Design optimization of energy absorption structures with origami patterns
Creators: name: YANG, Kai
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400204
subject: Automotive safety engineering
classificationCode: 400512
subject: Transport engineering
classificationCode: 461306
subject: Numerical computation and mathematical software

description: Conventional thin-walled tubes are structurally simple with good energy absorption capacity. However, they usually exhibit high initial peak force and violent fluctuations of plateau force in crush, which are detrimental as energy absorbers. Besides, their collapse modes are highly sensitive to random defects from manufacturing inaccuracy. To overcome these shortcomings, a common approach is to introduce properly designed geometric imperfections on the tube to trigger the crushing procedure in controlled folding modes and reduce the crushing force fluctuations. But the conventional method of introducing geometric imperfections may significantly reduce the energy absorption capacity of the tube. To increase the energy absorption capacity of tubes, many approaches have been used, e.g., the employment of stiffening ribs and the introduction of buckling controller. However, these methods may result in complicated mechanical response without significantly reducing the initial peak force. It is challenging to simultaneously reduce the initial peak force and crushing force fluctuations while maintain or increase the energy absorption capacity when designing thin-walled energy absorption structures. Origami technology, usually applied in the kinetic engineering field, has potential in controlling the folding modes of thin-walled tubes and reducing the impact force. However, there are few applications for the energy absorption in terms of origami technology. Also, the influence of different origami patterns on the energy absorption capacities of conventional tubes has not been systematically studied. Therefore, it is essential and necessary to conduct a systematic investigation on the energy absorption of structures with origami patterns. In this thesis, tubular structures with different origami patterns were specially designed and investigated experimentally and numerically. Firstly, Yoshimura (diamond) patterns were introduced to circular tube to create two types of origami tubes, i.e., full-diamond tube and diamond tube. The mechanical responses of the newly designed origami tubes were investigated through experimentally validated numerical simulations considering different wall thickness. The results showed that pre-folded origami patterns could significantly reduce the initial peak force while increasing (in full-diamond tube) or maintaining (in diamond tube) the specific energy absorption as compared to conventional circular tubes in crush when the tube wall was sufficiently thin. An alternative design was performed by introducing smoothed dimpled ellipsoidal patterns other than origami hinge lines on tube surfaces. The pre-designed ellipsoidal patterns were arranged in staggered manner in circumferential (concaving inwards) and longitudinal (concaving outwards) directions. The influences of various design parameters, such as the aspect ratio of ellipse, the number of structural units, dimple depth and wall thickness, on the mechanical properties and energy absorption capacities of dimpled tubes were investigated systematically via numerical simulations and experiments. The results showed that properly designed dimpled tubes had substantially lower initial peak force and remarkably less fluctuation in crushing force than circular tubes, without significantly sacrificing the mean crushing force. Additionally, the influences of the number of structural units and the base material properties on the mechanical properties and energy absorption capacity of the full-diamond tubes were numerically investigated. The results showed that, as compared to the dimpled tubes, the initial peak force of full-diamond tubes with identical arrangement of structural units was relatively lower, while the mean crushing force could be higher if the structural units were properly arranged. It was also found that the material property had remarkable influence on the energy absorption capacity owing to the sensitivity of material constitutive relation on the buckling mode of full-diamond tubes. As multi-cell tubes have been reported to be able to enhance the specific energy absorption as compared to conventional single-cell tubes, the combination of the multi-cell feature and origami pattern may bring innovative structural designs for energy absorption. In this thesis, origami folding patterns were introduced on the external walls to guide the buckling procedure, while the internal ribs of the multi-cell tube worked as stiffeners to enhance the strength. Three novel types of multi-cell thin-walled tubular structures with pre-folded diamond origami patterns were then proposed. The influences of various structural parameters on the mechanical properties and energy absorption capacities were systematically investigated via experimentally validated numerical simulations. Based on the numerical results, multi-objective optimizations were performed on the specially designed tubes by linearly weighted average method, aiming to find the optimal designs with low initial peak force, high specific energy absorption and small fluctuation of the crushing force. The response surface method (RSM) was utilized in the optimizations to formulate the objective functions. Theoretical analyses were conducted based on simplified buckling models and a theoretical solution for the mean crushing force was derived for the quadruple-cell origami-patterned tubes. A series of optimal designs were obtained with balanced initial peak force, specific energy absorption and fluctuation of the crushing force. It was found from the results that origami-patterned and origami-triggered quadruple-cell tubes could maintain relatively high specific energy absorption (SEA) as compared to the conventional quadruple-cell square tube, while the origami-patterned quintuple-cell tubes have the highest values. Furthermore, dynamic tests on specific optimal multi-cell tubes were conducted by using drop weight tests. The influence of the origami patterns on the dynamic mechanical properties and the buckling mechanisms of multi-cell tubes were investigated by using experimentally validated finite element modelling. The results showed that, for the origami-patterned quadruple-cell tube, the optimal design obtained from the dynamic simulations had almost identical geometric dimensions to the quasi-static ones, while the design objectives of origami-triggered quadruple-cell tube were increased simultaneously as compared to the quasi-static model. For the origami-patterned quintuple-cell tube, no evident differences were found between the quasi-static and dynamic models.