Reliability analysis of bistable composite laminates

Bistable composite laminates are smart composites that have been employed for engineering structures due to their superlative offering of features like ability to change shape and low densities. Because of the embedded geometrical nonlinearity factor, a small variation of input parameters leads to significant changes in the response of the bistable composite laminates. In other words, Uncertainty Quantification (UQ) makes a change in the bistability characteristics. As a result, bistability behavior is extremely reliant on geometrical dimensions and elastic material properties as design parameters. Reliability analysis deals with the quantitative assessment of the occurrence probability due to UQ. In this regard, the reliability and sensitivity analysis of bistable composite plate are investigated through the Monte Carlo Simulation (MCS) and multiple types of uncertain parameters, geometry and material properties, are assumed as random variables. The results indicate bistable composite plates have a high probability to be bistability behavior with the assumed statistical properties. Moreover, the sensitivity reliability analysis illustrates that the thickness and coefficient of thermal expansion have more effect on the bistability behavior in comparison to other input parameters. The results are confirmed by comparing them with those determined by the Finite Element Method (FEM)

Non-contact magnetic driving bioinspired Venus flytrap robot based on bistable anti-symmetric CFRP structure

The Venus flytrap takes advantage of its bistability to generate rapid closure motion for capturing its prey. A bioinspired Venus flytrap robot with bistable artificial leaves is presented in this paper. Non-contact electromagnetic driving method is proposed to actuate the Venus flytrap robot's artificial leaves, which are made of anti-symmetric carbon fiber reinforced prepreg (CFRP) cylindrical shells. Magnetic force is generated by using the electromagnet and applied on the shell's curve edge to unbend the shell, and then the bending process transmits from one edge to the whole surface. The required magnetic force for the snap-through process of the bistable CFRP structure is determined from experimental test and compared with the result of finite element simulation. The test of the snap-through process of the Venus flytrap robot show that the Venus flytrap robot can generate a rapid snapping motion by the electromagnet actuation

