretical buckling strength of an ideal elastic structure lt the structural eigenvalue for the tem load and constraints This is known as classical imilarity Euler buckling analysis Nonlinear buckling analysis employs non-linear Extract structural characteristics with excellent and large-deflection static analysis to predict buckling mechanical properties of organism loads. Its mode of operation is very simple: it gradually increases the applied load until a load level is found at Structural bionic design which the structure becomes unstable (i.e. suddenly a (Satisfy machining requests) very small increase in the load will cause very large deflection). The true non-linear nature of this analysis al property analysis thus permits the modeling of geometric imperfections, load perturbations, material nonlinearities and gaps 5.2.2 Results and discussion 1)Load-bearing efficiency Finish The load-bearing efficiency defined by Eq (4) Fig. 1l The flow chart of bionic design. alculated for the bionic structure and the conventional structrure(shown in Table 2 ). It can be seen that the load-bearing efficiency of the bionic structure is sig nificantly improved that is about 124.8% higher than that of the conventional one Table 2 Comparison of load-bearing efficiency onventional aprovement 8.237e+4 1.852e+5 124.8% Fig. 12 Bionic cylindrical shell based on bamboo (2)Failure mode a buckling mode represents a secondary deformed 5.2 FEM analysis shape that has the same potential energy as the primary The material parameters of steel for both cylindr deformation. There are two main buckling modes the cal shells are shown in Table 1 global buckling and the local bucklin Table 1 Material parameters of alloy steel Besides higher load efficiency, the failure modes of the bionic structure are also favorable. which N Ultimate compressive strength Elastic modulus was proved by the FME analysis result as shown in 7.8 210 0 Fig. 13. The conventional structure buckles locally while the bionic structure buckles globally236 Journal of Bionic Engineering (2008) Vol.5 No.3 Fig. 11 The flow chart of bionic design. Fig. 12 Bionic cylindrical shell based on bamboo. 5.2 FEM analysis The material parameters of steel for both cylindri￾cal shells are shown in Table 1. Table 1 Material parameters of alloy steel Density (g·cm−3 ) Ultimate compressive strength (GPa) Elastic modulus (GPa) Poisson ratio 7.8 2.5 210 0.3 5.2.1 Nonlinear buckling analysis A nonlinear buckling analysis is a static analysis with large deflection action, extended to a point where the structure reaches its limited load or maximum load. Before a nonlinear buckling analysis, an eigenvalue buckling is needed to achieve the upper limit of the bearing load. Eigenvalue buckling analysis predicts the theoretical buckling strength of an ideal elastic structure. It computes the structural eigenvalue for the given sys￾tem load and constraints. This is known as classical Euler buckling analysis. Nonlinear buckling analysis employs non-linear and large-deflection static analysis to predict buckling loads. Its mode of operation is very simple: it gradually increases the applied load until a load level is found at which the structure becomes unstable (i.e. suddenly a very small increase in the load will cause very large deflection). The true non-linear nature of this analysis thus permits the modeling of geometric imperfections, load perturbations, material nonlinearities and gaps. 5.2.2 Results and discussion (1) Load-bearing efficiency The load-bearing efficiency defined by Eq. (4) was calculated for the bionic structure and the conventional structrure (shown in Table 2). It can be seen that the load-bearing efficiency of the bionic structure is sig￾nificantly improved that is about 124.8% higher than that of the conventional one. Table 2 Comparison of load-bearing efficiency Conventional Structure Bionic structure Percentage of improvement Load-bearing efficiency (kN·kg−1 ) 8.237e+4 1.852e+5 124.8% (2) Failure modes A buckling mode represents a secondary deformed shape that has the same potential energy as the primary deformation. There are two main buckling modes: the global buckling and the local buckling. Besides higher load-bearing efficiency, the failure modes of the bionic structure are also favorable, which was proved by the FME analysis result as shown in Fig. 13. The conventional structure buckles locally while the bionic structure buckles globally