임의의 형상을 가지는 쌍안정 적층 쉘 구조물의 형상 구현 방법에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2016. 2. 조맹효.In this dissertation, the numerical analysis model and design technique of plate and shell is proposed based on the Gausss Theorema Egregium, in order to materialize the bistable shell structure with arbitrary shape. The classical bistable plate and shell structure is limited to the cylindrical shape. Besides which, the curvature value of cylindrical shape does not change independently without changing the thickness and material locally. The morphological limitation is blocking progress in the application research on the bistable plate and shell structure. In summary, this problem is categorized into two main engineering issue: how to change the cylindrical curvature value of classical bistable structure? and how to induce the bistable structure with non-cylindrical shape?. In order to address this problem, firstly, curvature tailoring technique of classical bistable shell structure is suggested by using the initially curved tool-plate. The suggested method is verified by Rayleigh-Ritz analysis and experiment. Secondly, second-generation technique which inducing bistable structure with arbitrary shape is proposed based on the Gausss Theorema Egregium. The suggested method is also verified numerically and experimentally. Specifically, the second-generation technique, which inducing bistable structure with arbitrary shape, is motivated from the geometrical characteristic that shear deformation does not occur in the case of transformation between two isometric surfaces. Based on this geometrical characteristic, the realization method of bistable shell structure with arbitrary shape is suggested through face-to-face perfect bonding of two non-developable surfaces. In the analysis of bistable structure in order to handle the above issue, various efficient and accurate numerical models are developed. Firstly, the classical bistable structure analysis model is mostly based on displacement field in order to build up the total potential energy. However, the total potential energy is not explicitly expressed by displacement field. For this reason, the analysis from the model based on the displacement field is not efficient. In order to address this problem, the new analysis model is proposed, which is combining the approximated implicit strain field and the compatibility equation. The efficiency and accuracy of the suggested model is validated, by comparing with the result obtained by FE analysis. Secondly, the classical bistable structure analysis model is mostly based on the plate theory due to the limitation of numerical derivative precision and the complexity of calculation, although the deformed curvature of bistable plate and shell is large. In this dissertation, however, in order to obtain the accurate solution, the bistable structure analysis model is developed based on the shell theory. In the development of corresponding shell model, the limitation problem of numerical derivative precision and the complexity of calculation are addressed by utilizing the matrix derivative method. As a result, the analysis of bistable plate and shell has become so accurately and so easily. Finally, for the practical application of the bistable shell structure, the effect of initial shape of bistable shell structure on the snap-through load is studied. Based on the snap-through load obtained from numerical analysis, the Shape memory alloy spring is suggested as actuator. At first, specification of SMA spring is suggested. The performance of SMA spring is simulated by FE analysis where the constitutive model of shape memory alloy is implemented based on the Lagoudas model. Then, for the verification of snap-through by means of SMA spring, snap-through FE analysis of the bistable structure with SMA spring is performed. From this FE analysis, it is verified that the snap-through of bistable shell structure is well induced when SMA spring is utilized as actuator. The morphological design technique and model of bistable plate and shell structure, which are developed and verified in the dissertation, overcome the morphological limitation of the existing bistable structure and improve the design degree freedom of it. If the improved design degree freedom and the bistability is applied into the classic mechanical system which have been focus on the mechanical property (i.e. strength or mass), the new mechanical system accompanied by the concept of morphing can be designed and expected as the high value-added system breaking stereotype.Chapter 1 Introduction 1 1.1 Paradigm change of structures 1 1.2 Bistable structure or composites 2 1.3 Literature survey 3 1.4 Issues of bistable structure or composite 5 1.5 Objectives and contributions 7 1.6 Organization 9 Chapter 2 Curvature tailoring of bistable composite with misalignment 13 2.1 Introduction 13 2.2 Analytical model development 14 2.3 Numerical simulation and verification 21 2.3.1 Numerical simulation 21 2.3.2 Experiments 22 2.3.3 Design guideline 23 Chapter 3 Effect of initial curvature on the snap-through load 31 3.1 Introduction 31 3.2 Snap-through and its driving mechanism 32 3.3 Snap-through of bistable composites subjected to line edge moment 37 3.3.1 Simple analytical model 37 3.3.2 Strain energy of bistable composite 37 3.3.3 Moment equilibrium 39 3.3.4 Minimization of total potential energy 40 3.3.5 Analysis result 40 3.4 Verification of pre-identified effect of initial curvature 43 3.4.1 FE analysis of snap-through moment of bistable composites 43 3.4.2 Experiment and FE analysis of snap-through vertical load of bistable composites 46 3.4.3 Comparison between experimental and FEA result 48 Chapter 4 FE model of bistable shell structure with SMA coil spring 61 4.1 Introduction 61 4.2 FE analysis of SMA spring and its design 62 4.2.1 FE model of SMA spring and constitutive equation of SMA 62 4.2.2 The snap-through load of bistable composite without SMA spring 68 4.2.3 Simple design of SMA spring for snap-through 69 4.3 Snap-through analysis of bistable composite with SMA spring 70 Chapter 5 Saddle shape bistable structure with constant curvature 85 5.1 Introduction 85 5.2 Strain fields of the saddle-shaped bistable structure 86 5.3 Analytical model to predict the final shape of the saddle-shaped bistable structure 90 5.4 FE model to predict the final shape of the saddle-shaped bistable structure 92 5.5 The comparison between the analytical result and FE result 94 5.6 Snap-through analysis of the saddle-shaped bistable structure with an actuator and its simple design guideline 97 Chapter 6 Analysis of saddle shape bistable structure with arbitrary strain field 107 6.1 Introduction 107 6.2 Compatibility equation in large deflection 108 6.3 Strain-based Rayleigh-Ritz analysis model considering compatibility condition 112 6.3.1 Strain field of saddle-shaped bistable strucutre 112 6.3.2 Total potential energy of saddle-shaped bistable structure 115 6.3.3 Minimization of total potential energy 116 6.4 Verification and analysis results 116 Chapter 7 Saddle shape bistable structure with large curvature 125 7.1 Introduction 125 7.2 Review of thin shell theory 126 7.2.1 Curvilinear coordinate system 126 7.2.2 The deformation gradient and Lagrange strain tensor 127 7.3 Strain fields of the saddle-shaped bistable structure 131 7.4 Analytical model 135 7.4.1 Strain energy density of saddle-shaped bistable shell structure 135 7.4.2 Minimization of total potential energy 136 7.5 The comparison between the analytical result and FE result 137 7.6 Manufacturing of saddle shape bistable shell structure 138 Chapter 8 Conclusion 153 Appendix 159 Bibliography 163 국문요약 171Docto